All posts by hitoshi

ソーラーハウス (Effizienzhaus) 見学

At February 1st, 2016, some of us visit to a solar house in Berlin, Fasanenstrasse. The minister of Environment, nature protection, construction, and reactor safety (Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit) built the house as an experiment of energy efficient house. The name of project is “Effizienzhaus Plus mit Elektromobilität.” This means efficient house plus with electric mobility.

They built 35 experimental houses in Germany. Each house has own outlook designed by different architect. The house in Berlin is shown in the picture. It has a modern cubic shape. But of course there are houses that outlook is a classic German house, too.

Berlin にある Effizienzhaus Plus
Effizienzhaus Plus in Berlin
Effizienzhaus Plus
An explanation session in a Effizienzhaus Plus

The house is called an efficient house however also “plus” is in a name. The goal of this house is to show “generating more energy than consuming it through a year.” This includes the energy of one electric car. In the experiment process, a few public offered families live in each house for a year. Two families lived in this house so far.

The house generates energy by solar panels and store it in the batteries. The architect puts the panels on the west and east side walls and the top of the house. It would be more efficient if the panel is at the south wall, however, a typical family consumes energy in the morning, the afternoon, and at night, but not in the noon time. If they use energy directly, it is more efficient. The south side has a large glass window to get the sun light. The architect made outside looking more important than the panels efficiency, so he has chosen a specific color panels but lower energy efficiency (10 to 15%).

Heating is the largest energy consuming component of typical house in Germany. Therefore most of the effort of saving energy is related with heating. In this house, the triple layer glass is used for the window. The ventilation system uses a heat exchange mechanism. The heating uses a heat-pump system. Efficient LED lights are used for the illumination. The wall is made of low thermal conductivity materials, yet the material is recycle friendly. All the house system is adapted to use electric energy, then the house doesn’t have other external dependency for energy.

Triple glass window panes with low heat transfer
Triple glass window panes with low heat transfer

The result of the first year did not generate all the energy they consumed. The house could only generate the energy consumed in the house, but not for the car. But this is an experiment. The researcher monitored the energy consumption details in the house and found the two unexpected behavior. One is the low efficiency of heat transfer system. It didn’t work as in the specification from the provided company. Thus, they exchange the device. The second problem was the energy consumption of the living room. This room was connected to the staircase and the heated air just ran away from this connection. So the architect put a glass door. The result of the second year (with the second family) was successful. The house generated the energy more than the family consumed including a car electricity. The architect thought that the motion sensor was good for saving energy for lights, but the first family had a cat. and they found out this was not so efficient.

It’s interesting for me that this house just lack of “one door” despite all the high technology for saving energy. The experience is useful. Another interesting issue in the report was about the mindset of the family. The family realized they don’t need to save energy, since the house generate it. So their mind set becomes a bit more extravagance about energy. I understand this, but is it a good for society at the end? I am not sure. This could be a question for the next experience. The architect prefers the fixed window, which you cannot open them, for the energy saving point of view. But, the family reported it is important to be able to open the window manually. It is also important for a house not only for the energy, but the house is the big place where the life is going on. So the house keeps the window that you can open them manually. All these results are published as following (online).

The following is my personal memo.

My first glance of this house was, “I don’t want to live in this house. It looks like a Borg cube!” But this is based on a specific architect and he has also limitation in design. The original plan was for three years experiment for this house and the architect can only use some limited technology. There are 35 different designs of the Effizienzhaus Plus. I found some houses attractive. But I like the inside design of this house.

My impression is that the technology is matured. This house was built at 2012. At that time, the German technology of this area was

Energy generation instead of energy saving

I first said about the design. This means that it is already not the technical issue even in my mind. I felt the design was important. I felt that the technology is matured. I recall when the five color iMac showed up in 1999. For me, the most important factor of a computer is performance, memory, and functionality. I thought “iMac? Power PC 750, 266MHz, sounds nice, but isn’t the main memory too small?” However, some of my friends told about iMac, “Which color did you buy?” I was shocked. Why color? Later I looked back that time, the computer becomes commodity. The design is very important if you put it in a house instead of an office. I understand when something became common in your life, the design matters.

The same as this house, the architect chose a specific solar panes color, and he has chosen a low efficiency panel (10-15% efficiency). He had chosen the design over the efficiency, yet to aim the primary goal. For the next generation solar panels, I think they need more colors. I already heard about such research for solar panels. The technology will create the solar panels of any colors, then we will not notice that is a solar panel one day. The design will be more important than the energy efficiency. If a house with green solar panels, you could not distinguish the house and the garden from the distance.

Other natural energy generators would go to such direction. For instance, a wind turbine would look not a wind turbine. One direction would be windmills in Netherlands, that made the scenery itself. Or a wind turbine looks like a tree. There is an vertical axis wind turbines. Maybe we could make a turbine that resembles a tree which fits in a forest. The wind turbine area becomes a park mixed the silent turbines and real trees. This is one direction of this technology. One day, we have a power plats that is a natural park. I imagine that kind of the future and I see it is good.


What can we (citizens) do to promote green energy? I sometimes think about this. There are of course many ways. Today I will introduce one of the methods using sharing economy.

The sharing economy is a type of economy that people share the goods and services. People share: code for open source, auction places with eBay, cars with Uber, rooms with Airbnb and CouchSurfing, and so on. Sometimes it is over the range of sharing and cause troubles, but, this sharing economy is popular these days.

Can we use the idea of sharing economy for green energy? I live in an apartment. I don’t have a roof for solar panels. I don’t have a garden to put a small wind turbine. However, now we have the Internet. Can someone connect between who has a roof and who wants to invest solar panels?

Yeloha [1] is an U.S. start-up company for solar sharing network, founded April 2015. For example, anyone can borrow one solar panel per year for US $64. The generated electricity will be sold to the market and some percentage will be return to the investors. Was it a good investment? Well, it is not sure as the usual investment. However, I would like to invest the future of the green energy as a citizen and definitely this helps green energy industry. Yeloha has developed a special software, that can estimate how much electricity can be generated in a year depends on the location and the building[2].

I like this idea and business. I hope the similar sharing with wind turbine, bio-gas, and other green energies. I am looking forward to
seeing this kind of activity or company in Japan and Germany, too.

Today (2016-1-23(Sat)), we see the oil price is low. Some people think that “this is good, we can use oil.” But now is the time to invest to green energy since we can use lower price energy today to prepare for our future. The green energy is local and distributed, so its price can be stable and not global like the oil price. I believe oil price will raise one day, I don’t know when, but, I believe it definitely will. To prepare that day, I would like to invest to green energy now.


  1.  Yeloha,
  2. Lauren J. Young, Startup Profile: Yeloha Brings Solar Into the
    Sharing Economy,,
    IEEE Spectrum, Nov. 2015

Lecture by Former Prime Minister Naoto Kan: Crisis Management — Lessons Learned from the Threefold Catastrophe in March 2011

Date: 2015-10-13 (Tue)
Venue: Heinrich Böll Foundation, Berlin

We had a lecture entitled “Crisis Management – Lessons Learned from the Threefold Catastrophe in March 2011” by Naoto Kan, former prime minister of Japan.

The hosts and German politicians started by introducing this lecture then explaining the current German situation. On German energy policy they mentioned the following:

  • Referring to Merkel’s Memorandum and her plan to replace all the German nuclear power plants with renewable energy, they said: “Concerning the fact that even one of the world’s leading technology countries like Japan has faced such a catastrophic accident, it makes sense for Germany to abandon its nuclear power plants.”
  • Compared to Germany, Japan has more natural energy. Japan can use wind energy, solar energy, and energy from biomass, but also geothermal and tidal energy. Moreover Japan has world class technology. The only missing piece would be the political decision.
Sylvia Kotting-Uhl, Grünen, atompolitische Sprecherin
Sylvia Kotting-Uhl, Grünen, atompolitische Sprecherin

Then, the organizer introduced Naoto Kan. The following is a summary of Kan’s lecture.

Just after the accident [March 11th, 2011], we found out there was no crisis management in Fukushima, because everything was built on the assumption that the atomic reactor was safe. Around March 22nd (2011), I asked a specialist to evaluate the worst-case scenario. He said that all the people who lived inside a circle of 250km radius from the reactors needed to be evacuated for a few decades. Tokyo lies within the circle. 50 million people would lose their home. I recognized that in fact the problem was, if Japan could continue existing. How could we manage 50 million refugees at once if the worst-case scenario happened?

At the early stage of the accident, both the government and TEPCO did not know what happened and could neither manage to circulate information about the accident. On the other hand, the plant manager called Yoshida improvised a new way to cool down the reactors because all the common methods had broken down. Japan was saved by mainly the people on the spot, including fire fighters, police, self defense forces and TEPCO workers. According to TEPCO, the melt down of nuclear fuel emits 70Sv/h radiation. The radiation can kill a nearby person within five minutes. The containment vessel was damaged due to the high pressure, but it only had holes. Therefore, fortunately, this fuel was not dispersed into the air, but melt down into the earth. We found out that there was no simulation for such a high pressure accident, since the assumption had always been, that an accident was impossible. If the containment vessel had blown up instead of just punching holes, we would have had no idea what happened. The fuel pool of reactor IV contained nuclear fuel, but the pool had no containment vessel. We worried that the water could dry, but we could not go near due to the high radiation. However, coincidentally, there was extra water due to the delay of the maintenance work that was being done there and so the meltdown was unexpectedly avoided. “I know this is not the words from a politician, but I can only think that God protected us.” Today we still need to cool down the fuel by putting 300 tons of water every day onto it. But the containment vessel has holes, so the water is leaking. We pumped up the water and put it in tanks. But we cannot pump up all the water. It is still not under control today.

Naoto Kan, Former Prime Minister of Japan (Photo:Tsukasa Yajima)
Naoto Kan, Former Prime Minister of Japan (Photo:Tsukasa Yajima)

We are working on Fukushima’s decommissioning. The current plan says it will take 40 years, but I personally think we need more time to finish it.

I thought about the question why this accident happened. There was a chain of the causes. They also lie equally in hardware and software, by software human factors are meant. The average height of the shore line of Fukushima is around 35m. TEPCO lowered 20m of this height and reported how they save the pumping water costs for cooling down the reactors. They put the emergency electricity generators at a low place. This severely failed design caused the accident. These are hardware problems. On the other hand, there were also software problems. In Japan many accidents of this kind are caused by earthquakes, which are often followed by tsunamis. However, this possible situation was not considered. The bureaucrats who are responsible for the security of accident are not specialists for atomic reactors. For example, when I met the responsible person of the reactor accident, I asked the responsible person, “are you a specialist for atomic reactor?” The responsible person answered, “I graduated from the economy department of Tokyo University. I don’t know technical details about the reactor.” The organization for the reactor accident and the organization of the propelling nuclear reactors were the same organization. This chain of problems led to the accident.

Before 3.11 I have always recommended to sell Japanese reactors to other countries. But after 3.11 I completely changed this opinion.

After the accident, we first separated the department of the nuclear safety and the department propelling the nuclear reactors. We also changed the regulation so that it becomes more safety oriented. This basically shut down all the reactors in Japan.

We introduced a law to encourage green energy. We studied the German FIT system.

In the future, I want to abandon the fossil fuel and want to shift to all the sustainable energy in Japan. A research report says that the current human energy consumption is only 1/10000 of energy from the sun to the earth. If each country can support the energy by its own, one of the large international conflict source will be solved. It seems the national security will be better if we could shift to the natural energy. I admire Germany as a forerunner. I heard there are many different opinions in Germany, though I was quite impressed that Merkel changed the German energy policy to be based on the sustainable energy just after a few months after the Fukushima accident. I am disappointed with the current Japanese energy policy since it is not going only towards sustainable energy. However, it was revealed that the nuclear energy is not cheap. Thus, I expect the nuclear energy will be abandoned in this century due to economical reasons. But, there is no guarantee that there will be no other accident before it is abandoned. Let’s not wait until it is too late.

At the end of the lecture, Kan concluded “Fortunately, we could avoid the destruction of the country. I felt there was a protection of God. But, I don’t know whether there will be another protection when the next accident happens. My aim is to abandon nuclear reactors all over the world before the next accident.”

After the lecture, we had a lively question and answer session.

Q: Why is Japan still not able to abandon the nuclear power, even after the accident?

A: According to the opinion polls, a majority of Japanese wants to abandon nuclear power. However, the Japanese business community and the people who depend on nuclear power businesses are still strong. At the end, we need to promote the denuclearization by the election, but the focus of the last election was economy policy, and the LDP, which promotes nuclear power, won the election. Therefore we have not achieved the denuclearization.

さまざまな質問に答える菅氏 さまざまな質問に答える菅氏
Lively discussion with Kan

Q: Why do power companies, such as TEPCO, continue to promote the nuclear power even after they faced an accident like Fukushima?

A: The government wanted to promote the nuclear power, the power companies however didn’t. The government gave the power companies the authority to add up to 3% on top of the electricity costs depending on how much they invest. It is a rate-of-return regulation for power companies. In other words, if a power company has higher costs to produce power, their profits become higher. The power company can get more profit not requiring the endeavor of the company. Therefore, the power companies would like to promote the nuclear power since it can increase the profit without any effort.

The power company can abuse the rate-of-return regulation legally. For example, a power company can have an order with deliberately high cost to a general contractor. They can raise the electricity price due to the regulation, so the user must pay this cost. There could be a secret agreement that the general constructor pays back a part of the higher cost. A book recently revealed this mechanism and the pay-back is estimated at around 200 billion yen per year. The power companies use this money to promote nuclear power. Even though the accident cost 10 trillion yen, until now it was mostly covered by the tax. Therefore this situation is quite attractive for the power companies in Japan which are also favored to the many politicians.

Q: How did Japan change after 3.11?

A: I think there were many changes. One thing I would like to mention is the change in court’s attitude. The court did not use not make decisions about the safety, they used to let the experts decide since nuclear power plants are highly technical. Even though this is only true for some members, but they changed their attitude. In the future, I expect that the nuclear energy business cannot sustain due to its high costs and also the emerging of renewable energies. I believe nuclear power plants will be abandoned in this century. However, this is an economical movement and not a political movement. That is unfortunate.

Q: Will the change not happen politically?

A: I think the change might happen from grassroots movements. But they are not seen in the outcome of the national election in Japan. I heard that the German system has more weight for the proportional representation than the Japanese system. Japan uses single-member district method for election. This system has a wasted vote problem. For example, if 10% of people are against the nuclear reactor, these people’s votes are wasted in single-member district method and these 10% people are considered as 0. We need to have enough anti-nuclear people in the Japanese diet, however, Japan has not yet reached so far.

Q: How has information been verified when the accident happened?

A: At the time, critical information had been hidden, many of them are still not publically available. The communication line between TEPCO Tokyo and Fukushima site had been connected for 24 hours. However, only the information chosen by TEPCO was made public. For example, at March 15th, I visited TEPCO and asked the TEPCO officials not to retreat from Fukushima site. The video has been published without voice. TEPCO said the voice was erased by mistake, but I personally don’t believe it. Now a prosecution of the officials is carried out, so I expect more information will come to light.

Q: What kind of person is Yoshida, the general manager, who prevented the accident to become a lot worse?

A: Unfortunately Yoshida, the general manager died of cancer two years after the accident. Whether the cancer is the cause of exposure is unclear. I was able to meet him once just after the accident. I recognized immediately that he was a reliable person.

Q: How have the decisions to evacuate the site or to allow people to return been made?

A: At the time of the accident, the government’s monitoring ability was low and there was a danger that the containment vessel was going to be destroyed. So we decided to evacuate the area within a certain radius having the reactors as its center. Then, we figured out that the distributed radioactive substance depends on the wind. But this took time. Evacuation criteria differed by experts. The current criterion is 1 mSv/y. The number of children being patients is increasing, but some experts say that this is due to our checking method which is strict and makes numbers only looks like they were increasing. Municipalities tend to lower the criterion to make it easier for the people to return, since they want them to return to the area. Basically, we decide according to the experts’ opinions, but I have question this is appropriate.

Q: Why can your party (Democratic Party of Japan) not win the elections?

A: The effect of single-member district election method is strong. Within this system, we always need to get the first position in the district. Therefore, even if the 10% of the people favor our party, it is possible that we do not get a seat in the diet.

After the lecture: Kan with the host and green party politicians

最終処分の話をしようや (10): 付録 4: 最終処分の保存期間10万年の根拠は?

Is the mined Uranium safe?

We have seen the graph of “Radioactivity attenuation of vitrified waste over time.” How long time we need to keep the waste is based on the radioactive level of mined Uranium ore. I wonder if it is save. I could not find information about this. I know that not everything in nature is safe. A venomous snake, poisonous mushroom, volcano gas, … they are all natural, but not always safe. Uranium ore is in nature, but is it safe?

A Wikipedia article entitled “Depleted uranium,” Japanese MEXT (Ministry of Education, Culture, Sports, Science and Technology) stated that the toxicity of depleted Uranium is the same of the Uranium in the sea or rocks [1] (in November, 2002). This doesn’t tell much. I would like to know about the safty of Uranium ore in the first place, then why all of sudden am I talking about depleted Uranium? You might think that I switched subject. Unfortunately, this is the information that I found on the Internet, which is only indirect. I could only find two connected things that Uranium ore has danger similar to depleted Uranium and that depleted Uranium is dangerous. Assuming they are both correct, we could conclude that Uranium ore is also dangerous. Yet I doubt there are many different types of depleted Uranium (density and so on) and many different qualities Uranium ore. I don’t believe all the Uranium ore have exactly the same density of Uranium rocks. I didn’t understand this information completely. Some say depleted Uranium is dangerous and some say it is not. The former say, “it is not dangerous, but it’s a harmful substance, so it must be controlled under the law (US government), and children should not take it (WHO).” Then, Uranium ore from nature is as safe as depleted Uranium (Japanese MEXT), or less safe. You could check this out yourself in Wiki [1]. Personally I cannot judge any risk based on such low quality information. Then my decision can only be to avoid them. Without information, we cannot decide on anything. We need more information.

Also it is not clear that “the corresponding radioactivity of 1t fuel is 1000GBq.” The value is 1GBq/kg (=1,000,000,000 Bq/kg) which is quite large. Common food has a safety threshold at 100 Bq/kg. 1,000,000,000 Bq/kg which does not sound safe at all to me.

Only one thing is certain, nuclear waste needs 100,000 years to get to this 1,000,000,000 Bq/kg state.

Most of the articles about final disposal mentioned this number, 100,000 years, and they usually ask: can we keep it for that long? I think that is a wrong and meaningless question, because even if we can manage nuclear waste for 100,000 years, it is apparently not safe. As far as I can understand, Uranium ore is not safe and 100,000 years is too short of a time for final disposal.


  1. Wikipedia ja, Depleted uranium (劣化ウラン): Health considerations (in Japanese: 医学的危険性の主張と反論),, (Online; accessed 2014-12-21)


Thanks to Daniel S., Enzo C., Carsten W., and Nikolaus B. for the proof reading and suggestions for the English version.

最終処分の話をしようや (9): 付録 3: 測定方法で放射線の強さは変わること,放射線には種類があること

A note on the measurement of radiation dosage

I realized that the dosage depends on how you measure it. This also depends on the measurement location. The measurement depends on the height of the measurement device. (Thus, it is mandated to be placed at the height of 1.5m above ground level.) If you clean up the measurement point, the dosage at that point becomes lower. We should care about the hotspot (a relatively small spot that has high radiation), however, we cannot say that the whole region has high radiation just because of one hotspot. In an extreme example, if we can avoid all the hotspots and the rest of the place has no radiation, we can just avoid all the hotspots and live safely. The existence of hotspots is just telling us that there could be some dangerous spots. When we observe some hotspots we usually need more measurement points. It could be that the measurement points are too sparse and we might miss some of the high radiation points. We should care about how the radiation is measured and we need to think about the risk ourselves.

For example, if the measurement point is located near a station, it is good since a lot of people are passing by. If the location point can not be accessed by anybody, it usually doesn’t matter. But such a place is usually cleaned up frequently, thus the dosage may be lower, however only in the surroundings of the measurement point. There might be higher dosage 20 meters away from the measurement point. When we are told about the values of today’s radiation, we should also know where are the measurement points. If the whole area has not been cleaned up and only some spots were, we cannot use the cleaned up spot as a measurement point.

If someone decides to live in a low radiation place, they should think what is the important place for them. If you almost never go to a station, the radiation measured there is not so important. For you, the important place could be a school, your working place, and so on.

Radiation is not just one kind (What is Sievert?)

If you check an introductory text of chemistry, you notice that the radiation is not just one kind. There are many kinds of radiation: alpha radiation, beta radiation, gamma radiation, neutron radiation, and so on. The different kind of radiation affects differently the human body even at the same absorption dosage (gray in unit). For example, alpha radiation is more dangerous than beta radiation at the same energy level. Therefore, there is a unit called Sievert that adjusts for this difference (Figure 8). It seems scientists agreed that we need some adjustment, but how much adjustment is needed has raised some discussions. For example, how much more dangerous alpha radiation is compare to beta radiation is difficult to determine. This adjustment is called “radiation type weighting factor.” This currently differs from country to country. In Japan, this factor is 20 for alpha radiation, 5 for proton radiation, based on a gamma radiation is value of 1. According to IPRP report 103 (Wikipedia, Sievert), the factor is 20 for alpha radiation, 2 for proton radiation, based on a gamma radiation is value of 1. This coefficient is multiplied by gray to get the value as Sievert. Sievert considers the effect to the human body, but this weighting factor is hard to determine, because this depends on many other factors like person’s age, sex, health status. It is also difficult to make detailed experiments with the human body.

The following analogy is only understandable for someone who likes computer games. But I think this is a good analogy, so I will try to use it here. In many fantasy games, usually a character has some attribute, like fire or water. If a character has a water attribute, he or she can resist more to the water magic. When a character is hit by some fire magic, the damage this character gets depends on his/her fire attribute. At the end, how many health points the character lost is the most important effect. The damage has been adjusted according to the attribute. For radiation there are different types, and the damage to the human body depends on the type. In a similar way, Sievert is an adjusted value of the absorbed energy (gray).

Figure 8. There are many kinds of radiation
Figure 8. There are many kinds of radiation

If a human body gets the same amount of energy but in a different amount of time, the effect of radiation would be different. For example, whether a person gets 10mSv of dosage in a day or in a year it is a different thing, we cannot add yesterday’s radiation dosage and today’s radiation dosage. However, we still have no better measurement than Sievert. It seems Sievert is the best approximation to measure the effect of radiation on the human body. The effect of radiation is not linear, but the Sievert unit assumes that the effect is linear. If you are not familiar with the word `linear’, it is somewhat similar to say that `you can add that up’.

For example, a person cannot eat 500g of salt in an hour, that probably causes death. However, if the same person uses 10g salt per day for 50 days, the danger is drastically less (yet, it still is too much salt). We usually cannot simply add up the amount to difference the effect on a human body.

However, we assume the radiation dosage (Sievert) can be added as an approximation. We should remember that this is an assumption. The Sievert unit is not like the meter unit, which can be added up.

I would like to clarify make clear the difference between 1 mSv/y and 1 mSv since I read many news articles about them. 1 mSv/y means that if you stay at a location where your measured radiation is 1 mSv/y for one year, you get 1 mSv dosage. If you stay in such a location for two years, you get 2 mSv. The current criterion of the evacuation counsel for disasters is 20 mSv/y in Japan (2014). If you stay in a location where you have 20 mSv/y location for five years and assuming that the radiation stays the same, the dosage is 100 mSv. Please notice this difference. If you decide to take the 10 mSv risk, you can only stay at a 1 mSv/y location for 10 years. Especially young children usually have higher risk for the same dosage, so you also need to consider long term exposure. The difference between mSv/y and mSv is similar to you need to pay 1000 Euro every year and you need to pay 1000 Euro only once. Please do not confuse every year payment and one time payment.

We have two criteria that define what is nuclear waste. One is based on the Sievert value, the other is based on the Becquerel value. If the waste consists of one kind of radioactive substance, it is reasonable to define the criterion based on the Becquerel value. Since the half life are depends on the radioactive substance, you cannot really estimate what the danger is if the substance are mixed. Therefore, there are criteria based on each nuclide. However, if many kinds of radioactive substances are mixed up, which is often the case, it is difficult to determine what is nuclear waste and what isn’t. If we can separate all the nuclides, we can still use the Becquerel value criterion separately, however, it is usually not easy to do. In that case, we use a criterion based on radioactive dosage — we use the Sievert value in this case.

If we read a newspaper, it seems that these criteria are used arbitrarily. Sometimes we see a Cesium 137 Becquerel value for cleaning up bi-product waste (e.g., [1]). I wonder if there are other nuclides, for example, is there Strontium 90 in the waste?

Another problem is what kind of radiation can the measurement devices measure. Most of the measurement devices can only measure gamma radiation, but there are other types of radiation.

If you review the periodic table in chemistry, you may notice there are mass numbers in it. For example, there are several kinds of the same element, e.g., Cesium 134, Cesium 137. They are isotopes. These numbers represent their mass number. For example, there are many kinds of radioactive Cesiums. If a newspaper mentions a radioactive Cesium, I would like to know which one it is. Because their half lives differ. The half life of Cesium 134 is around 2 years. The half life of Cesium 137 is around 30 years. This means, the Becquerel value of Cesium 134 becomes 1/1000 after 20 years. On the other hand, the Becquerel value of Cesium 137 becomes only less than half after 20 years. You could learn these things in high school. I found high school science is quite sufficient to know most of these things. I understand that the information sources have only limited time and amount of information they can give. If you know more about this basic chemistry knowledge, you can understand the provided information more.

This is maybe a small detail, the safety criteria of the radioactive waste depend on organizations, countries, and the year [2],[3]. According to Japanese prime minister office (首相官邸)[4], the criterion based on which you should leave an area is when there is more than 20mSv/y. This threshold for the Ukrainian government is 5mSv/y [5]. There is no right and wrong here. Risk is evaluated based on some assumptions and these assumptions differ from government to government. The governments determine these assumptions, therefore, the criteria depend on the country.

In the end, there is always a risk when there is radioactive waste. There is no absolute safety, but there is also an acceptable risk level. Governments usually provide documents about how they consider the risk and what are their assumptions. We need to determine whether we can accept the risk and the assumptions. (Although if a government forces people to accept the risk in some way, or if people cannot decide on their own, I believe this is violation of human rights.) To judge the risk, we first need to understand the information. Then we need to think on our own. The risk is usually probabilistic, we should think through it and decide whether we can accept it or not. If people cannot agree with the government decision, then they should change the government.

The message I’m sending here is to understand this information. This is a first step. It would be not so simple at the end, but the important thing is that we understand the information and we take our decisions on our own.


  1. Kahoku-shinpou (河北新報), The governor of Miyagi-prefecture has accepted for the investigation to build the final disposal repository (宮城県知事、詳細調査受け入れ 最終処分場),, (Online; accessed 2014-12-26)
  2. Ministry of Health, Labour and Welfare of Japan (厚生労働省), How we handle the radioactive substance in food (食品中の放射性物質への対応),, 2014, (Online; accessed 2014-12-21(Sun))
  3. Ministry of Health, Labour and Welfare of Japan (厚生労働省), We updated the safety criterion of radioactive substances in food (食品中の放射性物質の新たな基準値を設定しました),, 2014, (Online; accessed 2014-12-21(Sun))
  4. Prime Minister’s Official Residence (首相官邸), Keeping everyone’s safety (みなさまの安全確保), How we set up “the planned evacuation region” and “preparation necessary region when the emergency “(「計画的避難区域」及び「緊急時避難準備区域」の設定について),, 2011, (Online; accessed 2014-12-21(Sun))
  5. オレグ・ナスビット, 今中哲二, ウクライナでの事故への法的取り組み,, 2011, (Online; accessed 2014-12-21(Sun))


最終処分の話をしようや (8): 付録 2: 放射能・放射線について

Radioactivity and radiation

If you check Wikipedia or any chemistry course, you have some idea of what is an atom, what is radiation, what is radioactivity, and so on. Why is radiation dangerous? Because it can break the DNA in our body and that makes you sick. How much does it can break depends on the radiation energy, on how much energy our body absorbed and so on. In a way, it depends on how strong the offense is and how strong the defense is. To know more about this, first we should know about the concept of radioactivity, radiation, and their strength. Since we don’t know the meaning of those things, we are left with trusts the authorities on these matters. I would like to avoid such situation. Here I summarize the meaning of radioactivity, radiation, Becquerel, Sievert, and so forth.

We can use an analogy with light to think about these substances.

An analogy between a light bulb and radioactivity
Figure 6: An analogy between a light bulb and radioactivity

Radioactivity is also known as radioactive decay or nuclear decay. It is the process of a nucleus of an unstable atom losing energy by emitting radiation to move to a more stable state. If an atom can emit radiation, it is considered radioactive. From an observer point of view, saying that something is radioactive means that a substance can emit radiation. It is an ability of emitting radiation. If you think about a model with an offense and a defense, this is the offense side. If you think about this as light, a light bulb has the ability to emit light, so I could say that a light bulb is light-active. In this analogy, the emitted light is itself radiation. Figure 6 shows how a light bulb and a radioactive emitter that correspond to each other. Radioactivity is more like a property of a substance, that is similar to the property of a light bulb. Please note, radioactivity does not correspond to emitted light, but rather to a light bulb. A light bulb has the ability to emit light, but a light but is not light per se. We can grab a light bulb and move it to a box, then we can take it out from the box, but we cannot grab light and put it in a box. We can also use the analogy of sound. A speaker has the ability to create sound, so we could say it is sound-active, but, the speaker itself is not sound. I hope by now you know the difference between radioactivity and radiation.

Radiation is the emission of energy from the nucleus. When a nucleus changes the state, an emission happens. What kind of radiation will be emitted depends on the type of nucleus. The unit this quantifies how many times the decay happens in a second per a certain unit mass is called Becquerel (Bq). This is the strength of the offense side as we were saying earlier. A certain unit mass means for example 1kg or 1t, it is just some amount of mass.

Why do we need a certain unit of mass? Because even if we only have the same Bq radioactive substance, when we have more of it, the number of decay events increases. It is same as saying that if we have more light bulbs switched on, we get more light. Therefore, usually we see this amount of number of decay per kg (Bq/kg). If 1kg of radioactive waste is 8000 Bq it means that this 1kg of radioactive waste has 8000 decays per second. If there is 2kg of this waste, you observe 16000 decays per second. When the number of decays per second (Bq) increases, the corresponding radiation energy will also be increased. However the Bq/kg in this example is the same in both cases, that is 8000 Bq/kg. If an article only said Bq without ‘/kg’, then that should be the number of decay per second. If the certain unit of mass is smaller, then the number becomes smaller even if radioactivity stays the same. 8000Bq/kg is equal to 8Bq/g. If some food has 1000 cal/kg, it is the same as 1 cal/g. Please be careful with units.

Sometimes a criterion is defined on Bq/kg. For instance, a safety criterion defines that water is safe if it is less than 10Bq/kg. Personally, I have a problem with this criterion. Since you can add non-contaminated substances to mix with contaminated waste, you can fulfill this criterion. For example, if you have a 1kg 8000Bq/kg waste, if you mix it with a clean 1kg substance you have 2kg 4000Bq/kg waste. If you have high Bq/kg tritium water, you can just put more water and achieve low enough waste water that allows to throw it in the sea according to this criterion. If any poisonous substance has this density criterion (which sometimes make sense), we could put it in the sea and pass this safety criterion. Do you think we can continue with that? I find this is dangerous. For me this density criterion (Bq/kg) is questionable. At least I would like to know how much is the absolute value, like some “8000Bq/kg waste 10kg was trashed.” If you understand this unit (Bq/kg), I think you know what kind of information you would like to know more. If I only have the Bq/kg, I see that the information — How much waste have you actually trashed? — is hidden away.

An analogy between light and radiation
Figure 7: An analogy between light and radiation

Amount of radiation (energy)

By now, you see that the real danger is radiation rather than radioactivity. We cannot switch off radioactive substances in order not to emit radiation. (On the other hand, we can switch off a light bulb in order not to emit light.) Thus, radioactive substances are of course dangerous. But, we could block or weaken the radiation from radioactive waste if we can put it in a thick container of lead. Therefore, if radioactive waste is well under control, we can stop the radiation. Then there is no harm to life. The problem is not like in a situation, where some radioactive substance is dispersed in the environment. In that case, how much radiation is emitted is important.

A dosage shows how much radiation is there. To say that more exactly, a dosage shows how much radiation is absorbed by something. But we could think about this as first how much radiation is there and then how much that affect a person. Figure 7 shows an analogy between light and radiation. If you go away from the light source, the brightness your receive (irradiance) becomes lower, which means it gets darker. In that Figure you see two kind of units. For radiation, we consider the energy absorption instead of radiation energy itself. You see two kind of units, Gy (gray) and Sv (Sievert). Why do we consider the energy absorption? Because if a human body is exposed to the same radiation energy, the effect also depends on how much radiation energy was absorbed by the body. For a measurement about safety, the amount of absorption is important. We measure how much energy is absorbed by gray (Gy). It is defined as the absorption of 1J of radiation energy per 1kg of matter. (If you don’t know about what is 1J, Please look up what it is.) You can imagine that thinking of the amount of energy absorption is similar to thinking of how much damage you got.

If you play some role playing video games, you know the damage depends on what is your armor or how you got the damage. That is represented by decreased your health points. In these games, what is important is how many health points you lost, not how strong the attacker is. The amount of absorption for radiation is like the amount of decreased the health points. But actually the most important value is the remaining health points, not their past decrements. However, the remaining health points for radiation depend on the person, age, and so forth. There is no simple criterion for safety, but the amount of absorbed energy could be one of such criteria.

最終処分の話をしようや (7): 付録 1: リスクを自分で判断するための知識を理解しよう

Measures of radioactivity and the radiation: Becquerel and Sievert

The purpose of this section: Understand the science to determine your own risk

Radioactivity is an ability to emit radiation. Honestly I didn’t know the difference between radioactivity and radiation a while ago. If you also don’t, this article is for you.

As a citizen I am most interested in “safety.” But the problem of radiation is that we cannot see it directly. Also there is not so much available experimental data on safety of radiation. If we want to know it in a scientific way, we need to perform an experiment. That means we would probably need several thousand subjects and we would have to put them into some controlled environments with different radiation for many years. Then we could know what kind of dosage affects the human body. But this kind of experiment raises a lot of issues. Since we cannot make such an experiment, we cannot know for sure. Each specialist has different opinions. It is hard to make a constructive discussion about radiation safety. What we could do is basically avoid the radiation. However, if that is difficult we need to judge the risk on our own based on available information, although we saw what happened when we just believed some authorities in Fukushima as they told us “atomic reactors are safe”. We just didn’t know what they meant by “safe.” I think this time we should understand the problem on our own.

Here I can only provide some information from the government and from other sources. First we would like to understand it, because if we cannot understand what it means we cannot judge the risk. For example, what the Becquerel means. What is the difference between radioactivity and radiation. Let’s try to understand these words.

The goal of this appendix is to learn how to read and understand the information. Let’s get started.

The knowlege of basic words: Radiation, radioactivity, and so on.

The question “Whet is radioactivity?” is related to the one “what are atoms?” The concepts of atom and molecule is very common in nowadays industry, and we learn them in public school. When I learned them, I did not realize that these concepts are related to everyday life and to our surrounding industry, or I just missed it, and you might miss it too. What is electricity is also deeply connected with atoms. You use electricity everyday, but can you answer the question, “What is electricity?” if your children asked you? I learned it when I was in a junior high school. If you also forgot them, but suddenly the newspaper started saying, Cesium 137, Cesium 134, and so on, you can look up your old physics textbook. If you have a child in junior high or a high school, you can ask them. You can also find this information in the Internet.

One way to start to know what is an atom is looking up Wikipedia [1]. You can also find online chemistry courses (e.g. [2]). Usually such courses do not provide information about radiation safety, but at least you can find what is radiation. That is a good start to understand the issue of safety.

Japanese officials provide some information about radiation safety. For instance, “How to be safe for all of you (みなさまの安全確保) [3].” You can find some criteria for the radiation safety in it. However, it is written as “Assuming 1mSv/y internal exposure, drinking water should be less than or equal to 10Bq/kg [4].” You can also find a terminology list at [4]. If you can understand that, you can stop reading this article here. In case you do not understand that, I will try to explain how I understand it. For example, what is Sievert (Sv), what is Becquerel (Bq), why we see sometimes a unit like Bq/kg, what is the difference between mSv/y and mSv? Most importantly, why should I care? Even if we know the meaning of their terms, it is still difficult to determine the risk, but at least we can understand what it means. This could be a foundation of your own decision for the risk evaluation.

I tried to make this article as precise as possible, but there is a limit. Please do not just believe this article blindly. It is important to understand the problem yourself.


  1. Wikipedia En, Ionizing radiation,, [Online; accessed 2016-1-13(Wed)
  2. Khan academy, Chemistry,, [Online; accessed 2016-1-18]
  3. 首相官邸, みなさまの安全確保, 「計画的避難区域」及び「緊急時避難準備区域」の設定について,, 2011, [Online; accessed 2014-12-21(Sun)]
  4. 厚生労働省: 原子力被災者生活支援チーム, 原子力発電所外に適用されている放射能に関する主な指標例,, [Online; accessed 2014-12-26]

最終処分の話をしようや (6): 最終処分の資金はどうなっているのか

The budget of long term waste management

The budget for long term waste management depends on the country. Typically, the power companies that have nuclear power plants pool the budget for the back-end process. The size of the pool is based on the electricity fee. This is the user-pays principle: Someone who has a benefit must pay for it. This means that the consumers of electricity from the reactors pay for the decommissioning of the reactor and the long term waste management.

In Germany, the power companies pool the back-end budget of around 30-36 billion Euro. It seems that Germany has the largest back-end budget in the world, still there is no guarantee that it is large enough.

In Japan, some back-end budget is pooled, however, there is no budget for the long term storage. Since the Japanese plan assumes that the nuclear cycle will be established soon, and the nuclear cycle assumes that there is no nuclear waste (MOX used fuel).

In any case, the budget is most probably not enough and the people who did not use the energy need to pay the debt.

The status of long term waste management in the world

A final disposal facility for high level nuclear waste has not been implemented yet in the world (as of November 2014). The Onkalo used nuclear fuel repository on the west coast of Finland will be the world’s first deep geological repository for used fuel final disposal. It is currently under construction and planned to begin operation use around 2020. Here we summarize the current status of Germany and Japan.

The final used fuel disposal plan in Germany

For low-, middle-level nuclear waste final disposal, there were following plans in Germany. However, still many problems should be sorted out.

Schacht Konrad

  • 1000m deep under ground
  • Originally, this was an iron mine. The upper part is clay stratum.
  • The permission of operation has been issued. Use is planned for 2017. However, there are unresolved technical issues. There is a large possibility that the plan would be delayed.

Morsleben (at ex East Germany)

Asse (at ex West Germany)

  • 1000m deep under the ground
  • The deployment was begun in order to test whether the rock salt stratum is suitable for the purpose.
  • Water leaking was found. High level nuclear waste disposal was found. It was planed to remove all the nuclear waste.

Germany investigated the location of deep geological repository of high level nuclear waste at Gorleben. However, the discussion was cleared up. After that, the deep geological repository investigation committee has established and the committee representing many areas was gathered. Here is the current plan:

  • July, 2013, the law of how to decide the location of the final disposal facility.
  • The ministry of the final disposal facility has been established.
  • The procedure how to decide the location of final disposal facility will be established at the end of 2015.
  • The operation of the facility will be started in 2035. (Updated May 2015: The committee mentioned the operation of the final disposal facility should be postponed after 2170 due to not enough backend budget.)

At Gorleben, the stratum of Rock salt under 1000m from the ground was investigated. However, how to proceed is not clear yet.

In Germany, the first plan was an eternal repository. But the plan has
been changed. The operation time of the current plan is 1,000,000
years. For the first 500 years, we can still have access to the used
fuel. This is in case we could develop a technology to make the used
fuel innocuous in the first 500 years.

The final disposal plan in Japan

In Japan, the low level final nuclear waste disposal facility is in operation at Rokkasho-mura. The maximal depth of this repository is 100m.

Japanese plan of high level used fuel disposal is based on the assumption that the technology for a nuclear fuel cycle can be established soon. This means the reprocessing of the used fuel is a prerequisite and then the final disposal facility would not be necessary anymore. After the Fukushima’s accident, the discussion about establishing a final disposal facility raised, there is no concrete plan however of the final disposal yet both for used fuel and vitrified waste (as of May 2015).

A part of the high level nuclear waste is vitrified waste. 40,000 containers of vitrified waste will be produced in 2020 (estimate). For this waste, the government officially asked all the cities to be voluntarily a candidate location for the final disposal facility. There were around 10 candidate locations, but most of them were retreated and there is none as of December 2014. (Updated May 2015: The government gave up the public offering and has decided that the choice of the location will be up to the government [1].)

There are a few research facilities for a deep geological repository. At Horonobe-city in Hokkaido, the research is on going on a clay stratum, at the depth of more than 350m. At Mizunami-city in Gifu, a granite stratum at the depth of around 500m is being investigated.

However, Japan is a country with lots of ground water and has frequent earthquakes compare of to other countries. It is hard to find the location where “There is no ground water and the stratum is stable for more than 10,000 years.” The existence of ground water and the possibility of earthquakes are not well suited for a final disposal facility. This is a problem for Japan.

Yamauchi’s memorandum

Middle-/Low-level final disposal nuclear waste facility will be investigated in Miyagi prefecture [2] (Updated December 2014). This waste was the product of a decontamination process.

Principle of final disposal of spent fuel

The principle of final nuclear waste disposal is “In land and the user pays.” The consumers who actually used the electricity should pay all the cost. We should not pass this negative legacy to the next generations. But, it is not possible to avoid this anymore. We have a debt to the future.

What we could still do is, for instance, to invest in clean energy technology to alleviate the burden on the next generations. In our generation, we will not be able to finish the clean up of the negative legacy, i.e., reactor decomissioning and final waste disposal. Therefore, one way to decrease the next generation’s burden is to invest in sustainable energies and distribute the cost between the generations. Otherwise, the energy cost is not fairly distributed between the generations. If the generations of nuclear reactor put the cost to the next generation, the next generation will suffer from their development.

Yamauchi’s memorandum of the final disposal

Here is a conclusion including my personal opinions.

A nuclear power plant cannot run forever. Thus one day we need a decomissioning and a final waste disposal. This is independent of agreeing with or not for nuclear power. This is just a fact: a human made object will not stand forever. Fundamentally, human activity produces garbage.

The nuclear fuel cycle plan is based on an assumption that does not produce used fuel. The research into the nuclear fuel cycle in Japan spent more than 40 years and 100 billion yens, the prospect of the plan still does not stand [3]. I think we need a new plan since the assumption seems to have a problem. Many of the countries realized this problem and most of them have retracted the plan. Even if a nuclear fuel cycle plan is established, the reprocessing produces high level nuclear waste as vitrified waste. The amount of this high level waste is increasing (ref. a report of the federation of electric power companies of Japan [4]). This means we cannot avoid two negative legacies: decomissioning and final nuclear waste disposal.

I mentioned the “user-pays (beneficiary pays) principle”. This principle is for our future development. I think the energy problem is not a public service problem since the industry has a large role in energy consumption. We would in theory ignore the principle: Essentially we would not care about the future of our children and our country in order to gain something right now. Since these children do not exist yet, it is possible to have a democratic decision without them. I must ask this myself, is it ok? We elect governments that make a lot of debt for the future without a plan to pay it up. We could even decide that we do not want to return the debt. However, such people would lose trust. This means no more investment, since investors expect returns. I think we should think more about the meaning of the “user-pays principle.” If no investment is expected, we need a sustainable future, but what we are doing (living on the debt) is not sustainable.

It is not easy to find the information about the backend budget of Japan. (The backend budget for nuclear power plant is the budget for clearing up the plant: decomissioning, fanal disposal of waste, and so on.) The backend budget is about the user-pays principle. Today’s backend budget of Germany is 30 – 36 billion Euro (4 trillion yen as 136 yen/euro as of today (2015-7-3)). This is now considered not sufficient. According to the article [7], all the Japanese power companies as a whole should set aside 1.5 trillion yen for the decomissioning budget. The backend budget includes final waste disposal besides decommissioning. I am interested in how much backend budget the Japanese have set a side. I have not been able to find this information yet. Please notice that budget of Japan and Germany cannot be easily compared, since Japan has more than the twice reactors of Germany. The article [7] pointed out that Japanese power companies have a plan to collect the budget deficit even after the decommissioning. This means the people who did not use electricity will pay the backend budget as electricity fee. According to this plan, the nuclear energy fee cannot cover the whole life cycle of the nuclear energy, so fossile/water/solar power sources will cover the nuclear’s energy. I think the user-pays principle does not hold here. Moreover under the current law electricity consumers have no choice but to pay for the nuclear power life cycle via another type of energy. Our children have no choice as well, they need to pay for non-used electricity fee. I don’t find acceptable that they say “Here, there is some cheap stuff, use it!” then later say, “Hey, you have hidden debt because of that. Your children and grandchildren must also pay for that.” I also find hard to imagine, how our children and grandchildren look at it. Because of this, I find the backend budget an intersting item. I think that if someone uses them, he/she should also pay for it.

This is my personal opinion: I’d rather stop the investment to make the old system to just survive for a short time. It will be a burden to the country’s economic system. We can get a small gain for a few years span, but then we have a long term suffering negative effect. It’s this kind of effect that can cause the collapse of a country. I hope we are able to clear up the negative legacy as early as possible.

Another drawback of nuclear plants is negative effect for national security. One of the reasons that the U.S. have a hard time building a new nuclear plant is not only the cost itself, but also the security. You can find a discussion considering the terrorist danger for the nuclear plant [5]. In this discussion, nuclear power plants are good target for terrorists as a country can easily lose a large part of the land. On the other hand, natural energy, i.e., solar, wind, etc. is way safer in case of terrorism and war. Personally, I do not have enough knowledge to numerically evaluate this kind of cost, although some other countries have discussion this kind of costs. We could also consider them.

I would like to think about what future I would like to have, how we can decrease the negative legacy for our children, what can I do for that. I wish we and our children could have sustainable development in our future.

(Update: 2015-6-26(Fri) Ministry of Economy, Trade and Industry (Yoichi Miyazawa, Minister of Economy, Trade and Industry) agreed to establish the working group of “Nuclear cycle operation” to discuss how to continue the nuclear cycle development [6].)


  1. Asahi Shinbun (朝日新聞), “The govenment leads to choose the waste processing site. [Promised location] was presented. The cabinet’s decision (国主導で原発ごみ処分地選定、「有望地」提示 閣議決定)(2015-5-22),, [Online; accessed 2015-7-2]
  2. Kahoku shinpou (河北新報), The governor of Miyagi has accepted the candidate’s investigation of the final waste disposal (宮城県知事,詳細調査受け入れ 最終処分場 2014-8-5),, [Online; accessed 2014-12-22]
  3. Tokyo Shinbun (東京新聞), Spent 45 years and 100 billion yen. Nuclear fuel cycle has no concrete plan yet. {45年で10兆円投入.核燃サイクル事業めどなく),, [Online; accessed 2014-10-04]
  4. The Federation of Electric Power Companies of Japan (電気事業連合会), Nuclear power plant (原子力発電について): Vitrified radioactive waste (ガラス固化体),, 2014, [Online; accessed 2014-12-21(Sun)]
  5. Amory Lovins, A 40-year plan for energy, TEDSalon NY2012,, [Online; accessed 2014-12-22]
  6. Asahi Shinbun (朝日新聞), Return to the nuclear power. Question on restarting the reactors 4: Nuclear fuel cycle office is looking for reopening the process (原発回帰 再稼働を問う:4核燃サイクル、再開にらむ (2015-7-11(Sat)),, [Online; accessed 2015-7-11]
  7. Nishi-nippon Shinbun (西日本新聞), 40 percent deficit of nuclear decommisioning budget, Fill the budget by after the decommisioning through the electricity fees, investigated the back end budget of 9 power companies (原発解体費4割不足 廃炉後も電気料金で穴埋め 電力9社積立金調査 (2014-10-20)),, [Online; accessed 2015-7-3]

最終処分の話をしようや (5): 最終処分の方法

Deep geological repository

One method for the final disposal storage is the deep geological repository method. Surprisingly, there was also an ocean disposal method. However, this method has environmental problems and is no longer permitted by international agreements. The deep geological repository method basically digs a deep hole and stores the waste in the hole. This method is considered as the most practical method.

The deep geological repository method blocks the radiation by two

  • Artificial barrier: container, concrete wall
  • Natural geological barrier: stratum

Most of the radiation blocking effect is by the natural barrier.

The level of the waste and the criterion of how deep the waste should be stored depends on the country. Some examples are following:

Low-, Middle-level waste

  • shallow (a few hundreds meters (e.g., Japan))
  • middle
  • deep (around 1000m (e.g., Germany))

High-level waste (+TRU waste)

  • deep geological storage

The stratum suited for high level nuclear waste are following. Each has own characteristics.

  • Clay stratum
    Disadvantage: This stratum has low thermal conductivity and the
    heat would not be well diffused. Therefore, the stratum could be
    dried out and might generate cracks. The waste would possibly
    leak through such cracks.
  • Granite stratum
    Disadvantage: The rock is relatively hard, thus the cost of
    digging is quite high. There could be ground water and the water
    diffuses the contamination of the waste.
  • Rock salt stratum
    Advantage: This stratum has high thermal conductivity and the
    heat of the high level waste is well diffused.\\
    Disadvantage: It is highly possible to have ground water since it
    was a sea in the past. The water diffuses the contamination of
    the waste.

For long term geological waste management, the following conditions are necessary for the stratum to stably store the waste.

  • Uniformity. (If the stratum is uniform, there is less possibility
    to have cracks, or less possible to cause them.)
  • No ground water. (Ground water possibly diffuses the waste.)
  • No movement. (We cannot stably store the waste in moving strata.)

Ground water and cracks may distribute the radioactive contamination, especially for the long term waste storage. Therefore, the non existence of ground water is an important condition.

Example of long term deep geological repository

The deep geological repository method typically consists in digging two vertical holes and connecting them with a tunnel under the ground where the stratum is suited for long term waste management. The waste will be stored in the tunnel.

Figure 4 shows the long term storage facility for low-/middle-level waste in Morsleben in the Eastern Germany time. You can see the huge storage faciliy under the ground. Later the government decided to stop using it and closed the Morsleben’s storage facility since there is a danger of rockfall for the rocksalt stratum.

Figure 4: Picture: the structure blueprint of the long term waste storage facility in Morsleben

Gorlben (in Germany) had a plan to build a general waste processing facility. First, the central interim storage facility has been built. Then, a facility was built to check that whether the rocksalt stratum of this area is suitable for the long term storage. However, there were some questions regarding the suitability, the investigation was suspended and reopened, repeatedly. The government decided to start over the process of choosing a location. A committee that will choose the candidate location has been established at the parliament.
Picture: oil in the stratum (Gorleben, Germany)

Figure 5: Picture: the structure blueprint of the long term waste storage facility in Morsleben

Figure 5 shows a pictures of stratum in the tunnel of Gorleben. The black part is oil and that means the rocksalt stratum is not uniform.

最終処分の話をしようや (4): 最終処分とは? 放射性廃棄物と放射能減衰の推移

We talked about what is the nuclear waste, how it is generated and what kind of process we need to do in order to put it in a final disposal storage. Since we still do not have a practical (cost effective) nuclide conversion technology, the most practical method to render nuclear waste innocuous is its long term management. In the next section, we will review the property of nuclear waste. That will bring up what kind of problems we have with the final disposal of waste.

Transition of used fuel radioactive decay

A chart of radioactive decay over time

When used fuel is taken away from a reactor it is highly radioactive. Thus we need to store it in somewhere and wait for the radioactivity to become lower. At the meeting we saw a radioactivity attenuation chart, which shows that it takes a long time.

Yamauchi’s memorandum

How long do we need to store the used fuel? If we only need to store the used fuel for a few months and the radioactivity level became low enough, nuclear waste management might not be a big issue. However, it is not so easy.

Figure 3 shows the radioactivity attenuation of used fuel over time. You can find this chart at the web site of Research organization for Information Science & Technology (RIST) [1], that refers to the web site of Japan nuclear cycle development institute asthe source of the data.
radioactive_timeline_2_enFigure 3: Radioactivity attenuation of vitrified waste over time. The x-axis is time in years, the center is 0 years. The y-axis is labeled `1 ton nuclear fuel (MTU) corresponding radioactivity [GBq]’
[Original figure] Japan nuclear cycle development institute: 2nd period of research and development of deep geologically repository, summary report I-4 (1999-11-26)

How to read Figure 3:

Let me show you how to read this chart. First, please notice the graph scale is log-log. What does this mean? Both axes of a log-log graph are described by exponent. You may be familiar with a linear graph. In a linear graph, one tick of an axis means usually +1 (or +n), but one tick of this chart is × 10. For example, one tick of this chart means ‘times ten’ instead of ‘plus one’. If you go two ticks, the value increases 100 times more.

The vertical axis shows the radioactivity in Becquerel. When the used fuel was taken from a reactor, the radioactivity indicated 1010 GBq/t.

1010 means 10 zeros after 1. Therefore, it is 10000000000, which is 10 billion. The character ‘G’ (Giga) before the unit `Bq’ is a SI-prefix, and it means 109. If you are familiar with computers, you know the memory size is represented as GBytes, which is 1000 times larger than MBytes. This means, 1010 GBq is 10,000,000,000 GBq = 10,000,000,000,000,000,000 Bq = 10 quintillion.

According to the criterion of the Japanese government, though it depends on nuclide and food, we should avoid eating food with an activity of more than 100 Bq per kg. Compare to this number, radioactivity of the used fuel is enormous. It seems beyond my imagination.

There is the 0 on the x-axis at the center of the graph. This is the time when the fuel is first used. To make Uranium useful as fuel, it is enriched, i.e., its radioactivity is increased. As we go to the right, time passes. The axis ticks increases 100 years, 102 years, and so on.

The exponent number of 10 has the same meaning as in the last example about Bq, how many zeros after the 1. This means, 100 years is one year (zero zeroes after 1), 102 years is 100 years, 104 years is 10,000 years, and 108 years is 100,000,000 years.

The graph shows a horizontal blue dotted line. This line shows the radioactivity when Uranium ore is in a mine. The cross point of the red line and the blue line is between 104 and 105 years. Therefore, it takes about 10000 to 100000 years until the radioactivity of used fuel reaches the level of naturally occurring Uranium ore.

By the way, it is unfair to compare the 100 Bq/kg for food and 10 quintillion Bq/t for used fuel. Note that the units are different: Bq/kg and Bq/t. This means that radioactivity of 1 Bq/kg is 1000 times higher than 1 Bq/t. Therefore a fair comparison is between 100 Bq/kg for food and 10 quadrillion Bq/kg for used nuclear waste. We sometimes miss the unit difference. Sometimes we could find these units are not consistent in some news articles. The different units are not technically a mistake, but it is still misleading. When we use the same unit here, 100 and 10 quadrillion are quite different.

These large numbers are hard to see. We do not know what 10 quintillion or 10 quadrillion are. Scientist usually use the scientific notation to write these numbers. The scientific notation uses exponent. In other words, this is how many zeros are in the number. 100 has two zeros after one, in exponent writing this is 102. 1 quadrillion is 10,000,000,000,000,000. This has 16 zeros after 1, it is 1016. Many advertisements use large numbers since they have a high impact when heard. For example, a sport drink in Japan claimed that was an 1000 mg effective medicine dosage, but this has the same effect as 1g of medicine dosage. Still, 1000 has makes an impression on us, so it is a good advertisement strategy. This is fine for an advertisement, however, I recommend to be careful about units an article about radioactive contamination for the news.

How long shall we keep the used nuclear fuel?

If you search about radioactivity attenuation of nuclear waste (Figure 3) you find many similar figures on the Web. I later realized that this figure only shows it takes more than 10 thousand years for the used fuel radioactivity to decay to the same level of an Uranium mine. I found nothing about the safety of the level of an Uranium mine. My first impression was, “wow, at least 10 thousands years, that’s a long time!” But I never asked the question: “is it safe after 10 thousands years?”

The blue line in the figure indicates 1000GBq/t, which means 1GBq/t (one billion Bq/t). 1 GBq/t is quite a large radioactivity value. Though one thing is not clear here that in the explanation, “1 ton nuclear fuel (MTU) corresponding radioactivity [GBq]”, I assume that this unit means GBq/t. If I convert it to Bq/kg, this is 1000 MBq/kg, that is 1GBq/kg, and this is 10 billion Bq/kg. As we mentioned before, the recommendation of safety for food is 100 Bq/kg according to Japanese government, and a value that is 10 million times larger does not safe to me.

I do not know what is blue line in Figure 3 means. Can I safely get near to some radioactive substances if the level is lower than this blue line? As a citizen, I am more interested in safety, so I try to connect this figure to safety, but this is not even labelled as radioactive dosage. I think this figure only shows the relationship between time and radioactivity attenuation, but that is not related to safety.

Progress of radioactive decay and waste management

Figure 3 shows the progress of radioactive decay over time. When the fuel is taken out of the reactor, its radioactivity is 10 billion GBq/t. After three to five years of cooling down in the fuel water tank, it becomes a few tens of million GBq/t. Then, after 30 to 50 years the radioactivity of vitrified waste in interim storage becomes a bit less than ten million GBq/t. Until the radioactivity drops to the level of a Uranium mine, we need to wait approximately ten thousand years. The final disposal process starts after the interim storage stage. Let’s see what is planned for that.


  1. Research Organization for Information Science and Technology (RIST: 高度情報科学技術研究機構), “Safety problems of high level nuclear waste and its processing (高レベル放射性廃棄物と処分対策の安全問題), note: the decay graph of vitrified waste can be accessed from this page)”,, [Online; accessed 2015-7-1]