Procedures of handling the nuclear waste

Until now, we do not have a practical technology to render the nuclear waste innocuous. Therefore, what basically we can do is to wait for the nuclear waste to become low enough in radioactivity due to decay. To do so, we need to store the nuclear waste in a safe storage for a long time until it does not harm the environment.

The low level and middle level nuclear waste do not generate much heat, so it would be possible to store them in the final disposal storage immediately. But, what happened is that it gets stored in a middle term storage due to either of the following reasons:

• There is no such final disposal storage (Most of the countries that have nuclear reactors have no final disposal storage. Ex. Japan.)
• The process would take too long, even when there is a final disposal nuclear waste storage.

Since high level nuclear waste generates high temperature heat, we first need to cool it down. We store them in an interim storage facility to wait for it to cool down. Used nuclear fuel is a high level nuclear waste. First we usually store it in a fuel storage water pool for three to five years to cool it down. Next, we store it in a interim storage facility for 30 to 50 years. If it has cooled down enough, then we store it in a final disposal facility. There are some issues with this interim storage facility, for example where should we store and how should we store.

Japan also reprocesses used fuel, it is one of a few exceptional counties since most of the countries do not any more. In this case, the used fuel is stored in a fuel storage pool in the nuclear reactor building until it is sent to a reprocessing facility. This process of cooling down takes approximately 10 years in Japan. Reprocessing generates nuclear liquid waste as a by-product. One way to stabilize this waste is through vitrification. In the vitrification process, the high level waste is mixed with fragmented glass and melted. This is stored in a steel container called “canister.”

There are two interim storing strategy: 1. geologically distributing them among the nuclear power plants, 2. concentrating them in a few interim storage sites. In Germany, the used fuel is distributed among the nuclear power plants and the vitrified waste is stored in one storage facility.

There are two storing methods: 1. a used fuel pool method, where the used nuclear fuel is put in a water pool and cooled down with water. 2. A dry cask storage method, where the used fuel is put in a canister which in turn is put in a storage place on the ground and cooled down with air. The used fuel pool method needs less space than the dry cask storage method. It does not need special storage cases. Therefore, the cost of pool method for the used fuel lower than the dry method. However, if the water pool loses water for some reason, e.g., because of an earthquake, it is quite dangerous. The dry method needs more space but cooing only needs natural air, therefore this method can avoid the problems the pool method can have. But this method might still pollute the environment with neutron radiation. Despite Japan having relatively frequent earthquakes compare to other countries, the pool method is used. This means that even if all the nuclear reactors would not run, Japan is always under danger because of earthquakes.

Germany uses the dry method. The interim storage facility of Germany is located in Gorleben. In our meeting we saw a documentary film that shows the facility in Gorleben. We saw many casks with fins for cooling in the facility.

In either case pool or dry method, the waste is first stored for 30 to 50 years in the interim storage facilities, afterwords, it will be put in the final disposal storage facilities. This process flow is shown in Figure.

Yamauchi’s memorandum

Supplemental information on vitrified waste:

Vitrified waste emits high radiation right after having been generated, so high to kill a person near will die in 20 seconds. Its surface temperature is more than 200 degree C. (c.f. The web site of “The federation of electric power companies of Japan”[1])

This waste will be stored and cooled down for 30 to 50 years in a interim storage site. Reprocessed plutonium can be turned into a MOX (mixed oxides) fuel, Or, alternatively it can be reused in the nuclear cycle. A national research institute has been established to develop a feasible nuclear cycle, and this research has been going on for over 40 years (and 10 trillion yen been spent), but still there is no plan [2] and the government continues to invest on this.

Supplemental information of nuclear transmutation technology:

Nuclear transmutation technology is fundamentally a technology that is able to change the atomic elements. Nuclear fission is one of such technologies. Mankind has spent a few thousand years to efforts in a field called “chemistry” in order to be able to do precisely this. Element conversion at will is a very old dream of mankind. For example, alchemists were looking for a method to convert lead into gold. This is what nuclear transmutation technology could do, but unfortunately we still do not have a practical technology to achieve that, especially to process a large amount of nuclear waste. A national funded project in Japan, the Omega project [3] is an endeavor of such kind.

References

1. 電気事業連合会 (The Federation of Electric Power Companies of Japan), 原子力発電について (About Nuclear power plant): ガラス固化体 (Vitrified radioactive waste),  ([Online; accessed 2014-12-21(Sun)])
2. 東京新聞 (Tokyo Shinbun), 45年で10兆円投入．核燃サイクル事業めどなく (10 trillion yen been spent for 45 years, still no plan of nuclear cycle), [Online; accessed 2014-10-04]
3. Wikipedia ja, オメガ計画 (Plan Omega), [Online; accessed 2015-3-28]