In Japan the Nuclear Safety Commission has already completed its deliberations about the clearance levels for light water reactors, gas reactors, heavy water reactors, and fast reactors, as well as the nature of the inspection and approval process. Consideration of the Spent Fuel Reprocessing Plant and the Fuel Fabrication Plant still remains.

In parallel with the Nuclear Safety Commission's deliberations, based on the issues that have already been considered, the Radioactive Waste Safety Subcommittee of the Nuclear and Industrial Safety Subcommittee of the Advisory Committee for Natural Resources and Energy is starting to consider the type of system that will be required. Their report is scheduled to be completed this summer, and it is expected that a Bill to amend The Regulation of Nuclear Reactors and Related Matters Act will be submitted to the Diet early in 2005.

The basis for the calculation of the clearance level is an annual radiation dose of 10 micro sieverts. A radioactivity concentration (clearance level) is determined for reach nuclide, such that in one year the exposure dose from that nuclide will not exceed 10 micro sieverts, even if the huge amount of radioactive waste generated when a reactor is dismantled is reused as metal or concrete, or even if it is buried as industrial waste and that land is then used for agriculture and so on.

However, more than one type of radioisotope might be contained within the waste, so they have to ensure that even if there are multiple radioisotopes, the overall radioactivity concentration doesn't exceed the clearance level. Having said that, the fact is that it is virtually impossible to measure the concentration of radioactivity of all the radioisotopes and then calculate from that the total radiation dose. They deal with this by selecting nine 'principal radionuclides' (C-14 is added for Fast Reactors and Ba-133 for Heavy Water Reactors. Also, where prior assessment of individual batches of waste indicates that other nuclides should be considered, these may be added too.) The 'standard concentration' for each nuclide (measured in becquerels per gram) is the concentration that would, on its own, result in a yearly dose of 10 micro sieverts. The percentage of this standard concentration that is present for each nuclide is assessed. As long as the sum of the percentages of all the nuclides is less than 100%, the waste is considered to satisfy the clearance level. In fact, however, they don't even measure all of the above nine radionuclides. Co-60 is adopted as the 'principal measurement radionuclide'. A ratio compared to Co-60 is then derived for each other nuclide by measuring a sample of the waste. The total concentration of radioactivity of Co-60 in the batch is then multiplied by this ratio to calculate the concentration of radioactivity for the other nuclides. Tritium is the exception in that the concentration of radioactivity measured in the sample is applied as is to the whole batch, without making any adjustment based on its relative concentration of radioactivity compared to Co-60.

For all nuclides other than tritium, the standard falls within the range set by the International Atomic Energy Agency (Table 1), but depending on the particular nuclide, the figure varies between these maximum and minimum values. As for the radiation exposure scenario, the Nuclear Safety Commission states proudly in its report that it made its own assumptions and carried out its own calculations 'based on the Japanese lifestyle and social environment'.

Table 1: Major Radionuclide Clearance Levels (becquerels/gram)

Data is gathered, in the case where the waste is used to make fry pans, in regard to the surface area of fry pans, the corrosion rate of iron and the hours per year spent cooking with fry pans. Where it is used for drink cans, data is gathered on the concentration of iron in the drink and the amount consumed per year. Then again, if it is used to make a bed, the data relates to the distance from the person sleeping on the bed and the hours per year spent using it. In the case where the waste is buried and the land then used for agriculture, the hours spent farming the land and the amount of produce consumed are assessed. Using this data, a calculation is made of the concentration of radioactivity that would, in the worst case, lead to a dose of 10 micro sieverts per year if the waste were to be reused or buried.

The figure chosen for some nuclides, such as tritium, is much stricter than the IAEA standard, but the calculation is based on numerous assumptions and the fact that different calculations lead to variations of several magnitudes just goes to show how unreliable this calculation is. Witness the interim report regarding the calculation (April 1998), in which the clearance level for tritium was given as 7 becquerels per gram, whereas the current figure is 200 (Table 1). And they say that these levels may be revised again in future.

Another huge problem is that no warning or labeling whatsoever will be provided regarding this 'waste that doesn't need to be treated as radioactive waste' to the workers engaged in recovering the metals, handling the solutions and then processing them into finished products, nor to the consumers of these recycled products. Furthermore, if some sort of accident were to occur, the question of the allocation of responsibility is completely unclear. In particular, where the waste is reused, the allocation of responsibility becomes even more problematic and the responsibility of the electric power company that produced the radioactive waste is totally obscured.

What about medical implements and children's toys? Is it really possible to take into account the possibility of multiple sources of radiation becoming mixed up and still keep the level within the regulatory limit? There's no way we can expect accurate measurement of the radioactivity of the huge quantities of waste involved. If they were to really carry out the measurements properly, the cost in terms of time and money would be astronomical. The recycled products made from the waste would become so expensive that no one would be willing to buy them. To avoid this situation, they would have no choice but to carry out only the most perfunctory tests in the minimum time possible, in order to reach the desired conclusion: 'within the regulatory limit'. And as explained above, only Co-60 will be measured.

The end result will be that suspicions will always remain about whether the regulatory standards have been met. Besides which, a dose of 10 micro sieverts isn't safe in the first place. But whether it be safe or not, they should abandon their plans to bury radioactive waste as ordinary industrial waste, or to reuse it in everyday goods.

Baku Nishio

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