The Impact of a Possible MOX Fuel Accident at Fukushima I-3 Nuke Info Tokyo No. 80

The legal case against TEPCO’s use of MOX

On 9 August 2000, over 850 plaintiffs from across the country, including 138 from Fukushima Prefecture, took Tokyo Electric Power Co. (TEPCO) to the Fukushima District Court asking for a suspension of the use of MOX fuel at Fukushima I. The first hearing was held on the next day, when the plaintiffs explained their case to the court. Their main argument is that there is a strong possibility of falsification of the quality-control data for the 32 MOX fuel assemblies already on site at Fukushima I-3.

If it is assumed that Belgonucleaire’s proficiency in manufacturing MOX fuel pellets roughly is about equal to that of British Nuclear Fuel plc (BNFL), then Belgonucleaire’s relatively imprecise quality inspection of the pellets’ outer diameter should statistically result in a 35% rejection rate. This is because the inspection standards become more rigorous when the number of inspected pellets is low: smaller deviations will be cause for rejection. There are many reasons, such as the size of plutonium spots, which seem to justify the assumption that Belgonucleaire’s manufacturing proficiency is lower than BNFL’s. However, TEPCO has announced that no pellets were rejected during the outer diameter inspection for the lots prepared for Fukushima I-3. Hideyuki Koyama (Osaka Group Opposed to Mihama, Ohi, and Takahama Nuclear Power Plants) showed that statistically, this is extremely unlikely, and that there is a strong possibility that some kind of falsification took place.

The second hearing was held on 18 September. TEPCO was supposed to present its refutation, but were unable to offer a sufficiently credible refutation of the plaintiffs’ claim that a 0% rejection rate is statistically abnormal. Without admitting it, TEPCO had apparently given up trying to offer any explanation. On the same day, the second appeal was made with an increased number of 1,107 plaintiffs, of which 214 were from Fukushima Prefecture.

The danger of using MOX Fuel with dubious data

When MOX fuel is burned in nuclear plants designed for burning uranium fuel, many safety problems arise. For example, the control rods worth are reduced, the emission of radioactive gasses increase, and difficulties arise due to the lower delayed neutron ratio. (See International MOX Assessment report published by CNIC.) Using MOX fuel which is of a low quality, or which exceeds the reactor’s design criteria, further increases the likelihood of accidents. Damage to fuel rods and malfunctions in the cooling system are particularly likely in such circumstances. Large amounts of radioactivity may be released and diffused due to the functional failure of reactor vessels and filters.

If there is an accident at Fukushima I-3

Exposure doses for residents resulting from a diffusion of radioactivity caused by a severe accident at Fukushima I-3 were calculated by applying the same method used in the disaster assessment in ‘WASH-1400’, an accident analysis report produced by the U.S. Atomic Energy Commission.

The plan to burn MOX fuel in light water reactors is called the plu-thermal program in Japan. In the core of a pluthermal reactor, there are ten times more actinides such as plutonium, americium, and curium than the core of a uranium reactor. Actinides cause serious internal exposure in human bodies and thus pose a very serious threat to human health.

The main results from the calculations are shown in table 1. In short, exposure doses resulting from an accident at a pluthermal reactor would be twice those produced by an accident at a uranium reactor. A given exposure dose would be received by residents over twice the distance. The overall affected area would be four times larger. When fatalities by cancer from an accident at a pluthermal reactor is calculated with an assumption that Tokyo was downwind, the number of cancer fatalities would increase from 0.4 million in the case of an accident at a uranium reactor to 10.6 million (See table 2). In view of such risks, MOX utilization is simply too dangerous.