Safety at Monju reactor questioned

May 8, 1996
Issue 

TSURUGA, Japan — Nuclear expert Professor Jochen Benecke said after meetings with Power Reactor and Nuclear Fuel Development Corporation (PNC) officials at the end of March that he is not convinced by the company's safety analysis of its ability to protect against a disastrous nuclear explosion at its Monju fast breeder reactor. He is also worried that a December 8 sodium leak may be an indication of incomplete analysis in other components of the plant.

Benecke is a nuclear physicist with an extensive background analysing the safety of fast breeder reactors. He was touring at the invitation of Greenpeace Japan.

Benecke told a public meeting in Tsuruga on March 30 that PNC admitted to him that a severe "core-disruptive" accident is possible at Monju, as at any other fast breeder reactor, and that it is studying the topic. However, it insisted that quality control in the design and analysis of the reactor would prevent such an accident from happening.

"But the sodium leak in December seems to be a failure of quality in both design and analysis", Benecke told the meeting. "If it is possible to fail in such a simple and well-known matter as the thermocouple which caused the leak, how much confidence can we have that PNC has done everything absolutely perfectly with respect to a major accident?"

There is no reliable scientific method for estimating the size of an explosion which could occur during a worst-case accident in the Monju reactor. The safety calculations used by PNC were originally not meant to provide the type of firm numbers needed to design a reactor vessel so that it could withstand a severe core-disruptive accident.

But since there are no alternative methods available to engineers, they use the existing calculations to design safety-critical components — such as reactor vessels. Since the computer models are not adequate to this task, technicians are forced to make assumptions based on "best guesses".

"The resulting safety analysis is unconvincing and inadequate", Benecke said.

PNC officials declined to provide documents to support their view that their safety analysis is adequate.

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