TNAG-1503-FCO40-2061-Guangdong-nuclear-power-station-project-at-Daya-Bay-safety-c-1986 — Page 81

The consensus view of the experts was that the general features of the accident, as explained by the Russian delegation, were accepted. Everyone agreed that there were many matters of detail which still needed a considered explanation but none of these bore materially on the general conclusions that the accident was caused by a combination of design fault and operator error which lead to a prompt critical nuclear excursion whose consequences led to destruction of the

reactor.

A difficult situation now arose, where no country appeared willing to offer their own experience of similiar accidents. The Russians requested this information, but in vain. Eventually a discussion commenced on one of the questions that had been posed: "What was it that brought the nuclear chain reaction to a halt"? The workshop could not, however, agree an answer, some thinking that it was at least in part due to the fact that some of the fuel had disintegrated and dispersed. The question was identified as one upon which further collaboration was desirable.

The next area discussed was that of operator training, management procedures and organisational matters. Dr Brown of Ontario Hydro was the IAEA-designated expert on this and he outlined the practices in Canada. This stimulated similar contributions from Sweden, Italy and France, all in the spirit of supplying information in response to that which the Russians had supplied.

Attention next turned to "Design for Safety". Dr Frescura of Italy was the IAEA expert on this. Banks of Canada said that they had learned lessons in this area as a result of a relatively minor accident which occurred in the Canadian reactor NRX in 1954. They saw the need, afterwards, for a shutdown system which could be relied on to respond to all possible situations. The system must be quite separate from the reactor control system. That is: the reactor protection system must be separate from the reactor control system.

Derek Smith (UK, NNC) then described the UK design philosphy which is to employ interlocks which prevent the operators from switching off important safety systems. do, the reactor trips.

If they

D Taylor (EPRI) continued the discussion by summarising the changes in thinking concerning the design of Control Rooms in the aftermath of the accident at Three Mile Island (USA). Much was being done with computers, graphic displays and information processing. It was suggested that here was a topic to be added to the list of topics for future discussion.

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