A meeting of technical experts to discuss technical information relevant to the proposed restart of Unit 1 of the Kozloduy nuclear power plant took place in Sofia on 3 and 4 October. It was called on the suggestion of the Director General of the IAEA and co-organized by the International Atomic Energy Agency (IAEA) and the Government of Bulgaria. Participants from the Bulgarian Nuclear Safety Inspectorate, Committee of Energy and the operating organization along with specialists from Bulgarian research institutes and Gidropress (Russian design organization) took part. Also participating were experts from the Gesellschaft fuer Reaktor- und Anlagensicherheit (GRS) in Germany and the Institut de Protection et Surete Nucleaire (IPSN) of France, two institutes of a consortium of European safety institutes advising the Regulatory body.
The technical discussions centered on the condition of the reactor pressure vessel, particularly its ability to withstand a pressurized thermal shock during operation. Recent information from Bulgarian and Russian institutes were reviewed. The European institutes recognized the value of this information, but maintained that further analysis and examination of samples taken prior to start-up were necessary to provide confidence that sufficient safety margins exist during operation. They stated that the proposed restart at this time would require high confidence in the reliability of previous non-destructive testing and correct operator actions during operation. Gidropress, the Russian design organization, presented technical information, based on analysis supported by examination of other WWER reactor pressure vessels, to demonstrate their argument that sufficient safety margins exist to permit operation for the planned cycle of about 12 months before taking samples.
The Bulgarian Nuclear Safety Authority described requirements which are contained in the licensing approval for the restart of Kozloduy Unit l. In essence it consists of a 3 step programme of operation proposed by the utility as follows:
- reduced operating cycle of about 6 months duration;
- special operating regime to include,
- constant power operation to avoid system transients,
- revised operating procedures,
- special operator training,
- increased supervisory control; and
- comprehensive programme to prepare for sample taking and/or annealing of the reactor pressure vessel at the conclusion of the shortened operating cycle.
The meeting recognized that the proposed programme of operation includes technical steps to improve the current situation and that the regulatory authority is requiring the utility to carry out a programme of investigation during the proposed operation, to provide important additional information for subsequent actions including sample taking and/or annealing.
The Assistant Director General for Nuclear Safety of the IAEA, Morris Rosen, who co-chaired the meeting with Yanko Yanev, Chairman of the Bulgarian Committee on the Use of Atomic Energy for Peaceful Purposes (CUAEPP), stated that the final decision to permit restart of Unit 1 is the responsibility of the Bulgarian Authorities.