Summary

This project gave technical assistance to the Bulgarian Nuclear Safety Authority (BNSA) for safety evaluation of an outage programme proposed by the Kozloduy NPP for unit 1, and for analysis of the reached status.

This is part of the following series of reports related to safety evaluation of Kozloduy NPP, units 1&2.

1. a safety evaluation of two units. Safety deficiencies were identified on both design and operational aspects.
   

2. a position on minimal requirements to be fulfilled by the NPP in order to re-start for one cycle the unit 2. The review work was based on the conclusions of the first report (1) and on the analysis of an outage programme (4) proposed by the NPP to improve the situation.
   

3. an expertise on the reached safety level of the Kozloduy unit 2 after the implementation of the 1st stage measures of the NPP outage programme and the partial implementation of the Consortium recommendations given in (2).
   

4. comments on the content of the new outage programme proposed by the utility in order to improve the situation of unit 1 before its re-starting for one year cycle. It corresponded to the first step given in the terms of reference of the contract.
   

This report presented to BNSA the Consortium expertise on the reached safety level of Kozloduy unit 1 prior to its restarting for one fuel cycle.

Conclusions given in this report are based

- on the review work results provided in (1), (2) and (3),

- on the analysis of the upgrading measures proposed by the utility to improve the situation in unit 1,

- on the results of technical discussions between the industrial side (NPP and WANO) and the safety authority side (BNSA and Consortium), completed by internal discussions between BNSA and the Consortium.

Unit 1 of Kozloduy NPP, as well as unit 2, was shutdown in autumn 91 after international pres­sure was exerted on the status of these units following the IAEA mission on site.

After more than two years of stop, the NPP requested from the BNSA an authorization to re­start this unit. This request followed the implementation of an upgrading programme which be­gan in mid 93. In order to analyse the new status of this unit, the BNSA requested a Consortium of Western Technical Safety Organization to provide them an advice on the reached safety level of the unit. After review, it is obvious for the Consortium that many of improvements have been realized by NPP in order to enhance its safety level. Most of the recommendations given in mid 92 by the Consortium in order to complete the initial plans of NPP were taken into ac­count and corresponding studies, controls or modifications were performed.

The original aim of the Consortium was to upgrade the safety level of this plant in order to per­mit its operation during a limited time and was not to achieve a Western safety level, which can­not be reached without any major and may unfeasible reconstruction measures.

Compared to unit’s 2 status before its re-starting in December 92, the safety level of unit 1 is more satisfactory. However, some efforts are still necessary and complementary improvements should be implemented during the next outage (for modifications) or during the operation of the plant (for improvement of operational safety). Safety demonstration was provided in order to permit operation of the plant just for one fuel cycle.

It is more important to point out that some complementary improvements were also imple­mented following NPP decision. This may be shows that cultural evolution in mentalities began in
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