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Kozloduy NPP - Unit 2 - Status and Analysis of the Implementation of the Outage Programme Stage 2

Kozloduy NPP - Unit 2 - Status and Analysis of the Implementation of the Outage Programme Stage 2



In July 1991 the Commission of the European Communities (CEC) initiated an emergency action programme to restore and to improve nuclear safety in
Bulgaria/>/>. In the framework of this programme an international consortium of independent technical expert organizations from EU-member states has been contracted by the CEC to provide assistance to the Bulgarian Nuclear Safety Authority (BNSA).

The work of the Consortium, starting in October 1991, has been concentrated on the urgent needs of the BNSA for evaluating the overall plant safety status of the Kozloduy NPP.

Although all units at the plant site were concerned, the main effort was directed to the VVER-440/V-230 reactors. Particularly the Consortium at first carried out a safety assessment of units 1 and 2, the plant's oldest units. The analysis covered plant operational as well as safety design aspects. The Consortium's results of the safety assessment of the VVER-440/V-230 of the Kozloduy NPP have been presented to the BNSA and the CEC in June 1992 and finalized in October 1992, N.

As main conclusions from this assessment, safety improvements and additional analyses on priority-ranked safety issues were recommended to the BNSA. Secondly, the Consortium has reviewed an outage programme presented by the utility to the BNSA for safety upgrading of units 1 and 2. Comments on the outage programme already were included in another projects.

Envisaging only a limited operation period, safety improvements can be achieved taking into account inherent positive features of V-230 type by short-term measures strengthening operational safety and safety systems design. The Consortium therefore concentrated on the identification of a priority list of short-term measures with regard to the most serious safety concerns. Especially operational safety measures and short-term technical upgrading measures for the first outage period have been proposed. In addition to restoration of the conditions of the plant these measures have significantly improved the safety of the units. Most important are preventive measures (e. g. extensive and careful in-service inspection) in order to assure the integrity of the primary reactor coolant circuit and to avoid accidents resulting from transient events (e. g. additional scram signals, fire protection).

According to this approach the recommendations given by the Consortium were under the condition that further operation of these units only is assumed for a limited period of time. Thus, the recommendations proposed to the BNSA by the Consortium have had to be considered as conditions which have to be fulfilled before first restart of these units for a restricted period of operation time. The Consortium did not examine reconstruction measures, which would be necessary for longer-term operation.

In some cases, hardware upgrading measures could not be realized, or respectively implemented, on a short-term within the first outage period of unit 2. Interim solutions, applied in the meantime by the utility, however, only were considered as compensatory measures. For next outages further modifications had to be implemented and/or further safety demonstrations had to be provided. One of the goals for the ongoing Consortium's activities is to monitor these implementations.

The recommendations evaluated for the first outage period were aiming at the following goals:

  • restoring the systems to original design conditions (housekeeping), improving systems in normal operating conditions,
  • assure integrity of components under pressure,
  • improving safety systems to cope with a limited list of accidents and transients considered as design basis,
  • preventing the occurrence of beyond design basis accidents and developing of specific procedures,
  • requalification of safety systems by testing.

Reviewing the outage programme of the NPP, the Consortium additionally has elaborated recommendations and corresponding proposals for operational improvements and technical upgrading measures. As a result of the technical discussions held with BNSA and NPP during the first half-year of 1992, these recommendations have been accepted by the utility and have been taken into account in Revision 2 of the NPP outage programme, in June 1992. In the end of 1992 unit 2 was restarted and in February 1994, after more than 13 months of operation, shut down for refuelling and upgrading (stage 2).

On the basis of the lessons learned from the licensing process of units 2, 3 and 4 performed so far, especially the first outage of unit 2, NPP developed in 1993 a two volume outage programme for upgrading of units 1 to 4, stage 2 and 3, the so-called "Programme '93".

/> />/>A special outage programme for unit 2, stage 2 was prepared and the English version submitted to the Consortium in the first days of March 1994, only. It is based on the Programme '93. Both programmes are structured in a different way than all the other outage programmes before. This caused some problems when comparing the measures achieved in the old programmes and those foreseen in the second outage.

General Information

Kozloduy NPP - Unit 2 - Status and Analysis of the Implementation of the Outage Programme Stage 2
Budget year: 
Types of activities: 
On Site Assistance
Installation types: 
VVER 440-230
Duration (months): 
Old reference: 
Effective contract date: 
Closure date: