The overall objective was to transfer knowledge and capabilities to the Bulgarian Nuclear Regulatory Agency (BNRA) in the field of review of Severe Accident Management Guidelines (SAMG) , to assess SAMG’s and to verify their compliance with international practice.

The project results include:

• Developing a modern methodology for review and assessment of SAMG for Kozloduy NPPs units 3&4 (WWER-440) and units 5&6 (WWER-1000).
  

• performing the review for the KNPP SAMG based on internationally recognised safety principles and the developed methodology,
  

• reviewing and assessing the methodology applied to the analyses of severe accidents and the analysis performed for the SAMG
  

• performing on-the-job training of BNRA and Technical Support Organisations (TSO) staff in review of SAMG, transfer of know-how to local TSOs supporting the safety authority in a long-term perspective,
  

• performing a critical reflection of the review process and elaborating a proposal for a regulatory approach for SAMG review in close cooperation with the Bulgarian Nuclear Regulatory Agency.
  

The main findings were:

Review of SAMG for KNPP 3&4

The adopted KNPP 3&4 SAMG concept consisted of the following high level objectives: primary circuit depressurization, primary water injection, secondary water injection, confinement conditions management.

The strategy for confinement conditions management aims for the protection of the environment. The major vulnerabilities are radioactive releases due to the pre-existing leakages, hydrogen issue due to the small total volume of the confinement and the long term coolability of the molten corium. The confinement is equipped with the specially designed active filtered venting system HIERARCH, the hydrogen recombination system based on autocatalytic recombiners and the hydrogen monitoring system. The HIERARCH system produces a subpressure in the confinement and should prevent uncontrolled release of radioactive products through confinement leakages to the environment. However, a venting system releases all noble gases to the environment without any delay. This means a challenge for the emergency response in the case of a severe accident - specifically because next to KNPP there is another country,
Romania/>/>. In this case, international Conventions on Nuclear Safety and on Early Notification of a Nuclear Accident provide guidance.

The plant specific SAM guidance for the KNPP units 3&4 and the set of actions to be taken, is described in the SAM procedures. The detailed list of actions exists for both the Main Control Room staff and the Technical Support Centre. The number of separate procedures is rather high and could be reduced. The reviewed documents do not describe an appropriate validation program or give any information concerning validation and verification of SAMG. According to the oral information provided by the plant representatives, the validation and verification of SAMG were performed, but the results were not presented in the reviewed documents. Specific attention should be paid to the severe accident follow-up, the existing instrumentation qualification in case of severe accident conditions and its measurement range. The organisational structure, interactions and duties of the bodies and groups participating in the emergency response of the KNPP were described. Activation of emergency response, levels of notification, structure and methods of setting up a technical support group for operators were described. Staffing, qualifications and training was taken into account. Staff training includes emergency response training program, training courses and drills and exercises. An Accident Management Handbook should be developed for the Technical Support Centre and for training purposes

Review of SAMG for KNPP 5&6

During the review of the developed SAMG for the KNPP 5&6 a set of findings were identified. The major issues that were identified resulted in the following recommendations:

• the SAMG for power states should not be used directly for the shutdown states; all entry points into the SAMG should be clarified;
  

• in the present state of development of the SAMG it is entirely open at which status of the plant the SAMG will be terminated; this should be defined.
  

• focus more on "what can be monitored" than on "what do we need to monitor";
  

• any justification for the order of the steps in the SAMG is missing, therefore this should be developed;
  

• the process that was used for the identification of the strategies seems appropriate, but it is not complete; thus all strategies should be identified;
  

• possible interactions between SAMG strategies should be investigated and the SAMG should be modified as necessary;
  

• clear rules of usage should be developed;
  

• specific background information for all routes should be developed;
  

• investigate all fission product transfer paths.