PROBABILISTIC SAFETY ANALYSIS TECHNOLOGY

The primary objectives of this project were:

• To transfer the Western technology for performing probabilistic safety assessment, structural and seismic risk analysis to the Russian organizations involved in the design and back fitting of VVER plants. It consists of setting procedure and guidelines and of providing software for these analyses and a work station to run the codes;
• To assist in the review of the operating experience data in order to identify the most appropriate set of reliability data to be used in performing PSA for selected VVER plants;
• To assist the Russian specialist in setting the reliability data base for the selected VVER type plant, based on Eastern plants operating experience, and in providing the methodology and a Data Base Management System (DBMS);
• To assist the Russian specialists and collaborate in performing the probabilistic safety analysis and the structural and seismic risk analysis for a specific selected plant.

The project was subdivided into the following tasks:

Task 1: Project management and procedures

Project management that includes a detailed project plan, the work organization and the QA programme.

Definition of the procedures and applicable rules for performing:

• Plant specific PSA;
• Containment ultimate capability;
• Seismic risk analysis.
• Identification of the reference plant for the analysis.
• Issue of the Project Plan and time schedule.

Task 2: Hardware and software supply

• The consultant will supply to AEP the software, and related users manuals, needed.
• Supply by the consultant to AEP of one work station capable to run the structural and seismic codes.

Task 3: Setting of the Reliability Data Base

• Definition of the procedures, methodology and QA programme for the establishment of the reliability data base for the reference plant.
• Supply by the consultant to AEP of a Data Base Management System.
• Collection, by the Russian counterpart, of the reliability data for the establishment of the reference plant data base.
• Assistance in performing the data analysis.

Task 4: Level 1 PSA - Internal event analysis

• Performance of the probabilistic analysis for the reference plants, for internal events, including high and low power operation and refueling conditions.
• Issue of level 1 PSA interim report.
• Revision of the analysis when success criteria from project 1.3 and a specific data base are available.
• Identification of the areas where the design and/or operation need improvement.
• Issue of the final PSA report for internal events.

Task 5: Level 2 PSA - Containment analysis

• Performance of the probabilistic analysis for the containment.
• Identification of areas where design improvements are needed and verification of the effectiveness of the proposed modifications.
• Issue of the Interim level 2 PSA report.

Task 6: Level 3 PSA - Consequences analysis

• Identification of accidents/family of sequences for which external consequences analysis is needed.
• Performance of the off-site consequences evaluation.
• Performance of the risk analysis (consequences vs. probability).
• Issue of the risk analysis report.
• Issue of the final PSA report.

Task 7: Containment capability evaluation

• Performance of the containment ultimate capability and excessive leakage analysis.
• Identification of possible containment improvements and verification of their validity.
• Issue of the containment ultimate capability report.

Task 8: Seismic risk analysis

• Definition of the seismic risk curve (probability-intensity) for the reference site.
• Performance of the seismic risk analysis.
• Identification of areas where improvements are needed and verification of proposed modifications.
• Issue of the final seismic report.

Task 9: Quality Assurance Manual

A QA manual had to be set up.

The project has been performed according to the Tasks above and the expected results defined there, with the following constraints:

Due to the absence of initial data from projects R1.3/91 and R3.8/91, especially the original tasks 5 and 6, dealing with Level 2 and Level 3 PSA for the Balakovo-4 NPP, had to be modified, because they could not be completed in conformance with the TOR.

As part of the project the computer code ABAQUS with a two year annual license was installed in the counterpart’s offices in Moscow. The code is the key tool for the seismic analysis and containment ultimate capability analysis. Therefore the license, which already expired during the final stage of the project, was planned to be converted into a paid-up license (permanent), as part of the follow-up project, in order to take full benefit of the technology transfer.

The project participants identified during the project additional cases beyond the original scope of the TOR, where PSAs would also be needed, e.g. leakage from primary to secondary side under power operation, as well as shut-down conditions in general.

Additionally the failure of the containment, for which a model has not yet been available, needs to be analysed. In order to enable the counterpart to study these important cases, the completion of the planned technology transfer in its full scope as per the proposed project follow-up, was considered as a priority project in future.