Transfer of Western PSA Methodology for VVER-1000 NPPs

1. Project General Data • Beneficiary: Rosenergoatom • Contractor: NNC Ltd • Local Subcontractors: MOCHT-OTJIG (AEP, RRC-KI) • Sector of activities: Design Safety • Sites: Balakovo Unit 4 (as Reference Plant) • Installations: VVER-1000 • Status: Completed (15 October 1996) • Budget: 1 227 000€ • Duration: 40 months

2. Introduction • Within the framework of TACIS-91 Nuclear Safety Programme, Project 3.1, Probabilistic Safety Analysis Support Data was awarded by the CEC to a consortium of major nuclear power engineering companies from Belgium, Spain and UK, lead by NNC Ltd (UK). Rosenergoatom and Atomenergoproekt were Russian partner institutions. • The goal: transfer of Western PSA methodology/experience to Russian counterpart for performing PSA, structural and seismic analysis for VVER-1000 NPPs • Specific NPP chosen for PSA: Balakovo Unit 4

3. Objectives Primary objective: to transfer the Western technology for performing L1 PSA for internal events to Russians organisations to allow them to: • Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

4. Implementation (1) Implemented Tasks of the project: • Task 1: Project management and procedures • Task 2: Hardware and software supply • Task 3: Reliability database • Task 4: Level 1 PSA • Task 5: Level 2 PSA • Task 6: Level 3 PSA • Task 7: Containment capability evaluation • Task 8: Seismic PSA • Task 9: Quality Assurance 1.1.1        Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

5. Implementation (2) Development of reliability database (1): • Data collection procedures (assembling and collating) were developed by AEAT and accepted for use at Balakovo plant • Guidance was also provided on how to calculate reliability and failure rate information from the plant specific event data • Previously collected data was modified to include information, where available, to comply with the procedures • Following delivery to AEP of the Database ManagerTM reliability analysis software product, data was collected and processed using the software • A database report was developed by AEP that contained information for the initial quantification of core damage frequency • The component data has been compiled using many different sources and priority was given to any plant specific data or reactor type specific data Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

6. Implementation (3) Development of reliability database (2): • Database also holds information on initiating event data • The data used for the calculation of initiating events has been derived using Balakovo plant operational experience, VVER operational experience and also from PWR generic data sources • The final data report includes initiating event frequencies and safety related system component reliability parameters • The data reviewed covers the period from December 1985 to the second quarter of 1995 giving a collection period of about 26 reactor years. • The data was derived from on-site event reports, licensee event reports and from breakdown logs • Data was collected for all components identified in the TACIS-91, Project 3.1, Procedure for Systems Analysis reports Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

7. Implementation (4) Development of reliability database (3): • Database also holds information on initiating event data • The data used for the calculation of initiating events has been derived using Balakovo plant operational experience, VVER operational experience and also from PWR generic data sources • The final data report includes initiating event frequencies and safety related system component reliability parameters • The data reviewed covers the period from December 1985 to the second quarter of 1995 giving a collection period of about 26 reactor years. • The data was derived from on-site event reports, licensee event reports and from breakdown logs • Data was collected for all components identified in the TACIS-91, Project 3.1, Procedure for Systems Analysis reports Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

8. Implementation (5) Development of reliability database (4): • AEP produced two reports which have been reviewed and commented upon by AEAT and the consortium. The reports that have been issued in their final form are:  Database development for L1 PSA  Database collection report (plant-specific data) • A training course was given on the Database ManagerTM reliability software in Moscow in March 1995 • It is recommended that the data collection campaign will continue at Balakovo and that updated reports are produced in the future so that the PSA can be re-quantified using plant specific data Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

9. Project Results (1) Achieved Project Results (1): • PSA was carried out for Balakovo VVER-1000 NPP Unit 4 (reference reactor) • The following general phases completed: • Preparation of the technical procedures required to develop the different parts of the probabilistic safety analysis • Training, technical assistance and supervision during performance of the PSA • Review of the results of the analysis performed • In September 1993 AEP started to perform PSA related tasks as follows (1): • Identification of the design documentation needed and its review • Identification of initiating events Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

10. Project Results (2) Achieved Project Results (2): • In September 1993 AEP started to perform PSA related tasks as follows (2): • Accident sequence development • System analysis • Dependency analysis • Human reliability analysis • Importance analysis • Quantification • Documentation, Interim Report and final PSA report • The process has been widely achieved through the development of the technical procedures • Development of the PSA for Balakovo NPP Unit 4 has made it possible to work jointly with, train and assist the Russian counterpart Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

11. Project Results (3) Limitations of the analysis: • The work carried out corresponds to the standard for L1 PSA, however it is important to point out that there were a series of limitations that have to be taken into account regarding the use of the results of the analyses. More important ones are mentioned in the final task report, and are as follows: • The number of initiating events considered is not exhaustive due to absence of T-H calculations or specific data on the reference plant • The human reliability analysis was simplified • Common instrumentation failures have not been considered • A significant detailed technical issue that could not be addressed in the system analysis reports is modelling of common cause failure of the batteries Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

12. Project Results (4) Seismic risk analysis: • The overall value of core damage frequency 2E-06 was obtained based on the calculations of the following studies: • Derivation of seismic risk curves • Fragility analysis for plant equipment and structures • Seismic risk analysis Containment capability evaluation: • The task is completed and the following results have been achieved: • ABACUS code have been transferred to Russian partners • Design information was collected • Asymmetric containment finite element model was developed • 3-D equipment hatch finite element model was developed • Containment strength and leak tightness failure probability were estimated Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

13. Project Results (5) Main conclusions: • Atomenergoproekt has successfully applied the technology to perform a Level 1 PSA for the Balakovo Unit 4 NPP. Although there are some limitations in the analysis, the project results form a basis for: • Evaluation of the safety of VVER-1000 reactors • Support to decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improvement of the safety of reactors under construction or in design phase Recommendations: • To provide additional electric supply from separate sources • To include additional isolation valves in the steam generators • To perform additional analysis to reduce some uncertainties (ATWS) Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

14. References/Interface with other TACIS projects: • R1.3/91 VVER-230 Accident Analysis • R1.4/91 Probabilistic Safety Analysis • R1.5-91 Modernisation of VVER 440/V230 Projects • R1.10/91 VVER 230 Confinement Analysis • R3.1/91 Probabilistic Safety Analysis Support Data • R3.6-91 Fire Protection Technology Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner 

15. SUMMARY • CDF is equal to 4.1E-5/y - this value is basically dominated by the sequences of loss of off-site power (85%) • the main contributors being diesel failure and failure in recuperation of off-site electrical power • steam breaks in non-isolable areas (8%) • reactor trip (4%) • loss of the normal residual heat removal system (2%) • The contribution of the remaining initiating events is less than 1% • The analysis successfully calculated the frequencies of the plant damage states for input to Level 2 PSA • The study developed some important recommendations regarding equipment: • To provide additional electric supply from separate sources • To include additional isolation valves in the steam generators • High uncertainty area related to ATWS analysis were identified - Evaluate the safety of VVER reactors • Support the decision process relating to back fitting, operation and maintenance of operating plants of more recent design • Improve the safety of the reactors under construction or in the design phase Major outcome: the primary objective has been achieved and the project was considered useful by the project partner