Implementation of Methodologies for Adaptation and Support of Living PSA for Ukrainian NPPs

In 2003, NNEGC “Energoatom” developed and agreed with SNRIU the “Programme for Implementation of Risk-Informed Approaches to Regulation and Operation of Ukrainian NPPs”. At that time, Ukraine did not have a common (industry-wide) methodological basis and technical support for the development of Living Probabilistic Safety Assessment (LPSA) studies. Probabilistic safety assessments of Ukrainian nuclear power plant (NPP) units (probabilistic models, input data and PSA documentation) were updated occasionally and without coordination. Application of risk-informed approaches to NPP operation practices was difficult also due to absence of necessary normative and legal basis.
Pilot LPSA had been first developed for Khmelnitsky NPP 2 in 2010. For a good LPSA development at all Ukrainian NPPs, however, it was necessary to ensure that KhNPP 2 “Living PSA” had been developed in compliance with the best international practice and covered all procedural steps (key elements) for the development of an up-to-date LPSA. Therefore, this INSC project was proposed and contracted and Khmelnitsky NPP Unit 1 (KhNPP 1) was selected as the pilot plant.

The project was to provide LPSA methodologies that would be implemented at the pilot KhNPP 1, allowing for the transfer of advanced international practices of LPSA development to the other Ukrainian NPPs. Specialists of all NNEGC Energoatom NPPs were supposed to participate in the project from the very start allowing for later LPSA development and implementation at all Ukrainian NPPs based on the provided methodology and under full control of the NNEGC Energoatom.
The main objectives of the project were as follows:
• Development of a detailed methodology for development and support of Living PSA;
• Development of a methodology for integration of LPSA probabilistic models;
• Development of a manual for recompilation of existing PSA models from the SAPHIRE into the RіskSpectrum code;
• Training of Ukrainian NPP and NNEGC Energoatom personnel on actual LPSA creation, development and support;
• Development of KhNPP-1 LPSA using the developed methodologies and on the basis of KhNPP-1 “basic” PSA (for the purpose to justify correctness and applicability of the developed methodologies as well as to transfer the experience in LPSA development);
• Disseminate project outcomes to all Ukrainian NPPs.
The methodologies developed within the project were supposed to be accepted by the Ukrainian nuclear regulator SNRIU and LPSA was supposed to be developed at the pilot KhNPP-1 along with the integrated probabilistic model.

The project was implemented in two main technical tasks that were further divided into several subtasks as follows:
• Task 2: Development of Generic Methodological Guides on LPSA and their regulatory approval
• Subtask 2.1 Review of organization, resources, quality assurance and documentation for LPSA
• Subtask 2.2 Development of Generic Methodological Guide for Development and Maintenance of Living PSA (MG-LPSA)
• Subtask 2.3 Development of Methodological Guide on Integration of probabilistic models (MG - Integration)
A part of this task was also an approval of the developed methodologies by the SNRIU supported by another INSC project U3.03/08 (UK/TS/41) within a 2+2 approach.
• Task 3: Development of Living PSA for a pilot NPP
• Subtask 3.1 PSA model quality review to check existing and developing PSA model(s) at the pilot NPP with regard to the generally required PSA quality
• Subtask 3.2 Reliability database update to check adequacy of pilot NPP guidelines on reliability database updates including equipment failure rates, personnel errors, surveillance test results, etc.
• Subtask 3.3 Collection of Structures, Systems and Components (SSS) data and analysis of impact of SSS modifications on LPSA elements to verify adequacy of the pilot NPP technical manuals
• Subtask 3.4 Recompilation of probabilistic models from SAPHІRE into RіskSpectrum PSA code including development of the related manual
• Subtask 3.5 Integration of individual probabilistic models and finalization of the integral probabilistic model
• Subtask 3.6 Execution of Quantitative Assessment, Sensitivity and Uncertainty Analysis of the LPSA model(s)
• Subtask 3.7 Development of summary report "Living PSA for Khmelnitsky 1" and preparation of a final package of documents for SNRIU approval of LPSA.
As a result of the project, the Consultant developed the LPSA methodologies and recompilation manual. The methodologies were accepted by SNRIU for use at Ukrainian NPPs. The PSA databases were reviewed and updated, PSA models were recompiled from SAPHIRE into RіskSpectrum code and the integral PSA model was developed. A complete LPSA package was submitted for regulatory review and approval.