ACCIDENT ANALYSIS FOR KOLA

The objective of the project was to review the existing Accident Analysis done by Russian Experts for the VVER 230 projects at Kola and Novovoronezh and, if necessary, to complete this analysis.
The specific goal of the project "Accident Analysis" within the TACIS-91 program is to review and - as far as identified to be necessary - to extend the accident analyses for the above mentioned VVER reactor types, with the objective to provide a systematic and consistent "state of the art" safety analysis, in accordance to western practice. The accident analysis has been utilized to assess actual safety margins of the existing plants and the degree of safety improvement by for this project relevant upgrade measures.

The three leading European companies in the field of nuclear energy, Electricit de France, Framatome S.A. and Siemens AG (hereinafter referred to as the Consultant) combine their know-how, their experience and their resources to achieve the best result in the technical assistance to the CIS-countries in the frame of the TACIS-91 Project 1.3 "Accident Analysis".
The accident analyses have been performed in close co-operation with the CIS partners RRC Kurchatov Institute/Moscow and EDO Gidropress/Podolsk. The analysis methodology and main results from the different tasks have been presented to and discussed with the regulatory body Gosatomnadzor. NPP Kola and NPP Novovoronezh have been comprised into the project by the CIS partners.

A joint working group was established to coordinate as a whole and to perform some technical tasks of the project.

The results were achieved with the following methodology:

Installation of the tools:

• Transfer of Western safety analysis approach;
• Relevant computer codes to Kurtshatov Institute (KI) and Gidropress: RELAP5/MOD2.5, CATHARE, HEXTIME/COBRA, WAVCO;
• Supply of one HP-700 workstation (each) to KI and Gidropress including installation and trial operation;
• Preparation of input data sets for the a.m. codes were prepared, installed and used at KI and Gidropress as well.

Application of the tools:

• LOCA analyses. The most relevant LOCA events for a generic VVER-230 have been investigated with CATHARE. Additional calculations were made with TECH-M-4 and RELAP5;
• NON-LOCA Analyses. The major part of the analyses shows sufficiently large margins to the limits specified by the acceptance criteria. For these cases it can be expected that the criteria are also satisfied if conservative initial conditions would have been imposed;
• Confinement Analyses.A wide range of LOCA cases with leak sizes from 32 mm up to 200 mm have been investigated using the WAVCO code.

For most cases the source rates were calculated with the TECH-M code assuming cold leg break and hot leg injection from the ECCS. A few cases were based on source rates from CATHARE.

The following individual analyses were made:

• LOCA cases;
• Main steam line break;
• Re-circulation cooling;
• 3D Core Physics Analyses.
• Radioactivity release.
• Conclusion:

On the basis of Western licensing requirements, lists of initiating events to be analysed, events categorization and acceptance criteria to be applied have been developed and initial and boundary conditions were defined for each event.

Input data sets for CATHARE, RELAP5-MOD2.5, WAVCO, HEXTIME, DINAMIKA and TECH-M-4 computer codes have been developed.

Sixty (60) initiating events have been investigated using French methodology for LOCA and German methodology for Non-LOCA events.

Totally, more than 100 calculations have been performed with these computer codes. The technical conclusions from these accident analyses are described in detail in the Safety Analysis Summary Report issued both in English and Russian language.

Project 1.3 Safety Analysis has confirmed the safety of NPPs with VVER-440-V230 reactors in the frame of the Western approach. An important objective of the Project as defined by the Terms of Reference was the transfer of the Western accident analysis technology and experience to RSC Kurchatov Institute and Experimental & Design Organisation Gidropress. As an indivisible part of this know-how transfer some Western computer codes (including initial training of and subsequent consultancy for the Russian users) and the relevant hardware (including HP-700 work stations, PCs and office equipment) have been delivered to and successfully implemented in RSC Kurchatov Institute and EDO Gidropress to enable them to perform standard accident analyses for the operating and future VVERs taking into account the internationally accepted approaches. In the course of the project, a team of Western and Russian experts have gained the valuable experience in the application of Western safety philosophy and computer codes to VVER-type reactors.

The joint work was characterised by good co-operation between all partners who endeavoured to perform the various tasks as originally scheduled, and to look for alternative work paths in cases where problems arose.

The work was organized and controlled by a Joint Working Group, which contributed to achieve common decisions regarding actual and future tasks. As a result, all the tasks foreseen by the Terms of Reference have been performed successfully.