R/TSO/VVER/01-A : Lic Rel Assessm Acc An

The project "Licensing Related Assessments of the Accident Analysis performed for the VVER 230 Project, Kola 1,2" is an example of a Tacis TSO project aimed at assessing analyses performed by an Industrial TACIS Project (IP), in this case TACIS-91 project 1.3 "Accident Analysis.”

The main purpose is to bring together European Union TSOs and Russian TSOs to perform a concrete assessment of licensing related analyses and to exchange experience and knowledge in dealing with real safety analyses submitted by the nuclear power companies. This kind of co-operation is intended as an effective way of developing and strengthening the nuclear power plant (NPP) licensing systems within Russia.

The intent of the project is to cooperate with, and to assist the Regulator GAN-RF and related Russian Technical Support Organisations (TSO) in reviewing and assessing the results and the consequences of the-accident analysis accomplished for the industrial project.

The following transient categories were considered:

1. Loss of coolant accidents (LOCA), including small break LOCAs
2. Transients without LOCA, including overcooling transients and Anticipated Transients without Scram (ATWS)
3. Confinement behaviour during LOCAs.

Beyond-design basis accidents were treated within the above categories.

The planned Project Outputs were:

• Assessments of analysis results from the TACIS-91 industrial project 1.3.
• Comments on the proposals made by the industrial project.
• Assistance to preparation of a safety evaluation report.
• Comparison of Russian and Western regulatory rules.

The results and relevant information from the industrial project had to be reviewed and assessed against further relevant analytical results or experimental data. This had to be completed if necessary by selected verifying calculations and by engineering judgements, whereas the recent laws, licensing rules and standards as well as the licensing practice and domestic conditions in Russia had to be taken into account.

For each accident categories, the following tasks had to be executed:

• Task 1 Familiarization of EU-TSOs with the actual status and application of Russian licensing practices; laws, rules, standards, special conditions, in order to achieve a mutual understanding of the licensing documents. Discussion of possible weaknesses in the documents and the procedures and their adjustment.
• Task 2 Collection, evaluation and assessment of already performed analyses, calculations and assumptions. Discussion of the reasons for the selection of cases and initial and boundary conditions and all other relevant information used for the analyses.
• Task 3 Discussion of applied Russian codes and models. Status of the validation of the used codes. Assessment of results from VVER-440/230 specific tests and basic experiments.
• Task 4 Execution of selected supplementary/reproducible calculations (appropriate cases and initial and boundary conditions to be specified mutually) by using European codes:

1. accident analysis codes ATHLET and CATHARE
2. confinement (containment) codes RALOC and DRASYS
3. preparation of thermohydraulic initial and boundary conditions for the analysis of subcooling impacts on Reactor Pressure Vessel (RPV) integrity (refer to Project TACIS/TSO/VVER/01 subtask C)

• Task 5 Final discussion and assessment of the results of the analyses. Questions of quality assurance and accuracy and reliability of quantitative results.
• Task 6 Formulation of possible requirements for actions, accident management measures or different improvements to meet detected weaknesses and of proposals for upgrading programmes to be implemented at the KOLA-units.
• Task 7 Assistance to the preparation of the safety evaluation report - assessment of results with respect to safety margins and if necessary to a comparison with relevant EU regulatory rules and guidelines.

The description of the tasks changed during the project. The final task description and their results were:

Task1: Familiarisation of EU-TSOs with the relevant Russian licensing practices

Task 1 of the project focused on familiarisation of the representatives of the participating EU Technical Support Organisations (TSOs) with the actual status and application of the relevant Russian regulatory practices.

The relevant documents regarding the actual status and application of Russian licensing practices (laws, rules, standards, special conditions) were collected and translated. These practices were compared to Western practices and the findings were commented and reported.

Types of activities on which the Gosatomnadzor can issue a license are listed in an Appendix of the document "Regulations of licensing activity in the field of nuclear energy consumption", which had been put in force with Russian Federation Government Resolution 865 dated June 14, 1997 in correspondence with article 26 of Federal Law "About nuclear energy consumption". To reach a common understanding of the criteria which are used in expert reviews, the focus was on the technical questions connected with the formulation of such criteria, and with the formulation of technical requirements from Gosatomnadzor to the analyses and to their use in assessment of safety.

The organizational structure of Gosatomnadzor dealing with the provision of expertise was also partly discussed, because it gives a wider and clearer understanding of expertise practices and their quality assurance as well as SEC NRS structure as the leader of Russian's TSOs. A comparison of some relevant aspects of Russian and Western approaches to organisation and regulations, based on the results of a visit of a Russian expert delegation to Finland demonstrate that there are no serious problems concerning achieving a mutual agreement.

Task 2: Collection of information on already performed analyses in the consortium countries and Russia

Basic information about already performed relevant analyses in Finland, France, Germany and Russia were collected in tabular form.

The information is meant to be used as a reference and source for acquiring more relevant information when assessing the selection of accidents/transients and the results of the calculations presented in the IP. The information provides very brief descriptions of the analyses. However, it is considered to be sufficient in the context of this TACIS TSO project. The corresponding project participants have access to the details of the listed analyses.
The provided information included the transient type (initiating event), the main assumptions, the name of the code used and a brief qualitative description of the results. This information was used as a reference when assessing the selection of the accidents in the industrial project and when acquiring detailed information of relevant already performed analyses.

Task 3: Assessment of code validation

This task focused on assessment of the code validation presented by the industrial project. Special attention was paid to VVER specific validation. A Russian report on the requirements for certification of codes was reviewed and commented. Russian codes were used in accordance with the permission stated in the IP.

For Russian codes it can be stated that rather complete information about their validation is presented. As a shortcoming it was pointed out that the IP reports contained no adequate information about validation of used Western codes in VVER-440/230 conditions.
Russian regulatory requirements on validation are not fulfilled for Western codes in the reviewed reports, even though it is likely that they are adequately verified with regard to Western reactors and containments.

Task 4: Assessment of the accident analyses performed in the industrial project

The reasons for the selection of cases in the industrial project were assessed. This assessment focused on the initial and boundary conditions and other relevant information and assumptions used for the analysis. The results of the accident analyses were assessed based on experts' judgement and existing information and documents.

For this purpose, firstly some criteria were accepted against which the assessment was performed. These criteria are based on relevant Russian and Western regulatory guidelines and rules dealing with accident analyses, on IAEA recommendations for the safety evaluation of these reactor types and on purposes which were established for the implementation of the IP. Common approaches to criteria for safety analysis evaluation were elaborated and agreed on during the first stage (Task 1) of the Project.

LOCAs and Breaks in the Secondary Side

The IP case selection only partially covers the spectrum of the LOCA cases which should be included in Western safety analysis reports, although it was found out and concluded that all break sizes larger than 120 mm diameter are violating the acceptance criteria for LOCAs. Moreover, the results of break sizes larger than this diameter up to 2F break are necessary for the confinement safety analysis which was a part of this project.

Within the IP the break analyses for the VVER-4401230 plant have been performed using different Western (RELAP5, CATHARE) and Russian (TECH- M-4, DINAMIKA) computer codes.
Practically all LOCA calculations were performed by different institutions using these different computer codes or their versions. Because of mostly very short description and insufficient presentation of calculated parameters it is impossible to explain the differences of obtained results for the identical LOCA case and to judge the correctness of the particular calculation. There are significant qualitative and quantitative differences between the results of calculations performed using different codes and also between results of the same code calculation performed by different institutions. The reasons for these deviations have not been described in the submitted reports of the IP.

None of the reports can be considered as an example of a report to be included in the safety analysis report. The physical models which were used in the analysis are not described; the description of the nodalisation is in some cases only verbal. A very short description of the events during the transient is given with reference to only very few of the presented figures.

Task 5: Selection and execution of possible supplementary calculations

Based on the assessments in task 4 it was concluded whether supplementary calculations were necessary. Supplementary calculations were performed if code inputs for the Kola NPPs were available without spending substantial resources. Any suitable European code could be used to perform the calculations, including the ones listed in the TOR.

Task 6: Final assessment of the results of the industrial project

Final assessment of the results of the industrial project included additional assessment of the analyses based on the calculations performed in task 5, and, in addition, an assessment of actions, accident management measures and other improvements proposed by the industrial project. A particular objective of this final task was to assist the GAN-RF in preparation of a corresponding safety evaluation report.

Conclusions of the TSO Project

A detailed review and assessment of all the accident analyses performed in the Industrial Tacis-91 project (IP) 1.3 for the Kola NPP, units 1,2 has been performed. The main outcome of the assessment was that the primary goal of the IP to provide a systematic and consistent "state of the art" safety analysis in accordance with Western practice was not achieved.

The evaluation of the IP analyses revealed several shortcomings like incomplete descriptions of initial and boundary conditions, lack of model descriptions, the use of too simple models, insufficient explanation of results, and poor graphical presentations.

The depth of the assessment was limited by the quality of the IP reports. A problem of the IP has originally been the too extensive nature of the project.

The resources have not been sufficient for satisfactory evaluation of calculations and reporting. A smaller number of calculations and more effort to each analysis could have produced more useful results.

The analyses should be interpreted as an exercise and familiarisation with the Western practice of performing safety analyses, but it is not a complete state-of-the-art accident analysis for licensing a Nuclear Power Plant, in this case the Kola NPP units 1 and 2.

The proposed improvements to the reactor and plant protection system would improve safety of the plant, but implementation of such measures would need more prioritisation and detailed analysis, as well as improved models and methods.

The TSO project was reported as a successful project in assessing the results of the Industrial Project and supporting the work of the Russian Regulatory Body and its Technical Support Organisations in dealing with the submitted accident analysis reports.