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4  SAFETY ANALYSES
 

In 1998 UJD continued in the systemic development of activity in the group of safety analysis and technical support in compliance with the SWISSLOVAK project funded by the Swiss Government. The project is a part of financial and expert assistance from Switzerland for promotion of socio-economic reforms in the countries of Central and Eastern Europe.

The main goal of co-operation is to provide assistance in creating and training a group of specialists for safety analyses. The assistance is managed through the Swiss regulatory body. Within this project several training courses, working meetings and seminars were organized and funded. Last year these activities focused on enhancement of skills of the group members in using software which serves as analytical tools for assessment of nuclear safety. The group was getting acquainted with the methodology of performing safety analyses and using results of analyses for assessment of nuclear installation safety. Several training courses were dedicated to processes and methods for verification of safety technical documentation, as well as handing over experience and knowledge in the area of nuclear safety.

Currently this group is actively working and developing its capability.

Implementation of SWISSLOVAK project brought a significant strengthening of credibility and independence of UJD as a state regulator, and that is not only in Slovakia, but also in the eyes of professional public on the international level. The group of specialists provided UJD an independent analytical support in deterministic and probability safety assessment. It focused mainly on calculations and analyses of thermal-hydraulic, physical and chemical processes in nuclear energy installations. It also performed parametric and sensitivity analyses for selected transitional processes and model accidents. The group participated on review of safety documentation and on evaluation of draft measures to improve safety of nuclear installations in Slovakia, which were sent to UJD by the operator.

In co-operation with both domestic and foreign technical consultants the existing study of the probabilistic safety assessment (PSA) level 1 was complemented and extended for EBO V-2 NPP. For this nuclear installation the group prepared a study of probabilistic safety assessment, level 2, with significant technical assistance from foreign partners. The study focuses on review and risk assessment of possible damage on the reactor containment and possible leakage of radioactive materials into the environment. Significant effort was spent on thorough acquaintance with the project and the technical documentation of nuclear power plants in Slovakia, their construction, operation and safety systems.

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The group complemented and modified the existing and composed new files of entry data and models for simulating response of operated nuclear power plants on examined transitional processes and accidents. Independent analytical support in 1998 was focusing mainly on verification of the pre-operational safety analysis report of EMO NPP, operational safety analysis reports of EBO V-2 NPP and verification of the proposal for reconstruction of the containment of EBO V-1 NPP.

Verifications of safety documentation focused primary on review of completeness of initiation events under consideration, applied safety criteria, adequacy of entry data and models, as well as overall quality of submitted documentation. The initial and marginal conditions of models were also checked. Suitability of applied methodology and computer programs was evaluated, achieved level of their verification, adequacy, correctness and interpretation of results of safety analyses. UJD recalculated and checked representative thermo-hydraulic, neutron-physical and radiological safety analyses. Results of these independent safety analyses were evaluated with regard to the set criteria and were used for safety review of EMO NPP, EBO V-1 and V-2 NPP in licensing process. Verification was made in co-operation with foreign partner organizations (Energy Research Incorporation, USA) and in cooperation with the IAEA. It proved that the checked safety analyses are prepared in compliance with the established practice, according to recommendations of UJD and the IAEA. A high, internationally accepted safety level of EMO NPP was confirmed.

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The study of PSA, level 2 for EBO V-2 NPP was prepared according to the methodology recommended by the IAEA. In preparation of this study a probability model of nuclear power plant was used developed for the study of level 1, which characterizes the condition of the nuclear power plant and its safety systems at the time of damage in the active zone of the reactor. This model was expanded and complemented by a model of other safety systems necessary for evaluating the status of failures of the reactor containment. Based on the calculation of frequency of status of damage on the unit a group of hypothetical severe accidents was selected which had to be evaluated from the point of PSA level 2. For this accident sequence thermo-hydraulic, radiology and strength analyses of response of NPP were prepared.

The expert group composed and evaluated an "event tree" which could cause damage on the reactor containment. It quantified the existing risk and analyzed the most probable ways of leakage of radioactive materials into the environment. It reviewed and recalculated selected measures of emergency management focused on preventing emergence and development of over-design accidents and on limiting their possible consequences. Results of the study were used in evaluation of nuclear safety of EBO V-2 NPP and for proposing further safety improvement of this installation.

roup of safety analyses and technical support with its technical and human potential has contributed also to preparation and the course of national and international emergency exercises. Within the emergency staff, UJD has its members represented in the group for reactor safety and protection against radiation.


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© Nuclear Regulatory Authority of the Slovak Republic, 1999

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