5. SAFETY ANALYSES
Safety analyses are an indispensable part of the safety documentation to every nuclear installation and are used as a means for proving and review of nuclear safety. They give answer to how the nuclear installations are secured in case of some failure or accident, and they forecast consequences of such failures or accidents. Results of safety analyses must comply with generally accepted international criteria.
In 1999 Department of safety analyses and technical support concentrated on verification and development of safety analyses for NPP Mochovce, development of regulations for emergency plans of the Emergency response center of UJD, on review of operational events at NPPs and creation of database for recording and evaluation of operational events. UJD realized independent analyses of both deterministic and probability assessment of nuclear installations safety.
Verifications of safety analyses focused mainly on control and review of completeness of the initiation events under consideration, safety criteria, input data, adequacy of used calculation models, as well as overall quality of submitted documentation. Suitability of the used methodology and calculation programs, achieved level of their verification, correctness and interpretation of results were evaluated. Representative neutron-physical, thermo-hydraulic and radiology analyses were recalculated and checked at UJD.
Results of these independent analyses were evaluated with respect to the set of safety criteria used for assessment of safety of NPP Mochovce in the licensing process. Verifications were done within the SWISSLOVAK project, with a US organization ERI (Energy Research Incorporation) and in co-operation with partner organizations from Germany and France (GRS, IPSN). Verifications showed that the checked safety analyses are prepared in compliance with the international established practice, According to the requirements of UJD and recommendations of the IAEA. The analyses confirmed the high level of safety of NPP Mochovce.
In co-operation with the Research institute of nuclear power plants in Trnava (VUJE, a. s.) emergency regulations were elaborated for the Emergency response center of UJD. These emergency regulations are based on assessment of the status of protection barriers preventing leakage of fission products from the active zone of the reactor into the environment. The level of damage on the active zone is being assessed, integrity of the primary circuit, integrity of the hermetic containment or possible bypass of containment, based on which there is a source element attached to the selected emergency scenario and subsequently the necessary protection measures are adopted.
UJD pays great attention to analysis of operational events at nuclear power plants, realization of corrective measures and feedback on experience from operation of nuclear power plants. When assessing the safety significance of operational events it uses also probabilistic approach, while a valuable source of information are data contained in the reports on operational events. In co-operation with the operator of nuclear power plants a database was compiled to record and evaluate operational events.
After being filled with data this database will contain basic information on operational events of Slovak nuclear power plants, on their course, assessment of events, adopted corrective measures and also on the condition of facilities prior and during events. The database will enable searching for the required information according to the criteria specified, statistical processing of entered data and graphical outputs.
As of 31 December 1999 the SWISSLOVAK project funded by the Swiss Government was completed. The project was a part of the program of financial and professional assistance from Switzerland to promote socio-economic reforms in the countries of Central and Eastern Europe.
The main goal of the project was to create and train a group of staff in development and verification of safety manuals, in preparation and assessment of safety analyses and in application of decision of the regulator for safety improvements on nuclear installations. The SWISSLOVAK project started in 1996 and originally it was designed to last until the end of June 1998. Due to positive results, however, it was prolonged until the end of 1999.
Within this project training courses and seminars were organized and funded, focusing on improvement of group members in using calculation software, which serves as an analytical tool to assess nuclear safety, to get acquainted with the methodology for preparation of safety analyses, utilizing the results, as well as transferring experience and knowledge in the field of nuclear energy. During the project also UJD safety manuals were elaborated, safety documentation for NPP V 1, NPP V 2 Bohunice and NPP Mochovce was verified, technical reports and studies on safety assessment of nuclear installations in the Slovak Republic were worked out. Their results were used in the licensing process and in safety improvement of nuclear installations.
Credibility and independence of UJD as state regulator was significantly strengthened through realization of the SWISSLOVAK project not only in Slovakia, but also in the eyes of professional public internationally. It can be stated that the SWISSLOVAK project has been a significant step towards independence and quality in performance of the state regulation of nuclear safety of nuclear installations in Slovakia. In July 1999 SWISSUP project was launched as concluded between the Swiss Federal Inspectorate for nuclear safety, UJD and the administration of nuclear regulation in Ukraine. The project is sponsored by the Swiss Government and its goal is to provide assistance to Ukraine in improving the system of recording, assessment and analyzing operational events, including operational and safety indicators. UJD will participate on transfer of information and experience gained within the SWISSLOVAK project to Ukraine.