[en] In 1990 several reviews were carried out of the operational safety of the V-1 nuclear power plant at Jaslovske Bohunice. As a result, short- and long-term measures for upgrading the safety of the units were recommended. The extent of the ongoing backfitting programme, to be completed by the end of 1992, is assessed to cost approximately 15% of the original initial investment costs for the construction of the V-1 plant. The objectives of the safety system innovation programme (active and passive emergency core cooling systems, confinement system for accident localization, superemergency feedwater of steam generators, emergency on-site sources of power supply) are described. The design reliability of the ECCS expressed in terms of the probability of failure is specified at the maximum level of 10^-3 per reactor-year which is the level used in the design of western nuclear power plants. The strategic intention of the whole backfitting of the V-1 plant is to obtain the probability of severe core damage lower than 10^-4 per reactor-year. (Z.S.) 2 figs., 1 ref

[en] The problems of safety of WWER-440/V-230 type reactors are discussed, and the following conclusions are made. (1) The reactors have a very good operational record. (2) The reactors have serious design shortcomings, which should be eliminated by safety upgrading. Core damage frequency should be further reduced. (3) PSA methods constitute an appropriate tool for assessment of plant vulnerability to some initiating events and malfunctions, for prioritization of upgrading measures and for tolerability of deviations from current safety standards. (4) The most important safety merits, such as a large thermal inertia and low rupture probability, should be properly taken into account in the analysis. (5) Extensive safety upgrading is feasible and can lead to a considerable risk reduction. In certain circumstances such upgrading is the least expensive option even though the total cost is much higher than the initial plant construction cost. (6) Properly upgraded, the reactor units may be operable until better power resources are available within the country. (7) The existing gap between the technological and political judgements of nuclear safety should be reduced continuously by information exchange improvements. (8) A unified approach to nuclear safety should be adopted for all nuclear reactors (not just WWERs) built to earlier standards. 5 tabs., 1 fig

[en] Briefly described are the basic activities involved in the two stages, minor and major, of the backfitting of the Bohunice V-1 nuclear power plant. The backfitting strategy is aimed at two fundamental goals, viz., improving the safety and resistance of the units in accident situations (reducing the probability of serious reactor core damage to below 10^-4/reactor.unit operation year), and upgrading obsolete and worn equipment whose reliability is not perfect. The following activities are included for improving the unit safety and reliability in accident situations: 1) retrofitting the units of the V-1 NPP with technical means for managing the maximum design basis accident, for increasing the volume of deterministic accident situations not included in the initial design, and for attaining the prescribed earthquake resistance; 2) physical and electrical separation of the protection and control safety systems from the operating systems; 3) emergency reactor shutdown, emergency core cooling (active and passive), etc.; 4) making provisions for a higher control precision and for reducing brittle fractures of the pressure vessel material at the two units of the V-1 NPP; 5) applying the leak-before-break (LBB) approach to high-diameter tubes; 6) increasing fire safety; 7) retrofitting the units with technical means for mitigating the impacts of major accidents; 8) increasing the reliability of home consumption supply from the external grid; 9) increasing the resistance of protective functions of consumer sources; 10) upgrading the computerized information system and the system of automatic control of the main production process. The costs of implementation of the minor backfitting project are estimated to approximately 15% of the initial costs, the costs of the major backfitting project exceed the total capital costs of the construction of the V-1 nuclear power plant. (Z.S.). 43 refs

[en] 14 irradiated assemblies were analyzed using nondestructive high resolution gamma spectrometry (HRGS). Measured and calculated (on the basis of calorimetric data) axial burnup profiles and average burnup values were compared. The measurements of spent fuel were performed in the Bohunice A-1 dry hot cell by using a proper collimating system and the standard Agency equipment, consisting of PGT intrinsic Ge detectors and Silena MCA with 1024 channels. The method of ¹³⁴Cs/¹³⁷Cs fission product activity ratio was used for burnup determination. It was found that the burnup values for 14 measured assemblies determined by HRGS were systematically lower than the calculated values with about 4-5%. The difference between the nondestructively determined burnup value of the 2N0053 assembly (average over 11 measured points) and destructively determined burnup (average over 19 measured points) was less than 2%. Passive neutron measurements of the irradiated assembly showed that the neutron counting rate was high enough for practical use and that the neutron and gamma profiles were similar and close to the burnup profile. Some calculations of gamma ray activity angular distribution were made for different numbers of dummy elements inside the irradiated assemblies. The results show that, by using gamma spectrometry transversal method, it is possible to find a significant number of dummy elements in different types of assemblies

[en] An overview is given of the recommendations and regulations concerning IandC systems of nuclear power plants with WWER-440 reactors in the Slovak Republic, and of the relevant involvement of regulatory bodies. The issues included in regulatory decrees and pertaining to the safety aspects of IandC systems are mentioned point by point, with emphasis put on the upgrading of the systems. The power plants covered include the Bohunice V-1 and V-2 plants and the Mochovce-1 and Mochovce-2 units. (A.K.)

No abstract available

[en] The paper describes regulatory requirements on the safety upgrading of the Slovak nuclear power plants. The Nuclear Regulatory Authority of the Slovak Republic was established in January 1993 as the executive body in the area of nuclear safety supervision as the direct successor of the former Czechoslovak Atomic Energy Commission. All former legal documents are still in force, but none of the existing laws and/or regulations are specifically devoted to safety upgrading of reactors built according to earlier standards. The IAEA reports, Nuclear Safety Standards documents, Safety Analysis Reports and probabilistic safety analysis Level 1 reports are used as a background for regulatory requirements. The safety upgrading of NPPs in the Slovak Republic is first of all aimed to comply with present safety standards 'as far as reasonably achievable'. As a rule, the safety upgrading measures are oriented to reinforcement of capability, redundancy and independence of trains of safety systems. For effective regulatory control of the upgrading process, a combined deterministic and risk based approach is being used. The backfitting programme for older V-230 units has been scheduled in two major stages. The first stage covered safety upgrading measures which had to be implemented in the short or medium term (1991-1993). The second stage of the programme is oriented towards further significant improvement of safety. Safety upgrading of all reactors built according to earlier standards in general and WWER-440 reactors in particular represents a complicated technical, economic and even political problem. In spite of all problems, safety upgrading of WWER-440 reactors operating in Slovakia has already led to significant risk reduction. A continuous gradual safety upgrading during the whole plant lifetime should be a general regulatory requirement for any nuclear unit. (author). 1 fig

[en] Safety review and safety upgrading of NPPs represent a very complex task in Slovakia, which has two different types of WWER-440 reactors in operation and under construction, a considerable lack of energy resources and limited financial resources. Regulatory involvement in safety review and upgrading is based mainly on Act No. 28/1984 on State Supervision on Nuclear Safety of Nuclear Installations, which gives the regulatory body the right to issue supplementary licensing conditions. At present, the general approach to each of the different reactor designs is to handle the bulk of safety issues by means of long term plans in a consistent, complex way. The entire spectrum of information sources and opinions is used in the safety review and for the implementation of corrective measures. For operating NPPs in Slovakia, these sources consist mainly of safety reports that have been elaborated after ten years of operation, level 1 probabilistic safety assessments, IAEA reports on safety issues, proposals of experts taking part in missions to NPPs, and the results of various international technical projects. The process of safety upgrading is also important as a component of safety culture and should continue throughout the lifetime of the plant. These issues are applied in slightly different ways to all Slovak NPPs. The most stringent requirements are used for units under construction. The process of safety upgrading is most advanced for V-230 units, for which safety upgrading fully reflecting regulatory resolutions is laid down in contracts. During major upgrading of a plant, an operation permit is provided for a limited period of time, e.g. for one fuel campaign. Each step in safety upgrading is carefully checked by the regulatory body. After successful implementation of upgrading measures, all WWER-440 units in Slovakia will receive an operation permit that is valid up to the end of their design lifetime

[en] Implementation of nuclear power program is connected to establishment of regulatory body for safe regulation of siting, construction, operation and decommissioning of nuclear installations. Licensing being one of the most important regulatory surveillance activity is based on independent regulatory review and assessment of information on nuclear safety for particular nuclear facility. Documents required to be submitted to the regulatory body by the licensee in Slovakia for the review and assessment usually named Safety Analysis Report (SAR) are presented in detail in this paper. Current status of Safety Analysis Reports for Bohunice V-1, Bohunice V-2 and Mochovce NPP is shown

[en] The general principles of nuclear power plant safety are described such as are contained in the respective Czechoslovak laws. Also summed up are the results of the operation of Czechoslovak nuclear power plants with regard to nuclear safety. It is stated that all units of the nuclear power plants at Jaslovske Bohunice and Dukovany have a high level of safety. Attention is devoted to the probabilistic evaluation of nuclear power plant safety. CMEA countries cooperate in the development and application of methods of the probabilistic assessment of reactor safety risks with regard to WWER reactors within the complex programme of scientific and technical progress to the year 2000. Czechoslovakia will study WWER-440 reactors of the V-213 type and the Soviet Union will focus on WWER-1000 reactors. (Z.M.)