The State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS), a Ukrainian enterprise with a 29-year experience in the area of scientific and technical support to the national nuclear regulator (SNRIU), has been actively involved in international research activities. Participation in the IAEA coordinated research activities is among the SSTC NRS priorities. In the period of 2018–2020, the IAEA accepted four SSTC NRS proposals for participation in respective Coordinated Research Projects (CRPs). These CRPs address scientific and technical issues in different areas such as: 1) performance of probabilistic safety assessment for multi-unit/multi-reactor sites; 2) use of dose projection tools to ensure preparedness and response to nuclear and radiological emergencies; 3) phenomena related to in-vessel melt retention; 4) spent fuel characterization. This article presents a brief overview of the abovementioned projects with definition of scientific contributions by the SSTC NRS (participation in benchmarks, development of methodological documents on implementing research stages and of IAEA technical documents (TECDOC) for demonstration of best practices and results of research carried out by international teams).
The paper analyzed the advisability of zinc injection into the VVER primary system coolant in order to minimize radioactive fields of equipment. In the western NPPs with PWR, zinc injection into the coolant leads to permanent decrease of dose rates caused by radioactive cobalt. Zinc is introduced into the oxide film on the primary system equipment surfaces to form the most stable zinc spinel, which prevents the further introduction of radioactive cobalt in the oxide film. Predictive assessments for VVER-1000 show that under the zinc concentration of µg/dm3 in the coolant, cation vacancies in the spinel lattice will be occupied mostly by zinc, preventing the penetration of cobalt in the spinel and increase of radioactive fields of equipment.
Over recent years, many Ukrainian organisations have participated in the European projects in various fields of research and technology development. Ukraine has made significant steps to enter the European Research Area: in 2015, Ukraine has become an associated participant of the “Horizon 2020” programme of the European Union, and on 27 June 2016, the Agreement between the Government of Ukraine and the European Community on Atomic Energy on scientific and technological cooperation and the associated participation of Ukraine in the Euratom Research and Training Programme (2014—2018) has been signed. This paper briefly presents the experience and results of the SSTC NRS activities under the Euratom framework research programmes, as well as the near future prospects for the SSTC NRS involvement in the new European research projects.
An overview of the main improvements in updated version 2.1 of MELCOR computer code related to more representative mathematical modeling of complex thermohydraulic severe accident processes of core degradation, transfer of molten fragments to the bottom of the reactor, heating and failure of the bottom of the reactor pressure vessel is presented. The elements of WWER-1000 NPP computer model for the MELCOR 1.8.5 (control volumes, thermal structures and structures of the reactor core) that are reproduced for a reactor with the primary side, the secondary side and the containment are described. The changes implemented in WWER-1000 NPP model for MELCOR 1.8.5 to convert it to MELCOR 2.1 version that are mainly related to more detailed modeling of the reactor core and reactor pressure vessel bottom are provided. The paper presents the results of comparative analysis of severe accident scenario of total station blackout at WWER-1000 NPP with MELCOR 1.8.5 and 2.1. The comparison demonstrates good agreement between the main parameters’ results (pressure and temperature in hydraulic elements of the primary, secondary sides and the containment, temperature of core elements, the mass of the generated non-condensed gases and their concentration in the containment) obtained with these code versions for severe accident in-vessel phase. The identified differences in the time of core structures degradation and reactor vessel bottom failure are insignificantly affected by the behavior of the parameters in the primary side and the containment in the in-vessel phase of the severe accident and are related to more detailed modelling of the reactor core and bottom part of the reactor in MELCOR 2.1.
The paper describes the main areas of educational activities on nuclear and radiation safety, which have been formed in recent years and are currently implemented by the State Enterprise "State Scientific and Technical Center for Nuclear and Radiation Safety" (SSTC NRS). The experience of SSTC NRS in conducting training and advanced training for personnel of domestic enterprises on nuclear energy use is related to nuclear and radiation safety, radiation safety in using radiation sources (industry and medicine), mining and processing of uranium ores. The paper describes specialized areas of training prepared at the request of nuclear companies, in particular: support and training of management staff of NNEGC "Energoatom", transfer of experience in the use of computer codes and programs, exercise of practical approaches to the application of guidelines for severe accident management, training on indigenous analysis of NPP abnormal operation. The participation of SSTC NRS in international programs, projects and initiatives on training and transfer of experience within the EU technical assistance program Instrument for Nuclear Safety Cooperation and the Euratom Research and Training Program provides information on new initiatives for training on nuclear and radiation safety.
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