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Husinec, Czech Republic

Podlaha J.,UJV Rez
International Conference on Nuclear Engineering, Proceedings, ICONE | Year: 2014

After more than 50 years of operation of the research reactor operated by UJV Rez, a. s. (UJV) or the Research Centre Rez, as the case may be, a large amount of spent nuclear fuel (SNF) of Russian origin has accumulated. In 2005, UJV joined the Russian Research Reactor Fuel Return (RRRFR) program under the US-Russian Global Threat Reduction Initiative (GTRI) and started the process of SNF shipment from the LVR-15 research reactor back to the Russian Federation (RF) using the SKODA VPVR/M transport packaging system (TPS). Two SNF shipments from UJV were carried out in 2007 and 2013. After the shipments were completed, only low-enriched nuclear fuel with a maximum enrichment below 20% of 235U remained on the territory of the Czech Republic. UJV also participates in shipments of SNF from other countries. The services of UJV comprise mainly SKODA VPVR/M TPS leasing, technical oversight and expertise during cask handling, SNF loading and cask closing and sealing. Up to now, UJV has participated in thirteen shipments of SNF from eight countries; one shipment is currently being prepared. High-level radioactive waste (HLW) will be generated from SNF reprocessing. The vitrified HLW will be returned to the Czech Republic as stated in the Russian-Czech Intergovernmental Agreement on Co-operation in Nuclear Energy. The return of the waste represents very complex and complicated work, technically, legally and contractually.. Copyright © 2014 by ASME. Source

Hustak S.,UJV Rez
International Conference on Nuclear Engineering, Proceedings, ICONE | Year: 2014

PSA specialists in UJV Rez, a. s. maintain a Living Probabilistic Safety Assessment (Living PSA) program for Dukovany Nuclear Power Plant (NPP), a four-unit VVER-440 plant type, which is operated in the Czech Republic. This project has been established as a broad framework for all plant activities related to risk assessment and as a support for riskinformed decision making carried out at this plant. In addition to recommendations for design and operation measures in order to increase the plant safety, it provides a basis and platform for all PSA applications at Dukovany NPP. The Living PSA model for Dukovany NPP is an integrated model representing the complete scope of Level 1 and Level 2 PSA for all plant operational modes. It produces the unit specific outputs for any Dukovany NPP unit. The RiskSpectrum® PSA software has been used for development and quantification of the PSA model. It is continuously updated and extensively used for various PSA applications at Dukovany NPP (e.g. risk monitoring, evaluation of plant Technical Specification changes, support for procedure development and training process, event analysis, etc.). The paper focuses on the important features of the Living PSA project for Dukovany NPP. It also discusses the broad experience gained during model development and update as well as possible future enhancements. Copyright © 2014 by ASME. Source

Girault N.,Institute for Radiological Protection and Nuclear Safety | Bosland L.,Institute for Radiological Protection and Nuclear Safety | Dienstbier J.,UJV Rez | Dubourg R.,Institute for Radiological Protection and Nuclear Safety | Fiche C.,Institute for Radiological Protection and Nuclear Safety
Nuclear Technology | Year: 2010

The Phebus Fission Product (FP) program studies key phenomena and phenomenology of severe accidents in water-cooled nuclear reactors. In the framework of the Phebus program, five in-pile experiments were performed that cover fuel rod degradation and behavior of FPs released via the coolant circuit into the containment vessel. Analyses of FP behavior were performed using standard stand-alone versions of codes with input data mainly taken from measured boundary conditions. The FPT2 test used 33 GWd/t uranium dioxide fuel enriched to 4.5%, reirradiated in situ for 7 days to a burnup of 130 MWd/t. This test was designed to study low-pressure FP release and transport through a primary cooling system that included a noncondensing steam generator, with release into the containment vessel in steam-poor conditions. This test also investigated how diluted boric acid in the injected steam influenced FP speciation. In the containment vessel, the objective was to study iodine chemistry in an alkaline sump under evaporating conditions. The analytical approach consisted of progressive studies to explore and explain the main disagreements between base-case calculations and experimental results. Regarding releases in slightly degraded fuel zones, the fission gas behavior and characteristics are shown to be satisfactorily reproduced by the calculations. Electron microprobe analyses also validate the mechanisms for Mo and Ba releases, while the Cs mechanism requires further investigation. Concerning the transport of FPs, a strong connection is shown to exist between Cs, I, Mo, and Cd that substantially impacts vapor-phase chemistry in equilibrium and iodine volatility. Most of the cesium released from fuel is shown to rapidly convert into cesium borates and then into cesium molybdates when the molybdenum release becomes significant at the end of the hydrogen production phase. The main predicted iodine vapor species is cesium iodide. A low fraction of gaseous hydrogen iodide is also calculated at low temperature, but this fraction was found to be strongly dependent on the Cd release kinetics. Hydrogen iodide is the main candidate predicted by equilibrium chemistry calculations to explain the persistence at low temperatures of volatile iodine. Nevertheless, potential limitations on chemical kinetics in the primary circuit zones, characterized by a sharp decrease in temperature, could also be an explanation and are currently under investigation. In the containment, gas-phase reactions were found to predominate in governing iodine chemistry. As for the previous Phebus tests, the gaseous iodine fraction measured in the containment early in the test is thought to come from the primary circuit. However, this low gaseous iodine was hardly tractable by the few dedicated samplings mounted in the primary circuit cold leg upstream from the containment entrance. By favoring hydrolysis reactions of volatile iodine species, the alkaline sump is shown to act as an iodine trap despite the evaporating conditions that prevail during the long-term chemistry phase.however, during this latter phase, a persistent, low-level concentration of gaseous iodine was reached in the long term, as during the previous fpt0/1 tests, indicative of a competition in the containment between iodine traps and sources. Aside from the aerosol particles injected by the primary circuit, in situ iodine oxide particles were found to be continuously forming from the decomposition of i2 and ich3 by air radiolysis products. These particles are suspected to be fine, implying that they predominantly deposit by diffusion on all the containment surfaces. Therefore, in the long term, both the persistence of gaseous iodine and the survival of iodine oxide particles are shown to exist in the containment. Source

Zdarek J.,UJV Rez
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2013

After the Fukushima Accident there is a worldwide strategy to develop the Defense in Depth strategy to mitigate the Severe Accidents. This effort has long tradition for new designs of NPPs. However the existing NPPs are lacking such a systematic approach. For the VVER 440 type NPP family the concept of the IN Vessel Strategy was adopted many years ago for the Loviisa NPP in Finland. However the VVER 1000/320 Units are lacking final treatment with the Severe Accidents. Effort of our research is to prepare the analytical and experimental proof to justify this concept for higher power VVER type NPPs. Copyright © 2013 by ASME. Source

Machek J.,UJV Rez
International Conference on Nuclear Engineering, Proceedings, ICONE | Year: 2014

Paper describes original methods of signal validation, specially developed for in-core measurements, namely for Self Powered Neutron Flux Detectors (SPND) and for core exit coolant temperature measurements (thermocouples measurements). Some interesting examples of NPP Temelin data validation (SPND) and NPP Dukovany (thermocouple measurements) are presented; precision and sensitivity of methods used are discussed. Copyright © 2014 by ASME. Source

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