Probabilistic nonlinear analysis of reinforced concrete bubbler tower structure failure

This paper describes the reliability analysis of concrete bubbler tower structure of nuclear power plant with the reactor WWER 440 under high internal overpressure. There is showed summary of calculation models and calculation methods for the probability analysis of the structural integrity considering degradation effects and high internal overpressure. The uncertainties of the resistance and the calculation model were taking in the account in the RSM method.This paper describes the reliability analysis of concrete bubbler tower structure of nuclear power plant with the reactor WWER 440 under high internal overpressure. There is showed summary of calculation models and calculation methods for the probability analysis of the structural integrity considering degradation effects and high internal overpressure. The uncertainties of the resistance and the calculation model were taking in the account in the RSM method

Nuclear safety policy working group recommendations on nuclear propulsion safety for the space exploration initiative

An interagency Nuclear Safety Working Group (NSPWG) was chartered to recommend nuclear safety policy, requirements, and guidelines for the Space Exploration Initiative (SEI) nuclear propulsion program. These recommendations, which are contained in this report, should facilitate the implementation of mission planning and conceptual design studies. The NSPWG has recommended a top-level policy to provide the guiding principles for the development and implementation of the SEI nuclear propulsion safety program. In addition, the NSPWG has reviewed safety issues for nuclear propulsion and recommended top-level safety requirements and guidelines to address these issues. These recommendations should be useful for the development of the program's top-level requirements for safety functions (referred to as Safety Functional Requirements). The safety requirements and guidelines address the following topics: reactor start-up, inadvertent criticality, radiological release and exposure, disposal, entry, safeguards, risk/reliability, operational safety, ground testing, and other considerations

Risk Informed Support of Decision Making in Nuclear Power Plant Emergency Zoning - Generic Framework towards Harmonising NPP Emergency Planning Practices

The report provides a systematic overview of the essential aspects of risk informed support of decision making (RIDM) in nuclear power plant (NPP) emergency zoning (EZ) as a contribution to harmonising strategic practices in the area. Owing to the state-of-the-art understanding and increased characterisation of NPP severe accidents, overall management of them should be analysed as an integrated complex process. The interrelationship of NPP emergency operating procedures, safety and risk assessments, severe accident management guidelines, and emergency off-site actions should be planned and organised to minimize the consequences of such accidents. A deterministic approach, coupled with both probabilistic safety assessment (PSA) technology and PSA results can play significant role in the development of relevant nuclear utility, regulatory and all stakeholders policies. The report describes the background, objectives and current state of a corresponding activity within JRC-IE's Analysis and Management of Nuclear Accidents (AMA) Action on probabilistic safety / risk assessment methodologies and practices for RIDM approach applied to NPP EZ. The approach is interdisciplinary, based on integration of PSA technology, severe accident phenomenology, and radiological protection.JRC.F.4-Nuclear design safet

Issues of the Seismic Safety of Nuclear Power Plants

Seismic safety of nuclear power plants became an eminent importance after the Great Tohoku earthquake on 11th of March, 2011 and subsequent disaster of the Fukushima Dai-ichi nuclear power plant. Intensive works are in progress all over the world that include review of the site seismic hazard assessment, revision of the design bases, evaluation of vulnerability, and development of accident management capabilities of the plants. The lessons learned from the Fukushima-accident changed the paradigm of the design. Preparedness to the impossible, i.e. the development of means and procedures for ensuring the plant safety in extreme improbable situations became great importance. Main objective of the Chapter is to provide brief insight into the actual issues of seismic safety of nuclear power plants, provide interpretation of these issues, and show the possible solutions and scientific challenges. The “specific-to-nuclear” aspects of the characterisation of seismic hazard, including fault displacement are discussed. The actual design requirements, safety analysis procedures are briefly presented with main focus on the design extension situations. Operation aspects and problems for restart after earthquake are also discussed. The Chapter is more focusing on seismic safety of the inland plants, located on soil sites, in low-to-moderate (diffuse) seismicity regions

Risk Assessment of NPP Safety in Case of Emergency Situations on Technology

The last accidents of the nuclear power plant (NPP) in Chernobyl and Fukushima give us the new inspiration to verify the safety level of the NPP structures. This paper presents the new requirements to test the safety and reliability of the NPP structures due to the recent accidents in the world. The IAEA in Vienna required in the document ‘Stress tests’ the verification of the safety of the NPP structures under impact of the extreme loads as the earthquakes, the extreme climatic actions and the technology accidents. The new recommendations to load combinations and design criteria were defined. The risk assessment to verify the safety and reliability of the NPP structures based on probabilistic and nonlinear analysis is presented. The uncertainties of material model (behaviour of the reinforcement and liner, concrete cracking and crushing), degradation effects, the loads level (dead and live loads, extreme climatic and accidental temperature and overpressure) as well as other effects following from the inaccuracy of the calculated model and numerical methods were taken into account in the response surface method (RSM) method. The results of the deterministic and probabilistic analysis of the NPP structures are presented

External Reactor Vessel Cooling Evaluation for Severe Accident Mitigation in NPP Krško

The In-Vessel corium Retention (IVR) through the External Reactor Vessel Cooling (ERVC) is mean for maintaining the reactor vessel integrity during a severe accident, by cooling and retaining the molten material inside the reactor vessel. By doing this, significant portion of severe accident negative phenomena connected with reactor vessel failure could be avoided. In this paper, analysis of NPP Krško applicability for IVR strategy was performed. It includes overview of performed plant related analysis with emphasis on wet cavity modification, plant’s site specific walk downs, new applicable probabilistic and deterministic analysis, evaluation of new possibilities for ERVC strategy implementation regarding plant’s post-Fukushima improvements and adequacy with plant’s procedures for severe accident mitigation. Conclusion is that NPP Krško could perform in-vessel core retention by applying external reactor vessel cooling strategy with reasonable confidence in success. Per probabilistic and deterministic analysis, time window for successful ERVC strategy performance for most dominating plant damage state scenarios is 2.5 hours, when onset of core damage is observed. This action should be performed early after transition to Severe Accident Management Guidance’s (SAMG). For loss of all AC power scenario, containment flooding could be initiated before onset of core damage within related emergency procedure. To perform external reactor vessel cooling, reactor water storage tank gravity drain with addition of alternate water is needed to be injected into the containment. ERVC strategy will positively interfere with other severe accident strategies. There are no negative effects due to ERVC performance. New flooding level will not threaten equipment and instrumentation needed for long term SAMGs performance and eventually diluted containment sump borated water inventory will not cause return to criticality during eventual recirculation phase due to the lost core geometry

Natural Hazards and Nuclear Power Plant Safety

The safety of nuclear power plants with respect of natural hazards can be ensured by adequate characterization of hazards and proven design solutions to cope with natural hazard effects. Design and severe accident management require characterization of very rare event. The events identified for the design basis and for the safety analysis are with annual probability 10−4–10−5 and 10−7, respectively. In this chapter, a brief insight into the actual issues of natural hazard safety of nuclear power plants and related scientific challenges is provided. The state of the art of ensuring safety of nuclear power plants with respect to natural hazard is briefly presented with focus on the preparedness to the accident sequences caused by rare natural phenomena. The safety relevance of different hazards and vulnerability of NPPs to different hazards are discussed. Specific attention is made to the non-predictable phenomena with sudden devastating effects like earthquakes and fault ruptures. Post-event conditions that affect the on-site and off-site accident management activities are also considered. The “specific-to-nuclear” aspects of the characterization of hazards are discussed. This is a great challenge for the sciences dealing with hazard characterization. The possibility for ensuring nuclear safety is demonstrated presenting cases when the nuclear power plants survived severe natural phenomena

Bezpečnosti JE na Slovensku z pohľadu záťažových testov po nehode vo Fukushimi

This paper presents the new requirements to test of the safety and reliability of the NPP structures due to the last nuclear accidents in the world. The accidents of the NPP in Chernobyl and Fukushima give us the new inspiration to verify the safety level of the NPP structures. The probabilistic assessment of NPP structures for PSA level 2 of VVER 440 in the case of LOCA accident is presented. The results of the probabilistic nonlinear analysis of the NPP structures are presented.Článok sa zaoberá novými požiadavkami na testovanie bezpečnosti a spoľahlivosti konštrukcií JE v dôsledku posledných jadrových nehôd vo svete. Havárie JE v Černobile a vo Fukushimi dávajú nové inšpirácie pre verifikovanie úrovne bezpečnosti konštrukcií JE. Rozoberá sa pravdepodobnostná metodológia konštrukcií JE pre PSA úrovne 2 reaktora VVER 440 v prípade havárie LOCA. Uvádzajú sa výsledky pravdepodobnostnej nelineárnej analýzy konštrukcií JE