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[en] A survey of risk assessment methodology which is being given a lot of attention in the scientific world is presented in this paper. The maximum credible accident approach used for reactor safety assessment in the past has proved inadequate and a probabilistic approach has now caught the fancy of the scientific world. This method took to evaluating single accidents and making them the basis for decisions. This non-probabilistic approach had obvious drawbacks. Most importantly, it undermined less severe accidents which might be more important due to a high frequency of occurrence. (J.A.)
[en] This paper presents an overview of modelling features of the first revision of the V2.1 major version of the European severe accident integral code ASTEC which has been set-up by IRSN and delivered to the ASTEC worldwide community end of 2016. After some generalities concerning the software structure and the packaging of ASTEC V2.1 revision 1, the phenomena addressed by the different modules constitutive of ASTEC are detailed. Finally, perspectives as concerns the development of future versions of ASTEC V2.1 at IRSN are outlined. (author)
[en] • Rationale: – INPRO methodology (safety area) requires that “a major release of radioactivity should be prevented for all practical purposes. – Innovative nuclear energy system would not need relocation or evacuation measures outside the plant site. – Satisfying this requirement is crucial for public acceptance and for the sustainability of nuclear energy. • Objective: – Demonstrate that the evolution of safety requirements and related technical and institutional innovations in nuclear technologies provide continued progress to meet the INPRO requirement.
[en] Conclusion: IVR is one of important severe accident management strategies of CAP1400. The purpose of IVR-ERVC experiments is to obtain CHF at RPV lower head and research its relevant mechanism. IVR-ERVC experiment facility was designed and built with a series of improvements. Insights achieved in IVR-ERVC experiments contribute to IVR evaluation, design improvement and safety review of CAP1400.
[en] Experimental study on the thermal fragmentation of melt, including Sn, Pb and Sn-Pb alloy, has been carried out based on the SSFT (Small-Scale Fragmentation Tests) facility. The effects of the melt properties, release distance, initial melt temperature, and coolant temperature on the thermal fragmentation have been studied. By analyzing the debris characteristics and the distribution, several specific thermal fragmentation mechanisms have been given, corresponding to different parameters. Finally, a partition map of thermal fragmentation mechanisms has been drawn based on the previous work. (authors)
[en] Highlights: • Nuclear accident consequence index can assess overall consequences of an accident. • Correlations between the index and release parameters are developed. • Relation between the index and release amount follows power function. • The exponent of the power function is the key to the relation. - Abstract: Nuclear accident consequence index (NACI) which can assess the overall consequences of a severe accident on people and the environment is developed based on findings from previous studies. It consists of three indices: radiation effect index, relocation index and decontamination index. Though the NACI can cover large range of consequences, its assessment requires extensive resources. The authors then attempt to simplify the assessment, by investigating the relations between the release parameters and the NACI, in order to use the release parameters for severe accident consequence assessment instead of the NACI. NACI and its components increase significantly when the release amount is increased, while the influences of the release period and the release starting time on the NACI are nearly negligible. Relations between the release amount and the NACI and its components follow simple power functions (y = ax"b). The exponent of the power functions seems to be the key to the relations. The exponent of the relation between the release amount and the NACI was around 0.8–1.0 when the release amount is smaller than 100 TBq, and it increased to around 1.3–1.4 when the release amount is equal to or larger than 100 TBq.
[en] Response activities are important parts of both safety and security activities as a layer of defence, if prevention activities fail and deviation from compliance has been detected. Three levels of response can be differentiated based on the expected occurrence frequency of the event, its actual or potential consequences, and the scope of the involvement of various organizations. The operative level response to most frequently occurring, the least serious events requires efforts mainly from the operator by strictly following the routine procedures developed in advance; however, their repetition may attract the attention of the regulator and initiate enforcement actions. Examples for such events are the anticipated operational occurrences, expected failures of equipment, false and nuisance alarms, certain less serious unintentional or intentional human errors. Joint response with the involvement of more internal organizational units and competent authorities is needed to manage more serious events, which still have no unacceptable radiological consequences. Such events are accidents within and beyond the design basis, security events within the design basis threat. The response actions to those events are developed in advance and described in detail in the emergency operating procedures, severe accident management guidelines and the security contingency plans. The third and most severe level of response is needed, if unacceptable radiological consequences may or do appear on-site and off-site the facility, when the emergency response plans and if appropriate the contingency plans shall be implemented. (author)
[en] Conclusions: • Development of SAMG is a structured process, once strategies are selected; • Use a logic diagram to execute the various SAMG in proper order; • Develop Computational Aids to support SAMG; • Develop guidance for the TSC how to handle the SAMG, often called TSGs (Tech. Support. Gls); • Develop guidance for the MCR if the TSC is not readily available - e.g., for fast developing accidents.
[en] The experience from the last 40 years has shown that severe accidents can subject electrical and instrumentation and control (I&C) equipment to environmental conditions exceeding the equipment’s original design basis assumptions. Severe accident conditions can then cause rapid degradation or damage to various degrees up to complete failure of such equipment. This publication provides the technical basis to consider when assessing the capability of electrical and I&C equipment to perform reliably during a severe accident. It provides examples of calculation tools to determine the environmental parameters as well as examples and methods that Member States can apply to assess equipment reliability.