Cost per severe accident as an index for severe accident consequence assessment and its applications
Introduction
Probabilistic risk assessment (PRA; or probabilistic safety assessment) is widely used as a method to assess the risks of a nuclear power plant. PRA is divided into three levels in order to sequentially assess the occurrence possibilities and the consequences of nuclear power plant severe accidents. Level 1 PRA and level 2 PRA calculate the core damage frequencies (CDFs) and containment failure frequencies (CFFs), respectively. Level 3 PRA assesses the consequences from the radioactive materials emitted in the wake of severe accidents.
A number of calculation codes: MACCS [1], Cosyma [2], OSCAAR [3], [4], RSAC [5], HotSpot [6], etc., are developed to perform level 3 PRA. They simulate the dispersion of the emitted radionuclides in certain atmospheric conditions and estimate the individual or public dose or both of them. Most of the codes can take into account the radiation protection countermeasures. MACCS, Cosyma and OSCAAR also provide a function to estimate the costs regarding radiation protection countermeasures, decontamination and food intake restriction. There are many earlier studies [3], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16] related to severe accident consequence assessment using these calculation codes. Most studies concentrate on the evaluation of acute and chronic doses. This is because the probabilistic safety criterion related to the consequence of severe accidents which is commonly used by the regulatory bodies and utilities in several countries is the dose (some of them do not even have a criterion for the consequence of severe accident but only have annual probabilities of occurrence, e.g., core dame frequency (CDF) or containment failure frequency (CFF)) [17].
Nevertheless, the accident at the Fukushima Daiichi Nuclear Power Station (Fukushima accident) showed that a severe accident wreaks tremendous economic, social and environmental impacts even though the health effects due to radiation exposures are unapparent. Three huge tsunamis attacked the Fukushima Daiichi Nuclear Power Station after the Great East Japan Earthquake (M 9.0) which led to station blackout (SBO). There were hydrogen explosions in the units 1 and 3. Reactor core melting and reactor vessel/containment vessel failures were strongly suspected in the units 1–3. More than 140,000 people were sheltered and evacuated [18] as there was a large amount of radioactive materials emitted from the power plants [19]. Most of them would not be able to return home for several years. The evacuees lost their incomes throughout the period of evacuation, and thousands of square kilometers of area needed decontamination. Only a few nuclear power plants in Japan could restart after all were shut down [20], [21], and many Japanese decided to oppose the utilization of nuclear energy [22].
Circumstances after the Fukushima accident imply the need to include the evaluations of economic, social and environmental impacts into the consequence assessment of severe accidents. However, these impacts, together with the health effects due to the radiation exposures, have different characteristics and their evaluation results are shown in different ways. In order to comprehensively evaluate the consequences of severe accidents, various kinds of consequences must be converted into a common unit, and integrated to form a common index. The authors selected the cost per severe accident as a common index because previous studies [23], [24], [25], [26], [27], [28] proved that it can cover a large scope of consequences and it is easy-understanding. In ExternE [23], Hirschberg et al. [24] and IAEA technical reports series no. 394 [25], many kinds of consequences, including health effects regarding radiation exposures, economic, social and environmental impacts, are evaluated in terms of monetary value, referring to the consequences of the Chernobyl accident. However, the objective of these studies was to perform a comparative consequence assessment of severe accidents among the electricity generation systems. Therefore, the consequences selected for the evaluation are the consequences that can be commonly evaluated in all systems, and there is a possibility for consequences particular to nuclear severe accidents to be overlooked. The aim of the study of Park et al. [26] is to estimate the total damage cost of the severe accidents in extreme conditions, and the main purpose of NUREG/BR-0058 Rev. 4 [27] and NUREG/BR-0184 [28] is to provide a guideline for the regulatory analysis. Hence their results cannot represent the consequences of severe accidents, though the methods to convert the consequences of severe accidents to monetary values can be adapted to the consequence assessment methodology discussed in Section 2.
The primary objective of this paper is to consider the severe accident consequence assessment methodology that can take into account various kinds of consequences. We introduce the methodology to convert consequences of severe accidents into monetary values, and integrate them to form a common index: the cost per severe accident (Section 2). The authors must emphasize that the aim is not to estimate the total damage cost of the accident itself but to extend the scope of the consequence assessment. As a case study, the methodology was applied to a virtual 1100 MWe boiling water reactor (Section 3). The calculated cost per severe accident was compared with the amount of source terms emitted in the severe accidents, another index for severe accident consequences, in order to demonstrate the performance of the cost per severe accident. The secondary objective is to consider the applications of the cost per severe accident calculated by the proposed methodology. The ways to use it for optimization of radiation protection countermeasures and for estimation of the effects of accident management strategies were discussed (Section 4).
Section snippets
Overview of the calculation of cost per severe accident
The flow of the calculation of cost per severe accident is shown in Fig. 1. First of all, the type of the nuclear reactor and its location are determined. Then the severe accident sequences are defined in order to take into account all conceivable severe accidents. The accident sequences that do not proceed until the release of the radioactive materials from the containment vessel are excluded since their source term data are not provided. After that, the source term data of each sequence,
Model plant and its calculation condition
The methodology was applied to a virtual 1100 MWe boiling water reactor (BWR-5) which is located at the center of Tokai Research and Development Center (TRDC) of JAEA. Dominant severe accident sequences were selected, and the CFFs, release times, release duration times, and release ratios of those accident sequences were taken from the results of an open document of level 2 seismic PRA [46]. They are shown in Table 2. The reason that the seismic PRA was selected is that it covers the accident
Optimization of radiation protection countermeasures
In the conventional way, the countermeasures that can minimize the individual exposure dose have been selected as the optimum ones. Economic, social and environmental impacts resulted from severe accidents are not considered. Optimization of radiation protection countermeasures using the cost per severe accident which can take into account all consequences mentioned in Section 2.3 is introduced in this section.
If the objective of the optimization is to minimize the individual exposure dose, the
Conclusions
The cost per severe accident which is an index that can take into account various kinds of consequences of severe accidents and its calculation methodology was introduced.
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The methodology to convert various consequences of severe accidents into a monetary value, and integrate them to form the cost per severe accident was proposed.
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As a case study, the cost per severe accident of a virtual 1,100 MWe BWR-5 was calculated.
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The case study showed that the cost per severe accident can play an important
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2016, Nuclear Engineering and DesignCitation Excerpt :The radiation effect index and the decontamination index are nearly identical, while the relocation index is much smaller than the other two. This is slightly different from the result in the previous study (Silva et al., 2014) where the radiation effect index, the decontamination index and the relocation index were the three major consequences of a severe accident. This is because the dose level for starting relocation is changed from 20 mSv/year to 100 mSv/year, since it was revealed in the sensitivity analysis of the previous study (Silva et al., 2014) that larger dose level for starting relocation leads to smaller overall consequences.
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2014, Energy PolicyCitation Excerpt :Although their comparison did not explicitly address external costs from severe fatal accidents, it suggests that external costs from impacts on human health, climate change, and other environmental issues dominate. Following the Fukushima nuclear power accident the discussion on accident costs has recently been addressed from different viewpoints, including additional aspects such as social and institutional factors, risk targets and threat beliefs (Al Shehhi et al., 2013; Aoki and Rothwell, 2013; Hartmann et al., 2013; Kampanart et al., in press; Srinivasan and Gopi Rethinaraj, 2013; Vitazkova and Cazzoli, 2013). PSI׳s comparative risk assessment approach provides a comprehensive framework for the objective and quantitative evaluation of severe accidents in the energy sector, with the database ENSAD as the core element.