Extension of TACOM to the complexity of tasks designed for abnormal situations in nuclear power plants

TACOM (TAsk COMplexity) is a measure for evaluating the complexity of tasks prescribed for emergency situations in nuclear power plants. Five sub-measures constituting TACOM represent five different aspects of the task complexity exhibited in operating procedures for emergency situations. The practicality of TACOM has been verified through a series of empirical studies. However, tasks designed for abnormal situations that can significantly affect the safety of nuclear power plants, also need a proper measure for evaluating their complexity. TACOM provides a process, a systematic cognitive task analysis method and a set of guidelines to support its application. Therefore, although the characteristics of abnormal task situations are not the same as those of emergency situations, TACOM seems to be reasonably applied to abnormal situations or at least to offer meaningful insights for developing a measure for evaluating the complexity of tasks in abnormal situations. Thus this study examined the applicability of TACOM to abnormal situations through case studies. Particular attention was paid to the sufficiency and appropriateness of the three methodological tools, which are the process, the cognitive task analysis method and the set of guidelines. Collective consideration of the case studies and the characteristics of tasks prescribed for abnormal situations led us to draw the conclusion that TACOM could be reliably used for abnormal situations as well. This paper reports the process of how to apply TACOM to the tasks of abnormal situations and discusses some lessons learned through this application.     

Explosion hazards related to hydrogen releases in nuclear facilities

Hydrogen explosion risk needs to be carefully assessed and evaluated in nuclear facilities because of the potential catastrophic consequences: breakdown of safety equipments, failure of containment, dissemination of radioactive materials in the environment.When studying an indoor release, one possible simplification is to assume a perfect gas mixing inside the room. This assumption is effectively often used to evaluate toxic risks in the environment outside a building (Mastellone, Ponte, & Arena, 2003). However, perfect gas mixing assumption is only a rough approximation, as indoor concentrations can largely differ from mean values, due to buoyancy, recirculation zones or obstacles for example.In order to better evaluate the risk of explosion in case of an accidental release of hydrogen, IRSN conducted a numerical study using FLACS CFD software. Several parameters have been studied to identify dangerous situations and draw a representative picture of the risk: room size, position and direction of hydrogen leak, ventilation characteristics. Hydrogen release flow rates used for numerical simulations have been chosen as the highest leak rate which, by applying the assumption of perfect mixing, produces an average concentration in the room equal to hydrogen lower flammability limit (LFL).Simulation results indicate that in some particular configurations, especially for impinging hydrogen jets, hydrogen concentrations can locally be above LFL and then create explosive atmospheres with significant volumes.     

核电站气载放射性流出物环境辐射剂量计算

计算大亚湾核电站正常工况下气载放射性流出物对80km的大气环境防护距离内的公众所致辐射剂量。根据大亚湾核电站2001年气载放射性流出物排放量,逐时观测气象数据及相关参数,选用修正的高斯烟羽模型和美国核管会导则1.109的食物链模型,运用美国橡树岭国家实验室编制的AIRDOS-EPA程序,程序经修改后适合于中国核设施的计算。计算得到2001年大亚湾核电站气态放射性流出物对周边80km范围内的公众所致的年均集体剂量为4.722E-3人·希,最大个人有效剂量为1.362E-8希。结果表明,2001年大亚湾核电站正常工况下,气载放射性流出物对周围公众造成的剂量当量远低于国家标准,对周边地区居民健康几乎没有影响。     

Automation design in advanced control rooms of the modernized nuclear power plants

This study evaluated the effects of levels of automation (LOAs) decisions in advanced control rooms of the modernized nuclear power plants. Following advancements in design of digitalized human–system interfaces (HSIs), the roles of human operators have changed significantly. Negative performance and safety consequences may occur as a result of these changes. These problems are viewed as the out-of-the-loop (OOTL) performance problems. This study conducted an experiment to compare the effects of different LOAs under different operating procedures on operating performance. Experimental results indicated that blended decision-making (level 6 LOA) generates the lowest mental workload. Furthermore, the pattern of SA observed in this study is found better SA at intermediate LOA and poorer SA at low level of automation and full automation. Subjective rating results suggest that LOAs distribute the roles of option generation, and selection between human and/or computer servers which significantly impacts automated system performance. This study provides a direction for the HSI designers in nuclear power plants (NPPs). Additionally, based on results obtained by this study, the user interfaces of PCTRAN system and the alarm reset system should be improved to ensure safe operation of NPPs.     

浙江省核电建设与环境安全的协调性分析

浙江省缺乏常规能源,在能源结构中,火电比重已经过大,加快核电发展,是我省电力发展的必然选择。继中国第一座自行设计、建造的核电站--秦山核电站之后,浙江省第二座核电站三门核电站的两台目前国内最先进的百万千瓦级压水堆技术机组也即将在2015年投入运营。加速核电建设不仅保证能源安全、调整能源结构,而且能实现节能减排、减少环境污染,建设环境友好型、资源节约型社会、推动经济社会又好又快发展。我省核电建设应通过加强核电站的安全检查、设计建设中安全措施保障、解决核电建设存在的相关问题和加强监测网络的建设等,促进浙江省的核电建设与环境安全协调发展。     

核电站事故对上海地区影响的快速估算

为了能快速估算上海周围某核电站发生事故并伴有放射性物质泄漏时,上海地区可能受到的放射性污染情况,选用了一种基于拉格朗日动态烟团模式的剂量估算方法,模拟计算表明,在某些天气和核电站事故等级的条件下,上海地区将出现500mSv以上的高剂量区,因此需要制定应急预案以备用。     

A model for radiological consequences of nuclear power plant operational atmospheric releases

A dynamic dose and risk assessment model is developed to estimate radiological consequences of atmospheric emissions from nuclear power plants. Internal exposure via inhalation and ingestion, external exposure from clouds and radioactivity deposited on the ground are included in the model. The model allows to simulate interregional moves of people and multi-location food supply in the computational domain. Any long-range atmospheric dispersion model which yields radionuclide concentrations in air and on the ground at predetermined time intervals can easily be integrated into the model. The software developed is validated against radionuclide concentrations measured in different environmental media and dose values estimated after the Chernobyl accident. Results obtained using the model compare well with dose estimates and activities measured in foodstuffs and feedstuffs.     

海洋核动力平台核事故应急监测策略研究综

综述了国外核事故应急监测策略研究进展,以及我国在核应急监测法规标准、应急监测方法、应急辐射环境监测技术等方面的研究现状,从海洋核动力平台的法规标准、应急监测方案、应急辐射监测项目和应急监测方法4个方面进行了探讨,并提出了制定核应急监测政策及标准规范、建立应急监测预案库、加快研发应急采样与监测方法、建立海洋放射性监测体系等建议。     

Short and long term dispersion patterns of radionuclides in the atmosphere around the Fukushima Nuclear Power Plant

The Chernobyl accident and unfortunately the recent accident at the Fukushima 1 Nuclear Power Plant are the most serious accidents in the history of the nuclear technology and industry. Both of them have a huge and prolonged impact on environment as well as human health. Therefore, any technological developments and strategies that could diminish the consequences of such unfortunate events are undisputedly the most important issues of research. Numerical simulations of dispersion of radionuclides in the atmosphere after an accidental release can provide with a reliable prediction of the path of the plume. In this study we present a short (one month) and a long (11 years) term statistical study for the Fukushima 1 Nuclear Power Plant to estimate the most probable dispersion directions and plume structures of radionuclides on local scale using a Gaussian dispersion model. We analyzed the differences in plume directions and structures in case of typical weather/circulation pattern and provided a statistical-climatological method for a “first-guess” approximation of the dispersion of toxic substances. The results and the described method can support and used by decision makers in such important cases like the Fukushima accident.     

Provenance of unknown plutonium material

The determination of the provenance of 'unknown' plutonium material is demonstrated through a simulation study based on an isotopic fingerprinting approach. Plutonium of known provenance was considered as the 'unknown' nuclear material in order to evaluate the potential of the approach and verify its predictive capabilities. Factor analysis was used to compare the Pu isotopic composition of the 'unknown' material with Pu isotopic compositions simulating well known spent fuels from a range of commercial nuclear power stations. The provenance of the 'unknown material' is assigned to the commercial fuel with which exhibits the highest degree of similarity with respect to the Pu composition. The approach appears promising since it accurately predicted the provenance of the one 'unknown' sample considered; nevertheless, the approach is still at the development stage. Important challenging issues related to the simulation uncertainties and its testing on real laboratory samples have to be explored prior to evaluating the potential of the approach.