Radioecology and the accident at the Chernobyl nuclear power plant

The ecological features of the 1986 Chernobyl accident and the principles of radiation monitoring of the environment are described. The laws of migration of radionuclides in different media in the environment and the accumulation of radioactive substances in food products are presented. The effect of radiation on the plant and animal worlds in the region of the accident is assessed. A system of protective and remediation measures in the agricutural, forestry, and water spheres is presented, and their radiological and cost effectiveness are estimated. The significance of the complicated and contradictory political and economic conditions during the time of the accident in the USSR (Commonwealth of Independent States) for the assessment of the ecological consequences of the accident is indicated. __________ Translated from Atomnaya énergiya, Vol. 100, No. 4, pp. 267–276, April, 2006.     

Investigation of the development of the 1986 accident at the Chernobyl nuclear power plant

Important results obtained from investigations of the diverse processes that occurred during the accident in the No. 4 unit of the Chernobyl nuclear power plant on April 26, 1986 are presented in a concise form. The events occurring in the unit in connection with the preparation for runout tests to be performed on a turbogenerator are examined: from the characteristics of the test program to the actions taken by the plant personnel in preparation for the these tests. The events that determined the character of the evolution and the catastrophic consequences of the accident are noted: involuntary stopping of the reactor and subsequent power increase without unpoisoning of the core, stopping of feed-water flow with increasing loop flow, operators’ lack of information about the actuation of the technological shielding of the electric drives of the main circulation pumps and electricity generator. Computational analysis of the initial phase of the accident and other computational assessments revealed new factors which with a large void effect made reactor runaway on prompt neutrons unavoidable-cavitation steam reaching the core entrance from the shutoff-regulation valve and/or the cavitation shutdown of the feed to the remaining main circulation pumps after the pumps powered by the run-out turbogenerator were disconnected. The most likely picture of the evolution of the accident is constructed on the basis of an examination of the destroyed power-generating unit. __________ Translated from Atomnaya énergiya,Vol. 100, No. 4, pp. 243–258, April, 2006.     

核电厂全厂断电事故分析

全厂断电（SBO）可能发展成为堆芯熔化、安全壳超压失效的严重事故。本文首先研究全厂断电事故的必要性以及在辅助给水系统不可用情况下的全厂断电事故的进程,随后定性的分析了事故进程在主泵轴封泄漏和对一回路实施减压缓解措施的影响下所具有的不同的发展情况。最后以秦山核电厂为例对其在提高应对全厂断电事故的能力和改进缓解事故后果的措施方面提出了建议。     

核电站主给水管道破裂事故的运行研究

较为全面研究安全壳内主给水管道破裂事故,特别是在小破口事故。采用分析的方法,从介绍主给水管道破裂事故的定义开始,进而总结导致主给水管道破裂事故的原因。详细分析了给水管道在安全壳内出现小破口事故的演变过程,机组的主要风险或后果,提出了运行人员对其进行诊断的方法和针对不同泄漏程度的处理策略。     

Process resulting in the destruction of the No. 4 unit reactor at the Chernobyl nuclear power plant

The results of an investigation of structural fragments of the core of the destroyed reactor in the No. 4 unit of the Chernobyl nuclear power plant are analyzed. It is shown on the basis of investigations of the fission product distribution over the cross-section of the graphite blocks and the determination of the physical properties of graphite that the temperature of the graphite blocks, including the reflector, at the moment they were ejected from the core exceeded 1000°C. The heat content of the fuel was estimated on the basis of an analysis of fragments of the dispersed uranium dioxide particles and an analysis of possible graphite dispersal mechanisms at the moment of the explosion. It is shown that energy sufficient for dispersing and partial vaporization of the fuel and for dispersing the graphite could have been introduced into the fuel during the accident process. Analysis confirms the possibility of a core destruction scenario with ejection from the shaft and ejection of part of the fuel in the form of vapor and dispersed particles into the atmosphere. __________ Translated from Atomnaya énergiya, Vol. 104, No. 6, pp. 319–328, June, 2008.     

Recent applications of PSA for managing nuclear power plant safety

The safety design and regulation of nuclear power plants has traditionally been based upon deterministic approaches that consider a set of challenges to safety, e.g. design basis accidents, and determine how those challenges should be handled. The approach has been very successful since no plant designed or regulated to United States standards has ever harmed a member of the public. The arbitrary nature of these safety criteria, the potential inconsistencies in the judgments on relative probabilities, and the lack of definition for ‘safety’ became increasingly evident during the 1960s. Probabilistic approaches to reactor safety were proposed ^1,2,3 but did not take off in the United States until publication of the Reactor Safety Study ⁴ in 1975. Even as the methodology matured, there remained a challenge to integrate it into the regulatory process. This article will describe this integration process. A probabilistic approach to regulation enhances and extends the traditional deterministic approach by introducing the concept of safety (risk) significance that allows the designer/operator to focus on important issues. Emphasis was initially placed on relative risk but now regulatory decision-making is employing both relative and absolute risk. Measures of importance will be defined. Risk information can be used to prioritize the allocation of resources and three examples will be described. Equipment configuration control systems are being installed and used at nuclear power plants to enhance safety and to reduce Operating and Maintenance costs; they will be described. Finally, the US Nuclear Regulatory Commission's introduction of risk-informed decision-making into the regulatory process will be discussed.     

Numerical method for the containment of fission products at a hypothetical accident in an underground nuclear power plant

As one means to expand the siting of nuclear power plants, construction of underground plants is now under study. An underground nuclear power plant has the feature that ground surrounding the underground cavity can contain the fission products of a hypothetical accident.If it is assumed that in a hypothetical reactor accident the cooling system loses its capacity wholly or partially, and gas containing fission products is emitted into the underground cavity. As a result, temperature, gas concentration and gas pressure in the cavity increase and it can be supposed that the gas leaks up to the surface through the ground, and that ground-water contains and carries fission products. The present paper numerically simulates a course of movement as mentioned above by the finite element method and gives the underground containment effect for fission products from a hypothetical accident.     

Fire-induced loss of nuclear power plant safety functions

A methodology is developed for evaluating the probability for loss of nuclear power plant safety functions due to fire. A framework for the investigation of fire scenarios involving safety-related equipment is established which models fire development as an event tree consisting of a series of ignition, detection, suppression, and propagation steps. The methodology has been applied to a representative BWR. Variations in the methodology are discussed for application to specific plants. Conservative estimates of core-damage probabilities due to fire were obtained; application of the methodology to a particular BWR including specific knowledge of cable locations, fire-retardants, detectors, etc. would result in considerably lower probabilities.     

Estimation of the emission of radioactive substances during the 1986 accident in the fourth-power generating unit at the Chernobyl nuclear power plant (review of primary data)

Russian Science Center "Kurchatov Institute." Translated from Atomnaya énergiya, Vol. 78, No. 6, pp. 403–417, June, 1995.     

AP1000核电建设安全标准化管理

2002年国家颁布实施了《中华人民共和国安全生产法》,出台了一系列的方针和政策,加大了安全生产监管力度。安全标准化是继安全评价、安全生产许可证制度之后,在安全监管方面采取的一项重大举措,也是一项治本之策。安全标准化工作是一项战略性、长期性、基础性的工作,是实现企业安全科学管理,提高企业本质安全的基本途径。海阳AP1000核电,其模块化、平行法施工及开顶法施工颠覆了传统先土建后安装的建造的理念,缩短建设周期,与此同时特大型模块运输、吊装,立体交叉施工显著增加,对安全管理提出了更高的要求。本文结合海阳AP1000核电工程特点及安全管理难点,提出AP1000核电安全标准化管理的思路和措施,对AP1000核电建设安全管理工作有借鉴意义。     

Assessment of fuel-rod meltdown in a severe accident at Bushehr nuclear power plant(BNPP)

After the Fukushima disaster, interest in the evaluation of severe accidents in nuclear power plants and off-site consequences has significantly increased. Because experimental studies are difficult to conduct, computational methods play a substantial role in accident analysis. In this study, a severe accident in the Bushehr pressurized water reactor power plant caused by a station blackout with a total loss of alternating current power supply has been evaluated. This analysis presents the in-core damage of fuel rods and the release of fission products as well as the thermal hydraulic response of the station components during the loss of active emergency cooling systems. In this manner, a perfect model of the Bushehr nuclear power plant using the MELCOR code is prepared. The accident progression is simulated, and the thermal responses of the fuels and hydraulic components are presented. It is shown that, without operator intervention, steam generators will become dry in approximately 3000 s, and the heat sink of the reactor will be lost. The simulation results show that at approximately 8600 s, the upper parts of the core start melting. This model calculates the shortest available time for accident prevention and proves that the time available is sufficient for operator manual action to prevent a nuclear disaster.