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.     

核动力厂选址假想事故源项的探讨

介绍了美国核审管部门对核动力厂选址假想事故源项确定的历史演变以及相关研究进展。推荐了一套核动力厂选址假想事故源项,以及确定非居住区边界的评价分析方法和假设条件。计算了M310和AP1000核动力厂厂址的非居住区的最大径向距离。计算结果表明:(1)对于M310和AP1000核动力厂,采用确定论方法估算大气扩散因子,安全壳泄漏率(体积分数)取0.3%/d,非居住区最大径向距离分别不超过1.4 km和1.9 km;(2)在厂址选址阶段,考虑核动力厂的技术路线尚未明确或采用新技术路线,采用"不考虑安全壳喷淋系统等能动安全设施对核素的去除作用"的选址假想事故源项来确定厂址非居住区的边界基本上是可行的。     

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。     

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.     

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。     

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.     

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.     

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.     

The causes and consequences of the Chernobyl nuclear accident and implications for the regulation of U.S. nuclear power plants

As in the case of the TMI accident public concern around the world over nuclear safety has been aroused by the Chernobyl nuclear accident. Because of its severity and enormous impact on public opinion, it is important to study the accident and its implications carefully and to provide accurate information to the public.Since this was the first nuclear accident with large offsite releases of radionuclides, valuable insights are to be gained especially, for example, from Soviet actions to terminate the accident and mitigate its consequences, emergency preparedness and evacuation measures, medical treatment, protection against contaminated food and water supplies, and a variety of post-accident recovery measures.With the perspective of a year since the accident and a recent visit by the Author to Chernobyl with a U.S. nuclear safety delegation this paper reviews a number of new studies to draw conclusions about the causes of the Chernobyl accident, its health and environmental consequences and some of the implications for regulation of the safety of U.S. nuclear power plants.     

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.