Analysis of the Polonium Hazard in Nuclear Power Systems with Lead–Bismuth Coolant

Polonium presents no danger under normal operating conditions when the coolant loop is sealed. In our country, we have almost 40 years of experience in working with radioactive lead–bismuth coolant in the reactors used in nuclear-powered submarines and ground-based testing prototypes. This experience has made it possible to study how the polonium radiation conditions inside working enclosures are produced and to develop effective safety measures for different operating regimes, including irregular situations and accidents.Data are presented on the polonium radiation conditions in certain typical operating and accident situations in a nuclear submarine: spillage of a substantial amount of coolant directly into the reactor bay, the consequences of an interloop leak in a steam generator, and refueling with fresh nuclear fuel.Regular medical-biological examinations of the workers participating in the operation of the system, repair work, and liquidation of the consequences of accidents did not show any cases of irradiation by polonium above the established health norms.Inferences are drawn from studies performed in this and other countries of polonium emission from lead-based polonium-containing media when such media are heated in vacuum and in an inert-gas atmosphere in the temperature range 300–800°C.     

基于PSA分析事故序列场内工作人员辐射风险研究

从总风险控制的角度,提出了事故工况下场内工作人员剂量与辐射风险接受准则,并建立了相应的评估方法。以典型压水堆核电厂为例,采用概率安全分析（PSA）的全范围事故序列进行验证评价,评估了典型压水堆核电厂事故后场内工作人员的辐射剂量与辐射致死风险。通过验证结果可知,事故后场内工作人员总的辐射致死风险远低于公众由于自然灾害、疾病、交通事故及不同行业的总死亡风险值;事故后工作人员在燃料厂房进行操作时的辐射致死风险占比最高,故工作人员在燃料厂房进行相关操作时,可提前制定相应的辐射防护措施来降低辐射风险;工作群组中其他人员和意外受照人员事故后辐射致死风险占比较高,可通过采用气面罩等方式对气载放射性进行防护以降低其辐射风险。相应的分析结果可为后续核电厂事故后处理方案的制定和事故后场内工作人员辐射防护措施的制定提供借鉴。      

Modular HTR confinement/containment and the protection against aircraft crash

Does an HTR need a containment – pressure resistant – or is it possible – licensable – to have only a so-called confinement.The answer depends on both the results of the safety analysis of the accidents considered in the design and the acceptance by the licensing authorities and the public of a safety approach only based on severe core damage exclusion.The safety approach to be developed for modular HTRs must describe the application of the defence in depth principle for such reactors. Whatever the requirements on the last confinement barrier could be, a convincing demonstration of the exclusion of any severe core damage is needed, relying on exhaustive and bounding considerations of severe core damage initiators and the use of non-questionable arguments.The paper presents the containment issues for HTRs based on German experience background and considerations for modern modular HTR safety approach including beyond design situations.

• For the German HTRs (designed in the 80s), it could be shown in the licensing procedures in Germany that there was no need for a pressure retaining and gas tight containment to enclose radioactive nuclides released from the nuclear heat source. Instead, the confinement envelope acted in conjunction with other barriers to minimize the release of radioactive nuclides and the radiological impact on the environment.

• The confinement envelope consisted of the reactor building, a sub-atmospheric pressure system, a building pressure relief system, an HVAC systems isolation and a filtration system.

• During a major depressurization accident, unfiltered releases were discharged to the environment. The analyses results show that the environmental impact was far below the dose limits according to the German Radiological Protection Ordinance, even when the effect of filters was not taken into account.

• The demonstration strongly relied on the assumptions made for the source term definition, e.g. the fuel particles failure rates (under irradiation and during accidental conditions), the diffusion data, the dust data and the deposition/lift-off mechanisms.

• For modern modular HTRs, the last confinement barrier performances will have to be determined in accordance with the set of accidents to be considered in the design including internal and external hazards and the limits targeted for the public and the environment protection.

Further more the paper presents an analysis of effects of a deliberate crash of a large commercial airliner on a former German HTR design.     

Blowdown tests to verify calculation methods for loss-of-coolant accidents

The HDR Facility represents a full scale test rig for the simulation of nuclear power plant accidents. The experimental and analytical investigations are basically aimed at the identification of the main phenomena and influences occurring during severe accidents and at the verification of calculation models and codes to describe those accidental effects. During Phase I of the program (1975–1983) blowdown investigations covering design basis accidents aspects formed the focal point of the research activities. The investigated components were full scale isolation valves, pressure vessel internals (especially core barrel) and the containment vessel and internal structures.     

Radiation consequences of a hypothetical failure of a dam at the coolant reservoir of the chernobyl nuclear power plant

Mathematical simulation is used to estimate the possible radiation consequences of an accidental failure of the protective dam of the coolant reservoir at the Chernobyl nuclear power plant. The dynamics of the emptying of the reservoir and the escape of radionuclides is calculated. The additional contamination of bottom deposits in the Dnepr River, which can be caused by the accidental escape of radioactive substances from the coolant reservoir, is estimated. The additional dose load to the public is estimated taking account of the food chains. A single-step mathematical model, taking account of the contamination of the water and the bottom deposits, is constructed to study the fish food chain. It is established that for an accidental failure of the protective dam of the coolant reservoir of the nuclear power plant the dose to the public will not exceed 2.5·10⁻³ Sv in the first year after the failure. Therefore, the destruction of the protective dam of the coolant reservoir of the Chernobyl nuclear power plant, if it occurs, will not be a radiation accident, 2. figures, 1 table, 9 references. Translated from Atomnaya énergiya, Vol. 88, No. 4, pp. 303–307, April, 2000.     

Formation, characterisation and cooling of debris: Scenario discussion with emphasis on TMI-2

Regarding safety improvements for existing nuclear power plants, the TMI-2 accident is interesting because of the present commercial dominance of light water reactors (LWR). This accident demonstrated that the nuclear safety philosophy evolved over the years has to cover accident sequences involving massive core melt progression in order to develop reliable mitigation strategies for both, existing and advanced reactors. Although the TMI-2 core was reflooded, the results also appear applicable to the general melt progression phenomenology of most unrecovered (unreflooded) blocked core accident scenarios. Nevertheless, a large range in the initial conditions of core melt progression provides significant uncertainties in assessing the integrity of the lower head, the containment in severe reactor accidents, and the consequences of recovery actions in accident management, as well as core reflooding in particular. The probability of success of reflooding as an accident management strategy – in-vessel reflooding to terminate the accident and ex-vessel flooding to prevent reactor vessel melt-through – has to be assessed and discussed in detail.     

Radiation safety norms for atomic energy

The evolution of the dose limit and the admissable concentration of radionuclides in air and water in regulatory documents is analyzed. The legitimacy of classifying liquid radioactive wastes on the basis of the intervention level for radionuclide concentrations in drinking water is discussed. The SP AS-99 admissable irradiation levels for the general population due to emissions for nuclear power plants are compared with the dose in regions containing nuclear and thermal power plants.Translated from Atomnaya Ènergiya, Vol. 97, No. 4, pp. 299–308, October, 2004.     

辐射监测及危害评估是核应急医学救援的先导

针对核与辐射突发事件的医学救援工作,出于减少核事故对工作人员和公众的损害,保证救援人员和公众的健康和安全的目的,本文就应急救援中放射源项识别和威胁类型的确定,从辐射监测及危害评估入手,讨论多学科沟通和多单位合作的框架、内容和意义,从而为更加高效、安全地做好核应急救援提供知识和决策基础。     

Radiation Resistance of Fused Titanium Ceramic for Actinide Immobilization

The radiation resistance of ceramics proposed for solidification of actinide-containing wastes is studied. Their main concentrators (for uranium) in the samples are phases with fluorite type structure (zirconolite, pyrochlore, murataite), and brannerite. The critical dose for the transition of the crystal lattice of these phases into an amorphous state under irradiation with 1 MeV Kr⁺ at room temperature was 3·10¹⁸ m^–2 for zirconolite, (1.8–2.4)·10¹⁸ m^–2 for pyrochlore, (1.7–1.9)·10¹⁸ m^–2 for murataite, and 1.4·10¹⁸ m^–2 for brannerite. The forms of murataite with 3-, 5-, and 8-fold motif of the fluorite cell all have close radiation resistance. These data make it possible to estimate the transition time of the murataite structure into the amorphous state to be 6–7 hundred yr and 6–7 thousand yr with hypothetical content of ²³⁹Pu in it of 10% and 1%, respectively. The same values of the radiation resistance were obtained previously for titanates with pyrochlore structure, which were proposed by American researchers as matrices for immobilization of excess weapons plutonium.     

Radiation doses to the public from the nuclear industry

Section 1: It is shown that the dangers arising from power production in the past were greater than those arising from any form of power production today. Section 2: The specific ways in which radiation injures both the present and future generations are described. Section 3: The routine risks arising from nuclear power production are compared with those arising from other modern sources; first the risks to those employed in power production and then the risks to the general public, including the risks arising from efforts to conserve energy. Section 4: The risks to the public arising from major accidents are explained. Section 5: The radiation risks incurred by the public in the course of medical diagnosis and treatment are described and discussed. Section 6: Conclusion. It is pointed out that the dangers of nuclear energy are considerably less than those of all other sources other than directly piped natural gas; and that the reduction of the specific risks due to ionizing radiation arising from medical uses and from domestic heat conservation could save about a hundred times as many lives as would the complete elimination of the radiation arising from the production of nuclear power.     

核与辐射事件医学应急管理体系国际比较

介绍了我国核与辐射事件医学应急管理体系的构成,并将之与日本、美国、法国、俄罗斯和加拿大的核与辐射事件医学应急管理体系进行比较,分析其优缺点,同时介绍了WHO和IAEA在核与辐射事件医学应急中的作用,在此基础上提出建立健全我国核与辐射应急医学管理体系、提升医学应急救援能力的建议。     

事故性UF6释放的辐射环境影响估算

ＵＦ６是核燃料生产过程中一种重要的中间产品，生成于铀同位素分离过程中，因此，ＵＦ６大量向环境释放是核燃料生产厂运行期间可能发生的一种潜在事故。     

发展中的核工业四一七医院核应急医学救援分队

核事故医学应急救援的目的在于最大限度地减少核事故造成的损失和带来的不良后果,主要内容包括迅速有效地对受照人员和危重伤员进行医学处理,并对公众和应急工作人员做好防护,减少人员受到的各种伤害。本文介绍了核工业四一七医院核应急医学救援分队的组建、发展过程,并总结分析历次救援演习,以供承担核应急医学救援的工作人员参考。     

Safety assessment of the NET Predesign

Work carried out by European Associations on Safety and Environment inside the EC Fusion Technology Programme and by NET has been concentrated on safety-related guidance and on safety assessment of the NET Predesign. Emphasis has been put on analysis of accident sequences of regulatory concern up to worst case accidents, including quantification of consequences to components, systems, and plant, and of doses to the public. Probabilistic safety studies for the most important systems and broadly for the entire plant have been performed to supplement the calculated accidental doses by expectation values for their occurrence rate, and to check the relevance of the reference accident sequences selected initially by judgment. Waste masses per year of operation and for decommissioning have been quantified. For two countries and according to the practices and regulations of these countries, volumes of radioactive waste packaged for final disposal have been determined.Presented at the IAEA Technical Committee Meeting on Developments in Fusion Safety, Toronto, June 7–11, 1993.     

Simulation of the Radioactive Contamination of a Bukhta after a Radiation Accident

A mathematical model is developed for transport of radionuclides in the system consisting of water–hot particles in bottom deposits–particles of bottom deposits. This model is used to study the consequences of the radiation accident in bukhta Chazhma in 1985. The escape of ⁶⁰Co into the bukhta water from bottom deposits is estimated. Although the fraction of ⁶⁰Co escaping is small (about 10^–5), estimates show that its concentration in water can reach hundreds Bq/m³. The time dependence of the ⁶⁰Co concentration in the upper layer of bottom deposits is estimated.     

Subcritical power reactor with irradiation by a beam of accelerated protons

Conclusions The conversion of a nuclear power plant to operation with quite deeply subcritical reactors eliminates the primary reason for the appearance of reactivity accident situations associated with the probability of the reactor being transferred into a subcritical state and runaway of this state. There is no doubt that a nuclear power plant can in principle operate on the basis of a subcritical reactor and a high-power proton accelerator. To answer the question of whether or not it is desirable to equip nuclear power plants with accelerators, it must be kept in mind that besides achieving the main goal — complete elimination of the possibility of reactivity accidents and as a consequence of such accidents emission of solid radioactive products of uranium fission with enormous consequences for ecological and economic damage — such improvements have other important consequences. These include, for example, the possibility of constructing fuel cycles on the basis of the fuel depleted with respect to fissioning isotopes (^233,235U,²³⁹Pu), which will make it possible to decrease substantially the fuel component of the cost of a nuclear power plant; the possibility of more efficient utilization of nuclear fuel by increasing significantly the interval between loadings; and, control of the power and shielding of a reactor by changing the beam current of the accelerator. All this will make it possible, in principle, even at today's level of development of reactor and accelerator technology to build a subcritical power reactor with external irradiation with a high-energy particle beam. Institute of High Energy Physics. Translated from Atomnaya énergiya, Vol. 77, No. 4, pp. 300–308, October, 1994.     

放射工作人员外周血淋巴细胞染色体畸变分析

为了解不同职业照射类型、年龄、工龄放射工作人员外周血淋巴细胞染色体的畸变情况,采集四川省1 612名放射工作人员(放射组)和248名健康人员(对照组)外周血,用微量全血培养法培养淋巴细胞,MetaSystems系统分析记录染色体畸变,统计分析染色体畸变率。结果表明,放射工作人员染色体总畸变率显著高于对照组;放射工作人员中,核燃料循环组、工业应用组染色体畸变率明显高于医学应用组,40岁以上人员染色体畸变率高于40岁以下,工龄20年以上人员染色体畸变率高于20年以下。结果提示,放射工作人员较健康人群外周血淋巴细胞染色体畸变明显增加,应进一步提高核燃料循环和工业应用人员的职业防护意识,加强个人辐射防护。     

IIST small break LOCA experiments with passive core cooling injection

The purpose of this study is to evaluate the performance of a passive core cooling system (PCCS) with passive injection during the cold-leg small break loss-of-coolant accidents (SBLOCAs) experiments conducted at the Institute of Nuclear Energy Research (INER) Integral System Test (IIST) facility. Four tests were performed simulating break sizes of 0.2–2% (approximately corresponding to 1.25–4″ breaks for a referenced nuclear power plant) at cold-leg for assessing the PCCS capability in accident management. The key thermal–hydraulic phenomena to core heat removal for PCCS are observed and discussed. The experimental results show that the PCCS has successfully provided a continuous removal of core heat and a long term core cooling can be reached for all cases of SBLOCA.     

Experience in the Analysis of Accidents and Incidents Involving the Transport of Radioactive Materials

Abstract

Some half a million packages containing radioactive materials are transported to, from and within the UK annually. Accidents and incidents involving these shipments are rare. However, there is always the potential for such an event, which could lead to a release of the contents of a package or an increase in radiation level caused by damaged shielding. These events could result in radiological consequences for transport workers. As transport occurs in the public environment, such events could also lead to radiation exposures of members of the public. The UK Department for Transport (DfT), together with the Health and Safety Executive (HSE) have supported, for almost 20 years, work to compile, analyse and report on accidents and incidents that occur during the transport of radioactive materials. Annual reports on these events have been produced for 12 years. The details of these events are recorded in the Radioactive Materials Transport Event Database (RAMTED) maintained by the National Radiological Protection Board (NRPB) on behalf of the DfT and HSE. Information on accidents and incidents dates back to 1958. RAMTED cUlTently includes information concerning 708 accidents and incidents, covering the period 1958 to 2000. This paper presents a summary of the data covering this period, identifying trends and lessons learned together with a discussion of some examples. It was found that, historically, the most significant exposures were received as a result of accidents involving the transport of industrial radiography sources. However, the frequency and severity of these events has decreased considerably in the later years of this study due to improvements in training, awareness and equipment. The International Atomic Energy Agency (IAEA) and the Nuclear Energy Agency (NEA), have established the international nuclear event scale (INES), which is described in detail in a users' guide. The INES has been revised to fully include transport events, and the information in RAMTED has been reviewed with regard to the latest INES users' guide. Some preliminary classifications have been made for transport events.     

核事故医学救援辐射监测工作的几点思考

辐射监测对于核事故医学救援至关重要。做好核事故医学救援辐射监测工作应重点掌握辐射防护相关知识,熟练掌握辐射监测设备的正确使用方法,并对辐射监测结果进行正确分析。本文通过分析辐射监测工作的重要性,就如何做好核事故医学救援辐射监测工作提出些许建议。