Large Radioactive Release Research Articles

“Practical elimination” principle in the Akkuyu Nuclear Power Plant design

The paper considers the implementation of the “practical elimination” principle in the design of the Akkuyu NPP with VVER1200 reactors being under construction in Turkey. The “practical elimination” principle is defined as follows: for accident sequences or phenomena that contribute or lead to unacceptable radiological consequences for the public or the environment, it shall be shown with a high level of confidence that their occurrence is highly unlikely. “Practical elimination” is proved predominantly by results of a Level 2 probabilistic safety assessment. The implementation of the “practical elimination” principle was considered at the level of accident sequences leading to a large radioactive release. It has been shown that each accident sequence leading to an unacceptable release has the probability of occurrence below 4.45Е–8 per reactor per year, while their total probability not exceeding the value of 6.17Е–7 per reactor per year. For the phenomena inside the containment area during severe accidents, including hydrogen detonation, a large thermal explosion, direct containment heating, overpressure in the containment volume, and the containment damage at later stages due to the basement melting through, their “practical elimination” has been demonstrated. The paper also considers specific hard-to-assess scenarios of beyond design basis accidents, for which the applicability of the “practical elimination” principle is assessed as well: a major positive reactivity insertion, a rupture of the reactor pressure vessel and other largescale components, damage of fuel elements in the spent fuel pool, severe accidents with the containment bypass or containment failure, and severe accidents accompanied the means for mitigating with their consequences being unavailable. Criteria have been developed and used for the “practical elimination” assessment. A sensitivity analysis was undertaken as part of the Level 2 probabilistic safety assessment which has shown that estimated values slightly depend on the analytical assumptions, as well as on the random change in the parameters that the affect the progression of severe accidents.

Nuclear Power Plants Are Not So Safe: Fluid Transients / Water Hammers, Autoignition, Explosions, Accident Predictions and Ethics

Due to misdiagnosed hydrogen explosions and ethically flawed publications, nuclear power plants are not as safe as published to be for decades. Previous publications inaccurately, unethically, and inappropriately assessed reactor safety with respect to other industries and natural disasters, where nuclear industry publications non-conservatively applied data to promote nuclear reactor safety, and published models skewed accident data to present nuclear energy as safer than it is. Major findings of this one-man study were calculated with 95% confidence. 1) Explosions caused by fluid transients accompany nuclear power plant meltdowns. 2) A meltdown similar to Three Mile Island (TMI-2) has a 50% probability before 2039, with a one in two probability of a radioactive release like Fukushima. 3) A large radioactive release like Fukushima has a 50% probability before 2067. 4) Radioactive releases can be prevented by fluid transient control with the exception of Chernobyl type accidents, which are expected far into the future. 5) Nuclear power plant accidental deaths are not significantly less than other industries as claimed for many years, but are comparable to other industries. An improved explanation of nuclear power plant explosion safety is provided here to better control dangers in the radiation business. Items 1 and 2 were previously published, but are summarized here as proof of principle to support this new research, and items 3, 4, and 5 are new to the literature. These latter concerns are the thrust for this discussion of ethics, nuclear safety, and the prevention of loss of life, property damages, and catastrophic environmental damages. A personal history of the difficulties of being the first to invent new theory and the government obstruction and unethical cover up to thwart legitimate safety concerns are intertwined with statistical proofs for nuclear reactor disaster predictions. Such disasters explode radioactive dust clouds into the air to circle our planet, and spread radioactive contamination that radioactively rains down across parts of the earth following large accidental explosions. Although the ethical path to accomplish this task has great personal costs, such as difficulty, stress, complexity of thought, long hours, impacts on family life, and money, the rewards are that imminent nuclear power plant explosions and loss of life can be stopped!

Assessment of Adequate Margin to Liquefaction for Nuclear Power Plants

Design of nuclear power plant shall provide an adequate margin to protect items ultimately necessary to prevent an early large radioactive release in the case of earthquakes exceeding those considered in the design. An essential question is how large the margin should be to be accepted as adequate. In the practice, depending on the country regulation, a plant margin of at least 1.4 or 1.67 times the design basis peak ground acceleration is required to be demonstrated. The catastrophe at the Fukushima Daiichi Nuclear Power Plant revealed the fundamental experience that the plants designed in compliance with nuclear standards can survive the effects of the vibratory ground motion due to disastrous earthquake but may fail due to effects of phenomena accompanying or generated by the earthquakes. Liquefaction is one of those secondary effects of beyond-design basis earthquakes that should be investigated for NPPs at soil sites. However, the question has not been investigated up to now, whether a “margin earthquake”, vibratory effects of which the plant can withstand thanks to design margin, will not induce liquefaction at soil sites and will not result in loss of safety functions. In the paper, a procedure is proposed for calculation of the probability and margin to liquefaction. Use of the procedure is demonstrated on a case study with realistic site-plant parameters. Criteria for probability for screening and acceptable probabilistic margin to liquefaction are proposed. The possible building settlement due to margin earthquake is also assessed.

Considerations in relation to off-site emergency procedures and response for nuclear accidents

The operation of nuclear facilities has, fortunately, not led to many accidents with off-site consequences. However, it is well-recognised that should a large release of radioactivity occur, the effects in the surrounding area and population will be significant. These effects can be mitigated by developing emergency preparedness and response plans prior to the operation of the nuclear facility that can be exercised regularly and implemented if an accident occurs. This review paper details the various stages of a nuclear accident and the corresponding aspects of an emergency preparedness plan that are relevant to these stages, both from a UK and international perspective. The paper also details how certain aspects of emergency preparedness have been affected by the accident at Fukushima Dai-ichi and as a point of comparison how emergency management plans were implemented following the accidents at Three Mile Island 2 and Chernobyl. In addition, the UK’s economic costing model for nuclear accidents COCO-2, and the UK’s Level-3 Probabilistic Safety Assessment code “PACE” are introduced. Finally, the factors that affect the economic impact of a nuclear accident, especially from a UK standpoint, are described.

ICONE-23-2023 TECHNICAL INSIGHT OF THE HIGH LEVEL SAFETY GOAL FOR THE NPPS BUILT IN CHINA'S THIRTEENTH FIVE-YEAR (2016-2020)

The "Nuclear Safety Planning" has been published in Oct. 2012 in China, which stipulates the safety goals for the NPPs which will be built in the future. As for the nuclear power plants (NPPs) which will be built in China's Thirteenth Five-Year (2016-2020) and later, the high level safety goal is described as that "the possibility of the large radioactive release should be practically eliminated by design". A thorough investigation has been performed at SNERDI to explore the technical insight of this high level safety goal by using Multinational Design Evaluation Project (MDEP) hierarchical safety goal approach. The definition of large release is proposed accordingly, DID requirements and probabilistic requirements are derived from this high level safety goal.

Hydrogen management and overpressure protection of the containment for future boiling water reactors

New design and evaluation method for hydrogen management of containment atmosphere have been developed for application in the future boiling water reactor (BWR). These are intended as a part of consideration of severe accidents in the course of design so as to assure a high level of confidence that a large release of radioactivity to the environment that may result in unacceptable social consequences can reasonably be avoided. Emphasis on hydrogen management and protection against overpressure failure is based on the insights from probabilistic safety assessments (PSAs) that late phase overpressure (and associated leakage) and molten corium concrete reaction (MCCI) need attention to ensure that containment remains intact, in case energetic challenges to the containment such as DCH (direct containment heating) or FCI (fuel coolant interactions) are practically eliminated by design or resolved from risk standpoint of view. The authors studied the use of palladium-coated tantalum for hydrogen removal from containment atmosphere in order to avoid pressurization of the containment with small free volume by non-condensable gas and steam. Its effectiveness for ABWR (advanced boiling water reactor) containment was evaluated using laboratory test data. Although further experimental studies are necessary to confirm its effectiveness in real accident conditions, the design is a promising option and one that could be backfitted upon necessity to existing plants for which pressure retaining capability cannot be altered. Also new evaluation method for flammability control under severe accident conditions was developed. This method employes a realistic assessment of the amount of oxygen and hydrogen gases generated by radiolytic decomposition of water under severe accident conditions and their subsequent transport from water to containment atmosphere.

The impact of assessing lower head integrity on boiling water reactor probabilistic risk assessments

Abstract Over the last several decades, much effort has been directed at estimating the likelihood of a large early release of radioactivity during a nuclear accident. This effort has culminated in the Individual Plant Examinations (IPEs) for the over 100 US nuclear power plants and the NUREG 1150 study. The large early release of radioactivity requires core damage with loss of primary containment integrity during the accident. Given a successful reactor scram, early containment failure coupled with a large release of radioactivity will only occur if the reactor core vessel is breached by core debris. Most IPE/PRA studies performed to date have not considered the possibility of quenching core debris in the lower plenum. Consequently, lower head failure is presumed to closely follow the onset of core damage. Therefore, these assessments did not address the role that in-vessel debris retention plays in preserving primary containment integrity, nor do they propose a criterion for evaluating the integrity of the vessel lower head given that core damage has occurred. Yet preserving the vessel lower head integrity is a necessary condition for satisfying the plant design and licensing basis. Therefore, a more complete treatment of the risk associated with nuclear plant operation includes an evaluation of the ability to retain the core debris in-vessel. This paper presents a performance requirement for vessel integrity to be used in probabilistic risk assessments; evaluates the impact the core damage progression and lower plenum quenching models have on the likelihood of terminating the damage progression in-vessel; documents the significant reduction in BWR containment failure probability that can occur when appropriate core damage and lower head quenching models are used; reviews the implications of core debris quenching in the lower head on BWR PRA modeling; argues why crediting the capability to maintain vessel integrity is necessary from a safety point of view. These results and conclusions are derived from consideration of a BWR 4 plant with a 251 inch vessel. However, the concepts are generally applicable and results specific to other BWR designs can be developed using the methodology presented in this paper.

Simulation of the atmospheric transport and deposition on a local/meso- and regional scale after hypothetical accidents at the Kola nuclear power plant

An accident at the Kola nuclear power plant could cause a large release of radioactivity into the atmosphere. To illustrate possible effects on the environment, potential atmospheric transport and deposition are calculated for two different scales—the local/meso- and the regional, using two different models. A 3-dimensional meso-scale model, developed at the Kola Science Centre, and suitable for distances out to a few hundred kilometres, has been used for the local/meso-scale, and a model system based on the MATHEW/ADPIC code, for the regional scale. Some consequences for the population have been estimated by using the MACCS model. Calculated aerial radionuclide activity concentrations, ground contamination and consequences for the population of the Euro-Arctic Barents region are discussed for two scenarios. The results for the local scale show a considerable influence on the radionuclide ground contamination pattern from the presence of precipitation. The significance of wet deposition is confirmed by the results for the regional scale which also emphasise the importance of having access to high quality weather predictions in emergency response organisations. The importance of the specific Arctic nutrition pathways, not included in this study, is discussed. It is important to make further studies in order to investigate the significance of these pathways.

The impact of Chernobyl on national nuclear policies: Sweden after Chernobyl: no change of energy policy?

Outside of the Soviet Union, the effects of the large radioactive release from the Chernobyl accident have been most obvious along a strip of land running across Sweden from the coast of the Bothni ...

Safety and environmental issues of fusion reactors

This paper reviews the safety and environmental issues associated with magnetic fusion reactors and discusses approaches to reduce or eliminate related concerns. The radioactive material in a fusion reactor includes tritium, burned as a fuel, and activation products produced by neutrons from the fusion reactions. Ensuring that these materials will not affect the public requires a strategy to minimize inventories, develop adequate containment and control, and eliminate potential release mechanisms. The accident with the greatest potential for a large radioactive release is a lithium fire. Less active forms of lithium, under consideration for use in fusion reactors, would eliminate this concern. Potential energy releases from large magnet systems, and the health effects of long-term exposure to magnetic fields are also concerns. Fusion power has attractive safety and environmental features and addressing safety issues early in the development program should result in an abundant source of power with risks that are understood and acceptable to the public.