Severe accident risk reduction by containment leakage testing during operation

1990 ◽  
Vol 120 (1) ◽  
pp. 87-91 ◽  
Author(s):  
B. De Boeck
Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 295
Author(s):  
Matteo Spada ◽  
Peter Burgherr

The accident risk of severe (≥5 fatalities) accidents in fossil energy chains (Coal, Oil and Natural Gas) is analyzed. The full chain risk is assessed for Organization for Economic Co-operation and Development (OECD), 28 Member States of the European Union (EU28) and non-OECD countries. Furthermore, for Coal, Chinese data are analysed separately for three different periods, i.e., 1994–1999, 2000–2008 and 2009–2016, due to different data sources, and highly incomplete data prior to 1994. A Bayesian Model Averaging (BMA) is applied to investigate the risk and associated uncertainties of a comprehensive accident data set from the Paul Scherrer Institute’s ENergy-related Severe Accident Database (ENSAD). By means of BMA, frequency and severity distributions were established, and a final posterior distribution including model uncertainty is constructed by a weighted combination of the different models. The proposed approach, by dealing with lack of data and lack of knowledge, allows for a general reduction of the uncertainty in the calculated risk indicators, which is beneficial for informed decision-making strategies under uncertainty.


2004 ◽  
Vol 57 (1) ◽  
pp. 15-24 ◽  
Author(s):  
Wlodzimierz Filipowicz

Separation schemes together with Vessel Traffic Services improve existing standards. Since their role has proved to be rather passive it is assumed that the introduction of active measures could be beneficial and improvement in terms of collision or accident risk reduction is expected. The concept raises a wide variety of problems that are to be discussed, defined and solved.


2008 ◽  
Vol 238 (4) ◽  
pp. 1100-1105 ◽  
Author(s):  
Young Choi ◽  
Soo Yong Park ◽  
Kwang-Il Ahn ◽  
D.H. Kim

Author(s):  
Sergey E. Yakush ◽  
Nazar T. Lubchenko ◽  
Pavel Kudinov

Coolability of an ex-vessel debris bed in severe accident conditions is considered from the risk perspective. The concept of “load versus capacity” is employed to quantify the probability of failure (local dryout). Possible choices of “load” and “capacity” in terms of heat fluxes, thermal power or melt mass are discussed. Results of Monte Carlo simulations of distribution functions for the local heat flux and the dryout heat flux at the debris bed top point (defined as the extensions of one-dimensional counterparts) are presented. A surrogate model for the dryout heat flux is developed by the generalization of two-dimensional simulation results. Dryout probabilities are obtained under the conservative assumptions (neglecting the coolability improvement due to side ingress of water into a non-flat debris bed), and from the surrogate model. Outlook is given for the prospective development of the risk-informed approach to debris bed coolability in the context of comprehensive severe accident risk analysis.


Author(s):  
Sunil Nijhawan

The official report of The Fukushima Nuclear Accident Independent Investigation Commission concluded that “The TEPCO Fukushima Nuclear Power Plant accident was the result of collusion between the government, the regulators and TEPCO, and the lack of governance by said parties. They effectively betrayed the nation’s right to be safe from nuclear accidents. Therefore, we conclude that the accident was clearly ‘manmade.’ We believe that the root causes were the organizational and regulatory systems that supported faulty rationales for decisions and actions, rather than issues relating to the competency of any specific individual.” This wakeup call for the nuclear power utilities should require a public review of their relationship with of regulators. However, severe accident related risk reduction is a relatively uncharted territory and given the apparent lack of in-house technical expertise, the regulators are heavily relying on the qualitative and ‘hand waving’ arguments being presented by the utilities inherently disinterested in further investments they are not required to make under original license conditions. As a result, it has accelerated further deterioration of the safety culture and emboldened many within the regulatory staff to undertake or support otherwise questionable decisions in support of the utilities that prefer status quo. Case in point is the Canadian Nuclear Safety Commission (CNSC) which mostly accepts any and all requests by the nuclear power industry. After Fukushima, the CNSC took a year to publish a set of ‘Action Items’ for the Canadian Nuclear industry to prepare plans over 3 years and then accepted most if not all submissions that in many cases barely addressed the already watered down recommendations. In some cases the solutions proposed by the industry were economically expedient but technically flawed; and some could even be considered dangerous. CNSC also published a study on consequences of a severe accident with a source term that was limited to the desirable safety goal (100 TBq of Cs-137), which coincidently years later matched the utility ‘calculations’, but orders of magnitude smaller than predicted by independent evaluations. As a result, some well publicized conclusions on the benign nature of consequences of a CANDU severe accident were made and the local and provincial agencies that actually are supposed to prepare off-site emergency measures were left with an incorrect picture of what havoc a severe accident can cause otherwise. CNSC then published a much publicized video highlighting the available operator actions to terminate the accident early and later a report outlining the accident progression for a severe accident without operator action with conclusions that were immediately technically suspect from a variety of aspects. The aim was to claim that a severe core damage accident has no unfavorable off-site consequences. The regulator effectively, in this case, comes across as a promoter for the industry it is legislated to regulate. The paper outlines examples of actions being taken by the regulators that hinder development of effective risk reduction measures by the industry which otherwise would be forced to undertake them if the regulators had not stepped on the plate to bat for them. They vary from letters to editors to silence any safety concerns raised by the public, muzzling of its own staff, trying to silence external specialists who question their wisdom on to blatant disregard for any intervention by public they are required to entertain by law but are accustomed to factually ignore or belittle. The paper also outlines a number of examples of actions that an independent regulator would undertake to reduce the risk and enhance the safety culture. The nuclear regulatory regimes work well generally but in cases where it does not, the results can be disastrous as evident from the events in Japan and as is building up in Canada. The paper also summarizes the disparities between the number of Regulatory Actions instituted by the CNSC against small companies that use nuclear substances for industrial applications and almost none actions against the nuclear power plant utilities it regularly grants a pass in spite of the larger risk their operations pose to public.


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