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Insights on Fukushima Damage Progression based on PCV Inspections and Implications for Decommissioning Data Collection and Code Model Refinement [Slides]

Andrews, Nathan A.; Gauntt, Randall O.

Outline points are: Review what is known from experiments and how codes are modeling phenomena; Materials interactions are very important and key interactions will be identified and discussed; Chronology of damage progression roughly follows in order of increasing melting/liquefaction temperatures; Examine a plausible sequence to explain robotic visual examinations; Highlight MELCOR modeling observations; Highlight potential decommissioning phase data collection needs; and, Knowledge advance is iterative process of reconciling observations with code predictions, improving code models, and comparing to emerging new observations.

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TYPE Other Report YEAR 2018
DOIOSTI

Insights Gained from Forensic Analysis with MELCOR of the Fukushima-Daiichi Accidents

Andrews, Nathan A.; Gauntt, Randall O.

Since the accidents at Fukushima-Daiichi, Sandia National Laboratories has been modeling these accident scenarios using the severe accident analysis code, MELCOR. MELCOR is a widely used computer code developed at Sandia National Laboratories since ~1982 for the U.S. Nuclear Regulatory Commission. Insights from the modeling of these accidents is being used to better inform future code development and potentially improved accident management. To date, our necessity to better capture in-vessel thermal-hydraulic and ex-vessel melt coolability and concrete interactions has led to the implementation of new models. The most recent analyses, presented in this paper, have been in support of the of the Organization for Economic Cooperation and Development Nuclear Energy Agency’s (OECD/NEA) Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF) Project. The goal of this project is to accurately capture the source term from all three releases and then model the atmospheric dispersion. In order to do this, a forensic approach is being used in which available plant data and release timings is being used to inform the modeled MELCOR accident scenario. For example, containment failures, core slumping events and lower head failure timings are all enforced parameters in these analyses. This approach is fundamentally different from a blind code assessment analysis often used in standard problem exercises. The timings of these events are informed by representative spikes or decreases in plant data. The combination of improvements to the MELCOR source code resulting from analysis previous accident analysis and this forensic approach has allowed Sandia to generate representative and plausible source terms for all three accidents at Fukushima Daiichi out to three weeks after the accident to capture both early and late releases. In particular, using the source terms developed by MELCOR, the MACCS software code, which models atmospheric dispersion and deposition, we are able to reasonably capture the deposition of radionuclides to the northwest of the reactor site.

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TYPE Other Report YEAR 2017
DOIDOIOSTIOSTI

Treatment of Reactor Systems within Draft Regulatory Guide 1.183 DG-1199

Andrews, Nathan A.; Gauntt, Randall O.

In this note, a review of concerns relevant to Draft Regulatory Guide 1.183 rev.1 (DG-1199) is presented. These comments pertain to the treatment of the main steam line isolation valve (MSIV), emergency core cooling system (ECCS) and engineered safety features (ESF) during postulated accident scenarios contained within the regulatory guide. These comments are particularly salient to the mitigation and decontamination of the full core source created during a loss of coolant accident (LOCA) for boiling water reactors (BWRs).

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TYPE Other Report YEAR 2017
DOIOSTI
Results 1–25 of 121
Results 1–25 of 121