Development of dynamic PRA methodology for external hazards in sodium-cooled fast reactor via applying Markov chain Monte Carlo method to severe accident analysis code; Assessment of accident management of assigning independent emergency diesel generators to each air cooler

Li, C.-Y.; 渡部 晃*; 内堀 昭寛; 岡野 靖

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 10 Pages, 2023/05

Quantitative assessment of the effect of accident management on the various external hazards is essential in the nuclear safety analysis. This study aims to establish the dynamic probabilistic risk assessment methodology for sodium-cooled fast reactors that can consider the transient plant status under continuous external hazards with corresponding countermeasures operating stochastically. Specifically, the Continuous Markov chain Monte Carlo (CMMC) and Deterministic and Stochastic Petri Nets (DSPN) methods are newly applied to the severe accident analysis code, SPECTRA, which can conduct dynamic plant evaluation in the different severe accident conditions of nuclear reactors, to develop an evaluation methodology for typical external hazards. In the DSPN-CMMC-SPECTRA coupled frame, the latest safety functions of the plant components/systems can be stochastically determined by the DSPN-CMMC grounded on the current plant states under continuous hazard and the interaction between the multi-state components/systems; then, SPECTRA can evaluate the following plant state determined by the latest safety function of the components/systems. Therefore, the advantage of this newly developed DSPN-CMMC-SPECTRA frame is having the capability to quantitatively and stochastically evaluate the transient accident progressions that potentially lead to the core damage under the continuous external hazard scenario. As for the preliminary exam on the DSPN-CMMC-SPECTRA frame, one of the typical external hazards of continuous volcanic ashfall is selected in this research. In addition, the numerical investigation of alternative accident management' effects has also been carried out and quantitatively confirmed in this research.

Development of dynamic PRA methodology for external hazards (Application of CMMC method to severe accident analysis code)

Li, C.-Y.; 渡部 晃*; 内堀 昭寛; 岡野 靖

第26回動力・エネルギー技術シンポジウム講演論文集(インターネット), 4 Pages, 2022/07

https://doi.org/10.1299/jsmepes.2022.26.A234

シビアアクシデントに至る可能性のある事故シナリオを同定し、その発生頻度を評価することは重要な課題である。本研究ではナトリウム冷却高速炉を対象とし、時間依存や事象の相互依存性を考慮できる動的PRA評価手法の確立を目指す。具体的には過酷事故解析コードSPECTRAに対して新たに連続マルコフ連鎖モンテカルロ(CMMC)を適用し、外部ハザードに対する解析手法を開発する。現在、崩壊熱除去系における空気冷却器のフォルトツリーモデルをCMMCとして実装し、火山降灰に対するプラント過渡特性の試行解析が終了した。

Main findings, remaining uncertainties and lessons learned from the OECD/NEA BSAF Project

Pellegrini, M.*; Herranz, L.*; Sonnenkalb, M.*; Lind, T.*; 丸山 結; Gauntt, R.*; Bixler, N.*; Morreale, A.*; Dolganov, K.*; Sevon, T.*; et al.

Nuclear Technology, 206(9), p.1449 - 1463, 2020/09

https://doi.org/10.1080/00295450.2020.1724731

The OECD/NEA Benchmark Study at the Accident of Fukushima Daiichi Nuclear Power Station (BSAF) project, which started in 2012 and continued until 2018, was one of the earliest responses to the accident at Fukushima Daiichi. The project, divided into two phases addressed the investigation of the accident at Unit 1, 2 and 3 by Severe Accident (SA) codes until 500 h focusing on thermal-hydraulics, core relocation, Molten Corium Concrete Interaction (MCCI) and fission products release and transport. The objectives of BSAF were to make up plausible scenarios based primarily on SA forensic analysis, support the decommissioning and inform SA codes modeling. The analysis and comparison among the institutes have brought up vital insights regarding the accident progression identifying periods of core meltdown and relocation, Reactor Pressure Vessel (RPV) and Primary Containment Vessel (PCV) leakage/failure through the comparison of pressure, water level and CAMS signatures. The combination of code results and inspections (muon radiography, PCV inspection) has provided a picture of the current status of the debris distribution and plant status. All units present a large relocation of core materials and all of them present ex-vessel debris with Unit 1 and Unit 3 showing evidences of undergoing MCCI. Uncertainties have been identified in particular on the time and magnitude of events such as corium relocation in RPV and into cavity floor, RPV and PCV rupture events. Main uncertainties resulting from the project are the large and continuous MCCI progression predicted by basically all the SA codes and the leak pathways from RPV to PCV and PCV to reactor building and environment. The BSAF project represents a pioneering exercise which has set the basis and provided lessons learned not only for code improvement but also for the development of new related projects to investigate in detail further aspects of the Fukushima Daiichi accident.

Bayesian optimization analysis of containment venting operation in a BWR severe accident

Zheng, X.; 石川 淳; 杉山 智之; 丸山 結

Proceedings of 13th Probabilistic Safety Assessment and Management Conference (PSAM-13) (USB Flash Drive), 10 Pages, 2016/10

Containment venting is one of essential measures to protect the integrity of the final barrier of a nuclear reactor, by which the uncontrollable release of fission products can be avoided. The authors seek to develop an optimization approach to the planning of containment-venting operations by using THALES2/KICHE. Factors that control the activation of the venting system, for example, containment pressure, amount of fission products within the containment and pH value in the suppression chamber water pool, will affect radiological consequences. The effectiveness of containment venting strategies needs to be confirmed through numerical simulations. The number of iterations, however, needs to be controlled for cumbersome computational burden of severe accident codes. Bayesian optimization is a computationally efficient global optimization approach to find desired solutions. With the use of Gaussian process regression, a surrogate model of the "black-box" code is constructed. According to the predictions through the surrogate model, the upcoming location of the most probable optimum can be revealed. The number of code queries is largely reduced for the optimum finding, compared with simpler methods such as pure random search. The research demonstrates the applicability of the Bayesian optimization approach to the design and establishment of containment-venting strategies under BWR severe accident conditions.

State-of-the-art report on nuclear aerosols

Allelein, H.-J.*; Auvinen, A.*; Ball, J.*; Gntay, S.*; Herranz, L. E.*; 日高 昭秀; Jones, A. V.*; Kissane, M.*; Powers, D.*; Weber, G.*

NEA/CSNI/R(2009)5, 388 Pages, 2009/12

https://www.oecd-nea.org/nsd/docs/2009/csni-r2009-5.pdf

The TMI accident in 1979 motivated an interest in LWR source terms and resulted in the production of a supplement to the first state of the art report (SOAR) which concentrated on LWR aerosol issues. The second SOAR dealt with primary system FP release and transport that covers vapor the condensation on aerosols and aerosol agglomeration. The present third SOAR was prepared focusing on aerosol behavior in both the primary circuit and in containment such as mechanical resuspension, impact of chemistry, re-vaporization of deposits, charge effect, removal by spray, hydrogen-burn effects on suspended aerosols, penetration of aerosols through leak paths and so on. A large number of probabilistic safety analysis (PSA level 2) plant studies have been performed around the world, frequently involving aspects of aerosol behavior. This report provides some examples, including sensitivity studies that demonstrate the impact of aerosol-related processes.

Proceedings of Fuel Safety Research Specialists' Meeting; March 4-5, 2002, Tokai

燃料安全研究室

JAERI-Conf 2002-009, 491 Pages, 2002/08

JAERI-Conf-2002-009.pdf:102.1MB

2002年3月4,5日に、東海研究所で燃料安全研究専門家会合が原研主催で開催された。この会合の目的は、軽水炉の燃料安全にかかわる諸課題について、国内外の関係機関から参加した専門家との間で情報交換及び意見交換を行うこと、及び、原研における最近の燃料安全研究の成果及び今後の研究計画について討論することである。会合では、燃料研究の全般的状況、通常運転時及び事故時ふるまいの研究、シビアアクシデント時のFP放出ふるまい、及び「高度化軽水炉燃料試験計画」についての報告と討論がされた。あわせてポスター展示も行われた。会合は今後の燃料研究の展開にとって、また研究協力を推進するうえで非常に有益であった。本報告集は、これらすべての研究報告を取りまとめたものである。

Proceedings of the Workshop on Severe Accident Research held in Japan (SARJ-98); November 4-6, 1998, Tokyo, Japan

杉本 純

JAERI-Conf 99-005, 523 Pages, 1999/07

JAERI-Conf-99-005.pdf:36.05MB

1998年11月4日から6日にかけて、ホテル・ラングウッドにおいて、シビアアクシデント研究ワークショップ(SARJ-98)が開催された。このワークショップには、13か国より181名の参加者があった。ワークショップでは、各国における研究の現状、OECDにおけるシビアアクシデントの検討状況、圧力容器内溶融炉心保持、水蒸気爆発、圧力容器外冷却性、FP挙動、構造健全性、燃料挙動、水素挙動、事故解析とモデル化など、シビアアクシデントに関する実験及び解析を含む幅広い領域を対象として、合計65件の発表があった。パネルディスカッションでは、「シビアアクシデントの事故シナリオ、アクシデントマネジメント戦略及び将来炉の設計に対する解析手法の現状; どれ程実際に近いのか?」をテーマに、パネリスト及び会場の専門家により活発な討論が行われ、さまざまな意見や見解が交換された。

International Standard Problem (ISP) No.41; Computer code comparison exercise based on a Radioiodine Test Facility (RTF) experiment on iodine behaviour in containment under severe accident conditions

Ball, J.*; Glowa, G.*; Wren, J.*; Rydl, A.*; Poletiko, C.*; Billarand, Y.*; Ewig, F.*; Funke, F.*; 日高 昭秀; Gauntt, R.*; et al.

NEA/CSNI/R(99)7, p.311 - 325, 1999/00

The ISP No.41 exercise resulted from a recommendation at the fourth iodine chemistry workshop held at PSI, Switzerland in 1996 for an International Standard Problem on iodine behavior models. The test selected for the comparison was a Radio Test Facility experiment. It was conducted in a stainless steel vessel at 25C and at a dose rate of 1.4 kGy/h to evaluate the effect of pH on irradiated aqueous solutions containing CsI. This paper discusses the results of ISP 41 exercise, with a primary focus on the evaluation and comparison of calculated results, and what they demonstrate about the aqueous iodine reaction subset within each model. The paper will also discuss the relative importance of mass transfer, surface adsorption and aqueous chemistry, and the sensitivity of each of the models to these phenomena. Finally, it will assess the applicability of the ISP 41 exercise to qualitative validation of the iodine models, and provide recommendations for continuing model evaluation.

Proceedings of the Third CSNI Workshop on Iodine Chemistry in Reactor Safety; September 11-13, 1991, Tokai-mura, Japan

石榑 顯吉*; 佐伯 正克; 早田 邦久; 杉本 純

JAERI-M 92-012, 522 Pages, 1992/03

JAERI-M-92-012.pdf:15.92MB

OECD/CSNI主催の第3回原子力安全におけるヨウ素化学ワークショップが日本原子力研究所で1991年9月11日から13日にかけて開催された。このワークショップには、10ヶ国2国際機関から専門家約60名の出席があった。ワークショップでは、ヨウ素種の放射線分解及び表面における反応、基礎及び総合実験、解析モデル及びコードの開発など、原子力安全におけるヨウ素化学に関する合計29の論文が5つのセッションにおいて種々の観点から発表された。ワークショップにおける情報交換と発表後の討論により、軽水炉の事故時のヨウ素挙動に関するより深い理解が得られるとともに、今後の研究の進展に対しても大きな期待が寄せられた。