On the Neutron Kinetics during a Promptcritical Accident in a Heavy Liquid Metal Fast Reactor and the Importance of Low-Energy Neutrons

IF 1.9 3区工程技术 Q1 NUCLEAR SCIENCE & TECHNOLOGY

Annals of Nuclear Energy Pub Date : 2024-10-29 DOI:10.1016/j.anucene.2024.110975

Đ. Petrović , A. Rineiski , M. Zanetti , G. Scheveneels , X.-N. Chen , William D’haeseleer

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Abstract

Accidental scenarios that involve degradation of a fast reactor core and/or relocation of its fuel material call for particular attention with respect to promptcritical reactivity events. The dynamics of a power transient during such an event is governed by the Prompt Neutron Generation Time (PNGT), a parameter that is sensitive to the moderating power of the system. Since Heavy Liquid Metals (HLMs) have a boiling point that is higher than the melting point of stainless steel, the first degradation mechanism to occur in a Heavy Liquid Metal Fast Reactor (HLMFR) is likely to be the loss of structural material. This sequence holds the potential to create conditions for considerable spectrum softening and may thus have important implications for the value of the PNGT. In the framework of this study, a (postulated) complete absence of structural material in and around the reactor core of an HLMFR is demonstrated to lead to an increase in the PNGT by an order of magnitude.

The sensitivity of the fission energy release during a promptcritical event to the value of the PNGT is further investigated by employing the severe accident code SIMMER-III. To correctly model a degraded reactor core characterized by a considerably softer neutron spectrum when compared to the spectrum of its intact configuration, a new neutron data set is generated. This is done by introducing new energy groups to the already existing 11-energy-group structure and collapsing multigroup cross-section data by employing a weighting spectrum representative of a degraded core configuration of an HLMFR. Subsequent simulations demonstrate that an increase in the PNGT by a factor of ∼4 yields an increase in the fission energy release during a Core Disruptive Accident (CDA) by ∼50 %. It is therefore established that low-energy neutrons may play an important role during a promptcritical reactivity transient in an HLMFR.

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重液态金属快堆发生急临界事故时的中子动力学及低能中子的重要性

涉及快堆堆芯退化和/或燃料材料迁移的意外情况需要特别关注急临界反应性事件。在此类事件中，功率瞬态的动态受临界中子生成时间（PNGT）的控制，该参数对系统的缓和功率非常敏感。由于重液态金属 (HLM) 的沸点高于不锈钢的熔点，因此重液态金属快堆 (HLMFR) 的第一个降解机制很可能是结构材料的损失。这一系列降解过程有可能为相当大的频谱软化创造条件，从而对 PNGT 的价值产生重要影响。在本研究的框架内，通过使用严重事故代码 SIMMER-III，进一步研究了瞬时临界事件中裂变能量释放对 PNGT 值的敏感性。为了正确模拟降级反应堆堆芯，与完整构型的中子谱相比，降级堆芯的中子谱要柔和得多，因此需要生成新的中子数据集。具体做法是在已有的 11 能组结构中引入新的能组，并通过采用代表 HLMFR 退化堆芯构型的加权谱来折叠多能组截面数据。随后的模拟证明，将 PNGT 增加 4 倍，可使堆芯破坏事故（CDA）期间的裂变能量释放增加 50%。因此可以确定，低能中子可能会在高低温超临界堆内的瞬时反应性瞬态过程中发挥重要作用。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Annals of Nuclear Energy 工程技术-核科学技术

CiteScore

4.30

自引率

21.10%

发文量

632

审稿时长

7.3 months

期刊介绍： Annals of Nuclear Energy provides an international medium for the communication of original research, ideas and developments in all areas of the field of nuclear energy science and technology. Its scope embraces nuclear fuel reserves, fuel cycles and cost, materials, processing, system and component technology (fission only), design and optimization, direct conversion of nuclear energy sources, environmental control, reactor physics, heat transfer and fluid dynamics, structural analysis, fuel management, future developments, nuclear fuel and safety, nuclear aerosol, neutron physics, computer technology (both software and hardware), risk assessment, radioactive waste disposal and reactor thermal hydraulics. Papers submitted to Annals need to demonstrate a clear link to nuclear power generation/nuclear engineering. Papers which deal with pure nuclear physics, pure health physics, imaging, or attenuation and shielding properties of concretes and various geological materials are not within the scope of the journal. Also, papers that deal with policy or economics are not within the scope of the journal.