铅基研究实验堆假想堆芯解体事故分析研究

发布时间：2018-04-24 19:12

本文选题：铅基堆 + 假想堆芯解体事故　；参考：《中国科学技术大学》2017年博士论文

【摘要】：铅基反应堆(以下简称铅基堆)是第四代核能系统与加速器驱动次临界系统的重要候选堆型。与其他快中子反应堆一样,由于铅基堆在正常运行时堆芯布置不是使Keff为最大的,堆芯熔化后材料的重新布置,有可能导致反应性急剧增加,期间释放出的巨大能量可能会造成堆芯解体。为确保铅基堆在严重事故下能够包容放射性物质从而使人和环境免受辐射危害,对其进行假想堆芯解体事故(Hypothetical Core Disruptive/Disassembly Accident,HCDA)的研究是非常必要的。然而,目前国际上对铅基堆HCDA的研究还处于起步阶段,对HCDA分析在铅基堆安全评价中占据的地位以及所要达到的安全目标等尚不明确,对铅基堆HCDA相关物理现象及事故演化过程的认识也十分匮乏。本文以中国铅基研究实验堆为研究对象,针对上述铅基堆HCDA事故研究存在的问题,从宏观的评价方法到微观的事故现象机理,多尺度开展了安全研究与探索。具体工作如下:(1)基于福岛事故后最新的核安全理念,并借鉴钠冷快堆的先进经验,建立了一个适用于铅基堆HCDA的评价方法,提出了把HCDA作为铅基堆的"设计扩展工况"来处理,同时明确了其消除重返临界的确定论与概率论要求,首次阐明了铅基堆HCDA研究在安全评价中所处的地位以及所需达到的安全目标,并进一步指出铅基堆HCDA事故分析需采用现象学、机械论、概率论等相结合的分析方法,为后续章节的分析提供了方法论基础。(2)基于"现象学"的事故分析方法,借助NTC-2D程序对铅基研究实验堆HCDA过程中的主要物理现象展开了数值模拟研究。发现了铅基堆HCDA事故下独特的热工水力现象:堆芯熔融物能迁移出堆芯,从而有潜力消除重返临界;但在迁移过程中熔融包壳会再凝固导致堆芯流道堵塞、最终形成的熔池会发生组份分层导致熔融燃料的聚集,这两种行为可能使事故朝恶化方向发展,需要特别关注。基于此,本文还给出了未来一种开展铅基堆HCDA实验研究的思路。(3)基于"机械论"的事故分析方法,利用NTC-2D程序建立了铅基研究实验堆(包括临界堆与次临界堆)的事故分析模型,并全面探究了两种堆型在两类典型事故(无保护瞬态超功率与燃料组件瞬时全堵)始发的HCDA下全堆芯瞬态过程以及影响因素。研究发现,次临界堆比临界堆固有安全性更好,不会发生无保护超功率导致的HCDA。在发生燃料组件瞬时堵流事故时,燃料孔隙率对两者的HCDA事故进程均影响显著。两种堆型皆可通过对设计参数(包括燃料孔隙率、冷却剂的驱动形式等)的选取实现堆芯熔融物的漂浮并且冷却,而不需要额外的工程措施。本文的研究成果不仅为铅基研究实验堆实现消除重返临界的安全目标提供了重要依据;同时还完善了铅基堆严重事故现象学知识,对未来大型商用铅基堆的安全设计具有重要的借鉴意义。
[Abstract]:Lead based reactor (PBR) is an important candidate for the fourth generation nuclear energy system and accelerator driven subcritical system. As with other fast neutron reactors, the rearrangement of the core material after the melting of the core may lead to a sharp increase in reactivity because the core arrangement of the lead based reactor is not the largest in the normal operation of the reactor, and the rearrangement of the material after the core melting may lead to a sharp increase in reactivity. The huge energy released during the process may cause the core to break up. In order to ensure that lead based reactor can contain radioactive material and protect people and environment from radiation, it is necessary to study the hypothetical core break-up accident (Hypothetical Core Disruptive/Disassembly accident). However, the international research on lead based reactor (HCDA) is still in its infancy, and the position of HCDA analysis in the safety evaluation of lead based reactor and the safety goal to be achieved are not clear. There is also a lack of understanding of HCDA related physical phenomena and accident evolution in lead based reactors. In this paper, the lead based experimental reactor in China is taken as the research object. In view of the problems existing in the study of the HCDA accident of the lead-based reactor mentioned above, the safety research and exploration are carried out on many scales, from the macroscopic evaluation method to the microscopic accident phenomenon mechanism. The specific work is as follows: (1) based on the latest nuclear safety concept after the Fukushima accident, and drawing on the advanced experience of the sodium cold fast reactor, an evaluation method suitable for the lead based reactor (HCDA) is established, and it is proposed that the HCDA be treated as the "design extended condition" of the lead based reactor. At the same time, the requirements of deterministic theory and probability theory for eliminating the re-entry criticality are clarified, and the position of HCDA research in the safety evaluation and the safety objectives to be achieved are expounded for the first time. It is further pointed out that the HCDA accident analysis of lead based reactor should adopt the methods of phenomenology, mechanics, probability theory and so on, which provides a methodological basis for the analysis of the following chapters. 2) the accident analysis method based on "phenomenology". The main physical phenomena in the HCDA process of lead based experimental reactor were simulated by NTC-2D program. The unique thermohydraulic phenomenon of lead based reactor under HCDA accident is found: the core melt can migrate out of the core, thus it has the potential to eliminate the re-entry criticality, but the melting cladding will solidify during the migration and lead to the blockage of the core runner. The resulting molten pool will be stratified and lead to the accumulation of molten fuel. These two behaviors may lead to the deterioration of the accident and need special attention. Based on this, this paper also gives a method of accident analysis based on "mechanical theory", which is the train of thought of carrying out the HCDA experimental research of lead based reactor in the future. The accident analysis model of lead-based experimental reactor (including critical reactor and subcritical reactor) was established by using NTC-2D program. The transient process and influencing factors of two types of reactor under HCDA with two typical accidents (unprotected transient superpower and fuel assembly instantaneous complete plugging) are discussed. It is found that the subcritical reactor is more secure than the critical reactor, and no unprotected superpower HCDAs occur. The fuel porosity has a significant effect on the HCDA accident process of the fuel assembly when the transient flow blocking accident occurs. Both types of reactor can float and cool the core melt by selecting the design parameters (including fuel porosity, coolant driving form, etc.), without the need of additional engineering measures. The research results in this paper not only provide an important basis for the realization of the safety goal of eliminating the re-entry criticality, but also improve the phenomenological knowledge of the serious accidents in the lead-based reactor. It has important reference significance for the safety design of large commercial lead based reactor in the future.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TL364.4

【相似文献】