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Technology development to evaluate dose rate distribution in PCV and to search for fuel debris submerged in water

开发技术来评估 PCV 中的剂量率分布并寻找淹没在水中的燃料碎片

基本信息

批准号：
EP/N017749/1
负责人：
Malcolm Joyce
金额：
$ 51.67万
依托单位：
Lancaster University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FN017749%2F1
关键词：
Technology development evaluate dose rate

项目摘要

The Great East Japan earthquake off the pacific coast of Tohoku was the most powerful recorded earthquake ever to hit Japan and triggered powerful tsunami waves. These inundated the coast including the area of the Fukushima Daiichi nuclear power plant. The flooding that followed disabled the auxiliary cooling systems at the power plant which, although being shut down, caused the reactors to overheat as a result of the effect of decay heat. This resulted in core damage to 3 of the 6 reactors on the Fukushima site. The damage is strongly suspected to have resulted in fragmentation of the nuclear fuel inside the reactors themselves and thus they are inoperable and need to be decommissioned. A key task is the removal of the nuclear fuel from the reactors. Once this is removed and stored safely elsewhere, radiation levels will fall significantly rendering the plant much safer than at present which will enable the remaining decommissioning requirements of the plant to continue more quickly, easily and with reduced cost.However, the fuel debris cannot be removed until we know how much there is and the form it has adopted after the accident i.e. is it a molten lump confined to the reactor or a mixture of damaged fuel elements with some egress beyond the primary containment? The reason we need to know this information is that it is essential that the likelihood of re-criticality is assessed (the chance that the nuclear fission reaction could start up inadvertently when the debris is disturbed) and also that we know of the extent of radioactivity and the form it is in in order to plan disposal routes. This information is very difficult to obtain because the type of reactor affected at Fukushima operated in what is known as a primary containment vessel or PCV. This is a large, thick-sided steel tank that is bolted shut very securely. A PCV has only a few, narrow access routes by which it is possible to get inside. There is no light inside and in order to set the reactor into a safe state and maintain its cooling, each reactor at Fukushima has been flooded with sea water. As a result of the radioactivity from the fuel there are very high levels of radiation exposure which prevent human beings from getting near to the PCV, whilst access to the PCV would result in serious injury to people and could damage untested instrumentation. The water filling the PCVs further complicates matters but, for the timebeing, cannot be removed as it acts to cool the fuel debris and to shield the surrounding area from radiation emitted by the reactor.In this project we combine two world-leading research activities in the United Kingdom associated with the portable detection of radioactivity (Lancaster University) and the development of small, submersible remote-operated vehicles (Manchester) in collaboration with the Japan Atomic Energy Agency, the National Maritime Research Institute of Japan, BeamSeiko Instrument Co. Ltd (Tokyo) and the Nagaoka University of Technology. The key objective of the research is to determine whether we can combine these capabilities to produce a remote-operated submersible vehicle with a radiation detection payload to detect neutrons and gamma rays. This device will be either mobile in the PCV, and thus able to inform us of the distribution of fuel debris in the reactor, or tethered in place in order to provide a continual indication of the core state; neither capability currently exists and clean-up of the reactors cannot continue without an assessment of this type. The distinction of the neutron and gamma-ray detection recommended for the payload on the submersible in this project is that the combination of the information provided by these two radiation types can tell us about the resident radioactivity, the risk of re-criticality and also provide a means for comparison with severe accident calculations to determine what happened to the reactor fuel in the accident.

东北太平洋沿岸的东日本大地震是有记录以来袭击日本的最强烈的地震，并引发了强大的海啸波。这些洪水淹没了包括福岛第一核电站地区在内的海岸。随后发生的洪水使核电站的辅助冷却系统瘫痪，虽然该系统已被关闭，但由于衰变热的影响，反应堆过热。这导致福岛核电站6座反应堆中的3座受损。强烈怀疑损坏导致反应堆内部的核燃料碎裂，因此它们无法运行，需要退役。一项关键任务是从反应堆中取出核燃料。一旦这些物质被移除并安全地储存在其他地方，辐射水平将显著下降，使工厂比目前安全得多，这将使工厂的剩余退役要求能够更快、更容易地继续下去，并降低成本。在我们知道有多少燃料碎片以及事故发生后它的形态之前，燃料碎片是不能被清除的，即它是否是一个局限在反应堆内的熔融块还是受损燃料元件的混合物有一些出口超出了主安全壳？我们需要了解这一信息的原因是，必须评估再临界的可能性（碎片受到扰动时核裂变反应可能无意中启动的可能性），而且我们必须了解放射性的程度及其形式，以便规划处置路线。这一信息很难获得，因为福岛受影响的反应堆类型是在一级安全壳或PCV中运行的。这是一个大的，厚边钢罐是螺栓关闭非常安全。PCV只有几条狭窄的通道可以进入。内部没有灯光，为了使反应堆进入安全状态并保持冷却，福岛的每个反应堆都被海水淹没。由于燃料的放射性，存在非常高的辐射暴露水平，这阻止了人类接近PCV，而接触PCV将导致对人的严重伤害，并可能损坏未经测试的仪器。充入PCV的水使问题进一步复杂化，但暂时无法清除，因为它起到冷却燃料碎片和保护周围区域免受反应堆辐射的作用。在这个项目中，我们结合了英国与便携式放射性检测有关的两项世界领先的研究活动，即联合收割机（兰开斯特大学）和小型潜水遥控潜水器的开发（曼彻斯特）与日本原子能机构、日本国家海洋研究所、BeamSeiko仪器有限公司（东京）和长冈工业大学。这项研究的主要目标是确定我们是否能够将这些能力联合收割机结合起来，生产一种遥控潜水器，带有探测中子和伽马射线的辐射探测有效载荷。该装置可以在PCV中移动的，从而能够告知我们反应堆中燃料碎片的分布情况，或者固定在适当的位置，以便提供堆芯状态的持续指示;这两种能力目前都不存在，如果没有这种评估，反应堆的清理工作将无法继续。在该项目中，建议对潜水器有效载荷进行中子和伽马射线探测的区别在于，这两种辐射类型提供的信息相结合，可以告诉我们关于常驻放射性、再临界风险的信息，还可以提供一种与严重事故计算进行比较的手段，以确定事故中反应堆燃料的情况。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

A method for the prediction of the dose rate distribution in a primary containment vessel of the Fukushima Daiichi Nuclear Power Station

福岛第一核电站主安全壳内剂量率分布预测方法

DOI：
10.15669/pnst.6.108
发表时间：
2019
期刊：
Progress in Nuclear Science and Technology
影响因子：
0
作者：
K. Okumura;E. Riyana;Sato Wakaei;H. Maeda;J. Katakura;S. Kamada;M. Joyce;B. Lennox
通讯作者：
B. Lennox

The angular dependence of pulse shape discrimination and detection sensitivity in cylindrical and cubic EJ-309 organic liquid scintillators

圆柱形和立方体 EJ-309 有机液体闪烁体中脉冲形状辨别和检测灵敏度的角度依赖性