Monitoring Reactors for Nuclear Safeguards with T2K Technology

在过去的6-7年里，STFC领导了一个学术联盟，该联盟开发了一个大型中微子探测器，作为在日本进行的名为T2K的国际实验的一部分。利物浦集团相信，为这项国际工作开发的技术可以被改造成一种占地面积小、高度可靠的探测器，来表征运行中的核裂变反应堆核心发出的反中微子的特征。测量发电站反中微子辐射的数量和能量水平，并将其与反应堆功率输出相关联，是检测未宣布关闭以及高级核材料是否已从该过程中秘密移除的非常有效的方法，因此也是国际原子能机构检测不当行为的理想方法。为T2K实验建造的探测器是一个采样电磁量热计(ECAL)，环绕着近探测器的中微子目标探测器子系统。它是基于层层挤压的塑料闪烁体棒，中间夹着铅片。它为所有进出NEAR探测器的颗粒提供近乎密封的覆盖。这个高度分割的系统的功能是对中微子相互作用产生的粒子的轨迹和能量沉积进行成像。利用该系统实现了对低至~200keV带电粒子能量沉积的探测。在距离棒末端1米处，通过穿过棒的中心波长移动光纤来收集产生的光并将其传输到固态，被称为MPPC的光子探测装置实现了巨大的光产生率。MPPC在整个系统中提供了非常好的重复性，在长时间(几年)的运行中性能优于10%，并且非常可靠和坚固，整个探测器中几乎没有死通道(20,000个通道中有大约50个死通道)。对于该项目，设计和量热能力已经在T2K项目中得到验证，最近在日本发生的地震(2011年)证明了探测器的健壮性。该项目重复使用了许多来自T2K的备件电子元件。对于反应堆监测探测器，ECAL的设计已经重新配置，通过用Gd取代铅来进行反中微子探测。Gd被用来捕获反中微子相互作用中产生的中子。当一个中子被格拉核俘获时，它产生了大量的光子簇射(约8 MeV)，在探测器中留下了一个独特的信号。通过将这种独特的中子信号与较早的正电子信号相关联，我们可以有效地选择反中微子相互作用。该设备已经在利物浦大学的实验室中使用各种放射源进行了测试。为了在实际条件下测试该装置，并推进该项目，我们建议在一个商业核反应堆上部署该探测器。探测器的部署是在英国对国际原子能机构和能源和气候控制部的保障支持计划的帮助下谈判完成的。一旦取得成功，该小组将寻求开始与原子能机构进行实地测试。如果实地试验成功，将在世界各地的反应堆上部署反应堆监测探测器，作为原子能机构确保和平利用核材料的努力的一部分。

Over the last 6-7 years STFC has lead an academic consortium that has developed a large neutrino detector as part of an international experiment in Japan called T2K. The Liverpool group believe that the technology developed for this international work can be adapted to make a small footprint, highly reliable, detector to characterise the anti-neutrinos that are emitted from the core of operational nuclear fission reactors. Measuring the quantity and energy level of anti-neutrino emissions from a power station when correlated to the reactor power output is a very effective way of detecting undeclared shut-downs and whether or not high grade nuclear material has been covertly removed from the process, and so an ideal way for the IAEA to detect malpractice.The detector built for the T2K experiment is a sampling Electromagnetic Calorimeter (ECal) surrounding the neutrino target detector sub-systems of the near detector. It is based on layers of extruded plastic scintillator bars with Lead sheets sandwiched between them. It provides near-hermetic coverage for all particles exiting or coming into the near detector. This highly segmented system's function is to image tracks and energy deposition from particles produced in neutrino interactions. The detection of energy deposition from charged particles down to ~ 200 keV has been demonstrated with the system. Large light yield at 1 m away from the end of the bar has been achieved by threading the centres of the bars wavelength shifting fibres to collect the light produced and transport it to solid state, photon detecting devices called MPPCs. MPPCs give very good reproducibility of performance to better than 10% across the whole system and operation over long period of time (a few years) and are incredibly reliable and tough with few dead channels in the whole detector (~50 dead out of 20,000). For the project the design and calorimetric capabilities have already been proven in the T2K project, the recent earthquake in Japan (2011) is testament to the robustness of the detector. The project reuses many of the spares electronics components from T2K. For the reactor monitor detector, the ECal design has been reconfigured for anti-neutrino detection by replacing the lead with the gadolinium. The gadolinium is used to capture the neutrons produced in anti-neutrino interactions. When a neutron is captured by a gadolinium nucleus a large shower (~8 MeV) of photons it created leaving a unique signal in the detector. By correlating this unique neutron signal with an earlier positron signal we can efficiently select anti-neutrino interactions. The device has been testing in the laboratories at the University of Liverpool using various radio-active sources. In order to test the device in realistic conditions and advance the project, we propose to deploy the detector at a commercial nuclear reactor. Deployment of the detector has been negotiated with the aid of The UK Safeguards Support programme to the IAEA and the Department of Energy and Climate Control. Upon the successful outcome of the group will seek to start field tests with the IAEA. If the field tests are successful reactor monitoring detectors will be deployed at reactors around the world as part of the IAEA's efforts to ensure peaceful use of nuclear material.