STUDIES ON DEVELOPMENT OF AUTOMATIC FUEL MONITORING SYSTEM FOR A POOL-TYPE RESEARCH REACTOR

针对池型研究堆，研制了一种灵敏的燃料元件裂变产物可能释放量监测方法。它包括在反应堆冷却水中引入气泡，以有效地提取核心某处产生的溶解的裂变稀有气体^<89>Kr和^<138>Xe，并高效地计算它们各自的子核素^<89>Rb和^<138>Cs。测量方法有两种，一种是（方法一）在滤纸上通过吸吸反应器水箱的气泡气体和空气覆盖水，另一种是（方法二）在水面取样的气泡气体的洗涤水中进行测量。研究了影响两种方法子核素检测效率的各种因素。这些包括引入气体的流速，气体出口在水中的位置（深度和径向），冷却剂是否循环，以及（对于方法二）取样和用水冲洗气体之间取样气体的停留时间。在这些实验数据的基础上，我们采用方法二设计并构建了连续模式实验燃油自动监测系统，供日常使用。它是由在水面间歇取样冒泡气体到瓶中，将瓶传送到探测器附近，将瓶站立一定时间，摇晃瓶子，测量水中所含的核素组成的。作为常规燃油监测系统，该系统已实现了^<138>Cs的有效测量。

Studies on developing a sensitive monitoring method of possible release of fission products (FP) from a fuel element have been made for a pool-type research reactor. It consists of introducing gas bubbles into reactor coolant water to extract effectively the dissolved fission rare gases, ^<89>Kr and ^<138>Xe, produced somewhere in the core, and counting their respective daughter nuclides, ^<89>Rb and ^<138>Cs with high efficiency.The measurements were done by either method, (Method I) on a filter paper by sucking the bubbled gas and air covering water of the reactor tank, or (Method II) in the washing water of bubbled gas sampled into a bottle at the water surface. Various causes that influence the detection efficiency (DE) of the daughter nuclides in both methods were studied. These include the flow rate of introducing gas, position (depth and radial direction) of gas exit in the water, whether the coolant was circulated or not, and (for Method II) standing time of the sampled gas between the sampling and washing the gas with water. On the basis of these experimental data, we have designed and constructed an automatic fuel monitoring system of the continuous mode experiment, for routine use by adopting Method II.It is composed of an intermittent sampling of the bubbling gas into bottle at the water surface, conveying the bottle until near the detector, standing the bottle for a definite time, shaking the bottle, and measuring the nuclides contained in the water. The system have performed effectively measuring ^<138>Cs as a routine fuel monitoring system.