Analysis of Subcriticality Monitoring Results for First Loading of a PWR
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摘要: 某压水堆使用已活化的二次中子源（ASNS）完成首次装料。在首次装料期间，堆内临时中子探测器（TND）发生响应试验结果远高于仿真结果问题和计数率大幅度下降问题。为了查明上述问题的原因，监督工作组对二次中子源特性和由ASNS建立的辐射场进行了分析，对核燃料次临界增殖中子对TND计数率的影响进行了分析和验证，对使用ASNS进行反应堆首次装料的次临界监督数据进行了分析。结果表明：TND周围的辐射场为γ射线和中子形成的混合辐射场；在中子源组件与TND之间安装核燃料组件后，核燃料次临界增殖中子对TND计数率的影响是使其升高；ASNS衰变产生了大量γ射线，TND输出的γ脉冲在主放大器内发生峰堆积导致脉冲幅度畸变，TND响应试验结果远高于仿真结果的原因是脉冲幅度甄别器无法有效甄别畸变后的γ脉冲和中子脉冲；TND计数率大幅度下降的原因为核燃料中的铀屏蔽掉了由ASNS射向TND的大部分γ射线。源量程通道和TND的运行状态满足首次装料程序对次临界监督设备的要求。Abstract: An activated secondary neutron source (ASNS) is used to complete the first loading of a PWR. During the first loading, the response test results of the temporary neutron detector (TND) in the reactor are much higher than the simulation results and the counting rate drops significantly. In order to find out the causes of the above problems, the supervision working group analyzed the characteristics of secondary neutron sources and the radiation field established by ASNS, analyzed and verified the influence of subcritical multiplication neutrons of nuclear fuel on TND counting rate, and analyzed the subcritical monitoring data of reactor first loading using ASNS. The results show that the radiation field around TND is a mixed radiation field formed by γ-rays and neutrons. After installing the nuclear fuel assembly between the neutron source assembly and TND, the influence of subcritical breeder neutrons of nuclear fuel on TND counting rate is to increase it; The ASNS decay produced a large amount of γ rays, the peak accumulation of γ pulses from TND in the main amplifier leaded to pulse amplitude distortion. The reason why the TND response test results are much higher than the simulation results is that the pulse amplitude discriminator cannot effectively distinguish the distorted γ pulse and neutron pulse; The reason why the TND count rate drops significantly is that the uranium in the nuclear fuel shields most of the γ rays from ASNS to TND. The operation status of the source range channel and TND meets the requirements of the subcritical monitoring equipment for the first loading program.
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Key words:
- Reactor /
- Neutron source /
- Nuclear fuel /
- First loading /
- Subcriticality
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图 1 首次装料次临界监督设备布置图
Figure 1. Layout Drawing of Subcritical Supervision Equipment for First Loading
图 3 124Sb活度相对衰减量的变化曲线
Figure 3. Change Curve of Relative Attenuation Value of 124Sb Activity
图 4 参考机组DC探测器计数率的变化曲线
Figure 4. Change Curves of DC Detector Counting Rate of Reference Unit
图 5 参考机组DA探测器计数率的变化曲线
Figure 5. Change Curves of DA Detector Counting Rate of Reference Unit
图 7 L机组DB探测器计数率异常下降的曲线
Figure 7. Abnormal Decrease Curve of DB Detector Counting Rate of L Unit
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