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在加速器驱动的次临界(ADS)系统中,次临界反应堆的功率控制是通过控制束流强度来实现。监测堆外中子注量率,不仅提供了反应堆功率指示,也为反应堆保护系统在启动和运行阶段提供了重要的监测信息,因此,堆外中子注量率的监测在ADS系统的控制与保护中起着非常重要的作用。采用3套裂变室和3套非补偿电离室来监测ADS堆外中子注量率。由于裂变室有脉冲、电流和均方电压3种操作模式,1套裂变室可以监测源量程、中间量程和功率量程等宽范围的反应堆功率。所以,使用的监测方法有3个优点,即:增加了监测通道的冗余度,提高了保护系统的可靠性,以及能提供更多的轴向功率分布信息。由于这些中子探测器对中子能谱很敏感,提出了一种有效的校准方法,即先用一个标准的中子源校准这些中子探测器,然后再将中子注量率除以一个修正因素。基于Geant4仿真结果显示,所提取的裂变室和非补偿电离室的修正因素分别为5和42。
In an accelerator driven subcritical (ADS) system, the power control of a sub-critical reactor is achieved by controlling the beam intensity. The monitoring of the off-scale neutron flux rate not only provides the reactor power indication but also provides important monitoring information for the reactor protection system during the start-up and operation phases. Therefore, the monitoring of the heap neutron flux rate in the ADS system control and Protection plays a very important role. Three sets of fission chambers and three sets of uncompensated ionization chambers were used to monitor ADS neutron flux rates. Since the fission chamber has three operation modes of pulse, current and mean square voltage, one set of fission chamber can monitor a wide range of reactor power such as source range, middle range and power range. Therefore, the monitoring methods used have three advantages: increased redundancy of the monitoring channels, improved reliability of the protection system, and more axial power distribution information. Since these neutron detectors are very sensitive to neutron spectra, an effective calibration method is proposed, which uses a standard neutron source to calibrate these neutron detectors and then divide the neutron fluence rate by a Correction factors. Based on the Geant4 simulation results, the correction factors for the extracted fission chamber and un-compensated ionization chamber are 5 and 42, respectively.