New findings on neutron noise propagation properties in void containing water using neutron noise transport calculations

作者：Yamamoto Toshihiro^*; Sakamoto Hiroki

来源：Progress in Nuclear Energy, 2016, 90: 58-68.

DOI：10.1016/j.pnucene.2016.03.003

• Void
• BWR
• Neutron noise
• Frequency domain
• Monte Carlo
• Diffusion theory

This paper presents new findings in predicting the void fraction or void transit time of void-containing water flow using the results of multi-group neutron noise transport calculations. The neutron noise transport equation in the frequency domain is solved with a recently developed Monte Carlo method that uses complex-valued weights. In the calculations, the noise of thermal neutrons that penetrates a two-dimensional channel of void-containing water is obtained to predict the void properties. The thermal neutron noise is influenced by the slow down from the neutron noise in the higher energy range and by the transport of the thermal neutron noise. This influence becomes more notable in a lower void fraction or in a wider water channel. If the thickness of the channel is small enough, the void transit time can be accurately predicted using the CPSD between detector pairs aligned in the flow direction. In a wider channel, an anomalous void transit time would be obtained from the CPSD. The results of the multi-group calculation show that the APSD in a lower void fraction deviates from the Lorentzian form that holds in the one-energy group approximation. This deviation is caused by the higher energy neutron noise, whose frequency characteristics are different from the thermal neutron noise. Assuming that the one-energy group approximation is applicable, the relationship between the break frequency of the APSD and the neutron diffusion length or neutron age is clearly observed, which suggests that the measurement of the APSD could lead to the prediction of void properties.

• 出版日期2016-7