能谱变化对^(239)Pu裂变室测量快中子注量的影响

Fast neutron flux measurement uncertainty due to the variation of neutron spectra distribution

热中子和共振区的中子在快中子临界装置中所占的份额很小,但是由于其相对大的截面,在慢化物存在的情况下,热中子和共振中子份额的微小变化,对239Pu裂变室测量中子注量的结果影响很大。通过测量239Pu裂变电离室在包镉和包硼、周围有无慢化物等情况下的反应率,Au、In活化片的镉比,S活化片在能谱变化下与239Pu的反应率比等,分析了快中子临界装置中热中子和共振区中子的分布,讨论了中子能谱变化对239Pu裂变室测量快中子注量的影响及解决办法。

As the fission cross-section of ^(239)Pu is flat while the neutron energy is larger than 10keV, the ^(239)Pu fission chamber is often used to measure the absolute fast neutron flux in the fast reactors or assemblies. Due to a little fraction in the fast neutron assemblies, having a relative large cross-section, the thermal neutron and resonance region neutron make the measured reaction rate varied abruptly when some moderators are near the detector. The ^(239)Pu fission rate with and without ^(10)B capsule, the Cadmium rate of ^(197)Au and ^(115)In, and the ^(32)S reaction rate are measured to analyze the neutron spectra variation out of the CFBR-II reactor. The fast neutron flux measurement methods are concluded in the end.