Critical Device Neutron Spectrum Measurement

Neutron spectrum of critical facility can be used in the test of calculations and calibration parameters. The average cross-section can be calculated by the neutron spectrum for neutron flux measurement. The active region of the fast neutron critical assembly which is similar to Godiva critical assembly is high enrichment of uranium metal. There are no slow and reflective layers. The neutron spectrum is slightly moderated fission spectrum.Measurement methods for the slightly which is slightly moderated neutron spectrum are as follows:Hydrogen Recoil,6Li and3He Spectrometer, Time Of Flight, and foils activation. In which the foils activation is very simple operation. It is less demanding on equipment. And it is used for neutron spectrum measurement.There are four respects in the paper.1) We analysis the neutron spectrum;2) we measured the neutron spectrum by foils activation;3) given the advice for neutron spectrum measurement form the results of monoenergetic neutron measurement by3He;4) Proposed the evaluation advice for the uncertainty of neutron spectrum.The neutron field is analysised by239Pu fission chamber with Cd-cover, B-cover and nothing. And the reasults show that the thermal neutron, resonance neutron and fast neutron are about2.1%,2.1%and95.8%.Ten kinds of activation foils are choosen in the experments, in which there are six kinds of activation foils can be used in the SAND-â…¡ program to solve the neutron spectrum. Neutron spectrum into Fifteen groups by energy is given in this paper. Neutrons bellow10keV are about0.08%. Neutrons greater than lOMeV are0.1%.85%seutrons concentrated in0.2-3MeV. And the average energy is1.34MeV. The different between the reaction rate based on the spectrum and the measured reaction rate is less than5%.SP9spectrometer is used to measure some typical monoenergetic neutron. The response function of SP9is measured in the experments. According to the results, SP9 can be used in the neutron spectrum measurement of critical assembly, the expermental scheme is given in this paper.Key factors contributing to the uncertainty of the neutron spectrum are analyzed. This paper presents the combined uncertainty of20keV,0.6MeV and5MeV several typical energy points. And the largest contribution to the uncertainty of spectrum is the uncertainty of the average cross section.The main contributions of this paper are as follows. First, neutron field is annlysised by239Pu fission chamber. And this is first time to get the energy spectrum of the critical assembly by activation foil. A generally method for fast neutron spectrum measurement by activation foils is established. Key factors of uncertainty are ananlyzed. Expermental scheme for neutron spectrum measurement by3He is given.