A Study On Measurement Of Neutron Energy Spectrum For Thorium Molten Salt Reactor

The neutron energy spectrum is very important to the nuclear engineering design andapplication, as well as to the nuclear physics research. For a new type of reactor，the thoriummolten salt reactor, the neutron energy spectrum can provide a reference to the rationality of thedesign parameters. This thesis focuses on how to improve the measuring accuracy of the neutronenergy spectrum by activation method considering the related issues involved in experiments, inaddition to the measurement scheme of the neutron energy spectrum under the specificenvironment in the thorium molten salt reactor.The thesis is divided into eight parts. The first part mainly introduces the background of thethorium molten salt reactor and the significance of the neutron energy spectrum measurement tothe thorium molten salt reactor. In the second part, the theoretical calculation method of theneutron energy spectrum is researched. It is found that MCNP, based on Monte Carlo, can be asthe main tool to simulate the neutron energy spectrum after comparing the two methods,deterministic method and Monte Carlo method. In the third part, the measurement methods ofneutron energy spectrum are presented. The activation method is adopted by analyzing,considering the detecting principle of the neutron and the different measurement methods ofneutron energy spectrum. The fourth part briefly shows the activation method of neutron energyspectrum measurement, including the fundamental of the theoretical calculation andexperimental measurement，the methods of spectrum unfolding, the principle and process ofspectrum unfolding for SAND-Ⅱand MSIT, and the group cross-section affected by thethickness of the foil and the temperature of environment. In the fifth part, the active material andhigh purity germanium detector are researched, as the preparation work of the using activationmethod to measure the neutron energy spectrum. The selecting principle of active material andthe preparation principle of activation foil are stated. The main influence factors of the detectionefficiency are studied according to the shape and the absorptiong of the source. The sixth part isexperimental verification. The neutron energy spectrum in the radiation cavity of Xi’An pulsedreactor and prototype micro reactor is respectively measured by the activation method, choosingSAND-Ⅱand MSIT to unfold the spectrum. The uncertainty of the result is analysed using theMonte Carlo method, and the influence of initial input spectrum on the results is discussed. In the seventh part, the schemes for the theoretical simulation and the measurement of the neutronenergy spectrum for a proposed experiment reactor，the thorium molten salt reactor-solid facility(TMSR-SF1) are given, especially in the high temperature conditions when it is550oC～650oCin the reflector，along with the core, during TMSR-SF1normal working. The eighth part gives abriefly summary and prospect.In this thesis, the measurement of neutron energy spectrum in TMSR-SF1is studied, as wellas master the key measurement technology of neutron energy spectrum using activation methodwhen the temperature of environment is not higher than100oC.