Research On Nelkin Model Correction Of Neutron Scattering In Super Critical Water

As one of the fourth generation reactors, the supercritical water reactor is better than the previous with higher thermal efficiency and more economy. But it also faces a number of problems, especially, the research of neutron scattering behavior in supercritical water which is a key problem needed to be solved. In the current research in the field of nuclear reactor engineering, Nelkin model is mostly applied in thermal neutron scattering processing. In supercritical water, when the temperature is increasing, thermal motion of hydrogen atoms increases, water tetrahedral structural defects increase, and the average life expectancy of hydrogen bonds significantly reduce. These changes of hydrogen bonding have an impact on water molecules’ translation, rotates, and vibration. And affect the accurate calculation of the scattering cross section. There is no direct evidence to indicate that there is close relationship between the formula of Nelkin model and the changes in structure of water molecules. But the empirical parameters of Nelkin model are dependent on the temperature and pressure of the water.The design pressure of supercratical water is no more than 25MPa, and the design temperature is between 400 and 650 celsius degree. There are series research on such temperature and pressure conditions using Raman spectrum method. This work uses the research to obtain the empirical parameters of water molecules’ translation, rotates, and vibration under supercritical state. Then this work achieves the numerical solution of Nelkin model by using fortran language. The neutron scattering cross sections under room temperature and pressure below leV are both calculated by Nelkin model code and NJOY code. The comparison result indicates the numerical calculation method and coding work are both accurate and reliable. Then different groups of cross sections with different empirical parameters in same supercatical state (673K,256bar) are calcuted. And the results show small deviation between these groups. The energy parameters with breakage of hydrogen bonding and energy parameters with all hydrogen bonding existing are macroeconomic influence on the cross sections. So, average energy parameters are used to calculate the neutron scattering cross sections under supercritical state.It is compared with the neutron scattering cross sections under room temperature and pressure and the data under PWR condition. The results indicate that in the energy range above 0.1 eV they have good agreement with each other.But in the energy range below 0.1 eV, the cross section data show the large deviations between supercritical state and normal temperature and pressure, while it has good agreement between supercritical state and PWR conditions. The reason may be the rate of change of energy-related neutron scattering cross sections is increasing while the temperature T increases.In summary, the change of the scattering cross section data between supercritical and subcritical state is caused by the changes of translation, rotates, and vibration with breakage of hydrogen bonding, and also caused by the increasing of temperature T. This work of Nelkin model correction begins to analysis these factors. And the neutron scattering cross sections in supercritical water are preliminarily obtained. This work makes a good groundwork for updating the nuclear data libraries in supercritical water reactor research. And it has a positive meaning for other work in supercritical water reactor research.