Research On Thermal Neutron Scattering In Supercritical Water Based On IKE Model

The supercritical water reactor, which has many advantages over the traditional reactors with simpler system and higher thermal efficiency, is one of the most promising fourth generation reactors. The concepts of the supercritical water reactor design have been proposed and many basic studies have been done in the domestic and overseas. The thermal neutron scattering problem in supercritical water and its corresponding research of database which are basic data in the reactor physics have not yet been solved. Neutron thermalization effect in supercritical water will influence neutron spectrum, effective multiplication factor and so on, and will affect the reactor neutronics calculation and core physical design further.The task "Research on Thermal Neutron Scattering in Supercritical Water Based on IKE Model" is proposed in this paper. IKE model is a kind of mature model which applys to thermal neutron scattering research in light water. However, the properties of supercritical water are obviously different from that of normal water. By means of numerous surveys for the supercritical water, we find that hydrogen bond between water molecules is continually weakening with the increasing temperature and the number of hydrogen bond between supercritical water molecules decreases significantly. These properties will influence hindered rotation, translational motion and vibration of water molecules, which will affect precise calculation of scattering kernel model and the accuracy of the scattering cross section further. The basic data of IKE model, such as frequency spectrum, discrete oscillator energy and translational weights, are calculated through the theoretical derivation. These parameters will change in the supercritical state and this is the reason why we must do some researching on them.In this paper, we use Materials Studio to research the properties of supercritical water and calculate the frequency distribution of the supercritical water. Based on the research results of the supercritical water Raman spectra on the international, we modify the parameters of IKE model, such as frequency spectrum, discrete oscillator energy and translational weights, in order to apply them to the thermal scattering study of the supercritical water. In addition, we achieve the numerical solutions of EKE model correction by means of Fortran program. And we prove the rationalisation of the computing method for IKE model correction by comparing scattering law with the Evaluated Nuclear Data Library and the results calculated by NJOY.We use NJOY to develop the thermalization library in ACE format for the scattering law files in the Evaluated Nuclear Data Library and that calculated by Fortran. And the corresponding examples under supercritical status are designed for verification by cosRMC. Through the calculation of self-designed examples, some conclusions are obtained. The thermalization effect in supercritical water has a strong impact on k∞ in the thermal spectrum samples and is unimportant for the fast spectrum samples. Compared with other parameters, the frequency spectrum of the supercritical water has a more important influence on the k∞. In the design of supercritical water reactor, it’s necessary to correct the frequency spectrum of supercritical water in IKE model in order to ensure higher accuracy in reactor physics calculation. In addition, the supercritical water density varys widely at different temperatures, so that it is necessary to be fully considered in transport calculation.In summary, the thermalization libraries of supercritical water are developed by the calculation of the IKE model correction and are verified. 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.