Abstract
The objective of this work is to establish the capability to accurately generate the temperature-dependent cross-section data for Monte Carlo code MCNP and lattice code DRAGON. NJOY system is now the most reliable and popular way to generate the temperature-dependent cross sections. Although the process of running NJOY is tedious and time consuming, it provides the most accurate temperature-dependent cross section for neutronic simulation. The accuracy of neutronic simulation relies on correct cross sections. Therefore, the capability of processing the cross-section data is critical. The NJOY generated nuclear data library, after being verified, is used to assess the approximation methods for obtaining temperature-dependent cross section. The errors of the approximation methods are case dependent. For MCNP calculation, the assessment shows that makxsf has better performance than other methods. Errors are still about 1 mk. The performance of the three term Lagrangian interpolation in DRAGON is found to be quite well. Two HTTR benchmark problems shows the importance of the role of NJOY in generating the temperature-dependent cross section. The first problem utilizes NJOY to process the JENDL-4.0 library into ACE-format for MCNP calculation of a first critical benchmark problem HTTR-FC2. The results shows that the updated carbon cross sections in JENDL-4.0 improve the agreement of HTTR criticality calculation with the experiment results. Second problem is the evaluation of isothermal temperature coefficient in benchmark problem HTTR-TC. NJOY is used to generated cross-section data at the range 350 to 450 K for MCNP calculation for temperature coefficients. The calculation results are compared with the experimental data. The influences of cross section at incorrect temperature for U-238 and graphite in HTTR core calculation is clarified in this study. Using the existing S(α, β) at 1000 K to approximate case at 900 K will result in underestimation of k value by 7 mk. Using the existing CE at 900 K to approximate case at 1000 K will result in overestimation of of k value by 3 mk. The NJOY cross section processing system is widely used around the world. Through the established capability of running NJOY, the temperature-dependent cross section can be generated for neutronic analysis such as MCNP and DRAGON. This ensures the accuracy of whole core calculation for very high temperature reactor design.