IAEA coordinated research program on HTGR uncertainty analysis: Results of exercise 1-1 model and the application of the RPT method

The IAEA Coordinated Research Project on high temperature gas-cooled reactor uncertainty analysis in modelling (HTGR UAM) was initiated with clearly defined requirements, which are the development of novel and reliable methodologies and the establishment of well-defined models for accurate and efficient HTGR uncertainty analysis. It is based on the OECD/NEA light water reactor (LWR) uncertainty analysis in best-estimate modelling benchmark that has the same overall goal to evaluate uncertainty and sensitivity analysis (UA/SA) on LWRs. It is expected that for the HTGR UAM benchmark, some of the unique features of HTGRs (the coated particle fuel, higher operating temperature, and large mass of graphite) will result in some unique aspects to be identified in the uncertainty calculations. This paper represents the uncertainty result in the multiplication factor due to the covariance matrices for Exercise 1-1 (cell calculation) of Phase I (local neutronics) of the prismatic HTGR design. It contains four sub cases with two hexagonal and two triangular unit cell models defined to be at two operating conditions (293K and 1200K). Each of the models has a homogenous case where the TRISO particles are smeared in the graphite matrix, and a case where the fuel particles are explicitly modelled within the fuel compact. The latest version of SCALE6.1.3/TSUNAMI cannot perform the UA/SA studies for double-heterogeneous systems (as models using the application of the DOUBLEHET cell treatment) and therefore the Reactivity-Equivalent Physical Transformation (RPT) method is introduced as an approximate model in these uncertainty analyses. The reference results were produced with the available codes (SERPENT, MCNP, KENO), the multiplication uncertainties calculated with SCALE, and the major nuclide reaction covariance contributors identified for all the exercises