PARAMETERIZATION OF TWO-GROUP NODAL CROSS SECTION DATA FOR POLCA-T BWR TRANSIENT APPLICATIONS

During the last decade, the use of coupled three-dimensional nodal neutron kinetics and thermal hydraulics simulation tools has gained increased popularity in performing comprehensive nuclear reactor design and safety analyses for BWRs. One of the advantages of using these coupled codes is the capability of providing full consistency between static core analyses and corresponding transient safety analyses. Therefore, the quality and accuracy of the underlying nodal method including the nodal cross section representation model play an important role in the successful application of these multi-physics tools. In this paper, the cross section parameterization required for BWR transient applications is considered with the objective to find a representation that provides complete transparency to users with regard to both steady-state and transient core analyses. It is demonstrated by means of simple 2D unit assembly test cases that if coolant boiling occurs below hot core operation conditions one needs to include both the coolant density and the moderator temperature as explicit state parameters in the cross section tabulation.