Verification of a Three-Dimensional Nodal Transient Neutronics Routine for the TRAC-PF1/MOD3 Thermal-Hydraulic System Analysis Code

The verification of a three-dimensional nodal transient neutronics routine in the TRAC-PF1/MOD3 Version 1.0 thermal-hydraulic system analysis computer code is discussed. This neutronics algorithm is based on a fully implicit transient version of the well-known nodal expansion method. Results from running TRAC-PF1/MOD3 with this new neutronics routine were compared with the results of running two established neutronics/thermal-hydraulic space-time codes, HERMITE and ARROTTA. The transient chosen for this code verification was a rapid ejection of an off-center control rod in a Westinghouse pressurized water reactor, which is initially at hot standby. This severe prompt-critical transient provides a stringent test of TRAC-PF1/MOD3's new multidimensional neutronics routine and its coupling to the existing thermal-hydraulic solution methodology. Because of its speed, the transient tests only the fuel rod heat conduction coupling and not the coolant thermal-hydraulic coupling.

Acceptable agreement was obtained among the results from TRAC-PF1/MOD3, HERMITE, and ARROTTA during all phases of this transient. Agreement was in the areas of time dependence of total-core and peak-assembly powers, as well as the time dependence of the core-average and peak-assembly fuel temperatures. In addition, comparison of several steady-state calculations that provide initial conditions for the transient analysis showed acceptable agreement in the calculated eigenvalues and normalized assembly-power distributions.