Direct whole core modeling and simulation of the SPERT III E-Core experiments by nTRACER

The SPERT III E-core experiments are modeled and simulated by a direct whole core calculation code nTRACER as an effort to validate its dynamics calculation capability. The control rod ejection experiments performed for the E-core of the Special Power Excursion Reactor are faithfully modeled by explicitly representing all the complex components such as fuel cans and the cruciform transient rod. The unknown experiment conditions such as the initial position of the ejected rod is estimated rigorously to yield the proper rod worth. The simulations are performed in the one-step manner such that the entire calculation for rod ejection is carried out with a single input deck without any prior calculation. All the kinetics data such as the fractions and decay constants of the delayed neutron precursors are directly obtained from the suitable evaluated nuclear data files. Doppler feedback is modeled by the direct estimation of the fuel temperature profiles inside each pellet. The transient results for the five ejection tests are compared with the measured data such as the peak time and magnitude of the power pulse, the net power release up to the power peak, and the post-burst power level. The good agreement between the nTRACER results and measured data demonstrates the efficacy of direct whole core dynamics calculation as well as the accuracy of nTRACER. In addition, a comparison is made with a two-step calculation to demonstrate the advantage of the direct whole core transient calculation.