Use of Fuel Thermocouple Transient Response for Data Verification and Fuel Rod Modeling

Time-varying response of fuel centerline thermocouples can be used to

1. cross-check steady-state temperature/power estimates
2. make the centerline temperature data more definitive in verification of fuel modeling computer codes.

Two kinds of transients are analyzed—quasi-steady-state response to linear power decrease, and transient response to rapid power decrease. Sample data are taken from the Halden reactor assembly IFA-432 in a test sponsored by the U.S. Nuclear Regulatory Commission. It is concluded that the linear power decreases can confirm initial steady-state temperature and power values within 6% relative. The step-power decreases can be used to assess various combinations of models. This is important because various combinations of models can be adjusted so that they all match a given set of data points for steady-state temperature versus power. However, these same combinations may result in divergent transient predictions. Thus, fuel modeling efforts can be enhanced by considering the transient as well as steady-state fuel thermocouple data.