Analysis of SPRIHTE LOPA flow excursion tests

摘要

The SPRIHTE FLOPA flow excursion tests, the results of which are presented here, have been modeled using FLOPA, the assembly thermal-hydraulics limits analysis code for the LOPA. FLOPA calculations show T(sub wall) = T(sub sat) is a reliable precursor to the onset of thermal excursion at prototypic flow rates during the ECS addition phase of the LOPA. A FLOPA model was created based on nominal dimensions for the SPRIHTE rig and an assumption that the rig's cylinders were concentrically located. This model can determine when T(sub wall) = T(sub sat) if adjustments are made to account for differences between measured and calculated subchannel flow and heat transfer rates. To make these adjustments, a multiplier (beta) was applied to the wall saturation temperature criterion (T(sub wall) = (beta) T(sub sat), in degrees C) to match measured and calculated powers at which the saturation temperature was first exceeded at the wall. Based on preliminary test results, a multiplier of 0.878 was recommended for use in calculating LOPA limits for the K-15.1 subcycle. This multiplier provides margins of 14% to 19% between the calculated wall saturation temperature limits and the measured powers at the onset of thermal excursion. The effective margins used in the final LOPA limits, which include dimensional and heat transfer model uncertainties and biases due to eccentricities, range from 38% to 41%. It is estimated that use of the wall saturation temperature criterion lowers the K-14.1 subcycle LOPA core power limit, which is based on a Stanton number of 0.0025, from 41% to 37% of the historical full power of 2400 MW. This report describes the SPRIHTE LOPA tests, describes and evaluates the FLOPA Model for the SPRIHTE tests, discusses selection of a limit criterion for the SPRIHTE tests, and evaluates the transition between high and low flow rate criteria. Calculated results and a sample of FLOPA input for the analysis of the SPRIHTE tests are provided.