Critical Heat Flux Evaluation of a Conceptual Fuel Bundle Design with the ASSERT Subchannel Code

Abstract

An assessment of a new 61 element conceptual fuel bundle design has been conducted f or EPDC (Electric Power Development Company) in the conceptual design study of a Highly Advanced Core (HAC) CANDU plant. Given the conceptual nature oft he fuel design, the subchannel code ASSERT-IV with a CHF model developed based on Stern experiments, was used to assess the bundle performance. The study included the effects on CHF of axial flux shape, variable radial flux shape, creep, and turbulence enhancement. To complete the analysis of critical channel power, the cross sectional average code NUCIRC was required. This necessitated the development of a methodology to use ASSERT to provide the necessary corrections for the NUCJRC assessment. Overall, the ASSERT code proved to he a valuable tool in predicting the conceptual bundle design performance. Along the way, several interesting trends were observed which have impacted on the general understanding of the competing effects leading to dryout in a CANDU fuel string. This study also demonstrates the potential value of a subchannel code such as ASSERT for assisting in design development of new bundles.