WESTINGHOUSE 2-LOOP PLANT LOADING PATTERN OPTIMIZATION FOR LAST FEW CYCLES BEFORE SHUTDOWN

Abstract

This paper presents the optimized operating scenario of a Westinghouse 2-loop pressurized water reactor (electrical power of 640 MW) for the last few cycles before shutdown. 121 fuel assemblies (FAs) of type ACE07 (16 pins by 16 pins) are loaded in the core. The target combined length of the last two cycles (cycle N-1 and cycle N), including overhaul period and coastdown period, is set as 1121 days. The two main goals of the loading pattern (LP) optimization study are maximizing the full power operation period and maximizing the discharge burnup at end of operation (shutdown) while abiding by the design safety limits regarding the two-dimensional (2D) power peaking factor (Fxy), three-dimensional (3D) power peaking factor (Fq), moderator temperature coefficient (MTC) and axial shape index (ASI). To extend the full power operation time, two sensitivity studies are performed. First, two different burnable absorber types are investigated for use in the core: PYREX (12.5 w/o contents of B-10) and gadolinia with 6.06 w/o enriched Gd2O3. Then, eleven LPs are investigated for cycle N-1 (six patterns with 56 fresh FAs and five patterns with 60 fresh FAs) and seven LPs are investigated for cycle N (three patterns with 56 fresh FAs and four patterns with 60 fresh FAs). The optimization calculations are conducted with the STREAM/RASTK2.0 deterministic two-step code system developed at Ulsan National Institute of Science and Technology and the ENDF/B-VII.1 neutron cross-section library (with the exception of the plutonium isotope data which comes from the JENDL-4.0 library).