Long-cycle Soluble Boron-free SMPWR with Zircaloy Reflector

Abstract

This paper suggests an optimal model of boron free SMPWR for long-cycle operation without refueling. The target cycle length is set as 1,500 Effective Full Power Days (EFPDs) and four design limits are checked: Axial Shape Index (ASI) in the range -0.4 to 0.4, 3D power peaking factor (Fq) < 5.09, shutdown margin (SDM) > 3,000 pcm and Isothermal temperature coefficient (ITC) < 0. To achieve the target cycle length within the design limits, three design concepts are introduced: ring-type burnable absorbers (R-BA), a zircaloy reflector and an axiallyheterogeneous central control rod. In details, the optimal core employs eight HfB2 (80 w/o enriched B-10) adjuster control rods of height 200 cm whereas the axially-heterogeneous central control rod is composed of 140 cm of HfB2 (80 w/o enriched B-10) in the lower part and 60 cm of stainless steel in the upper part. As for burnable absorbers, 2 w/o and 8 w/o enriched gadolinia, natural gadolinium R-BA and Al2O3/B4C (80 w/o enriched B-10) Wet Annular Burnable Absorber (WABA) are loaded in the assemblies. An optimal core model with a cycle length of 1,577 EFPDs within the design limits is successfully designed through calculations with the deterministic two-step code system STREAM/RAST-K-2.0 based on the ENDF/B-VII.1 neutron cross-section library and JENDL-4.0 kappa (fission Q-value) library. The STREAM/RAST-K-2.0 two-step code system has been verified in previous publications for SMPWR R-BA applications against the Monte Carlo code SERPENT2.1.27 and the two-step code system CASMO4e/SIMULATE3.