Advances in Nuclear Fuel Management IV (ANFM 2009) Hilton Head Island, South Carolina, USA, April 12-15, 2009, on CD-ROM, American Nuclear Society, LaGrange Park, IL (2009) © ANS 2009, Topical Meeting ANFM 2009, p. 1/11 TESTING 3-D NODAL CODES SIMULATE-3/5 FOR REFUELING SHUTDOWN MARGIN PREDICTIONS WITH CASMO-5M Zhiwen Xu, Joel Rhodes and Kord Smith Studsvik Scandpower, Inc. 504 Shoup Avenue, Suite 201, Idaho Falls, ID 83402, USA zhiwen.xu@studsvik.com , joel.rhodes@studsvik.com, kord.smith@studsvik.com Keywords: Reactor refueling, shutdown margin, partially loaded core ABSTRACT Reactor shutdown refueling is a crucial task for BWR operations. In this paper, based on a realistic BWR core refueling sequence, the SIMULATE-3 and SIMULATE-5 shutdown margin (SDM) predictions are benchmarked against CASMO-5M results. The 2-D core in this exercise is established from the middle plane of a typical 748-bundle BWR core. There are thousands of fuel move steps from the end of previous cycle to the beginning of next cycle, most of which are so-called partially loaded core configurations where empty fuel locations are filled with water. During this process, eigenvalue predictions from CASMO-5M and SIMULATE-3/5 are compared for the all-rod-in (ARI) case and the ARI except the maximum-worth rod (ARI-M) case. Based on more advanced neutronic models, SIMULATE-5 shows sizable improvements in agreeing with the CASMO-5M reference solution over the SIMULATE-3 results for partially loaded cores. 1. INTRODUCTION Reactor shutdown refueling is a crucial task for BWR operations. Typically there are thousands of fuel move steps between the end of previous cycle and the beginning of next cycle. The core shutdown margin (SDM) requirement needs to be satisfied during every step of the fuel shuffling and core reload process, which necessitates an accurate core eigenvalue prediction for partially loaded cores under cold conditions. In the production analysis, the advanced 3-D nodal code, SIMULATE, is utilized for this purpose. Note that the shutdown margin evaluation assumes all control blades inserted except the maximum-worth one (ARI-M). In this paper, based on a realistic BWR core refueling sequence, the SIMULATE version 3 and version 5 SDM predictions are benchmarked against reference CASMO- 5M results. Since CASMO-5M 1 is a 2-D lattice physics code capable of modeling M×N fuel segments in rectangular geometry, the benchmark exercise is proposed as a 2-D core problem established from the middle-plane of a typical 3-D 748-bundle BWR core. It is recognized that 2-D BWR core calculations are not realistic. Therefore, the calculations reported here serve for benchmark purposes only.