Soluble Boron Free Small Modular Pressurized Water Reactor Core Design by Using NECP-Bamboo

Abstract Small Modular Pressurized Water Reactor (SM-PWR) refers to small, flexible and modularizable PWR designs. In this study, a SM-PWR without soluble boron is designed and analyzed by using the PWR-core physics analysis code NECP-Bamboo. The reactivity of the core is completely controlled by using burnable poisons and control rods. (1) The rated full thermal power was selected as 200MW, while the diameter and the height of the core were limited as 1.4m and 1.2m, respectively. In this reactor core, hexagonal fuel assemblies were employed, while both the control rods and detectors can be placed in the center of each selected fuel assembly. (2) The fuel rod is wrapped with wire, which not only enhances the heat transfer process, but also serves as structural support. (3) To find the most appropriate fuel arrangement, iterative manual optimization was performed among core arrangements, control schemes, detector arrangements and fuel assembly design to assess acceptable neutronic and thermo-hydraulic core characteristics that can meet the safety margin requirements. (4) The neutronics effects of different burnable and movable neutron absorbers were also analyzed, which leads to the selections of Gd2O3 and B4C as burnable absorbers and AIC as movable control rods, to achieve the cycle length of 1120 effective full power days and to control the reactivity changes during normal operations and load subsequent operations. (5) In addition, the core shutdown allowance exceeds 5000 pcm in the stuck rod criteria. The design of control rod grouping and operation strategy can reduce the core power peak factor fxy to 1.7 and the assembly average burnup 52.5 GWd/tU while pin burnup limited under 70GWd/tU. The Doppler coefficient, moderator temperature coefficient and power reactivity coefficient are all negative during the entire operation process. The radial and axial power distribution results of the deepest burnup fuel rods and fuel rod power envelope show that there is a significant safety margin in terms of fuel temperature limitation. The calculation of fast neutron flux of pellets provides a basis for the subsequent fuel performance analysis. (6) What’s more, the power capacity of the core under Class I conditions were analyzed, including the maximum line power density, Xenon oscillation power distribution and so on, which provides a reference for the nuclear physical design of a new rod-controlled reactor with high U-235 enrichment and no soluble boron.