Stability and Safety analysis of Tight Lattice Breeding LWR - 14276

For the next generation of breeder/burner reactors, Hitachi has proposed a LWR tight-lattice fuel design the Resource-Renewable Boiling Water Reactor (RBWR). One of the principal features is that the RBWR has a large axial blanket region centered at the core mid-plane. The power to flow ratio of the two reactors is also different. This leads to significant differences in the axial power shape, as well as the boiling length, coolant mass flux, void fraction, hydraulic diameters, assembly layout, and reactivity coefficients. The MIT code, STAB, was applied to the RBWR instabilities. Three stability modes were modeled: single channel thermal hydraulic, thermal hydraulic-point kinetics out-of-phase and thermal hydraulic-point kinetics in-phase. For all three modes, the decay ratio of the RBWR was lower than the ABWR. An ABWR TRACE model was then extended to simulate the RBWR safety performance using point kinetics. The turbine trip without bypass, total loss of feedwater, and total pump trip transients were simulated in TRACE for an ABWR and the RBWR. The ABWR results matched those found in the literature, and the RBWR results indicated very different behavior during the same transients depending on the assumed void coefficient direction and magnitude. (authors)