Streaming Effect of Void Reactivity in LWR Critical Experiments with Streaming Channel

The void reactivity of a fuel assembly with a streaming channel was measured in a simulated light water reactor critical lattice. The void reactivity was defined as the difference of reactivity ρ between different void conditions. Stainless steel and Zircaloy are candidates for the streaming channel material. Aluminum was used in this measurement because it is inexpensive and its absorption cross section is similar to that of Zircaloy. Two types of streaming channels were used: one made of aluminum and the other made of stainless steel. The two streaming channels were compared in terms of the difference in void reactivity. Measured values were calculated using a continuous-energy Monte Carlo code, MCNP6.1, with the JENDL-4.0 and ENDF/B-VIII.0 nuclear data libraries. The measured values and the calculated values agree within an error range of approximately 10% for the aluminum streaming channel and approximately 20% for the stainless steel streaming channel. The streaming effect of reactivity was deduced from the changes of migration area and buckling, which were measured using the water-height coefficient of reactivity and the axial fission-rate distribution.