PURPOSE: To increase stability margin in the case where flow resistance is small in a high flow condition and large in a low flow condition, enlarge stability by controlling inlet flow change in a restraint condition in which reactor core loss is constant, and increase a flow control range by reducing pressure loss in the high flow condition and increasing the maximum reactor core flow.
CONSTITUTION: A nuclear reactor and fuel assemblies are provided with flow resistant elements 13. Flow resistance is small in a high flow condition in the neighborhood of rating operation in a coolant flow passage between a core inlet 11 of the reactor and a fuel lower tie plate 9 of the fuel assembly 5, the flow resistance is large in a low flow condition in which stability is an operation limit, and a stability margin is increased. The flow resistant elements 13 in which critical flow is produced in a venturi type inside in which a vena contracta part 15 is formed is provided.
YAMAMOTO YASUSHI
TSUKUMO YOSHIAKI
MOROOKA SHINICHI
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