Natural Circulation in a PWR for a Sinusoidal Heat Input: Analytical Model

Abstract

Natural circulation is a crucial passive heat removal process for all light water reactors. To understand the consequences of decreasing primary coolant inventory on natural circulation, an analytical one-dimensional model has been developed for a sinusoidal input heat distribution, based on solutions to the continuity, momentum and energy equations and expressions for the natural circulation parameters have been derived for PWR plant. The model encompasses all potential types of natural circulation (single-phase, combined single and two-phase, and two-phase). In this paper, it is found that the transition between the different modes of natural circulation with various system inventories is smooth. As the flow mode changes from single-phase (100% mass inventory) to two-phase natural circulation, the loop mass flow rate increases and exhibits a peak within a narrow band of inventory (usually between 60-80%). Also, it is demonstrated that natural circulation in a PWR type system can provide an effective mechanism for the rejection of core decay heat to the secondary over a primary coolant inventory range of 100 to 60%, and a core decay power range of 1.5 to 5% of full power. Comparisons are made between pervious experimental results and prior research and the analytical outcomes are found to be in reasonable accord.