BWR loss of coolant integral tests with two bundle loop, (I) Thermal-hydraulic characteristics in parallel channels.

Abstract

Two simulation tests of a BWR loss-of-coolant accident (LOCA) by a postulated guillotine rupture of a recirculation suction line were conducted using the Two Bundle Loop (TBL), which was volumetrically scaled to a BWR/5 plant with 764 fuel bundles. The major objective of the tests was to clarify thermal-hydraulic difference in parallel bundles. In the tests, the failure of a diesel generator for two low pressure coolant injection (LPCI) pumps was as-sumed, and the initial bundle power combinations were 4.0 and 5.9 MW in the first test, and 5.0 and 4.9 MW in the second.In one of the two bundles, the rods heated up locally in the radial direction. In the other, the rods heated up rather uniformly and later than in the former bundle. Much water fell locally into the former bundle, while ascending steam flow from the lower plenum was larger in the latter. A difference in thermal-hydraulic responses was observed even in the case of nearly identical bundle powers, but the difference was less than in the case of dif-ferent bundle powers. The peak cladding temperatures in the tests were lower L han 704 K.