Pressure Drop through Broken Cold Leg during Reflood Phase of Loss-of-Coolant Accident of Pressurized Water Reactor

Abstract

In an integral system test on the reflood phenomena of a PWR LOCA with the Cylindrical Core Test Facility (CCTF), a high pressure drop was observed through the broken cold leg of the pressure vessel side. In order to understand the pressure drop and to assess the applicability of the CCTF result to the LOCA analyses for PWRs, the pressure drop characteristics through the broken cold leg is analyzed with CCTF and FLECHT SET data. The high pressure drop is explained quantitatively with the homogeneous flow model of the two-phase flow. The difference of the pressure drop between the FLECHT SET and the CCTF is attributed to the differences of the flow area scaling of the broken cold leg and the ECC water injection method. It is confirmed analytically that the high pressure drop as in the CCTF tests is expectable in a PWR system with a cold leg break due to the pressure losses at the broken cold leg nozzle and the break.

KEYWORDS:

• reactor safety
• PWR type reactors
• loss of coolant
• reftood
• two-phase flow
• thermohydaulics
• pressure drop
• CCTF
• broken loop
• flow rate
• pressure dependence