Effect of Pressure Drop through Broken Cold Leg on Thermal Hydraulic Behavior during Reflood Phase of PWR-LOCA

Abstract

Studied is the effect of a pressure drop through the broken cold leg of pressure vessel side on thermal hydraulic behavior during the reflood phase of a PWR-LOCA using CCTF data to consider how to treat the pressure drop in reactor safety assessment. It is confirmed both experimentally and analytically that the pressure drop pressurizes inside the core and increases the mass flow rate at the core inlet. It is also confirmed quantitatively that the increase of the core pressure and the core inlet mass flow rate arising from the effect of the pressure drop results in the lower peak clad temperature and faster quench time. For the conservative evaluation of the core cooling, it is recommended to use a low pressure loss coefficient at the broken cold leg in reactor safety assessment calculations. The current evaluation code is still conservative because it usually predicts low pressure drop through the broken cold leg.

KEYWORDS:

• reactor safety
• PWR type reactors
• loss of coolant
• reflood
• two-phase flow
• thermohydraulics
• CCTF
• pressure drop
• system effect
• broken cold leg