Experimental Study on Reflooding Behavior in PWRs under Downcomer Injection

Abstract

In order to clarify differences in reflooding behavior between a PWR in which a part of the ECC water is directly injected into the downcomer and that in which it is injected into the cold legs, an experimental study has been performed with Cylindrical Core Test Facility. Two experiments were conducted under the same test conditions only except for injection location of the Low Pressure Coolant Injection (LPCI) water. In one test LPCI water was injected into the downcomer, whereas into the cold legs in the other.

Through investigation of the experimental data, the following has been clarified: Periodic oscillation of pressures in primary system, fluid temperatures around downcomer and so forth appear under the downcomer injection, whereas does not appear under the cold leg injection. The cause of the oscillation is that water at the top of the downcomer is subcooled under the downcomer injection due to incomplete mixing between steam flowing into the downcomer and LPCI water. Downcomer water is saturated under the cold leg injection. However, average values of the oscillatory data are almost the same as those of the cold leg injection, and hence, overall reflooding behavior is almost the same in the two cases.

KEYWORDS:

• reactor safety experiment
• PWR type reactors
• loss of coolant
• ECCS
• downcomer-injection-type ECCS
• reflood experiment
• downcomer
• Cylindrical Core Test Facility