Small-Break LOCA Recovery in B&W Plants

Abstract

A break of approximately 0.0012 m² in the cold leg of a B&W plant results in an interruption of natural circulation when steam accumulates in the hot-leg U-bend. A small-break loss-of-coolant accident of this size was simulated by TRAC-PF1 to evaluate strategies for recovery and for re-establishing natural circulation. In the absence of operator action, core cooling occurs when water supplied by the high-pressure-injection system boils, then is discharged through the break. Raising the steam-generator secondary level, venting steam from the steam-generator secondary, venting steam from the hot-leg U-bend, “bumping” the reactor-coolant pumps, and injecting a portion of the high-pressure-injection system into the hot-leg U-bend aided in cooling and depressurizing the primary system but were ineffective in reestablishing natural-circulation flows in the primary-coolant loops.