THERMAL CYCLING AND LEAKAGE TESTS OF 12-INCH VALVES FOR SODIUM SERVICE

Tests were performed to determine the effect of thermal cycling on the across-the-seat leakage characteristics of valves for use in the sodium coolant system of the Hallam Nuclear Power Facility. Four 12-in. valves were cycled between 680 and 1100 deg F in a sodium loop and periodically tested for across - the-seat sodium leakage. The valves tested were two throttling (ball) valves and two blocking (gate) valves. The first-ball valve had a consistent leakage pattern which vas primarily a function of valve temperature, but also varied with pressure differential and number of thermal cycles. The second ball valve showed high initial leakage rates which became excessive after some sodium circulation. Using data obtained with the first-ball valve, a general equation for the rate of leakage across the valve seat was obtained for this type and size of ball-valve as a function of temperature, pressure differential, and number of thermal cycles. No sodium leakage was exhibited by either gate valve throughout the test. None of the walves exhibited any leakage through the freeze-seal along the stem. (auth