Integrated Burst Tests - Recent Experimental Investigation into Consequences of Pressure Tube / Calandria Tube Failure

Abstract

Experimental investigations into consequences of a pressure tube failure under normal reactor operating conditions have been on going under the direction of the COG R and D program. The initial tests focused on the measurement of annulus pressure transients. Subsequent tests investigated calandria tube response to a pressure tube rupture. Calandria tube strength was also examined under fast pressurisation transients to confirm the observed calandria tube strength margins for pressure tube failure scenarios. The current series of tests, called integrated burst tests (IBT), focused on simulating simultaneous failure of the pressure and calandria tube, by suitably defecting the pressure tube, to study the consequences. A total of six tests were conducted under the IBT series with the initial two tests being conducted in an open topped tank. The remaining four tests were conducted in a closed tank with simulated moderator flexibility. In all the tests, a single channel was simulated with all the associated channel hardware included in the test loop. The pressure tube was suitably defected with an axial groove to allow the tube to burst at the desired pressure. This paper presents a detailed description of the test facility used in the test series. A detailed account of the instrumentation employed to measure the pressure, temperature, strain and force transients in the experiments and the method of testing is also presented. The calandria tube did not fail in the first test while in the second test the failure of the calandria tube resulted in guillotine failure of the pressure tube as well. Calandria tube failure was obtained in only test five when the calandria tube had been defected in the weld. From the test results it is noted that bellows failure occurs when ever the calandria tube survives the pressure tube failure. The results from each test are presented along with the observed fuel damage to the ejected bundles. The significance of the experimental results on CANDU safety - analysis is also discussed.