Leak-before-break experience in CANDU reactors

Conference · Fri Jan 01 04:00:00 EST 1988 · Trans. Am. Nucl. Soc.; (United States)

OSTI ID:6947642

Price, E G; Moan, G D; Coleman, C E

In the Canada deuterium uranium (CANDU) reactor, each of the approx. 400 hot pressure tubes containing the fuel bundles and the pressurized heat transport water is surrounded and insulated from the cold moderator by a calandria tube. The pressure tubes are made from cold-worked Zr-2.5 Nb with a minimum wall thickness of 4.19 mm, and the calandria tubes are made from annealed Zircaloy-2 with a minimum wall thickness of 1.37 mm. The annulus between these two tubes contains an inert gas. Leak-before-break has developed into an operational tool in CANDU reactors to prevent unstable failure of pressure tubes. A procedure for leak detection and reactor response has been developed from the use of the annulus gas, whose dew point is measured to ascertain if leaks have crept into the annulus. The characteristics of the crack are used to establish the response time for leak detection. The reactor is required to be shut down before the length of the slowly growing crack has reached the critical stage. This critical crack length, determined using slit burst tests on tubes, is the crack length at which the crack growth becomes unstable. The most likely crack growth mechanism is delayed hydride cracking. This mechanism requires three conditions to occur simultaneously: the material must be sensitive to delayed hydride cracking; zirconium hydrides must be present in the material; and the tensile stress must be sufficiently great.

• OSTI ID: 6947642
• Report Number(s): CONF-880422-
• Conference Information: Journal Name: Trans. Am. Nucl. Soc.; (United States) Journal Volume: 56
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
210400* -- Power Reactors
Nonbreeding
Otherwise Moderated or Unmoderated
CALANDRIAS
CANDU TYPE REACTORS
CONTAINERS
CRACK PROPAGATION
FAILURES
HEAVY WATER MODERATED REACTORS
HYDRIDES
HYDROGEN COMPOUNDS
LEAK DETECTORS
LEAKS
PERFORMANCE
PRESSURE TUBE REACTORS
PRESSURE TUBES
REACTOR SAFETY
REACTORS
RELIABILITY
RUPTURES
SAFETY
STRESSES
THERMAL REACTORS
TRANSITION ELEMENT COMPOUNDS
TUBES
ZIRCONIUM COMPOUNDS
ZIRCONIUM HYDRIDES