Year
1997
Abstract
Under IAEA Criteria, loss of surveillance of spent nuclear fuel could lead to a requirement that a significant portion of the fuel be re-verified. At CANDU nuclear stations, fuel bundles are stored horizontally on trays which are stacked up underwater, in tightly packed arrays in a spent fuel bay. Giving random access to a large proportion of the bundle population would represent a significant effort for the facility operator. In-situ access is possible, but extremely limited. A narrow slot less than 25 mm high between the fuel layers is available. Radiation levels near freshlydischarged fuel exceed 105 R/hr. A novel instrument has been developed which, through a difference measure, responds to the beta emissions coming through the fuel cladding. The plastic-bodied sensing head contains signal processing electronics, including two identical silicon sensors, one of which is shielded against beta. It is small enough to fit within the physical space available, responds quickly to the bundle being tested, should survive 10 to 100 hours of use and will be relatively inexpensive to replace. Its output is a unique signal that would be impractical to forge. The paper describes the operating principles and test results.