Development of a Model for Calculating Sheath Thermocouple Finning Losses for Application in In-Reactor Severe Fuel Damage Tests

Abstract

The use of mechanical clamps to attach high- temperature thermocouples to the surface of CANDU-type fuel elements has been developed as a means of improving the reliability of temperature measurements during in-reactor Severe Fuel Damage (SFD) tests. While helping - to ensure good thermocouple-to-sheath contact, the clamps also result in fairly significant finning losses to the surrounding steam coolant. To quantify these losses (and thus relate the measured sheath thermocouple responses to the actual local sheath temperatures), a series of electrically heated simulation tests was performed at Whiteshell Laboratories in 1995 January. This paper presents the results of CATHENA simulations of these tests and the development of a heat transfer model for calculating the finning losses from the strapped sheath thermocouples.