Approach to the HTGR core outlet temperature measurements in the United States

The purpose of this paper is to describe the methods used to measure the primary coolant temperature at the outlet of the core of the High Temperature Gas-Cooled Reactors (HTGR) in the United States. The HTGR constructed at Fort St. Vrain Colorado (330 MWe) used Geminol thermocouples to measure the primary coolant temperature at the core outlet. The Germinol thermocouples installed in the Fort St. Vrain reactor have provided accurate data for several years of power operation without any failures. The indicated temperature of the core outlet thermocouples agrees with a traversing thermocouple measurement to within +- 20C. The next large HTGR design will incorporate replaceable thermocouples. An acoustic thermometer with a solid wave guide is being considered for use in the core outlet area. The thermometer is manufactured by Panametrics, Inc. in Waltham, Massachusetts. The system provides up to 16 temperature measurements on one wave guide that is as small as 1.6 mm in diameter. This temperature measuring system would simplify the mechanical design of the core outlet temperature measurement assembly