OPTICAL MEASUREMENTS OF HIGH-TEMPERATURES FOR MATERIAL INVESTIGATIONSIN NUCLEAR-REACTOR ENVIRONMENTS

An optical method for high-temperature thermometry in heavy radiation fields has been demonstrated. The measurement system consisted of sign al generator, transmitting optical fiber and optical detector. The sig nal generator was a small blackbody cavity and the radiance from the c avity was used to determine the temperature. The method is applicable to high temperature measurements of small material samples in reactor environments also in strong electromagnetic fields. The theory of oper ation was confirmed in an experiment at Japan Materials Testing Reacto r where the tip of the transmitting pure-silica-core fiber itself serv ed as blackbody cavity and the temperature of a small alumina sample w as determined by optical means. It was shown that thermally powered in frared emissive sensors have the ability to be used for the full lifet ime of the transmitting optical fibers as temperature data could be ob tained for 2 full-power (50 MW) weeks. In the performed experiments th e heating was induced mainly by gamma-radiation and optically measured temperatures ranged from 250 to 800 degrees C. The demonstrated metho d relies on simple and compact sensors that require no electro-optical sources and can be used in environments where both nuclear radiation and electromagnetic fields are prevalent for extended periods of time. (C) 1998 Elsevier Science S.A. All rights reserved.