Optical dosimetry in a high-temperature gas-cooled reactor

Applicability of fused silica core optical fibers to in-reactor dosimetry was demonstrated at elevated temperatures and a special irradiation rig was developed for realizing high-temperature optical dosimetry in a High Temperature Test Reactor (HTTR) in Oarai Research Establishment of JAERI (Japan Atomic Energy Research Institute). The paper will describe present status of preparation for the high temperature dosimetry in HTTR, utilizing radiation-resistant optical fibers and radioluminescent materials. Temperature measurement with a high-speed response is a main target for the present optical dosimetry, which could be applied for monitoring transient behaviors of the HTTR. This could be realized by measuring intensity of thermoluminescence and black body radiation in infrared region. For monitoring reactor powers, optical measurements in visible region are essential. At present, measurement of intensity of Cerenkov radiation will be most promising. Other possibilities with radio-luminescent materials having luminescent peaks in visible region are under survey. One of the candidates will be silica, which has a robust radioluminescent peak at 450 nm.