Development of measuring device for inner surfaces of embedded piping (Contract research)

The measuring device for inner surfaces of embedded piping (MISE) was developed to evaluate low-level radiological contaminations of inner surfaces of piping. The MISE consists of a cylindrically-formed double layered type detector and a piping crawling robot, which were designed and manufactured separately. In measurements of the contaminations, an outer cylindrical detector close to the surface of piping measures β-rays and γ-rays and an inner cylindrical detector set after a shielding plate for shield of β-rays measures γ-rays. The β-ray counting rates are derived by subtracting γ-ray counts measured by the inner detector from γ- and β-ray counts measured by the outer detector. The piping crawling robot transports the cylindrically-formed double layered type detector with observing inner surfaces of piping. The detection limit for the contamination of 60Co was found to be about 0.17 Bq/cm2 with measurement time of 30 seconds. It is expected that 0.2 Bq/cm2 corresponding to clearance level of 60Co (0.4 Bq/g) can be evaluated with measurement time of 2 seconds, which is equal to measurement speed of 54 m/h. (author)