Development of colored alumilite dosimeter

In the ITER (International Thermonuclear Experimental Reactor), in-vessel components such as blanket and divertor, which are installed in the vacuum vessel of the ITER, are maintained by remote handling equipment (RH equipment). The RH equipment for maintenance is operated under sever environmental conditions, such as high temperature (50 approx 100 degC), high gamma-ray radiation (approx 1 kGy/h) in an atmosphere of inert gas or vacuum; therefore many components of the RH equipment must have a suitable radiation resistance efficiency for long time operation (10 approx 100 MGy). Typical components of the RH equipment have been extensively tested under an intensive gamma-ray radiation. Monitoring of the radiation dose of the components of the RH equipment is essential to control the operation period of the RH equipment considering radiation resistance. However, the maximum measurable radiation dose of the conventional dosimeters, such as ionization chamber, liquid, glass and plastic dosimeters are limited to be approximately 1MGy which is too low to monitor the RH equipment for the ITER. In addition, these conventional dosimeters do not involve sufficient radiation resistance against the high gamma-ray radiation as well as are not easy handling and low cost. Based on the above backgrounds, a new dosimeter with bleaching of an azo group dye to be applied to a radiation monitor has been developed for high gamma-ray radiation use. The colored alumilite dosimeter is composed of the azo group dye (-N=N-) in an anodic oxidation layer of aluminum alloy (Al sub 2 O sub 3). It can monitor the radiation dose by measuring the change of the bleaching of azo dye in the Al sub 2 O sub 3 layer due to gamma-ray irradiation. The degree of bleaching is measured as the change of hue (color) and brightness based on the Munsell's colors with a three dimensional universe using spectrophotometer. In the tests, the dependencies such as colors, anodized layer thickness, type of azo dy of the crature and ultraviolet radiation were investigated using the various colored alumilite samples. The followings were clarified from the test results; - a red colored alumilite sample has shown remarkable bleaching change compared with blue and green colored alumilite samples, - the characteristic of bleaching depends on dose rate, - the degree of bleaching of thick-anodized layer sample is lower than that of thin- anodized layer, - the bleaching is activated under high temperature (over 75degC), - there is no effect of ultraviolet radiation (310 approx 410 nm). As a whole, a red colored and a blue colored alumilite samples are suitable to measure under high dose rate and low dose rate conditions, respectively. For example, a red colored alumilite sample made of TAC-RED 105 dye with layer thickness of 25 mu m is measurable up to 70 MGy under high dose rate of 10 kGy/h. On the other hand, a blue colored alumilite sample made of TAC-BLUE RCD dye with layer thickness of 10 mu m is measurable up to 10 kGy under low dose rate of 2 Gy/h. In this paper, the outline of the colored alumilite dosimeter, bleaching mechanism, measurement method and details of the various test results are described.