Akihiro Hiroki

Preparation of polymer gel dosimeters based on less toxic monomers and gellan gum

New polymer gel dosimeters consisting of 2-hydroxyethyl methacrylate (HEMA), triethylene glycol monoethyl ether monomethacrylate (TGMEMA), polyethylene glycol 400 dimethacrylate (9G), tetrakis (hydroxymethyl) phosphonium chloride as an antioxidant, and gellan gum as a gel matrix were prepared. They were optically analyzed by measuring absorbance to evaluate a dose response. The absorbance of the polymer gel dosimeters that were exposed to (60)Co γ-rays increased with increasing dose. The dosimeters comprising HEMA and 9G showed a linear increase in absorbance in the dose range from 0 to 10 Gy. The dose response depended on the 9G concentration. For others comprising HEMA, 9G and TGMEMA, the absorbance of the polymer gel dosimeters drastically increased above a certain dose, and then leveled off up to 10 Gy. The optical variations in these polymer gel dosimeters were also induced by x-irradiation from Cyberknife radiotherapy equipment. Furthermore, the exposed region of the latter polymer gel dosimeter exhibited a thermo-responsive behavior.

Radiation-Induced Degradation in Ion Exchange Resins for a Water Detritiation System

The combined electrolysis and catalytic exchange process has been selected for the water detritiation system for the ITER. In the front-end process of tritiated water electrolyzer composed of a solid polymer electrode, ion exchange resin beds are installed for processing effluent ions in the enriched tritiated water from the catalytic exchange column to avoid the deterioration of the solid polymer electrode. The tritium concentration in the circulation resin bed is evaluated to reach 1.09x1015Bq/m3. It is thus important to note the radiation-induced degradation in ion exchange resins. We studied the degradation effects in Amberlite[registered] and Diaion[registered] organic ion exchange resins caused by the irradiation with electron beam up to the integrated dose of 1500kGy. The procedures D2187-94 of the American Society for Testing and Materials were adopted for the evaluation of the water retention capacity, the backwashed and settled density, the salt splitting capacity, and the total exchange capacity of particulate ion exchange resins. A 20% decrease of total exchange capacity of the cation exchange resin, when irradiated up to 1500 kGy at room temperature, has been observed.

New polymer gel dosimeters consisting of less toxic monomers with radiation-crosslinked gel matrix

New polymer gel dosimeters consisting of less toxic methacrylate-type monomers such as 2-hydroxymethyl methacrylate (HEMA) and polyethylene glycol 400 dimethacrylate (9G) with hydroxypropyl cellulose (HPC) gel were prepared. The HPC gels were obtained by using a radiation-induced crosslinking technique to be applied in a matrix instead of a gelatin, which is conventionally used in earlier dosimeters, for the polymer gel dosimeters. The prepared polymer gel dosimeters showed cloudiness by exposing to 60Co γ-ray, in which the cloudiness increased with the dose up to 10 Gy. At the same dose, the increase in the cloudiness appeared with increasing concentration of 9G. As a result of the absorbance measurement, it was found that the dose response depended on the composition ratio between HEMA and 9G.

SOLID-POLYMER-ELECTROLYTE TRITIATED WATER ELECTROLYZER FOR WATER DETRITIATION SYSTEM

Abstract A solid-polymer-electrolyte (SPE) water electrolyzer for high-level tritiated water was designed for the Water Detritiation System (WDS). Polymeric materials were selected from a main viewpoint of radiation durability to keep their functions beyond ITER-WDS requirement (530kGy). Our selection was Pt + Ir applied Nafion® N117 ion exchange membrane, VITON® O-ring seal and polyimide insulator. A γ-ray irradiation test of the SPE cell demonstrated the durability of the cell against 530kGy. The electrolyzer is designed to handle around 9TBq/kg of high-level tritiated water. The detritiation of the polymeric materials is thus a critical problem for the maintenance or for the disposal of the electrolyzer. As for the Nafion membrane, most of tritiated water in the membrane was rapidly removed by such as vacuum dehydration. It was difficult, by contrast, to remove bound tritiated water in the membrane. An effective method to remove tritiated water in the bound water is to promote an isotope exchange.

Enhancement in dose sensitivity of polymer gel dosimeters composed of radiation-crosslinked gel matrix and less toxic monomers

Polymer gel dosimeters based on radiation-crosslinked hydroxypropyl cellulose gel were prepared, which comprised 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol #400 dimethacrylate (9G) as less toxic monomers and tetrakis (hydroxymethyl) phosphonium chloride (THPC) as an antioxidant. The dosimeters exposed to 60Co γ-rays became cloudy at only 1 Gy. The irradiated dosimeters were optically analyzed by using a UV- vis spectrophotometer to evaluate dose response. Absorbance of the dosimeters linearly increased in the dose range from 0 to 10 Gy, in which dose sensitivity increased with increasing 9G concentration. The dose sensitivity of the dosimeters with 2 wt% HEMA and 3 wt% 9G was also enhanced by increment in THPC.