Simple internal exposure measurement for tritium by expiratory water trapping method using water bubbler

The Tritium Process Laboratory (TPL) is the first facility which uses tritium over 1 gram (1 g=3.58 x 1014Bq) in the fusion research of Japan. Main objections of the TPL are to study basic engineering technology of tritium processing in the fusion fuel cycle and to develop tritium safety systems. Therefore, the few grams of tritium is handled in TPL. Internal exposure is more important than external exposure for the exposure control such as tritium treated facilities. In TPL, the internal exposure inspection is carried out by a simple internal exposure measurement method for tritium using expiratory water trapping apparatus with a water bubbler. The method is applied for workers who have a possibility to intake the tritium with their work. All the workers must also undergo the internal exposure inspection every month period. Generally method for measuring amount of tritium in the urine is used to evaluate the internal exposure. But a pre-processing equipment of urine is needed in this method. The expiratory water trapping apparatus only collect the expiratory water by the water bubbler. Therefore, the tritium internal dose is evaluated using expiratory water trapping apparatus in TPL. However, the fluctuation of collection efficiency of the apparatus before remodeling was about 40 - 90%. The collection efficiency is an important coefficient to evaluate the dose. The factor of fluctuation of the collection efficiency is that all of the tritiated water of the water bubbler in the apparatus can't be poured in the vial. Then, the apparatus was remodeled in order to collect the residual tritium in the apparatus. As the result, the collection efficiency increased about 85 - 96% with small fluctuation after the remodeling. (author)