May. 22, 2006

The Japan Atomic Energy Agency (President Yuichi Tonozuka) (herein after referred to as JAEA) has studied an advanced tritium removal technology as a significant subject for fusion safety. Tritium is a fuel of fusion reactors, and must be removed in the case where the tritium is released into buildings of fusion facilities. It has first been successful in the world to remove tritium by using bacteria in stead of a conventional method under the collaboration with Ibaraki University (Professor Yusuke Ichimasa).

The fusion reactor treats gaseous radioactive tritium as a fuel, so that it is significant to confine tritium in a system safely. In ITER, tritium is multiply confined in a facility. The tritium released into the facility is oxidized to water by the noble metal catalyst at high temperature, and is then removed by an adsorption bed as water. The tritium in a facility is thus controlled to prevent environmental release.
Professor Ichimasa found that bacteria oxidized hydrogen into water at atmosphere temperature. The microbes commonly live in soil. We, JAEA pay attention to this remarkable result, and started studies to develop an original tritium removal method using the bacteria under the collaboration with Ibaraki University. The tritium removal method using the bacteria would allow us to increase the efficiency of the tritium removal facilities.

Conventionally, bacteria have been used for the industries of fermentation, food and medicine. In this research, however, we tried to use a special ability of bacteria for rather fast oxidation reaction of hydrogen gas in air. A lot of bacteria were sampled and cultured from various soil in forest, and tested the HT oxidation ability (hydrogenase enzyme activity). Fortunately, we succeeded in finding the special bacteria with larger hydrogenaze activity and its active conditions. Using the special bacteria, we fabricated bio-detritiation reactors and connected to the Caisson Assembly for Tritium Safety study (12 m³) in JAEA/TPL (Tokai-village, Ibaraki-pref.), in where tritium could be released intentionally up to 37 GBq, and confirmed its detritiation factor (DF). The result showed that the bio-reactor could oxidize tritium gas in reasonable speed comparing with the catalytic reactor and that the DF corresponded to the level required for ITER. Moreover, a hydrogenaze activity of the cultured bacteria was maintained about 70% after one year storage under 4 degree-C. Therefore, it was found that the bio-reactor could be used to a new detritiation system. In future, if this bio-reactor technology is used to a practical plant, the system dose not require any high temperature rare metal catalyst and its expensive cost for fabrication and operation. Furthermore, the waste can be minimized even at the replacement of reactors. From now on, we plan further long-term durability tests of bio-reactor to use as a practical detritiation system. Also we proceed to R&D of bio-reactor for processing hydrogen and/or other gases.

•Success in development of the epoch-making the detritiaiton method by using the biotechnology --Realization in collaboration with Ibaraki University and JAEA--