Evaluation of In-water Wireless Transmission System under the Conditions Simulated the Severe Accident

Since the accident of TEPCO Fukushima Daiichi Nuclear Power Station [1], [2], monitoring instruments for commercial LWR have been required to be able to maintain measurement function and transmit important information of the nuclear facilities to outside even under environment with high-temperature and radiation(severe environment). Therefore, as a part of R&D program for Plant Safety Enhancement of the Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry (METI), Japan, development of monitoring system which can be used under the severe environment was started. The developing system, by transmitting critical information (water temperature, water level and etc.) of spent fuel storage pool to the outside with wireless transmission of visible light signal, is for monitoring spent fuel. However, under severe environment that this system is used, maximum gamma-ray total dose of 1MGy, temperature rise up to $100^{\circ}C$ and etc. are predicted [3]. Furthermore, if bubbles, turbidity, and obstacle occur in water of the pool, it is predicted that the transmission of visible light signal will be affected by them.