Separate steam seal system for turbines for nuclear power generation

As the results of the reduction in permissible radiation exposure at the periphery of the nuclear power station and the adoption of activated charcoal hold-up device in off-gas system, the influence of turbine gland-seal off-gas system on radiation exposure became relatively higher. So, the adoption of the separate steam seal system (4S system) was considered and put into practice in No.3 plant of Fukushima Nuclear Power Station for the first time in the world. The 4S system does not employ the turbine leakage steam to its axial seal portion, but is provided with the steam evaporator to heat non-radioactive water with main or extracted steam to generate the steam that seals each turbine axial seal portion. This is explained by being compared with the conventional system. Since the 4S system is employed for the first time, the performance tests were carried out to inspect the system-and evaporator performance, using the practical turbine in No.3 plant in Fukushima Nuclear Power Station. It was divided into the start-up confirmation, steam evaporator performance, and transient response tests, and the satisfactory results were obtained. (Wakatsuki, Y.)