Even if the coolant is conditioned out of the reactor before the first filling, impurities and contamination will degrade its quality during operation, and mainly during the outages, when the vessel has to be open to the outside, for the maintenance of its components. Therefore, heaters are foreseen at the very bottom of the reactor to heat the bulk up to the required temperature, at which gas (H2 or steam) is injected at the bottom. A structure is attached to the four boxes. That structure supports a frame installed on the bottom of the inner vessel. The frame supports spray tubes and electrical heaters used for the control of the coolant chemistry. The purification process operates with a satisfactory kinetics only above 350 to 400 °C. Hence, the bottom frame supports a grid made of heating elements and spray tubes. Using the 4 boxes to route the gas lines and the electrical leads to the outside, there are four groups of heaters/sprays, each made of three independent electrical heaters and two gas lines running parallel to each other. The electrical power required is evaluated to some 600 kW, for the compensation of the heat losses at 400 °C, to allow a reasonable time to reach the process temperature and to provide some reserve, in case of failure of a heating element. |