The containment shell is sealed at all times during plant operation. Entry to the shell will be made only after the reactor has been shut down, the shell purged with air, and the radiation level has dropped below 200 mr per hour. The bottom half of the shell rests in a cradle of steel surrounded by a 48-inch-thick wall of reinforced concrete. The top half of the containment shell is covered by a 6-inch layer of lead plus a 6-inch layer of polyethylene. During normal power operation, this reduces the radiation level to less than 0.6 mr per hour at the nearest point of access by the crew. CONTAINMENT SHELL AIR CONDITIONING This system maintains a constant maximum ambient temperature of 140° F. and a maximum relative humidity of 72 percent inside the containment shell. The system operates in conjunction with the intermediate cooling water system, using 95° F. water. During normal operation, the containment shell is sealed and no outside air will enter or leave the vessel. Ambient conditions will be maintained by regulating the cooling water flow as required according to instrument readings on the control panel. In all areas where crew members have unlimited access, radiation levels will be less than 5 rem integrated dosage per year, the recommended maximum annual exposure of workers in the atomic energy field. Assuming that passengers would move about the ship, and on the basis of their calculated average distance from the reactor, the average exposure of a passenger remaining aboard for a year would be under 0.5 rem, i.e. ¹/₂₀ of the occupational value. The 5 rem area is relatively small and not in general use. No crew member will be aboard ship or in the 5 rem area continuously for a full year, and it is doubtful that any crew member will actually receive an integrated dose of more than 0.5 rem in a year. ELECTRICAL SYSTEM This system supplies power to the reactor system and its auxiliaries and is designed to operate with a high degree of reliability to assure reactor safety during all phases of operation and shutdown. It includes all load control and protective devices, containment wiring, metering, interlocking and alarms associated with electrical loads for the reactor system. Power for the system normally is supplied by two turbine-generators, each rated at 1,500 kw, 0.8 pf, 450-volts, 3 phase and 60 cycles. For increased reliability, a double bus type arrangement is used. In the event of a bus fault, an automatic transfer of all vital loads to the other bus will occur. During normal operation, a circuit breaker ties the two busses together. RADIATION MONITORING The radiation monitoring system of the SAVANNAH keeps a constant check on the intensity of radiation at various points within the reactor system as well as areas remote from the power plant. This system is divided into two areas for this description. They are power-plant monitoring and health physics monitoring. The latter is covered under its own heading.