10 CFR 50.71(e) - Maritime Administration - U.S. Department of ...

Updated Final Safety Analysis Report - (STS-004-002)Following a major pipe rupture inside the containment, it was desirable to reduce the post-accidentpressure. The following design features permitted this pressure reduction:Either the normal or emergency cooling coils in the CC system were used. Heat was removedby forced air circulation if the fans were operable or by natural air circulation if they were not.The possibility of forced circulation was enhanced because the fans at half speed were capableof operating in a steam air atmosphere below 100 psi. Either forced or natural circulation couldhave been increased after the accident by the automatic opening of two large side plates in thecooling ductwork located just below the fans.Pressure reduction was accomplished by spraying water from the fire main into the containmentthrough the CO 2 injection system.Heat removal and pressure reduction was accomplished by partially flooding the lower reactorcompartment so that heat flows through the containment shell into the flooding water.Following the MCA, the possibility existed that radioactivity could escape through some of the fluidpenetrations. In the case of most penetrations, this escape would have occurred only if the MCAbroke a pneumatic, hydraulic, or water pipe inside the containment to permit radioactive fluid toleave the containment through the pipe. However, this escape was prevented because each fluid linethat is in service during normal operation contained either a check valve or a quick closing shutoffvalve. With only two exceptions, these quick closing valves are tripped closed if containmentpressure reaches 5 psig. The two exceptions were the two heavy-walled, 8-inch main steam lines,which were secured from the main control room because of the possible desire to continue operatingthe ship’s service turbine generators for a brief period after the accident.Because the containment was inaccessible during operation, hydrogen content of the containmentatmosphere, neutron level outside the primary (neutron) shield tank and the gamma level near thecontainment air lock plus temperature, pressure and humidity parameters could be monitored.The use of hydraulic oil in the containment meant that there was a possibility of fire if a combustionsupportingatmosphere is present. When the NSS began operations some leaking of hydraulic fluidfrom the control rod drive system into the containment was experienced. Since the fluid wasflammable and under some conditions was subject to flashing when spilled on the hot vesselsurfaces, the containment atmosphere was inerted with a nitrogen (N 2 ) blanket to eliminate thepossibility of combustion (less than 10% oxygen). There were other occasions of leaking hydraulicfluid after the containment was inerted, but no combustion problems resulted. A complete sparecharge of nitrogen was kept aboard the ship to recharge the containment if an outside supply wasunavailable. The containment inerting arrangement is shown in Figure 4-2.Another feature of the containment design provides assurance that the containment would notcollapse should the ship be involved in an accident which results in sinking. On the lower half of thevessel are two spring-return, bolted, flooding hatches which open and permit sea water to enter thecontainment if the ship sinks to a depth of 100 feet or more. When the containment is flooded andthe pressures are equalized, the hatches re-close, thereby preventing escape of water from thecontainment through the flooding hatches. These hatches remain installed but have not been verifiedfunctional since final shutdown in November 1970.For a sinking accident in shallow water, the containment has four 2” salvage connections on thecupola head. Shutoff valves are located immediately adjacent to the vessel on each of theseconnections and blank flanges are installed on the open end of each valve.Rev. VI 35