Reactor auxiliary systems plant shutdown

After various maintenance work, plant operation started again at the beginning of February 1987 but was again hampered successively by water hammer on the A auxiliary feedwater plant piping, putting it out of action for three months, then at the end of March by the detection of a sodium leak on the storage drum. This led to reactor shutdown at the end of May 1987, after a second calibration test on the clad rupture detection systems at 90% of nominal power. 

All safety-grade systems in the PIUS plant are located within the reactor building which encloses the containment, the fuel handling equipment, the fresh fuel storage, the spent fuel storage pool and the emergency control room (the auxiliary shutdown facility) with associated instrumentation, control equipment and batteries for electric power supply. 

The HPCS system can operate independently of normal auxiliary AC power, plant service air, or the emergency cooling water system. Operation of the system is automatically initiated from independent redundant signals indicating low reactor vessel water level or high pressure in the primary containment. The system also provides for remote-manual startup, operation, and shutdown. A testable check valve in the discharge line prevents backflow from the reactor pressure vessel when the reactor vessel pressure exceeds the HPCS system pressure such as may occur during initial activation of the system. A low flow bypass system is placed into operation until pump head exceeds the nuclear system pressure and permits flow into the reactor vessel. 

The four divisions (guard lines) of the protection and safety monitoring system and its uninterruptible power supply, the electrical penetrations through the containment, portions of the plant control system, the main control room and the remote shutdown workstation are concentrated within the northern section of the Auxiliary Building. A large fire or explosion in this area could render these features imusable for a significant amount of time. Such an event would most likely result in an immediate reactor trip, due to the loss of power and control... 

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