Thirty-three experiments or more are included in the system with a plant factor of about 45%. It has been an extremely reliable system despite the usual crop of minor incidents.

In general, the design was overenthusiastic about scram signals. There are trips on period, flux, sodium level, coolant flow rate, flow rate of change, upper plenum pressure, 12 trips of primary pumps, fire in the building, bulk sodium temperature, and many other temperatures. There are check points against changes in interlocks. As a result scrams occur two or three times a month from these 69 independent signals. Each scram wasted about 8 hr when diagnostic and return to power periods are included. Now the number of trip signals is being reduced. Excessive tripping facilities create an un­healthy and unsafe atmosphere of a nuisance protective system. Operators are under considerable pressure to keep things running and a large number of trips that are spurious create a hazardous frame of mind. On some occa­sions in some plants this has lead to a manual locking out of some sensors. It is far better to include power setbacks in the system and to avoid scrams on selected signals. (It is worthwhile also to note the French experience (37), in which 161 design primary pump trips were eventually reduced to one. This stated that the pump should be tripped if there were no flow. This trip was also removed.)