APPENDIX 1
EXAMPLE INFORMATION ON THE SIZEWELL B HPI SYSTEM
Refer to Fig 1 for a line drawing of the essential process routes of the system.
The Sizewell B HPI system is a 4-train system, injecting water to the primary circuit through a route connected from each train to one leg of the circuit.
System dependencies are:
AC electric power pump motors )
Component cooling system (pump motors & room cooling) ( operation in the absence of component cooling has not been quantified and is not assumed in the safety case )
Two pumps are cooled from CCW train A, and two from CCW train B.
Water supply is initially from the refuelling water storage tank, Recirculation is direct from containment sumps, and switchover is automatic. HPI recirculation routes are not cooled by heat exchangers.
Pumps are segregated into two separate halves of the auxiliary building, and to a lesser extent within each half (see Fig 2 )
Pump shutoff head is less than normal primary pressure. System initiation is on a safety injection signal.
Success criteria
Large LOCA
:
Small LOCA
3 HPI pumps are necessary for success in the absence of any function of the LPI system
1 HPI pump is necessary in conjunction with one LPI pump functioning.
One HPI pump is adequate for injection and recirculation.
( Medium LOCA is not specifically considered in the safety case, but is inc- orporated into large and small LOCA categories. Hence the requirement for one HPI pump in some large LOCA cases. )
(Note that the HPI system capability to perform the LPI injection function for a large LOCA is unusual for a PWR )
(For all cases of broken legs, the HPI train connected to the broken leg is assumed unavailable for injection. Hence the requirement for 3 HPI pumps in large LOCA is a 3 out of 3 requirement in the absence of LPI system function
Additional information
HPI control can be achieved via two local motor control centres, one in each half of the auxiliary building. Initiation signals and power switching are accomplished by the 4-train plant protection system and emergency safety features actuation system, located in the control building and annex. Delayed action ( circa 1 hr ) of two pumps can be achieved from the emergency control room, which is normally unmanned.
Design of the HPI system is to full safety and seismic standards (glass 1 ) The design reliability target for fully supported operation is 10 failures per demand.
(This item is not necessarily expected for Daya Bay systems ) .
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