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16 Cards in this Set

  • Front
  • Back
Identify the purposes of the RWCU System.
maintain reactor water quality by removing fission products, corrosion products and other soluble and insoluble impurities. to minimize the fouling of heat transfer surfaces and limit impurities available for neutron activation.

- The secondary purpose of RWCU is to provides for removal of reactor water from the reactor during all modes of operation, to maintain circulation in the RPV bottom head during periods of low core flow to minimize thermal stratification in the bottom head region and to provide a means for alternate decay heat removal using the non-regenerative heat exchangers.
a. RWCU pumps
Provide force to establish required flow rates, through piping, HX, filters & back to RPV
pump & motor Cooling water supplied by CRD (↑pressure) - then cooled by RBCCW
a. RWCU pumps
Suction from B recirc suction, and bottom head drain
- A pump - primary 100% capacity, rated 400gpm, restricted to 270 if RPV is depressurized
- B&C pumps – 50% capacity, rated 170gpm, restricted to 135gpm if RPV Temp< 200F
a. RWCU pumps
The RWCU pumps will trip on the following conditions:
1) Low system flow of <70 gpm (This trip is bypassed on pump start for about 3 minutes or whenever the pump handswitch is held in “START”.)
2) System suction valves, HV-044-*F001, or *F004, or *F040 not full open
3) Low RECW pressure of 47# with a 10 second time delay
4) Pump high vibration with a 10 second time delay on the 50% capacity pumps.
5) High pump motor cavity temperature on 100% capacity pumps at 140F.
function of the following RWCU components
b. Regenerative heat exchangers
Provide initial cooling prior to demins, and preheats prior to return to vessel.
function of the following RWCU components
c. Non-regenerative heat exchangers
Provide cooling to decrease temp to less than 130F for demin,
Cooled by RECW
Alternative Decay heat removal cooled by DWCW (normally maintained at lower temp.)
function of the following RWCU components
d. Filter demineralizers
Remove impurities from reactor water, two 50% capacity filters, both normally in-service

a. Filter/demins are used to remove impurities in the coolant to maintain purity of the coolant. The filter/demins provide both ion exchange and mechanical filtration.

b. Two (2) 50% capacity filter/demins are provided and normally both are in service. The filter/demin effluent valves normally control system flow rate automatically. When one or both filter/demins are not in service, the bypass valve, HV-044-*F044, is used to establish the desired system flow rate. Note that if 50% capacity pumps are being used when one F/D is removed from service, the bypass valve is throttled open rather than securing a RWCU pump. This limits the number of starts/stops on the pumps, which reduces required maintenance. Throttling is not required if the 100% capacity pump is used.

c. Non-regenerable mixed bed H-OH resin is used in the filter/demins. The mixed bed crushed resin is held on to the filter elements by differential pressure resulting from system flow through the filter/demin vessel. The effluent pH should be in the range of 6.5 - 7.5 with effluent conductivity <0.1 umho/cm. The crushed resin will filter ionic impurities, suspended solids, and fission products.

d. Filter/demin differential pressure of 30 psid will cause the filter/demin outlet valve to close. Also, a resin trap high dp will cause the outlet valves to close. High differential pressures in the filter/demins may cause resin to be forced through the elements, so the unit is shutdown by closing the outlet valve.
function of the following RWCU components
e. Demineralizer holdup
One pump per filter, auto start on low filter flow, prevents resin intrusion into system is restarted (holds precoat on elements when demin is not inservice or on low flow conditions)
9. Filter/Demin Holding Pumps
a. Hold pumps are used to prevent resin from falling off filter elements during RWCU low flow conditions. They are mechanically sealed, single stage, centrifugal pumps that auto start on a low flow condition through the on-line filter/demin.
function of the following RWCU components
f. Drain line restricting orifice
With RPV at 1000psig, limit RPV blowdown flow to 150 gpm
RWCU Line up
a. Normal system Operation
- RWCU takes a suction from the “*B” recirculation pump suction line and from the bottom head drain.
- Coolant at 520F and 350 gpm then passes through two system isolation valves and into one 100% capacity pump with two 50% capacity pumps as backup.
- Flow is then directed to the regenerative heat exchanger on the tube side and then at 210F to the non-regenerative heat exchanger through the tubes.
- Coolant at 110F then passes through two parallel filter demineralizers and then back through the regenerative heat exchanger on the shell side.
- Coolant at 430F is returned to the reactor via “*A” feedwater line and through the RCIC discharge line which is connected to the “*B” feedwater line.
RWCU Line up
c. Blowdown mode
- When RWCU is aligned to remove inventory from the reactor, the flow path is similar to the normal flowpath with the exception that part of the flow heading back to the shell side of the regenerative heat exchanger is diverted to the dump line through the dump flow controller.
- This dump flow can be sent to the main condenser, the equipment drain tank or condensate storage tank.
- Note that since less flow is passing through the regenerative heat exchanger, more heat load is placed on the non-regenerative heat exchanger and filter/demin inlet temperature must be monitored to prevent automatic system isolation at 140ºF. This prevents resin damage.
RWCU Line up
d. Refueling mode
- Alternate decay heat removal is accomplished using RWCU by bypassing the regenerative heat exchanger (on the return path – shell side) and aligning Drywell Chiller Water as the heat sink for the non-regenerative heat exchanger.
- Coolant return flow is directed to the reactor through two manual primary containment isolation valves which bypass the high pressure feedwater piping (*016 & *017 valves).
- The feedwater isolation valves are normally closed during an outage.
RWCU system support system
Removes heat from non regen HX, cooling to RWCP pumps seal cooler, pedisal and bearings, RWCP pump trips if RECW pressure < 47 psig for 10 seconds
RWCU system support system
b. 480 VAC Distribution
- RWCU pump power supplies are “A” D*34, “B” *24B, “C” *14B.
RWCU system support system
d. CRD
purge flow for 100% capacity to A RWCU pump only, high temp in seal will trip the pump
Select the conditions, which will cause a RWCU isolation (Gp. III NSSSS) and summarize the sequence of events that occur upon receipt of an isolation signal.
RPV level < -38 inches *F004 and *F001
Non- Regenerative HX outlet temp > 140F *F004 only
SLC initiation "*A” or “*C” pump will isolate *F001, “*B” pump start will isolate *F004
High Diff Flow> 54.9 gpm for 45 seconds *F004 and *F001
High pump room ventilation delta T> 52F *F004 and *F001
High HX room ventilation delta T > 32F *F004 and *F001
High equipment area temp (pump room 155F, HX room 132F) *F004 and *F001
** RWCU pumps trip on closure either *F001 and/or *F004

RRCS auto start Div will isolate *F001 and Div II will isolate *F004