PP-21 and SL-37 Primary Purification and Buffer Seal System
1. One set of letdown coolers is in service with cooling water regulated to maintain 110F. outlet temperature.
The other set of coolers is on standby.
2. One ion exchanger is in service with letdown flow regulated between 10 gpm and 30 gpm. For higher letdown flows between
30 gpm and 60 gpm a second ion exchanger is used. For letdown flow requirements of less than 10 gpm, a particular ion exchanger
is to be designated. Depending upon the letdown flow rate, one or two units are on standby.
3. The ion exchanger and effluent filter bypass valves are closed.
4. One effluent filter is in operation with pressure drop less than 25 psi. The other filter is on standby, for
letdown flows of 30-45 gpm, the second filter is used.
5. Makeup may be in either Auto or Manual. Dump is to be in Manual only.
6. One booster pump is supplying 50 psig or more discharge pressure. The other pump is on standby.
7. Two charge pumps are in operation at half speed. Pump discharge pressure is approximately 60 psi above
primary system pressure. The third pump is in a reserve status and switched off.
8. Corresponding desurgers for the operating and standby charge pumps are in service.
9. Gland cooling flow is being supplied to the operating charge pumps.
10. During a primary system heatup or cooldown of 30F. or more, a flush flow of between 0.5 and 2 gpm is being supplied
to the primary pumps with the exception of PS-P1.
11. Pressure breakdown and flow control bypass valve PP-6V is not used when primary pressure is above 900 psig.
12. Pressure drop through one charge pump discharge strainer is less than 25 psi. The other strainer is on standby.
13. One buffer seal cooler is in operation with outlet seal water temperature 120F or below. The other cooler is on
standby. SL surge tank is less than 140F.
14. Once a charge pump has created a discharge pressure, a charge pump is running at all times to prevent loss of desurger
15. Letdown flow is being controlled between 10-30 gpm by one flow control valve, the other is closed and on Manual.
For flows between 30-45 gpm, both valves are used.
16. Bypass SL 9V is in Auto and regulating charge pump discharge pressure at approximately 60 psi above primary system
17. Primary makeup valve SL-121V is in Auto to maintain pressurizer level at approximately 27 in. Auxiliary makeup valve
SL-6V is in the off position and is only used to makeup when the port loop is isolated.
18. Makeup water is supplied to the primary system at a minimum temperature of 80F when the primary system temp. is
250F or above.
19. Seal water is supplied to the rods, and the seal return flow from an individual control rod is less than 0.5 gpm.
20. NOTE: Letdown flow is limited to 45 gpm due to flashing of CW water in letdown coolers.
[Flashing means boiling in this context.]
Minimum Conditions for Reactor Operation
1. One letdown cooler is capable of reducing primary water letdown temperature to 130F or lower.
2. An SL surge tank pressure of 5 psig is available.
3. One operable desurger in system.<
4. Charge pump discharge pressure maintained at least 25 psig above primary system pressure. SL-8V closes when pressure
drops to 10 psi above primary system pressure.
5. One effluent filter is in service.
6. One ion exchanger is in operation to act as a filter even though the resin is depleted.
7. One buffer seal cooler has an outlet buffer seal water temp. of 120F or below, and SL surge tank temp. is less than
8. Surge tank water level must be implied to be in its operating range by instrumentation of indicated levels, alarms and
9. The buffer seal bypass control valve (SL-9V), the primary system makeup valve (SL-121V) and the auxiliary makeup valve
SL-6V, can be controlled from the control console.
10. Makeup water is supplied to the primary system at a minimum temperature of 80F when the primary system temperature is
250F or above.
11. One letdown flow control valve (PP-7V or PP-8V) is operable.
12. The following requirements apply to the buffer seal water:
a. Seal water must be supplied to the rods at least thirty (3) minutes prior to rod withdrawal when the primary
system temperature is less than 250F.
b. Seal water must be supplied to the rods at least four (4) hours prior to rod withdrawal when the primary system
temperature exceeds 250F.
c. After seal flow has been stopped or interrupted for any reason, run seal flow for fifteen (15) minutes plus
the time of interruption to to a maximum of four (4) hours before withdrawing any control rod.
d. Seal water is supplied to the rods when any rod is not fully in.
e. Seal return flow from an individual control rod should not exceed two (2) gpm for normal seal operating conditions.
13. The following requirements apply to the primary pump flush water.
a. Flush flow to the pumps must be established when the primary system temperature is to be varied more than 30F.
b. When a pump is stopped for more than thirty (30) minutes, flush flow must be on for at least ten (10) minutes
before the pump is restarted.
c. Flow must be continuous when contamination of the primary system is suspected.
My text copyright 2020 Tommy Johnson, all rights reserved. I believe the Savannah documentation is property of
MARAD or the US government.