Emergency Operating Procedure

EOP 6 Rupture in Buffer Seal System Revision 2 2/6/64

A. Symptoms

• 1. Important annunciators which may be actuated:
  • a. LOW LEVEL BUFFER SEAL SURGE TANK.
  • b. LOW PRESSURE SEAL BOOSTER PUMP DISCHARGE.
  • c. LOW DIFF. PRESSURE REACTOR VS. SEALS.
  • d. LOW LEVEL PRESSURIZER.
  • e. LOW PRESSURE PRIMARY SYSTEM.
• 2. Reactor may scram automatically due to primary system pressure loss below 1505 psig.
• 3. Low seal water flow to and from seals.
• 4. Low combined-seal-water return flow.
• 5. SL-9V fully closed in automatic operation.
• 6. Low buffer seal booster pump discharge pressure.
• 7. Low buffer seal charge pump discharge pressure.

B. Immediate Action

• 1. EVALUATE THE SITUATION to determine that a rupture has occurred in the buffer seal system. Locate and isolate the rupture if possible. Check visually in the charge pump rooms and port stabilizer room for leaks in piping downstream from booster pumps.
• 2. ACKNOWLEDGE ANNUNCIATORS as convenient.
• 3. If the pressurizer water level is dropping, close PP-1V, PP-3V, PP-2V, and PP-4V, letdown cooler isolation valves. If the pressurizer level continues to drop then it is a primary system rupture. (Refer to EOP #1).
• 4. If the pressurizer water level is not dropping, transfer makeup to primary system from SL-121V to SL-6V to ascertain that the leak is not in the makeup line. If the leak cannot be isolated, shut down the buffer seal and purification system when surge tank level reaches "0", if not done before. Scram the reactor, cut back the primary pumps to three at half speed and start DK system when buffer seal system is shut down. If the pressurizer level starts dropping after shutting down the buffer seal system, then it is a primary system rupture. (Refer to EOP #1).
• 5. Check that the ADGs have started and paralleled with the main bus.
• 6. Trip the turbine generators and secure the boiler blowdown valves SS-21V and SS-22V.
• 7. REPAIR LEAK, if possible.
• 8. Makeup may be added to buffer seal surge tank as follows:
  • a. CLOSE (or check closed) VALVES PD-36V, PD-37V, PD-38V.
  • b. OPEN VALVE PD-46V (or 47V), VALVE PD-35V, and ISOLATION VALVES ON PURIFICATION ION EXCHANGERS AND FILTERS.
  • c. START WASTE TRANSFER PUMP to makeup into the buffer seal surge tank.
  • d. Makeup may also be supplied from the secondary demineralizer.

C. Follow-Up Action

• 1. Start the auxiliary boiler to supply the hotel steam load.
• 2. Put the primary loop purification and buffer seal systems back into operation.

D. Discussion

The rupture postulated here is a large leak in the buffer seal system. Leaks in this system could be classified in two ways: those occurring in the piping inside the containment vessel, and those occurring in the piping outside the reactor space. High pressure is normally subjected to the piping from the discharge of the buffer charge pumps. The worst type of leak could be one between the check valve SL-5V and the seals; this rupture would be comparable to that discussed in EOP #1 for primary system rupture. For such a rupture the leakage rate would be something less than 10 gpm per seal. This condition would cause the primary system pressure to drop. The reactor should be scrammed as soon as possible if not done so automatically.

The lower O-rings which are made of Buna-N material are the only portion of the seal assembly which is susceptible to damage when the buffer seal charge pumps are shut off. These O-rings depend on the seal water to keep them below 350F. Sustained exposure in excess of 350F for periods of six to eight hours cause them to harden and reduce their effectiveness as seals.

As soon as the rupture can be isolated and repaired, the primary system purification and buffer seal systems should be started again. The operator should closely observe the operation of the system, particularly the flow rates into the buffer seals and the return from the seals. The primary purification letdown flow rate should be observed also. For this accident, it is expected that there will be an increase in seal leakage inward to the primary system due to hardening of the O-rings. My text copyright 2020 Tommy Johnson, all rights reserved. I believe the Savannah documentation is property of MARAD or the US government.