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84

Information Notice No. 93­84: Determination of Westinghouse Reactor

Coolant Pump Seal Failure

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

October 20, 1993

NRC INFORMATION NOTICE 93‐84: DETERMINATION OF WESTINGHOUSE REACTOR COOLANT

PUMP SEAL FAILURE

Addressees

All holders of operating licenses or construction permits for pressurized

water reactors (PWRs).

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to a potential problem that could result from the

use of Westinghouse‐designed reactor coolant pump (RCP) shutdown procedures

for pumps whose No. 1 seals have failed. It is expected that recipients will

review the information for applicability to their facilities and consider

actions, as appropriate, to avoid similar problems. However, suggestions

contained in this information notice are not NRC requirements; therefore, no

specific action or written response is required.

Background

Westinghouse supplied the Braidwood Station RCPs, incorporating a three‐stage

seal series arrangement to limit coolant flow up the pump shaft. The No. 1

seal, the main seal of the pump, is a controlled‐leakage, film riding face

seal. The No. 2 and No. 3 seals are rubbing face seals. During normal

operation, an injection flow of nominally 30.3 liters [8 gallons] per minute

enters the pump below the No. 1 seal (see Attachment 1). Here the flow

splits. A portion (approximately 18.9 liters [5 gallons] per minute) flows

down through the thermal barrier heat exchanger and enters the reactor coolant

system. In this manner, the primary coolant is prevented from entering the

radial bearing and seal section of the pump unit. The remainder (11.4 liters

[3 gallons] per minute) (controlled leakage) passes through the pump radial

bearing and enters the No. 1 seal. Above the No. 1 seal, most of the flow

leaves the pump through the No. 1 seal leakoff line and returns to the

chemical and volume control system. Minor flow passes through the No. 2 seal

and its leakoff line to the reactor coolant drain tank. A back flush

injection of 0.8 liters [0.21 gallons] per hour from a head tank flows into

the No. 3 seal between its "double dam" seal area. At this point, half of the

flow passes through one side of the seal and out the No. 2 seal leakoff line

while the remaining flow passes through the other side and out the No. 3 seal

leakoff line. This arrangement ensures essentially zero leakage of reactor
coolant from the pump.

9310140192.

IN 93‐84

October 20, 1993

Page 2 of 3

During normal operation, the No. 1 seal is subject to full reactor coolant

system pressure. When the injection flow passes through the No. 1 seal, it

produces a pressure drop of approximately 15.41 MPa [2235 psi]. The No. 2

seal has the capability to withstand full operating pressure, and its major

function is to act as a backup in case the No. 1 seal fails. If the No. 1

seal fails, leakage through the No. 2 seal increases. The No. 2 seal high

leak flow alarm actuates at 3.8 liters [1 gallon] per minute.

Description of Circumstances

In the middle of 1992, while developing shutdown procedures for the RCPs at

the Braidwood Station, Commonwealth Edison Company (the licensee) found that

its abnormal operating procedure contained inadequate instructions for

responding to a failure of the RCP No. 1 seal. On a high RCP No. 1 seal

leakoff condition, the abnormal operating procedure directed the operating

personnel to check the condition of the No. 2 seal. If the No. 2 seal was

acting as the primary pressure boundary on the basis of leakage of at least

3.8 liters [1 gallon] per minute from the No. 2 seal, the procedure required

that the RCP be shut down. If the condition of the No. 2 seal was normal, the

procedure required no further action and gave no further guidance.

Discussions with Westinghouse indicated that the condition of the No. 2 seal

might not be a sufficient indication of the operability of the No. 1 seal.

Discussion

The inadequacies in the operating procedure stem from the limitations of the

instrumentation used to monitor the leakage. The relevant No. 1 seal

instrumentation limits maximum readings to 22.7 liters [6 gallons] per minute.

Although the No. 2 seal high leak flow alarm was set at 3.8 liters [1 gallon]

per minute, very high No. 1 seal leak rates, more than 113.6 liters

[30 gallons] per minute, are needed for the No. 2 seal to reach this flow

rate. Thus, the No. 1 seal could have substantial leakage (e.g., 22.7‐113.6

liters [6‐30 gallons] per minute) even though the No. 2 seal high leak flow

alarm was not actuated. In the mean time, the RCP seal system might be

severely damaged if loss of injection were to occur or the No. 1 seal leak

rates were more than 30.3 liters [8 gallons] per minute. Therefore,

monitoring for high No. 2 seal leakage is not a reliable method of determining

whether the No. 1 seal has failed.

After finding that the condition of the No. 2 seal might not indicate the

operability of the No. 1 seal, Westinghouse provided guidance for the

Braidwood Station that significantly enhances operator ability to determine if

immediate shutdown of an RCP is required or if a more orderly shutdown can be

conducted. Westinghouse completed a safety evaluation and issued Technical

Bulletin, NSD‐TB‐93‐01‐R0, "Revised Procedures for RCP Shutdown with No. 1

Seal Leakage Outside Operating Limits," dated March 30, 1993, to other PWRs

that might be affected. An excerpt from this document is attached to this

information notice (see Attachment 2).

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IN 93‐84

October 14, 1993

Page 3 of 3
This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

/s/'d by BKGrimes

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Steve DuPont, RIII

(815) 458‐2852

Martin Farber, RIII

(708) 790‐5774

Chu‐Yu Liang, NRR

(301) 504‐2878

Attachments:

1. Simplified Braidwood Seal Water Injection

and Leakoff Flow Diagram

2. Excerpt from Westinghouse Technical

Bulletin, NSD‐TB‐93‐01‐R0, "Revised

Procedures for RCP Shutdown with No. 1

Seal Leakage Outside Operating Limits"

3. List of Recently Issued NRC Information Notices

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