Bulletin 85-01: Steam Binding of Auxiliary Feedwater Pumps
OMB No.: 3150-0011
Expiration Date: 9/30/86
IEB 85-01
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
October 29, 1985
IE BULLETIN 85-01: STEAM BINDING OF AUXILIARY FEEDWATER PUMPS
Addressees:
For Action - Those nuclear power reactor facility licensees and construction
permit (CP) holders listed in Attachment 1.
For Information - All other nuclear power reactor facilities.
Purpose:
The purpose of this bulletin is to inform licensees and CP holders of a
potentially serious safety problem that has occurred at certain operating
facilities involving the inoperability of auxiliary feedwater (AFW) pumps as
a result of steam binding. Certain PWR licensees and all PWR CP holders are
requested to take further action to prevent similar events from occurring at
their facilities and to document those actions taken or planned.
Description of Circumstances:
Numerous events have been reported where hot water has leaked into AFW
systems and flashed to steam, disabling the AFW pumps. Events at Robinson 2
in 1981 through 1983, Crystal River 3 in 1982 and 1983, and D. C. Cook 2 in
1981 were summarized in IE Information Notice (IN) 84-06, issued in January
1984. Also in January 1984, the Institute of Nuclear Power Operations (INPO)
issued Significant Event Report (SER) 5-84 detailing events at Robinson 2
and Farley. In April 1984, INPO issued Significant Operating Experience
Report (SOER) 84-3 that discussed another event at Surry 2 in 1983.
The NRC's Office for Analysis and Evaluation of Operational Data (AEOD)
issued a case study report entitled "Steam Binding of Auxiliary Feedwater
Pumps" in July 1984. This study identified 22 events since 1981; 13 of these
occurring in 1983. Based on operating experience, it appears that
backleakage into AFW could occur in any PWR. In a number of plants, the two
motor-driven pumps feed into a single pipe which feeds into the steam
generator; therefore, a leaking valve in that pipe increases the probability
of steam binding in both trains of AFW. Also, multiple AFW pumps often take
suction from a common manifold; therefore, if one pump becomes steam bound
because of leaking check valves, the steam can heat the common suction and
cause other pumps to become steam bound.
8510250539
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IEB 85-01
October 29, 1985
Page 2 of 4
AFW capability is needed for normal shutdown and transient conditions as
well as for accident mitigation. The AEOD case study examined the effects of
steam binding on a sequence in which there was a loss of the power
conversion (steam generation) system after a transient other than
loss-of-offsite power. A probabilistic risk analysis had previously shown
this sequence to be a dominant contributor to the core-melt risk for a
sample plant (Sequoyah). The case study indicated that unavailability of the
AFW system as a result of steam binding contributes significantly to the
risk of core melt in PWRs. Monitoring AFW to detect backleakage and to
promptly correct the situation if backleakage occurs would reduce the
probability of steam binding.
Since the AEOD study was issued, a series of events involving backflow of
hot water into the AFW system occurred at McGuire 2 over a period of 7 days
in August 1984, before effective corrective action was taken. One of these
events involved overpressurization of the suction line and damage to
instruments. In November 1984, Catawba 1 experienced backflow of hot water
into AFW resulting in fumes from insulation and blistering of paint. In
December 1984, the NRC's Office of Nuclear Reactor Regulation (NRR)
determined that steam binding of AFW was a generic issue and assigned it a
high priority (Generic Issue 93, "Steam Binding of Auxiliary Feedwater
Pumps").
To determine the extent of the safety issue and the need for short-term
corrective actions, the NRC's regional offices conducted a survey in April
and May of 1985. Of the 58 operating reactors surveyed, 39 had temperature
monitoring of AFW piping at least once per shift. Of the remaining 19, 17
had normally closed gate or globe valves in the pump discharge path in
addition to check valves, or some unique feature such as complete separation
of trains that made serious safety problems unlikely. The remaining 2
licensees have subsequently decided to monitor AFW piping temperature.
Although some degree of action has been taken at all units, many have not
incorporated these actions into procedures to detect or correct steam
binding. Without these provisions, there is little assurance that effective
actions will continue. For this reason, the addressees are requested to take
the following actions:
Action for Addressees Listed in Attachment 1
1. Develop procedures for monitoring fluid conditions within the AFW
system on a regular basis during times when the system is required to
be operable. This monitoring should ensure that fluid temperature at
the AFW pump discharge is maintained at about ambient temperature.
Monitoring of fluid conditions, if used as the primary basis for
precluding steam binding, is recommended each shift.
This item is not intended to require elaborate instrumentation. A
simple means of monitoring temperature, such as touching the pipe, is a
satisfactory approach.
2. Develop procedures for recognizing steam binding and for restoring the
AFW system to operable status, should steam binding occur.
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IEB 85-01
October 29, 1985
Page 3 of 4
3. Procedural controls should remain in effect until completion of
hardware modification to substantially reduce the likelihood of steam
binding or until superseded by action implemented as a result of
resolution of Generic Issue 93.
Schedule: For operating plants, develop and implement procedures within 90
days of the date of this bulletin. For plants under construction, develop
and implement procedures within 90 days after receiving an operating license
or provide an appropriate response and commitment within 1 year of the date
of this bulletin, whichever comes first.
Reporting Requirements: Prepare and submit a report describing the methods
used to accomplish these actions. Include the date(s) that procedures and
training were implemented or scheduled to be implemented. State the
frequency of monitoring of the temperature. For operating plants, submit
this report within 120 days of the date of this bulletin. For plants under
construction, submit the report within 120 days after receiving an operating
license or within 1 year of the date of this bulletin, whichever comes
first. It is not necessary to submit the procedures for review.
The written report, requested above, shall be submitted to the appropriate
Regional Administrator under oath or affirmation under provisions of Section
182a, Atomic Energy Act of 1954, as amended. In addition, the original copy
of the cover letter and a copy of the attached report should be transmitted
to the U. S. Nuclear Regulatory Commission, Document Control Desk,
Washington, DC 20555 for reproduction and distribution.
This request for information was approved by the Office of Management and
Budget under blanket clearance number 3150-0011. Comment on burden and
duplication should be directed to the Office of Management and Budget,
Reports Management, Room 3208, New Executive Office Building, Washington, DC
20503.
Although no specific request or requirement is intended, the following
information would be helpful to the NRC in evaluating the cost of this
bulletin:
1. staff time to perform requested review and testing
2. staff time to prepare requested documentation
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IEB 85-01
October 29, 1985
Page 4 of 4
If there are any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this
office.
James M. Taylor, Director
Office of Inspection and Enforcement
Technical Contacts: Mary S. Wegner, IE
(301) 492-4511
C. Vernon Hodge, IE
(301) 492-7275
Attachments:
1. Addressees for Action
2. List of Recently Issued IE Bulletins
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Page Last Reviewed/Updated Tuesday, March 09, 2021