Information Notice No. 86-96: Heat Exchanger Fouling Can Cause Inadequate Operability of Service Water Systems
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
November 20, 1986
Information Notice No. 86-96: HEAT EXCHANGER FOULING CAN CAUSE
INADEQUATE OPERABILITY OF SERVICE WATER
All nuclear power reactor facilities holding an operating license or a
This notice is provided to alert recipients to the potential for fouling in
heat exchangers in raw water systems. The result of this fouling could
affect the facility's ability to reject heat to the ultimate heat sink,
which could be adverse under accident and post-accident conditions. It is
suggested that recipients review the information for applicability to their
facilities and, consider actions, if appropriate, to preclude these
conditions at their facilities. However, suggestions contained in this
information notice do not constitute requirements; therefore, no specific
action or written response is required.
Description of Circumstances:
Over an extended time period, the nuclear service water (NSW) system at
McGuire Nuclear Station was degraded by mud and silt buildup and corrosion.
This degraded the pathway to the ultimate heat sink (UHS), composed of Lake
Norman and its backup source, the standby nuclear service water pond.
Therefore, the heat removal capability assumed in the accident analysis
could no longer be satisfied.
The intake screens are too large to filter out the suspended solids and silt
from the lake. Over the years, a combination of organic and inorganic
compounds fouled a number of heat exchangers, including the containment
spray, component cooling water, and control room chiller heat exchangers.
Adequate performance of these heat exchangers is crucial for safely
operating a unit in accident and post-accident conditions and for bringing
it to cold shutdown during normal operation or following an accident.
NRC inspections conducted at McGuire in 1985 and 1986 revealed significant
fouling problems with NSW system heat exchangers, indications of degraded
NSW flow, and inadequate flow balance tests to ensure system capability
under design accident conditions.
November 20, 1986
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Additionally, the licensee notified the NRC that prior to January 27, 1986,
the NSW systems for Units 1 and 2 had not been tested under the most
limiting design basis accident configuration. Specifically, the system had
never been verified to supply the required flow concurrently to essential
headers for both units with the system taking suction solely from the common
standby nuclear service water pond rather than Lake Norman.
At Farley 1 on August 1, 1986, the licensee discovered that silt in the
service water system had caused overheating of gearboxes on two of three
charging pumps while the third pump was out of service for maintenance. In
addition to their normal function, these pumps function as part of the
emergency core cooling system. Service water is used to cool the lube oil
coolers for the charging pump gearboxes. One of the pumps was taken out of
service when its gearbox temperature exceeded 155F. The temperature of
the gearbox on the other pump was 148F and increasing. The vendor
recommends operating the pumps with caution above 140F and not
operating the pumps above 155F. The lube oil coolers were flushed to
reduce the temperature of the gearbox lube oil below 140F.
Service water systems are designed to meet General Design Criteria 44, 45,
and 46 of 10 CFR 50, Appendix A. By these criteria, plant designs provide
the ability (1) to transfer heat from safety-related components under normal
and accident conditions to an ultimate heat sink; (2) to conduct periodic
inspections of the system to ensure integrity and capability; and (3) to
test the system under conditions as close to design as practical.
Fouling of service water systems has been recognized for some time as having
the potential for compromising system operability. Information Notice No.
81-21 and IE Bulletin 81-03 addressed the potential for fouling of safety-
related heat exchangers by Asiatic clams, mussels, and debris from other
shell fish. Duke Power Company responded with a program designed to monitor
fouling of several typical NSW supplied heat exchangers. Through this
program and other mechanisms the licensee identified numerous affected heat
exchangers. However, because these data were not adequately evaluated to
identify adverse trends, these programs were not totally effective. The
affected heat exchangers included containment spray, containment
ventilation, control room air conditioning, reactor coolant pump motor
coolers, and component cooling water. In 1986 the licensee identified
several individual components, including containment spray heat exchangers,
which were not capable of meeting FSAR-specified performance requirements.
The containment spray heat exchangers were of particular concern since they
are normally inactive and gradual degradation from fouling can go unnoticed.
As noted above, the licensee at Farley 1 determined that charging pump
gearbox lube oil,coolers are also important heat exchangers that can be
affected by silting.
To ensure minimum NSW component flows, including adequate flow to the
containment spray heat exchangers during design LOCA conditions, the
normally throttled valves associated with each NSW component were set during
November 20, 1986
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testing of the NSW system. These throttled positions were to be incorporated
into operating and surveillance procedures for future operations. In some
cases, the throttled valve positions listed in the licensee's NSW operating
procedures and locked valve verification procedures were not consistent with
earlier preoperational "as left" data. Flow balance tests of the system had
not been performed from the initial preoperational test in 1982 until
December 1985, even though the positions of established throttle valves were
changed and some heat exchangers exhibited fouling problems. The test
conducted in 1985 revealed that flow rates through several safety-related
heat exchangers were below FSAR values.
IE Bulletin 81-03 does not by itself provide a high degree of assurance that
a long-term resolution has been achieved. The NRC also is formally studying
this subject, under Generic Issue 51, "Proposed Requirements for Improving
Reliability of Open Cycle Service Water Systems." This project depends on a
research program now well under way. Task 1 (of 4), determining the
applicability of documented biofouling surveillance and control methods to
open cycle water systems in nuclear power plants, is complete
(NUREG/CR-4626, Vol. 1)*. The resulting recommendations of Task 1 include:
(1) a thorough system evaluation to focus surveillance and control efforts
for the best return on plant safety and efficient operation, (2) revision of
plant technical specifications to reflect improved procedures, (3)
monitoring the effectiveness of control procedures as part of the
surveillance program, and (4) including biofouling surveillance in the
routine maintenance program.
No specific action or written response is required by this information
notice. If you need any additional information regarding this matter, please
contact the Regional Administrator of the appropriate regional office or the
technical contact listed below.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: C. Vernon Hodge, IE
Frank Jape, Region II
Attachment: List of Recently Issued IE Information Notices
* A copy of this document is available in the NRC Public Document Room,
1717 H Street N.W., Washington, DC 20555 for inspection and copying.
Page Last Reviewed/Updated Friday, May 22, 2015