Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 85-96
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
December 23, 1985
Information Notice No. 85-96: TEMPORARY STRAINERS LEFT INSTALLED IN
PUMP SUCTION PIPING
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This information notice is provided to alert recipients about a potentially
significant problem pertaining to temporary construction strainers left in-
stalled in the suction piping of safety-related pumps. It is suggested that
recipients review the information for applicability to their facilities and
consider actions, if appropriate, to preclude a similar problem occurring at
their facilities. However, suggestions contained in this information notice
do not constitute NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances:
Davis-Besse 1
On August 2, 1985, at Davis-Besse Unit 1, operated by Toledo Edison Company
(TEC), personnel discovered temporary strainers left installed in the
suction piping of two high-pressure injection (HPI) pumps. The strainers
were installed during plant construction to prevent debris from entering
pump internals. These temporary construction strainers are normally removed
before hot functional testing. Other pumps in safety-related systems
including the decay heat removal, containment spray, and component cooling
water systems, have subsequently been re-checked by radiograph or actual
disassembly; however, no strainers were found.
With the Davis-Besse plant in cold shutdown, the first HPI pump strainer was
found during maintenance to repair a flange leak. The discovery occurred
when TEC Engineering processed a report indicating strainer damage.
Evidently the strainer was damaged as maintenance personnel attempted to
remove what appeared to be a pipe spacer ring. The ring was actually part of
the strainer. Strainer identification was made difficult because, once
installed, the visible ring closely resembled the spacer rings used to
replace strainers in other systems. Strainers normally were removed from the
ring and then the rings were reinserted as pipe spacers. The stainless steel
strainers consist of a perforated conical basket that is attached to a
circular flange plate bolted to pump suction piping.
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IN 85-96
December 23, 1985
Page 2 of 3
The principal cause for the temporary strainer oversight at Davis-Besse was
a failure of the system turnover checklist to include construction strainer
removal after system flushing.
Summer
On August 27, 1985, during maintenance on the "B" train of the reactor
building spray (RBS) pump, personnel at the V.C. Summer nuclear power plant
found a startup construction strainer installed in the pump suction piping.
The strainer, installed during the 1982 plant startup, was removed and the
RBS pump returned to service. Similarly on August 29, 1985, maintenance
personnel determined that the suction piping for the "A" train RBS pump had
a construction strainer installed. This strainer also was removed and the
pump returned to service. A review of quality assurance records confirmed
that strainers installed for pumps in other safety-related systems were
removed before plant startup. However, records for the RBS system indicated
that the strainers had not been removed.
Although left installed in the RBS system since startup, the construction
strainers were checked annually for debris accumulation as part of a
preventive maintenance program. Other checks also were performed to
determine if structural failure had occurred. Apparently the strainers were
assumed to be a permanent design feature rather than a temporary one.
Differences in the notation on system drawings may have contributed to the
false assumption that the strainers were to be installed permanently. RBS
system drawings, unlike those of other safety-related systems, noted the
location of temporary strainers with a symbol which was described in the
legend. Other system draw-ings had a specific footnote about the location on
the drawing.
Discussion:
There are several mechanisms by which temporary construction strainers could
cause safety systems to be made inoperable. These include physical failure
of the non-safety related strainer which could cause pump or valve failures,
flow restrictions under extremes of pump flows associated with an accident,
and accumulated blockage of the construction strainer resulting insufficient
flow. An example of impaired operations specific to strainers in systems
used during the recirculation mode is temporary strainer clogging by debris
passed through the intake screen, resulting in loss of pump net positive
suction head.
Because construction strainers were not designed as safety related
components and their modes of failure or contribution to system
inoperability were not evaluated, such temporary strainers constitute an
unanalyzed plant condition.
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IN 85-96
December 23, 1985
Page 3 of 3
No specific action or written response is required by this information
notice. If you have any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or the tech-
nical contact listed below.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Ronald Young, IE
(301) 492-8985
Attachment: List of Recently Issued IE Information Notices
