Bulletin 80-13: NRC: Cracking in Core Spray Spargers
SSINS No.: 6820
Accession No.:
8002280661
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
May 12, 1980
IE Bulletin No. 80-13
CRACKING IN CORE SPRAY SPARGERS
Description of Circumstances:
Instances of cracking in core spray spargers have occurred at two BWR
facilities. This trend indicates a need for more intensive inspection of
these components during subsequent refueling outages.
Oyster Creek Nuclear Generating Station
Jersey Central Power and Light Company notified the NRC on October 18, 1978,
that a crack had been found in Core Spray Sparger System II during remote
visual inservice inspection at their Oyster Creek Nuclear Generating
Station. The crack was located at 2080 azimuth and extended at least 1800
circumferentially around the sparger. An evaluation of the event by the
licensee postulated that deformation of the sparger had occurred during
fabrication and installation which led to cracking by Intergranular Stress
Corrosion Cracking (IGSCC) during service in the BWR environment. A
temporary repair was effected by installing a clamp assembly over the crack.
The licensee's analysis indicated that the crack had relieved the stresses
present and therefore precluded further cracking. The NRC safety evaluation
permitted operation until the next refueling outage and required inspection
of the sparger at that time.
The NRC was informed by the Jersey Central Power and Light Company on
January 16, 1980 that further cracking was discovered in the core spray
spargers during an inservice inspection conducted in conjunction with the
refueling outage. A total of twenty-eight cracks 0.001 to 0.002 inches in
width and of varying lengths were identified in both core spray spargers.
The licensee stated that they believed the majority of additional cracks
were present earlier and not discovered during the 1978 inspection due to
inspection equipment limitations. Near term repair consisted of the
application of nine additional clamp assemblies in areas of the spargers
where cracks were visually observed on the accessible portion of the sparger
and UT indications were present in the inaccessible portion of the sparger
and in the junction box region. The licensee analyzed the flow
characteristics of the spargers and determined that adequate flow
distribution would be maintained if thru wall cracking .005 inches wide and
180 in length were present. The licensee stated that the installation
of the clamps would assure the sparger would maintain its physical integrity
and remain in place.
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IE Bulletin No. 80-13 May 12, 1980
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The repair measures proposed were determined by the NRP to be adequate until
the following refueling outage. The NRC evaluation stated that actions
should be taken to develop and install an improved replacement system at the
following refueling outage.
Pilgrim Nuclear Power Station
On January 31, 1980 the Boston Edison Company (BECo) informed the NRC that
five indications in the upper core spray sparger and two indications on the
lower core spray sparger at the Pilgrim Nuclear Power Station were
identified during remote visual inservice inspections. The indications were
confirmed as cracks after hydrolasing and brush cleaning. The licensees
evaluation indicated that the sparger will retain structural integrity
throughout the next cycle, although core spray flow distribution may be
affected due to through-wall cracks. However, core spray flow delivery to
the shroud interior would not be expected to decrease. A loose parts
analysis was presented which addressed (1) corrosion, (2) flow blockage, and
(3) control rod interference.
To support power operation in Cycle 5 with the core spray sparger in its
present condition, BECo has reanalyzed ECCS taking credit only for core
spray reflood, taking no credit for core spray heat transfer. The submission
by BECo is currently under review by the staff. The analysis is expected to
cover a full spectrum of core spray failures. It is expected that the
limiting condition will be the failure of recirculation suction line. A
MAPLHGR limit reduction will likely be imposed during Cycle 5 to compensate
for the assumption of no core spray heat transfer.
Based on results from other sparger inspections and previous pipe cracking
experience, cold work and sensitization during fabrication and installation
stresses are considered to be the major factors in causing the observed
cracks at the Pilgrim Station. The cracks are hypothesized to be initiated
and propagated by intergranular stress corrosion (IGSCC).
A meeting was held with representatives from GE in Bethesda, Maryland on
March 13, 1980 to discuss core spray sparger cracking at BWRs. At the
meeting GE provided the following information:
1. In February 1979, GE issued to BWR licensees Service Information Letter
(SIL) No. 289 that recommended inspection of the core spray spargers
for visual indications of cracking. To date, 19 of 21 plants inspected
have no observed cracking. Cracks have been found at 2 facilities
(Pilgrim and Oyster Creek).
2. The key contributors to IGSCC vary from plant-to-plant, although
stresses from cold work and sensitization during fabrication and
installation are considered prime factors leading to IGSCC at Pilgrim
and Oyster Creek. Because the cause of cracking is not yet confirmed by
metallurgical analysis, GE is developing tooling to extract sparger
samples to verify the postulated cracking mechanism.
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IE Bulletin No. 80-13 May 12, 1980
Page 3 of 3
3. GE is evaluating methods of improving the sparger inspection
techniques, and is considering a modification to the SIL, if warranted.
The staff agreed that improved inspection techniques should be developed and
metallurgical examinations should be performed to determine the mode of
failure. The staff asked GE to keep them informed of progress in these
areas.
Actions to be Taken by Licensees:
For all boiling water power reactor facilities with an operating license:
1. At the next scheduled and each following refueling outage until further
notice, perform a visual inspection of the Core Spray Spargers and the
segment of piping between the inlet nozzle and the vessel shroud.
Remote underwater TV examinations are acceptable if adequate resolution
can be demonstrated. The viewing in situ of 0.001 in. diameter fine
wires is considered as an acceptable means of demonstrating suitable
resolution of the TV examinations. Such techniques as the use of
oblique lighting, and the ability to light from each side independently
are considered useful in enhancing the image of cracks to facilitate
detection.
2. In the event cracks are identified during examination of the core spray
sparger system, the location and extent of the indications shall be
recorded and reported to the NRC. Supplementary examinations using
volumetric methods may be performed to aid in characterizing the extent
of cracking in nonvisible locations. An evaluation shall be submitted
to NRR for review and approval prior to return to operation.
3. Any cracking identified in the core spray cooling system shall be
reported to the Director of the appropriate NRC Regional Office within
24 hours of identification.
4. A written report of the results of the examinations including any
corrective measures taken shall be submitted within 30 days of the
completion of the examination to the Director of the NRC Regional
Office with a copy to the NRC Office of Inspection and Enforcement,
Division of Reactor Operations Inspection, Washington, D.C. 20555.
Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was
given under a blanket clearance specifically for identified generic
problems.
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