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. 
.

IE Bulletin No. 80-13                                      May 12, 1980 
                                                           Page 2 of 3 

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. 
.

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.