United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #:  9608010243

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                                ENGINEERS

                                                  Serial - 15150-120R3

                         TECHNICAL WORK RECORD    Engineer D.  SHUE

                                                  Date  5/8/96

Project Title  Summary of Reactor Coolant Pump
               Thermal Barrier Nozzle Reworks  Tab RC Page 1 of 5
               during Refuel-8 and 9 per NCNs
               5166, 5415, 5429 and 5429A

SCOPE:         This TWR provides the cause and corrective action and the
               10CFR21 evaluation for NCNs 5415, 5429 and 5429A. In
               addition, a summary discussion of Reactor Coolant Pump
               thermal barrier nozzle work is included.

DISPOSITION:   Disposition is a "CLARIFICATION" to provide the 10CFR21
               evaluation and address cause and corrective action.

POST DISPOSITION TESTING: None required for this Clarification.

DISPOSITION BASIS:  No basis is required; however, the following summary
                    of nozzle work is provided to enhance the
                    understanding of the work performed on the Reactor
                    Coolant Pump nozzle welds at thermal Barrier Flange.

                    The initial problem with the nozzle welds at the
                    Reactor Coolant Pump (RCP) Thermal Barrier Flange was
                    discovered in May of 1987.  This problem was a
                    through wall crack on the upper portion of the "C"
                    RCP Seal Injection Line at the socket weld where it
                    enters the pump thermal barrier.  At that time the
                    weld was partially excavated and rewelded.  NCN-2765
                    contains the details on this work.

                    In December of 1994 during Refuel-8, the same "C" RCP
                    Seal Injection Line again had a through wall leak on
                    the same socket weld.  This time the crack was on the
                    lower portion of the weld.  Again the weld was
                    partially excavated and replaced.  After the
                    replacement of the affected portion of the weld, all
                    of the original Westinghouse weld had been removed.
                    The details of this work are contained in NCN-5166.

                    Subsequent to the second weld failure on the "C" Seal
                    Injection line, EPRI was contacted to determine if a
                    NDE method existed to properly examine the RCP
                    Thermal Barrier nozzle welds for similar conditions.
                    At the time there was no appropriate method; however,
                    EPRI worked to provide an "information only" method
                    to examine the December 1994 failure.  This method
                    was tested on the failure with some success in
                    finding the known crack.

                    After Refuel-8 was completed, EPRI worked to provide
                    an acceptable NDE method for examining all of the RCP
                    Thermal Barrier nozzle welds.  After appropriate
                    testing, it was determined that the developed method
                    was suitable for inspection of the nozzle to thermal
                    barrier welds during Refuel-9.  It was decided

                                ENGINEERS

                                                  Serial - 15150-120R3

                         TECHNICAL WORK RECORD    Engineer D.  SHUE

                                                  Date  5/8/96

Project Title  Summary of Reactor Coolant Pump
               Thermal Barrier Nozzle Reworks Tab RC Page 2 of 5
               during Refuel-8 and 9 per NCNs
               5166, 5415, 5429 and 5429A

                    that the EPRI method would be utilized to examine the
                    Seal Injection nozzles on all of the RCPs.  It is
                    noted that this NDE technique is recognized to be a
                    "go" or "no-go" type technique.  The technique will
                    determine if a flaw exists; however, it is unable to
                    specifically size and locate the flaw in the weld.

                    The Seal Injection nozzle inspections were performed
                    during the list week of April, 1996 during Refuel-9.
                    The results of the inspection were somewhat
                    surprising.  The "C" RCP which was rewelded in 1987
                    and 1994 showed no indications. The "B" RCP also
                    showed no indications.  However, inspection of the
                    "A" RCP showed that weld flaws existed and that
                    corrective action was required.  NCN-5415 was written
                    and dispositioned to Rework the subject weld.

                    It was determined that per this Rework, the entire
                    weld should be excavated and remade.  This was done
                    based on concerns with stressing the remaining
                    portions of the weld should partial excavation and
                    rewelding be performed.  Additionally, it was known
                    that partial excavation did not remove the entire
                    problem on the "C" RCP when performed in 1987.

                    After removal of the nozzle assembly from the "A" RCP
                    actions were taken to reuse the existing nozzle;
                    however, upon closer examination it was discovered
                    that there was significant pipe distortion and wall
                    thinning of the existing nozzle.  It was then
                    determined that a new nozzle assembly would be
                    fabricated.  Disposition 2 to NCN-5415 provided for
                    replacement of the entire nozzle assembly.

                    Based on the previous problems with the "C" RCP Seal
                    Injection Line and the discovered problem on the "A"
                    RCP Seal Injection Line, Engineering provided a
                    recommendation to perform additional inspection It

                    was known that the Component Cooling Water (CCW)
                    nozzles at the Thermal Barrier Flange are identical
                    to the Seal Injection nozzles; therefore, after
                    reviewing the stresses on the lines to each pump,
                    Design Engineering recommended inspection of the RCP
                    "C" CCW Inlet and "A" CCW Inlet.  This was based on
                    the fact that these two locations exhibited the
                    highest bending stress ratios and were on pumps with
                    previous weld flaws.

                    It is important to note that the Design Engineering
                    nozzle evaluation is contained in TWR-15053 by C.
                    Barbier dated 2/29/96.  It is noted that the date on
                    the TWR should be 4/29/96.  This TWR is contained in
                    NCN-5429.  As noted above, the TWR provides the
                    bending stress ratio for each nozzle connection.  It
                    is noted that none of the nozzles are considered to
                    be overstressed; however, the nozzles with

                                ENGINEERS

                                                  Serial - 15150-120R3

                         TECHNICAL WORK RECORD    Engineer D.  SHUE

                                                  Date  5/8/96

Project Title  Summary of Reactor Coolant Pump
               Thermal Barrier Nozzle Reworks Tab RC Page 3 of 5
               during Refuel-8 and 9 per NCNs
               5166, 5415, 5429 and 5429A

               the highest stresses were determined to have the highest
               probability of failure concurrent with potential weld
               flaws.

               It is also noted that clarification is required to better
               understand the table at the bottom of page 2 of the
               subject TWR.  In the right most column of the TWR entitled
               "VCS Observed Nozzle Defects In Pump" , "yes" means that
               the subject pump had a history of nozzle defects prior to
               inspection of the CCW nozzles.  The "C" RCP had the work
               of NCNs-2765 and 5166, and the "A" RCP had the work of
               NCN-5415.

               The "A" and "C" RCP CCW Inlets were subsequently
               inspected.  The "A" Inlet was found to have existing weld
               flaws.  The "C" Inlet was found to be acceptable.  NCN-
               5429 was written to address the weld flaw in the "A" RCP
               CCW Inlet.  Disposition 1 of this NCN provided a Rework to
               replace the nozzle with new material and remake the nozzle
               to pump weld.  Additionally, Disposition 1 required that
               the "C" RCP CCW Outlet nozzle be inspected.  This was
               based on the fact that the nozzle had the third highest
               bending stress ratio.

               The "C" Outlet nozzle was inspected and found to be
               acceptable; however, Refuel-9 Outage Management made the
               decision to inspect all of the RCP CCW nozzles from a
               prudency standpoint.  Suprisingly, out of these
               inspections, the "A" RCP Outlet nozzle and both nozzles on
               the "B" RCP were found to have weld flaws, although there
               bending stress ratios were very low.

               It is additional noted that the "B" RCP CCW Inlet excited
               signs of through wall leakage.  Subsequently, this line
               was penetrant tested which confirmed the presence of the
               through wall indication; however, it is noted that during
               flange disassembly to correct the subject indication, a
               pipe snubber, CCH-1374, was found locked.  See NCN-5442
               for details concerning the snubber.

               The "A" RCP CCW Outlet was replaced per Disposition 2 to
               NCN-5429.  Associated NCN-5429A was written and
               dispositioned in Disposition 1 to allow for replacement of
               the Inlet and Outlet nozzles on the "B" RCP.  After
               initial replacement, the CCW Inlet nozzle on "B" RCP
               failed the post replacement test utilizing the EPRI probe
               and was again replaced.  This replacement occurred per
               Disposition 2 to NCN-5429A.

               A summary of all the work performed to date and the
               associated work documents is included as Table I of this
               TWR.  This table lists the NDE and corrective action work
               documents for the nozzles sorted by the applicable nozzle
               and RCP.

                                ENGINEERS

                                                  Serial - 15150-120R3

                         TECHNICAL WORK RECORD    Engineer D.  SHUE

                                                  Date  5/8/96

Project Title  Summary of Reactor Coolant Pump
               Thermal Barrier Nozzle Reworks Tab RC Page 4 of 5
               during Refuel-8 and 9 per NCNs
               5166, 5415, 5429 and 5429A

10CFR21 EVALUATION: The subject condition appears to be a generic
                    hardware defect in manufacturing of a basic component
                    which has the potential to cause a loss of safety
                    function and a major reduction in the degree of
                    protection provided to public health and safety.

                    Because the nozzle weld defect are in both the Seal
                    Injection and Component Cooling Water connections at
                    the Reactor Coolant Pump Thermal Barrier Flange the
                    potential exists that both could fail simultaneously.
                    Should this occur there would be no cooling to the
                    RCP seal or lower pump bearing.  Both would be
                    subjected to Reactor Coolant System cold leg
                    temperature in excess of 550 degrees F.  This has the
                    potential to initiate a RCS cold leg loss of coolant
                    accident.  See Westinghouse WCAP-10541 and NRC
                    Generic Issue 23 for possible safety significance.

10CFR50.72/73 EVALUATION: Provided in a previous disposition.

10CFR50.59 EVALUATION:    Not required for this type disposition,

CAUSE AND CORRECTIVE ACTION:  The cause of the subject failures appears
                              to be associated with the initial welding
                              of these nozzles by the OEM.  NCN-5166
                              provided an initial review of these nozzle,
                              problems and subsequently Root Cause 508-
                              108 was issued to further address the
                              issue.  Currently, it appears that there
                              may be evidence of incomplete penetration
                              and subsequent flaw initiation.  This has
                              been corrected by removing and replacing
                              the subject weld.

                                ENGINEERS

                                                  Serial - 15150-120R3

                         TECHNICAL WORK RECORD    Engineer D.  SHUE

                                                  Date  5/8/96

Project Title  Summary of Reactor Coolant Pump
               Thermal Barrier Nozzle Reworks Tab RC Page 5 of 5
               during Refuel-8 and 9 per NCNs
               5166, 5415, 5429 and 5429A

TABLE I  "REACTOR COOLANT PUMP SEAL INJECTION & COMPONENT COOLING
NOZZLE
INSPECTIONS\REPLACEMENT omitted.

*** END OF DOCUMENT ***

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