Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9608010243
NOTE: This text document was processed from a scanned
version or an electronic submittal and was processed
as received. Some tables, figures, strikeouts,
redlines, and enclosures are not included with this
submittal, and are omitted due to ASCII text
conversion limitations. In order to view this
document in its entirety, you may wish to use the
NUDOCS microfiche in addition to the electronic text.
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 ***
