Information Notice 2003-11, Leakage Found on Bottom-Mounted Instrumentation Nozzles
| ML040050433 | |
| Person / Time | |
|---|---|
| Issue date: | 01/08/2004 |
| From: | Beckner W NRC/NRR/DIPM |
| To: | |
| Foster J, NRR/IROB, 415-3647 | |
| References | |
| IN-03-011, Suppl 1 | |
| Download: ML040050433 (8) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 January 8, 2004 NRC INFORMATION NOTICE 2003-11, SUPPLEMENT 1: LEAKAGE FOUND ON
BOTTOM-MOUNTED
INSTRUMENTATION NOZZLES
Addressees
All holders of operating licenses or construction permits for nuclear power reactors, except
those that have permanently ceased operations and have certified that fuel has been
permanently removed from the reactor.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert
addressees to indications of leakage in the form of boron deposits discovered on bottom- mounted instrumentation (BMI) nozzles at South Texas Project Unit 1 (STP Unit 1). This
supplement specifically provides additional information regarding the STP Unit 1 licensees root
cause analyses, as discussed in licensees final licensee event report on this topic, dated
October 15, 2003 (ADAMS Accession No. ML032950483). It is expected that the recipients of
this IN will review the information for applicability to their facilities and consider actions, as
appropriate, to avoid similar problems. However, suggestions contained in this IN are not NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances
An extensive description of the STP Unit 1 BMI penetration leakage event was given in
IN 2003-11, Leakage Found on Bottom-Mounted Instrumentation Nozzles, dated August 13,
2003. The relevant pre-August 2003 information is summarized herein.
In April 2003, the STP Unit 1 licensee identified small boron deposits around two of the 58 STP
Unit 1 BMI penetrations (penetrations 1 and 46), the only evidence of BMI nozzle penetration
leakage reported by a U.S. facility to date. The STP Unit 1 BMI penetrations were constructed
from an drilled Inconel 600 bar stock connected to the reactor vessel lower head by an Inconel
82/182 J-groove weld. The licensees subsequent nondestructive examination (NDE)
campaign, which included ultrasonic test (UT), visual, and eddy current testing, resulted in the
identification of three axially oriented cracklike indications in the penetration 1 nozzle wall and
two axially oriented cracklike indications in the penetration 46 nozzle wall. One of the
indications in penetration 1 was characterized as an axial crack with a length of about 1.38 inches, surface-breaking on the outside diameter (OD) of the nozzle above and below the
J-groove weld, as well as surface-breaking on the inside diameter (ID) of the nozzle. The other
two indications in penetration 1 were characterized as being small, embedded cracks near the
interface between the nozzle wall and the root pass of the J-groove weld. One of the
IN 2003-11, Sup 1 indications in penetration 46 was characterized as an axial crack with a length of about 0.98 inches, surface-breaking on the OD of the nozzle above and below the J-groove weld. The
other indication in penetration 46 was characterized as an embedded crack having an axial
length of 0.95 inches.
The results of the licensees UT inspection identified other features within the BMI penetrations
which were deemed to be relevant by the licensee. UT reflectors were observed and
characterized as discontinuities at the interface of the nozzle and the J-groove weld in all 58 of
the STP Unit 1 BMI penetrations. These discontinuities were particularly evident in seven
penetrations, including penetrations 1 and 46. The discontinuities in penetrations 1 and 46 were located in the same general azimuthal locations as the cracklike indications.
To further investigate the potential root causes of the STP Unit 1 BMI penetration cracking, the
licensee attempted to cut material samples (known as boat samples), by means of a specially
designed electrical discharge machining (EDM) tool, from STP Unit 1 BMI penetrations 1 and 46 for destructive examination. Due to the difficulties of the EDM cutting process, only one
sample, from penetration 1, was successfully removed and destructively evaluated. The
penetration 1 boat sample was taken from the same azimuthal location as the 1.38 inch flaw, was intended to sample the nozzle and J-groove weld material, and was intended to contain
portions of the 1.38 inch flaw as well as one or more of the observed UT discontinuities at the
nozzle-to-weld interface. Figure 1, discussed in more detail below, provides a composite
overlay of the penetration 1 boat sample with the tube (nozzle) wall and the penetration 1 J-groove weld.
Figure 1 Overlay of cross section of boat sample from STP Unit 1 penetration 1 with
drawing of penetration 1 tube and weld geometry.
IN 2003-11, Sup 1 The licensees destructive examination of the STP Unit 1 penetration 1 boat sample provided
the following information:
(1) The axial crack in the penetration 1 tube wall was entirely intergranular in nature and
consistent with primary water stress corrosion cracking (PWSCC) as the mechanism of
crack propagation. Essentially no PWSCC of the J-groove weld material was observed
in the boat sample.
(2) The UT discontinuity at the tube-to-weld interface which was captured in the boat
sample (the dark area in the boat sample in Figure 1) was confirmed to be a weld
lack-of-fusion zone from initial fabrication. A weld material ligament of approximately
80 mils (0.080 inch) separated the weld lack-of-fusion zone from the surface of the
J-groove weld. The length of the lack-of-fusion zone in the circumferential direction was
about 0.2 inch. The axial PWSCC crack in the tube wall was located at one end of the
lack-of-fusion zone.
(3) A second cracklike defect was observed in the weld material (the dark line in Figure 1),
running in the circumferential direction. The length of this defect was about 0.2 inch, consistent with the length of the lack-of-fusion zone. This defect was completely
through the 80 mil weld ligament and would have permitted primary water to leak into
the lack-of-fusion zone. The precise mechanism for the initiation and propagation of this
defect through the weld material could not be determined from the boat sample.
However, its location and size relative to the associated lack-of-fusion zone suggest that
the formation of this defect was also related to initial fabrication processes.
Based on this information, and the results of the licensees NDE campaign, the licensee
concluded that the following scenario most likely explains the PWSCC flaws observed at STP
Unit 1:
(1) Initial fabrication of the STP Unit 1 BMI penetrations resulted in lack-of-fusion zones
between the nozzle (tube) and the J-groove weld. In addition, in penetrations 1 and 46, conditions existed from initial fabrication which resulted in the formation of defects
through the J-groove weld, subsequently allowing primary water to flood the embedded
lack-of-fusion zones early in the facilitys operating history.
(2) Primary water flooding of the embedded lack-of-fusion zones established conditions
(i.e., a high-temperature, high-purity water environment, a susceptible material, and high
local stresses) which are known to promote PWSCC.
(3) PWSCC flaws initiate inside the weld joint, adjacent to the lack-of-fusion zones, and
propagate through the tube wall, eventually establishing a leakage path to the exterior of
the reactor pressure vessel lower head.
In addition to the boat sample analysis discussed above, this scenario is supported by the
observation that the large, 0.95 inch flaw in penetration 46 was not, based on NDE results, surface-breaking either on the ID of the nozzle wall or above the J-groove weld. Assuming that
the same mechanism was responsible for all of the flaws observed in the STP Unit 1 BMI
penetrations, this observation points toward a scenario which is not dependent on PWSCC
initiation at a normally wetted surface.
IN 2003-11, Sup 1 Discussion
The NRC has closely monitored the inspections conducted at STP Unit 1 and the licensees
evaluation of the root cause for the observed cracking. At this time, the NRC staff has
concluded that the scenario summarized above is the explanation which is most consistent with
the available information from the licensees NDE campaign and material sample testing. The
NRC staff expects to further review details associated with the licensees root cause
determination as part of NRCs normal reactor inspection and oversight process. The NRC
staff will consider the need to supplement this IN if additional information is discovered which
may modify the NRC staffs assessment of the scenario described above.
The NRC staff expects that licensees whose facilities may be subject to conditions which could
lead to degradation like that observed at STP Unit 1 will evaluate the information in this IN and
determine what, if any, actions may be prudent to maintain the integrity of their facilities reactor
coolant pressure boundaries consistent with NRC regulatory requirements.
This IN requires no specific action or written response. If you have any questions about the
information in this notice, please contact one of the technical contacts listed below or the
appropriate Office of Nuclear Reactor Regulation project manager.
/RA/
William D. Beckner, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: Jack Foster Matthew A. Mitchell
(301) 415-3647 (301) 415-3303 E-mail: jwf@nrc.gov E-mail: mam4@nrc.gov
ML040050433 *See previous concurrence
DOCUMENT NAME: C:\ORPCheckout\FileNET\ML040050433.wpd
OFFICE IROB:DIPM Tech Editor PM:PDIV-1 SC:PDIV DE:EMCB
NAME JWFoster PKleene* RG for DJaffe RAGramm MAMitchell
DATE 12/18/2003 12/17/2003 01/05/2004 01/05/2004 12/17/2003 OFFICE SC:EMCB BC:EMCB D:DE SC:IROB:DIPM C:IROB:DIPM
NAME SMCoffin BBateman RJBarrett TReis WDBeckner
DATE 12/22/2003 12/23/2003 12/23/2003 01/08/2004 01/07/2004
Attachment
IN 2003-11, Sup 1 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2003-22 Heightened Awareness for 12/09/2003 All medical licensees and NRC
Patients Containing Detectable Master Materials License medical
Amounts of Radiation from use permittees.
Medical Administrations
2003-21 High-Dose-Rate-Remote- 11/24/2003 All medical licensees.
Afterloader Equipment Failure
2003-20 Derating Whiting Cranes 10/22/2003 All holders of operating licenses
Purchased Before 1980 for nuclear power reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel; applicable
decommissioning reactors, fuel
facilities, and independent spent
fuel storage installations.
2003-19 Unanalyzed Condition of 10/06/2003 All holders of operating licenses
Reactor Coolant Pump Seal or construction permits for
Leakoff Line During Postulated pressurized water reactors
Fire Scenarios or Station (PWRs).
Blackout
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