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 bottommounted instrumentation (BMI) nozzles at South Texas Project Unit 1 (STP Unit 1). This

supplement specifically provides additional information regarding the STP Unit 1 licensee’s root

cause analyses, as discussed in licensee’s 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 licensee’s 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

ML040050433
IN 2003-11, Sup 1

Page 2 of 4

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 licensee’s 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

Page 3 of 4

The licensee’s 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 licensee’s 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 facility’s 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

Page 4 of 4

Discussion

The NRC has closely monitored the inspections conducted at STP Unit 1 and the licensee’s

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 licensee’s NDE campaign and material sample testing. The

NRC staff expects to further review details associated with the licensee’s root cause

determination as part of NRC’s 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 staff’s 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
____________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment 

IN 2003-11, Sup 1

Page 1 of 1

LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2003-22 Heightened Awareness for

Patients Containing Detectable

Amounts of Radiation from

Medical Administrations

12/09/2003 All medical licensees and NRC

Master Materials License medical

use permittees.

2003-21 High-Dose-Rate-RemoteAfterloader Equipment Failure11/24/2003 All medical licensees.

2003-20 Derating Whiting Cranes

Purchased Before 1980

10/22/2003 All holders of operating licenses

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

Reactor Coolant Pump Seal

Leakoff Line During Postulated

Fire Scenarios or Station

Blackout

10/06/2003 All holders of operating licenses

or construction permits for

pressurized water reactors

(PWRs).

Note: NRC generic communications may be received in electronic format shortly after they are

issued by subscribing to the NRC listserver as follows:

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