UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

August 13, 2003

NRC INFORMATION NOTICE 2003-11: LEAKAGE FOUND ON BOTTOM-MOUNTED

INSTRUMENTATION NOZZLES

Addressees

All holders of operating license 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). It is

expected that the recipients will review the information for applicability to their facilities and

consider actions, as appropriate, to avoid similar problems. However, suggestions contained in

this information notice are not NRC requirements; therefore, no specific action or written

response is required.

Description of Circumstances

On April 12, 2003, licensee personnel performed boric acid corrosion control (BACC) program

walkdowns of STP Unit 1 during the unit’s 1RE11 refueling outage as part of the licensee’s

program in response to Generic Letter (GL) 88-05, “Boric Acid Corrosion of Carbon Steel

Reactor Pressure Boundary Components in PWR Plants.” Licensee personnel performed a

100-percent bare metal visual examination of the STP Unit 1 reactor pressure vessel (RPV)

bottom head as part of the BACC program inspections. Similar inspections had been

performed during prior STP Unit 1 and Unit 2 outages and no evidence of boron deposits had

been identified. In April 2003, however, licensee personnel identified white deposits around

STP Unit 1 BMI penetrations 1 and 46. Penetration 1 is centrally located 8.5 inches from dead

bottom center of the STP Unit 1 bottom head. Penetration 46 is located on the “hillside” of the

RPV bottom head, near the periphery of the RPV, approximately 60 inches (by planar

projection) from dead bottom center of the STP Unit 1 bottom head. The licensee quantified

the amount of observed deposits as 150 milligrams around penetration 1 and 3 milligrams

around penetration 46.

Licensee personnel obtained samples of the deposits from STP Unit 1 BMI penetrations 1

and 46 for chemical and isotopic analysis. The licensee’s chemical analysis confirmed the

presence of lithium and boron in the samples, which is consistent with leakage of reactor 

coolant system (RCS) water. To establish an approximate average age of the deposits, the

licensee performed a cesium isotopic analysis. The licensee found that the samples were, on

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IN 2003-11

Page 2 of 3

average, about 4 years old. Based on the chemical and isotopic analyses of the samples, the

licensee concluded that reactor coolant pressure boundary leakage was the most likely source

of the deposits.

Subsequently, the licensee initiated a nondestructive evaluation (NDE) program to inspect the

STP Unit 1 penetrations for evidence of cracking or other degradation. The capability of the

major elements of the NDE inspection was demonstrated through blind and nonblind testing of

the inspection equipment, personnel, and procedures. The major elements of the licensee’s

NDE program to detect cracking or other degradation were ultrasonic testing (UT) of all 58 STP

Unit 1 BMI nozzles from the nozzle inside diameter (ID) using axial, circumferential, and zero

degree probes to inspect the nozzle wall material; enhanced visual testing (EVT-1) of the

J-groove weld surfaces of all 58 STP Unit 1 BMI penetrations for evidence of cracking; eddy

current testing (ECT) using a bobbin coil probe to examine four nozzles, including penetrations

1 and 46, for evidence of cracking at the ID of the nozzles; ECT using an array probe mounted

on a pole to examine eight of the STP Unit 1 BMI penetration J-groove weld surfaces for

evidence of surface-breaking cracks; and phased-array UT from the outside surface of the RPV

bottom head to inspect the low-alloy steel RPV head in the vicinity of penetrations 1 and 46 for

evidence of corrosion.

The licensee reported three axially-oriented, crack-like indications in the penetration 1 nozzle

wall and two axially-oriented, crack-like, 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, breaking surface on the OD of the nozzle above and below the J-groove weld, as well

as on the 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 indications in penetration 46 was characterized as an axial crack

with a length of about 0.98 inch, breaking the surface 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 inch. The UT inspections conducted by the licensee were

not demonstrated to be effective for the purpose of examining the subsurface volume of the Jgroove weld. No cracklike indications were identified in any of the other 56 STP Unit 1 BMI

nozzle penetrations.

The UT inspection identified other features of the BMI penetrations which the licensee

considered relevant. UT reflectors were observed and characterized as “discontinuities” at the

interface of the nozzle and the J-groove weld in all of the STP Unit 1 BMI penetrations. The

licensee concluded that these discontinuities were possibly evidence of weld lack of fusion,

porosity, or other welding defects from original fabrication. These discontinuities were

particularly evident in 7 penetrations, including penetrations 1 and 46. The licensee also

concluded that discontinuities in penetrations 1 and 46 were located at the same general

azimuthal locations as the cracklike indications.

The licensee concluded that no cracking of the 58 BMI penetration J-groove welds was evident

based on the EVT-1 and ECT examinations of the J-groove weld surfaces. In addition, based

on the phased-array UT examination of the penetration 1 and 46 low-alloy steel base materials

the licensee concluded that there was no indication of wastage of the low-alloy steel due to

exposure to borated RCS water (the source of the deposits identified at penetrations 1 and 46). 

Subsequent visual examination of the nozzle bores during the repair of penetrations 1 and 46 

also supported the conclusion that there was no evidence of low-alloy steel wastage.
IN 2003-11

Page 3 of 3

On July 11, 2003, the licensee submitted a preliminary root cause analysis. The conclusion of

the analysis was that the most likely root cause explanation for the degradation observed in

STP Unit 1 BMI penetrations 1 and 46 was “manufacturing (welding) flaws resulting in

excessive stress in the nozzle/weld material leading to crack initiation with low cycle

fatigue/primary water stress corrosion cracking then supporting crack propagation.” To further

investigate the potential root causes of the STP Unit 1 BMI penetration cracking, the licensee

cut material samples from STP Unit 1 BMI penetrations 1 and 46 for destructive evaluation. 

These samples were taken by cutting material from the nozzle-to-J-groove weld interface with a

specially designed electrical discharge machining tool. Information gained from the analysis of

these material samples is expected to provide additional insights into the initiation and/or

propagation of the flaws in STP Unit 1 BMI penetrations. The licensee plans to submit its final

root cause report to the NRC in October 2003.

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, insufficient information

exists to make a determination as to the root cause of the STP Unit 1 cracking. The evaluation

of the material samples taken from STP Unit 1 BMI penetrations 1 and 46 is expected to

provide additional information to differentiate between potential causes of crack initiation and

propagation, including fabrication defects, PWSCC, fatigue, or some combination of these.

Based on the information currently available, the degradation that occurred at STP, Unit 1 may

be relevant to other PWR facilities. The NRC staff is in the process of evaluating what

information regarding PWR RPV lower head penetrations may be needed for licensees to

demonstrate that reactor coolant pressure boundary integrity is maintained at each facility. The

NRC staff will develop other generic communications, as necessary, to address this issue.

This information notice 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 (NRR) project manager.

/RA/

William D. Beckner, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contacts: Jack Foster, NRR Matthew Mitchell, NRR

(301) 415-3647 (301) 415-3303

E-mail: jwf@nrc.gov E-mail: mam4@nrc.gov

Attachment: List of Recently Issued NRC Information Notices