Information Notice 2000-17, Crack in Weld Area of Reactor Coolant System Hot Leg Piping at V.C. Summer
ML010570353 | |
Person / Time | |
---|---|
Issue date: | 02/28/2001 |
From: | Marsh L Operational Experience and Non-Power Reactors Branch |
To: | |
Benner E | |
References | |
IN-00-017, Suppl 2 | |
Download: ML010570353 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 February 28, 2001 NRC INFORMATION NOTICE 2000-17,SUPPLEMENT 2: CRACK IN WELD AREA OF
HOT LEG PIPING AT V. C.
SUMMER
Addressees
All holders of operating licenses for nuclear power reactors except those who have ceased
operations and have certified that fuel has been permanently removed from the reactor vessel.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN)
supplement to provide updated information about the crack found in a weld in the A loop hot leg
pipe in the reactor coolant system (RCS) at the V. C. Summer Nuclear Station. It is expected
that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, no specific action or written response is
required.
Description of Circumstances
On October 7, 2000, during a containment inspection after entering a refueling outage, the
licensee identified a large quantity of boron on the floor and protruding from the air boot around
the A loop RCS hot leg pipe. Ultrasonic testing (UT) and eddy current testing (ET) identified
an axial crack-like indication approximately 2.7 inches long located approximately 7 degrees
counterclockwise from top dead center of the first weld between the reactor vessel nozzle and
the A loop hot leg piping approximately 3 feet from the reactor vessel. Based on the UT data, the axial crack-like indication began at the inner diameter and shows evidence of complete
through-wall extension. Visual examination from the outer diameter identified a small weep
hole in the center of the weld at approximately the same circumferential location as the UT and
ET indications.
The NRC developed a Web page to keep the public informed of this event:
http://www.nrc.gov/NRC/REACTOR/SUMMER/index.htm
The NRC issued IN 2000-17 and Supplement 1 on October 18, 2000, and November 11, 2000,
respectively, to inform addressees of this information.
IN 2000-17 Supp. 2 Discussion
Based on non-destructive examination (UT, ET, and visual) results, the A loop hot leg weld
was cut out and destructively tested. The 2.7-inch long indication was determined to be an
axial crack approximately 2.5 inches long and almost through wall which was caused by primary
water stress corrosion cracking (PWSCC). High tensile stresses were present in the weld as a
result of extensive weld repairs during original construction and these stresses were considered
a contributing cause for the PWSCC. The extensive weld repairs complicated previous in- service inspections of the weld because weld roughness made it difficult to perform UT on
portions of the weld. In addition to the axial crack, the licensee identified several other ET
indications in the A loop hot leg weld. The destructive examination of the A loop hot leg weld
confirmed that a number of the ET indications were PWSCC cracks. The licensee also
identified other ET indications in four of the other five reactor coolant system nozzle to pipe
welds. Westinghouse performed an evaluation to justify continued operation of V. C. Summer
without repair of these ET indications.
The NRC conducted a special inspection from October 18, 2001 to February 8, 2001, which
evaluated the licensees root cause determination and corrective actions in response to the A
loop hot leg weld crack. The special inspection team concluded that the licensees root cause
determination was thorough and supported PWSCC as the mechanism which led to the leak.
The team identified no licensee performance issues. The team concluded that all welding and
non-destructive examination (UT, ET, visual, and liquid-penetrant) met American Society of
Mechanical Engineers (ASME) Code requirements. The A loop hot leg weld was removed
and replaced in its entirety. The removal and acceptable replacement of the A loop hot leg
weld eliminates near-term staff concerns regarding this weld. The team noted that the licensee
intended to make several enhancements to their leak detection capability including: 1)
performing noble gas sampling, 2) performing a reactor coolant system water inventory balance
once per day, 3) addition of a main control board annunciator for a 0.75 gallon per minute leak, and 4) revising the procedures for boric acid inspections to list specific components and
locations to be inspected and to provide specific guidance on evaluation methodologies. The
special inspection report number is 50-395/2000-08, and it will be available at ADAMS when it is
issued.
The NRC staff reviewed the Westinghouse evaluation to justify continued operation of V. C.
Summer without repair of existing ET indications in the B loop and C loop hot leg welds. The
Westinghouse evaluation concluded that V. C. Summer could be operated for at least two fuel
cycles without repair of existing ET indications. The staff performed an independent evaluation
using a bounding primary water stress corrosion cracking (PWSCC) growth rate, the initial ET
indication length and depth, and the flow stress for the weld material, and concluded that V. C.
Summer could be operated with ET indications in the B loop and C loop hot leg welds for
one fuel cycle. The staff used a crack growth rate 50 percent higher than that used by the
licensee because of limited crack growth rate data for Alloy 182 weld material. The staffs
evaluation was issued on February 20, 2001 and is available at ADAMS Accession Number
IN 2000-17 Supp. 2 As a result of its evaluation of the event at V. C. Summer, the NRC identified several generic
issues to be addressed. These issues include: 1) potential weaknesses in the ability of ASME
Code-required non-destructive examination techniques to detect and size small inner-diameter
stress corrosion cracks, 2) potential weaknesses in the ASME Code in that it allows multiple
weld repairs which affect residual weld stress and PWSCC, 3) potential weaknesses in RCS
leak detection systems, and 4) questions regarding the continued applicability of leak before
break analyses. The NRC has held two public meetings with industry representatives on
January 25, 2001 and February 16, 2001, to discuss resolution of these issues. The NRC will
assess the need for further generic action as new information becomes available.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please call or email one of the technical contacts
listed below or contact the appropriate Office of Nuclear Reactor Regulation (NRR) project
manager.
/RA/
Ledyard B. Marsh, Chief
Events Assessment, Generic Communications
and Non-Power Reactors Branch
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contacts: Eric Benner, NRR Billy Crowley, Region II
301-415- 1171 404-562-4612 E-mail: ejb1@nrc.gov E-mail: brc@nrc.gov
C. E. Carpenter, NRR
301-415-2169 E-mail:cec@nrc.gov
Attachment:
List of Recently Issued NRC Information Notices
IN 2000-17 Supp. 2 As a result of its evaluation of the event at V. C. Summer, the NRC identified several generic
issues to be addressed. These issues include: 1) potential weaknesses in the ability of ASME
Code-required non-destructive examination techniques to detect and size small inner-diameter
stress corrosion cracks, 2) potential weaknesses in the ASME Code in that it allows multiple
weld repairs which affect residual weld stress and PWSCC, 3) potential weaknesses in RCS
leak detection systems, and 4) questions regarding the continued applicability of leak before
break analyses. The NRC has held two public meetings with industry representatives on
January 25, 2001 and February 16, 2001, to discuss resolution of these issues. The NRC will
assess the need for further generic action as new information becomes available.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please call or email one of the technical contacts
listed below or contact the appropriate Office of Nuclear Reactor Regulation (NRR) project
manager.
/RA/
Ledyard B. Marsh, Chief
Events Assessment, Generic Communications
and Non-Power Reactors Branch
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contacts: Eric Benner, NRR Billy Crowley, Region II
301-415- 1171 404-562-4612 E-mail: ejb1@nrc.gov E-mail: brc@nrc.gov
C. E. Carpenter, NRR
301-415-2169 E-mail:cec@nrc.gov
Attachment:
List of Recently Issued NRC Information Notices
Note 1: The V.C. Summer Communications Team reviewed and approved the information notice on 02/XX/2000. The Team
composition was dictated in a memorandum from J. Zwolinski to B. Sheron on November 14, 2000 (Protocol for NRC Response to
Cracked Weld at V. C. Summer - ADAMS Accession Number ML003768599)
Distribution:
IN File
PUBLIC
ACCESSION NO. ML010570353 TEMPLATE NO. NRR 052
- See previous concurrence
To receive a copy of this document, indicate in the box C=Copy w/o attachment/enclosure E=Copy with attachment/enclosure N = No copy
OFFICE REXB C MULTIPLE N Tech Ed C:REXB
NAME EBenner Communications TeamNote1 out of office LMarsh
DATE 02/27/00 02/27/00 02/27/00 02/28/00
OFFICIAL RECORD COPY
Attachment
IN 2000-17, Supp. 2 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
______________________________________________________________________________________
2000-22 Medical Misadministrations 12/18/00 All medical use licensees
Caused by Human Errors authorized to conduct gamma
Involving Gamma Stereotactic stereotactic radiosurgery
Radiosurgery (GAMMA KNIFE) treatments
2000-21 Detached Check Valve Disc 12/15/00 All holders of OLs for nuclear
not Detected by Use of power reactors except those who
Acoustic and Magnetic have ceased operations and have
Nonintrusive Test Techniques certified that fuel has been
permanently removed from the
reactor
2000-20 Potential Loss of Redundant 12/11/200 All holders of operating licenses
Safety Related Equipment Due 0 or construction permits for
to Lack of a High-Energy Line nuclear power reactors
Break Barrier
2000-19 Implementation of Human Use 12/05/200 All medical use licensees
Research Protocols Involving 0
U.S. Nuclear Regulatory
Commission Regulated
Materials
2000-18 Substandard Material Supplied 11/29/200 All 10 CFR Part 50 licensees and
by Chicago Bullet Proof 0 applicants. All category 1 fuel
Systems facilities. All 10 CFR Part 72 licensees and applicants
2000-17 S1 Crack In Weld Area of Reactor 11/16/200 All holders of OLs for nuclear
Coolant System Hot Leg Piping 0 power reactors except those who
At V.C. Summer have ceased operations and have
certified that fuel has been
permanently removed from the
reactor vessel
2000-17 Crack In Weld Area of Reactor 10/18/200 All holders of OLs for nuclear
Coolant System Hot Leg Piping 0 power reactors except those who
At V.C. Summer have ceased operations and have
certified that fuel has been
permanently removed from the
reactor vessel
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit