Information Notice 2000-17, Crack in Weld Area of Reactor Coolant System Hot Leg Piping at V.C. Summer

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)
	v • d • e

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

REACTOR COOLANT SYSTEM

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.

ML010570353

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

ML010510338.

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

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