Bulletin 87-01: Thinning of Pipe Walls in Nuclear Power Plants
SSINS No.: 6820
OMB No.: 3150-0011
NRCB 87-01
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
July 9, 1987
NRC BULLETIN NO. 87-01: THINNING OF PIPE WALLS IN NUCLEAR POWER PLANTS
Addressees:
All licensees for nuclear power plants holding an operating license or a
construction permit.
Purpose:
The purpose of this bulletin is to request that licensees submit information
concerning their programs for monitoring the thickness of pipe walls in
high-energy single-phase and two-phase carbon steel piping systems.
Description of Circumstances:
On December 9, 1986, Unit 2 at the Surry Power Station experienced a
catastrophic failure of a main feedwater pipe, which resulted in fatal
injuries to four workers. This event was reported in IE Information Notice
(TN) 86-1069 "Feedwater Line Break," on December 16, 1986; IN 86-106,
Supplement I., on February 13, 1987; and TN 86-106, Supplement 2, on March
18, 1987. The licensee submitted Licensee Event Report (LER) 86-020-00 on
January 8, 1987; Revision 1, LER 86-020-01, on January 14, 1987; and
Revision 2, LER 86-020-02, on March 31, 1987. A comprehensive report
entitled "Surry Unit 2 Reactor Trip and Feedwater Pipe Failure Report," was
attached to the updated LER, Revisions 1 and 2. The findings of NRC's
Augmented Inspection Team were issued on February 10, 1987, in IE Inspection
Report Nos. 50-280/86-42 and 50-281/86-42.
Investigation of the accident and examination of data by the licensee, NRC,
and others led to the conclusion that failure of the piping was caused by
erosion/corrosion of the carbon steel pipe wall. Although erosion/corrosion
pipe failures have occurred in other carbon steel systems, particularly in
small diameter piping in two-phase systems and in water systems containing
suspended solids, there have been few previously reported failures in large
diameter systems containing high-purity water. Consistent with general
industry practice, the licensee did not have in place an inspection program
for examining the thickness of the walls of feedwater and condensate piping.
Main feedwater systems, as well as other power conversion systems, are
important to safe operation. Failures of active components in these systems,
for example, valves or pumps, or of passive components such as piping, can
result in undesirable challenges to plant safety systems required for safe
shutdown and accident mitigation. Failure of high-energy piping, such as
feedwater
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NRCB 87-01
July 9, 1987
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system piping, can result in complex challenges to operating staff and the
plant because of potential systems interactions of high-energy steam and
water with other systems, such as electrical distribution, fire protection,
and security systems. All licensees have either explicitly or implicitly
committed to maintain the functional capability of high-energy piping
systems that are a part of the licensing basis for the facility. An
important part of this commitment is that piping will be maintained within
allowable thickness values.
Actions Requested:
Within 60 days from the receipt of this bulletin, licensees are requested to
provide the following information concerning their programs for monitoring
the wall thickness of pipes in condensate, feedwater, steam, and connected
high-energy piping systems, including all safety-related and
non-safety-related piping systems fabricated of carbon steel:
1. Identify the codes or standards to which the piping was designed and
fabricated.
2. Describe the scope and extent of your programs for ensuring that pipe
wall thicknesses are not reduced below the minimum allowable thickness.
Include in the description the criteria that you have established for:
a. selecting points at which to make thickness measurements
b. determining how frequently to make thickness measurements
c. selecting the methods used to make thickness measurements
d. making replacement/repair decisions
3. For liquid-phase systems, state specifically whether the following
factors have been considered in establishing your criteria for
selecting points at which to monitor piping thickness (Item 2a):
a. piping material (e.g., chromium content)
b. piping configuration (e.g., fittings less than 10 pipe diameters
part
c. pH of water in the system (e.g., pm less than 10)
d. system temperature (e.g., between 190 and 500 F)
e. fluid bulk velocity (greater than 10 ft/s)
f. oxygen content in the system (e.g., oxygen content less than 50
ppb)
4. Chronologically list and summarize the results of all inspections that
have been performed, which were specifically conducted for the purpose
of identifying pipe wall thinning, whether or not pipe wall thinning
was discovered, and any other inspections where pipe wall thinning was
discovered even though that was not the purpose of that inspection.
a. Briefly describe the inspection program and indicate whether it
was specifically intended to measure wall thickness or whether
wall thickness measurements were an incidental determination.
b. Describe what piping was examined and how (e.g., describe the
inspection, instrument(s), test method, reference thickness,
locations examined, means for locating measurement point(s) in
subsequent inspections).
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NRCB 87-01
July 9, 1987
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c. Report thickness measurement results and note those that were
identified as unacceptable and why.
d. Describe actions already taken or planned for piping that has been
found to have a nonconforming wall thickness. If you have
performed a failure analysis, include the results of that
analysis. Indicate whether the actions involve repair or
replacement, including any change of materials.
5. Describe any plans either for revising the present or for developing
new or additional programs for monitoring pipe wall thickness.
The written report shall be submitted to the appropriate Regional
Administrator under oath or affirmation under provisions of Section 182a,
Atomic Energy Act of 1954, as amended. In addition, the original of the
cover letter and a copy of the report shall be transmitted to the U.S.
Nuclear Regulatory Commission, Document Control Desk, Washington, D.C. 20555
for reproduction and distribution.
This request for information was approved by the Office of Management and
Budget under blanket clearance number 3150-0011. Comments on burden and
duplication may be directed to the Office of Management and Budget, Reports
Management, Room 3208, New Executive Office Building, Washington, D.C.
20503.
NRC intends to summarize the information collected under this bulletin and
study it to help determine if additional actions are required by the staff
and/or industry. The information will be analyzed and placed in the PDR.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate NRC regional office or the technical
contacts listed below.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Paul Wu, NRR
(301) 492-8987
Conrad McCracken, NRR
(301) 492-7042
Attachment: List of Recently Issued Bulletins
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