Information Notice 2020-04, Operating Experience Regarding Failure of Buried Fire Protection Main Yard Piping
| ML20223A333 | |
| Person / Time | |
|---|---|
| Issue date: | 12/17/2020 |
| From: | Mark Lintz, Chris Miller NRC/NRR/DRO/IOEB |
| To: | |
| Mark Litz NRR/DRO/IOEB, 415-4051 | |
| References | |
| IN-20-004 | |
| Download: ML20223A333 (7) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 December 17, 2020
NRC INFORMATION NOTICE 2020-04: OPERATING EXPERIENCE RELATED TO FAILURE
OF BURIED FIRE PROTECTION MAIN YARD PIPING
ADDRESSEES
All holders of, or applicants for, a fuel facility license under Title 10 of the Code of Federal
Regulations (10 CFR) Part 40, Domestic licensing of source material.
All holders of and applicants for an operating license or construction permit for a nuclear power
reactor issued under 10 CFR Part 50, Domestic licensing of production and utilization facilities, including those that have permanently ceased operations and certified that fuel has been
permanently removed from the reactor vessel.
All holders of and applicants for a power reactor combined license, standard design approval, or
manufacturing license under 10 CFR Part 52, Licenses, certifications, and approvals for nuclear
power plants. All applicants for a standard design certification, including such applicants after
initial issuance of a design certification rule.
All holders of, or applicants for, a fuel cycle facility license under 10 CFR Part 70, Domestic
licensing of special nuclear material.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform the
addressees of operating experience involving the loss of function of buried cast iron fire water main
yard piping due to multiple factors, including graphitic corrosion 1, overpressuration, low-cycle
fatigue, and surface loads. Some of the operating experience has not been captured in industry- wide operating experience reports. The NRC expects that recipients will review the information for
applicability to their facilities and consider actions, as appropriate, to avoid similar problems. INs
may not impose new requirements, and nothing in this IN should be interpreted to require specific
action.
BACKGROUND
Appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR Part 50 establishes the
minimum criteria for materials, design, fabrication, testing, inspection, and certification of all
structures, systems, and components important to safety. In 10 CFR 50.48, Fire protection, the
NRC requires that each operating nuclear power plant has a fire protection plan that satisfies 10 CFR Part 50, Appendix A, General Design Criterion 3, Fire protection. General Design Criterion 3 states that fire detection and fighting systems of appropriate capacity and capability be provided
and designed to minimize the adverse effect of fires on structures, systems, and components that
1 Graphitic corrosion is a form of galvanic corrosion that occurs in wet or moist environments; it is also known as
selective leaching.
ML20223A333 are important to safety, and that firefighting systems be designed to assure that their rupture or
inadvertent operation does not significantly impair the safety capability of these structures, systems, and components. Subpart H of 10 CFR Part 70 establishes the NRC's fire protection program
requirements for fuel cycle facilities. Some specific source material licensees have similar
commitments in their NRC license. In 10 CFR 70.61 of Subpart H, the NRC requires each
applicant or licensee to limit the risk of each credible high-consequence event. Several fuel cycle
facilities, including some specific source material facilities, have fire suppression systems credited
as mitigative controls needed to meet these performance requirements. The purpose of these
programs is to safeguard any nuclear material on site and protect the public from radioactive
releases due to a fire event.
The fire protection main yard piping is typically maintained at required operating pressures using
pressure maintenance components, such as a jockey pump. The smaller pump accommodates
nominal system leakage from either non-pressure-boundary sources (e.g., packing, gaskets) or
pressure boundary sources (e.g., through-wall defect). The jockey pump prevents cycling of the
larger main fire pumps, which start on decreasing header pressure or another anticipatory signal.
As pipes leak, over time, the water pressure inside becomes more difficult to maintain within the set
points of the jockey pump.
The water supply of any fire protection system is often considered the most critical component of
the system. The function of underground or buried fire water main yard piping is to move the water
from its source to its final point of use. This piping must be extremely reliable, capable, and able
automatically to distribute enough water directly to a fire to extinguish it or to hold it in check until
the fire brigade arrives.
Internal corrosion of ferrous piping materials (cast iron, ductile iron, and carbon steel) can be a
problem for fire water supply systems. Microbiological action is the most common mechanism
causing the internal corrosion process to occur. Living microorganisms such as sulfate-, iron-, and
manganese-reducing bacteria cause this form of corrosion. These bacteria can develop in the
piping environment with or without oxygen. They can be concentrated and accelerate internal
corrosion, causing either pitting (creating pinhole leaks) or mineral deposits that introduce
increased pressure loss due to the turbulence of the water flow. This is referred to as
microbiologically induced corrosion. External corrosion of buried fire water main yard piping has no
adverse effect on the flow of water through the piping system, up to the point of pipe failure.
Factors influencing external corrosion of buried cast iron piping include piping material, soil
corrosivity, and stray electric ground currents.
Actions to mitigate external corrosion typically include properly designed and applied coatings;
appropriately specified and installed backfill; and properly designed, tested, and maintained
cathodic protections systems. Coatings, however, have a finite effective life, and coating
degradation has been identified in some instances of external corrosion. One method of minimizing
both internal and external corrosion of buried fire water main yard piping is to use nonferrous piping
materials such as HDPE. Some plants have replaced cast iron piping with HDPE piping because it
is immune to service water corrosion and highly resistant to fouling.
Some plants have replaced cast iron piping with HDPE piping because it is immune to service water
corrosion and highly resistant to fouling. However, HDPE piping is a relatively new material
compared to cast iron piping, and therefore long-term service-life data does not exist in significant
quantities. The NRC has approved the replacement of steel piping with HDPE piping in American
Society of Mechanical Engineers Class 3 safety-related nuclear service water system piping associated with the essential service water system at Callaway Plant (ADAMS Accession No.
ML083100288), the emergency diesel generator jacket water coolers at Catawba Nuclear Station
(Catawba) (ADAMS Accession No. ML091240156), and the plant service water at Hatch, Unit 2 (ADAMS Accession No. ML15337A414). In addition, Catawba has installed aboveground HDPE for
nonsafety-related applications. Nonsafety-related use is not part of the NRC approval.
Monitoring jockey pump run times and fire water storage tank levels for adverse trends may help to
detect leaks that could further degrade piping. Excessive jockey pump cycling or a pump that is
continuously running may be indicative of a leak that can erode the supporting soil, resulting in the
cast iron piping being unsupported and subject to tensile stress. These conditions can result in
catastrophic failure of the fire main.
DISCUSSION
Many probabilistic risk assessments (PRA) have shown that fire is a potentially important risk
contributor for U.S. nuclear power plants and may be a significant contributor to a plants total core
damage frequency. 2 This IN gives examples in which failures of the buried fire water system main
yard piping involved degradation from selective leaching (graphitic corrosion), overpressure, cyclic
fatigue, and surface loads. Degradation of buried fire water main yard piping could impair the
operation of the fire water suppression system and thus impact the overall risk at the plant.
Cast iron piping is susceptible to the loss of material caused by selective leaching, and it is prone to
sudden ruptures because of its brittle nature. Multiple failures have occurred when pressure
transients from main fire pump starts caused significant cracking in the cast iron piping. These
ruptures have mostly occurred during periodic pump testing and indicate an increased likelihood of
failures during an actual demand on the fire protection system. Taking steps to minimize pressure
transients during periodic testing may mask potential piping degradation.
Leakage from the fire protection water system can be assessed by monitoring pressure
maintenance during component activity (e.g., jockey pump run times). However, non- pressure-boundary leakage cannot be distinguished readily from through-wall degradation, and the
ability to find leakage locations in buried piping will depend on the leak rate and soil drainage
characteristics. In addition, long-term non-pressure-boundary leakage may contribute to higher soil
corrosivity, resulting in more aggressive degradation of the piping. The examples discussed in this
IN illustrate the importance of an effective fire water system aging management program and
represent operating experience related to the failure of buried fire water main yard piping at
operating nuclear power plant sites.
Buried fire water piping systems are built to withstand high levels of pressure. However, the sudden
starting and stopping of flow caused by such components as pumps or hydrants can trigger a
sudden and even dangerous increase in pressure that those systems cannot handle. Buried fire
water piping is vulnerable to cracking from applied loads, such as pressure surges or other dynamic
loading.
2 These include the NRC technical opinion paper Fire PRA Maturity and Realism: A Technical Evaluation, issued January 2016 (Agencywide Documents Access and Management System (ADAMS) Accession
No. ML16022A266), and various detailed plant fire risk analyses related to license amendment requests for the
transition to a risk-informed, performance-based fire protection program in accordance with National Fire
Protection Association (NFPA) 805, Performance-Based Standard for Fire Protection for Light Water Reactor
Electric Generating Plants, and Technical Specifications Task Force Traveler TSTF-505, Provide Risk-Informed
Extended Completion TimesRITSTF Initiative 4b. Nothing in this IN should be interpreted to require specific action; however, enhancements used at
other sites include 1) replacing buried piping with high-density polyethylene (HDPE) piping;
2) incorporating current National Fire Protection Association (NFPA) code and standard
requirements; and 3) expanding the scope of inspection so that the intended function(s) of
structures, systems, and components will be maintained consistent with the current licensing basis
through the period of extended operation.
DESCRIPTION OF CIRCUMSTANCES
Operating experience has indicated that multiple failures of the buried cast iron fire water main yard
piping have occurred due to aging effects, including graphitic corrosion (i.e., selective leaching),
corrosion buildup, low-cyclic fatigue, and general wall thinning or localized loss of material.
Degradation can occur internally or externally to the pipe, or both. Degradation may develop due to
environmental conditions, or it may be initiated as a result of deficiencies in system design, installation, or maintenance. Licensees can detect only such flow blockage as fouling from silt or
sediment, internal coating failures that block flow, or internal tuberculation (i.e., small mounds of
corrosion products on the inside of the pipe). Internal degradation due to corrosion, selective
leaching, or cracking cannot be detected by NFPA periodic testing. Below are descriptions of
recent or recently available operating experience concerning failures of buried fire water main yard
piping.
Edwin I. Hatch Nuclear Plant, Units 1 and 2
On January 25, 2019, a buried 12-inch-diameter fire protection cement-lined cast iron main yard
pipe ruptured as a result of fire water sectional valve isolation capability testing. The pressure
drops from the rupture led to all three fire water pumps starting on a low-pressure signal. After
securing the two diesel-driven fire water pumps, the licensee was able to maintain the system
header pressure with only the motor-driven and jockey pumps running.
The piping rupture was caused by the start of a fire pump and the subsequent pressure surge. The
resulting leak eroded the supporting soil around the pipe, intensifying the bending forces on the
pipe, with a catastrophic pipe failure occurring four hours after the initial pressure change. During
the four-hour period between the fire water sectional valve isolation capability testing and the pipe
rupture, the licensee observed that the jockey fire pump was cycling excessively, indicating a loss
of pressure in the fire protection system from the leak. The licensee later identified a preexisting
pipe crack that had propagated over time until the remaining piping material could no longer
withstand the stresses and ultimately failed.
Surry Power Station, Units 1 and 2
On July 13, 2019, during a periodic test of the electric fire pump, a rupture occurred in a buried
section of 12-inch-diameter fire protection main yard piping. The resulting loss of system pressure
initiated an automatic start of the diesel-driven fire pump. Operators isolated the leak, restoring the
fire protection system function after approximately 18 minutes, but the leak resulted in a loss of an
estimated 112,000 gallons from the fire protection water tanks.
The fire protection main yard piping was made of gray cast iron, internally lined with cement mortar
and externally protected with a bituminous coating. Initial investigation into the rupture found a
10-foot longitudinal crack along the bottom surface of the pipe, and a second circumferential crack
on an adjacent pipe segment that was apparently caused by uplift forces from flow through the initial longitudinal crack. Subsequent evaluations determined that long standing exposure to moist
or wet soil had resulted in the external reduction in wall thickness at several locations due to
graphitic corrosion. The thin asphalt coating could not protect the pipe from the highly corrosive
environment. The piping was approximately 49 years old. The licensee modified its selective
leaching aging management program to increase the number of examinations that it performed to
identify selective leaching. Additional information can be found in Virginia Electric and Power Co.,
Supplement to Subsequent License Renewal Application, dated October 31, 2019 (ADAMS
Accession No. ML19310E716).
July 2019 Surry Power Station Fire Main Yard Loop Piping Rupture
(ADAMS Accession No. ML20056D677)
North Anna Power Station, Units 1 and 2
In October 2001, a 12-inch buried fire water main yard pipe ruptured during routine fire pump
performance testing. Excavation identified a crack more than eight feet long that had progressed
mainly in the axial direction down the length of the pipe. The analysis of the gray cast iron piping
determined that the failure most likely occurred as a result of a low-cycle fatigue process that
originated at a pre-existing manufacturing flaw in the pipe. Periodic pump tests apparently caused
pressure surges in the system. Otherwise, the overall condition of the pipe appeared to be good, with no indications of damage to the internal mortar lining or of external corrosion. This information
was recently provided as part of the North Anna Power Station, Application for Subsequent License
Renewal, August 24, 2020 (ADAMS Accession No. ML20246G696).
CONTACT
Please direct any questions about this matter to the technical contacts listed below or to the
appropriate Office of Nuclear Reactor Regulation (NRR) or Office of Nuclear Material Safety and
Safeguards (NMSS) project manager.
/RA/
Christopher G. Miller, Director
Division of Reactor Oversight
Office of Nuclear Reactor Regulation
Technical Contacts: Naeem Iqbal, NRR James A. Gavula, NRR
301-415-3346 630-829-9755 E-mail: Naeem.Iqbal@nrc.gov E-mail: James.Gavula@nrc.gov
Brian D. Allik, NRR James Downs, NMSS
610-337-5376 301-415-7744 E-mail: Brian.Allik@nrc.gov E-mail: James.Downs@nrc.gov
John Dymek, Region II
404-997-4496 E-mail: John.Dymek@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library/Document Collections.
ML20223A333 *concurred via e-mail
OFFICE APLB:DRA:NRR* NCSG:DNLR:NRR* NCSG:DNLR:NRR* BC:EB2:DRS:RII*
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OFFICE EB2:DRS:RII* Tech Editor* BC:APLB:DRA:NRR* BC:NCSG:DNRL:NRR*
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DATE 12/01/2020 12/17/2020