Information Notice 1999-01, Deterioration of High-Efficiency Particulate Air Filters in a Pressurized Water Reactor Containment Fan Cooler Unit: Difference between revisions

Deterioration of High-Efficiency Particulate Air Filters in a Pressurized Water Reactor Containment Fan Cooler Unit
	ML031040519
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	01/20/1999
From:	Matthews D, Teneyck E; NRC/NMSS/FCSS, Office of Nuclear Reactor Regulation
To:	;
References
	IN-99-001, NUDOCS 9901220109
	Download: ML031040519 (6)
	v • d • e

Latest revision as of 10:59, 16 January 2025

t

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

January 20, 1999

NRC INFORMATION NOTICE 99-01:

DETERIORATION OF HIGH-EFFICIENCY

PARTICULATE AIR FILTERS IN A PRESSURIZED

WATER REACTOR CONTAINMENT FAN

COOLER UNIT

Addressees

All holders of licenses for nuclear power, research and test reactors; and fuel cycle facilities.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert

addressees to previously unknown service life and service condition limitations of high

efficiency particulate air (HEPA) filters that are used in ventilation systems by licensees of

power, research and test reactors; and certain fuel cycle facilites. It is expected that recipients

will review the information for applicability to their facilities and consider actions, as appropriate.

However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response to this notice is required.

Descriotion of Circumstances

On September 13, 1998, the operators at Consolidated Edison's (Con Edison's) Indian Point 2 (IP-2) Nuclear Power Plant received a low-flow alarm on one of the five containment fan cooler

units (FCUs). Con Edison personnel inspected the FCU's internal components and found that

one of the HEPA filters in the bottom row had failed and clogged the fan intake screen. The

FCU contains a bank of 64 HEPA filters, each 2 feet by 2 feet in size. Five other filters near

the failed filter were badly damaged. To confirm the extent of the problem, Con Edison

subsequently inspected the other 4 FCUs. One FCU had HEPA filters in which the urethane

seal had pulled away from the filter frame and the filter medium had assumed an hour- glass

shape. Con Edson concluded that the problem had a potential common-mode failure

mechanism that could significantly degrade both the cooling of the FCU and the filtering by the

HEPA filters.

Discussion

The HEPA filters in the two affected FCUs were Series Model 8 manufactured by Flanders

Filter Corporation; they are no longer made. The Series 8 filter consists of a square stainless

steel frame and a convoluted filter medium made of glass fibers held together by an acrylic

latex binder and coated with a silicone waterproofing agent. The filter medium is secured to all

990122 An

c

IN 99-01 January 20, 1999 four sides of the filter frame by a urethane coating and, unlike many other HEPA filter designs, does not have internal stiffeners or corrugated separators to support the glass fibers. These

HEPA filters were installed in 1991 and, due to being located in the normal air flow, have been

in almost continuous use since then; many other FCU designs have the filters in service only

during testing or an accident.

Con Edison identified many causes contributing to the unexpected failure and degradation of

the HEPA filters, such as (1) excess water (from condensation as well as carryover from the

upstream de-misters, which had plugged or partially plugged drain lines) which Increased filter

loading and distortion, (2) inadequate surveillance for detecting filter degradation or determining

when HEPA filters should be replaced, and (3) no established service life. A technical report

prepared for Con Edison following testing of samples of new and used HEPA filter media

provided quantitative support for this root cause determination. While inherent weaknesses in

the FCU design (such as having the HEPA filters in the normal flow stream) and poor

preventive maintenance practices (such as not monitoring the condition of the upstream FCU

de-mister drains) were noted, previously unknown limitations regarding HEPA filter service life

and the effect of service conditions were revealed.

HEPA filters used in the FCUs at IP-2 are required by Technical Specifications to be

surveillance tested every refueling outage. Such testing involves (1) visual inspection in

accordance with ANSI Standard N510-1975 for indications of filter damage (e.g., filter medium

tears, cracks, or bums, and damage to seating gaskets) and excessive dirt loading, (2) a check

for filter bypass by a dioctylphthalate (DOP) aerosol efficiency test, and (3) measurement of air

flow and differential pressure across the filter bank. This testing does not check for evidence of

current or prior media wetting. The initial qualification testing of the HEPA filters, as specified in

Military Specification F-51068, did subject the filter to a continuous water spray during the

resistance-to-pressure test performed at higher than accident condition flows. However, the

filters were not subsequently subjected to any type of testing to demonstrate that they remain

capable of performing their intended function. Consequently, loss of structural strength and

deterioration can go undetected and can result in failure during design-basis conditions when

the filters will be subjected to a much higher temperature, much higher differential pressure and

much more entrained moisture than during normal service conditions.

Filter media testing found a significant loss of silicone waterproofing agent from filter media

samples that had seen a long service life - up to 7 years. This reduction allowed the filter

medium to absorb water readily; little or no observable water absorption was observed on new

filter media. As the water is absorbed, the medium expands and closes the medium filter

pores. However, since the differential pressure is typically measured across an entire bank of

filters, local water loading in one or more filters does not enable the overall differential pressure

to rise sufficiently to disclose a problem with the HEPA filters. Moreover, a damaged or failed

filter could reduce the differential pressure across the filter bank. Water absorption also

increases the weight of the filter medium and can weaken it. The service life of a filter is highly

dependent upon HEPA service conditions, which includes high moisture content, entrained

solids In the air, and elevated temperatures.

The Department of Energy (DOE) recently sponsored research into HEPA filter deterioration

when several HEPA filters in a ventilation system at the Rocky Flats Environmental Technology

Site failed. Those filters had been in service for more than 15 years and had been repeatedly

subjected to wetting by an upstream fire protection deluge system test. The testing conducted

involved filter media from a variety of HEPA filter manufacturers, although most manufacturers

~1- IN 99-01 January 20, 1999 use similar filter media. This research also showed significant losses in the tensile strength of

HEPA filter following the wetting of used filters; it also showed that the tensile strength was not

recovered fully restored after drying. Further water exposures resulted in additional losses in

filter media tensile strength. The results of this research were publicized at the 25th DOEINRC

Nuclear Air Cleaning and Treatment Conference. The DOE research data cannot be used to

quantify the useful life of a HEPA filter, but the data do demonstrate that there is a finite HEPA

filter life and that wetting of the filter medium reduces its strength.

In response to the research findings, Con Edison replaced the filters in the two affected FCUs

with new Flanders Series F & W filters that incorporate internal stiffeners to help support the

filter medium. Con Edison has limited the service cycle of the FCU HEPA filters to 6 years and

implemented inspections to confirm the following: (1) the integrity of the urethane seal between

the filter medium and filter housing, (2) proper drainage from the FCU, and (3) the extent of

water condensation and/or direct wetting of the filters.

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, the appropriate regional office, or the appropriate office of Nuclear Reactor

Regulation (NRR) Project Manager.

Dire

r

Division of Fuel Cycle Safety

and Safeguards

Office of Nuclear Material Safety

and Safeguards

David B. Matthews, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical Contacts:

Richard S. Barkley, Region I

610-337-5065 E-Mail: rsbl@nrc.gov

John J. Hayes, NRR

301-415-3167 E-Mail: hh@nrc.gov

John P. Segala, NRR

301-415-1858 E-Mail: jpsl@nrc.gov

Jerry Carter, NRR

301-415-1153 E-Mail: tjc@nrc.gov

Bill Troskoski, NMSS

301-415-8076 E-mail: wmt@nrc.gov

Attachments: List of Recently Issued NMSS Information Notices

List of Recently Issued NRC I foation Notices

Vdss

jaflon:a-

A

&\\1 Attachment

IN 98-45

December 15, 1998 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject- Issuance

Issued to

98-45 Cavitation Erosion of Letdown Line 12/15/98

All holders of operating licenses

Orifices Result in Fatigue Cracking

of Pipe Welds

for nuclear power reactors, except

those that have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor.

98-44 Ten-year Inservice Inspection

12110/98 (ISI) Program Update for Licensees

that Intend to Implement Risk-Informed

ISI of Piping

98-43

98-42

Leaks in the Emergency Diesel

Generator Lubricating Oil and

Jacket Cooling Water Piping

12/04/98

All holder of operating licenses

for nuclear power reactors, except

those that have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor

All holder of operating licenses

for nuclear power reactors, except

those licensees that have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor vessel

All holders of operating licenses

for nuclear power reactors

All holders of operating licenses

for nuclear power reactors, except

for those who have ceased

operations and have certified that

fuel has been permanently

removed from the reactor vessel

Implementation of 10 CFR 50.55a

12/01/98 (g) Inservice Inspection Requirements

98-41 Spurious Shutdown of Emergency

11/20/98

Diesel Generators from Design

Oversight

OL = Operating License

CP = Construction Permit

_

99-01 January 20, 1999 use similar filter media. This research also showed significant losses in the tensile strength of

HEPA filter following the wetting of used filters; it also showed that the tensile strength was not

recovered fully restored after drying. Further water exposures resulted in additional losses in

filter media tensile strength. The results of this research were publicized at the 25th DOE/NRC