Information Notice 1999-01, Deterioration of High-Efficiency Particulate Air Filters in a Pressurized Water Reactor Containment Fan Cooler Unit
t January 20, 1999NRC INFORMATION NOTICE 99-01:DETERIORATION OF HIGH-EFFICIENCYPARTICULATE AIR FILTERS IN A PRESSURIZEDWATER REACTOR CONTAINMENT FANCOOLER 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 alertaddressees to previously unknown service life and service condition limitations of highefficiency particulate air (HEPA) filters that are used in ventilation systems by licensees ofpower, research and test reactors; and certain fuel cycle facilites. It is expected that recipientswill 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 CircumstancesOn 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 coolerunits (FCUs). Con Edison personnel inspected the FCU's internal components and found thatone of the HEPA filters in the bottom row had failed and clogged the fan intake screen. TheFCU contains a bank of 64 HEPA filters, each 2 feet by 2 feet in size. Five other filters nearthe failed filter were badly damaged. To confirm the extent of the problem, Con Edisonsubsequently inspected the other 4 FCUs. One FCU had HEPA filters in which the urethaneseal had pulled away from the filter frame and the filter medium had assumed an hour- glassshape. Con Edson concluded that the problem had a potential common-mode failuremechanism that could significantly degrade both the cooling of the FCU and the filtering by theHEPA filters.DiscussionThe HEPA filters in the two affected FCUs were Series Model 8 manufactured by FlandersFilter Corporation; they are no longer made. The Series 8 filter consists of a square stainlesssteel frame and a convoluted filter medium made of glass fibers held together by an acryliclatex binder and coated with a silicone waterproofing agent. The filter medium is secured to all990122 An c IN 99-01January 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. TheseHEPA filters were installed in 1991 and, due to being located in the normal air flow, have beenin almost continuous use since then; many other FCU designs have the filters in service onlyduring testing or an accident.Con Edison identified many causes contributing to the unexpected failure and degradation ofthe HEPA filters, such as (1) excess water (from condensation as well as carryover from theupstream de-misters, which had plugged or partially plugged drain lines) which Increased filterloading and distortion, (2) inadequate surveillance for detecting filter degradation or determiningwhen HEPA filters should be replaced, and (3) no established service life. A technical reportprepared for Con Edison following testing of samples of new and used HEPA filter mediaprovided quantitative support for this root cause determination. While inherent weaknesses inthe FCU design (such as having the HEPA filters in the normal flow stream) and poorpreventive maintenance practices (such as not monitoring the condition of the upstream FCUde-mister drains) were noted, previously unknown limitations regarding HEPA filter service lifeand the effect of service conditions were revealed.HEPA filters used in the FCUs at IP-2 are required by Technical Specifications to besurveillance tested every refueling outage. Such testing involves (1) visual inspection inaccordance with ANSI Standard N510-1975 for indications of filter damage (e.g., filter mediumtears, cracks, or bums, and damage to seating gaskets) and excessive dirt loading, (2) a checkfor filter bypass by a dioctylphthalate (DOP) aerosol efficiency test, and (3) measurement of airflow and differential pressure across the filter bank. This testing does not check for evidence ofcurrent or prior media wetting. The initial qualification testing of the HEPA filters, as specified inMilitary Specification F-51068, did subject the filter to a continuous water spray during theresistance-to-pressure test performed at higher than accident condition flows. However, thefilters were not subsequently subjected to any type of testing to demonstrate that they remaincapable of performing their intended function. Consequently, loss of structural strength anddeterioration can go undetected and can result in failure during design-basis conditions whenthe filters will be subjected to a much higher temperature, much higher differential pressure andmuch more entrained moisture than during normal service conditions.Filter media testing found a significant loss of silicone waterproofing agent from filter mediasamples that had seen a long service life -up to 7 years. This reduction allowed the filtermedium to absorb water readily; little or no observable water absorption was observed on newfilter media. As the water is absorbed, the medium expands and closes the medium filterpores. However, since the differential pressure is typically measured across an entire bank offilters, local water loading in one or more filters does not enable the overall differential pressureto rise sufficiently to disclose a problem with the HEPA filters. Moreover, a damaged or failedfilter could reduce the differential pressure across the filter bank. Water absorption alsoincreases the weight of the filter medium and can weaken it. The service life of a filter is highlydependent upon HEPA service conditions, which includes high moisture content, entrainedsolids In the air, and elevated temperatures.The Department of Energy (DOE) recently sponsored research into HEPA filter deteriorationwhen several HEPA filters in a ventilation system at the Rocky Flats Environmental TechnologySite failed. Those filters had been in service for more than 15 years and had been repeatedlysubjected to wetting by an upstream fire protection deluge system test. The testing conductedinvolved filter media from a variety of HEPA filter manufacturers, although most manufacturers
~1-IN 99-01January 20, 1999 use similar filter media. This research also showed significant losses in the tensile strength ofHEPA filter following the wetting of used filters; it also showed that the tensile strength was notrecovered fully restored after drying. Further water exposures resulted in additional losses infilter media tensile strength. The results of this research were publicized at the 25th DOEINRCNuclear Air Cleaning and Treatment Conference. The DOE research data cannot be used toquantify the useful life of a HEPA filter, but the data do demonstrate that there is a finite HEPAfilter 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 FCUswith new Flanders Series F & W filters that incorporate internal stiffeners to help support thefilter medium. Con Edison has limited the service cycle of the FCU HEPA filters to 6 years andimplemented inspections to confirm the following: (1) the integrity of the urethane seal betweenthe filter medium and filter housing, (2) proper drainage from the FCU, and (3) the extent ofwater condensation and/or direct wetting of the filters.This information notice requires no specific action or written response. If you have anyquestions about the information in this notice, please contact one of the technical contactslisted below, the appropriate regional office, or the appropriate office of Nuclear ReactorRegulation (NRR) Project Manager.Dire rDivision of Fuel Cycle Safetyand SafeguardsOffice of Nuclear Material Safetyand SafeguardsDavid B. Matthews, DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical Contacts:Richard S. Barkley, Region I610-337-5065E-Mail: rsbl@nrc.govJohn J. Hayes, NRR301-415-3167E-Mail: hh@nrc.govJohn P. Segala, NRR301-415-1858E-Mail: jpsl@nrc.govJerry Carter, NRR301-415-1153E-Mail: tjc@nrc.govBill Troskoski, NMSS301-415-8076E-mail: wmt@nrc.gov
Attachments:
List of Recently Issued NMSS Information NoticesList of Recently Issued NRC I foation Notices#Vdss jaflon:a- A&\1AttachmentIN 98-45December 15, 1998 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject- Issuance Issued to98-45 Cavitation Erosion of Letdown Line 12/15/98 All holders of operating licensesOrifices Result in Fatigue Crackingof Pipe Weldsfor nuclear power reactors, exceptthose that have permanentlyceased operations and havecertified that fuel has beenpermanently removed from thereactor.98-44Ten-year Inservice Inspection 12110/98(ISI) Program Update for Licenseesthat Intend to Implement Risk-InformedISI of Piping98-4398-42Leaks in the Emergency DieselGenerator Lubricating Oil andJacket Cooling Water Piping12/04/98All holder of operating licensesfor nuclear power reactors, exceptthose that have permanentlyceased operations and havecertified that fuel has beenpermanently removed from thereactorAll holder of operating licensesfor nuclear power reactors, exceptthose licensees that havepermanently ceased operationsand have certified that fuel hasbeen permanently removed fromthe reactor vesselAll holders of operating licensesfor nuclear power reactorsAll holders of operating licensesfor nuclear power reactors, exceptfor those who have ceasedoperations and have certified thatfuel has been permanentlyremoved from the reactor vesselImplementation of 10 CFR 50.55a 12/01/98(g) Inservice Inspection Requirements98-41Spurious Shutdown of Emergency 11/20/98Diesel Generators from DesignOversightOL = Operating LicenseCP = Construction Permit
_ 99-01January 20, 1999 use similar filter media. This research also showed significant losses in the tensile strength ofHEPA filter following the wetting of used filters; it also showed that the tensile strength was notrecovered fully restored after drying. Further water exposures resulted in additional losses infilter media tensile strength. The results of this research were publicized at the 25th DOE/NRCNuclear Air Cleaning and Treatment Conference. The DOE research data cannot be used toquantify the useful life of a HEPA filter, but the data do demonstrate that there is a finite HEPAfilter 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 FCUswith new Flanders Series F & W filters that incorporate internal stiffeners to help support thefilter medium. Con Edison has limited the service cycle of the FCU HEPA filters to 6 years andimplemented inspections to confirm the following: (1) the integrity of the urethane seal betweenthe filter medium and filter housing, (2) proper drainage from the FCU, and (3) the extent ofwater condensation and/or direct wetting of the filters.This information notice requires no specific action or written response. If you have anyquestions about the information in this notice, please contact one of the technical contactslisted below, the appropriate regional office, or the appropriate office of Nuclear ReactorRegulation (NRR) Project Manager.orig IsI'd by orig Is! 'd byElizabeth 0. Ten Eyck, Director David B. Matthews, DirectorDivision of Fuel Cycle Safety Division of Reactor Program Managementand Safeguards Office of Nuclear Reactor RegulationOffice of Nuclear Material Safetyand SafeguardsTechnical Contacts: Richard S. Barkley, Region I John J. Hayes, NRR610-337-5065 301-415-3167E-Mail: rsbl@nrc.gov E-Mail: jjh@nrc.govJohn P. Segala, NRR Jerry Carter, NRR301-415-1858 301-415-1153E-Mail: jpslnrc.gov E-Mail: tjc~nrc.govBill Troskoski, NMSS301-415-8076E-mail: wmt@nrc.gov
Attachments:
List of Recently Issued NMSS Information NoticesList of Recently Issued NRC Information NoticesDOCUMENT NAME: g:\TJC\HEPA2AIN.WPDTo receive a coDv of this document, indicate in the box C=Coov wlo attachment/enclosure E=Copy with attachment/enclosure N = No copyr \ I _[OFFICE PECI I Rl1 I PERB D:NMSS PECB I lPEC Il ['NAME J Carter* _RBarkely* JCMiller* _ETen Eyck* IRDennig* JStolz* DMatthew[ DATE 1 12/23/98 l 12/24/98 1 12/28/98 1 01/11/99 I 12/24/98 1112/99 I 014/99OFFICIAL RECORD COPY IN 98-xxDecember xx, 1998 use similar filter media. This research also showed significant losses in the tensile strength ofHEPA filter following the wetting of used filters; it also showed that the tensile strength was notrecovered fully after drying. Further water exposures resulted in additional losses in filter mediatensile strength. The results of this research were publicized at the 25th DOE/NRC NuclearAirCleaning and Treatment Conference. The DOE research data cannot be used to quantify theuseful life of a HEPA filter, but the data do demonstrate that there is a finite HEPA filter life andthat wetting of the filter medium reduces its strength.In response to the research findings, Con Edison replaced the filters in the two affected FCUswith new Flanders Series F & W filters that incorporate internal stiffeners to help support thefilter medium. Con Edison has limited the service cycle of the FCU HEPA filters to 6 years andimplemented inspections to confirm the following: (1) the integrity of the urethane seal betweenthe filter medium and filter housing, (2) proper drainage from the FCU, and (3) the extent ofwater condensation and/or direct wetting of the filters.Con Edison has also applied for a Technical Specification amendment that would delete therequirement for HEPA filters and the downstream charcoal beds from the containment FCUs.This amendment is based on analyses that show the equipment can be removed withoutsignificantly affecting the radiological consequences of a design-basis loss-of-coolant accidentat IP-2.This information notice requires no specific action or written response. If you have anyquestions about the information in this notice, please contact one of the technical contactslisted below or the appropriate office of Nuclear Reactor Regulation (NRR) Project Manager.Elizabeth Q. Ten Eyck, Director Jack W Roe, Acting DirectorDivision of Fuel Cycle Safety Division of Reactor Program Managementand Safeguards Office of Nuclear Reactor RegulationOffice of Nuclear Material Safetyand SafeguardsTechnical Contacts: Richard S. Barkley, Region I John J. Hayes, NRR610-337-5065 301-415-3167E-Mail: rsbl@nrc.gov E-Mail: jh@nrc.govJohn P. Segala, NRR Jerry Carter, NRR301-415-1858 301-415-1153E-Mail: jps1@nrc.gov E-Mail: tjcenrc.govta~h~merS List of Recently Issued NRC Information NoticesDOCUW NT NAME:To receive a copy of this document, Indicate In the box C=Copy w/o attachment/enclosure E=Copy with attachmentfnclosure N= No copyOFFICE 1IECB I I RI, Gl IPERB I JI D:NMSjz II l E it lPECB I IADDRPNAME JlFfer I Wlarke1 I CMillerNtkkETEN EfCK I F ia9' I l6t7- L eD --98- k ilts -- I I 1..9. /OFFICIAL RE 9 COPY