LiuAq i-ruu_

NUREG/CR-6029

PNL-8594

Vol. 1

_ Aging Assessment of

Nuclear Air-Treatment System

HEPA Filters and Adsorbers

Phase I *. 7 f

Prepared by

W. K. Winegardner

Pacific Northwest Laboratory

Operated by

Battelle Memorial Institute

Prepared for

U.S. Nuclear Regulatory Commission

R A 44'at
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NUREG/CR-6029

PNL-8594

Vol. 1

RX

Aging Assessment of

Nuclear Air-Treatment System

HEPA Filters and Adsorbers

Phase I

Manuscript Completed: March 1993

Date Published: August 1993

Prepared by

W. K. Winegardner

Pacific Northwest Laboratory

Richland, WA 99352

Prepared for

Division of Engineering

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

NRC FIN B2911
Abstract

A Phase I aging assessment of high-efficiency particulate air (HEPA) filters and activated carbon gas adsorption units

(adsorbers) was performed by the Pacific Northwest Laboratory (PNL) as part of the US. Nuclear Regulatory Commission's (NRC) Nuclear Plant Aging Research (NPAR) Program. Information concerning design features; failure

experience; aging mechanisms, effects, and stressors; and surveillance and monitoring methods for these key airtreatment system components was compiled. Over 1100 failures, or 12 percent of the filter installations, were reported

as part of a Department of Energy (DOE) survey. Investigators from other national laboratories have suggested that

aging effects could have contributed to over 80 percent of these failures. Jensile strength tests on aged filter media

specimens Indicated a decrease in strength. Filter aging mechanisms range from those associated with particle loading

to reactions that alter properties of sealants and gaskets. Low radioiodine decontamination factors associated with the

Three Mile Island (TMI) accident were attributed to the premature aging of the carbon in the adsorbers. Mechanisms

that can lead to impaired adsorber performance include oxidation as well as the loss of potentially available active sites

as a result of the adsorption of pollutants. Stressors include heat, moisture, radiation, and airborne particles and

contaminants.

iii NUREG/CR-6029
Contents

Abstract ............................................................... iii

Summary ............................................................... vii

Acknowledgments ............................................................... ix

Nomenclature ..................................................................................... xi

1 Introduction ................................................................................... 1.1

2 Background .................................................................................. 2.1

3 Component Design and Construction .............................................................. 3.1

3.1 HEPA Filters . .............................................................................. 3.1

3.2 Adsorbers .................................................................................. 33

3.3 Supporting Documents . ...................................................................... 3.4

4 Aging Mechanisms, Effects, and Stressors .......................................................... 4.1

4.1 HEPA Filters ............................................................................... 41

4.2 Adsorbers .................................................................................. 4.2

5 Failure Experience . .............................................................................. 5.1

5.1 Licensee Event Reports ....................................... 5.1

5.2 DOE Site Survey ....................................... 5.1

5.3 TMI Accident ..... ............. ...................... 5.2

6 Inspection, Surveillance, and Monitoring Methods .......................... ............. 6.1

6.1 HEPA Filters ........................................ 6.1

6.2 Adsorbers ........................................ 6.2

7 Conclusions ................................ 7.1

7.1 Normal Operating and Error-Induced Conditions ................... .................... 7.1

v NUREG/CR-6029
Contents

7.2 Reactor Accident Conditions ............................ 7.1

73 Conclusions and Recommendations ............................ 7.4

8 References ................................ &

NUREG/CR-6029 vi
Summary

Nuclear air-treatment systems are one of a variety of systems that provide a safe environment for plant personnel and

equipment during normal operations as well as retain radionuclides during accidents. High-efficiency particulate air

(HEPA) filters and activated carbon gas adsorption units (adsorbers), designed to capture radioactive particulate and

gaseous contaminants, are the key components of these systems. This report presents the results of a Phase I aging

assessment for these two key components. Information concerning design features and construction; failure

experience; aging mechanisms, effects, and related stressors (the agents or stimuli that can result in degradation); and

inspection, surveillance, and monitoring methods (ISMM) are included in the report.

Information is summarized from the standards, codes, and specifications that combine to provide the basic physical,

chemical, test, and performance criteria for the glass fiber filter media (paper) and impregnated activated carbon as

well as for assembled components. Failure experience, based on analyses of over 60,000 licensee event reports (LERs)

and a survey of Department of Energy (DOE) sites, is summarized and, where possible, related to aging (Moeller 1979,

Moeller and Sun 1983, Jacox 1989, Sommer and Otermat 1992, and Carbaugh 1983). Although less than one percent

of the LERs appeared to be related to filters and adsorbers, several instances of the premature aging of carbon, from

error-induced conditions, were reported. Over 1100 failures, or a total of 12 percent of the filter applications, were

reported as part of the DOE survey (Carbaugh 1983). Investigators from other national laboratories have suggested

that the effects of aging could have contributed to over 80 percent of these filter failures (Johnson et al. 1989). These

same investigators reported results of an experimental evaluation of the tensile breaking strength of aged filter media

specimens that revealed that 42 percent of the samples did not meet the specifications for test specimens obtained

from new material. A significant loss in water repellency from values specified for new media was also measured.

Low radioiodine decontamination factors associated with the Three Mile Island (IMI) accident were attributed to the

premature aging of the carbon in the adsorbers. Inspection, surveillance, and monitoring methods have been

established to observe filter pressure drop buildup, check both HEPA filters and adsorbers for bypass, and determine

the retention effectiveness of aged carbon. Exemptions to TMI technical specifications postponed the latter,

surveillance tests that could have revealed the extent of carbon aging.

Aging mechanisms associated with filters range from particle loading of the media to corrosion of metal members, and

physicochemical reactions that alter properties of sealants, gaskets, and water repellents. Filter media may embrittle

from prolonged exposure to air. In the case of adsorbers, it has long been established that aging mechanisms lead to

impaired performance in terms of the capture of volatile iodine species. The deterioration in performance is caused by

oxidation as well as the competitive loading of other airborne constituents. Many airborne constituents, including

moisture, can readily react or be adsorbed by carbon beds reducing the number of active "sites" that otherwise would be

available for radioiodine adsorption. Stressors include heat, humidity, radiation, and airborne contaminants and

pollution.

The Phase I study found that the HEPA filters and adsorbers are considered to have a long service life, especially the

filters. Thus, if a severe accident happens it is likely to occur at a time when these two final confinement barriers have

been in use for an extended period, even years. Even with existing ISMM, the aged, and possibly degraded components, could fail to provide the controlled environment needed by personnel to ensure safe shutdown following the

accident, or be the weak link that allows the release of radionuclides to the environment. Further, the Phase I

assessment has revealed the need for an improved definition of accident conditions and the possible need for

additional information to comprehensively evaluate the performance of aged components under such conditions. The

expansion of the Phase I aging assessment to other components of nuclear air treatment systems, namely demisters,

vii NUREG/CR-6029
Summary

heaters, coarse filters, fans or blowers, and dampers, is recommended. Several of these components, although not

designed to retain radionuclides, could mitigate the impact of conditions that threaten to cause failure of aged HEPA

filters and adsorbers during accidents.

NUREG/CR-6029 vi viii
Acknowledgments

The author would like to thank Dr. John (Jack) J. Burns Jr., Office of Nuclear Regulatory Research, Division of

Engineering, for his programmatic guidance and careful review of this effort.

The author would especially like to acknowledge the efforts of PNL staff member Elizabeth (Liza) J. Eschbach in the

collection and cataloging of many of the references that formed the basis of the assessment. The author would also

like to thank Liza (PNL) and Melvin W. First, Sc.D., Harvard Air Cleaning Laboratory, for their review of this

document and valuable comments. Finally, the author would like to acknowledge the following PNL staff for their

outstanding efforts in assisting with the preparation of this report: Susan (Sue) J. Arey, Norma J. Reed, and Sharon K

Loverne.

ix NUREG/CR-6029
Nomenclature

ACS air cleaning system

ANSI American National Standards Institute

ASME American Society of Mechanical Engineers

ASTM American Society for lbsting and Materials

CFR Code of Federal Regulations

Cs! cesium iodide

DBA design-basis accident

DF decontamination factor

DOD Department of Defense

DOE Department of Energy

DOP dioctyl phthalate

EPRI Electric Power Research Institute

ESF engineered safety feature

GDC general design criteria

HEPA high-efficiency particulate air

ISMM inspection, surveillance, and monitoring methods

KI potassium iodide

LER licensee event report

LOCA loss-of-coolant accident

MEK methyl ethyl ketone

MIL military standard

NEA Nuclear Energy Agency

NPAR Nuclear Plant Aging Research

xi xi ~~~~~~NUREG/
Nomenclature

NRC Nuclear Regulatory Commission, U.S.

OECD Organization for Economic Cooperation and Development

PNL Pacific Northwest Laboratory

RG regulatory guide

RH relative humidity

SGTS standby gas treatment system

SSC systems, structures, and components

STCP Source RTrm Code Package

TEDA triethylenediamine

TMI Three Mile Island

USAEC U.S. Atomic Energy Commission

NUREG/CR-6029 xdii
1 Introduction

This report presents the Phase I aging assessment of the

high-efficiency particulate air (HEPA) filters and gas

adsorption units (adsorbers) of nuclear air-treatment or

cleaning and ventilation systems. The study was performed by Pacific Northwest Laboratory (PNL)(a) for

the U.S. Nuclear Regulatory Commission (NRC).

Information concerning the design and construction of

the two air-treatment system components is provided

including summaries of related sections of the NRC

regulatory guides (RG), American Society of Mechanical Engineers (ASME) standards and codes, and military

and American Society for Testing and Materials

(ASTM) specifications. These documents combine to

provide basic physical, chemical, test, and performance

standards for filter media and impregnated activated

carbon as well as for assembled components.

Aging mechanisms and effects are discussed in conjunction with stressors, the agents, or stimuli that can result

in degradation. Failure experience, based on analyses of

licensee event reports (LERs) and a survey of United

States Department of Energy (DOE) sites, is summarized and, where possible, related to aging. The discussion of failure experience also includes exhaust-air

treatment experience associated with the Three Mile

Island (TMI) accident. Although TMI treatment systems provided a significant final barrier to radioactivity

release, lower than expected radioiodine removal was

attributed to "...poor performance from aged charcoal

filters' (Wilhelm and Deuber 1991).

Inspection, surveillance, and monitoring methods

(ISMM) are reviewed. These methods are used to establish the condition of the filters and adsorbers once the

components have been placed in operation. Surveillance tests, which are a series of tests periodically

performed to monitor component condition and

demonstrate the current ability to remove fine particles

and iodine and Iodine compounds, are described along

with summaries of related sections of NRC regulatory

guides and ASME standards.

Definitions related to aging that are used in the report

were obtained or derived from the results of a study to

provide uniform common terminology for addressing

aging of systems, structures, and components (SSC) in

nuclear power plants (EPRI 1992). Aging from normal

conditions assumes properly-designed, fabricated,

installed, operated, and maintained SSC and is defined

as the "general process in which characteristics of [the]

SSC gradually change with time or use." It should be

noted, however, because of the variety of normal conditions and stressors encountered, when considering

HEPA filters and adsorbers, the use of gradually to

describe change may not always appropriately reflect the

rate at which aging can occur. Normal aging degradation is often the result of exposure to airborne contaminants and concentrations and properties fluctuate. Further, contaminants and pollutants vary from site-to-site

and can result from maintenance and testing and possibly even standby or shutdown as well as normal operation. Filters and adsorbers are also used in several systems and large air flows can be involved. Therefore,

general rules concerning design service life associated

with even normal conditions are essentially impossible

to develop. A service life of several years is not uncommon, but significantly shorter periods may be involved,

despite the fact that protective components, namely prefilters, demisters, and air heaters, are used to extend

usable life. Error-induced conditions leading to early

aging are also discussed in the report. Although wearout, including reduced retention efficiency, from errorinduced aging degradation can be viewed as premature

aging, the root cause of failure in this case is human

error, not aging.

(")Operated for the U.S. Department of Energy by Battelle Memorial

Institute under Contract DE-AC06-76RL0 1830.

1.1 NUREG/CR-6029
2 Background

This Phase I aging assessment of HEPA filters and gas

adsorption units (adsorbers) is part of an evaluation of

the effects of aging on engineered safety feature (ESF)

systems, one of the groups of systems of current interest

in the Nuclear Plant Aging Research (NPAR) Program

(USNRC 1991). The identification of potential safetyrelated aging issues, coupled with the need to avoid

duplication, were the key considerations in identifying

candidate ESF systems for initial study. Air-treatment

or cleaning and ventilation systems were ultimately

selected because failure of these systems can impact

both plant and public safety. System components can be

the last barrier in preventing the release of radioactivity

to the public following an accident including that associated with the airborne iodine and cesium radionuclides

that can provide a substantial contribution to total dose.

Further, air-treatment systems are needed to ensure safe

shutdown of the plant or to allow equipment to be

serviced. Satisfactory performance of certain airtreatment systems is essential to ensure control room

habitability. Air-treatment systems and components are

also used to provide a safe and/or controlled environment for personnel and equipment during normal

operations. Operability of some safety-related equipment is dependent upon particular systems to remove

heat from the rooms where these components are

installed.

As shown in Figure 2.1, air-treatment systems consist of

some or all of the following components: moisture separators or demisters, electrical heaters, prefilters, HEPA

filters, adsorbers, postfilters, fans or blowers, ductwork,

and dampers and valves. Not shown are the instrumentation and equipment to sample and monitor system

performance. The first step in the Phase I study was to

identify a boundary to isolate the components that

would be assessed. The fundamental components in

terms of providing plant and public safety are those

designed to capture radioactive gaseous and particulate

contaminants, namely the adsorbers and HEPA filters,

respectively. One or both are installed in nuclear airtreatment systems. The particles could be radioactive

chemical compounds or otherwise inert airborne material contaminated by radioactive species. Gasses of

primary interest include the elemental and organic

forms of radioiodine. Activated carbon is used to

remove the gaseous or volatile forms of iodine and is

usually impregnated with other chemicals to enhance

the removal of the organic species. HEPA filters and

activated carbon adsorption units were selected as the

focus for initial Phase I assessment not only because

they are essential for safety, but in the case of the

adsorbers, it has long been established, and was evidenced again during the TMI accident, that there are

aging mechanisms that can lead to impaired performance (Burchsted et al. 1976, Wilhelm and Deuber 1991).

2.1 NUREG/CR-6029
Background

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FIgure 2.1. Common Air-TReatment System Configuration

NUREGICR-6029 2.2
3 Component Design and Construction

Particle filtration and gas (vapor) adsorption units (adsorbers) are included in nuclear air-treatment systems

and are designed to remove radioactive materials. The

materials, airborne particles or volatile species, may be

suspended in or exist as gas phase constituents of recirculating aerosols, gaseous effluents, or accidental releases. The adsorbers, activated carbon beds, can effectively remove elemental radioiodine and are often

impregnated with other chemicals to enhance the retention of organic species. The fine particle filters, HEPA

filters, may also be significantly involved in radioiodine

removal because iodine can be in the form of solid

cesium iodide (Csl). Design and construction of the two

components are discussed below.

3.1 HEPA Filters

HEPA filters clean or treat aerosols by separating suspended particles from an essentially atmospheric pressure gas stream. The filter media is made from a mixture of glass fibers and is in the form of filter 'paper."

Particles are collected by interception, impaction, and

Brownian diffusion. The continuous gas phase passes

through virtually unchanged. HEPA filters are defined

as a "high-efficiency particulate air filter having a fibrous

medium with a particle removal efficiency of at least

99.97% for 0.3 gm particles of dioctyl plithalate [DOP]

(ASME 1989a).

An excellent review of the construction and service characteristics of HEPA filters has been prepared by First

(1991). This reference also includes a brief history of

the development of filters for the nuclear industry and

includes additional details concerning filtration mechanisms. Much of the information presented in this section

was either abstracted or taken directly from First or referenced military specifications. As indicated by First,

'Filters constructed with paper pleated the full depth of

the rigid outer frame and with adjacent pleats held apart

by full-depth corrugated separators are the most widely

used." In other words, as shown in Figure 3.1, the glass

fiber filter paper is in the form of a continuous sheet

pleated vertically over the separators.

Figure 3.1. HEPA Filter

Physical and chemical filter medium/paper standards are

contained in Military Specification MIL-F-51079D, "Filter Medium, Fire-Resistant, High-Efficiency," and include those for air flow resistance, particle penetration,

and tensile strength (U.S. Department of Defense

[DOD] 1985). The latter, tensile strength criteria,

includes requirements after exposure of the filter paper

to heated air, water immersion, and after exposure to

gamma irradiation. Standards for water repellency prior

to and after exposure to gamma irradiation and mildew

resistance are also included. The penetration criteria

(not to exceed 0.03% for 0.3 /m DOP particles) is directly related to the minimum efficiency used in the

above definition. The penetration criteria is associated

with tests specifying a flow rate of 0.032 m3/min and an

exposed test area of 100 cm2. Maximum pressure drop

related to the preceding test specifications (minimum

velocity of 320 cm/min) is 0.39 kPa (40 mm of water).

The minimum average tensile breaking strength specified for media specimens (N/n or lb/in. of width in the

cross direction), initially, after exposure to heated air at

371°( ± 28°C (700TF ± 50TF) for 5 min, after being

3.1 NUREG/CR-6029
Component Design

soaked for 15 min, and after radiation exposure are 350

or 2.0 (438 or 2.5 in the machine direction), 105 or 0.6,

175 or 1.0 (wet) and 175 or 1.0, respectively. The

military specification also includes the requirement that

the combustible material in the filter medium shall not

exceed 7 wt%. First (1991) notes that the latter 'permits

incorporation of . .. organic matter, divided between

(1) a latex addition to give the paper strength and

resistance to cracking at the bends [where the sheet is

pleated] and (2) a water repellent to protect the paper

against wetting from deposition of liquid droplets,

should they be present.' Specifications for the filter

medium, derived from MIL-F-51079, are also presented

in the ASME Code on Nuclear Air and Gas Iteatment,

ASME/American National Standards Institute (ANSI)

AG-i- 1988 Section FC, 'HEPA Filters' (ASME/ANSI

1988).

In addition to the medium, HEPA filter components indude the frames, gaskets, face guards, and the corrugated separators that are used to separate adjacent

sheets of filter paper. Specifications for these components are presented in MIL-F-51068F, 'Filters, Particulate (High-Efficiency Fire Resistant),* along with

criteria for the adhesives, sealants, and paints used to

assemble and finish the units (U.S. Department of

Defense 1986). A rigid outer frame or housing is used

to fully enclose the paper-separator assembly on four

sides, and provide the connections to adjacent ductwork.

Specifications for frame material include those for plywood, wood particle board, laminated veneer lumber,

aluminum alloys, cold-rolled steel sheet, chrome steel

sheet, and stainless steel A flame spread classification

is given for plywood. First (1991) notes that 'face gaskets are usually constructed from flat strips of expanded

closed cell neoprene sponge rubber... cork and other

rubber formulations are also permitted [a proprietary

fluid seal design is also discussed].' It is specified that

the corrugated separators be made from aluminum

alloys or epoxy-coated aluminum. The specification

requires that "adhesives used to splice the medium,

fasten the gasket to filter face, and sealants or adhesives

used to seal the filter pack to the frame shall be selfextinguishing after direct contact with an open

flame ...

Performance specifications for assembled standard-sized

filters (nominal rated capacity ranging from 0.71 to

57 m3/min or 25 to 2000 ft3/min) are included In

MIL-F-51068F for DOP particle penetration (ho

greater than 0.03% at specified flow rates) and resistance to air flow, pressure, heated air, and environmental exposure. Maximum pressure drop specified at rated

air flow ranges from 0.25 to 032 kPa (1.0 to 1.3 in. of

water), depending on size. The pressure test for 61 by

61 cm units involves assuring that the assembled unit,

after conditioning for not less than 24 hours in a chamber at 350C (-95*F) and at a relative humidity (RH) of

95%, will then withstand a specified air flow (needed to

produce a 2.49 + 0.05 kPa or 10± 0.2 in. water pressure

differential across filter) and water spray environment

without rupture of the filter medium. Evaluation of

environmental performance involves cyclic exposure for

a total of 9 weeks to specified conditions termed arctic

(-540C or -650F), desert (45*C or 1600F and 10% RH)

and tropical (450C or 1130F and 88% RH). Particle

penetration criteria also include minimum values for the

wet filter following the pressure test, after exposure to

specified flow rates of heated air (371 ± 28TC or 700±

500F for at least 5 min), and after the environmental

exposure cycles.

Materials, design, and fabrication standards are also included in Section FC of the ASME Code on Nuclear Air

and Gas 'Teatment (ASME/ANSI 1988). Three types of

HEPA filters are addressed: folded filter media with

corrugated separator/supports (described above); minipleat medium with glass fiber or noncombustible thread

separators (made from a series of flat panels of pleated

filter media assembled in a V-shape, with adjacent

pleats separated and supported by ribbons of glass fiber

or noncombustible threads glued to the media, maximum pleat height of 20 mm); and continuous corrugated

filter media folded without separators. Steel and stainless steel sheet frames are emphasized. A sequence of

qualification tests is described that includes evaluation

of resistance to air flow, particle penetration, resistance

to rough handling, resistance to pressure, resistance to

heated air, and spot flame and radiation resistance and

involves a specified number of filters. No attempt was

made to define all differences between the above

UREG/CR-6029 3.2
Component Design

military specifications and Section FC, but It was noted

that combustible material in the filter media is limited

to 5 wt% by the latter.

3.2 Adsorbers

As indicated above, adsorbers are used to remove gaseous radioiodine species from effluents. Various standards and specifications permit the use of any adsorbent

medium that has been demonstrated to be equal to or

better than activated carbon in terms of radioiodine retention. However, only activated carbon is discussed

because it Is essentially the only material used and supporting testing procedures and acceptance criteria are

specific to its use.

Gasses are directed through tightly-packed beds of activated carbon granules. The carbon or charcoal is prepared by controlled heating in a steam environment to remove volatile organic material. The heating generates a

material with a large surface-to-mass ratio and internal

surfaces or sites where adsorption of iodine molecules

can take place. Ile active media is usually . ... activated

charcoal that is derived from either coal or coconut

shells. Although elemental radioiodine is retained efficiently by activated carbon alone..., the charcoal is

often impregnated with additional chemicals to improve

its retention of organic species (e g., methyl iodide).

Typical impregnants include potassium iodide (KI), triethylenediamine (IEDA), or derivatives of TEDA.

Mixtures of these compounds are also used. ... With KI

as the impregnant, iodine retention is mainly due to

isotopic exchange [nonradioactive iodine in the impregnant substitutes for the radioactive iodine of the organic

species and then passes through the bed]. .. With

TEDA or its derivatives as the impregnant, the primary

retention reaction is due to the formation of quaternary

salts. Even in this case, however, isotopic exchange is an

important factor ... .t (Wilhelm and Deuber 1991).

Standards for the adsorbent media are included in the

"Code on Nuclear Air and Gas ikeatment," ASME/

ANSI AG-1-1988, Section FF, Adsorbent Media

(ASME/ANSI 1988). In addition to specifications for

physical properties, Section FP lists requirements for

testing the adsorbent to verify retention performance. A

free-flowing granular substance is specified. Activation

and impregnation processes are left to the discretion of

the manufacturer. Physical tests specified after impregnation include those for apparent density, particle size

distribution, ignition temperature, and hardness. Qualification tests to establish the suitability of a grade or

type of impregnated activated carbon require verification that elemental iodine removal efficiency is not less

than 99.9% at 300C and 95% RH. Corresponding efficiency values for methyl iodide are 99.0% at WC and

95% RH and 98% at 1300C and 95% RH. Further,

batch tests at the time of manufacture, to assure that the

material being used has the same characteristics as the

material qualified in testing, require demonstration of

minimum elemental iodine and methyl iodine retention

efficiencies of 99.5% (at 180IC) and 97% (at 30C and

95% RH), respectively. Definitions and terms included

in Section FP include those for 'batch," 'grade or type,"

and "qualification test."

ASTM standards are referenced in Section FF of

AG-1-1988 that describe methods for testing the adsorbent with radioactive material to verify retention characteristics as well as to evaluate physical properties such

as density and particle size distribution. The former,

ASTM D 3803-89, 'Standard lbst Method for NuclearGrade Activated Carbon,' is ... a very stringent procedure for establishing the capability of... activated carbon to remove radio-labeled methyl iodide from air and

gas streams' (ASTM 1989). As will be discussed later in

the report, the test method is used to quantify the extent

of degradation of aged carbon as well as to qualify new

carbons. Physical properties and performance specifications for new, virgin impregnated activated carbon for

removing gaseous radioiodine are specified in ASTM D

4069-90, 'Standard Specification for Impregnated Activated Carbon Used to Remove Gaseous Radio-lodines

from Gas Streams" (ASTM 1990). Test methods for

evaluating the various physical properties are included

as referenced documents.

Specifications for materials, design, fabrication, and the

inspection and testing of two types of adsorbers are presented in Sections FD, "Iype II Adsorber Cells," and FE,

"Type III Adsorbers,' of ASME/ANSI AG-1-1988

(ASMEIANSI 1988). 'lype 304 or 304L series stainless

steels are specified for materials that contact the adsorbent. General design of the Type II adsorber unit is

based on a single cell consisting of 50.8-mm (2-in.) thick

3.3 NUREG/CR-6029
Component Design

minimum beds in a modular tray-type arrangement. A

minimum residence time of 0.25 sec. and maximum

pressure drop of 0.31 kPa (1.25 in. water) at the rated

capacity of 9.43 m3/min (333 ft3/mnin) is specified. Type

11 design is based on single or multiple permanent units

where carbon is filled and emptied in place (sometimes

called deep bed or gasketless, see ASME/ANSI

AG-1-1988 Section FE for additional details).

3.3 Supporting Documents

In summary, basic qualifications for the filter medium

and assembled HEPA particulate filters are contained in

two military specifications (U.S. Department of Defense

1985, 1986). Primary standards for adsorbent media, assembled adsorbers, and related testing methods are presented in Sections FD, FE, and FF of ASME/ANSI code

AG-1 and two ASTM specifications (ASMEJANSI 1988;

ASTM 1989, 1990). Numerous documents supplement

and/or support the preceding five references, including

NRC and other ASME and ASTM publications. One of

the most closely related NRC publications, RG 1.52,

'Design, Testing, and Maintenance Criteria for Post

Accident Engineered-Safety-Feature Atmosphere

Cleanup System Air Filtration and Adsorption Units of

Light-'Water-Cooled Nuclear Power Plants," is currently

being revised (USNRC 1978; Bellamy 1991). This guide

presents methods for implementing the appropriate

general design criteria (GDC) described in Appendix A

of 10 CFR 50 (U.S. Code of Federal Regulations 1992)

and as suggested by the title of the guide, *... applies

only to post accident engineered-safety-feature atmosphere cleanup systems designed to mitigate the consequences of postulated accidents ... land) does not apply

to atmosphere cleanup systems designed to collect airborne radioactive materials during normal plant operation, including anticipated operational occurrences.'

Regulatory Guide 1.140, "Design, Testing, and Maintenance Criteria for Normal Ventilation Exhaust System

Air Filtration and Adsorption Units of Ught-WaterCooled Nuclear Power Plants' provides guidance for the

latter, normal systems (USNRC 1979).

Regulatory Guide 1.52 references two ANSI/ASME standards for the design and testing of engineered safety

feature (ESE) system components including HEPA filters and adsorbers. The latest revisions of these two

standards have been published by the ASME as American National Standards ASME N509-1989, 'Nuclear

Power Plant Air-Cleaning Units and Components," and

ASME N510-1989, "Ibsting of Nuclear Air 'Teatment

Systems' (ASME 1989 ab). These two ASME standards, in addition to being connected to the regulatory

guides, are also at least the initial link to the basic five

references that contain various construction, material,

test, and qualification specifications for new HEPA

filters and adsorbers. Specifically, requirements of

ASME N509-1989 include the use of the two military

specifications and the three sections of the nuclear air

and gas treatment code (the above two ASTM standards

are referenced in Section FF of code, ASME/ANSI

AG-1). There is no intent to imply that all of the

information presented or referenced in the latest revisions of the two ASME standards has been evaluated by

the NRC in terms of applicability or acceptability.

Further, the use of the term requirement in conjunction

with the various standards, codes, and specifications

does not necessarily mean that a particular requirement

has been accepted by the NRC. Finally, it should be

noted that some of the information included in the two

ASME standards and NRC regulatory guides will be discussed in greater detail later in the report in conjunction

with surveillance tests that are used to monitor the condition of installed filters and adsorbers.

NUREG/CR-6029 3.4
4 Aging Mechanisms, Effects, and Stressors

This section combines information concerning aging

mechanisms and effects and the various stressors that

are involved. As will be detailed below, stressors, the

agents or stimuli that can contribute to aging (including

the direct degradation in performance in terms of radionuclide retention) include heat, humidity, steam, radiation, and airborne contaminants and pollutants.

4.1 HEPA Filters

The obvious effect of service associated with HEPA filter use is the increased pressure drop (resistance to air

flow) through the filter media arising from particle retenuon (loading). ms ndicated in Section 3.0, new or

clean filters are designed to provide a resistance of

about 0.25 kPa. First (1991) notes that "a dust pickup of

approximately 1 kgllOOOm3/h of design filtration

capacity represents a resistance increase of 0.25 kPa

from a new condition. In a relatively clean environment, filters may be used for several years before replacement is required. Dust loading, along with heat

and radiation, also have the potential to reduce the effectiveness of the organic materials used to strengthen

the filter medium and provide water repellency.

High moisture content is another stressor that can lead

to increased pressure drop as well as reduced filter medium strength. Ricketts, Ruedinger, and Wilhelm

nI>ote that 'Moisture .nduced .... [deterioration]

in filter performance and filter structure failure result

principally from the presence of liquid water in the fiber

structure of the filter medium." These authors discuss

incorporation of liquid water into the filter medium by

sorption, condensation, or droplet filtration (interception) and also summarize a large number of other literature sources that deal with moisture effects on filter media and construction materials and assembled units. In

conclusion, they note that * ... water in the filter

medium leads to an increase in differential pressure and

to. . . [deterioration] in filter pack stability and in filter

medium performance characteristics, especially the

tensile strength. The mechanical load on the filter is

thus increased at the same time that the structural

strength is decreased. The end result is that filter

structural failure can occur for unacceptably low values

of &P, even at design flow rates....' (Ricketts,

Ruedinger, and Wilhelm 1987). In reporting the results

of an experimental program these same authors note

that 'the 21 filters tested at 500C, constant volumetric

air flow rate, and ambient pressure demonstrated that

the differential pressure of new clean filters increased

significantly only above 95% RH, rose up to 0.5 to 2 kPa

at 100% RH and reached values between 6 and 9 kPa

during filtration of liquid-water aerosols ... .

(Ruedinger, Ricketts, and Wilhelm 1985). Additional

information concerning the effects of moisture, emphasizing immediate failure rather than gradual deterioration and including details related to dust-loaded filters,

is presented later in this report.

processs that cancnge the- ph sca ca -

acteristics of HEPA filter components other than the

media include corrosion of metal members and physiccMenucai reactions that alter the properties of sealants,

gaskets, ano water repellents. Metal components that

could be affected include the frames and corrugated separators. Stressors associated with physicochemical reactions potentially affecting face gaskets and the adhesives

and sealants that are used to splice the medium, fasten

the gaskets to the filter face, and seal the filter pack to

the frame, include heat and radiation.

Johnson et al. (1989) have reported results of tests to

quantitatively evaluate the effect of aging on HEPA filters. In one group of tests aged, flat, sheet media samples (obtained by dismantling filters with 13 to 14 years

of service) were tested using the equipment and procedures of MIL-F-5Y1079 (Department of Defense 1985),

the specification discussed earlier that includes the physical and chemical criteria for the media used in new filters. In summary, 42% of the samples failed tensile

strength tests; i.e., the samples did not meet specifications for new media. Johnson et al. also note that 'due

to the brittleness of the bend area of the pleat, a sample

culd'notbe obtained for testing. There is no doubt,

Towfver,t hat tareao eagedHEPA filter m eia

4.1 NUREG/CR-6029
Aging

represents the weakest part and it should have even

lower tensile strength value.' The bench-scale tests also

revealed a signican loss or water repellency. All samples failed when the top or dirty side of sheets were

tested while four of the seven samples failed to meet the

requirements for water repellency when the bottom or

clean side was examined. As anticipated, due to service,

71 % of the samples failed the pressure drop test. However, all samples passed the DOP efficiency tests (met

the 99.7% requirement for new material).

In addition to the above bench-scale tests, several of the

aged filters were exposed in a wind tunnel to generate

pulses equal to those associated with the standard NRC

Region I design basis tornado, and using a shock tube,

to shock wave overpressures. Six filters, in service for

15 to 19 years, and two filters, in service for 14 years,

were subjected to the tornado pulse and additive shock

overpressure tests, respectively. Johnson et al. report

that *the average breaking pressure of the six aged filters

was 1.38 ± 0.95 psi 19.51 + 6.6 kPal. The comparable

breaking pressure of a new unused filter is 2.89 psi

119.9 kPal The average breaking pressure of the two

aged filters utilizing small incremental pressure

increases is 1.8 psi 112.4 kPal. The comparable breaking

pressure of a new unused HEPA filter is 2.5 psi

117.2 kPal...." In addition to these 52% and 28%

decreases in breaking pressure, a large increase in complete filter pack blow-out was reported for the aged filters during the simulated tornado tests.

4.2 Adsorbers

Exposure to air containing stressors, namely moisture

and contaminants or pollutants, can slowly and continuously degrade ete performane of gas rbers with

ime. ihis aginigalso termed weatvierhng, is inherent

use of the nature of the material used, i.e., one that

has been 'activated' to dramatically increase surface to

mass ratio and provide countless reaction sites, coupled

with the essentially ubiquitous nature of the contaminants. Many airborne constituents, including moisture,

can readily react or be adsorbed by carbon beds reducing

the number of active "sites" that otherwise would be

available for radioiodine adsorption. During normal

operation, charcoal may be exposed to air flows containing contaminants including volatile organic solvents,

sulfur dioxide, nitrogen oxides, and carbon monoxide.

Because of system flow rates, even traces of pollutants

can have a significant, cumulative effect. Oxidation, as

well as competitive loading, can impair bed performance, including decreasing the efficiency of the impregfian. Because airborne constituents can vary dramaticarlywith time and from site-to-site, it is essentially

impossible to provide criteria concerning the useful life

of impregnated activated carbon.

Aging degradation or weathering of iodine adsorbers as

a result of exposure to various stressors has been treated

extensively in the literature, particularly in terms of

methyl iodide retention efficiency. Results of numerous

experimental investigations involving the latter compound have been reported. Two summary reviews,

which also include numerous pertinent references, have

been prepared by Wilhelm and Deuber (1991) and a

group of Nuclear Energy Agency (NEA) experts

[Organization for Economic Cooperation and Development (OECD) 19841. Briefly, studies have revealed that

increasing temperature and humidity can be agents that

cause aging and aging effects. Deitz (1978) notes that

0... there is strong evidence that the interaction of water

vapor and charcoal is a significant factor in the degradation of the charcoals when the RH is 70% and greater.

The laboratory air mixtures studied [in this investigation

of methyl iodide penetration] were water vapor, water

vapor and sulfur dioxide, water vapor and ozone, and

water vapor and carbon monoxide....'

Wren and Moore (1991a) in an investigation of the adsorption and desorption behavior of contaminants studied the effect of dry and humid conditions on adsorption

of NO2, SO2, methyl ethyl ketone (MEK), and NH3.

Their conclusions concerning the latter, humid conditions include the observations that '. . . adsorbed water

increases the adsorption rate and capacity of TEDA

charcoal for NO2, while it does not significantly change

those for SO2. However, it appears that SO2 is adsorbed

as H2SO4 on the wet charcoal. Adsorbed water slightly

reduces the adsorption capacity of the charcoal for

MEK, but does not affect the adsorption of NH3.'

These same authors, reporting on the effect of contaminants on CH31 removal efficiency, noted 'he efficiency

of TEDA charcoal is degraded most by NO2 and SO2,

NH3 has a negligible effect, and MEK produces a mild

degradation. The degree of degradation parallels the

NUREG/CR-6029 4.2
Aging

contaminant's ability to be chemisorbed.... Nitrogen

dioxide adsorbed under dry conditions is more effective

in degrading the CH31 removal efficiency of the charcoal

than when adsorbed under humid conditions. On the

other hand, a completely opposite result is observed for

SO2. The MEK contaminant behaves similarly to SO2,

but the effect of humidity was less significant than for

SO2. Ammonia has no effect on the efficiency of the

charcoal regardless of humidity" (Wren and Moore

1991b).

Amine (TEDA or derivatives to reduce volatility) impregnated carbons age less rapidly than those where KI

is used or that are unimpregnated (OECD 1984). In an

investigation of temperature and humidity on the aging

of TEDA impregnated charcoals, Billinge and

Broadbent (1989) note that "... KI impregnated charcoals ... rapidly lose efficiency when exposed to high

humidity air land) this deterioration was mainly caused

by oxidative aging of the carbon surface... Amines are

a class of compounds well-known for their anti-oxidant

properties so TEDA carbon may age more slowly than

KI material because the rate of formation of organooxygen surface groups is reduced; a second possibility is

that the basic properties of the amine neutralize any

surface acidity formed...."

The effect of the accumulation of organic contaminants

on the aging process was investi ated be Hyder (1289).

As in the case of the above investigation involving

MEK, results 1. . .show the effect of organics on carbon

performance [in terms of methyl iodide] is limited ...

Some inference is possible regarding the mechanism by

which sorbed organics affect methyl iodide retention. In

these used carbon samples, all of the impregnant TEDA

has been lost by evaporation or reaction. Methyl iodide

retention depends on the availability of the potassium

iodide impregnant for exchange with the methyl iodide.

Other aging processes chemically alter this impregnant

or remove it, but the sorbed organics do neither...."

As indicated above, much of the literature concerning

aging mechanisms and effects is related to methyl iodide

penetration. It is noted in an older but valuable and

comprehensive review of air cleaning systems (ACS)

(Burchted, Kahn, and Fuller 1976) that "the loss in

capacity for elemental iodine is much slower than that

for methyl iodide. Beds exposed continuously to flowing

air at one installation showed adequate remaining

capacity for elemental iodine after 4 years of service. At

other installations, however, exposure of beds to paint

and solvent fumes reduced capacity to the point that

efficiency fell to unacceptable levels in only a few

months...." Adequate long-term performance in terms

of removing elemental iodine from plant ventilation

exhaust air under normal operating conditions is also

reported in Pelletier et al. (1978). The associated filter

systems were used continuously for treating effluents

from the auxiliary building. Average efficiency over a

3-year period was 99.23%.

Relatively rapid deterioration of stainless steel components can result from contact with wet carbon. Severe

pitting resulting from galvanic corrosion has been reported (LIening 1991). Obviously, carbon should be removed immediately if it becomes wet. The revised NRC

RG 1.52 . . . will clearly indicate that wetting of

impregnated activated carbon should be avoided

because it establishes conditions for rapid chemical corrosion between the impregnants and stainless steel

structural material supporting the charcoal beds"

(Bellamy 1991).

Finally, it should be emphasized that the possibility of

impaired performance in terms of radiolodine retention

as a result of the aging or weathering of impregnated

activated carbon has been a concern almost from the

start of the nuclear industries' existence. In fact,

concern about the useful life of carbon could be considered one of the first, if not the first, aging issue. As

will be detailed later in the report, the issue is addressed

by a surveillance test, a series of tests that are

periodically conducted to define the remaining radioiodine retention capacity of used or exposed carbon.

However, as will also be discussed, additional consideration of aging issues is believed to be warranted for both

HEPA filters and adsorbers, especially in relation to

accident environments.

4.3 NUREG/CR-6029
5 Failure Experience

This section describes failure experience that has been

reported for HEPA filters and adsorbers. Where possible, the experience is discussed in terms of aging effects

and degradation and in conjunction with specific stressors. Information related to both normal operating and

accident conditions is presented. Analyses of LERs submitted by commercial nuclear power plant operators are

reported along with results of a survey of DOE sites to

obtain information on the number of and reasons for

HEPA filter changeouts and failures. Information to

evaluate air-cleaning system performance during the

TMI accident is also summarized.

5.1 Licensee Event Reports

An unusually large amount of potentially useful failure

data were found in the literature. Analyses of LERs

covering the periods from January 1, 1975 through

June 30, 1978, 1978-1981,1985-1987, and 1988-1991, to

identify those pertaining to air-monitoring, airtreatment, and ventilation systems, have been prepared

by Moeller (1979), Moeller and Sun (1983), Jacox

(1989), and Sommer and Otermat (1992). In summary,

15% of 43,500 reports were associated with the subject

systems while an estimated, roughly 100, or about 2% of

the system reports, appeared to be associated with

HEPA filters and carbon adsorbers. No relationship to

aging was reported.

Moeller and Kotra (1985) and Moeller and Sun (1987)

reviewed LERs for the periods 1981 through 1983 and

1984 through 1986, respectively, to isolate those pertaining to control room habitability. Of the approximately

20,800 reports, 4% were related to this focus. During

the 1981 through 1983 period, 28 of the LERs were

associated with impaired filter or adsorber efficiency.

Moeller and Kotra note that 'The majority of LERs related to HEPA filters and charcoal adsorbers reflect that

the performance of such units degrades with time and

that routine tests reveal that their efficiencies do not

meet technical specifications. The normal licensee response is to replace the units. More serious occurrences, however, include the fouling of charcoal

adsorbers by welding and/or paint fumes and the

occasional wetting of filters or adsorbers by drainage

water or the inadvertent actuation of their associated

fire protection deluge systems. At one plant, paint

fumes contaminated the control room emergency charcoal filters so severely that their measured removal

efficiencies were significantly degraded. Apparently, the

control room emergency ventilation system was in a recirculation mode during painting in an adjacent room.

Backflow through component drain lines into filter

packages necessitated their replacement at one plant...

Unintentional actuation of fire suppression systems was

reported at three... plants... [that] rendered the filters

and adsorbers inoperable and they had to be replaced."

Moeller and Sun note that "a total of 30 LERs related to

charcoal adsorber problems were filed between 1984 and

1986. Many of these events resulted from tests having

revealed that the charcoal adsorber bank associated with

an emergency ventilation system was not able to remove

the required more than 99% of the halogenated hydrocarbon refrigerant test gas as stipulated by the Technical

Specifications [test is discussed later in the report in

Section 6.2]. In most cases, the reduction in adsorption

capability was thought to be due to moisture having

gained access to the charcoal. Compounding the problem was the fact that round robin tests had shown that

commercial charcoal testing laboratories, both in the

U.S. and abroad, lacked the capabilities of determining

the adsorption capacity of such charcoals on an accurate

and reliable basis.'

5.2 DOE Site Survey

Using a survey, Carbaugh (1983) collected data on the

numbers of and reasons for HEPA filter changeouts and

failures at DOE sites for the years 1977 through 1979.

A total of 1105 filter failures, or 12% of the 9154 filter

applications, was reported. The ratio of filters changed

to those failed, 6.2 to 1, suggested that most filters are

changed out prior to failure. Carbaugh notes that "the

largest majority (63%) of filter changeouts were attributed to high differential pressure (0P) across the filter,

indicative of filter plugging.... The vast majority of

filters were reported as [having been] exposed to no

5.1 NUREG/CR-6029
Failure Experience

distinguishing environmental characteristics (i.e., they

filtered essentially clean, dry, air environments similar

to those that might be found in typical building ventilation systems or in systems with good pre-HEPA treatment features).... The majority of [the 11051 failures

occurred for unknown or unreported reasons.... The

incidences of frame failures, gasket or seal failures and

filter media raptures were approximately equal; each

constituted between 5% and 6% of all filter failures.

When frame failure was identified, essentially all failed

frames (58 out of 65) were wood. No observation of

steel frame failure was reported... calculating the

ratios of seal-type failures to seal-type applications

[3920 gaskets and 151 fluid seals] can lead one to conclude that little difference may exist between gasket and

fluid seal failure rates.... Al media ruptures occurred

in wood-frame filters, and almost all (48) had aluminum

separators and polyurethane foam sealants. [Media to

frame] Sealant failure was not identified as a significant

filter failure mode (3 occurrences reported out of 1105).

... Ratios of filters failed to filter applications in which

these failures were experienced are several times higher

for HF acid and high moisture environments than for

environments having no distinguishing characteristics,

or the average of all single environment exposures

[exposure of filters to a single significant environmental

factor, e.g., solvent, high moisture, high dust]...."

Johnson et al. (1989) explain the results of the above

survey in the following manner: "If one examines the

categories reported for filter failure, it is evident that the

effects of aging could contribute to 81% of these failures, except for the 19% resulting from handling or installation damage." Johnson et at. also provide two

other references that include qualitative information

that reveal indications of aging: a technique to dismantle

and separate HEPA filter components, based on unfolding the pack and rerolling the media, worked well on

new filters but became impractical on used filters because of the "weakness of the filter paper"; and as part of

a report concerning the in-service aging effects of unused and used cleanroom, chemical, and radioactive

contaminated HEPA filters it was noted that "aluminum

spacer deterioration was observed in all used filters examined with the most significant levels observed when

high humidities and acid gases were present."

5.3 TMI Accident

As suggested earlier in the report, selection of adsorbers

for Phase I study was reinforced by literature references

revealing that the low radioiodine decontamination factors (DF) associated with the TMI accident were attributed to the premature aging of charcoal. Before presenting details related to aging issues, it should be

emphasized that building ventilation systems played an

important role in decreasing the radionuclide release associated with this incident and in fact, prevented the release of most of the radioiodine. The estimated quantity

of I-131 released was 5.6 x 10-9 Bq or 15 Ci (in contrast

to about 9.3 x 104 Bq or 2.5 million Ci of noble gas)

(Rogovin and Frampton 1980).

Despite the above, the terms "somewhat dismal results'

and 'rather unsatisfactory" have been used to describe

exhaust air filtering experience during the TMI accident

(OECD 1984; Wilhelm and Deuber 1991). In summary,

it was determined that the filtering systems installed at

the time of the accident provided a DF of 9.5 for all species of radioiodine (corresponds to a retention efficiency

of 89.5%), and the radioiodine releases were higher by

about a factor of five than they would have been if there

had been no system deterioration. The preceding values

and reasons for the degradation are detailed in Rogovin

and Frampton (1980) and discussed by Bellamy (1981)

in a paper that was prepared to summarize pertinent

(related to air-cleaning technology) efforts and recommendations of various investigative groups. Briefly, system degradation and the fact that radioiodine retention

was associated with an efficiency of 89.5% was ultimately attributed to pre-accident aging of the impregnated activated carbon. For a number of reasons ventilation air was passed through exhaust systems from the

time of carbon installation to just shortly after the accident. This approximately 1-year time frame included

periods of exposure of the carbon beds to fumes from

painting and cleanup efforts. Furthermore, exemptions

to technical specifications postponed surveillance tests

that could have revealed the extent of aging. (Tests are

described in the next section and involve the periodic

laboratory evaluation of exposed carbon samples.) The

exemptions also permitted the use of carbon with a

methyl iodide removal efficiency of 96.97%.

NUREG/CR-6029 5.2
Failure Experience

Carbon removed from four filter trains following the

accident, along with data on various iodine species obtained from an air sample, suggest removal efficiencies

ranging from 49.1% to 75.6% and 98.5% to 99.9% for

methyl iodide and elemental iodine, respectively. These

efficiencies are based on calculated releases conservatively assuming 95% RH and percentages of volatile

species of 40% and 35% for organic and elemental

iodine, respectively. The efficiency range is attributed to

unbalanced ventilation flows. It should be noted that it

was estimated that the highest RH that existed inside

the auxiliary building during the accident was 80%.

Review indicated that releases of radioactive material in

particulate form were negligible. Postaccident efforts

included changeout of HEPA filters as well as carbon.

As indicated in Rogovin and Frampton (1980) These

HEPAs were visually examined before changeout and

were intact and in satisfactory condition, but were damaged during changeout.... Unfortunately, no used

HEPA filters or sections of filter media were retained

for analysis." Again, the highest RH estimated for the

auxiliary building was only 80%.

5.3 NUREG/CR-6029
6 Inspection, Surveillance, and Monitoring Methods

This section describes the inspection, surveillance, and

monitoring methods (ISMM) that are used to establish

the condition of HEPA filters and adsorbers once the

components have been placed in operation. As will be

detailed below, the use of surveillance tests, series of

tests periodically performed to monitor component condition and demonstrate the current ability to remove

fine particles and iodine and iodine compounds, is emphasized. Surveillance tests include in-place leak tests

and visual inspections to evaluate filter banks and adsorbers in terms of component damage and bypass. Also

included, and specifically related to aging concerns, are

laboratory tests of used or aged carbon samples to determine remaining radioiodine adsorption capacity. In addition to the surveillance tests, HEPA filter pressure

drop is continuously monitored (alarmed and

indicated).

6.1 HEPA Filters

Instrumentation provisions, including alarms, for aircleaning systems and components are presented in

ASME N509-1989 (ASME 1989a). High differential

pressure alarms are specified for local as well as remotemanned control panel locations for the HEPA filters of

ESF air-cleaning systems. Pressure drop indication is

specified for the local location. For non-ESF units, differential pressure indication and high differential pressure alarms are recommended only for the local location. Particle loading along with the moisture content

of the air most adversely influence the rate and extent of

filter pressure drop increase. As indicated earlier, most

filters are changed out prior to failure, primarily as a the

result of an indication of a high differential pressure

across the filter.

Criteria for surveillance tests involving installed systems

and the various components are presented in ASME

N510-1989 (ASME 1989b). As in the case of new components, other documents, including NRC RG 1.52 and

RG 1.140, supplement and support this basic reference

(USNRC 1978,1979). Visual inspection is recommended before each test series and specific guidance is

provided for HEPA filters and adsorbers. Air flow

distribution tests for both HEPA filter and adsorber

banks are described. 'Testing to verify uniform mixing in

the air stream approaching the HEPA filter bank or

adsorber stage is a prerequisite for conducting surveillance leak testing of the installed filter bank. The recommended frequency for this "air-aerosol mixing uniformity test" includes performance after completion of

initial construction and after major system modification

or repair (acceptance tests). The method is based on the

introduction of DOP aerosol and '. . . concentration

readings ... taken across a plane parallel to, and a short

distance upstream of, the HEPA filter bank or adsorber

stage (ASME 1989b).

Surveillance leak testing of installed HEPA filters is

specified because gradual deterioration and leaks could

develop under standby as well as service conditions.

This test is also based on a DOP challenge aerosol introduced upstream of the filters. Concentrations upstream

and downstream are then measured. Recommended frequency given in Tible 1 of ASME N510-1989 includes

acceptance testing, after each HEPA filter replacement

and at least once each operating cycle (ASME 1989b).

Nuclear Regulatory Commission RG 1.52 states that

'HEPA filters should be tested in place (1) initially,

(2) at least once per 18 months thereafter, and (3) following painting, fire, or chemical release in any ventilation zone communicating with the system to confirm a

penetration [ratio of downstream to upstream concentration in percent] of less than 0.05% at rated flow...

Filters that fail to satisfy this condition should be

replaced....' (USNRC 1978). Nuclear Regulatory

Commission RG 1.140 contains essentially the same

information (USNRC 1979). It is recognized that this

original guidance should be changed and as indicated

earlier, revisions to RG 1.52 are planned. Specifically,

Bellamy (1991) notes that guidance in the revised version of the RG will be supplemented such that the

18-month criteria will include"... or once per refueling

outage. The requirement for testing after painting, fire,

or chemical release will include additional guidance to

indicate that this testing need be done only if communication with the system occurred in such a manner that

the HEPA filters or carbon adsorbers could become adversely affected by the fumes, chemicals, or foreign

6.1 NUREG/CR-6029
Inspection

materials. Testing will also specifically be required

(1) after each partial or complete replacement of a

HEPA filter bank...." (Bellamy 1991).

The surveillance leak test of the installed filters should

not be confused with the efficiency tests for new individual filters that were described earlier in the report. A

polydisperse DOP aerosol is used for the former, inplace test while a 0.3,um monodisperse aerosol is used

for the latter. It should be noted that both RG 1.52 and

RG 1.140 state that a filtration system satisfying the

above 0.05% maximum penetration requirement

'. . . can be considered to warrant a 99% removal efficiency for particulates.. .' (USNRC 1978, 1979).

6.2 Adsorbers

The information concerning visual inspection and the

air flow distribution and aerosol mixing tests discussed

briefly in the previous section also pertains to adsorbers.

In the case of the installed adsorber bank, the surveillance leak test is based on a halide challenge gas. The

slightly adsorbable and readily desorbed halide (halogenated hydrocarbon refrigerant, fluorocarbon) gas is injected upstream of the adsorber bank. As in the case of

the filter test, concentration is then measured upstream

and downstream of the bank and percent of penetration

determined from the ratio of downstream to upstream

values. The recommended test frequency given in

ASME N510 (ASME 1989b) is the same as that for the

filters and includes acceptance testing, after each adsorber replacement, and at least once each operating cycle. Regulatory Guides 1.52 and 1.140 require testing

initially, at intervals of 18 months thereafter, following

removal of samples for laboratory tests (if the integrity

of the adsorber section is affected), and following painting, fire, or chemical release in any ventilation zone

communicating with the system (USNRC 1978, 1979).

Both RG also indicate that bypass leakage through the

adsorber should be less than 0.05%.

The above planned revisions to RG 1.52 to supplement

the 18-month test frequency and require testing only if

communication occurred in a manner that components

could become adversely affected by fumes, etc., will also

influence adsorber testing. In addition, 'testing will also

specifically be required (1) after each partial or

complete replacement ... of a carbon adsorber in an

adsorber section or bank, (2) following detection of, or

evidence of, penetration or intrusion of water or other

foreign material into any portion of an ESF atmosphere

cleanup system, and (3) for adsorber banks following

removal of an adsorber sample for laboratory testing if

the integrity of the adsorber section is affected'

(Bellamy 1991).

As in the case of the polydisperse DOP test of filters, the

in-place halide challenge test is a leak rather than an efficiency test. For adsorbers, however, the leak test is

supplemented with laboratory tests of aged or used carbon samples to determine system efficiency and remaining capacity for methyl iodide. It is stated in ASME

N509 that 'sufficient test canisters or other means of obtaining samples ... of used adsorbent shall be installed

in the adsorber system to provide a representative determination of the response of the adsorbent to the service

environment over the predicted life of the adsorbent.

lest canisters shall be installed in a location where they

will be exposed to the same air flow conditions as the

adsorbent in the system, shall have the same adsorbent

bed-depth as the adsorbent in the system, and shall be

filled with representative adsorbent from the same batch

of adsorbent as that of the system' (ASME 1989a).

Recommendations concerning the number of canisters

to be provided based on the expected frequency of operation are also included in ASTM N509. Details concerning the design basis for samplers and the general

types are presented in Appendix A of ASTM N509,

'Sampling of Installed Adsorbents for Surveillance

Testing.'

Recommended frequency for the above laboratory adsorbent tests, presented in Tbble 1 of ASME N510,

includes acceptance tests, before each adsorber replacement, and at least once each operating cycle. Supplemental footnotes state that 'adsorbents must be tested

before installation or replacement to establish efficiency. Samples for laboratory testing should be taken

before the routine in-place testing of the installed system to verify the condition of the adsorbent. . . Laboratory tests shall be made to confirm performance at

intervals not exceeding 720 hr of system operation or for

any system immediately following inadvertent exposure

to solvents, paints, or other organic fumes or vapors that

could degrade performance of the adsorbent. The

NUREG/CR-6029 6.2
Inspection

720 hr requirement may be modified based on laboratory test histoiy (ASME 1989b). As in the case of the

qualification of new carbons, the test method and laboratory apparatus described in ASTM D3803 are specified for use in the quantitative evaluation of the retention properties of the aged carbon samples (ASTM

1989). Information to improve repeatability and accuracy is provided in Appendix B of ASME N510, 'Additional Guidance for use of ASTM D3803, 1979.0

Frequency guidelines listed in NRC RG 1.52 and RG

1.140 for the surveillance test involving adsorbent

sampling and laboratory testing are essentially the same

as those recommended above. Used carbon decontamination efficiencies are specified for both ESF and

normal systems for a variety of air-filtration system locations, carbon bed depths, and relative humidities. For

example, a 95% decontamination efficiency is specified

for both elemental iodine and organic iodide, for a

50.8-mm (2-in.) bed depth, an ESF system designed to

operate outside the primary containment, and where

RH is controlled to 70% (USNRC 1978).

6.3 NUREG/CR-6029
7 Conclusions

This section presents conclusions and describes concerns originating from the study. Opinions and recommendations concerning the need for expanded or more

comprehensive assessments are also presented. Considerations related to the need for additional studies

include the safety significance of failure modes and

experience, evaluation of ISMM, and the range of conditions that HEPA filters and adsorbers may experience.

Safety significance was emphasized as part of the background information provided earlier in this report. In

review, component failure can impact both plant and

public safety. Satisfactory performance is essential to

ensure control room habitability, and HEPA filters and

adsorbers can be the last barrier in preventing the

release of radioactivity. Monitoring and surveillance

tests have been established to observe HEPA filter pressure drop buildup, check both HEPA filters and

adsorbers for bypass or pathways through which air can

escape treatment, and determine the retention effectiveness of aged carbon. Conditions range from those associated with normal operating environments to those

estimated for reactor accidents. Further development of

the preceding considerations, in terms of normal, errorinduced, and accident conditions, follow. The need for

the expansion of the Phase I interim aging assessment to

other air-treatment system components is also

discussed.

7.1 Normal Operating and ErrorInduced Conditions

Normal operating conditions are characterized as ranging from the exposure of components to dry air containing trace atmospheric contaminants or stressors (e.g.,

sulfur dioxide and nitric oxides) to relatively humid air

and even occasionally to potentially polluted air flows

from routine activities such as maintenance and testing.

Because of large air flows, even traces of pollutants or

contaminants can have a significant cumulative effect on

adsorber performance. Two examples of error-induced,

degraded adsorber retention efficiency from relatively

high contaminant levels (i.e., from the exposure to

fumes from cleanup and/or painting) are reported in

Sections 5.1 and 5.3. The surveillance test involving the

laboratory quantification of the extent of degradation of

used carbon samples is specifically designed to reveal

aging or premature aging as a result of the normal or

error-induced exposure of adsorbers to contaminants or

pollutants.

fteatment of large volumes of air containing small particle concentrations can, of course, result in a gradual

but continuous increase in pressure drop through filters.

Pressure drop or resistance to air flow across HEPA filter banks is monitored. First (1991) notes that

'although HEPA filters are qualified to maintain their

integrity and filtering efficiency up to a minimum resistance of 2.5 kPa, they are seldom operated up to that

resistance level because of fan and fan motor limitations. An increase to 1.0 kPa before change is common

for nuclear installations to maintain a large reserve

capacity at all times in readiness for extended service life

in the event of an emergency' (First 1991). The surveillance test involving the leak test of HEPA filter banks

should detect defects in the filter media or unit arising

from normal service conditions and that result in bypass,

including those that could result from the aging of gasket material. However, neither pressure drop monitoring nor the in-place surveillance test using a polydisperse DOP aerosol will provide indications of aging in

terms of reduced filter medium strength. The latter, the

lack of indication of reduced strength, may be important

when considering reactor accident conditions.

7.2 Reactor Accident Conditions

Nuclear Regulatory Commission regulations require atmospheric cleanup systems to mitigate the consequences

of postulated accidents by removing radioactive materials released during the accident from containment vessel or building atmospheres. General Design Criterion

(GDC) 41, 'Containment Atmosphere Cleanup* of Appendix A, 'General Design Criteria for Nuclear Power

Plants," to fltle 10, Part 50 of the Code of Federal Regulations states that 'systems to control fission products .. which may be released into the reactor containment shall be provided as necessary to reduce, consistent with the functioning of other associated systems,

7.1 NUREG/CR-6029
Conclusions

the concentration and quality of fission products released to the environment following postulated accidents ... I General Design Criterion 61, Ehel Storage

and Handling and Radioactivity Control" states that the

fuel storage and handling, radioactive waste, and other

systems which may contain radioactivity shall be designed to assure adequate safety under normal and

postulated accident conditions. These systems shall be

designed ... with appropriate containment, confinement, and filtering systems, ... ' General Design Criterion 19, "Control Room' requires that' ... adequate

radiation protection shall be provided to permit access

and occupancy of the control room under accident conditions ... . (10 CFR 501992).

Nuclear Regulatory Commission RG 1.52 presents

acceptable methods for implementing the above (and

other) GDCs and includes guidance that aging as well as

postulated accident conditions should be considered

during component design. As indicated earlier, this RG

applies '.. . to postaccident engineered-safety-feature atmosphere cleanup systems designed to mitigate the consequences of postulated accidents. It addresses the ESF

atmosphere cleanup system, including the various components and ductwork, in the postulated DBA [designbasis accident) environment.... systems that must operate under postulated DBA conditions inside the primary

containment. . . (i.e., recirculating systems) are

designated as... [primary). ESF systems required to

operate under conditions that are generally less severe...

(i.e., recirculating or once-through systems) are

designated as ... [secondary]. Secondary systems

typically include the standby gas treatment system

[SGTS] and emergency ACS for the fuel handling building, control room, and shield building.... Unless the

applicable engineered-safety-feature atmosphere

cleanup system operates continuously during all times

that a DBA can be postulated to occur, the system

should be automatically activated upon the occurrence

of a DBA.. . (USNRC 1978). Information is included

in the RG in recognition of the fact that environmental

conditions preceding a postulated DBA may contribute

to aging and degraded performance of filters and

adsorbers. It is specifically noted that aging needs to be

considered during design and operation. Furthermore,

remembering that the guide was developed for accident

mitigation systems, it is also indicated that all components need to be designed for reliable performance in

potentially hostile environments.

Typical DBA environmental conditions, including pressure surge, maximum pressure, maximum temperature

and RH of the influent, average radiation levels for airborne materials and iodine buildup on the adsorber, and

airborne iodine concentrations for elemental iodine and

for methyl iodide and particulate iodine, are tabulated

in RG 1.52 for the primary and secondary ESF systems

described in the preceding paragraph (USNRC 1978).

The radiation levels are based on U.S. Atomic Energy

Commission (USAEC) RG 1.3 and RG 1.4, which provide acceptable assumptions for use in evaluating the

radiological consequences of one of the postulated accidents for boiling- and pressurized-water reactors (i.e.,

the design basis loss-of-coolant accident [LOCA]). In

both of these regulations, it is stated that "twenty-five

percent of the equilibrium radioactive iodine inventory

developed from maximum full power operation of the

core should be assumed to be immediately available for

leakage from the primary reactor containment Ninetyone percent of this 25 percent is to be assumed to be in

the form of elemental iodine, 5 percent of this 25 percent in the form of particulate iodine, and 4 percent of

this 25 percent in the form of organic iodides (USAEC

1974a,b).

One of the two major concerns arising from this Phase I

study is that the conditions developed for the above design basis assessments may not realistically represent

those under which HEPA filters and adsorbers, including aged components, may operate. Design-basis accident evaluations are based on non-mechanistic hypothetical events. Pasedag, Blond, and Jankowski (1981) note

that ... the Design-Basis Accidents (DBAs) are a set of

accidents which have been chosen to envelope the anticipated worst credible conditions in what was perceived to be a very conservative manner. Thus these

accidents are not representative of expected or realistic

conditions but have been judged to bound any credible

accident... The DBA-LOCA cannot be expected to be

predictive of any specific accident situation.' Over the

past 10 to 15 years, a large amount of information has

been developed that may permit significantly better estimates of the conditions, including radiation levels, temperatures, humidities, and the chemical and physical

properties of the materials that aged components might

encounter during severe accidents. This information

was developed as part of, or in support of, probabilistic

risk studies and extensive efforts to reassess source

terms (characterization of radionuclide releases from

NUREGICR-6029 7.2
Conclusions

reactor accidents) and has included efforts to provide

improved analytical models to describe thermalhydraulic behavior and mass transport. The latter

includes detailed models that take Into account the

chemical and physical processes associated with the release of fission products from the degraded core and the

subsequent transport and retention of material through

and in the reactor vessel, coolant systems, containment,

and exterior compartments.

A system of computer codes, the Source Tbrm Code

Package (STCP), has been developed for analyzing specific postulated accident situations and calculating the

quantity, timing, and characteristics of the release of

radioactive material to the environment following the

incident (Gieseke et al. 1986). This code system or the

more recently developed MELCOR computer code for

source term and risk assessment analyses could be used

to provide significantly more realistic insights into the

impact of an accident on filters and adsorbers (Summers

et al. 1991). For example, rather than using assumptions, information could be developed from calculations

that would be extremely useful in estimating the range

and combination of accident conditions that may be encountered, e.g., in providing best-estimates of the likelihood for large particle concentrations and/or moisture

conditions that could saturate and overwhelm HEPA filters. An improved definition of accident conditions may

also reveal that aging concerns associated with the filters

and adsorbers of 'normal' treatment systems may equal

those of ESF systems and that the designations of primary and secondary for the latter may be trivial in terms

of accident considerations. One of the findings resulting

from investigations into the TMI accident was the fact

that". . . a nonengineered safety feature filter system designed for normal operation only, i.e., the auxiliary

building exhaust ventilation filtration system, greatly reduced the quantity of radioiodine release to the environment. .. The safety grade versus nonsafety grade designation [for the two air treatment systems operating at

the time of the accident] was meaningless...." (Rogovin

and Frampton 1980).

It should also be noted that in a recent study Beahm,

Weber, and Kress (1991) used the STCP to address the

issue of the chemical form of iodine in the coolant system and in containment. Using calculated data from

seven severe accident sequences, it was found that 'in

most of the calculations for the seven sequences, iodine

entering containment from the reactor coolant system

was almost entirely in the form of CsI with very small

contributions of I or HI The study did not address ultimate disposition. Iodine could, of course, subsequently

be converted to the volatile form, e.g., if the CsI dissolved in low pH water, was ultimately converted to

organic form, or decomposed after being captured on

filters. However, the study suggests the perhaps unexpected conclusion that, during accidents, intact HEPA

filters could be significantly involved in iodine retention.

Furthermore, past design basis evaluations based on the

assumption that iodine is primarily in the volatile form

may neither be correct nor conservative when evaluating

air-cleaning system performance. L1l-defined accident

conditions even where a DBA philosophy is applied" are

described as a major problem by the group of NEA experts. As further support for the possibility of nonconservative assumptions, this group also notes that *. . . the

DBA may not represent the most severe conditions

under which the ACS has to operate" (OECD 1984).

The second major concern arising from the Phase I

study is that even if details concerning accident conditions were available, there may be insufficient information to develop reliable predictions concerning the performance of aged components in such potentially

extreme environments. In 1984, the group of NEA

experts characterized the extent of knowledge that is

available to evaluate aged HEPA filter and adsorber

performance during accidents as non-existent and for

the most part, poor, respectively. The group of experts

stated that "...the available information on HEPA filters

relates primarily to new filters and virtually no data exist

for the normal or accident condition behavior of aged

filters. Many ACS HEPA filters remain in place for

more than 5 years. It is unrealistic to expect that accidents will occur only with freshly installed HEPA filter

banks" (OECD 1984). When considering aged HEPA

filters in conjunction with accident environments, the

group described the extent of knowledge as non-existent

for the following parameters: pressure differential,

vibration, high humidity/free water, chemicals, radiation,

temperature, and loading capacity. When appraising the

extent of knowledge for aged adsorbers, pressure differential was identified as good; vibration as nonexistent; radiation as fair, and high humidity/free water,

chemicals (weathering), temperature, and loading

capacity as poor.

7.3 NUREG/CR-6029
Conclusions

The above relative gloomy picture has brightened somewhat in recent years, presumably as the result of the

emphasis on severe accidents. Information has been obtained to at least partially fill in some of the gaps associated with the above parameters. As indicated earlier,

above saturation, new or clean filters are vulnera to

deterioration and failure. Obviously, high humidity air

flows can jeopardize dirrtice iloaded filters. Eke

m6s -an M&ch__amsms of the failure of dfust-loaded filters under high humidity conditions are discussed in

Ricketts, Ruedinger, and Wilhelm (1987) and in

Ruedinger, Ricketts, and Wilhelm (1985). The structural limits, in terms of AP at failure, are tabulated in the

latter reference for HEPA filters tested under high air

humidities at 1700 m3ih and 500C. Norman (1987) reports results from the exposure of filter media to steam.

The media were dried subsequent to exposure and evaluated with respect to penetration and tensile strength.

IncreasedPettion (using DOP aeross)was obsvedvef the media to high humidities

andcelevated temperature. Tensile strength decreased to

a6ut 40% of its original value. Aspects of the increase

in pressure drop of 1HEPA filters under fog conditions

was also investigated by Ricketts, Ruedinger, and

Wilhelm (1990). 'Airstreams with between 80% and

100% RH primarily threaten dust-loaded filters. At

conditions above saturation, new clean filters also

become subject to rapid deteriorations in performance."

Penetration of water through filters by seepage was

characterized as 'rather rapid." Such penetration suggests that water soluble salts containing radionuclides

could penetrate even intact filters. The performance of

downstream adsorption units could also be affected.

Performance limitations and efficiency of and releases

from HEPA filters at high temperatures were the topics

of three of the papers of Session 3B, "Response of

HEPA Filters to Physical Stress,' of the 20th DOE/NRC

Nuclear Air Cleaning Conference (Kratzke 1989). Effects of temperature on HEPA filter media was again a

topic for discussion at the most recent, 22nd, conference

where" .. . observed changes in strength and paper stiffness ... [were) explained in terms of alterations to the

binder due to thermal degradation" (Hamblin and

Goodchild 1992).

A comprehensive study of the performance of TEDA

and KI impregnated charcoals under 'reactor accident

conditions" is reported in Wren et al. (1989), "The

efficiency of these charcoals in removing CH3I and I2

was studied as a function of temperature (250 to 800C),

RH (O to 90% RH), radiation field (0 to 2kGy.hr-) with

and without H2 , contaminants (SO2, NO2, NH3, and

MEK) and other factors." Deitz (1985) reports that

"based on the experimental results, it appears that

reactor-grade activated charcoal can satisfy the stipulation in RG 1.52 that requires successful trapping of

radiolodine during a DBAwith radiation levels up to

[107 Gyl io1 rads." In fact, it was found that exposure to

levels of 167 to 169 regenerates the iodine isotope exchange capacity. Paraphrasing Deitz, where the trapping of methyl iodide-131 is concerned, radiation

improvement rather than damage is observed.

7.3 Conclusions and Recommendations

The Phase I study found that the HEPA filters and adsorbers are considered to have a long service life,

especially the filters. Thus, if a severe accident happens

it is likely to occur at a time when these two final confinement barriers have been in use for an extended

period, even years. Even with existing inspection, monitoring and monitoring methods, aged, and possibly

degraded components, could fail to provide the radiation protection needed for safe shutdown or be the weak

link that allows the release of radionuclides to the

environment Furthermore, the assessment has revealed

the need for an improved definition of accident conditions and the possible need for additional information

to evaluate the performance of aged components under

such conditions. It is recognized that this improved

definition of accident conditions is outside the scope of

the NPAR program. It is also recognized that comprehensive assessments limited solely to the development

of information for performance evaluation could be

made. However, for such studies to be definitive, knowledge concerning challenges must ultimately be obtained, as will be discussed below.

Limited information concerning the range of challenges

expected for filters and adsorbers during accidents is

already available as a result of source term reassessment

and reactor risk studies (Silberberg et al. 1986; USNRC

1990). Additional insights concerning accident conditions should also become available as a result of recent

regulatory efforts to provide improved source term

NUREG/CR-6029 7.4
Conclusions

definitions. As part of several regulatory activities to

incorporate severe accident insights into the safety

assessment of future plants, the NRC has issued a

proposed revision of the reactor accident source terms.

The proposed revision is in terms of fission product

composition, magnitude, timing, and iodine chemical

form, for release into containment (Soffer 1992). Utilization of these revised source terms should provide

improved estimates of accident conditions and the associated challenges to filters and adsorbers. For example,

evaluation of iodine chemistry during the portion of the

transient that follows release into containment will be

needed, resulting in better estimates of whether iodine

remains primarily in the particulate form or is converted

to a volatile species before it reaches filters and

adsorbers.

As previously indicated, even if details concerning accident conditions were available, there may be insufficient

information to develop reliable predictions concerning

the performance of aged components. Quantification of

the structural limits and failure mechanism of aged filters in moist airflows and of the particle loadings that

would cause failure of reduced strength and/or particleladen filter media are examples of potential information

needs. Statistically-designed engineering scale experiments, involving aged components and utilizing the

improved estimates of the ranges and combinations of

challenges, may ultimately be justified. It is also possible that improved estimates of conditions could negate

the need for further work, because either moderate or

extremely severe stressors are predicted. In the case of

moderate stressors, for example, additional study

appears unwarranted if near normal operating conditions are identified. In the case of severe conditions,

HEPA filters are simply not sized to handle the massive

loading of non-radioactive particles that conceivably

could result from molten core-concrete interactions.

An improved understanding of severe accident conditions could also further emphasize the importance of

other air-treatment system components. For example,

along with HEPA filters, greater emphasis would be

placed on coarse or roughing pre-filters and even

demisters if it were determined that high particle concentrations were involved. As a result, expansion of the

Phase I interim aging assessment to other components

of nuclear air-treatment systems, namely demisters,

heaters, coarse filters, fans or blowers, and dampers is

recommended. Several of these components, although

not designed to retain radionuclides, could mitigate the

Impact of conditions that threaten to cause failure of

aged HEPA filters and adsorbers during accidents. The

aging of these protective components is, therefore,

also of concern. The information that is developed for

fans can be used in the assessment of other ESF systems

specifically installed to ensure public and plant safety.

In addition to air cleaning, fans or blowers are included

in heating, ventilation, and air conditioning and containment cooling and pressure suppression systems.

Finally, it should be emphasized that information used

to estimate the performance of aged air-treatment system components can have a significant impact on the

calculated consequences of postulated accidents. This is

illustrated by the analyses of a postulated loss of decay

heat removal accident at Browns Ferry. The SGTS failure model used, listed as the area of greatest uncertainty

with respect to informal sensitivity analyses, includes

best estimates concerning the filter loading that will

cause failure, the type of failure, and the functioning of

the adsorber under the projected accident environment.

It is noted that "the SOTS failure model assumes prime

importance because the SGTS is the last barrier to the

atmosphere in this accident sequence' (Wichner et al.

1984).

7.5 NUREG/CR-6029
8 References

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Vol. 2, ed. MW. First, pp. 1058-1096. CONF-840806,

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NUREG/CR-6029 8.4
NUREG/CR-6029

PNL-8594

Distribution

No. of

Copies

No. of

Copies

OFFSITE ONSITE

R. R. Bellamy

US. Nuclear Regulatory Commission

RGN-1

Washington, DC 20555

20 J. J. Burns

US. Nuclear Regulatory Commission

Office of Nuclear Regulatory Research

MS: NS217B

Washington, DC 20555

D. A. Casada

Oak Ridge National Laboratory

P.O. Box 2009

Oak Ridge, TN 37831-8038

M. W. First

Harvard University

655 Huntington Avenue

Boston, MA 02115-9957

R. J. Lofaro

Brookhaven National Laboratory

Building 130

Upton, Long Island, New York 11973

H. L Magleby

EG&G Idaho, Inc.

P.O. Box 1625

Idaho Falls, ID 83415-2406

2 DOE Richland Field Office

D. C. Langstaff (2)

47 Pacific Northwest Laboratory

R. P. Allen (10)

D. E. Blahnik

S. H. Bush

E. H. Carbaugh

M. E. Cunningham

M. K Drost

E. 1. Eschbach

J. L Ethridge

K R. Hoopingarner

D. B. Jarrell

A. B. Johnson Jr.

L. D. Kannberg

1. S. Levy

M. W. 1Ugotke

R. L. Moffitt

W. C. Morgan

J. V. Ramsdell Jr.

W. K Winegardner (15)

Publishing Coordination

Technical Information (5)

M. Vagins

U.S. Nuclear Regulatory Commission

Office of Nuclear Regulatory Research

MS: NS217B

Washington, DC 20555

J. P. Vora

U.S. Nuclear Regulatory Commission

Office of Nuclear Regulatory Research

MS: NS217B

Washington, DC 20555

Distr.1
NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

2-891 (A112ned by NRC. Add Vol., Supp., Rev.. NRCM 112 end Addendumn Numbei, It anyJ1

3201,3202 BIBLIOGRAPHIC DATA SHEET NUREG/CR-6029

{See instnxctins on the reverse) PNL-8594

2. TITLE AND SUBTITLE Vol. 1

Aging Assessment of Nuclear Air-Treatment System

HEPA Filters and Adsorbers 3. DATE REPORT PUBLISHED

MONTH YEAR

Phase I August 1993

4. FIN OR GRANT NUMBER

B2911

5. AUTHOR (S) 6. TYPE OF REPORT

Technical

7. PERIOD COVERED 7Inclusiw Dvta

W. K. Winegardner

8. PERFORMING ORGANIZATION - NAME AND ADDRESS litfNRC. provide DVion, Offi, or Resion, U.S Nuckar Aegutatory Cernmiuioa dcf :N lingt addre itcoracor, provide nuae and Hilin .dd s&)re

Pacific Northwest Laboratory

Richland, WA 99352

S. SPONSORING ORGANIZATION -NAME AND ADDRESS hRC. oVe -- ~a a if onrrctor, Provdr JAVC Div, Offier r epgon, t& t.S.aruguiatoqy ConCnin. - ailn g .fdd4=1s

Division of Engineering

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

10. SUPPLEMENTARY NOTES

11. ABSTRACT Vo" wordserka

A Phase I aging assessment of high-efficiency particulate air (HEPA) filters and activated carbon gas adsorption units

(adsorbers) was performed by the Pacific Northwest Laboratory (PNL) as part of the U.S. Nuclear Regulatory Commission's (NRC) Nuclear Plant Aging Research (NPAR) Program. Information concerning design features; failure

experience; aging mechanisms, effects, and stressors; and surveillance and monitoring methods for these key airtreatment system components was compiled. Over 1100 failures, or 12 percent of the filter installations, were reported

as part of a Department of Energy (DOE) survey. Investigators from other national laboratories have suggested that

aging effects could have contributed to over 80 percent of these failures. Tensile strength tests on aged filter media

specimens indicated a decrease in strength. Filter aging mechanisms range from those associated with particle loading

to reactions that alter properties of sealants and gaskets. Low radioiodine decontamination factors associated with the

Three Mile Island (TMI) accident were attributed to the premature aging of the carbon in the adsorbers. Mechanisms

that can lead to impaired adsorber performance include oxidation as well as the loss of potentially available active sites

as a result of the adsorption of pollutants. Stressors include heat, moisture, radiation, and airborne particles and

contaminants.

1Z KEY WORDS/DESCR.PTORS 1t aw*d erphrs iWwat Ossswsea In 1, h em ,por.j 13. AVAOLABILITY STATEMENT

IEPA filters Unlimited

Phase I aging 14.SECURITYCLASIFICATION

adsorbers (his page)

air-treatment system Unclassified

design feature (TsM Reprt)

failure experience Unclassified

aging mechanisms 15. NUMBER OF PAGES

stressors

16. PRICE

NRC FORM 335(2891
Federal Recycling Program
NUREG/CR-6029, Vol. 1 AGING ASSESSMENT OF NUCLEAR AIR-TREATMENT SYSTEM

HEPA FILTERS AND ADSORBERS

AUGUST 1993

UNITED STATES

NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555-0001

FIRST CLASS MAIL

POSTAGE AND FEES PAID

USNRC

PERMIT NO. G-67

OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300