ML20212R268

Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants.Lwr Edition.Proposed Revision 2 to Section 6.5.2, Containment Spray as a Fission Product Cleanup System. for Comment

ML20212R268
Person / Time
Issue date:	04/30/1987
From:	Office of Nuclear Reactor Regulation
To:
References
NUREG-0800, NUREG-0800-06.5.2-R2, NUREG-800, NUREG-800-6.5.2-R2, SRP-06.05.02, SRP-6.05.02, NUDOCS 8704270036
Download: ML20212R268 (80)

Text

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l U.S. NUCLEAR REGilLATORY COMMISSION l

NUREG-0800 l " STANDARD REVIEW PLAN FOR THE REVIEP OF SAFETY l I.NALYSIS REPORTS FOR NUCLEAR POWER PLANTS" h

6 . NOTICE OF ISSUANCE AND AVAILABILITY l "FOR COMMENT" ,

F PROPOSED REVISION ? TO SRP SECTION 6.5.2 l AND REGULATORY ANALYSIS AND SUPPORTING TECHNICAL DOCUMENTS The U.S. Nuclear Regulatory Comission (NPC) has published prcposed revision 2 to Section 6.5.?, " Containment Spray as a Fission Product Cleanup System,"

of NUPEG-800 " Standard Raview Plan for the Review of Safety Analysis Reports l for Nuclear Power Plants," LWR Edition (SPP).

l The proposed revision to SRP fection 6.5.2 consists of revision 2, its supporting Regulatory (value/ impact) Analysis, and two supporting technical documents, " Containment Sprays," and Technical Report, " Fission product Removal Effectiveness of Chemical Additives in PWR Containment Sprays."

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2 This revision would delete the requirement for imediate initiation cf caustic additives to the spray and would reduce the minirrum pH to be achieved from 8.5 to 7.

This revisions would be required for future plants, but would be optional for present licensees and are part of a proposed series of SRP ard Peculatory Guide changes intended to implement the Conr.ission's Severe Accidert Policy b

and to introduce the result of recent severe accident regulatory research into .

staff practices. Coments are being solicited from irterested organizatiers, groups and individuals. The staff will evaluate the correents received, and address them, as appropriate, in the final docurrents.

Copies of the "for Comment" documents will be available af ter April 6.1987 Copies will be sent directly to utilities, utility industry groups and associations and environmental and gublic interest groups. Other copies will be available for review at the NRC Public Document Room, 1717 F Street, PW, Washington, D.C. and the Comission's local Pubite Document Rooms located in the vicinity of nuclear power plants. Addresses of these Local Public Document Rooms can be obtained from the Chief, Public Document Branch, U.S. Nuclear Regulatory Comission, Washington, D.C. 20555, telephone (202) 634-3273.

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l Comments should be sent to the Secretary of the Comission U.S. Nuclear i l j Regulatory Comission, Washington, D.C. 20555, Attention: Docketing and i 1 ,

I Service Branch, by June 5,1987. l l

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. Dated at Bethesda, Maryland, this 6th day of April 1987.

r FOR THE NUCLEAR REGULATORY COMMISSION (

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l Harold R. Denton, Director  !

Office of Nuclear Reactor Regulation l

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(%'s j STANDARD REVIEW PLAN

\...../ OFFICE OF NUCLEAR REACTOR REGULATION Proposed Revision Standard Review Plan PSRP-6.5.2, Rev 2 This proposed revision of the Standard Review Plan and its supporting value/ impact statement and associated technical documentation have not received a complete staff review and approval and do not represent an official NRC staff position. Public comments are being solicited on the proposed SRP section and the associated regula-tory analysis and technical support document A-3788, " Fission Product Removal Effectiveness of Chemical Additives in PWR Containment Sprays" prior to a final re-view and decision by the Office of Nuclear Reactor Regulation as to whether this proposed revision should be approved. Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Atten-

! tion: Docketing and Service Branch. All comments received by June 5, l'387 will be

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considered, and all of the associated documents and comments considered will be

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) made publicly available prior to a decision by the Director, Office of Nuclear Reactor Regulation, on whether to implement this revision. Single copies of each of these documents are available upon written request to the Division of Informa-tion Support Services (Attention Distribution Section), U.S. Nuclear Regulatory Commission, Washington, D.C. 20555.

Rev. 2 USNHC STANDARD fl[ VIEW PLAN sia,.d.,d e. view pt.no .,e propa ed in, ih. guidance ne the of fer. of Nue l.ee it..ctae Ft.autation etaf f ensponed l. f ne the r view ni appier.nnne in construc t and on ..i. nuos., pnw., pionee t hee. darum.nte ... med. ve,i.hi. i, th. pubiie me p.et af the Commeenion a pokry to inform th nus. leet industry and the g.n.t.4 publ6r. of regulatory pentodures se a palettee Standard feview piene at. not euhetitutes fat tegulatory guldes of the Commise6nn e eeuulatione and enmpliam. west them is not requ6ted Th.

/n\ etandard f eview plan esce6one ee hoy.d to the Standard intmat and Cantent of Safety Aneivete fiepne's Ice Nuti..e Pow.e Plants Nnt all sertinne of the Standard Futmat hav. e ente.aponding rev6ew plan (V) ruid.,b.a st.nd.,d ,o. .. pione wai h. .v.co,f ,.nnd,<.ii,. .e .pp,np, .t.. .. .,.c ommna.i. omm.nte .nd io t.fi.ct n.w inf o,m.

tio#, and .s peelant e Commente and suggestinne fue impenvement will be enneotered and ohnutd be sent to th. U S Nuv.e# Naquietney cammleeinn.

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!@gjf STANDARD REVIEW PLAN t, o, OFFICE OF NUCLEAR REACTOR REGULATION e.e.e Proposed Revision 2 to 6.5.2 CONTAINMENT SPRAY AS A FISSION PRODUCT CLEANUP SYSTEM REVIEW RESPONS!8tLITIES i

Primary - Plant Systems Branch i Secondary - None I

1. AREAS OF REVIEW The containment spray and the spray additive or pH control systems are reviewed to determine the fission product removal effectiveness of the system whenever the ap-plicant claims a containment airborne fission product cleanup function for the sys-tem. The following areas of the applicant's Safety Analysis Report (SAR) relating to the fission product removal and control function of the containment spray system (p) are reviewed.

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1. F f ssion Product Removal Requirement for Containment Spray Sections of the SAR related to accident analyses dose calculations and fis-s e sion product removal and control are reviewed to establish whether fission product scrubbing of the containment atmosphere for the mitigation of offsite doses following a postulated accident is claimed by the applicant. This re-view usually covers Sections 6.2.3.1 and 6.5.2.le and Chapter 15 of the SAR. l

2. Desian Bases  !

l The design bases of such containment spray systems are reviewed to determine whether they reflect the requirements placed upon this system by the assump-tions made in the accident evaluations of Chapter 15.

1 Rev. 2 UFNHC STANDAHD HEVIEW PLAN Atat dard review piene are peepared in# the g avence of the office of Nuclear Heactor iteoulat6on staff toepanoihle fo# the review of applicatinne to tonettutt enet operate nutie et pnwee plante these statumente a#e made available to the publie as part of the Commiseson e polery to 6nfutm the nucleet P dvetty and the genef el public of fogulatory proe.edutee and politsee Standard fev6ew

, plane see t et oubetitutes foe regulatory g a stee or the Commimen e ti.gulatione end enmpliants w6th them 6e not eentuiteit The

/m standard rev6ew plan settinne see hoved to the Standa#d Fnemet and Content of Befety Analve6e Hoporte for Nutteet Power Plante (v}j Nni .u est emne of ihe si.nd.,4 e.,mai he.o e en,,Gepondin. ,o.iew iden ruesiehed standa,d ,e.,ew piano wai be ,e,.e.d pe,iod><.,i, .s epp,op, .to to e.c ommodai. commento and to ,etiati now info,me linft and espotient e Commente and suggestions for 6mprovement wil he reneideeed and should he sent to the U 8 Nuclear Megulato#y Comm6es6on, Office of Nuclear Heattof Megulation. Wash 6ngton. D C. 20%8

3. System Design The descriptive information concerning the design of the spray system, includ-ing any subsystems and supporting systems, is reviewed to familiarize the re-viewer with the design and operation of the system. The review includes:

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a. The descriptive information usually contained in SAR Sections 6.2, 6.5.2.2, 6.5.2.4, 6.5.2.5, and 6.5.2.6 to establish the basic design concept, the systems, subsystems, and support systems required to carry out the fission product scrubbing function of the system, and l the components and instrumentation employed in these systems,

b. The process and instrumentation diagrams of SAR Section 6.5.2 or 6.2.2, whichever contains the relevant information.

c. Layout drawings (plans, elevations, isometrics) of the spray distri- ,

bution headers, from SAR Chapter 1.0 and Section 6.5.2 or 6.2.2. l

d. Plan views and elevations of the containment layout in Chapter 1.0 ,

j of the SAR.

4. Testing and Inspections Section 6.5.2.4 of the SAR is reviewed to establish the details of the preoperational test to be performed for system verification and the post-operational tests and inspect. ions to be performed for verification of the continued status of readiness of the spray system.

5. Technical Specifications l At the operating license stage, the applicant's proposed technical speci-l fications in Chapter 16 of the final Safety Analysis Report (FSAR) are reviewed to establish permissible outage times and surveillance requirements.

In addition, the reviewer will coordinate other evaluations that interface with i the review of the containment spray system as follows: any chemical additive l storage requirements, materials compatibility and organic material decomposi-l tion including formation of organic lodide as part of SRP Sections 6.1.1 and

, 6.1.2, the heat removal and hydrogen mixing function of the containment spray system and the containment sump design as part of SRP Sections 6.2.2 and 6.2.5.

The acceptance criteria for the review and the methods of application are con-tained in the referenced SRP sections.

II. ACCEPfANCE CRITERIA The acceptance criteria are based on meeting the relevant requirements of the l following regulations:

A. General Design Criterion 41 (Ref. 1) as related to the containment atmos-phere cleanup system being designed to control fission product releases to the environment following postulated accidents, i

B. Genoral 02 sign Critorion 42 (Raf. 2) as rolated to tha containment atmos-phere cleanup system being designed to permit appropriate periodic inspections, i

x C. General Design Criterion 43 (Ref. 3) as related to the containment atmos- l phere cleanup system being designed for appropriate periodic functional testing.

Specific criteria necessary to meet the relevant requirements of G0C 41, 42, and 43 are:

Design Requirements for Fission Product Removal l

1.

The containment spray system should be designed in accordance with the ANSI requirements of Reference 4, except that requirements for any spray l l additive or other pli control system in this reference need not be followed. l

a. System Operation The containment spray system should be designed to be initiated auto-matically by an appropriate accident signal and to be transferred automatically from the injection modo to the recirculation mode to assure continuous operation until the design objectives of the system i have been achieved, in all cases the operating period should not be less than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. Additives to the spray solution may be initiated manually or automatically, or may be stored in the containment sump to be dissolved during the spray injection period.

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b. Coverage of Containment Volume In order to assure full spray coverage of the containment volume.

the following should be observed:

l (1) The spray nozzles should be located as high in the containment as practicable to maximize the spray drop fall distance.

(2) The layout of the spray nozzles and distribution headers should be such that the cross-sectional area of the containment covered by the spray is maximized and that a nearly homogeneous distri-bution of spray in the containment volume is produced. Unsprayed regions in the upper containment and, in particular, an unsprayed annulus adjacent to the containment liner should be avoided ,

wherever possible.

(3) In designing the layout of the spray nonle positions and orien-l tations, the offect of the postaccident atmosphere should be l considered, including the offccts of postaccident conditions that l result in the maximum possible atmosphere density,

c. Promotion of Containmont Mixina Because the offactiveness of the containment spray system depends on a well mixed containment atmosphere, all design features enhancing postaccident mixing should be considered.

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Rev. 2 6.5.2-3 l

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d. Spray Nozzles The nozzles used in the containment spray system should be of a design that minimizes the possibility of clogging while producing drop sizes offective for iodine absorption. The nozzles should not have internal moving parts such as swirl vanes, turbulence promoters, etc. They should not have orifices or internal restrictions which would narrow the flow passage to less than 1/4-inch diameter, l

e. Spray Solution l The partition of iodine between liquid and gas phases is enhanced by the alkalinity of the solution. The spray system should be designed such that the spray solution is within material compatibility con-l straints. Iodine scrubbing credit is given for spray solutions whose l chemistry, including any additive 3, has been demonstrated to be effec- '

j tive for iodine absorption and retention under postaccident conditions,

f. Containment Sump Mixing '

l l The containment sump thould be designed to permit mixing of emergency l l core cooling system (ECCS) and spray solutions. Drains to the engi-l neered safety features (ESF) sump should be provided for all regions of the containment which would collect a significant quantity of the spray solution. Alternatively, allowance should be made for " dead" volumes in the determination of sump pil and the quantities of addf-l tives injected.

g. Containment Sump and Recirculation Spray Solutions l The pil of the aqueous solution collected in the containment sump after completionofinjectionofcontainmentsprayandECCSwater,andall additives for reactivity control, fission product removal, or other l

purpose, should be maintained at a level sufficiently high to provide assurance that significant long-term iodine re-evolution does not occur. Long-term fodine retention is calculated based on the expected long-term partition coefficient. Long-term iodine retention may be assumed only when the equilibrium sump pil, after mixing and dilution with the primary coolant and ECCS injection, is above 7 (Ref 5). This pil value should be achieved by the onset of the spray recirculation mode. The material compatibility aspect of the long-term sump and ,

recirculation spray solutions is reviewed under SRP Section 6.1.1. I i

h. Storage of Additives The design should provide facilities for the long-term storage of any I spray additives. These facilities should be designed such that the additives required to achieve the design objectives of the system are stored in a state of continual readiness whenever the reactor is cri-l tical during the design life of the plant. The storage facilities I should be designed to prevent freezing, precipitation, chemical reac-l tion, and decomposition of the additives. For Na0li storage tanks, heat tracing of tanks and piping is required whenever exposure to 6.5.2-4 Rev. 2

temperatures below 402F is predict:d. An inert cov:r gas should be provided for solutions that may deteriorate as a consequence of ex-posure to air,

i. Single Failure The system should be able to function effectively and meet all the i

above criteria with a single failure of an active component in the l spray system, in any of its subsystems, or in any of its support systems. l

2. Testing l

Tests should be performed to demonstrate that the spray systems, as in-stalled, meet all design requirement.s for an effective fission product i

'- scrubbing function. Such tests should include preoperational verification of:

a. freedom of the containment spray piping and nozzles from obstructions, b, capability of the system to deliver the required spray flow, and

c. capability of the system to deliver spray additives (if any are l I

needed), and to achieve a sump solution pH above 7. For a system whose performance is sensitive to the as-built piping layout, such as a gravity feed system, the testing should be performed at full flow.

3. Technical Specifications The technical specifications should specify appropriate limiting conditions for operation (tCOs), tests, and inspections to provide assurance that the system is capable of performing its design function whenever the reactor is I critical. These specifications should include:

a. The operability requirements for the system, including all active and passive devices, as a limiting condition for operation (with acceptable outage times). The following should be specifically ,

included:

a containment spray pumps,

- additive pumps (if any),

a additive mixing devices (if any),

a valves and nozzles, e additivo quantity and concentration in any additive storage I tanks, and

- nitrogen or other inert gas pressure in any additive storage l tanks, 6.5.2 5 Rev,-2

b. P riodic inspection and sampling cf the cont:nts cf any additiva tanks to confirm that the additive quantity and concentrations are within the limits established by the system design.

c. Periodic testing and exercising of the active components of the sys-tem and verification that essential piping and passive devices are free of obstructions.

Acceptable methods for computing fission product removal rates by the spray system are given in subsection !!!.4.6, " Review Procedures - Evaluation -

Fission Product Cleanup Models."

111. REVIEW PROCEDURES The reviewer selects and emphasizes aspects covered by this SRP section as appropriate for a particular plant. The judgment of which areas need to be

• given attention and emphasis in the review is based on a determination that the l material presented is similar to that recently reviewed on other plants or that I items of special safety significance are involved. The review of the fission -

I product removal function of the containment spray system follows the procedure outlined below.

l The reviewer determines whether the containment spray system is used for fission product removal purposes. Chapter 15 of the SAR should be reviewed to establish whether a fission product removal function for the containment spray system is assumed in accident dose evaluations. If the containment spray system is not used for dose mitigation purposes, no further review is required under this i section. I

1. System Desian Review of the system design includes an examination of the components and design features necessary to carry out the fission product scrubbing func- l tion, including:

a. Spray _ Chemistry The forms of lodine for which spray removal credit is claimed in the accident analyses (SAR Chapter 15) are established. Containment spray systems may be designed for removal of todine in the elemental form i (i.e. vapor), in the form of organic compounds, and in the particulate I form. Spray removal credit for other particulate fission products is l ,

also established. '

The systems or subsystems required to carry out the fission product scrubbing function of the containment spray, such as the spray system, recirculation system, spray additive system, and water source are identified. The design of the systems involved is reviewed in order l to:

(1) Determino any chemical additivo and ascertain its offectiveness l for elemental and organte lodine removal.

6.5.2 0 Rev. 2 1

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l (2) Ascertain that the amount of additiv3 is sufficicnt to meet the acceptance criterion of subsection II above or that adequate justification is supplied for the iodine removal and retention

,Q effectiveness for the range of concentrations encountered. The concentrations in the storage facility, the chemical addition Q

a lines, the spray solution injection, the containment sump solu-tion, and the recirculation spray solution should be examined.

The extremes of the additive concentrations should be determined with the most adverse combination of ECCS, spray, and additive pumps (if any) assumed to be operating, and a single active failure of pumps or valves should be considered. l The reviewer verifies that the spray and sump water solution stability,l and the corrosion, solidification, and precipitation behavior of the chemical additives, have appropriately been taken into consideration for the range of concentrations encountered.

< b. System Operation The time and method of system initiation, including additive addition, is reviewed to confirm that the acceptance criteria of subsection II above are met. Automatic initiation of spray is reviewed under SRP l Section 6.2.2. Credit for immediate initiation is assumed if the sys-tem can be shown, by test, to deliver the spray solution through the nozzles within 90 seconds, post-LOCA. For those systems where the spray solution is delivered after 90 seconds, post-LOCA, credit for spray removal of fission products will be assumed to commence upon the l time of actual flow through the nozzles. The system operation should

' be continuous until the fission product removal objectives of the sys- I tem are met. If a switchover from the injection to a recirculation 4 V mode of operation is required during this time period, the reviewers should confirm that all requirements listed in the acceptance crite-ria, particularly those concerning spray coverage and solution pH, are met during the recirculation mode following the initiation of the l spray system operation must be automatic to prevent the damage of the l spray pumps through loss of suction upon the emptying of the storage tank.

c. Spray Olstribution and Containment Mixina The number and layout of the spray headers used to distribute the spray flow in the containment are reviewed. The reviewer verifles that the layout of the headers assures coverage of essentially the entire cross-section of the containment with spray, under minimum i spray flow conditions. The effect of the post-accident high tempera- l ture and pressure conditions in the containment on the spray droplet trajectories should be taken into account in determining the area

covered by the spray.

The layout of the containment is reviewed to determine if any areas I of the containment free volume are not sprayed. The mixing rate due to natural convection between the sprayed and unsprayed regions of the containment, provided that adequate flow area exists between these 6.5.2-7 Rev. 2

regi:ns, is assumed to b] 2 turn:v:rs of the unsprayed region (s) p;r hour, unless other rates are justified by the applicant. Fan systems to mix air volumes within containment under accident conditions are reviewed under SRP Section 6.2.5. The containment may be considered a single, well-mixed volume if the spray covers regions comprising at least 90% of the containment volume and if a ventilation system is available for adequate mixing of any unsprayed compartments.

d. Spray Nozzles The design of the spray nozzles is reviewed to confirm that the spray nozzles are not subject to clogging from debris entering the recircu-lation system through the sump screens.

e. Sump Mixing The mixing of the spray water containing any chemical additive and l water without additive (such as spilling ECCS coolant) in the contain-ment sump is reviewed. The areas of the containment which are exposed to the spray but are without direct drains to the recirculation sump (such as the refueling cavity) are considered. The reviewer confirms that the required sump concentrations are achieved within the appro-priate time intervals. The long-term sump pH should be reviewed in regard to iodine re-evolution, using the criteria given in subsec-tion II.1.g above.

The equilibrium partitioning of iodine between the sump liquid and the containment atmosphere is examined for the extreme additive con-centrations determined above, in combination with the range of tem-peratures possible in the containment atmosphere and the sump solu-tion. The minimum iodine partition coefficient (H) determined for these conditions forms the basis of the ultimate iodine decontamina-tion factor in the staff's analysis described below. See Reference 8 for a discussion of iodine partition coefficients.

f. Storage of Additives The design of any additive storage tanks is reviewed to establish I whether heat tracing is required to prevent freezing or precipitation J in the tanks. The reviewer determines whether an inert cover gas is provided for the tanks to prevent reactions of the additive with air, such as the formation of sodium carbonate by the reaction of sodium hydroxide and carbon dioxide. Alternatively, the reviewer verifies by a conservative analysis that an inert cover gas is not required.

g. Single Failure The system schematics are reviewed by inspection, postulating single failures of any active component in the system, including inadvertent operation of valves that are not locked open. The review is performed with respect to the fission product removal function, considering con-l ditions that could result in too fast as well as too slow an additive

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injection.

6.5.2-8 Rev. 2

2. Testina At the construction permit stage, the containment spray concept and the proposed tests of the system are reviewed to confirm the feasibility of verifying the design functions by appropriate testing. At the operating .'

license stage, the proposed tests of the system and its components are reviewed to verify that the tests will demonstrate that the system, as

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installed, is capable of performing, within the bounds established in the description and evaluation of the system, all functions essential for effective fission product removal following postulated accidents. l

3. Technical Specifications The technical specifications are reviewed to verify that the system, as designed, is capable of meeting the design requirements and that it remains in a state of readiness whenever the reactor is critical.

a. Limiting Conditions for Operation (LCO)

The LCOs should require the operability of the containment spray pumps, all associated valves and piping, the appropriate quantity l of additiv(s, and any metering pumps or mixing devices.

b. Tests Preoperational testing of the system, including the additive tanks, pumps (if any), piping, and valves is required, as discussed above.

In particular, the preoperational testing should verify that the system, as installed, is capable of delivering a well mixed solution containing all additives with concentrations falling within the design margins assumed in the dose analyses of Chapter 15 of the SAR.

Periodic testing and exercising of all active components should in-clude the spray pumps, metering pumps (if any), and valves. Confir-mation should be made periodically that passive components, such as all essential spray and spray additive piping, and any passive mixing devices are free of obstructions. The contents of the spray additive tanks should be sampled and analyzed periodically to verify that the concentrations are within the established limits, that no concentra-tion gradients exist, and that no precipitates have formed.

4. Evaluation A calculation of the fission product removal effectiveness of the system I is performed to establish the degree of dose mitigation by the containment spray following the postulated accident. The mathematical model used for this calculation reflects the preceding steps of the review. The analysis and assumptions are as follows:

a. The amounts of fission products assumed to be released to the contain-ment are obtained from Regulatory Guide 1.3 or 1.4, as appropriate.

The amounts of fission product airborne inside containment depends upon plate-out on interior containment surfaces, removal by the spray 6.5.2-9 Rev. 2

and acti:n of cther engine:r:d safsty features present, radio ctive decay, and outleakage from the containment.

b. Theremovaloffissionproductsfromthecontainmentatmospherebythej spray is considered a first-order removal process. The removal coefficients A (lambda) for each of the sprayed regions of the con-tainment is computed. Removal coefficients representing time-dependent wall plate-out are also calculated. The coefficients for spray removal and wall plate-out are summed. The removal lambdas are used as input parameters into a computer model used for dose calcula-tion.

c. Fission Product Cleanup Models The reviewer estimates the area of the interior surfaces of the con-tainment building which could be washed by the spray system, the .

volume flow rate of the system (assuming single failure), the average drop fall height and the mass-mean drop diameter of the spray from inspection of the information submitted in the SAR. The effectiveness .

of a containment spray system may be estimated by consideration of the chemical and physical processes that could occur during an accident in which the system operated. Models containing such considerations are reviewed on case-by-case bases. In the absence of detailed models, the following simplifications may be used:

All available experiments (Refs. 6 and 7) and computer simulations of the chemical kinetics involved (Ref 8) show that the most important I factor determining the effectiveness of sprays against elemental i l iodine vapor is the concentration of iodine in the sprayed solution.

For fresh sprays having no dissolved iodine, solutions have approxi-mately equal effectiveness regardless of their pH and chemical redox potential (Ref 9). Solutions having dissolved iodine, such as recir-culated sump solutions following an accident, may revolatilize iodine if acidic (Refs 5 and 10). Any chemical additive in the spray solu-tion has no significant effect upon aerosol removal.

1. Elemental iodine removal during spraying of fresh solution During injection, the removal of elemental iodine by wall deposition may be estimated by A =K g A/V Here, A ,is the first-order spray removal coefficient to be used in the dose assessments in Chapter 15 of the SERs, A is the wetted surface area, V is the containment volume, and gK is a mass-transfer coefficient. All available experimental data are co'nservatively enveloped if K is taken to be 4.9 meters per hour (Ref 11 page 17).

During injection, the effectiveness of the spray against ele-mental iodine vapor is chiefly determined by the rate at which 6.5.2-10 Rev. 2

fresh solution surface area is introduccd into the containment atmosphere. The rate of solution surface created per unit gas volume in the containment may be estimated as (6F/VD), where F i is the~ volume flow rate of the spray pump, V is the containment volume, and D is the mass-mean diameter of the spray drops. All j

experimental data are conservatively enveloped ifs A , the first-order spray removal coefficient, is taken to be (Ref 12) 1 6Kg TF s VD and if Kg, the gas phase mass transfer coefficient, is assumed l to be 3m/ min. T is the time of fall of the drops, and may be estimated by the ratio of the average fall height to the termi-nal velocity of the mass-mean drop.

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-1 to prevent extrapolation beyond As , is to be limited to 20 hour2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> the existing data for boric acid solutions with a pH of 5 (Ref 6).

I 2. Elemental iodine removal during recirculation of sump solution The sump solution at the end of injection is assumed to contain fission products washed from the core as well as those removed 4

from the containment atmosphere. The radiation absorbed by the

! sump solution, if the solution is acidic, would generate hydro-

gen peroxide in sufficient amount to react with both iodide and todate ions and raise the possibility of elemental iodine re-l evolution (Ref. 5). For sump solutions having pH values less than 7, molecular iodine vapor should be conservatively assumed to evolve into the containment atmosphere. (Ref. 10).

! The reviewer should consider all sources and sinks of acids or base that would occur naturally (e.g. , alkaline earth and alkali 1 metal oxides) or by design (e.g. , alkaline salts or lye addi-4 tives) in a post-accident containment. Any active spray addi-tive system that is not automatic should be reviewed to assure that it is capable of performing its design function during either spray injection or recirculation or both, given a single failure.

' For sequences during which the sprays would begin recirculation of the sump solution prior to releases of fission products into the containment, credit is given from the beginning of the re-I lease for any spray additive either dissolved from storage baskets in the sump or added by manual or automatic initiation j of an engineered safety feature additive system. The spray should be assumed to be free of dissolved iodine until half of the sump solution volume has been recirculated following the t beginning of fission product release.

The first order removal coefficient for molecular iodine may I i be calculated by a staff contractor computer code such as f 1

l I 6.5.2-11 Rev. 2 l

J

_ . _ _ . . . - . _ - - - _ _ _ _ . .-.____ -,.-- . - , - - - _ . - . - _ . . - - . . _ _ . - _ _ _ . - . ~ . . - - . - . .

describ:d in refer:nce 8, or by methods d: scribed as tha

" realistic model" in reference 11, or by other methods that can be shown to yield acceptably accurate estimates.

3. Organic Iodine It is conservative to assume that organic iodides are not re-moved by either spray or deposition. Radiolytic destruction of iodomethane may be modelled, but such model must also consider radiolytic production. Engineered safety features designed to remove organic iodides are reviewed on a case-by-case basis.

4. Particulates The first-order removal coefficient for particulates may be estimated by 3hF E)

A p = 2T (D)

(

Here, h is the fall height of the spray drops, F is the spray flow and E/D is the ratio of a dimensionless collection effi-ciency to the average drop size. Since the removal of particu-late material depends markedly upon the relative sizes of the particles and the drops, it is convenient to combir.9 part; meters that cannot be known (Ref. 11). It is conservative to assume (E/0) to be 10 per meter initially (i.e., 1% efficiency for 1 mm drops), changing abruptly to 1 per meter after the aerosol mass has been depleted by a factor of 50 (i.e., 98% of the suspended mass is ten times more readily removed then the re-maining 2%).

d. The maximum iodine decontamination factor, DF, for the containment atmosphere achieved by the spray system is determined from the equa-tion (Ref. 4):

DF=1+[V c H

where:

H = equilibrium iodine partition coefficient (see reference 14)l Vs = volume f liquid in containment sump and sump over flow Vc = containment net free volume less Vs The maximum decontamination factor for plain water, boric acid solutions, sodium hydroxide and hydrazine additive systems is DF max

= 200.

DF is defined as the maximum iodine concentration in the containment atmosphere divided by the concentration of iodine in the containment atmosphere at some later time after decontamination.

6.5.2-12 Rev. 2

The offectiven2ss of the spray in removing elemental iodina shall ba l presumed to end at that time, post-LOCA, when the maximum elemental

! iodine DF is reached. Because the removal mechanisms are signifi-cantly different (and slover) for organic iodides and particulate j O iodines, there is no need to limit the DF allowed in.the analysis for these iodine forms.

l IV. EVALUATION FINDINGS After the reviewer determines that the containment spray system is effective, l the following can be reported in the staff's safety evaluation report (SER):  !

The staff concludes that the containment spray system as a fission product cleanup system is acceptable and meets the relevant requirements of General Design Criterion 41, " Containment Atmosphere Cleanup," General Desgin Cri-

j. terion 42, " Inspection of Containment Atmosphere Cleanup Systems," and l General Design Criterion 43, " Testing of Containment Atmosphere Cleanup Systems." This conclusion is based on the following:

l The concept upon which the proposed system is based has been demonstrated j to be effective for fission product removal and retention under post- l -

i accident conditions. The proposed system design is an acceptable appli-

' cation of this concept. The system provides suitable redundancy in com-l ponents and features such that its safety function can be be accomplished assuming a single failure. The staff concludes that the system meets the requirements of General Design Criterion 41.

] The proposed pre-operational tests, post-operational testing and surveil- l lance, and proposed limiting conditions of operation for the spray system l provide adequate assurance that the fission product scrubbing function of f the containment spray system will meet or exceed the effectiveness assumed in the accident evaluation and, therefore, meets the requirements of

! General Design Criteria 42 and 43.

V. IMPLEMENTATION i

l The following provides guidance to applicants and licensees regarding the staff's plans for using this SRP section.

Except in those cases in which the applicant proposes an acceptable alternative l method for complying with specified portions of the Commission's regulations, the method described herein will be used by the staff in its evaluation of conformance with Commission regulations.

) Implementation of the acceptance criteria in Section II.4 is as follows:

(a) Operating plants and OL applicants pending at the date of issue of this revision need not comply with the provisions of this revision, but may do so voluntarily.

(b) Future applicants will be reviewed according to the provisions of this

revision.

, 6.5.2-13 Rev. 2 1

i

. . , , - . . - - , , - - - . , - - - . - , , - - - . - - . - , - - - - - ...n - - - - , , . - . - - - - - - . - - --...-.. ,. ,. . . - . --, . - - - ,

VI. REFERENCES

1. 10 CFR Part 50, Appendix A, General Design Criterion 41, " Containment Atmosphere Cleanup."

2. 10 CFR Part 50, Appendix A, General Design Criterion 42, " Inspection of Containment Atmosphere Cleanup Systems."

3. 10 CFR Part 50, Appendix A, General Design Criterion 43, " Testing of Containment Atmosphere Cleanup Systems."

4. ANSI /ANS Standard 56.6-1979, "PWR and BWR Containment Spray System Design Criteria."

5. R. M. Sellers, A Review of the Radiation Chemistry of Iodine Compounds in Aqueous Solution, CEGB-RD/ BIN-4009, Berkeley Nuclear Laboratories, United Kingdom (June 1977).

6. R. K. Hilliard, A. K. Postma, J. D. McCormack, L. F. Coleman and C. E. Lunderman, Removal of Iodine and Particles From Containment Atmospheres - Containment Systems Experiments, BNWL-1244, Pacific Northwest Laboratories (February 1970).

7. S. Barsali, F. Bosalini, F. Fineschi, B. Guerrini, S. Lanza, M. Mazzini and R. Mirandola, Removal of Iodine by Sprays in the PSICO 10 Model Containment Vessel, Nuclear Technology 23, pages 146-156, (August 1974).

8. M. F. Albert, The Absorption of Gaseous Iodine by Water Droplets, NUREG/CR-4081 (July 1985).

9. A. K. Postma, L. F. Coleman and R. K. Hilliard, Iodine Removal from Containment Atmospheres by Boric Acid Spray, BNP-100 (July 1970).

10. A. O. Allen, The Radiation Chemistry of Water and Aqueous Solutions, Van Nostrand, New York (1961).

11. A. K. Postma, R. R. Sherry and P. S. Tam, Technological Bases for Models of Spray Washout of Airborne Containments in Containment Vessel, NUREG/CR-0009 (October 1978).

12. R. E. Davis, and M. Khatib-Rahbar, Fission Product Removal Effectiveness of Chemical Additives in PWR Containment Sprays, Technical Report A3788, (August 1986).

13. G. B. Wallis, The Terminal Speed of Single Drops or Bubbles in an Infinite Medium, Int. J. Multiphase Flow 1, pp. 491-511,1974.

14. E. C. Beahm, W. E. Shockley, C. F. Weber, S. J. Wisbey and Y-M. Wang, Chemistry and Transport of Iodine in Containment, NUREG/CR-4697, October 1986.

6.5.2-14 Rev. 2

m REGl'LATORY ANALYSIS OF THE AUTOMATIC ACTUATION OF SYSTEMS FOR CHEMICAL ADDITIONS TO CONTAINMENT SPRAY AND SUMP SOLUTIONS

1. Statement of the Problem - At most pressurized water reactors having large dry containments, the initiation of containment sprays also initiates the automatic addition of either hydrazine or sodium hydroxide into the boric acid spray solution. In those plants in which sodium hydroxide is added to the spray, three purposes are met: 1) the scrubbing of elemental iodine vapor from the containment atmosphere is enhanced, 2) the evolution of dissolved iodine from containment sump is diminished, and 3) the long-term corrosive effects of hot boric acid 1 on equipment are avoided. In those plants in which hydrazine is added i to the spray, only the first purpose is met, and the second and third are accomplished by storing a solid alkaline salt, trisodium phosphate, in baskets in the sump to be dissolved by the boric acid sprays. In either case, sufficient alkali or alkaline salt is supplied not only to neutralize the boric acid, but also to render the sump recirculating spray solution slightly alkaline. The resulting solution is similar in both boron concentration and basicity to that resulting from melting the borated ice in plants having ice condenser containments.

[\ Automatic addition of hydrazine or sodium hydroxide is based upon Regulatory Guide 1.4, " Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss-of-Coolant Accident for Pressurizea Water Reactors," Regulatory Position C.1.a which states " Twenty-five percent of the equilibrium radioactive iodine inventory developed from maximum full power operation of the core is insnediately available for leakage from the primary containment." This position flows from the l TID-14844 assumptions referenced as a point of departure in 10CFR100.

As implemented by Standard Review Plan (SRP) Sections 6.5.2 and 15.6.5, Appendix A, radioiodine is assumed to begin to escape from the contain-ment inmediately, being diminished only as the sprays reduce the radio-iodine concentration within the containment atmosphere. In many instances, the off-site thyroid doses calculated using SRP guidance are due predominantly to iodine releases in the first few minutes of the accident.

It has long been recognized that immediate release of fission products cannot occur, and that in any core damaging accident containment sprays  !

would be initiated at least several minutes prior to the transport of radiofodine from the reactor fuel into the containment.

The sole reason for automatic initiation of spray additives has been to

.:~

counter very rapid release of large amounts of elemental iodine vapor postulated to be instantaneously released into the containment atmosphet s.

It is now expected that much smaller quantities of elemental iodine could O be released, and that these quantities would enter the containment atmosphere at later times during core-damaging accidents. Consequently,

0 the need for automatic initiation of the edditives no loncer exists.

Furthermore, all existire information indicates that for fresh spray solutions having no dissolvec iedire, the spray removal capability is virtually independent of the pH of the solution. Hence, the benefits of the additives themselves are much less than previously supposed. The disadvantages of spray additive systems, which include the costs of maintenance including periodic replacement of chemicals, and the hazards to personnel and property from accidental spillage or spraying of the additives can no longer be easily justified.

2. Consequences The consequences of this change are judged to result in no change in safety significance in terms of public risk. Since research results referenced in the draft revised SRP indicate that fresh spray removal capability is virtually independent of the pH of the solution, the effectiveness of the spray in dose mitigation will not be reduced, provided appropriate post-accident pH control of the containment sump solution is maintained. In addition, operational safety will be improved by elimination of hazards to personnel and property from accidental spillage or inadvertent spraying of additives and by reduced maintenance.

3. Alternatives - Because of design differences, the preferred alternative will very widely among licensees. Three general alternatives are presented below, each with e discussion of the dependence of its costs and benefits upon variables of plant features; a) No change - This alternative would continue the following present dysbenefits: The costs of meintenance, testing and purchase of replacement additive are estimated to be between $10,0C0 and $100,000 per unit-year. The financial risk of plant damage caused by inadvertent actuation or the use of sprays during non-core-damaging accidents might be large compared to

$10,000 per year for '. hose plants having sodium hydroxide spray additive. No monetary value is assigned to personnel hazards from inadvertent initiation, but licensee concerns over such a situation are considered significant. Downtimeandcleanupcoststhatcogid result from 0.01 inadvertent initiations per reactor year at 10 dollars per clean-up are $10,000/ reactor-year.

For those plants at which it is possible to add chemical to the spray at any time or at which neutralization by trisodium phosphate stored in sump baskets will occur, there are no identifiable advantages to this option.

For those few plants at which the sodium hydroxide additive can be injected into the spray only during the early period of containment spraying, when boric acid is teing withdrawn from the refueling water storage tank, there is an advantage to this alternative in that the likelihood of "ailure to neutralize the boric acid solution following an accident is essentially avoided, although there would be no reduction 11 maintenance costs. Such plants could, however, profit by alternative c., below, and are discussed further under that alternative.

i 3 ,

l For those plants that do not have a containment spray additive i system, there is no cost to this alternative. ]

b) Delete automatic actuation of spray additive system - For those

plants that are capable of adding sodium hydroxide only during initial injection and not during spray solution recirculation, this alternative would introduce the risk of failure to neutralize  !

i the boric acid due to operator error. Such plants would be unlikely to elect this option over c., below.

1 For those plants capable of sodium hydroxide addition during I recirculation, there could be small reductions in the costs of maintenance and testing, and avoidance of the financial risk of  !

plant damage caused by inadvertent actuation. There would also be small licensing costs in documenting changes and modifying i technical specifications. No reduction in the benefits of the

)' additives would occur.

l l

~

c) Delete spray additive system - There would be a complete elimination of the costs of maintenance and testing and of the i risk of spills and inadvertent actuation. For plants which rely i upon trisodium phosphate to neutralize the boric acid sprays, l l there would be no reduction .in the benefits of acidity control, 1 1 while between $10,000 and $100,000 per unit-year would be saved I in maintenance and testing. If TSP baskets were needed as replacement pH control, the savings would be reduced by about

$5,000 per unit-year and by $50,000 to $100,000 initial expense, l which are the estimated of costs of periodic chemical renewal and sump basket installation, respectively. All plants could have small licensing costs. NRC costs for review of submittals

! supporting system deletion are estimated at about one person-month i per plant, about $10,000,

4. Information Collection Requirements 1

i Table 1 lists all licensees and applicants having pressurized water i

reactors, and identifies those plants also having automatic injection of hydrazine or sodium hydroxide into their containment sprays. Plants i having automatic addition of those chemicals would be informed of the

revised staff position, and could consider either replacing auto-j matic addition with an acceptable' procedure to assure proper manual

actuation, or eliminating the additive system.

i

No duplications with other collections of information are foreseen, j and no consultations with other parties are considered necessary.

5. Impacts on Other Requirements ,

This proposal is not intended to displace any safety-related backfits or plant modifications needed to improve safety.

6. Constraints l There are no identifiable constraints to implementation, except those plant-specific constraints discussed under each alternative.

,,-_ - O

4

7. Decision Rationale As discussed in Sections 1 and 2, above, there are bases for expecting that pressurized water reactors having automatically actuated containment spray additive systems will demonstrate that these systems may be modified to provide either improved safety function or equivalent safety function at less cost. This proposal will permit affected licensees to investigate the possibility of modifications to achieve improvements or savings and to submit proposals for implementation where they are found to be advantageous.

8. Implementation Changes in the Standard Review Plan are presented in draft fom in Attach-ment A. This proposal is one of a series flowing from source term research results. This series of regulatory revisions was identified in a Commission Infomation Paper, SECY 86-76, along with a schedule for further imple-mentations.

O O

dE 1 CONTAINMENT SPnWY ADDITIVE SYSTEMS ADDITIVE ADDITION PLANT ADDITIVE PH CONTROL INITIATE SIGNAL DURING RECIRDULATION Arkansas 1/2 NaOH Na0ll High Pressure No Beaver Valley'l NaOH NaOH High Pressure No J Beaver Valley 2 NaOH Ha0H liigh Pressure Yes Braidwood 1/2 Na0H NaOH High Pressure No Byron 1/2 Na0ll NaOH High Pressure No Callaway 1 Na0H Na0ll High Pressure Yes j

! Calvert C1,1ffs 1/2 None TSP - Yes 1

Catawba 1/2 Nap47 B 0 in Ice Na 247 00 High Pressure Yes Cessar NH TSP liigh Pressure Yes 24 Comanche Peak 1/2 Na0H Na0H High Pressure Yes D. C. Cook 1 NaOH NaOH High Pressure Yes D. C. Cook 2 Na247 B 0 in Ice Na247 8 0 in Ice Yes Crystal River NaOH NaOH High Pressure No None TSP - Yes Davis-Besse 1 Diablo Canyoi 1/2 NaOH Na0ll High Pressure No Farley 1/2 Na0H NaOH High Pressure No Ft. Calhoun None None - -

R. E. Ginna NaOH N30H liigh Pressure Yes i No Haddam Neck None None -

ADDITIVE ADDITION PLANT _

ADDITIVE PH CONTROL INITIATE SIGNAL DURING RECIRCULATID_N llarris 1 NaOH NaOH High Pressure No Indian Point 2/3 Na0H Na0ll High Pressure No Kewaunee NaCll Na0H liigh Pressure flo Maine Yankee NaOH NaOH liigh Pressure No McGuire 1/2 Na 0 0 in Ice Na247 80 247 High Pressure Yes Hillstone 2 None TSP - -

Hillstone 3 NaOH Na0H High Pressure No North Anna 1/2 Na0ll NaOH liigh Pressure No Oconee 1/2/3 None None -

No Palisades None None - -

Palo Verde 1 NH TSP High Pressure Yes 24 Point 3each 1/2 HaOH NaOH High Pressure No Prairie Island 1/2 NaOH NaOH High' Pressure No Rancho Seco 1 Na0ll NaOH High Pressure Yes RESAR SP/90 None None - -

Robinson 2 NaOH HaOH High Pressure No St. Lucie 1 NaOH Na0H High Pressure, Yes Safety Injection St. Lucie 2 NH TSP High Pressure. Yes 24 Safety injection 1

Salem 1/2 Na0H NaOH High Pressure No San Onofre 1/2/3 Na0H NaOH High Pressure Yes O O -

O

,-~

(n)

\' ADDITIVE ADDITION

( ')

'x _ _ '

PLANT ADDITIVE PH CONT INITIATE SIGNAL DURING RECTRCULATION Seabrook 1/2 NaOH Na0H High Pressure No Sequoyah 1/2 Na 0 0 in Ice Na247 00 247 High Pressure Yes South Texas 1/2 Na0H NaOH High Pressure No Sumer Ha0H Na0H High Pressure No Surry 1/2 Na0li NaOH High Pressure No THI 1/2 NaOH NaOH High Pressure No Trojan Na0ll NaOH High Pressure Yes Turkey Point 3/4 None None -

No Vogtle 1/2 NaOH Na0H High Pressure No Waterford 3 None TSP - -

Watts Bar 1/2 Na B 0 in Ice Na 0 0 High Pressure Yes 247 247 Wolf Creek Na0H Na0ll High Pressure Yes Yankee Rowe NO SPRAYS Zion 1/2 Na0H Na0ll High Pressure No

8 O

Containment Sprays In the event of a loss of coolant accident, many PWRs are equipped with spray systems to condense steam from their containment atmospheres. Since the sprayed liquid would necessarily mix with any spilled reactor coolant and might be later recirculated into the reactor, the liquid used must contain a neutron absorbing solute. In all U.S. PWRs, the spray solution is the refueling water normally stored in tankage between refueling outages. This solution is about 0.2 M (M= molar, or moles per liter) in boric acid (orthoboric acid, H B0 )*

3 3 Boric acid is a weak acid, meaning that it is only partially dissociated in aqueous solution. This dissociation can be written as:

F [+ QO M3 60 3 (3) 10 I The equilibrium constant for this dissociation is 5.'t x 10 M at 20*C, such that a 0.2 M solution has a pH of 5. The pH of pure water is 7.0 at 25 C. At higher temperatures greater fractions of both water and boric acid will dissociate. At 90 C, for example, pure water has a pH of 6.1, rather than 7.

The dielectric constant of water diminishes with increasing temperature, how-ever, which acts to counter the tendency of increase solute dissociation. As a result of these conflicting temperature variations, the pH of 0.2 M boric acid has a minimum at 77'C of about 4.9. (see, e.g., R.W. Gurney Ionic Processes in Solutions, McGraw Hill,1953)

9 l

I i

,\ To prevent corrosion of rretals other than stainless steel that might be expnsed to containment sprays, it is usual for some basic material to be stored for dissolution into the sprayed solution to neutralize the boric acid. The two bases used for this purpose are trisodium phosphate (TSP, Na3PO 4 12H 2

0) and sodium hydroxide (lye, NaOH). TSP is a powder similar to dishwater detergent in consistency and solubility, and lye is stored as a 30% solution by weight. As purchased, TSP contains some impurities which lead to " caking" in humid atmospheres. Lye solution reacts with atmospheric carbon dioxide to form a sodium carbonate precipitate and must be stored in tanks with nitrogen-filled ullage.

In a typical PWR containment spray system, the spray and the ECCS share the refueling wter, and can drain this supply in 20 to 45 minutes. Plants

[ \ using TSP keep it stored in open baskets in the containment sump where it may be dissolved by the falling spray. Plants using lye are more diverse.

Some can add the lye solution into the spray both during the initial draw-down of the refueling water storage tank and during the recirculation of the solution from the sump back into the spray system. Other plants can only

! mix lye with refueling water and cannot add it during recirculation.

1 4

Other processes that may be expected in a containment following an accident I

can also affect the pH of sump and spray solutions. Chief of these would be the dissolution of pretransition element oxides and hydroxides in these solutions. Examples would be the rubidium, cesium, strontium and borium fission products, and calcium, sodium and potassium from concrete which i

10 would be volatilized as strong or moderately strong bases. Of lesser importance would be the effects of carbon dioxide fror' concrete abletion and nitrogen oxides from air radiolysis, which would produce straller potential amounts of acids. A trivial effect would be the acid generated by iodine hydrolysis and oxidation. For example, the acid produced by the air oxidation of iodine to the thermodynamically preferred iodate, if all the core inventory were involved, would be less than 0.1% of the equivalence of the boric acid.

i 502.+ 2.I2.+ 'A.M t o @ 4 Io 3 tiH (2)

Overall, these other processes are estimated to produce a neutralizing effect upon the boric acid, generally supplying more base than acid.

In addition to preventing corrosion, the boric acid is neutralized to enhance the dissolution into the spray solution of any iodine-containing vapors dispersed into the containment atmosphere. Although reaction (2), above, is favored in overall equilibrium, it is very slow in occurring and could taken many hours to approach equilibrium. In addition, radiolytic processes due to the effects of ionizing radiation on the sump and spray solution are capable of producing iodine-containing gases that might evolve into the containment atmosphere. Chief amongst these radiolytic processes is the production of hydrogen peroxide (H 22 0 ) by water irradiation in the presence of air.

O

. --. -. . - _ - . . . .. - - - -- . =_ _

'}

11 I

Although it was conservatively assumed in Reg. Guides 1.3 and 1.4 that fission product iodine would be released as molecular iodine vapor (I2 )'

j other processes that would be expected to occur within a containment after an accident would limit the occurrence of 12 . Any accident that might I release iodine into the containment atmosphere would necessarily also 1

release noble gas tission products. These Krypton and Xenon isotopes, amounting to as much as 7 x 100 C1, transmute to rubidium and cesium For the release of the core inventory isotopes, respectively, upon decay.

of noble gases into a large PWR containment, there would be 8 x 10I4 such l decays per cubic meter per second occurring in the early hours of the 1

accident. Each alkali metal atom produced in the containment atmosphere would recoil from the decay as a highly charged cation, and as a result of the action of its electric field upon the dipoles of water molecules present as vapor, would create a small, highly basic aerosol particle.

l This process would neavily deplete any molecular iodine vapor also present.

1 ,

1  !

Any core-damaging accident would be likely to release hydrogen gas as well as iodine. The reaction between molecular iodine and hydrogen, while less exoergic than that between oxygen and hydrogen, proceeds rapidly without 1 the necessity of a large activation energy (ignition).

i

2. HT (3) 1 l

%' -t Iz& -

l i

{

l I

I 1

4

12 The product, hydrogen iodide (hydroioddacid, HI) 1s easily oxidized by air to reform iodine 2.Y 'L (4)

The net result is the catalytic oxidation of hydrogen. Note, however, that any molecular iodine present would spend some fraction of its time as hydrogen iodide, subject to ready solution or other depletion. Hydrogen iodide is a very strong acid, beina virtually totally dissociated in aqueous solution.

Molecular iodine is a comparatively unlikely substance to be made in fluids in which iodine is in low concentration. This is because the formation of I pmust necessarily involve the collision between two moieties each containing a single lodine atom. If iodine atoms are very rare, then it is more likely that they will react with other components of the mixture prior to undergoing a rare collision amongst themselves. This may be seen in the experimental results of spray experiments at varying iodine concentrations in Y. Nishyawa, S. Oshima and T. Maekawa, " Removal of Iodine from Atmosphere by Sprays,"

Nuclear Technology 10, pp 486-98, April 1971. These results show that as the iodine concentration is decreased, both the rate of molecular iodine dissolution and the fraction dissolved increased markedly.

O

13 n

' V) As an example, consider the iodine hydrolysis reaction discussed in J.T. Bell, j M.H. Lietyke and D. A. Palmer, " Predicted Rates of Formation of Iodine Hydrolysis Species at pH Levels, Concentrations and Temperatures Anticipated l

in LWR Accidents," NUREG/CR-2900, October 1982.

I 2 +R 10 g I't [ +ROI (3)

This reaction is, in effect, first order in 1 , since 2

the concentration of water in aqueous solutions is virtually unchanged by the reaction proceeding to the right. The reverse reaction is first order in hydrogen ion, but depends upon the product of two iodine species. It is apparent that unless the total of all iodine species concentrations is large compared to the l nydrogen ion concentration, the net hydrolysis rate will depend more markedly upon the local iodine concentrations than upon the pH.

Of much greater importance to the chemistry of iodine in a post accident environment is the potential for reaction with radiolysis products. The radiolysis of water has been. described by the equation.

~

4.9 (0 % 1.Te t 2.3 0B +1.y[,0.30i+ 0.yrH +. . (6)

• O.3 $ QC + 0.6 H l

In equation 6, the coefficients are "G-values" at 10-7 second, i.e., the molecules destroyed or created per 100 electron volts of deposited ionization O

O

14 energy. The G-values decrease markedly with time after a pulse of ionizing radiation as the short-lived species on the right-hand side of equation 6 6

reunite to form water molecules and heat. In a radiation field of 10 Rads / hour, equation 6 estimates that 2 x 10-7 moles per liter per second of hydrogen peroxide are produced by water radiolysis.

The British CEGB has produced a critical review of the literature in R.M. Sellers, "A Review of the Radiation Chemistry of Iodine Compounds in Aqueous Solution,"

RD/B/N4009, June, 1977. The available literature shows that molecular iodine production in iodide solutions under radiation is quite small unless either the pH is less than about 4 or the concentration of iodide is much larger than 10-3 M. E.C. Beahm, W.E. Shockley and 0.L. Culberson " Organic Iodide Formation Following Nuclear Reactor Accidents," NUREG/CR-4327 show that iodomethane production in iodide solutions being sparged by argon-methane gas is similarly much greater at pH of 6 or less than at higher pH. In both cases, there is no firm evidence that more alkaline solutions would greatly improve iodine retention.

Iodine is also known to catalyze the decomposition of hydrogen iodide by the net effect of the two following reactions:

Ro t-* 2.B*+7fv 1u to + .r7 (7)

~

(o, t It;# lI + RH*+oL O

.- - - _ - _ _ - - _. . . - _-= -

15 These are called the Harcourt-Essen reactions. Under acid conditions the l first becomes taster such that each iodine atom spends more time as 1 2 on the average, before reactino by the second equation. When the hydrogen peroxide is made radiolyticly, however, the effect of pH is less clear cut, due to the likelihood of competing reactions of other species in reaction (6.) as well as trace containments.

C.C. Lin, " Chemical Effects of Gamma Radiation on Iodine in Aoueous Solutions,"

Journal of Inorganic and Nuclear Chemistry 42, 1101-7, 1980, reports that significant molecular iodine production occurs by radiolysis at pH value below 4, with progressively less occurring at higher pH values. Lin's

experiments were performed while the sparging of the solutions with helium, h

O which might be considered to imitate the evolution of noble gas daughters expected in a post-accident sump solution. At values of pH above 8, radio-lytic reduction of iodate was observed. In general, neutral solutions (pH=7)

were about as effective as alkaline solutions in retaining iodine in non-volatile forms.

S. Barsali et.al., " Removal of Iodine by Sprays in the PSICO 10 Itodel Containment Vessel," Nuclear lechnology 23, pp 146-56, August, 19/4 reported a I series of twelve spray tests using either tap water or 1% sc.fium thi- alphate solution (Na223 S 0 ). They concluded that "the elemental iodi e remoni  ;

half-times obtained by spraying service water do not differ greatly from those found by spraying thiosulphate solution. The sprayed solution was, in some 1

i cases, recirculated for a period ranging from 1 to 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> without any

16 release of iodine to the atmosphere. Some runs were performed with fractians of the model containment vessel not sprayed. The elemental iodine removal half-times in the sprayed and unsprayed regions do not essentially diff, r."

These University of Pisa experiments were at spray solution flow rate to sprayed volume ratios less than those in U.S. PWR containment spray designs.

R.E. Davis and M. Khatib-Rahbar, " Fission Product Removal Ettectiveness of Chemical Additives in PWR Containment Sprays," BNL Technical Report A-3788, October,1986, reviewed the literature and concluded that for all cases of interest the rate of iodine removal by sprays during refueling water injection was limited by gas transport of iodine to the surface of the drops. In such cases, the composition of the spray solution itself does not have a great effect upon the rate of removal unless the solution contains dissolved elemental iodine. Should the solution have a significant dissolved molecular iodine concentration, then its re-evolution could compete with the reverse process of iodine dissolution.

Henry's Law (Joseph Henry, 1797-1878) states that the ratio of the concentration of a substance in a gas phase to that in a liquid phase at equilibrium is a function only of temperature. Henry's Law holds only for true solutions of non-reactive gases, and does not hold for the ratio between iodine vapors in the gas phase to the concentration of iodine hydrolysis products in the liquid phase. The existing SRP 6.5.2 assumes that a

" partition coefficient" exists for iodine in equilibrium between air and borate solutions which is a function only of the pH of the solution (Figure 6.5.2-1). There is, however, no experimental evidence that the rate of dissolution of iodine vapor into borate solutions is chiefly dependent upon l

pH, and no theoretical reason to suppose that sucn might be the case. l l

17 O In the early years of this century, A. Einstein computed a simple relationship between the mean square displacement of an atom2 (r ) during time interval t and the diffusivity D of that atom.

h ADI (8)

Ine diffusivities of molecular iodine and its hydrolysis products in hot aqueous solutions are between 2 and 5 x 10-5 cm2 /sec. Spray drops of about 0.1 cm diameter require several seconds to fall through a typical PWR containment. It follows trom these comparative magnitudes that only the smallest of spray drops are capable of being diffusively mixed during their time of fall.

O Larger drops could be mixed by other mechanisms than diffusion, as, for example, by convective flows. In addition, due to the greatly different fall velocities of drops of different sizes, the collision and agglomeration among .

drops will also lead to mixing, both between and within drops. Nonetheless, it is not assured that all spray drops will be a equilibrium or steady state  !

with respect to iodine during their fall, even if they do approach thermal equilibrium with steam.

Current models of core melt accidents predict that fission product iodine released into the containment in an accident will be released over a time span 1

of at least tens of minutes, and that there will be a delay between the release of steam and that of fodine of at least ten minutes. In addition, that iodine which is released is more likely to be in the form of an iodide in aerosol than as molecular vapor.

18 We conclude that there are no compelling reasons to adjust the pH of O

containment sprays prior to the recirculation of the sprayed solutions, and that there are likewise no compelling reasons to adjust recirculated solutions to a pH of much above 7.

O O

I t

I l 1 ,

f too  !

a 4

l g . SNITBAL l' CONCENTRATNN8:

f o is-> = l J

so -

a so-* m t

O ied u .

i s .

5 ee - .

t I

aa  !

T I

> i a se -

i l

I t

' = i j m -

l O _

1 I O 9 e a

, 12 e 2 4 e e to pH .

l Efects of pH on the I: yicid in deaerated iod".de solutions irradiated at 4.5 x !# R/li for I hr.

1 From C.C.Lin, J. Inorg. Nucl. Chem. 42, 1101-7, 1980 a

J l 4

I

APPENDIX A TECHNICAL REPORT A-3788 8-12-86 l

1

? l j

j FISSION PRODUCT REMOVAL EFFECTIVENESS OF CHEMICAL ADDITIVES IN PWR CONTAI MENT SPRAYS 4

i t

! R. E. Davis, H. P. Nourbakhsh, and M. Khatib-Rahbar l

j Accident Analysis Group j Department of Nuclear Energy i Brookhaven National Laboratory l Upton, NY 11973 i

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i I

l August 1986 I

i l

Prepared for U. S. Nuclear Regulatory Comission Washington, DC 20555 Under Contrac E-ACO2-76CH00016 1

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1, l

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. . . - . . . . _ . __,-,,_m,_.,- - . _ , , . . _ , . . _ _ _ . . _ _ _ _ _ , _ , _ , _ _ _ _ _ . . . , _ _ , _ _ _ , , . _ , _ _ _ _ , _ . _ _ _ _

ABSTRACT The presence of gaseous iodine in severe accident situations is based upon a regulatory source term prescription whose basis predates the accident at Three Mile Island-Unit 2 and the source term research that TMI-2 stimul ated . Tnis report reviews the current best-estimate of source term characteristics, and the experimental bases that establish the effectiveness of spray additives. Based on this review, several current operating practices, vis-a-vis the addition of additive (s), may warrant regulatory reevaluation.

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i O l i

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l l

l l

A-1 1 l

ACKNOWLEDGEMENTS The authors would like to thank Dr. J. Read (NRC) for the guidance he provided during the course of this effort. In addition, the authors appre-ciate the skillful preparation of the manuscript by Ms. Cheryl S. Conrad and Ms. Theresa Skelaney,

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A-2

s_- CONTENTS Page

1. INTRODUCTION........................................................ 1

2. PAST AND CURRENT SOURCE TERM CHARACTERISTICS........................ 3

3. CSS EFFECTIVENESS AS A FP REMOVAL SYSTEM............................ 9

4. SPRAY N0DELS........................................................ 13-

, 4.1 An al y t i c al P roc ed u re . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.2 Reeval uation of Exi sti ng Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5. DISCUSSION AND C0NCLUSION........................................... 19

6. REFERENCES.......................................................... 23 APPENDIX A.............................................................. A-1 APPENDIX B.............................................................. B-1 O Figure LIST OF FIGURES Title Page 1 Comparison, for Zion, of the airborne aerosol mass suspended in containment with and without containment sprays.............. 6 2 Comparison for Surry of the airborne aerosol mass suspended in containment with and without containment sprays.............. 7 3 Removal constant versus normalized, new drop surface area; fresh spray data................................................ 17 LIST OF TABLES Table Title Page 1 Summary of CSE F i rst Spray Resul ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2 Sunna ry of PISCO F i rst Spray Resul ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3 Summa ry R es ul t s of J AE R I Te s t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 A-3

1. INTRODUCTION Commercial pressurized water reactors (PWR) are equipped with Containment Spray Systems (CSS) to limit the peak pressure in containment below the design pressure in the event of a blow down associated with a design basis accident.

The CSS is composed of spray pumps, spray rings, nozzles, and necessary pipes

} and valves. Coolant is supplied by the Refueling Water Storage Tank. Many

) CSS are also equipped with a spray additive tank and an associated pump.

These additives are intended to increase the capacity of the coolant to absorb gaseous iodine in the event of fuel clad failure or core melt. Hence, an important secondary function of the CSS is the attenuation of fission products released to the containment. Section 6.2.2 of the Standard Review Plan (SRP)1 l describes the performance objectives of the CSS as a heat removal system,

while SRP 6.5.2 addresses the function of the CSS as a fission product cleanup system.

The performance objective of CSS as a fission product cleanup system, given the source term assumptions given in Regulatory Guide 1.4,2 coupled with the containment leakage rate is try aid in meeting the design basis accident (DBA) dose guideline of 10CFR100. The basis of source term prescription given in Regulatory Guide 1.4 is given in Reference 3. The source term con-sists of 100% of the noble gases (Xe, Kr), 25% of the iodine and 1% of other solids. Iodine is assumed to be primarily gaseous based on the observed release from the Windscale accident. (Regulatory Guide 1.4 further prescrib'es the following iodine chemical composition: 91% elemental, 5% particulate, and 4% organically bound). The Atomic Energy Commission adopted this source term to establish criteria for licensing of plant / site combinations and assessing the potential hazard to the public. The use of this hypothetical source term, which would be associated with substantial core damage to assess the conse-quences of a DBA, which should not result in any substantial core damage since the Engineered Safety Features (ESFs) should terminate the accident prior to l core damage, was viewed as intentionally conservative. Application of this approach led to the conclusion that gaseous iodine dominated the off-site radiation doses. This in turn led to increased efforts to scrub iodine from the containment atmosphere, including the use of a chemical additive to increase the effectiveness of the sprays to absorb and retain gaseous iodine.

On March 28, 1979, Three Mile Island Unit 2 experienced a partially mitigated loss of cool ant accident. Substantial core damage occurred and significant amounts of radionuclides were released from the fuel.

Environmental monitoring of the accidental releases indicated 0.02 to 0.08 of the nobl e gas inventory and only 3x 10-7 of the iodine inventory were l released to the environment. No metallic radionuclides are known to have been l rel eased. The difference in the fractional releases of noble gases and iodine were attributed to the following:

1. Noble gases are inert, volatile, and only slightly to fairly soluble in water.

2. The chemically reducing environment in the reactor vessel promotes the stability of cesium iodide which is nonvolatile (in the containment atmosphere) and water soluble.

A-4

I

' 3. Injection of sodium hydroxide into the CSS would have enhanced the

( absorption of gaseous iodine if it was released during the accident.

i

! 4 Filters ef fectively trapped iodine in the auxiliary fuel' handling i building from which environmental releases occurred.

1 The inference that the majority of iodine released from the TMI-2 reactor vessel was Csl and not molecular iodine focused attention upon the TID-14844

source term assumptions and the measures taken in response to these assump-tions, e.g., the design of the engineered safety features.

This report focuses on the technical data base that is available to sup-port the use of chemical additives in the CSS. Computer searches of several literature data bases were also carried out to identify relevant materials.

These searches are documented in Appendix A.

I 4

I 3

l 1

l A-5

2. PAST AND CURRENT SOURCE TERM CHARACTERISTICS Regulatory Guide 1.4 prescribes that the following source term be con-sidered, for example, in assessing the DBA doses guidelines values set forth in 10CFR100:

1. 100% of the noble gas inventory,

2. 25% of the iodine inventory; Composition - 91% molecular, 5% particu-late, 4% organic.

3. Release to the containment assumed to be instantaneous and well mixed in the containment atmosphere.

NUREG- addressed the impact of source term assuniptions on regulation.g772Specifically, the impact of the observation that particulate Csl and not gaseous 12 was the predominant chemical form of iodine released to containment was assessed. Based upon the analyses presented in NUREG-0772, it would appear that except for those accidents in which the fission products are released through water, the amount of iodine calculated to be released would not be substantially reduced by the chemical form (1 2 or Csi).

As a result of the observations of radionuclides releasad et TMI, sub-stantial research efforts were initiated. An effort sponsored ty the NRC has resulted in a set of computer codes, the Source ferm Code "ackage (STCP),

which simulates the progression of severe nuclear reactor accioents and esti-mates the release of materials from the fuel, through the reactor coolint sys-tem and to the environment. The function and status of these codes are described in NUREG-0956: 6 some typical results of the code package and pre-liminary observations regarding accident source terms are also presented. In addition, the basis of STCP me3hodology has been reviewed by a study group of the American Physical Society. While this review understandably noted many areas of uncertainty and identified several phenomena not fully analyzed, it generally concluded that considerable pro cation of the Reactor Safety Study (RSS).gress has been (The RSS, made published since also in 1975, the publi-predicted substantial releases of gaseous iodine to the containment, and was more or less consistent with the Regul atory Guide 1.4 Source Term Prescription.)

In comparison to the Regulatory Guide 1.4 source terms, several substan-tial differences exist in regard to the characteristics of the fission product (FP) release predicted by current, state-of-the art methods of source term estimation. These characteristics have been described elsewhere, e.g., see References 7 and 8. A brief summary of the characteristics is given below.

The total release of FP material to the containment can be divided into two distinct phases: the initial, in-vessel phase where material is released from the damaged or melted fuel and the ex-vessel phase where material *is released from the core / concrete interaction. In the in-vessel phase, the release is dominated by nobl e gases ( -100% release), cesium ( -100%) ,

iodine (-100%), and tellurium (-30-701.) , which are rather volatile at the temperature excursions predicted during core degradation. Very much smaller amounts of the ref ractory groups, Ba, Sr, Ru, La, and Ce, are predicted to be released in-vessel . As the volatile materials, with the exception of the A-6

( ) noble gases, migrate away from the core to cooler regions in the reactor cool-V ant system (RCS), they are assumed to condense on surfaces or onto aerosols.

Based upon observations made at TMI-2, and subsequent thermochemical analy-ses,5 iodine is assumed in the STCP to be present as Csl, and any iodine release from the RCS is modeled as an emission of Csl in aerosol form. The behavior of aerosols released from the RCS can be modeled in several alternate fashions which depend upon the particular type of reactor and sequence being considered. For BWR sequences, where the RCS blowdown is vented through a suppression pool,9 aerosol decontamination factors (DF) are calculated by SPARC, a computer code within the STCP. Similarly, for PWR's' equipped with ice condensers, the ICEDF code within STCP is executed to estimate aerosol DF's associated with this ESF. Ultimately, the behavior of aerosols in the containment atmosphere is simulated by the code NAVA-4. This code models several natural processes, e.g. aerosol agglomeration and settling, that can deposit airborne aerosol s onto reactor surfaces and, hence, result in a decrease in the airborne activity. The duration of the in-vessel FP release is limited to the period from the start of core degradation to bottom head failure. The onset of core damage is plant and sequence dependent. Typical estimates of the times for the start of core melt are 25 minutes, Surry AB sequence, and 135 minutes, Surry 2S 0,8 from the time of scram. In the AB sequence, the CSS is assumed to fail. In the S D 2 sequence, the CSS is opera-tional, and sprays initiate 20 minutes after scram. It is interesting to note that by the time the release of FP's has begun, the CSS has already entered the recirculation mode. It should be noted that current regulatory guidance ef fectively requires immediate injection of additives into the sprays, once p the CSS is initiated.

t i V The ex-vessel FP releases result from the core / concrete interaction where gases generated from the decomposition of concrete sparge through the molten core debris. The large volumes of gases which pass through the melt and the increased surface area associated with these gases accelerate the vaporization of melt constituents, which subsequently condense into aerosols af ter leaving the mel t. Another mode of aerosol generation is also modeled. This is the formation of mechanical aerosols which are e result of the gas bubbles break-ing through the upper melt surf ace. Hence, all FP release from the core / con-crete interaction is modeled as being in aerosol form. The ex-vessel release is dominated by the Ba, Sr, Ru, La, and Ce groups. In general, a small frac-tion of the core inventory of iodine is predicted to be retained in the core debris at the time of bottom head failure and is passed to VANESA, a computer code in the STCP which estimates ex-vessel releases, for release during the ex-vessel phase. VANESA assumes this iodine release to be in the form of Csl aerosol. The duration of the ex-vessel release starts shortly af ter bottom head failure and is typically calculated ten hours beyond initiation, although the majority (-907.) of ex-vessel release generally occurs within three hours of the initiation of the core / concrete' interaction. l In summary, results of severe accident simulation with the state-of-the-art methodology incorporated into the STCP indicate two phases for fission product release. The in-vessel phase is associated with core degradation and releases are dominated by noble gases, cesium, iodine, and tellurium. lodine is as form Cst. With the exception of the noble gases,sumed to befrom all releases in the chemical the RCS are in aerosol form. The ex-vessel release (O ,/ phase results from the interaction of the molten core and the concrete A-7

basemat. The ex-vessel release is dominated by the Ba, Sr, Ru, La, and Ce groups. Small amounts of volatiles are also released ex-vessel, notably iodine in the form of Csl. All releases are in the form of aerosols. Wnen appropriate intermediate codes, SPARC AND ICFDF, estimate FP aerosol retention in ESFs. The removal of airborne aerosols, generated either in-vessel or ex-vessel, by natural deposition processes is estimated in NAUA.

The STCP, as currently implemented, does not model any gaseous iodine release, nor is there any explicit modeling of gaseous iodine behavior, or the effect of any chemical additive to the CSS. The physical washout of aerosol by sprays is modeled and results in substantial removal of aerosols from the containment atmosphere. Figure 1 shows a typical comparison of the accumula-ted masses of material leaked to the environment for a sequence, Zion S 2D-c, where the CSS op,erates and another sequence, Zion TMLB'-c, where the CSS is assumed to fail . A similar comparison for the Surry plant is shown in Figure 2.8 The reduction of Csl aerosol leaked to the envirogment for these reactor-sequence combinations is approximately 50 to 10 , respectively.

Hence, given the current best estimate of the fission product, release charac-teristics and the processes that can act on the FP releases, the physical action of the CSS and natural aerosol removal processes which proceed with or without the CSS can substantially reduce airborne concentration of FP's. This includes iodine as it is modeled to appear in aerosol form. It is noteworthy to mention at this point that the CSS chemical additive (s) effect only gaseous forms of iodine,1,2 HI, and, depending upon the specific additive, organic iodine, and do not contribute to the physical removal of aerosols. Aerosol removal by CSS washout is modeled as a purely physical process. The most com-mon gge (namely, NaOH), however, may play a secondary but important role in ~, _ 4 the sump pH and mitigating radiolysis assisted evolution of iodine in gaseous form.

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{ TIME, NIN TINE, N!N ACCUMULAT[0 tEAtto IsuCL10ES.2 $ 0 - c. ACCUMultYt0 t(Atto IIUCLIDES. TML8' - c. ,

! Figure 1 Comparison, for Zion, of the airborne aerosol mass suspended in containment with and without containment sprays. >

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3. CSS EFFECTIVENESS AS A FP REMOVAL SYSTEM As mentioned heretofore, adoption of the TID-14844 source term assump-

tions to assess the consequences of DBA resulted in the conclusion that molec-

! ular iodine dominated of f-site dose. This, in turn, fostered consideration of l the CSS as a fission product removal system and resulted in the addition of i additives, namely, sodium hydroxide for 1 2 and HI removal and sodium thio-sulfate for the further removal of organic iodine, to increase the effective-ness of the spray solution to absorb and retain iodine.

A primary data base upon which much of the thinking regarding the effec-1 tiveness of spray as a fission product removal system was the large scale con-

+. tainment system experiments (CSE).10 The CSE were carried out in a one-fifth

! linear scale containment having an internal volume of 751 m3 . Experiments j A-3, A-4, A-6, A-7, and A-8 were performed to determine the effectiveness of

.. CSS to remove airborne FP. The major variables considered included contain-1 ment temperature and pressure, spray solution composition, and initial or

. recirculatgy phase. Details of the experiment may be found in the original references or the concise summary provided by Albert, I which is reproduced l'

here as Appendix B. The results are displayed in the appendix in Figures 46 through 50 (original text numbering) as plots of airborne iodine to the con-centration versus time. The absorption iodine was generally interpreted as

{

] being governed by a first order process:

i j h = -AC, i where C is the airborne concentration of iodine, t is the time, and A is the first order removal constant. The results are tabulated in Table 1. Only the j first spray period results are given since other processes, such as desorption

! from wall or the effect of inhomogeneous mixing, complicate the interpretation of subsequent spray periods.

l ,

l Several observations can be noted. The DF's, ratio of iodine concentra-j tion prior to spray initiation divided by the concentration immediately after

spray has been stopped, range fron 5 to 100. The differences in run A-3 and run A-4, may in part, reflect the change in spray flow rate. The differences in A-4 and A-6 could result from either the increased buffering capacity of

the spray solution or the change in initial containment temperature, 25 versus

, 124'C, respectively. However, a comparison of runs A-5 and A-6 with run A-7,

! where the solution is unbuffered H 3803 , suggest the latter. In addition, it j is interesting to note that runs A-6 and A-7 gave comparable DF's, indicating that in the initial injection phase buffering, pH control, had little observ-able ef fect. A superficial comparison of the results given in Table 1 for runs A-7 and A-8 indicate comparable performance on the basis of DF, while i showing significant difference in A or t1/2 This results from two changes in the experimental procedure: spray nozzles that delivered a smaller mean ,

drop size and a shorter duration of initial spray operation. Given these l changes to the experimental protocol, the results of run A-8 would appear con-j sistent with the former runs.

A-11 1

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Table 1 Summary of CSE First Spray Resultsa Run Solution Composition b t g

C (min) A (min-1) DF d

A3 525 ppm H3 B03 , pH 9.5 5.5 0.13 5 A4 525 ppm H3 B03 , pH 9.5 1.4 0.50 100 A6 3000 ppm H3 803 , pH 9.5 2.1 0.33 30 A7 3000 ppm H3 B03 , pH 5 2.2 0.32 30 A8 3000 ppm H3 B03 , pH 9.5 0.64 1.1 30 a

Adapted from Reference 10.

Fresh room temperature soluticr.

cCorrected for other removal mechanisms, e.g., reac1! ion wall; corrections d

were <10%; t1/2

• In 2/l*

Ratio of airborne iodine concentration direct before and after spray opera-tion.

9 l

l A-12 0

- - . . . = _ _ _ - .- _ .___

l h Two additional experimental sources of information on the effectiveness located. These experiments were performed in the of spray additivgs 2wereand by JAERI.13 PISCO 10 facility 3

The PISCO 10 model containment had an interval volume of 95 m . Twelve experimental runs were carried out. Service water and 1% sodium thiosulfate j!

(Na2S02 3) solutions were tested. Service water can certainly be considered j additive free. The authors of Reference 12 concluded that the removal rates were similar for both service water and 1% thiosulfate solution. A summary of these results is given in Table 2.

Nishio et al .13 quoted results obtained at the Japan Atomic Energy Research Institute (JAERI). However, no citation was given and the original

~

I manuscript could not be located. Based upon the description given by Nishio, the experiments were carried out in a 708 m cylindrical vessel . Two experi-j ments, BIS-1 and BIS-2, were done under conditions that simulated a BWR LOCA.

One experiment (PIS-9) was performed for conditions which simulated a PWR 4 LOCA. Summary results are given in Table 3. The range of values observed in the JAERI tests is in fair agreement with previous studies. However, direct comparison in all cases is not possible since the spray flow rates.are atypi-cal of the regime anticipated in domestic PWRs. However, these results are applicable to BWR containments.

1 1

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A-13 4

,-w. .w-.-.-..- , - . . _ - , _ _ - , , _ _ , , , , ___.,y_ ,_ _ . , _ _ _ _ . , , .-,,,-,----._,,,-s m.,.__y-7 _ _ . .,,,

Table 2 Summary of PISCO First Spray Resultsa Run Solution Composition b t A (*i"'!)

1/2 (*I")

101 1% Na 2 50, 23 62*C 1.3 0.53 106 1% Na 2 0 3, 30*C 1.0 0.69 107 1% Na 2 0, , 18 C 0.3 2.3 108 1% Na 203, 14*C 1.5 0.46 103 service water, 86 C 3.0 0.23 102 service water, 80 C 0.3 2.3 104 service water,16 C 2.0 0.35 109 service water, 26"C 3.0 0.23 110 service water, 34 C 2.0 0.35 111 service water, 35*C 3.5 0.20 112 service water, 33*C 1.2 0.58 a

Adapted from Reference 12. DF's not calculated, since spray duration ~ varied widely.

bSolution composition, temperature of spray. l l

Table 3 Summary Results of JAERI Testsa l Run Solution Composition D t A I*I"~ l) 1/2 (*I") l BIS-1 pure water, 70 C 2.9 0.24 815-2 pure water, 70*C 6.5 0.11 PIS-9 1.4% H3 803 , pH 9.6, 40 C 0.50 1.4 a

Adapted from Reference 13. DF not calculated; insufficient data.

Solution composition, temperature of supplied spray.

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,, .,a - -m.-.---,u. . . _ - _rs2 ~ x =u -,1,.-. - - -..w_ a s .a. - - -

l i 1

p 4 SPRAY MODELS

' G 4.1 Analytical Procedure The original treatment of the removal of iodine from the containment

! atmosphere is presented in Reference 10. Th 4 is based upon the discussion given by Albert.g summary description given her The removal of iodine from the containment atmosphere is traditionally J modeled as a first order process:

h=-AC, (1)

I where C is the airborne iodine concentration, t is the time, and A i s the i removal rate constant. Integration of Equation (1) yields

-At l C=Coe (2) t with Co is the initial concentration of iodine. The removal coef ficient has been defined 10,1" as i

i i A = FP c/V, (3) l where F is the volumetric flow rate, P is the partition coefficient of iodine j between the spray liquid and the gas phase, V is the sprayed containment vol-J ume, and c is the removal ef ficiency. The removal efficiency has been theo-retically defined for several mass transport limiting processes. These expressions are for the stagnant drop model 4

2 c = 1 - E (6 N e "$)/an [a n+Nsh(Nsh-1)3 I4) for the stagnant film model c=1-exp[(-6kt)/d(P+k/k{)], ge g (5) for the well mixed drop model c = 1 - exp [(-6 k t, M , W I

A-15 1

and for the gas phase controlling resistance model c=6k h/P v d. (7) g In these equations, k = gas film mass transfer coefficient, kj = liquid film mass transfer coefficient (no reaction),

t, = drop exposure time, ,

d = drop diameter, N

sh ' g d + (2 P D1 )

D 3

= liquid phase diffusion coefficient, 4 =4D gt /d e 2, a

n = nth root of the equation na cot (a n )

• sh - 1 = 0 h = drop f all height, and v

g

= terminal drop velocity.

In the initial spray phase, when the solution is fresh and therefore con-tains no dissolved iodine, it might be expected that the mass transfer to the drop is limited by gas phase transfer. Combining Equations 3 and 7 one obtains 6k Fh A" yy g

• f(P). (8) 9 Note that if gas-phase transfer is the rate limiting step, then the first order removal coefficient is predicted to be independent of solution composition. Similar first spray removal rate coefficients for various solu-tions have been observed (see previous section), although the equilibrium par-tition coefficient certainly does vary with the composition of the solution.15 Another variable, which will find use in the next section, is the total drop surface area, A, created per unit time per unit sprayed containment volume.

A-16

i l.

L l

A= =

d

=h(h3)(ud), 2 (9)

! A is simply the total surface area (ST = nSd ) created by drops of mean j diameter, d, at the flow rate F, and divided by V, the sprayed containment j volume. Substituting Equation 9 into 8 yields:

1 A=k h A/v g. (10) 4.2 Reevaluation of Existing Data

<- In an earlier section, available data on the iodine removal effectiveness i was reviewed. Care was taken to select and display only data for fresh spray solutions. In both the CSE and PISCO experiments, multiple spray periods, including recirculation, were investigated. These latter results are expected to reflect the effects of increased iodine concentration in the drop, as well as the heretofore mentioned complications of wall desorption and inhomogeneous mixing. However, when the spray solution was fresh, all solutions appeared to ef fectively reduce the airborne iodine concentration, regardless of the pres-4 ence or absence of an active spray additive. To demonstrate this contention, and account for the major variables causing variation, selected first spray data from the CSE, PISCO, and JAERI tests are displayed in Figure 3. In this figure, the first order removal rate coefficient is plotted against the nor-malized total new drop surface, A. Also displayed are the range of flow i regimes of several typical PWR's. These were estimated from information obtained from the Sorry FSAR 16 and information provided in References 17 and

18. The upper limit of a range represents both spray header systems are oper-ating, while the lower limit represents operation of only one of the two redundant spray systems. Approximately 3/4 of the PISCO data and both JAERI BWR test data are not plotted, as they would lie well beyond the anticipated range of A for domestic PWRs.

Although the plotted data exhibit some scatter, a generally good correla-i tion is found. Hence, when spray solution is fresh, the removal of iodine i

from the containment atmosphere is dominated by gas phase mass transport and is effectively independent of the equilibrium iodine partition coefficient of the solution, and primarily controlled by the amount of available surface to which iodine rey be transported. At a first level of approximation, the good correlation of A and A observed indicates that the combination of terms not explicitly examined in Equation 10 is effectively constant or slowly varying over the range of experimental conditions investigated. It should also be noted that 3/4 of the PISCO and JAERI data not plotted, that data which was taken in a flow regime atypical of domestic PWR's, does not correlate well with A alone. There are several potential reasons why this occurs, however, these have not been examined since it is felt that the experimental conditions are basically atypical of those conditions associated with domestic commercial l PWR's.

)

s A-17 l

l l- . . - . . --_ - _ - _ -_--_- -- . -, _ _ _ - - _ _ .. _ _ - _

Values of k g, computed f rom Equation (10) and for the experimental data displayed in Figure 3, are given in Table 4 For comparison, estimates of kg and A, based upon a well known correlation for heat transfer to a single drop, are al so given. Assuming the minimum observed experimental k, 3 m/ min, maximum fall height l 18 and that both spray headers are operating, first order removal coef ficients of 0.8 min-1 and 2.0 min-1 are estimated f rom Equation (10) for the Surry and Zion pl a nt s , respectively. If it is assumed that structures, e.g., the reactor pressure vessel and steam gener-ators reduce the ef fective drop fall height by 50% to 60% of the maximun, then estimated A's of 0.4 min-1 and 1.3 mi n-1 are obtained for these pl a nts ,

respec tively.

O A-18 O

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{ e CSE a

- a PISCO A JAERI 4

l 1 I I I I

! 0 1 2 3 4 5 6 l A (m-min)"I k

l Figure 3 Removal constant versus normalized, new drop surface area;

fresh spray data.

A-19

5. DISCUSSION AND CONCLUSION In previous sections of this report, the current best estimate descrip-tion of source term characteristics was summarized and available data on the effectiveness of spray as a fission product removal system were presented, reviewed, and reevaluated. CSS can effectively reduce airborne concentrations of aerosols which current methods of source term estimation predict to over-whelmingly dominate fission product releases. The inert noble gas releases are unaffected by sprays. Aerosol removal by the sprays is a physical process and this process is not altered or aided by the presence of chemical additives. Other natural processes, modeled by NAVA-4, can also reduce air-borne aerosol concentration. The relative benefit accrued is closely related with the time available prior to containment failure for these natural proc-esses to act. Data presented in Chapter 2 indicated that the combined effect of these processes can reduce airborne Csl aerosol concentrations by a factor 50 to 10 , depending upon the specific reactor and accident sequence being .

examined.

Current NRC sponsored analytical modeling of severe accidents, i.e., the STCP, does not predict the emission of gaseous iodine in the anticipated acci-dent environment associated with commercial LWR's. This is based upon an examination of the TMI-2 accident, and subsequent thermochemical analyses.

The actual chemical form of iodine is still subject to a de on uncertainty. Evolving experimental and analytical evidence 6 42 greeindi-cates boron may be chemically associated with Cs; hence, boron may be in com-petition with iodine and potentially liberate iodine in another form, possibly gaseous. Prel iminary experimental resul ts 2 ,22 also suggest reaction of Cs0H and Csl with the stainless steel surf aces of the RCS, with the reported emission of gaseous iodine in some cases. The reproducibility of these exper-imentg3are currently being investigated. In addition, some experimental evi-dence has been obtained that indicates the conversion of Csl aerosol to I gaseous iodine during hydrogen burns. These observations certainly reinforce '

the diversity of material interactions and phenomena that can occur and give rise to uncertainty. Additional research is in progress and is required to i resolve this uncertainty. However, regardless of the extent of gaseous iodine '

conversion, the washout by an operational CSS would occur and the data pre-sented in Chapters 3 and 4 clearly suggest that it is effective. Moreover, the fresh spray data suggest ef ficient iodine removal regardless of the pres-ence of additives during the initial injection phase. This is not to say that Na0H is not ul timately required to increase the absorption capacity of the spray solution and mitigate iodine reevolution fro.n the reactor sump. On the contrary, suf ficient evidence exists to warrant pH control in the long term.

The regulatory option to be reconsidered is whether or not the presence of NaOH is required during the initial injection phase of CSS operation. Two items affect this decision. One, is the effectiveness of fresh spray solution, and the other is that since the CSS is activated on high containment pressure, it is quite possible that the CSS will have switched from the injec-tion to the recirculation phase prior to the release of any fission prodbct activity.

A potential alternative is to add pH control directly to the reactor sump i rather than in the initial injection supply of the CSS. Additionally, it  ;

would be attractive to initiate pH control on some feedback directly related '

to the release of activity rather than on high containment pressure. This l

A-20 '

i l

l .

}

would have the obvious advantage of not introducing the additive (s) until j 9 required. A secondary benefit should the reactor incident be terminated with-out the release of FP activity, would be a simplified cleanup recovery, i

h 1

1

• l c

\ ,

i

\

I i

A-21 l

Table 4 Comparison of Experimental and Estimated Mass Transfer Constants m

Run A(m-min) I t e(*1") A(*1"~ l) A est 9*" g est a D C d A3 0.40 0.0S0 0.13 0.14 6.5 6.f A4 1.55 0.050 0.50 0.52 6.5 6.7 A6 1.55 0.050 0.33 0.65 4.3 8.4 A7 1.55 0.050 0.32 0.65 4.2 8.4 A8 2.45 0.083 1.1 1.8 5.4 8.9 PIS-9 5.36 0.092 1.4 3.7 2.9 7.4 109 0.74 0.029 0.23 0.15 11 6.7 110 1.35 0.020 0.35 0.18 13 6.9 111 1.19 0.020 0.20 0.16 8.6 6.9 112 0.79 0.029 0.58 0.16 25 6.9 (a) Calculated from reported data for F, V and d.

(b)te = h/vg. Velocity calculated from vg = (4(Pa - Pg) g d/3 pg ()1/2, where ( = 18.5/Re 0 .6, and pa is the drop density, og is the gas density, g is the gravitation constant, ( is the drag coef ficient and Re is the Reynolds number; Handbook of Multiphase Systems, G. Hetsroni, Hemisphere Pub. Corp.,

New York, NY, 1982.

(c)Aest = A te kg est.

(d)kgback calculated from experimental data.

(e)kg est estimated from the correlation of Ranz and Marshall, Chem.

Eng. Prog., 3 , 1952.

k g = D/d (2+0.6(pdvg/u)1/2(u/p0)l/3),

where D is the diffusitivity of 12 . All gas phase variables are for air.

A-22

(~N 6. REFERENCES b 1. U. S. NRC, " Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants," NUREG-0800, July 1981.

2. U. S. NRC Regulatory Guide 1.4, " Assumptions Used for Evaluating the Po-tential Radiological Consequences of a Loss of Coolant Accident for Pres-surized Water Reactors," Rev. 2 June 1984.

3. U. S. NRC,10CFR100, " Reactor Site Criteria," 27FR3509, April 12,1962.

4. J. J. DiNinno et al., " Calculation of Distance Factors for Power and Test

'- Reactor Sites " U. S. Atomic Energy Commission. TID-14844, March 1962.

5. U. S. NRC, " Technical Bases for Estimating Fission Product Behavior Dur-

- ing LWR Accidents," NUREG-0772, June 1981.

6. M. Silberberg et al ., " Reassessment of Technical Bases for Estimating Source Terms," NUREG-0956, 1986.

7. R. Wilson et al., " Report to the American Physical Society of the Study Group of Radionuclide Release from Severe Accidents at Nuclear Power Plants," Rev. Mod. Phys., 57(3), Part 11, July 1985.

8. J. A. Gieseke et al ., "Radionuclide Release Under Specific LWR Accident Conditions," B91-2104, July 1983, t

(/ 9. H. P. Nourbakhsh et al., " Effectiveness of BWR Pressure Suppression Pools in Retaining Fission Products," Brookhaven National Laboratory, Technical Report A-3788, July 1,1986.

10. R. K. Hilliard et al ., " Removal of lodine and Particles from Containment Atmosphere by Sprays: Containment Systems Experiment Interim Report,"

BNWL-1244, February 1970.

11. M. F. Albert, "The Absorption of Gaseous lodine by Water Droplets,"

NUREG/CR-4081, July 1985.

12. S. Barsali et al., " Removal of lodine by Sprays in the PISCO 10 Model Containment Vessel," Nuc. Tech., 23, August 1974.

13. G. Nishio et al ., " Containment Spray Model for Predicting Radiotodine Removal in Light Water Reactors," Nuc. Tech., 54, July 1981.

14 A. K. Postma et al ., " Technological Bases for Models of Spray Washout of Airborne Contaminants in Containment Vessels," NUREG/CR-0009, October 1978.

15. Reference 14 and citations contained therein.

16. VEPC0, Surry Power Station Units 1 and 2. Final Safety Analysis Report, Virginia Electric and Power Company, v

A-23

17. " Westinghouse Nuclear Training--Four Loop Plant Information Book," West-inghouse Electric Corp., Pittsburgh, PA, 1978.

18. U.S. NRC, " Preliminary Assessment of Core Melt Accidents at the Zion and Indian Point Nuclear Power Plants and Strategies for Mitigating Their Ef-fects," NUREG-0850, Nov. 1981.

19. D. Powers, "High Temperature Fission Product Chemistry," Severe Fuel Dam-age and Source Term Research--Program Review Meeting, Oak Ridge, TN, April 1986.

20. A. T. D. Butland et al ., " The Ef fect of Variations in Chemical Species and Associated Properties on Primary System Retention in PWR Severe Acci- '

dent," to be published.

21. R. M. Elrick et al ., " Reaction Between Some Cesium-lodine Compounds and '

the Reactor Materials 304 Stainless Steel, Inconel 600 and Silver,"

NUREG/CR-3197 (3 volumes), June 1984

22. D. Powers and R. Elrick, "SNL Radiation Effects Experiments," Severe Fuel Damage and Source Term Research--Program Review Meeting, Oak Ridge, TN, April 1986.

23. L. S. Nelson et al . , "The Behavior of Reactor Core-Simulant Aerosols During Hydrogen / Air Conbustion," inirteenth Water Reactor Safety Research Information Meeting, Gaithersburg, MD, Oct. 1985. l 9

A-24 0'1 l

A-1 p APPENDIX A Computerized searches of the literature were performed to obtain perti-nent citations on the subject containment spray and spray additives for PWRs.

The following databases were queried:

EDB (Energy Data Base, DOE / RECON, 1976-present) r The search resulted in 171 citations; of which 18 were selected and ac.

quired in support of the research project; and NSA (Nuclear Science Abstracts, DOE / RECON, 1967-1976)

The search resulted in 8 citations.

The search strategy was:

PWR and

[ containment spray systems or (containment system) and (atmospheres)

\ or t

, ((sprays or droplets or particles or iodine removal or particulates or additive (s)) and (containment systems))].

I 1

i V A-25 l

l B-1 1

i APPENDIX B

} The following chapter was reproduced from NUREG/CR-4081. It provides a i brief description of the CSE and a concise sunnary of the CSE results and their precision.

l I

i A

1 i

O 1

i 1

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t j

85

7. EXPERIMENTAL DATA The experimental data used to compare with the results of the spray model are f rom the Containment System Experiments (CSE).3 Expe rime nt al runs A-3, A-4, A-6, A-7, and A-8 of this series are large scale spray j system tests to de te rmine the effectiveness of a spray system for removing airborne fission products. The results of these tests are reported in terms of the gas phase elemental iodine concentration versus time and also in terms of the liquid phase elemental iodine concentra-l tion versus time. The parameters for the spray experiments are the spray flux, the drop size, the gas phase temperature, pressure, and humidity, and the liquid spray composition. The physical dimensions of the CSE vessel are listed in Table 3 and are shown in Figure 44. Since 1

l Table 3. Physical conditions common to all spray

! experiments (liillard 3)

Volume above deck including drywell 21,005 ft 3 595 m3 Surf ace area above deck including 6,140 ft 2 569 m2

. drywell t

^

Surface area / volume 0. 29 3 f t-l 0.958 m-1 i

Cross section area, main vessel 490 ft2 45.5 m2 Volume, middle room 2,089 ft 3 59 m3

Surface area, middle room 1,363 ft2 127 m2 I Volume, lower room 3,384 ft3 96 m3 Surface area, lower room 2,057 ft2 g9g m2 Total volume of all rooms 26,477 ft3 751 m3 l

Total surf ace area, all rooms 9,560 ft2 888 m2

)1

] Drop fall height to deck 33.8 ft 10.3 m i

Drop fall height to drywell bottom 50.5 ft 15.4 m Surface coating All interior surf aces I

coated with phenolic paint."

i 1hermal insulation All exterior surfaces covered with I-in.

fiberglas,s insulation.b GTwo coatn Phenotino 302 over one coat Phonoline 300 primer. The Cirbo t t ne Co. , St. Louis , Missourt .

hk = 0.027 8tu/(hr) (ft2) (eF/ft) at 200'F, Type PF-bl5, Owens-Cornin:; Fiberglans Corp.

A-27

86 C H *. L #L 44 f t .' t ( T D RUN RUN A3 A 4 6 7. 8 m

J I

• O

R

• 6Y b PLAN Vi[W OF NO22LC ARR ANG[M(NT j$ PRAY NO22LES

+=j**,* '

j MAYP ACK CLU$T E R (14)

M AIN CONT AINMENT ORYWELL g vgg5(L L10 ,l b SOLUTION *A \ s j

OROP COL LECTOR (4)

$ TOR AGE T ANK g -yl(WING WINDOW Y YY- -TmtF $AYPLER ,

k. nfCw WALL TROUGH

$PR AY PUMP #

c FIS$lON PRODUCT WCT WILL -

AEROSOL ICLCSIO OF 71- j( ~

OR YWE L L -

~io Ql/ - MIDDLE ROO*.1 LIQUID $ AYP(([

PvYPS LOnt A 840CM Rt CIRCUL ATION .I" PUMP Fig. 44. Schematic diagram of containment arrangerent used in CSE spray tests (llillard 3 ).

O these tests were made in realistic and not idealized equipment and con- l ditions, the liquid and gas flow patterns are complex and not well l characterized. The results from the new spray model will be compared I with theme results, but no better than approximate agreement can be ex- '

pected. This data, however, can still provide a means for useful and meaningful evaluation of the spray model. )

l The CSC vessel is a large scale vessel (see Tabic 3 and Figure 1 44). The overall dimensions of the vessel are 20.34 meters high and a diameter of 7.62 me ters. The vessel has a drop fall height of 15.4 meters. The overall volume of the vessel is 751 cubic meters.

The tests varied the tempe ra t ure, pressure, pit of the drop, spray nozzle contiguration and drop size. The conditions f or run A-3 are a temperature of 298K, I atmosphere of pressure, pit of 9.5 and a drop dia .

meter of 1210 mic rons. For all of the tests, the spray solution ten-perature was at 25'C, and the soluttons were all buffered. For run A-4,'

the conditions were the an*e as f or A-3 execrt for a higher spray flow rate and a different spray noz zle configurat ion. Run A-6 inercased the temperature of the gas to 397X and the pressure to 1 atmonpheres. Run A-1 changed the pH to 5, lowered the tenperature to 394K and raised the A-28 9l' l

87 pressure to 3.4 atmospheres. Run A-8 changed the drop diameter to 770 microns. See Figure 44 for spray nozzle arrangements, Table 4 for spray

/] nozzles used, Table 5 for the atmospheric conditions, Table 6 for the (V )

spray flow rates and solutions used in the tests and Table 7 for the timing of the spray periods.

The e xpe r in.e n t a l procedure for the molecular iodine spray absorp-tion tests involved first heating the containment vessel with steam until the specified temperature was reached. A flask containing.

molecular iodine traced with ! curie of iodine-131 was heated electri-

'cally. Air was passed over the flask to release molecular iodine.

Samples were taken prior to turning on the sprays to determine how molecular iodine behaves without sprays. After the first spray period Table 4. Nozzles used in CSE spray experiments (ltillard 3)

Ru n s A3 , I. , 6, 7 Nozzle type: Spraying Systems Co. 3/4 - 7G3 Nozzle characteristics: Tog type, full cono A3 A '. , 6, 7 Number 3 12 Layout Triangula r Square grido g ' '

I Spacing 10 ft 5 in. 6 ft apart v $..

1. 2part

(

Pressure 40 asid 40 psid

'\ ,

, .) j

• Rated flow 4 gpm 4 gpm 4 p J- MMD 1210 p 1210 p o 1.5 1.5 g

1 Run A8 Nozzle type Spray Systems Co. 3/8 A 20 Nozzle characteristics: Fine atomization, hollow cone Number used 12 Layout Square grid y, Spacing 6 ft apart

%g '

e. Pressure 40 paid

,$ Y Rated flow 4 gpn MMD 770 u l'

a b

i A-29 v

88 Table 5. Atoespheric conditions in CSE spray experiments (H111ard 3)

Run Run Run Run Run A3 A4 A6 A7 A8 Contain=ent vessel No No Yes Yes Yes insulated Forced air circula- Yes Yes No No No tion a Start of 1st spray Vapgrtemperature. 77 77 255 248.7 250

'F Pressure, psia 14.6 14.6 44.2 50.0 50.7 -

Relative humidity, ,*. 70 88 100 100 100

, End of 1st spray -_

Vapor temperature, 77 77 229 234.5 243

.po Pressure, psia 14.6 14.6 38.6 44.4 48.2 Start of 2nd spray Vapgrtecperature, 77 77 237 240 243

• F Pressure, psia 14.6 14.6 40.8 46.0 243 End of 2nd spray vapor temperature, 77 77 202 203 188 ego Pressure, psia 14.6 14.6 29.5 36 34.1 Start of 3rd spray Vapgrtemperature, 77 77 233 230 218

'F Pressure, psia 14.6 14.6 40.7 41.8 32.2 Start of 4th spray Vapgrtemperature, o o a 232 247

'F Pressure, psia o o o 42.4 52.4 End of 4th spray Vapgrtemperature, o o a 192 175

'F Pressure, psia o o o 32.7 32.4 c ran without duct located in bottom of drywell.

2400 ft /3 min discharge.

b Average of 5 thermocouples located at various eleva-tions and radii.

1. No fourth spray.

A-30

89 Table 6. Spray flow rates and solutions 9

i O, used in CSE experiments (H111ard3 )

! Run Run Run Run Run A3 A4 A6 A7 A8  ;

1 1st spray )

Total flow rate, gpm 12.8 49 49 49 50  !

, l Volume sprayed, gal 128 490 490 490 150 Spraying pressure, 40 40 40 40 40 psid Solution a a b c b ,

1

2nd spray l Total flow rate, gpm 12.8 49 50 48.5 50 i Volume sprayed, gal 385 1480 1500 1455 1850 Spraying pressure, 40 40 40 40 40 psid i

Solution a a b c b l 3rd spray

• 1 Total flow rate, gpm 12.5 42 16 45 5 47 Volume sprayed, gal 735 1890 960 2730 2820 Spraying pressure, 40 29 4 36.5 36.5 Solution d e e e a 4th spray

! Total flow rate, gpm g g g 48.6 50.4 i Volume sprayed, gal g g g 2428 2520 Spraying pressure, g g g 40 40 psid Solution g g g f f a Fresh, room temperature. 525 ppm boron as H3B03 in

. demineralized water. NaOH added to pH of 9.5.

b Fresh, room temperature. 3000 ppm boron as H3503 in i desineralized water. NaOH added to pH of 9.5.

Fresh, room temperature. 3000 ppm boron as H3B03 in demineralized water. No NaOH added. pH 5.

d Fresh, room temperature demineralized water.

{

1. S olution in main vessel sump recirculated. No heat ex- ,

changer used.

[ Fresh, room temperature. 't wt% Na2S203, 3000 ppm boron as H3B03 in demineralized water. NaOH added to pH 9.4.

EN o fourth spray.

I A-31 IO

! U 1

90 Table 7. Timing of spray periods (Enllard3 )

Time after start of iodine release, min Run Run Run Run Run A3 A4 A6. A7 A8 First spray Start 40 40.5 30 30 30 Stop 50 50.5 40 40 33 Duration 10 10 10 10 3 Second spray Start 140 140 80 80 80 -

Stop 170 170 110 110 117 Duration 30 30 30 30 37 Third spray Start 1473 1205 1565 1323 200 Stop 1533 1250 1525 1383 260 Duration 60 45 60 60 60 Fourth spray Start a a a 1443 1350 Stop a a a 1493 1400 Duration a a a 50 50 "No fourth spray.

of each run was started, many samples were taken from the gas phase, from the liquid in the sump, from the wall trough and from the spray drop collectors. When the first sp' ray period was ended, more samples were taken to determine how molecular iodine acts. A second, third, and somer.imes a fourth spray period were used with many samples taken f rom the gas and liquid phases. The gas phase concentrations were determined by Maypack samplers (see Figure 45), and the liquid phase concentrations were de t e rmined by measuring the amount of iodine-131 tracer present.

For more information see Reference 3.

Results of these experimental tests are shown in Figures 46 through.

55 and Table 8. Table 8 shows the material balance of iodine for all of the experimental runs.

It should be noted in this table that between 25.65% and 57.58% of the iodine delivered to the containment vessel is unaccounted for and is assumed to be deposited on surf aces. Figures 46

{ through 50 show the concentration of elemental iodine in the gas phase as a function of time. The data is reported in terms of the half lif e A-32 I

m *N

\

h w (%Jl J

}

Table H. loeline material lealances 4

( tilliard 3 )

Run Al Run A4 Run A6 Rain A7 Run A8 Location Crams Grams 4 Grams 4 18 Crams 1"

%a  %  % Crams Acrnsol Ceneration Starting material 101.00 100.00 101.50 1:10. 0 0 101.00 100.00 101.00 100.00 101.00 100.00 Ceneration apparatus 2.57 3.54 1.11 1.11 0.14 0.14 1.06 1.05 1.45 3.42 Injection line 22.32 22.05 29.32 2R.99 1.49 1.47 2.05 2.01 1.62 1.60 Injection line 0.36 0.36 0 . I,5 0.15 1.030 1.02 0.12 0.12 0.32 0.12 samples Acenunted for 25.25 25.00 30.59 10.14 2.66 2.63 1.43 3.40 5.19 5.14 Del tvered to con- 75.75 75.00 70.91 69.86 98.34 97.16 97.57 96.60 95.61 94.68 t a i nme n t (by dif- i ference) e h h b h 5 --

, Crams t Crams t Grams  % Crams  % Crams  %

$ Con t a i nme n t Delivered to con- 75.75 100.00 70.91 100.00 98.14 100.00 97.57 100.00 95.61 100.00 tainment In liquid pools # 45.32 59.83 37.67 53.11 53.97 54.88 39.28 40.26 53.15 55.59 (Prior to decon-tamination)

Samples 0.48 0.63 8.87 12.51 0.556 0.57 0.59 0.60 0.88 0.92 Purge to stack 0.52 0.69 0.73 1.03 0.086 0.09 0.16 0.17 0.11 0.11 be c ont ami na t ion 5.90 7.78 5.46 7.70 0.R20 0.83 1.36 1.39 1.44 1.50 Accounted for 52.22 68.93 52.73 74.35 55.43 56.37 41.39 42.42 55.57 58.12 On surfaces (by 23.52 31.06 18.18 25.65 42.91 43.63 56.18 57.58 40.04 41.88 difference) a Percent of starting mass.

b Percent of delivered mass.

C lncludes spray solution and steam condensate.

92 opM,-DAG e4-6533 ETo

/ 15

) FLOW a

6 $\ 1 o

3 13 1 INLET 6 SIX SILVER PLATED SCREENS 11 SCREEN ,

2 TEFLON BALL 7 btLVER MEMBR ANE FILTER 12 SPRING 3 NOSE CONE 8 CHARCOAL LOADED FILTER 13 BODY 4 TEFTON GASKET 9 STOP RING 14 END CAP S TWO PARTICLE FILTERS 10 CHARCOAL BED 15 OUTLET Fig. 45. Maypack Sampler.

of iodine, defined as t1/2 = - Ln (1/2)/A , (65) O l l

l

= 0.693/A , (66) where A is the removt rate constant. l The reason the da :.a are in this form is because the old spray models ( Equa tions I through 7 of Chapter I, Section 2) are in terms of the .emoval rate constant. Figures 51 to 55 shows the concentration of iodine in the liquid versus time. As can be seen in these figures, there is a delay in the response of the increase in the concentration of iodine in the liquid phase. ,

In these tests there are many processes for the removal of molecu- l lar iodine from the gas phase. In these large scale realistic ~ tests, there are painted surfaces, non-painted surfaces, insulation, sprays, l wet walls, and dry walls. All of these features can contribute to iodine sorption, and heat transfer can also have an effect on the re-moval rate of molecular iodine from the gas phase. Therefore, one can only hope to develop an approximate model which accounts for the major phenomena involved and considers only the removal by the sprays. If one looks at the drop data, these data are " difficult to interpret, not only because of sampling inadequacies but because the relative fractions of the various iodine forms and particle sizes were changing rapidly with time."3 A-34

. . . _ . . . .- - -- _ . _ , . . . . . . - . . ..~ . _ _ . - . . _ , . . ._ _- ,__--._.a.,_. . - . - . _ . , , ~ - - . _ . , . . , . . ..

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5 F LOW R ATE: 49inen t PR E SSUH E - 14 6 sma . T E MPE R ATUf!E: 77"F i

i SPRAY ADDITIVE: 525 piwn BORON j t y, 4 1.4 min PRESSUHE: 14 G enea tJ OH. pH - 0 5 -

/ SPH AY A00lT1VE: 525 :>pm BORON 46 >

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The data for the gas phase are the result of the combined effects of all of the processes for the removal of molecular iodine from the gas phase. But if all of the processes except for the sprays exerted only a small overall effect in the removal of molecular iodine from the gas phase, then these data would be acceptable from the standpoint of use-fulness in determining the efficiency of the spray model. The data for liquid in the sumps should eliminate some of the sources of error be-cause these data shows how much molecular iodine is transferred to the liquid. Nevertheless, any iodine that is on the surfaces and is not chemically . held to the walls could be washed off in the sumps. Since the sprays were not started at the instant the molecular iodine was released, a significant amount of molecular iodine released into the cont ainme nt may have deposited on the surfaces, and subsequently been -

washed off into the sumps or might have been transferred back into the gas phase later when the partial pressure of molecular iodine in the gas phase was smaller than the partial pressure of molecular iodine on the surfaces. The latter effect could result in an underestimate of the removal ra'te of molecular iodine.

To remove some of the possible sources of error, the comparison of experimental results to the results of the spray model will be limited to the area of the drywell. The drywell had a cross sectional area of 8.8 square meters (which is a diameter of 3.35 meters), a drop fall height of 15.4 meters, and a volume of 135.52 cubic meters. For example, in run A-3, at the start of the first sgrayperiod,theinitial gas phase concentration was approximately 5 x 10 micrograms / cubic, meter (1.97 x 10-7 mole s/ li te r) and the final concentration was approximately 1.25 x 10" micrograms / cubic me ter (4.9 2 x 10-8 moles / li t e r) . The amount of iodine removed from the gas phase during the first spray was 5.082 grams. Also, at the start of the first spray, the concentration of the liquid in the drywell sump was approximately 8x 102 micrograms / liter and the initial volume was approximately 150 liters. At the end of the l first spray, the concentration in the drywell sump was 4 x 10" micro-  !

grams / liter .and the volume was approximately 332 liters. The number of grams of iodine transferred to the liquid in the drywell sump was 13.15 i g rams . The difference between the number of grams of iodine removed (

from the gas phase and the number of grams of iodine transferred to the J liquid phase was -8.1 grams. The resulting relative error based on the l gas phase is j l

, fgrams removed f rom cas -- grams transferred to liauid\ 7)

\ grams removed from gas /

x 100% ,

( .02 13.15) x 100; = -133.4% . (68) e rror =

Results of the nther runs we re similar with more iodine appearing trans-ferred to the liquid than was removed from the gas. In fact, for many (

cases the error is much greater. l A-40 l

C FoRu 335 7" U.S. Nt.ECLEGR REGULQTORY COMMIESION BIBLIOGRAPHIC DATA SHEET NUREG-0800

. TSTLE AND SUBTtTL (A dd Volume No., rf wormris te) in ev 2

2. (tenve bimkl

)tandardReview lan for the Review of Safety Analysis aeports for Nucl r Power Plants, LWR Edition, Proposed 3. RECtPIENT*S ACCESSION NO.

Revision 2 to SRP ection 6.5.2, " Containment Spray as a /

Fission Product Cleenuo System" (For Comment)

7. AuTwoRcS

5. DATE REPORT COMPLETED

\ uouru

\ lvE4R March 1987

9. PERFORMING ORGANIZAleON'N AME AND M AILING ADDRESS (lactude lip Codel DATE REPORT ISSUED Office of Nuclear React'or Regulation U.S. Nuclear Regulatory' Commission fuonm lvEAR April 1987 Washington, DC 20555 \ s-(te,<< u.a*>

\

\ / e. nuove unn&>

12. SPONSORING ORGANIZATION N AME AND MAILING ADDRESS (include le Codef Office of Nuclear Reactor Regulation ,

U.S. Nuclear Regulatory Commission Washington, DC 20555 \ M CONTRACT NO.

\

\

13. TYPE OF REPORT i / PE RICO COVE RED (Inclusive detrs/

Proposed SRP Section (Guide) I

/

15. SUPPLEMENTARY NOTES \ /

PSRP Section 6.5.2,'. Revision 2 14. (Leeve unnAf

16. ABSTR ACT 000 words or less) l\

oposed revision 2 to SRP Section 6.5f2 would incorporate changes in the requirements r containment spray chemical additive sy odels which had only appeared in re erence,sstems, and explicitly in previous revisions. states computational I

for immediate initiation of caustic,[ addition to the sprayThe requirement would be deleted, and the minimum pH to be achieved would be/ reduced fr,om 8.5 to 7. If adopted, this revision would be required to be used for future plants, and would be optional for present licensees. The proposed revision is accompanied by a regulatory analysis and two supporting technical documents,/ \

\

i

\

./ \

s

\

/

/ \i

17. CCEY WORDS AND DOCUMdNT AN ALYStS 17s. DESCRIPTQRs Containment Spray' Fission Product \

ContainmentSujn/CleanupSystem p pH

/

l 17b. IDENTIFIE RS/ ' EN-EN DE D TERMS 1

( VAILABI TY STATEMENT

19. SECURITY CLASS (This dport) 21. NO. OF PAGES Unclassified Unlim. ed 2o. SECURITY CLASS (rai,,,ges 22. PRICE NRC FORM 335 (7-77)

Unclassified s

• U. S. GCVU490 %T PR14TihG Grr!CE s1987- 191-642:69346 1

i l

120555078877 1 1A011X US NRC-0 ARM-ADM SVCS OIV 0F PUB & PUB MGT BR-POR NUREG POLICY W-501 CC 20555 l

WASHINGTON

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