ML20211M586

Forwards non-proprietary & Proprietary Response to NRC 990708 RAI Re TS Change Request 272,reactor Coolant Sys Coolant Activity.Proprietary Encl Withheld

ML20211M586
Person / Time
Site:	Three Mile Island
Issue date:	09/02/1999
From:	Langenbach J GENERAL PUBLIC UTILITIES CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20138C825	List: ML20211M586
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1920-99-20447, NUDOCS 9909090150
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{ GPU NuclearJnc.

( Route 441 South NUCLEAR Post Office Box 480 Middletown. PA 17057-0480 Tel717-944 7621 1920-99-20447 September 02, 1999 i

(

U.S. Nuclear Regulatory Commission j Attention: Document Control Desk '

Washington, DC 20555 Ladies and Gentlemen:

Subject:

Three Mile Island Nuclear Station, Unit 1 (TMI-1) 4 Operating License No. DPR-50 Docket No. 50-289 Response to Request for Additional Information Technical Specification Change Request No. 272 Reactor Coolant System Activity This letter is in response to the NRC's request for additional information dated July 8,1999 regarding TMI-l Technimi Specification Change Request No. 272 - Reactor Coolant System Activity, submitted to NRC on October 19,1998. GPU Nuclear believes the results as submitted are accurate and appropriately conservative because the iodine partitioning used by GPU Nuclear is representative for application in the OTSG for the treatment of main steam line break (MSLB) kinetic expansion region leakage. Note that GPU Nuclear will not apply this iodine partitioning in the steam generator should leakage be projected or develop in areas other than the kinetic expansions. The primary-to-secondary leakage during a hypothetical MSLB evaluation will l consider projected leakage from the kinetic expansions and areas other than the kinetic expansions.

The responses are discussed in detail in Attachment I, which contains proprietary information as defined in 10 CFR 2.790 (a)(4). Accordingly, it is requested that Attachment I be withheld from public disclosure. An aflidavit certifying the basis for this application for withholding as required i by 10 CFR 2.790 (b)(1) is also attached to this letter.

Also provided as Attachment IV is an additional discussion of the inherent conservatism existing in the proposed analytical approach. The iodine spiking data base in this attachment demonstrates that iodine release from spiking would be far lower than that used per the Standard Review Plan (SRP). Conservative iodine spiking assumptions more realistic than the SRP guidance would .  ;) i require less reliance on iodine retention in the OTSG. \

9909090150 990902 s a,ww PDR ADOCK 05000289: I le D 3 U;9 P PDR {./ 9 p l 1

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L 1920-99-20447 Page 2 of 2 GPU Nuclear personnel are available to meet with NRC staff as necessary to support this amendment request. If any additional information is needed, please contact Mr. David J. Distel, Nuclear Licensing and Regulatory Affairs at (973) 316-7955.

Sincerely, Q

James W. Langen ch Vice President and Director, TMI 3

/DJD  ;

Attachments-  !

Attachment I Itemized Question / Response - Proprietary Attachment II Itemized Question / Response - Non-Proprietary Attachment III Polestar Applied Technology,Inc. AfTidavit Attachment IV Conservatisms in Iodine Spiking Assumptions cc: Administrator, Region I TMI-1 Senior Project Manager TMI-1 Senior Resident Inspector File No. 98076 i

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1920-99-20447 i

METROPOLITAN EDISON COMPANY JERSEY CENTRAL POWER AND LIGHT COMPANY PENNSYLVANI A ELECTRIC COMPANY d/b/a GPU ENERGY GPU NUCLEAR, Inc.

Three Mile Island Nuclear Station, Unit 1 Operating License No. DPR-50 Docket No. 50-289 Technical Specification Change Request No. 272 Response to Request for Additional Information (RAI) l l

COMMONWEALTH OF PENNSYLVANI A )

) SS: {

COUNTY OF DAUPHIN )

This GPUN Inc. response to the NRC Staff s RAI on Technical Specification Change Request No. 272 is submitted in support of Licensee's request to change Appendix A to Operating License No. DPR-50 for Three Mile Island Nuclear Station, Unit 1. All statements contained in this submittal have been reviewed, and all such statements made and matters set forth therein are tme and correct to the best of my knowledge.

BY: u14

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[ Yice' President apirector, Tiil Sworn and subscribed before me this Ad Day o,f ,

, I L 999.

Notary Public Notarial Seal n e - at p n Cou y 999

My Commission E

xpires Nov. 22,1

~ Member.Pennsylvanha Association of Notanes

Attachment III 1920-99-20447 ATTACHMENT III Polestar Applied Technology, Inc. )

AfYidavit Certifying Request for '

Withholding from Public Disclosure i

I F

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9 Polestar Applied Technology,Inc.

AFFIDAVIT I, David E.W. Leaver, being duly sworn, depose and state as follows:

(1) I am a Principal and an Officer of Polestar Applied Technology, Inc. (" Polestar")

and am responsible for the function of reviewing the information described in paragraph (2) which is sought to be withheld, and have been authorized to apply ,

for its withholding.

(2) The information sought to be withheld is contained in portions of the following Polestar report prepared for GPUN in support of a response to an NRC Request for Additional Information (RAI) on the GPUN application of iodine behavior i insights on iodine retention in the secondary side of once through steam generators (OTSG) for the design basis iodine spiking accident for the Three Mile Island Unit 1 Nuclear Plant:

Attachment 2 - Non-QA Response to RAls (RAI based on NRC review of GPU Nuclear letter to the NRC dated October 19,1998 (1920-98-20210) titled, " Technical Specification Change Request (TSCR) No. 272" (3) In making this application for withholding of proprietary information of which it is the owner, Polestar relies upon the exemption from disclosure set forth in the NRC regulations 10 CFR 9.17(a)(4),2.790(a)(4), and 2.790(d)(1) for " trade secrets and commercial or financial information obtained from a person and privileged or confidential" (Exemption 2.790(a)(4)).- The material for which exemption from disclosure is here sought is all " confidential commercial information".

- (4) Some examples of categories of information which fit into the definition of proprietary information are:

a. Information that discloses a process or method, including supporting data and analyses, where prevention of its use by Polestar's competitors without license from Polestar constitutes a competitive economic advantage over other companies.

b. Information which,if used by a competitor, would significantly reduce his expenditure of resources or improve his competitive position in the analysis, design, assurance of quality, or licensing of a similar product; I

c. Information which reveals cost or price information, production capacities, budget levels, or commercial strategies of Polestar, its customers, or its suppliers;

d. Information which reveals aspects of past, present, or future Polestar customer-funded development plans and programs, of potential commercial value to Polestar;

e. Information which discloses patentable subject matter for which it may be desirable to obtain patent protection.

The information sought to be withheld is considered to be proprietary for the reasons set forth in both paragraphs (4)a and (4)b, above.

(5) The information sought to be withheld is being submitted to GPUN (and, we trust, to NRC) in confidence. The information is of a sort customarily held in confidence by Polestar, and is in fact so held. The information sought to be withheld has, to the best of my knowledge and belief, consistently been held in confidence by Polestar, no public disclosure has been made, and it is not available in public sources. All disclosures to third parties including any required transmittals to NRC, have been made, or must be made, pursuant to regulatory provisions or proprietary agreements which provide for maintenance of the information in confidence. Its initial designation as proprietary information, and the subsequent steps taken to prevent its unauthorized disclosure, are as set forth in paragraphs (6) and (7) following.

(6) Initial approval of proprietary treatment of a document is made by the manager of the originating component, the person most likely to be acquainted with the value and sensitivity of the information in relation to industry knowledge.

Distribution of such documents within Polestar is limited to those with a need to know.

(7) The approval of external release of such a document typically requires review by the project manager, and the Polestar Principal closest to the work, for technical content, competitive effect, and determination of the accuracy of the proprietary designation. Disclosures outside Polestar are limited to regulatory bodies, customers, and potential customers, and their agents, suppliers, and licensees, and others with a legitimate need for the information, and then only in accordance with appropriate regulatory provisions or proprietary agreements.

(8) The information identified in paragraph (2), above, is classified as proprietary because it directly relates to a methodology developed by Polestar and applied under the Polestar 10 CFR 50, Appendix B Quality Assurance Program. The methodology addresses iodine (as I,) retention in the secondary side of the OTSG 2

1 during the design basis iodine spiking accident for the Three Mile Island Unit 1 Nuclear Plant. The RAI addresses the post-flash liquid droplet behavior on the secondary side of the steam generator and the evaporation to dryness aspect of the methodology. Iodine retention on the secondary side of the steam generator has not traditionally been considered in USNRC licensing design basis calculations, and thus new methods development was required, including methods to address the post-flash liquid droplet behavior and evaporation to dryness.

The methodology used in the Three Mile Island calculations is one of a number of Polestar developed methods, models, and codes. Development of these methods, models, and codes was achieved at a significant cost to Polestar, on the order of $100,000, which is a significant fraction of internal research and development resources available to a company the size of Polestar.

The development of the methods, models and codes, along with the interpretation and application of the results,is derived from the extensive experience database that constitutes a major Polestar asset.

(9) Public disclosure of the information sought to be withheld is likely to cause substantial harm to Polestar's competitive position and foreclose or reduce the availability of profit-making opportunities. The information is part of Polestar's comprehensive technology base on application of the revised source term to operating plants and advanced light water reactors, and its commercial value extends beyond the original development cost. The value of the technology base goes beyond the extensive physical database and analytical methodology and includes development of the expertise to determine and apply the appropriate evaluation process. In addition, the technology base includes the value derived from providing analyses done with methods which have been developed and are being maintained in accordance with 10 CFR 50, Appendix B requirements.

The research, development, engineering, analytical and review costs comprise a substantialinvestment of time and money by Polestar.

1 The precise value of the expertise to devise an evaluation process and apply the correct analytical methodology is difficult to quantify, but it clearly is substantial.

I Polestar's competitive advantage will be lost if its competitors are able to use the results of the Polestar experience to normalize or verify their own process or if they are able to claim an equivalent understanding by demonstrating that they can arrive at the same or similar conclusions.  ;

i The value of this information to Polestar would be lost if the information were disclosed to the public. Making such information available to competitors .

3

i,- .

without their having been required to undertake a similar expenditure of resources would unfairly provide competitors with a windfall, and deprive Polestar of the opportunity to exercise its competitive advantage to seek an adequate return on its relatively large investment in developing these very valuable analytical tools.

4

n STATE OF CALIFORNIA )

) ss:

COUNTY OF SANTA CLARA )

David E.W. Leaver, is being duly sworn, deposes and says:

That he has read the foregoing affidavit and the matters stated therein are true and correct to the best of his knowledge, information, and belief.

Executed at Los Altos, California, this II day of bP'd 1999.

ftrt David E.W. Leaver Polestar Applied Technology,Inc.

Subscribed and sworn before me this // day of M os 1998.

/

N C

• o Sante clara county v Notary Public, State of California

-l MyComm. Expires Oct8,1999 I .

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l Attachment Il

[ 1920-99-20447 Page1of8 NON-PROPRIETARY l

ATTACHMENT II NRC Ouestion No.1.a:

In the " Flashing and Evaporation to Dryness Calculation" in Enclosure 4 (page 6 of 20) to the above referenced letter, you used an equation derived in NUREG/CR-5950 (equation 15 on page 13) to determine the primary coolant iodine partition coefficient.

This equation was developed for use in determining an iodine partition coefficient in a quiescent water pool and is not applicable for the once through steam generator (OTSG) primary coolant flashing into the secondary side.

Response

I Equation 15 from NUREG/CR-5950 applies to any gas-water system in which the water contains dissolved 12 and undergoes a throttling process and associated flashing. The issue of whether or not equilibrium is attained between the phases during the flash and whether or not equilibrium is simultaneously reached within the liquid phase with respect to iodine speciation, is discussed below.

Regarding the issue ofiodine speciation, Equation 12 of NUREG/CR-5950, the companion equation to l

Equation 15, may be applied to any water-iodine system containing iodine as a dissolved salt. It is used '

to identify the equilibrium speciation ofiodine in the liquid phase; hence, it determines the fraction of the total dissolved iodine to which Equation 15 applies. Equation 12 is really appropriate for systems at 298 K; it is conservative when applied to systems at temperatures above 298 K (i.e., it overstates the conversion of F to I). Therefore, when applied to systems at higher temperatures (as is done here), it conservatively overpredicts the fraction of the dissolved iodine that is elemental (to which Equation 15 then applies).

NUREG/CR-5950 states that Equation 15 provides " . the equilibrium distribution that is likely in a  ;

bubbling suppression pool. In a quiescent pool, it might take some time to approach such an equilibrium." This statement is pointing out the key feature of Equation 15i that it is an equilibrium equation. To the extent that iodine distribution equilibrium is not reached between the phases during the flash, I2initially dissolved in the water will tend to remain in the water.

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r Attachment 11 1920-99-20447 j Page 2 of 8 l

l The process of flashing is, by its nature, a process of reaching equilibrium when an existing equilibrium

! has been disturbed. As a saturated liquid passes to an area oflower pressure, the liquid by definition l

becomes superheated. Nucleation sites form, and bubbles (thousands to tens of thousands per cubic 1 centimeter) begin to grow. It is the very large surface area to volume ratio that allows the new gas-l liquid equilibrium to be reached so quickly. Just as water molecules must make a net movement from the liquid phase to the gas phase to continue the process of flashing, so must iodine atoms also move from the liquid phase into the gas phase. It must be remembered that at the stan of the flashing process, all of the iodine exists in the liquid phase. The iodine must then cross the steam-liquid interfaces being formed at the nucleation sites to become airborne, and even after the liquid is fragmented into droplets, this process continues. 1 The time-dependent flashing fractions for the leaked primary coolant are shown on Figure 1 of the referenced calculation for the MSLB/AIS case and on figure 2 for the MSLB/ PAS case provided in GPU l Nuclear letter to NRC 1920-98-20210, dated October 19,1998, It is important to note that the largest i fraction of the water mass remains liquid after the flash even though the volume of steam is very large  !

(i.e., the flashing fraction is always substantially less than one). This volume of steam carries and i surrounds the liquid droplets allowing the equilibrium processes to continue even after fragmentation is complete. The very large surface area to volume ratio afforded by dispersed droplets in the steam plume encourages equilibrium between the phases to be reached.

However, it should be recognized that the attaining of equilibrium within the dispersed droplets (in terms ofiodine speciation and pH) is actually a penalty on iodine conversion to airborne 2I . This is because of the increase in the concentrations ofiodine and orthoboric acid that results from the loss of some tens of percent of the liquid phase water mass during the flash. The whole purpose of developing and applying the iterative series of equations on pages 8 through 10 of the calculation is take the

concentration effects ofiodine and onhoboric acid into account so that the release of12 during the flash is not underestimated. If one were to assume that only the dissolved 12 present in the unflashed liquid (as predicted by Equation 12 of NUREG/CR-5950) were released during the flash, then the fraction of iodine released during the flash would be greatly underestimated.-

1 To summarize, Equation 15 of NUREG/CR-5950 may be applied to any gas-water system in which the water contains dissolved I2. Equation 15 is an equilibrium equation; as pointed out in the NUREG/CR document, itself, the more rapid the attaining of equilibrium between the gas and liquid phases, the more applicable Equation 15 is. It is believed that suflicient time, proximity, and surface area to volume ratio are available for equilibrium to be reached in the steam-water system resulting from the flash; indeed, this is the definition of the flashing process. However, any failure to come to equilibrium, either in terms ofiodine moving from the liquid phase to the gas phase or ofiodine speciation within the liquid phase failing to respond to increases in iodine and/or orthoboric acid concentration would result in less, not more, iodine being released to the gas phase.

NRC Ouestion 1.b:

The primary coolant which leaks into the shell side of the OTSG will flash to steam and iodine in the leaked primary coolant will be immediately vaporized and become airborne due to the flashing and atomization.

Attachment II 1920-99-20447 Page 3 of 8

Response

The'only portion of the iodine which will become vaporized is that _which leaves the liquid phase across the steam-water interface created by the nucleating and growing bubbles. As these bubbles expand and the liquid fragments into dispersed droplets surrounded by the steam phase, the iodine in the steam phase will increase until it is in equilibrium with that remaining in the liquid phase. Meanwhile, the liquid phase iodine speciation, itself, is adjusting to the changing iodine and orthoboric acid concentration due to the loss of water mass and of some of the iodine.

At the end of the fisshing process all of the iodine will be airborne in the sense that it will be either in

- the steam phase (as I2) ce in the dispersed droplets. . However, the bulk ofit will be in the liquid phase and not vaporizedi In fact, because of the lower volatility of the iodine species as compared to water,

the fraction of the iodine mass lost from the liquid phase will be generally less than that of the water (i.e., the " flashing fraction"). However, for the AIS case as the iodine concentration increases with time and as the decreasing temperatur:mf the primary coolant decreases the flashing fraction, a point is reached at about 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> where the iodine release fraction during flashing actually exceeds that of the flashing fraction. The iodine release fraction during flashing at that time is about six percent.

L The key issue is what happens to the bulk of the iodine which remains with the dispersed liquid phase.

This depends on whether or not the liquid phase comes in contact with metal structures within the steam generator or evaporates in the gas phase. This issue is addressed in the response to Question No. 2 below.

NRC Ouestion 1.c:

The staff assumes an iodine partition coefficient of 1 (no iodine partition) for the primary coolant leaked to the OTSG since the secondary side of the OTSG will contain no water during the MSLB accident.

The staff requests that you recalculate the radiological consequence with no iodine partitioning.

Response

Technically, an assumed partition coeflicient of unity means that the iodine concentration in the liquid phase is equal to that in the accompanying gas phase. If one assumes further that the liquid phase volume becomes zero,'then it becomes obvious that all of the iodine initially in the liquid phase would then be in the gas phase. However, such an assumption during the flashing process is not accurate.

Clearly, there will be a liquid phase present, and it will reraain until some form of heat transfer is able to

. add sufficient energy to the steam and to the dispersed water droplets to bring about evaporation. The internal energy of the unflashed liquid is insufficient to achieve complete evaporation; in fact, it is this internal energy deficit that limits the flashing fraction. Therefore, it is not accurate to say that the secondary side of the OTSG will not contain water; a dispersed liquid phase will always be present in the vicinity of the leak. There is no need to recalculate doses based on the assumption that all of the iodine in the liquid becomes vaporized or aerosolized during the flash, since that is not the case.

Attachm:nt Il 1920-99-20447 Page 4 of 8 NRC Ouestion No. 2.a:

In the " Flashing and Evaporation to Dryness Calculation" in Enclosure 4 (page 10 of 20) to the above referenced letter, you used iodine volatility values provided in a table contained in NUREG/CR-5732 (Table 3.8 in page 28) to determine primary coolant iodine decontamination by evaporation to dryness on the OTSG tube surfaces.

These figures are only applicable to iodine evaporation in a quiescent state and only up to 95 C (this reference used evaporation ofiodine solution in a beaker to dryness on an hot plate). These figures are not applicable for the OTSG primary coolant flashing into the secondary side.

Response

[ Polestar Proprietary Material Deletedj The conclusions reached from the considerations listed above are as follows:

1. The data from NUREG/CR-5732 are applicable to the OTSG conditions. The experimental conditions associated with these data, while different from OTSG conditions following a steam line break in terms of temperature, materials, geometry, and mass transfer rates, are for the most part conservative with respect to these conditions. The temperature may not be conservative, but the OTSG temperature conditions are much closer to the experimental conditions than either temperature is to the boiling point of CsI.

2. [ Polestar Proprietary Material Deleted], while not showing as much sensitivity to radiation as the NUREG/CR-5732 data, are generally consistent with the NUREG/CR-5732 data. These data indicate that carry-over fractions during evaporation-to-dryness beginning with basic, neutral, or even mildly acidic initial conditions will be less than 20%. Accounting for conservatisms in materials and mass transfer rates could reduce these carry-over fractions still more.

_N_Bf.Ouestion 2.b:

The staff believes that atomized primary coolant will not be able to settle on the OTSG tubes to be evaporated. Instead it will vaporize instantaneously and become airborne.

Response

[ Polestar Proprietary Material Deletedj To summarize, if primary-to-secondary leaks were small and dispersed, large droplets would be created which would be difficult to evaporate to dryness in the gas phase even if they fell perfectly vertically

< and avoided all contact with tubes. It is interesting to note in this regard that the calculated diameter of the gravity-formed drops is almost identical to the spacing between the steam generator tubes.

. If, on the other hand, primary-to-secondary leaks were large and not well distributed, sub-mm droplets -

(down to 125 m) would be possible; but these would be produced at high velocities and would certainly impinge on nearby tubes. Local desuperheating of the steam generator gas phase would occur

y Attachment II 1920-99-20447

.Page 5 of 8 l

because heat transfer from the tubes in the vicinity of the leak would simply not be able to keep up with the cooling provided by the " spray".

In both situations evaporation-to-dryness would occur on the steam generator metal surfaces, not in the steam generator secondary atmosphere.

NRC Ouestion 2.c:

The staff requests that you recalculate the radiological consequences with no iodine ~ decontamination due to evaporation to dryness on the OTSG tubes.

Response

There is no need to recalculate doses based on the assumption that all of the iodine in the liquid would become airborne as a result of evaporation-to-dryness in the OTSG gas phase. Because the leaks occur

' within the' tube sheet, and because of the nature of the available mechanisms to transfer the leakage from l

the tube sheet / tube annulus to the OTSG secondary side, the behavior of the liquid phase will be such

. that evaporation-to-dryness will occur on the metal surfaces of the steam generator. Applicable data are available which show that the fraction ofiodine becoming airborne as a result of evaporation to dryness for the conditions stated is limited to less than 22 percent.  !

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Attachment II l 1920-99-20447 Page 6 of 8 NRC Ouestion No. 3.a:

In the " Flashing and Evaporation to Dryness Calculation:" in Enclosure 4 (page 15 of 20) to the above f referenced letter, you used NUREG/CR-2713 to determine vapor deposition velocity ofiodine on the j OTSG tube surfaces.

l l The iodine deposition velocity measurement provided in the NUREG has limited application since it was performed on a simple and limited scope as stated in the NUREG. The staff believes this l experiment is not applicable for estimating iodine deposition velocities on the surfaces of the OTSG l

tubes.

Resnonse:

i The use of NUREG/CR-2713 as a resource for iodine vapor deposition data in licensing applications is l not limited to Enclosure 4 (" Flashing and Evaporation to Dryness Calculation", as noted). In Reference 4, NUREG/CR-2713 is identified as the resource for data used by the BWR Owner's Group in the develoment of their model for iodine retention in the steam lines and in the main condensers of BWR l plants. This application is similar to the application being considered here. In the Conclusions of l Reference 4, Appendix A (under item 5) specific sources of potential non-conservatisms in the BWROG }

model are identified and discussed; nowhere in this discussion is any objection to the use of the NUREG/CR-2713 data mentioned. The only objection to using the NUREG/CR-2713 data mentioned in ,

the entire appendix appears in Section 2.3.3.2, and states that the data may be too conservative in light of 1 the predominant form of the iodine being Csl instead of12 or HI.

NRC Ouestion 3.b: 1 In addition, you have indicated that this iocine deposition velocity becomes only important late in the cooldown period when the tube surface temperature drops below on or about 300 F (about 11.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the accident). Justify the applicability of the iodine deposition velocity measurement provided in NUREG/CR-2713 for estimating iodine deposition velocities on the surfaces of the OTSG tubes.

Response

The fact that surface deposition does not become important until the tube surface temperature goes below 300 F is already reflected in the overall iodine DFs used in the dose analysis. It is precisely the absence of surface deposition that causes the overall iodine release fraction to remain high (i.e., near 25% ) prior to about 11.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.' Beyond 11.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, the impact of surface deposition from the gas-phase is calculated; however, it is not used in the dose analysis.

- The impact of assuming that the tube surface temperature is equal to the coolant temperature is an important conservatism in the overall approach. In reality (as noted above), the tube surface temperature would be less than 300'F at any location in the steam generator where tube-to-liquid heat transfer were taking place. However, it is tme that tube surface temperatures would not be universally below 300 F until about the time stated.

The use of a DF of two (iodine release fraction equal to 50%) for the first 10 minutes of the dose -

calculation during which the primary coolant flashing fractions could be as great as 45% and a DF of 4

Attachment II 1920-99-20447 Page 7 of 8 (iodine release fraction equal to 25%) for the remainder of the duration of the dose calculation effectively ignores any benefit ofiodine deposition from the gas phase onto the tube surfaces once the iodine is airborne. However, the impact ofignoring this benefit (i.e., the associated conservatism) should be recognized.

ILeferences

[ Polestar Proprietary Material Deletedj Reference 4: Ridgely, J.N. and Wohl, M.L., " Resolution of Generic issue C-8", NUREG-1169, United States Regulatoiy Commission, August 1986

Attachment II 1920-99-20447 Page 8 0f 8 Fieure 1

[ Polestar Proprietary Material Deleted]

c Attachment IV 1920-99-20447 Page1of3 i

ATTACHMENT IV Conservatisms in Iodine Soikinn Assumptions Introduction This discussion identifies the conservatism which exists in the analysis performed by GPU Nuclear for iodine release from tube leakage during a postulated main steam line break (MSLB) at TMI-1. The source of the conservatism is the iodine spiking methodology. GPU Nuclear utilized the Standard Review Plan (SRP) assumption of an accident-induced spiking factor of 500 times the maximum iodine release rate during equilibrium conditions. GPU Nuclear also used the SRP assumption (60 Ci/g) for pre-accident spike (PAS), but the PAS will not be discussed further here since the accident-induced spike is limiting for TMI-l dose calculations per the tables in Section 2.0 of Reference 1.

Evaluation of Conservatism i

An iodine spiking data base has been assembled by Polestar Applied Technology, Inc. under contract to EPRI(Reference 2). The data base covers a seven year period from 1990 to 1997. Polestar evaluated the following parameters from the data base:

Pre-trip equilibrium iodine concentration ( Ci/g)

Pre-trip iodine release rate (Ci/hr)

Post-trip iodine concentration Spiking rate (i.e., post trip iodine release rate)

These parameters were evaluated for a total of 117 transient events (plant trips). The results of this data base evaluation indicate that the 95% confidence limit of the 90th percentile spiking rate was about 400 Ci (DEI)/hr (that is, there is 95% confidence that 90 percent of the events will have a spiking rate less than 400 Ci/hr). The maximum spike event observed in a B&W plant was 1325 Ci/hr.

A similar evaluation was performed by Idaho National Engineering Laboratory (INEL) under contract to NRC in 1989 (Reference 3) which included 168 events from the 1980s. This evaluation using the NRC-sponsored 1980s data indicated that the 95% confidence limit of the 90th percentile spiking rate was about i100 Ci (DEI)/hr. The improvement noted for the 1990s was attributed to better fuel performance which would reduce the size ~of(or eliminate) the spike [2,3]. The combined data base of 283 events gave a 95% confidence limit of the 90th percentile spiking rate of about 700 Ci/hr.

An analysis was also performed of spiking factor vs. initial iodine concentration, both by Polestar for the 1990 to 1997 data, and in the NRC-sponsored study of 1980s data. Spiking factor is the ratio of pre-trip iodine release rate (Ci/hr) vs. post-trip release rate. The SRP methodology specifies a spiking factor of 500 as noted above, which with initial iodine concentration of I Ci/g, gives post-trip iodine r~elease rates of~16,000 Ci/hr.

I

r-Attachment IV 1920-99-20447 Page 2 0f 3 Figure I shows a scatter plot based on the Polestar 1990 to 1997 data which indicates approximately 30 events with spiking factors greater than 500. For all of these events, however, the initial iodine concentration is less than 0.1 Ci/g. In fact, with one exception, all events with spiking factor greater than 500 have initial iodine concentration less than 0.03 pCi/g. Figures 6 and 7 in Reference 3 show similar plots based on the NRC-sponsored 1980s data. These plots show the same result which led the NRC-sponsored study to state that the spiking factors are large, "not because the absolute post-trip release rate is high, but rather because the steady-state release rate is so low." The NRC-sponsored study went on to conclude that the ~16,000 Ci/hr post-trip release rate " appears to be overly conservative and could be reduced, per this analysis, by approximately a factor of 10 and could still provide adequate protection to the public if the 90th percentile iodine spike is an acceptable probabilistic bound." )

l Conclusion Based on the conclusion of the NRC-sponsored study and the more recent spiking data which show a ,

similar result, the GPU Nuclear analysis (1) which calculated a post-trip I-131 release rate of 162 l

Ci/ minute is overly conservative by about a factor of about 14, (i.e., 60* 162/700).

References

1. " Dose Consequences from OTSG Tube Leakage During a Main Steam Line Break with a Dell 31 of 1 pCi/g," GPUN Calculation C-1101-900-E000-065, Rev.1.

2. Polestar Applied Technology, Inc., " Statistical Analysis of Recent Iodine Spiking Events in PWRs,"

PSAT 07301H.05, July 31,1998.

3. J. Adams and C. Atwood, " Probability of the lodine Spike Release Rate During an SGTR," Prepared for the U.S. NRC, EGG-NERD-8648, September,1989.

Attachment IV 1920-99-20447 Page 3 of 3 Figure 1. Spiking Factor vs. Initial lodine Concentration 100000

,e y 10000

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