ML20052A000

Forwards Comments on Facility Probabilistic Safety Study as Provided to ACRS by Consultants

ML20052A000
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	04/19/1982
From:	Novak T Office of Nuclear Reactor Regulation
To:	Klopp G COMMONWEALTH EDISON CO.
Shared Package
ML20052A001	List: ML20052A000 ML20052A003 ML20052A004 ML20052A059
References
ACRS-CT-1410A, NUDOCS 8204260416
Download: ML20052A000 (15)

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DISTRIBUTI0ft Docket File w/o enclosure:

APR 191982 flRC PDR S. Hanauer Local PDR F. Rowesome ORB 1 File D. Eisenhut C. Parrish Docket lios. 50-295 D. Wigginton and 50-304 OELD I&E (1)

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Dear Mr. Klopp:

/c) l Enclosed are coerents on the Zion Probabilistic Safety Study as provided to the ACRS by several of their consultants.

It is requested that your consaents be submitted to this office at your earliest convenience.

Sincerely, Originni cigma ty:

ThomnnM. EVA Thomas !!. tiovak, Assistant Director for Operating Reactors Division of Licensing

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Robert J. Vollen, Esquire 109 North Dearborn Street Chicago, Illinois 60602 Dr. Cecil Lue-Hing Director of Research and Development Metropolitan Sanitary District of Greater Chicago 100 East Erie Street Chicago, Illinois 60611 Zion-Benton Public Library District 2600 Emmaus Avenue Zion, Illinois 60099 Mr. Phillip P. Steptoe Isham, Lincoln and Beale Counselors at Law One First National Plaza 42nd Floor Chicago, Illinois 60603 Susan N. Sekuler, Esquire Assistant Attorney General Environmental Control Division 188 West Randolph Street, Suite 2315 Chicago, Illinois 60601 U. S. Nuclear Regulatory Commission Resident Inspectors Office 105 Shiloh Blvd.

Zion, Illinois 60099 James P. Keppler Regional Administrator - Region III U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

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Dr. David Okrent 5532 Boelter Hall University of California, Los Angeles Los Angeles, California 90024

Dear Dave:

Enclosed is a summary of the limited review I have performed on the Site Consecuence Analysis portions of the Zion PRA.

Please Ict me know if you have any questions or desire additional information.

Sincerely,.and 6 dia'ru-lublou David C. Aldrich Safety and Environmental Division 4415 (505)S44-9164 FTS: 844-9164 DCA:4415 :dm Enclosure Copy to: Dr. J. Michael Griesmeyer Advisory Co=ittee on P.cactor Safeguards U.S. Nuclear Regulatory Comission Washin5 ton, D. C. 20555 M l O4 **

a A 4 Review of the Zion PRA: Site Consequence Analysis Performe'd for: ACRS By: David C. Aldrich Safety and Environmental Studies Division Sandia Nationhl Laboratories Albuquerque, New Mexico 87185 January 31, 1982 I have performed a limited review of the site consequence analysis portions of the Zion PRA, attempting to focus only on those aspects of the m deling or evaluation that could signifi-cantly impact predicted results, estimates of uncertaingy, or major conclusions. Specific sections of the Zi'on report included in this review were: Section 6 - Site Consequence Analysis (Module 5, Volume 9) Section II.6 - Site Analysis (Module 1, Volume 1) Section II.8 - Existing Plant Risk--Results Section 1I.10 - Reflections, Advancements and Limitations In my opinion, the Zion site consequence analysis is a reasonably comprehensive,'well performed and well-documented assessment of the public health impacts from potential acci-dents at that site. The comments I have provided below ('particularly on the emergency response assumptions employed) could result in altered predictiorn of early health effects .(fatalities and injuries). However, I have no major concerns i or criticisms that would invalidate any significant conclu-sions of the study. The authors shculd be commended not only

s 4 -2 for their evaluation but for extending the state-of-the-art in several modeling areas. In addition, I commend the attempt made to quantify the uncertainties inherent in the offsite consequence calculations. Admittedly subjective (and difficult), I think a reasonable job was done. This does not m'ean, however, that I necessarily concur with the uncertainty distribution assigned. The CRACIT code used for the Zion site analysis is a substantially modified version of the Reactor Safety Study consequence model, CRAC. Modifications were made to the s atmospheric-dispersion and evacuation submodels to more 1 adequatply treat specific site conditions. The two funda-montal changes are the use of variable direction plume trajectories and the incorporation of a variable direction evacuation scheme. In contrast, CRAC models both plume travel and evacuation in straight lines extending radially outward from the plant. Specific modeling additions or improvements to the original atmospheric transport and dispersion submodel in CRAC include: pidme trajectories based on hourly wind-direction changes; a three-dimensional model for determining terrain effects on wind flow and plume trajectory; use of different wind speeds based on plume ~ evalua-tion;. l use of meteorological data from many surrounding-l stations in.the. site region; ~ O L

e 4 improved or additional models for wet deposition (washout), plume rise, lid penetration, plume " lift off," terrain height correction, and trap-ping and fumigation under inversion lids: a turbulent internal boundary layer (TILL) model to account for lake effects; and ability to modify plume characteristics based on expert judge. ment. These modeling in.provem'ents do provide some additional con-fidence in predicted r'esults (i.e., reduce'd uncertainty)*. However, I suspect that their overall impact on the predicted . risk curves is small. This is supported by preliminary results of the International Benchmark Exercise on Reactor i d j Accident Consequence Models [ Reference 13 which show CRACIT C and CRAC results to be similar when assuming no immediate l emergency response. There is one aspect of both the CRACIT and CRAC atmo-t I spheric dispersion submodels that, if improved, could i significantly alter (most likely lower) predicted early I health effects. Both codes assume that all radioactive material released.during an accident follows the same l trajectory. However, for long duration releases ( > l hour) I such as predicted for Zion, wind shifts during and follow-t ing"the release would likely send portions of the released l l material over entirely different trajectories. Use of a-

• Although the terrain surrounding the Zion site is flat and does not significantly influence wind-ficw patterns, lake effects were shown to.significantly impact the transport and dispersion plumes released frem the plant under some weather conditions.

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s s .. 4 multi-phase or " puff" modc1 would therefore predict lower doses to individuals and (most likely) reduced early health effects. This aspect is discussed in the Zion report (Vol-ume 9, Page 6.3-6). The other major"imodification in gR$ CIT involves the evacuation submodel. A s'cheme is employed that allows consideration of likely' evacuation routes at the site (CRAC assumes evacuees move radially away from the plant), as well as "bc'ttlenecks" that could occur along the evacuation path. However, the selection of input parameter values for the modified model is somewhat arbitrary. The following assump-tions are made in the Zion study: evacuation radius = 11 miles evacuation begins 1 hour after warning by plant (delay time = 1 hour) pcrsonnel average evacuation speed = approximately 3 mph (varies) no consideration of "non participating" population (i.e., people who either are not warned or groups refuse to leave) .upon reaching the end of the assumed evacua. tion path (at 11 mile radius), evacuees remain at that location for 4 hours beyond 11 miles, relocation after 24 hours of exposure A number of analyses have been performed at Sandia National Laboratories [2, 3, 4, 5] to examine the impact of emergency response assumptions cn1 predicted health effects. p MM

j s; e , 4 These analyses indicate that early effects (fatalities) are very sensitive to assumed evacuation parameters, particularly to the delay time before public movement. Unfortunately, 'there is not a great deal of information available about how effectively (delays, speeds, etc.) an evacuation would be implemented during a'n' actual accident situation.* In most cases, the largest (and most important) uncertainties are associated with estimated warning and delay times, rather than the specific route followed. The authors of the' Zion study are aware of these issues, generally agree with them,' and discuss them explicitly (see Volume 9, Page 6.3-4, and Volume J, Page II.10-5). Because evacuation parameters are important and involve large uncertainties, it would have been preferable to assign distributions to them rather than point ("best") estimates. The CRAC2 code (recently released) does this. An alternative would have been to perform (and include in the report) a sensitivity analysis of the key parameters. I would not be surprised if other " reasonable" evacuation assumptions caused the left-hand side (P 2 1) of the early fatality CCDFs to rise by a factor of 5, perhaps more. The tails of the CCDFs v,ould n6t be influenced, however, since they tend to occur b'eyond the evacuated zone. The tails predicted for Zion are

• I would expect the effoqtiveness to vary with time of d

~ weather, and perhaps other factors that may be associated ay, with the cause of.the accident (e.g., scismic, loss-of-offsite power). I

e 4 4 likely to be overpredicted because of the assumption of no immediate response beyond 11 miles. A large fraction of the risk at the Zion site is pre-dicted to result from seismic events. Seismic accelerations sufficient to cause serious damage to the plant could also severely impact (or. destroy) offsite power availability, roads, communication systems, warning systems, or avai!)bility of response personnel.* Emergency response warning and implemen-tation might therefore be seriously degraded. The possibility and effects of such a degraded response should have been discussed and evaluated in the study. hheZionstudywaslimitedtocxaminingoffsitehealth 1mpacts and did not specifically assess either the contamina - tion of land areas or the financial consequences resulting from potential accidents. In addition, the study did not include an assessment of potential health i= pacts resulting from contamination of surface-or ground-water bodies (liquid pathways). Other recent studies [6] have indicated that, for most sites, risks via the liquid pathways are small compared to those via the atmosphere. However, several possibly important pathways for surface-water contamination were not considered in those studies, including deposition (especially by washout) of contaminants directly on the surface of a water body, or washoff of materials deposited

• A similar statement could perhaps be made for loss-of-offsite power as the initiating cvent.

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,4 4 _7 4 on the 1and surface into a water body. I would cuecs that the inclusion of a liquid pathway consequence assessment for the Zion site would increase predictions of latent cancer fatalities by less than a factor of 2. The early fatality dose thresholds'(LD50) employed in the Zion study were thosb developed in the Reactor Safety Study (WASH-1400) assuming " supportive" medical treatment following exposure. WASH-1400 estimated that approximately 5000 personc could be treated at that level in the United States. Therefore, for very hi h consequence events (CCDP ~ 5 tails) in which more than 5000 persons are predicted to receive bone marrow doses in -excess of 200 rem, calculations should be performed assuming the dose thresholds for " minimal" medical treatment. This would tend to increase the ",ta il s " of the early fatality CCDFs. Finally, as a limited check on the Zion consequences estimates, the results of some recent calculations performed at Sandia National Laboratories [5] for a large core melt release at the Zion site are compared to the Zion PRA results.on the attached figures. The Sandia calculations were performed with the CRAC2 code assuming an 1120 MWe FWR, the population distribution and windrose for Zion, Chicago meteorology, and a distribution of 10 mph evacuations ( t o' 10 miles) after delays o* 1, 3, and 5 hours. The results-e O

".4 _g. presented are for an SST 1 release which h'as the following characteristics: Time of Release Warning Release Release Duration Time Height Release (hr) (hr) (hr) (meters) Enercy 1.5 2 0.5 10 0 Core Inventory Rele,ase Fractions (to at=osphere) Xe-Kr I Cs-Rb, Te-Sb Ba-Sr Ru La 1.0 .45 .67 .64 .07 .05 9 x 10~3 The SST 1 release is similar in magnitude to Zion release categories Z-1, 2, 2R, 23, and Z5, although the release duratio'ns, warning times, and release energies are somewhat different. Nevertheless, the comparison of results is enlightening. Peak predicted early fatalities and injuries (tails) for the two codes (CRACIT and CRAC2) are similar. The predicted probability of getting lower (non-zero) con-sequences (P 1 0, left-hand side of curves) is substantially higher for CRAC2. This is due primarily to the longer delay times, shorter warning time, and smaller release duration assumed in the Sandia calculations. Predictions of latent' cancer fatalities by the CRACIT and CRAC2 codes are essentially identical. e G G 9 e G

- g-References 1.

Aldrich, D.

C., et al., " International Standard Problem for' Consequence Modeling: Results," International ANS/ ENS Topical Meeting on Probabilistic Risk Assessraent, Port Chester, New York, September 20-24, 1981. 2.

Aldrich, D.

C., P. E. McGrath, and N. Rasmussen, Exami-nation of Offsite Radiological Emergency Protective _ Measures for Nuclear Reactor Accidents Involving Core Melt, NUREG/CR-ll31, June 1978. 3.

Aldrich, D.

C., L. T. Ritchie, and J. L. Sprung, Effect of Revised Evat:uation Model on Reactor Safety Study Accident Consecuences, SAND 79-OO95, February 1979. 4. Chapter 9, PRA. Procedures Guide, Draft, NUREG/CR-2300, September 19el. 5.

Aldrich, D.

C., D. R. Strip, et al., Technica1 Guidance ~ for Siting Criteria Develocment, NUREG/CR-2239, to be published. 6.

Niemgzyk, S.

J., et al., The Consecuences from Liouid Pathways Af ter a Reactor 'Seltdown Accidcat, ~ 1596, June 1981. NUREG/CR-F 0 a e i S J e ' l f I i I s.pt

Reproduced from Zion report, Volume 9 l 1.0 --- ~ ~ ~ \\ N Sandia results for \\ SST 1 release ~ 21 A \\ 10~1 \\ ~ /'S \\ ~ 23 0 =<C h10-2 __ X t \\ o / s / I Dc Z-5A wc" Y.10-3 2R r E r o b ~ u g \\ d 10 ~ (ALL OTHER RELEASE CATEGORIES ~ -PRODUCE NO F ATALITIES) 33 5 l l I l 0 1 2 3 4 5 10 10 10 10 10 10 EARLY FATALITIES Figure 6.4-1. Conditional Consequence Curves for Various F.clease Categories - Dat. age Index: Fatalities

Reproduced from Zion report, Volume 9 0 10 T~ ~~ Sandia results for l i \\g SST 1 release \\ \\ 1A ~ ~ -c-- . ~. - ~' 2A L;-

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w u 2< 10'l ~2-- c / W 5 \\ u / u . Z-3... ~ ~ O y ~ y 2 W ~ 2:5A g ~ w c: u .J ~ i \\ P 5

10 2 __.(ALL OTHE R RELE ASE CATEGORIES l

_ PRODUCE tiO INJURIES) C u i ( 2nv ~ l f \\ t \\ i 4 I i i i 1 10'3-I 0 1 2 3 4 105 10 10 10 10 10 ( INJURIES 1 1 ficare 6.4-2. Conditional Consequence Curves for Various j Release Categories - Damage Index: Early Injuries j 4

. o 4 o. Reproduced from Zion report, Volume 9 Sandia results for 0 SST 1 release 3e \\ ~ 1A \\ \\ 2A AND 2R / \\ 5A \\ z-3 uy lo-1 ~ _. e \\ O 4 5 E ~ ~ BB W / L e 6 i 5 7 / R a .l s g 2Rv c t E 10-2 c u 3o 3 I I I I 0 10 101 102 103 4 5 10 10 CANCER F ATALITIEs (OTHER THAN THYROlDS) Figure 6.4-4 Ccnditicnel Cohse:;uence Curves for Various Release Categories - Damge Index: Other Cancers ,}}