ML20099J446

Applicant Exhibit A-141,consisting of Undated Pages III.7-4 & III.7-5 of Unidentified Rept Re Sheltering Effectiveness & Revised Model of Public Evacuation

ML20099J446
Person / Time
Site:	Limerick
Issue date:	05/22/1984
From:	AFFILIATION NOT ASSIGNED
To:
References
OL-A-141, NUDOCS 8411290050
Download: ML20099J446 (4)

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which account for regional dif ferences in the frequency of bricki

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ences in building occupancy. Sheltering in regions such as the Northeast, where a large fraction of homes have basements, offers the greatest protection, and is represented by averag.o. shielding factors of 0.5 and 0.08 for airborne and ground deposited radio-nuclides, respectively. Sheltering in areas where most homes do not have basements (i.e. , Southwest or Pacific Coast) offers the

, least protection, and is characterized by corresponding average i

shielding factors of 0.75 and 0.33.*

! To estimate the potential ef fectiveness of sheltering in i reducing the quantity of radionuclides inhaled, a' multicompart-e ment vent'ilation model was developed for' th'e calculation of air-i borne radioactive material concentrations inside of structures i [8]. Using "best estimate" values for all parameters, the model

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i indicates that sheltered individuals would inhale roughly 35 percent less radioactive materi,al than if they were outside during the passage of the cloud. Larger reductions would be possible

if the ventilation rate (air turnover rate) could be reduced i either by tighter building construction or by the sealing of 4

openings in the structure. Further. analysis indicated that the strategy of opening doors and windows, turning. on ventilating systems, etc. , in an attempt to " air-out" the structure af ter

the cloud of radioactive material has passed would most likely l not contribute significantly to reducing the amount of inhaled i

radionuclides unless very low ventilation rates are achieved during cloud passage.

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Sheltering effectiveness was evaluated using the range of i average shielding factors described above. Sheltering of the public was assumed to be completed prior to the. arrival of the cloud of radioactive material, and persons were assumed to remain sheltered until relocated. In an actual accident situation, sheltered individuals might be exposed to ground contamination while sheltered and while being relocated. However, to simplify ,

i this analysis, exposure to ground contamination was presented

in terms of effective exposure durations assumed to occur only t while sheltered. For example, an effective exposure time of

i. 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> while sheltered (with SF for ground contamination = 0.2)

might, in fact, be due to 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of exposure while sheltered (with SF = 0.2) and=1/2, hour exposure while relocating (with

SF = 0.8). Because som'e exposure would be received while

! relocating (with little shielding), and it would take some time i to determine affected areas and initiate a relocation, 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />

• Note that the use of average shielding f actors for the l assessment of radiological consequences results in the i i

assignment of average doses to all individuals within a l- given area rather than the distribution of doses that would actually occur due to the variation in shielding protection afforded individuals. The adequacy of this simplification is discussed in reference [7]

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-'S           was chosen as a practical lower limit for effective exposure time.

t _,/ The modeling of public evacuation as a protective measure , for reactor accidents is discussed in reference [9]. A simple s evacuation model, based upon a statistical analysis os evacua-tion data gathered by the U.S. Environmental Protection Agency (EPA) [10], was included in the RSS consequence model for use in the estimation of public risk from reactor accidents. Howev9r, for reasons which are-discussed in reference [9], that model.is ,, inappropriate for use in evaluating evacuation.as a radiological emergency response. Therefore, a revised model of public evacua-tion was developed for this purpose. The revised treatment incorporates a delay time before public movement, followed by

             ' evacuation radially away from the reactor at a higher constant speed than previously assumed in the RSS evacuation model.         Both the delay time and evacuation speed are required as input to the model, and different shielding factors are allowed while persons are stationary and in transit. As detailed in reference

[9), the revised model also calculates more realistic exposure durations to airborne and gropnd deposited radionuclides than the RSS evacuation model. Persons within the designated evacua-

     -          tion area are assumed to move as a group with the same delay time and speed, and all people in the area are assumed to eva-cuatre. This latter assumption results in upper bound estimates of' evacuation effectivenss, given a specific delay time and   -

g speed.. .

--                     The evacuation data gathered by the EPA contains suf ficient information for the estimation of delay times before evacuation if a specific speed while evacuating is assumed. Transit speeds of 10 miles per hour and greater have been recorded during actual evacuation events [9], and do seem reasonable given the low popu-lation _ density surrounding reactor sites. Therefore, the speed of evacuation was assumed to be.a constant 10 miles per hour throug6-out this analysis. The EPA data        was analyzed to estimate rep:e-sentative evacuation delay times.       The mean delay time was shown to be approximately 3 hours, and the 15*-85 percent level range of delays was shown to be approximately 1 to 5 hours.

To evaluate the ef fectiveness of iodine prophylaxis, reduc-tion factors were applied to the thyroid dose from inhaled radio-iodines. For example,,1f stable iodine was administered shortly before or immediately af ter the release of radioactive material begins, reduction f actors of 0.01 or less might be appropriate (99% or greater dose reductions) [6] . The dose to the thyroid from external radiation sources, radioiodines in organs other than the thyroid, and other inhaled radionuclides are unaf fected by these factors.

                   *15% of evacuations for which data is available had estimated delay times of approximately 1 hour or less.

III.7-5

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