ML20207S225

Discusses Proposed Revs to Meteorological Model for Part 100 Evaluations.Requests That Listed Positions for Site Probability Level Be Approved for NRR & Applied to Std Being Developed

ML20207S225
Person / Time
Issue date:	07/25/1978
From:	Muller D Office of Nuclear Reactor Regulation
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20207S219	List: ML20207S218 ML20207S220 ML20207S225 ML20207S235 ML20207S238 ML20207S240
References
NUDOCS 8703190148
Download: ML20207S225 (2)

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i MEMORAtMM FOR: Harold R. Denton, Director Office of Nuclear Reactor Regulation FROM: Daniel R. Muller, Acting Director Division of Site Safety and Environmental Analysis

SUBJECT:

METEOROLOGICAL MODEL FOR PART 100 EVALUATIONS The Regulatory Requirements Review Committee (RRRC) has considered proposed revisions to the Meteorological Model for Part 100 evaluations on several occasions, specifically in February 1977. Noverber 1977, and May 1978.

During the most recent meeting on this subject, May 2,1978, the staff discussed several alternatives of sector and overall probabilities for use in the Regulatory Guide being developed. Historical approaches were discussed in some detail as bases for the selection of the probability of t i

dispersion conditions in limiting sectors, and the overall limiting site probability level of 55 analogous to the SRP model was also discussed.

The staff presented infomation based on a parametric study of representative sites which indicated that the average of worst sector probabilities experi-enced in case review was about 0.6%. There was a considerable spread in the worst sector probability levels for the sites examined in the parametric study. In addition, the staff identified the relative contribution of both meander and variable exclusion area boundaries to anticipated changes In estimated dispersion conditions at the exclusion area boundary, and compared these changes to dispersion estimates produced by the SRP model.

At the conclusion of the RRRC meeting of May 2,1978, the staff views on what had been accepted, reconnended, or decided at the meeting varied, except that the staff should proceed with production of the standard and

preparation of a conoission Infomation Paper.

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Subsequent to the RRRC meeting, the staff of the Division of Site Safety and Environmental Analysis has further considered the sector average and the overall site probability level, concluding that the overall site probability specification was not necessary, and that detailed analysis of the parametric study results indicated a sector probability level of t 0.5% would accurately reflect the avernoe of the parametric study. These matters, and the numerous connents on the extensive and complex guide, have restrained, to some degree, progress in moving the guide into a more final form. Some major staff connents are included in memoranda from D. Bunch to H. Denton (dated June 19,1978) and 1.. Hulman to H. Denton (dated June 26,1978). The staffs of NRR and 050 have been proceeding with resolution of those connents which are within the context of the proposed guide. Detailed conrients for final wording of the guide are ready for transmittal to OSD.

While progress in guide development is being made, the resolution of the sector probability level, and the question of whether the overall site probability level should be included, have not been fully resolved. I therefore request that you approve the following positions for NRR;

1. A limiting sector probability level of 0.5% be used in the new model (the basis for this is described in the memo from L. Hulman to H. Denton on 6/23/78).

i 2. An overall site probability limit of 5% be retained. It may well be that this factor has no influence in practice, but it will provide a limit for sites where adverse dispersion is non-directional.

These would apply to the standard being prepared and to the Hydrology-Meteorology Dranch Technical Position on the sector dependent model.

ORIGINAL SIGG

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