ML20037D227
| ML20037D227 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/19/1981 |
| From: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-02-02.C, TASK-2-2.C, TASK-RR A01452, A1452, NUDOCS 8105220320 | |
| Download: ML20037D227 (4) | |
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s Ma 9 1981 Docket No. 50-245 A01452 Director of Nuclear Reactor Regulation Attn:
Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch #5 U. S. Nuclear Regulatory Commission Washington, D.C.
20555
References:
(1)
D. G. Eisenhut letter to SEP Plant Licensees, dated January 14, 1981.
(2)
W. G. Counsil letter to D. G. Eisenhut, dated February 27, 1981.
Gentlemen:
1 Millstone Nuclear Power Station, Unit No. 1 SEP Topic ll-2.C, Atmospheric Transport and Diffusion Characteristics As part of the redirection of the Systematic Evaluation Program, Reference (1), Northeast Nuclear Energy Company (NNECO) committed to develop Safaty Assessment Reports (SAR's) for certain SEP tcpics which would be subnitted for Staff review. NNECO detailed this connitment and provided a schedule for submittal of SAR's in Reference (2).
In accordance with this commitment, NNECO hereby provides the Safety Assessment Report for SEP Topic ll-2.C, Atmospheric Transport and Diffusion Characteristics, which is included as Attachment 1.
We trust the Staff will appropriately use this information to develop a Safety Evaluation Report for this SEP topic.
Very truly yours, NORTHEAST NUCLEAR ENERGY C ANY
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. N(./A W. G. Counsil Senior Vice President 4o55 8105220300 f
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MILLSTONE NUCLEAR POWER STATION, UNIT NO. 1 SEP SAFETY ASSESSMENT REPORT Topic ll-2C - Atmospheric Transport and Diffusion Characteristics 1.0 Introdu-tion The objective of this topic is to review on-site and near-site atmospheric transport and diffusion characteristics necessary to establish conformance with the 10 CFR Part 100 guidelines, using present modeling guidance and recent meteorolo'ical data.
2.0 Criteria Ihe short-term relative concentrations (X/Q) for ground-level and elevated accident releases are calculated using meteorological data from the past five years and the atmospheric dispersion models specified in Regulatory Guide 1.145.
A brief histroical note is important to this topic. Millstone is a multiple-unit site: Unit 1 began operating in 1970, Unit 2 in 1975, and Unit 3 is expected to begin operation in 1986. Initial collection of preoperational meteorological data for Unit 1 began in 1966, using a small (40m) meteorological tower witn instrumentation of relatively low sensi-tivity. In 1973, this was replaced by the present, taller (136m) tower and more sensitive instruments, meeting the specifications of Regulatory Guide 1.23.
Atmospheric diffusioa modeling also went through evolutionary cycles, from preliminary versions of Regulatory Guides 1.3 and 1.4, through various NRC branch positions, to the present Regulatory Guide 1.145.
Over the years since 1967 a number of different diffusion calculations have thus been made for different release points at different units, for backfit structures such as the Unit 1 Offgas Treatment Building, and with different meteoro-logical data bases from different towers, using several different sets of modeling guidelines.
3.0 Discussion This evaluation of short-term X/Q values at the Millstone site uses five l
years (January 1975 - December 1979) of onsite meteorological data from tall tower, which meets the requirements of Regulatory Guide 1.23.
For postulated ground level releases from the Offgas Treatment Building, the l
only ground level release point for Unit 1, wind speed and direction are l
taken from the 10m level. Horizontal and vertical atmospheric stability are determined from the vertical temnerature gradient between the 10m and 40m levels. For postulated elevateo.eleases from the Unit 1 Stack, the only elevated release point, wind speed and direction are taken from I
the 136m level. Horizontal atmospheric stability is determined from the 136m wind direction variance, and vertical atmospheric stability is determined from the vertical temperature gradient between the 10m and 136m levels.
l The atmospheric dispersion model used in this evaluation is essentially that described in Regulatory Guide 1.145, which incorporates the results of recent atmospheric tracer tests and whicn considers atmospheric dis-persion conditions as a function of downwind direction. Specifically, th's l
direction-dependent model considers the following effects:
(1) For postulated ground-level releases, lateral plume meander as a function of atmospheric stability, wind speed, and distance from the source, during periods cf low wind speed l
and neutral or stable atmospheric conditions;
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(2) Exclusion area boundary distance as a function of downwind direction from the plant; (3) Atmospheric dispersion conditions when the wind is blowing in a specific direction, and (4) The fraction of time that the wind can be expected to blow into each of the 16 compass directions.
The ~following X/Q values (the ~aighest for any of the five years) were deter-mined using this model for an assumed ground level release from the Offgas Treatment Building for various time periods at the exclusion area boundary (EAB) and the outer boundary of the low population zone (LPZ):
Time Period Receptor (Distance. Direction)
X/Q(sec/m )
0-2 hours EAB (566m, ENE) 5.28 E-04 0-8 hours LPZ (3860m, SSW) 4.76 E-05 8-24 hours LPZ (3860m, SSW) -
4.00 E-06 1-4 days LPZ (3860m, SSW) 1.95 E-06 4-30 days LPZ (3860m, ENE) 1.12 E-06 The following X/Q values (the highest of any of the five years) were determined using-the model for an assumed elevated release from the ll4m Unit 1 Stack for various time periods at the EAB and the oater boundary of the LPZ:
3 Time Period Distance and Direction X/Q sec/m 0-2 hours EAB (1677m, N) 1.75 E-06 (non-fumigation) 0-4 hours EAB (496m, NE) 9.90 E-05 (fumigation) 0-8 hours LPZ (3860m, NNW) 1.82 E-06 8-24 hours LPZ (3860m, NNE) 2.36 E-07 1-4 days LPZ (3860m, SE) 1.75 E-07 4-30 days LPZ (3860m, SE) 9.24 E-08 Both ground level and elevated X/Q values are reasonably consistent with those calculated before at various times in the past, using different meteorological data bases and modeling. guidance.
4.0 Conclusions The method used to calculate these X/Q values conforms to current licensing criteria. These values are less limiting than thcse used in the accident analyses, therefore no further action on C.is topic is planned.