ML20010F523
| ML20010F523 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 09/04/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| References | |
| TASK-02-02.C, TASK-2-2.C, TASK-RR LSO5-81-09-013, LSO5-81-9-13, NUDOCS 8109100314 | |
| Download: ML20010F523 (5) | |
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September 4, 1981 Docket No.50-029 A
Q, LS05-81-09-013
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Mr. James A. Kay 1'
Senior Engineer Licensing 3
Dgpuu Yankee Atomic Electric Cunpany 1671 Worcester Street
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Q Framingham, Massachusetts 01701
Dear Mr. Xay:
SUBJECT:
SEP TDPIC II-2.C. ATMOSPHERIC TRANSPORT AND DIFFUSI0fl CHARACTERISTICS FOR ACCIDENT ANALYSIS - YANKEE R0WE Enclosed is the staff's final evaluation of SEP Tppic II-2.C " Atmospheric Transport and Diffusion Characteristics for Accident Analysis" for Yankee Rowe. The staff has concluded that the values provided in your safety analysis dated June 30, 1981 are apprppriate. Therefore, the values provided in the enclosed evaluation are to be used for all accident radiological consequer:ce calculations.
This evaluation will be a basic input to the integrated safety assessment for your facility unless you identify changes needed to reflect the as-built conditions at your facility. This assessment may be revised in the future if your facility design is changed or if NRC criteria relating to this subject are' modified before the integrated assessment is completed.
Sincerely, Dennis H. Crutchfield, Chief 3
Operating Reactors Branch No. 5 Division of Licensing
Enclosure:
) ha As stated
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Mr. Jarres A. Kay cc Mr. Janes E. Tribble, President Yankee Atomic Electric Conpany 25 Research Drive Westborough, Massachusetts 01581 Greenfield Community College 1 College Drive Greenfield, Massachusetts 01301 Chairman Board of Selectmen Town of Rowe Rowe, Massachusetts 01367 Energy Facilities Siting Council 14th Floor One Ashburton Place Boston, Massachusetts 02108 U. S. Environmental Protection Agency Region 1 Office ATTN: EIS C0ORDINATOR JFK Federal Building Boston, Massachusetts 02203 Resident Inspector Yankee Rowe Nuclear Power Station c/o U.S. NRC Post Office Box 28 Monroe Bridge, Massachusetts 01350 l
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'f SEP TOPIC II-2.C ATMOSPHERIC TRANSPORT AND DIFFUSION CHARACTERISTICS FOR ACCIDENT ANALYSIS YANKEE R0WE I.
INTRODUCTION The safety objective of this review is to determine the appropriate on-site and near. te atmospheric transport and diffusion characteristics necessary to establish conformance with the 10 CFR Part 100 guidelines.
In particular, the short-term relative ground-level air concentrations (x/Q) are determined for use in estimating offsite exposures resulting from postulated accidents.
II.
REVIEW CRITERIA Section 100.10 of 10 CFR Part 100, " Reactor Site Criteria," states that meteorological conditions at the site and surrounding area should be considered in determining the acceptability of a site for a power reactor.
III. _RELATED SAFETY TOPICS Topic II-1.A, " Exclusion Area Authority and Control" provides the proper exclusion boundary distance over which the licensee has control.
Various section XV topics utilize the atmosphere dispersion coefficients to deter-mine the offsite radiological consequences of postulated accidents.
IV. REVIEW GUIDELINES The atmospheric dispersion factors were calculated usir.g a modified Gaussian dispersion model estoutlined below.
In order to account for the valley terrain at the site, dilution f actors were calculated asing a 10-sector downwind wind rose for both the EAB and LPZ.
For all winds from the S clockwise through WSW cardinal wind direction sectors, it was assumed that effluents would remain in the valley.
As such, winds from these four -
cardinal direction sectors were assumed to affect one upstream' downwind sector.
Likewise, winds from the N clockwise through ENE cardinal wind direction sectors were also assumed to remain in the valley and affect one
' downstream' downwind sector. Winds from the other eight cardinal wind direction sectors, W clockwise through NM4 and E through SSE, were assumed to be cross-valley flows which affected the E through SSE and W through NNW downwind sectors, respectively, f
The procedure for determining the dilution factors for the design basis accident evaluation reflects variations in atmospheric dispersion that occur as a function of wind direction frequencies and downwind receptor distances.
Dilution factors were compn 6 e for each sequential hour of measured meteorological data and for,ece tr.c3 positioned in each of the ten' downwind sectors. These hourly y!! r iv:
we.*e calculated using a mod-cutlined in Regulatory Guide 1.145.
ification of the Gaussian disper;b 3 e Plume centerline values were used to deturpine the short-term dilution factors 4
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(up through eight hours) and sector avarage values were used for the longer term dilution factors. The dispersion model for the plume centerline x/Q values considered the following effects:
- 1) Plume horizontai and vertical standard deviations were adjusted to account for building wake effects.
- 2) Lateral plume meander was allowed during periods of low wind speed and neutral and stable atmospheric conditions.
- 3) Lateral dispersion in the upstream and downstream downwind sectors was limited by the valley walls and included an increase in con-centration due to multiple eddy reflections from the valley walls.
In addition, the sector width used to determine the hourly sector average x/Q values for the upstream and downstream downwind sectors was adjusted to account for the limited lateral dispersion potential due to the valley walls.
V.
EVALDATION The staff has reviewed and evaluated the Yankee Atomic Electric Compcny's (licensee) assessment dated June 30, 1981. Meteorological data collected at the Yankee Rowe site from January 1, 1980 through December 31, 1980 were used to determine the atmospheric transport and diffusion characteristics.
Short-term x/Q values for a ground-level release have been computed for various time intervals at the exclusion area boundary (EAB), a circle with a radius of 3,100 feet, and the outer boundary of the low population zone (LPZ),
an approximately S-shaped boundary reflecting the fact that releases from the plant under certain meteorological conditions will raain within the Deerfield River valley.
Estimates of effluent plume dispersion and transport are complicated by the.
,' ant's location in the Deerfield River Valley whose sides rise over 800 feet above plant grade.
There is evidence that the 32-foot wind sensors are' r,
often affected by localized nocturnal drainage winds flowing down the east slope of the river valley, thus biasing the lower level wind rose frequencies toward the east. As such, the 196-foot wind direction values were used to determine whether the wind flow for any given hour followed the valley or was cross-valley. The 32-foot wind speed values were used in the analysis.
Vertical atmospheric stability was determined from the vertical temperature gradient between the 32-foot and 196 foot levels.
Horizontal atmospheric stability was defined by fluctuations of the 196-foot horizontal wind direction (sigma theta) when winds were greater than 1.5 meters per second (mps) and by the vertical temperature gradient between the 32-foot and 196-foot levels when the wind speed was less than 1.5 mps.
Using tbc hourly x/Q values calculated as described above, average x. Q values for each downwind sector were then determined for successive averlapping time intervals of 1, 2, 8, 24, 96, and 720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> corresponding to time periods
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of zero to one hour, one to two hours, zero to eight hours, eight to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, one to four days and four to 30 days, respectively, For each selected down-wind sector and interval size, the averaging process began with the.first hourly dilution value on record and was then repeated for the same interval size starting with each subsequent hour of dispersion data.
In the averaging process, the only non-zero values within a given time,'or the interval were interval which were considered in evaluating the average dilution factor f tnose hours during which the wind was blowing into the downwind sector of interest.
The averaged x/Q values were then classified into groups as a function of interval size and downwind sector, and corresponding cumulative frequency distributions of non-zero values for each group were prepared.
The x/Q value which was exceeded 0.5% of the total time was then determined from each group, and the maximum 0.5% downwind sector value from each time interval was chosen as the design-basis x/Q value for that time interval.
The follwing x/Q values were determined using the above model for an assumed ground level release for the various accident time intervals at the EAB and LPZ:
3 Time Periodt Distance & Direction CHI /O(sec/my 0-I hours EAB (3100 feet upstream) 2.8x10f 1-2 hours EAB (3100 feet downstream) 2.3 x 10-0-
8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> LPZ (2 miles upstream) 2.8x10j 8-24 hours LPZ (6 miles downstream) 1.9 x 10-5 24 - 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> LPI (6 miles downstream) 1.6 x 10 96 - 720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> LPZ (6 miles downstream) 20 x 10-5 The staff has carried out an independent analysis of the dispersion charac-teristics of the site.
This analysis has verified the adequacy of the applicant's relative concentrations for the exclusion area boundary.
For the non-circular LPZ however, the staff has not attempted to utilize the more sophisticated techniques used by the applic ant.
The staff was only able to calculate the relative atmosphere dispersion factors at the LPZ assuming. a straightline trajectory.
The shortest straight-line LPZ in the upwind sector is 1551 meters; the corresponding shortest straightline distance in the downwind sector is also 1551 meters.
Following the guidance in Regulatory Guide 1.145, the staff has calculated generally equivalent concentrations compared with those presented by the applicant, but at the smaller distances.
7 VI.
CONCLUSION The: staff concludes that the X/Q valves presented in Section V are appro-priate for estimating exposures from postulated accidents and should be used in all accident calculations.
This conforms to current licensing practi.ce, no additional SEP is required.
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