ML13333A344
| ML13333A344 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/08/1979 |
| From: | Ziemann D Office of Nuclear Reactor Regulation |
| To: | James Drake Southern California Edison Co |
| References | |
| TASK-02-02.C, TASK-2-2.C, TASK-RR NUDOCS 7902260199 | |
| Download: ML13333A344 (29) | |
Text
DISTRIBUTION NRC PDR Local POR ORB #2 Reading Docket No. 50-206 NRR Reading VStello RVollmer OELD OI&E (3)
DLZiemann 979 ABurger Mr. James H. Drake HSmith Vice President BGrimes Southern California Edison Company TERA 2244 Walnut Grove Avenue JRBuchanan Post Office Box 800 ACRS (16)
Rosemead, California 91770 DKDavis
Dear Mr. Drake:
Enclosed is a copy of our draft evaluation of Systematic Evaluation Program Topic II-2.C. You are requested to examine the facts upon which the staff has based its evaluation and respond either by confirming that the facts are correct, or by identifying any errors.
If in error, please supply corrected information for the docket.
We encourage you to supply for the docket any other material related to this topic that might affect the staff's evaluation.
Your response within 30 days of the date you receive this letter is requested.
If no response is received within that time, we will assume that you have no comments or c6rrections.
Sincerely, 0
nrgn e d b y Dennis L. Ziemann, Chief Operating Reactors Branch #2 Division of Operating Reactors
Enclosure:
Topic II-2.C cc w/enclosure:
See next page 790226099
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NRC FORM 318 (9-76) NRCH 0240 U.S. GOVERNMENT PRINTING oIce:
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cc w/enclosure:
Charles R. Kocher, Assistant General Counsel Southern California Edison Company Post Office Box 800 Rosemead, California 91770 David R. Pigott Samuel B. Casey Chickering & Gregory Three Embarcadero Center Twenty-Thi'rd Floor San Francisco, California 94111 Jack E. Thomas Harry B. Stoehr.
San Diego Gas & Electric Company P. 0. Box 1831 San Diego, California 92112 U. S. Nuclear Regulatory Commission ATTN:
Robert J. Pate P. 0. Box 4167 San Clemente, California 92672 Mission Viejo Branch Library 24851 Chrisanta Drive I Mission Viejo, California 92676 K M C, Inc.
ATTN:
Jack McEwen 1747 Pennsylvania Avenue, N. W.
Suite 1050 Washington, D. C. 20006
San Onofre Unit 1 Topic II-2.C Atmospheric Transport and Diffusion Characteristics The objective of this review is to determine the appropriate on-site and near-site 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 used to estimate offsite exposures resulting from postulated accidents.
Short term X/Q values for a ground level release have been computed for various time intervals at the exclusion area boundary (EAB),
varying over land from 283 meters to 1005 meters, and the outer boundary of the low population zone (LPZ), a circle with a radius of 2900 meters (Topics II-l.A and II-1.8).
Southern California Edison's meteorological data collected at the San Onofre site for three years (January.25, 1973 to January 25, 1976) were used.
Wind direction and speed were measured at the 10-meter level, and estimates of atmos pheric stability were based on vertical temperature dffferences (Topic II-2.8).
X/Q values were calculated in each of 16 downwind sectors for both the EAB and LPZ. However, the values considered in this analysis are those calculated for only the onshore sectors,
-2 The evaluation made use of a model that allows consideration of direction dependent diffusion conditions, wake effects, and effluent plume meander, as applicable. A wake factor of 800 square meters was used in the analysis. The model used is a modification of the calculational procedures described in Standard Review Plan Section 2.3..4 and is described in draft Regulatory Guide 1.XXX, "Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants", dated September 23, 1977. Our current position, established on August 2, 1978, modifies the model discussed in Regulatory Guide 1.XXX by changing the percentile at which the X/Q values are calculated in each sector from 0.3% to 0.5%. Based on the review of the onsite tracer program discussed in Topic II-2.3, we have concluded that the Regulatory Guide 1.XXX model is suitable for this site. The appendix to this evaluation contains our assessment of the onsite tracer program and the application of its data to calculate diffusion estimates for the site. Some of this work was performed for the Units-2 & 3 OL review.
The estimated 0-2 hour X/Q values will be exceeded on the average no more than 44 hours5.092593e-4 days <br />0.0122 hours <br />7.275132e-5 weeks <br />1.6742e-5 months <br /> per year (0.5 percent of the total time) and were cal culated at the EAB and LPZ for Unit 1 for each sector. Of the onshore sectors, the northwest downwind sector was found to have the highest X/Q values at both the EAB and LPZ. These values were used in the evaluation of short-term accidental releases and are listed below. (X/Q values for some overwater sectors at both the EAB and LPZ, which were excluded from the analysis, are greater than the maximum onshore sector values).
-3 SHORT-TERM RELATIVE CONCENTRATION VALUES APPLICABLE FOR ACCIDENT ANALYSIS SAN ONOFRE N.G.S. UNIT 1 Time Period Location X/Q (sec/meter 3 0-2 hours EAB 9.5 x 10-4 0-8 hours LPZ 2.6 x 10-5 8-24 hours LPZ 1.8 x 105 1-4 days LPZ 8.2 x 10-6 4-30 days LPZ 2.7 x 10-6 We conclude that.the meteorological data 'provided by Southern California Edison Company are sufficient for us to evaluate the local diffusion conditions applicable to the design of the San Onofre N.G.S. Unit 1.
We also conclude that the three years of onsite meteorological data together with the onsite atmospheric tracer test data provide acceptable bases for calculating the reasonably conservative relative concentration values of post-accident atmospheric diffusion conditions listed above.
This completes the evaluation of this SEP topic.
Since the plant conforms to current licensing criteria, no additional SEP review is required.
0 0
Appendix Evaluation of Onshore Atmosoheric Dispersog at the San Onofre Nuclear Generating Station During the review of the Sphere Enclosure Project for Unit 1, we concluded that without additional information the data collected on the site meteorological tower during 1973 and 1974 could not be used to estimate atmospheric diffusion conditions for the San Onofre vicinity. The data characteristics were anomalous compared to data from other sites we had reviewed. Differences included a very high occurrence of the unstable stability classes and average wind speeds decreasing with height.
To explain these anomalies, Southern California Edison (SCE) had presented several hypotheses concerning the relationships among the site meteorology, the complex local topography, and the site data collection system.
Eovever,.
SCE did not provide any supporting onlte data.
Thus we could not conclusively determine whether the anomalies were real and whether the permanent tower data could be used to estimate the site atmospheric diffusion conditions as described in Standard Review Plan (SRP) 2.3.4.
In the sphere enclosure review, we took the position that SCE should install additional towers to aid in defining the atmospheric diffusion characteristics of the site.
Until they presented information that substantiated site diffusion characteristics, we concluded that our diffusion estimates for short-term releases in the onshore directions should be based on the atmospheric conditions described in Regulatory Guide 1.4, Revision 2, "Assumptions Used for Evaluating the Potential Radiological Consequences
of a Loss of Coolant Accident for Pressurized Water Reactors".
For time periods less than eight hours, the condition is equivalent to Pasquill Stability Class P with a windspeed of one meter per second.
We judged that this condition would overestimate the relative concentrations that would be calculated using SRP 2.3.4 and representative site data.
Table 1 lists this diffusion estimate for Unit 1.
In response SCE told us they were designing an onsite atmospheric tracer program to meet the following objectives (Septoff, et al. 1976):
"1. to measure and characterize atmospheric dispersion to permit realistic calculations of short-term accident dispersion factors;
- 2.
to demonstrate the appropriateness of using bluff tower meteorology to estimate dispersion; and
- 3. to characterize dispersion under less restrictive atmospheric conditions representative of routine release meteorology."
In the program, the tracer gas was released under meteorological dispersion conditions which ranged from the "moderately restrictive" (moderate windspeeds and/or neutral atmospheric stability which produce average dilution) to "least restrictive" (high windspeeds and/or unstable atmospheric stability which produce the most dilution).
Tests were also to have been run during "most restrictive" conditions (low windspeeds and/or stable atmospheric stability which prqduce little dilution); however, these periods were not successfully sampled.
Tracer gas concentrations were sampled on arcs 300 and 700 meters from the release points (at Unit 1 and Unit 2).
Meteorological measurements were made at eight towers within the vicinity of the plant.
Primary test measurements of wind speed and direction, standard deviation of wind direction, and temperature difference were made at the permanent onsite 4 0-meter bluff tower and at a 4 0-meter tower located 700 meters inland.
Atmospheric stability was determined by the vertical temperature gradient in accordance with Regulatory Guide 1.23, "Onsite Meteorological Programs".
In our operating license review for Units 2 and 3, we concluded that our evaluation procedures for this site should provide estimates of the varia tions-in atmospheric dispersion that occur as a function of wind direction and distance from the source to receptor. Certain air flow directions can exhibit substantially more favorable diffusion conditions than others, and the wind can transport effluents in certain directions more frequrently than others.
SRP 2.3.4 procedures involve the use of onsite meteorological data in a direction-independent model to estimate atmospheric diffusion conditions which occur no more than five percent of the time (438 hours0.00507 days <br />0.122 hours <br />7.242063e-4 weeks <br />1.66659e-4 months <br /> per year) around the site at a distance equal to the minimum exclusion area boundary distance.
An interim staff Branch Technical Position,-approved by the Regulatory Requirements Review Committee at their May 2, 1978 meeting, allows the use of either this direction-independent approach or the direction-dependent approach as outlined in the draft Regulatory Guide 1.XXX, "Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear
Power Plants", September 1977.
The direction-dependentiapproach considers reduction of plume concentration due to enhanced lateral plume spread, variation of meteorological conditions by direction, and variable exclusion area boundaries.
In our evaluation of short-term diffusion estimates, we modified the calculational procedures described in SR2 2.3.4 by using the approach outlined in the draft guide.
SCE also used this direction-dependent approach as outlined in Appendix C of Septoff, et al. (1977).
One objective of our independent evaluation of the site tests was to determine whether a reduction of concentration equivalent to the enhanced lateral plume spread factors of the draft guide could be used for the site short-term diffusion evaluation.
We thus evaluated the test data, attempting to correlate the bluff tower data to the measured tracer concentration data.
Our NOAA consultant also reviewed the test data and his conclusions are in Attach ment A.
'Nearly 40 test runs were successful ranging over the unstable and neutral stability classes (A-D). Unfortunatelyduring the testing period stable onshore flow occurred much less frequently than observed historically; and no successful test run was made during stable atmospheric diffusion conditions (E, F, G).
For near-ground level releases, these conditions generally produce the poorest atmospheric dispersion, and are the conditions of prime interest for short-term (SRP 2.3.4) diffusion estimates.
Due to this shortcoming of the tests, we attempted to extrapolate concentration estimates for the stable classes from the measured data.
Looking at the data as a function of atmospheric stability alone, Figure 1 indicated that normalized peak concentrations measured during Class D stability were within the same range as those in Class A.
CNormalized concentration, Iu/Q, is a measure of the atmospheric dilution and is concentration, X, normalized for source strength, Q, and the average 10-meter wiadspeed, u.)
Classically, as stability increases (i.e., going from Class A to G), normalized concentrations for a ground-level release should increase. However, no pattern was evident from which we could conclusively extrapolate concentrations for the stable classes from the onsite tracer data measured during unstable and neutral conditions.
Because the San Onofre site data alone were not sufficient to predict onsite diffusion during stable atmospheric conditions, we compared the available ousite tracer data to data obtained in other tracer tests.
Over the past few years, other atmospheric tracer tests were run at various locations in the United States. Van der Haven (1976) summarized several test series conducted during periods of poorest atmospheric dispersion (low windspeeds and stable atmospheric conditions).
These tests.were run at inland sites in varied terrain, but without the presence of buildings.
In 1975, tests were conducted at the Rancho Seco Nuclear Station to determine
the effect buildings would have on concentrations (Start, et al.,
1977).
The staff evaluation of the Rancho Seco tests were included in the develop amt of draft Regulatory Guide 1.=.
These tests demonstrated that during A
periods of low windspeeds and a stable or neutral atmosphere, measured concentrations were lower than those predicted using traditional Pasquill Gifford dispersion coefficients (Gifford, 1968).
The tests reviewed by Van der Hven (1976) also support this conclusion.
To account for this observation, one facet of the draft guide allows reductions of calculated concentrations.
But in developing the draft guide, only that amount of extra dispersion (above the tradition coefficient values) attributed to the lateral plime spread dispersion coefficients was,used to reduce the traditionally derived concentrations.
(?lme concentration is a function of both lateral and vertical plume spread.)
In the draft guide we did not include the extra mixing attributable to the vertical plume spread, because we could make no specific generic conclusions.
Due to this potential extra vertical mixing, predicted concentrations using the draft guide would still tend to over-predict measured concentrations.
Inherent in the reduced values are the contributions of both thermal and mechanical turbulence.
The amount contributed by each cannot be readily separated from the test data.
Simply expressed, little mixing of the air occurs when cooler (heavier) air underlies warmer (Lighter) air, i.e., when the air is thermally stable.
Mixing occurs when the air is thernall.y
unstable, with rising warm (lighter) air displacing cooler (heavier) air aloft.
As air flows over an obstacle (such as a building or a bluff),
mechanical turbulence is generated that will better mix an effluent released near the obstacle compared to an effluent released in an open area.
This is often called the "building wake" effect.
At the San Onofre site, both the coastal bluff and the'plant structures contribute to the mechanical turbulence.
At Rancho Seco the plant structures are the primary mechanical turbulence generators.
Figures 1-4 of Attachent A show the comparison between the Rancho Seco data and the San Onofre data.
The solid line on the figures represent traditionally derived values for a ground-level release using the Pasquill-Gifford dispersion coefficients for the given stability class.
We concluded that there was a general agreement between the normalized concentration data from the two sites.
le analyzed the San Onofre data in a manner similar to our analysis of the Rancho Seco data for the draft Regulatory Guide 1.I, evaluating only the lateral plume spread component.
Figure 2 shows the ratio of observed lateral plume spread (Zyobs) to Pasquill-Gifford lateral plume spread (ZyG) versus the 10-meter wind speed.
The solid line is the concentration reduction factor developed from the Rancho Seco tests for the draft guide.
No reduction was justifiable for Stability Class A.
For most
0 cases of Stability Class D, the draft guide allows less concentration reduction than observed in the San Onofre tests.
More reduction was apparent as stability increases (from Class A to Class D).
We conclude that using the draft Regulatory Guide 1.= reduction factors would produce a conservative assessment for our short-term (SRP 2.3.4) diffusion estimates.
We based this on the following:
- 1. For the unstable and neutral stability classes for which we could compare San Onofre and Rancho Seco data, the normalized concentrations and lateral plume spread parameters were similar.
- 2.
More concentration reduction is apparent as stability increases for the Rancho Seco tests and those at other sites;*this is true for the unstable and neutral cases for the San Onofre site and we expect this pattern to occur in the stable classes for San Onofre.
- 3.
Because we had not considered reduction for the total plime concentration (both vertical and lateral), we would still overestimate plume concentrations using only a lateral plum spread reduction factor.
In December 1977, we met with SCE to discuss our assessment of the tests and application to short-term-diffusion estimates. Their analysis of the tests and application to short-term diffusion estimates is described in Appendix C of Septoff, et al. (1977). Our assessment for Unit 1 using the draft guide methodology resulted in an estimated relative concentration
(X/Q) value about eight times greater than SCE's estimate for the exclusion boundary that had the maximum X/Q value (the northwest sector at 285 meters) (see Table 1).
SCE claimed that our analysis was overly conservative. A basic difference existed in the statistical techniques we each had used to evaluate the test data:
SCE based their results on the mean of the data, whereas we used an enveloping technique that encompassed most of.the data. Further, SCE has considered the full plume, whereas we had limited our analysis to the lateral plume spread.
Because in past case reviews of tracer tests we had considered the full plume, we agreed to reanalyze the data using our enveloping technique to consider the full plume and to allow full plume reduction if we determined it justifiable.
We reanalyzed the data using the ratio of traditionally predicted normalized concentration to measured normalized concentration (thus analyzing the full plume).
Figure 2 shows these ratios versus windspeeds.
Again, no reduction was considered justifiable for Stability Class A.
For Stability Class D, a reduction of concentration by a maximum of a factor of 10 appeared reasonable, yet enveloped the data.
To account for the lack of onsite tracer data during stable conditions, we assumed that the total reduction factor for Stability Classes E, F, and G would be the same as we observed for Class D.
As noted above, this ratio inceased with increasing stability for test data at other sites, again maning that the traditional methodology overestimated concentrations more for Class G than Class D.
But by keeping this ratio constant, we concluded
that application of our evaluation should still overpredict actual concentrations in the site vicinity.
Figure 4 shows the total plume reduction factor we derived for the San Onofre site; the figure also shows the reduction factors used in the draft Regulatory Guide 1.= (Figure 3 of the draft guide).
We consider that using the total plume reduction factor is meteorologically reasonable for the San Onofre site.
Boweve; because test data during stable cases are not available to verify this conclusion, we have used the draft guide reduction factors for estimating the short-term diffusion. We would consider using total plume reduction factors with the draft guide method ology if further data obtained in the future substantiates doing so.
Table 1 lists the short-term (0-2 hour) relative concentration values estimated using the techniques we have described.
These models were:
(1) Regulatory Guide 1.4; (2) draft Regulatory Guide 1.=;
(3) draft Regulatory Guide 1.=I, but with Figure 3 of the draft guide replaced with the site-derived total plume reduction factors of Figure 2.3.A-4; and (4)
SCE Appendix C of Septoff, et al. (1977).
In our evaluation of Topic II-2.B, we used the onsite meteorological tower data provided by-SCE.
The tracer program led to our conclusjon that using these data to calculate diffusion estimates with the draft Resulatory Guide 1.XXX model with or without site-derived reduction factors would overpredict concentrations for neutral and stable conditions.
Likewise assuming a around level release, :he
model described in Regulatory Guide 1.111, "Methods for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors", would also overpredict annual-average ground level concentrations.
Thus, we have concluded that although the onsite meteorological data appeared anomalous compared to other sites, it can be used to estimate site atmospheric diffusion conditions using the draft Regulatory Guide 1.XXX and Regulatory Guide 1.111 models.
References Gifford, F. A., Jr., 1968:
"An Outline of Theories of Diffusion in the Lower Layers of the Atmosphere", Chapter 3, Meteorology and Atomic Energy, 1968.
TID-24190, National Technical Information Service, -Springfield, Virginia Septoff, M., Mitchell, A. E.,
and L. H. Teuscher, 1976: NUS-2002, The Design of an Onshore Tracer Program at the San Onofre Nuclear Generating Station.
NUS Coporation, Rockville, Maryland.
1977: NUS-1927, Final Report of the Onshore Tracer Tests Conducted December 1976 Through March 1977 at the San Onofre Nuclear Generating Station.
NUS Coporation, Rockville, Maryland.
Start, G. E., Cate, J. R., Dickson, C. R., Ricks, N. R., Ackrnmann, G..R.,
and J. F. Sagendorf, 1977:
Rancho Seco Building Wike Effects on Atmos pheric Diffusion.
NOAA Technical Memorandum EEL ARL-69, Air Resources Laboratories, Idaho Falls, Idaho.
U. S. Atomic Energy Commission, 1972:
Regulatory Guide 1.23, Onsite Meteorological Programs.
U. S. Nuclear Regulatory Commission, Office of Standards Development,. Washington, D. C.
U. S. Atomic Energy Commission, 1974:
Regulatory Guide 1.4, Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss of Coolant Accident for Pressurized Water Reactors, Revision 2.
U. S.
Nuclear Regulatory Commission, Office of Standards Development, Washington, D. C.
U. S. Nuclear Regulatory Commission, 1977:
DRAFT Regulatory Guide 1.=,
Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants.
U.S.N.R.C.
Office of Standards Development, Washington, D. C.
1977:
Regulatory Guide 1.111, Methods for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors.
USNRC Office of Standards Development, Washington, D. C.
Van der Hoven, 1., 1976:
A Survey of Field Measurements of Atmospheric Diffusion Under Low-Wind Speed Inversion Conditions.
Nuclear Safety, March-April 1976, Vol. 17, No. 4
0 0
TABLE 1 SHORT-TERM RELATIVE CONCENTRATION VALUES CALCULATED FOR THE SAN ONOFRE N.G.S.
UNIT 1 BY FOUR METHODS The values are short-term (0-2 hour) relative concentration (X/Q) values calculated for releases from Unit 1. The values are for a distance of 285 meters northwest from the Unit buildings (the downwind sector with the maximum X/Q values).
The four models are:
- 1) that described in Regulatory Guide 1.4; 2) that described in draft Regulatory Guide 1.XXX;
- 3) that described in draft Regulatory Guide 1,XXX, but with Figure 3 of the draft guide replaced with the site-derived plume concentration reduction credits of Figure 4; and 4) that described in Appendix C of Septoff, et al (1977).
Model X/Q (seconds/cubic meter)
- 1. Regulatory Guide 1.4 1.8 x 10-3
- 2. Draft Regulatory Guide 1.XXX 9.5 x 104
- 3. Draft Regulatory Guide 1.XXX amended 5.2 x 10
- 4. Appendix C 1.2 x 104
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ATTACHMENT A -
U.S. DEPARTMENT O COMMERCE National Oceanic and Atmospheric Administration ENVIRONMENTAL RESEARCH LABORATORIES Silver Spring, Maryland 20910 May 27, 1977 R32 Mr. Earl R. Markee Nuclear Regulatory Commission Division of Site Safety and E.nviromental Analysis Washington, DC 20555
Dear Earl,
In response to your request for a review of the preliminary draft of the NUS report on the on shore tracer tests, I would like to submit -the comments which follow.
I think the key question which remains somewhat unanswered is what happens during stable onshore flow as measured by AT/dz or sigma theata from the bluff tower.
As it stands, only unstable and neutral conditions existed (dT/dz criteria) during the tests and one case of slightly stable existed when sigma theta was u.ed to classify stability.
It, therefore, might be useful to compare the results of the Rancho Seco building waka study (which contained many stable cases) with that of the San Onofre study.
The enclosed figures 1 through 4 is a plot of the observed peak concentrations at the various arcs for the two sites.
?asq.u"il conditions A and D as defined by AT/iz are shown and the data are separated into ground and elevated releases.
The curves are not corrected for building wake.
I would draw the following conclusions:
- 1.
There appears to be general agreement between the data from the :wo sites, despite the rather marked difference in terrain because of the shoreline bluff at San Onofre.
- 2.
The San Onofre data show little difference between ground and "elevated" releases.
- 3.
There does not seem to be any reason to give additional dilution credit for the Type A cases.
- 4.
There appears to be a definite element of over-prediction for the neutral cases, even if the cA factor were used.
V4)
-2 T6 further develop conclusion 1, it might be useful to look at some of the stable cases for the Rancho Seco test series.
The tendency seems to be that the more stable the condition, the greater the over-predicion it the AT/Az criteria are used to determine the diffusion type.
Fig. 5 is an example for type G, ground release for Rancho Seco.
The points close to the G curve are tests 57 and 87 which were towards the higher terrain.
I would, therefore, conclude that the San Onofre site would show the same tendency of over-prediction.
It is of interest to note that in the case of the San Onofra tests, the sigma theta criteria over-predicts concentration to the same degree that AT/Az does.
Sincerely, Isaac Van der Hoven Air lescurces Laboratories Inclosures as stated cc:
R. Abbey, RC, RES, v/enclosures J. Goll, NRC, MWR, w/enclosures
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