ML19221A952
| ML19221A952 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-02.3.4, NUREG-75-87, NUREG-75-87-2.3.4, SRP-02.03.04, SRP-2.03.04, NUDOCS 7907120035 | |
| Download: ML19221A952 (5) | |
Text
NU R EG-75/087 fpR Ricg%o
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't U.S. NUCLEAR REGULATORY COMMISSION be(h> o,(
oj j STANDARD REVIEW Pi AN
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OFFICE OF NUCLEAR REACTOR REGULATION SECTION 2.3.4 SHORT TERM DIFFUSION ESTIMATES
_ REVIEW RESPONSIBILITIES Frimary - Site Analysis Branch (SAS)
Secondary - Accident Analysis Branch (AAS) 1.
AREAS OF REVIEW Information is presented by the applicant and reviewed by the staf f concerning atmospheric diffusion estimates for ace W tal relenes of ef fluent; to the atmosphere. The feview covers the following specific areas:
1.
Atmospheric diffusion rrodels to calculate relative concentrations for accidental radioactive and toxic gas release modes as determined by Accident Analysis Branch, 2.
Meteorological data summaries used as input to diffusion models.
3.
Derivation of dif fusion parameters f rom meteorological data.
4 Probability distributions of relative concentrations.
5.
Relative concentrations used for assessment of consequences of radioactive releases for design basis (10 CFR Part 100) accidents, e. site and of fsite toxic gas releases, and accidents that result in linited releases of radioactivity.
II.
ACCEPTANCE CRITER_IA This section
.1 be acceptable if the applicant has provided conservative estimates of atmospheric diffusion at appropriate distances from the source for postulated accidental releases of rad cactive and toxic materials to the atmosphere considering the plant as both a source and a receptor. Guidelines for acceptability of nodels and conservatisa appropriate to design basis calculations are Regulatory Guides 1.3, 1.4, 1.5 1.24 e
1.25, and 1.77; National Oceanic and Atmospheric Administration (NOAA) Tect..
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randum ERL ARL-42; standard references such as " Meteorology and Atomic Energ G"
and Arcident Analysis Branch and Site Analysis Branch positions. Since the staff makes USNRC STANDARD REVIEW PLAN si.nd.rd review piene e,. pr.p.,od for th. g.+ dent. af the o<fic. of Nuci r R osetor Reguistion et eef respor o.oie fo, the rewow of appuce, ion. to conet, vet.nd epeesto nwc6eer power plente These documente are me$e avaalebte to the pubhc os part of the Commesseon a pobey to inform the nucleer endustry and the genered puebMc of regulatory proceduree and poht.ee Standard rewow plane are not ouberrtutes for reguistory guidea or the Cornmeseson a reguistione and cc mphence weth them se not required The etendeed rewow pren sect 6one are keyed to Rowenon 2 of the Standard Format sad Content of Safogy Ame4yees Reports for Nucieer Power Pfents Not est sectione af the Standard Formet have e correspond *ng reweew plan.
Pubbehed stenderd rewow piene wvH be rewood pertodocelly, es appropnete, to accommodate commente and to reflect new hformatsn ered espertence Commente ensf Suggest3one for Improvement wtH be considered Snd should be sent to the U S Nucleer Reguietory Commession. Office of Nucteer Reactor Regwietton INeehengton D C 20ME gna uvv 7907129935
an independent evaluation of atmospheric diffusion estimates Msed on data from the onsite meteorological measurements program and other nearby neteorologic_ data, it is not neces-sary for the applicant to duplicate the staf f's final estimates. However, the applicant's diffusion estimates should reasonably reflect staff positions and state-of-the-art atmospheric diffusion knowledge. Specifically the following information is reouired:
1.
The atmospheric diffusion models used by the applicant to calculate relative con-centrations resulting from accidental airborne releases of radioactive and toxic gases must be documented in detail and substantiated so that the staff can evaluate their appropriateness to site and plant characteristics.
2.
Meteorological data summaries to be used as input to the diffusion models must be pre ;cr.ted in joint frequency distribution fem. These tumraries must have been generated from the isest available annual periods of data on record and contain data acceptable to the staff which represent appropriate hourly values of wind direction, wind speed, and atmospheric stability for each mode of accidental release.
3.
The atmospheric fiffusion parameters, such as lateral and vertical plume spread (o and c,) as a function of distance and windspeed, must be related to measured meteorological parameters and substantiated as to their validity and degree of con-servatism for use in estimating the consequences of " cidents within the range of distances which are of interest for the plant.
4.
Cumulative frequency distributions of relative concentrations (X/Q) based on mode of release over appropriate time periods and on the aforementiored atmospheric diffusion models, meteorological data summaries, and atmospheric diffusion para-meters must be presented for appropriate distances such as the site boundary distance and the outer boundary of the low population zone as specified in Section 2.3.4.2 of the " Standard Format and Contents of Safety Analysis Reports for Nuclear Power Plants," Revision 2.
The methods of generating these distributions must be adequately described.
5 Relative concentrations used for assessment of consequences of radioactive releases for design basis (10 CFR Part 100) accidents, for onsite and offsite releases of toxic gases, and for radioactive releases resulting from other accidents must be presented.
III. REVIEW PROCEDURES 1.
Atmospheric Diffusion Models The applicant's diffusion models are compared to the general Gaussian models which are contained in Regulatory Guides 1.3 and 1.4 for elevated releases and ground level releases with a wake correction (see also Reference 3). The suitability of the models for mode af release, plant configuration, and site topography are re-viewed. Accident Analysis Branch defines the modes of release and accidents to be considered.
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2.3.4-2
A determination is made as to whether the release should be considered as an elevated point source or a ground level point source with a volumetric correctica for turbu-9 lent mixing in the wake of buildings. Generally the release is considered to be elevated if the release point is at least twice as high as nearby solid structures.
Oth;r se. a ground level volumetric release formulation is usually used. The volumetric scrrection is usually based on 1/2 the minimum cross-sectional area of the structate from which the effluent is released.
Ros' atcidc d releases are considered a, continuous releases (i.e., >5 minutes duration). However, in some instances, usually with explosions resulting in the release of toxic chemicals, the releases may be considered as instantaneous (puffs).
For puff releases, instantaneous point source Gaussian diffusion equations are used with a correction for initial source volume (Ref.10).
If a site is located such that the horizontal (or vertical) plume spread via dif-fusion is restricted by topography (or unusual metenrological conditions), the models are examined for appropriate modification. Some of these conditions are narrow, deep valleys, " fumigation" from elevated sources, and low level subsidence inver-sions of temperature in the vertical direction.
2.
Meteorological Data Summaries The data sumaries in joint frequency distribution form are reviewed for compata-bility of data with the models utilized in the section above. General criteria are stated in Regulatory Guide 1.23 and in III.2 of Standard Review Plan 2.3.3.
3.
Atmospheric Diffusion Parameters Horizontal and vertical plume spread parameters, o and a, as functions of distance and atmospheric stability are reviewed. The current procedurc is to relate c (X)y and g (X) to vertical temperature difference classes as stated in Table 1 of Regu-iatory Guide 1.23.
Departures from this procedure are reviewed for adequate justifica-tion. Such departures may be appropriate in the case of unusual sites (e.g., valley or coastal). The curves of and a with distance, which appear in " Meteorology and Atomic Energy - 1968" are usually acceptable with the addition of a G stability class.
In instances when a puff diffu' ion equation is used, c, = a is usualiy a good assumption.
4.
Cumulative Frequency Distributions of X/Q A check is made vr the cumulative frequency distributions for inclusion of pertinent modes and time periods of release, and adequacy of input data in accordance with the guidelines set forth in Section 2.3.4.2 of the Standard famat. The methods used to generate these distributions are reviewed for adt w a y and conservatism.
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2.3.4-3
5.
Relative Concentrations Used for Accidents The X/Q values used for assessment of consequences of radioactive releases for design basis accidents, for onsite and offsite releases of toxic gases, and for radioactive releases resulting from other accidents are reviewed for appropriate-ness and completeness of infomation.
An independent calculation of the probability distributions of X/Q is made for pertinent distances (usually the exclusion area boundary and the low population zone outer boundary, LPZ) using the computer program CHI /Q (Ref. 11) and the. joint fre-quency distribution data for input. The nest restrictive annual average X/Q values are also computed at the site boundary and the LPZ using the same progran and input data. For assetsment of tne consequences of design basis accident releases, the value of X/Q at the "5% level" (value which is exceeded 5% of the time) is evaluated at the exclusion bourdary and the LPZ. These values ara assumed to represent condi-tions for a two-hour period. X/Q valJes for time periods greater than two hours are estimated for the LPZ distance by assuming a logarithmic relationsnip betwoen the "two-aour" value and the annual average value.
Conservative (5t) values of X/Q from appropriate models for appropriate time intervals and distances are transmitted to AAB for dose assessment of design basis accidents.
For assessment of other accidents, the median (50!) values of X/Q for appropriate time intervals and distances (usually the site boundary) are evaluated and trans-mitted to AAB.
X/Q values based on site-specific meteorological data are calculated, as needed, for control room dose calculations and onsite and offsite releases of toxic gases.
These estimates are made on a case-by-case basis since the mode of release and,
therefore,the diffusion models vary.
IV.
EVALUATION FINDINGS The reviewer verifies that adequately conservative atmosoheric diffusion models, with adequate onsite meteorologicai data as input to the xdels, have been used to calculate relative concentrations at appropriate distances and directions from pcstulated release points during accidental airborne releases of pr tentialiy hazardous ma erials. If adequate onsite meteorological data are not availaDle for the Construction pemit review, the reviewer must assure that adequate conservatism has been applied to the calculated relative concentrations for accident 31 airborne effluent releases based on available data.
Tha reviewer's evaluation must support the following type of concluding statement, to be used ir the staff's safety evaiuation report:
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i 2.3.4-4
"Conser va ti va assessments of post-accident atmospheric dif fusion conditions have been nade by the staff from the applicant's meteorolugical data and appropriate diffusion models."
The input to the safety evaluation repcet will also include a brief sucriary of the rela-tive concentrations (X/Q) calculated by the staff, reference to diffusion models used, and a conparison between the values computed by the staff and the applicant.
V.
REFERENCES 1
Regulatory Guide 1.3, " Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss-of-Coolant Accident for Boiling Water Reactors."
2.
Regulatory Guide 1.4, "Assunptions Used for Evaluating the Potential Radiological Consequences of a loss-of-Coolant Accident for Pressurizcd Water Reactors."
3.
Regulatory % ide 1.5, " Assumptions Used for Evaluating the Potential Radiological Consequences of a Steam Line Break Accident for Boiling Water Reactors."
4.
Regulatory Guic'e 1.23, "0nsite Meteorological Programs."
5.
Regulatory Guide 1.24, " Assumptions Used for Evaluating the Potential Radiological Consequences of a Pressurized Water Reactor Gas Stnrage Tank Failure."
6.
Regulatory Guide 1.25, " Assumptions Used for Evaluating the Pctential Radiological Consequences of a Fuel Handling Accident in the Fuel Handling and Storage Facility for Boiling and Pressurized Water Reactors."
7.
Regulatory Guide 1.70, " Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants," Revision 2.
Pegulatory Guide 1.77, " Assumptions Used for Evaluating a Control Rod Ejection u
Accident fnr Pressurized Water Reactors."
9.
- 9. H. Slade (ed.), " Meteorology and Atomic Energy - 1968," TID-24190, Division of Tec.5nical Information, USAEC (1968).
10.
G. R. Yanskey, E. H. Markee, and A. P. Richter, "Climatography of the National Reactor Testing Station," 100-12048, Idaho Operations Office, USAEC (1966).
11.
J. F. Sagendorf, "A Program for Eva; ating Atmospheric Dispersion From A Nuclear Powcr Station," Technical Memorandum ERL ARL-42, National Oceanic and Atmospheric Adn.inistration (1974).
145 26fM 2.3.4-5