ML20141D301

Discusses Peer Review of Updated building-wake Model Held on 940510 in Washington,Dc

ML20141D301
Person / Time
Site:	Point Beach
Issue date:	05/20/1994
From:	Ramsdell J Battelle Memorial Institute, PACIFIC NORTHWEST NATION
To:	Jun Lee NRC (Affiliation Not Assigned)
Shared Package
ML20141D306	List: ML20141D301 ML20141D314 ML20141D327 NUREG/CR-5055, Informs of 970422 Telcon Re Plant,Unit 1 & 2 Applicability of NUREG/CR-5055, Atmospheric Diffusion for Control Room Habitability Assessments. Ltrs from Pnl & 0823 Encl
References
NUDOCS 9705200060
Download: ML20141D301 (4)

Text

. .. . - . . _ . . . . .

j OBaHelle

, , Parific Norihweu taboratorie6 aseienes wi m ia e o e.. m a.c hia ad. wa.h.ocio., ,93 Mecheae #6m376-8626 May 20,1994 1 .

j Mr. Jay Y. Lee Radiation Protection Branch Office of Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555-0001

Dear Jay:

Peer review of the updated buildmg wake model was held in the Bartelk: offices at 901 D St. SW.

' Washington DC on May I 10, 1994 The peer review panel consistad of J irdividuals selected from the list of potential reviewers verbally approved by you on April 3.1994. The panel members werc

!. Spickler, R. P. Hosker. J. F. Sagendorf, A. H. Huber, and W. B. Petersen. The reviewers made 1

5 specific recommendations related to the model. The recommendations are listed at the and of this

' letter. In my assessment. these resme.rdations are reasonable, knplementation of the recommendations does not involve either a major revision of the alternate diffusion model or a major research effort.

This letter desenbes the essence of the peer review. The agenda for the review included introductory remarks by Tom Easig i

• 1 description and evaluation of building wake models in current NRC regulatory guidance description and evaluation of the updated building wake model description of applications of the updated building wake model 9

discussioni of building wake models in general e formulation of panel is,-,sdations .

l Building. wake dispersion models are found in NRC Regulatory Guloia 1.3,1.4 and 1.145 and in the Murphy-Campe procedure referenced in Standard Review Plan 6 4 (NU).EG 0800). With only on i exception these models estimate concentrations assuming that the receptor (or air intake) is at cemer

' of a plume represented by straight line Gaussian model. These models account for building wa i

ENCLOSURE 1 KO i q,oe520cw &9 #3

m ,

4 E modifying the diffusion coefficients. Regulatory practice senerally limits the reduction in

( concentrations in building wakes to a factor of 3 or less. The basic equation for these models is l O " uz,z,u where x is the concentration, Q is the release rate, I, and I, are diffusion coefficints corrected for building wake effects, and U is the wind speed at 10 m.

The exception to the Gaussian straight line modeling approach is found in the Murphy-Campe procedure. In this procedure, when there two widely separated air intakes, material is disperses

! outward uniformly in all directions with a speed equal to the mean wind speed. Concentrations l calculated with this model are assurned to cover both intakes simultaneously for a period of 30 minutes each day.

l ,

Regulatory Guide 1.145 adds a second correction to NRC dispetsion models. This factor reduces l concentrations to account for plume meander when wind speeds are less than 6 m/s and the atmospheric stability is neutral or stable. Concentrations calculated using the meander correction are compared with concentrations calculated using the building-wake model, and the lower concentration l is assumed for regulatory applicauons.

Plume centerline concentrations predicted by the various NRo building wake models were compared ,

, with. experimental data under NRC FIN B2970 " Atmospheric Diffusion for Control Room Habitability i

Assessments *, The result of this work, published in NUREG/CR 5055 AtmosphericDgusionfor Control Room Habitability Ausssments showed that the models did not predict variations in l concentrations related to changes in building area and atmospheric conditions very well. It also l showed that the models significantly over-predict concentrations at low wind speeds The updated building wake model, which was published in Atmospheric Environment in 1990, l provides new definitions for I, and I,. The definition of I, is E,-(ej*o}.W8 l

l where e, describes the diffusion in the absence of a building wake, and a,. describes the increased diffusion in building wakes. The increased diffusion in wakes is further defined by

.:, - ***Y,ni wer .

where k is a constant with a value of about 11 a,,, is the increase in the horizontal component of

, turbulence caused by the building: A is the cross-sectional area of the building; u. is a turbulence l scaling velocity in the atmosphere that is related to wind speed, atmosphenc stability, and surface l .

I

) 2 1

I

i

{

voughness; WEF is and WEF is a wake expansion factor that is a function of distan err = (1 - ( . j* Q exp( , gl) -

The value of a is a function of atmospheric stability an .

atmospheric stability, were derived for I . atmospheric stability, the value Two assumptions related to I, and E were made in the Armarpheric Environ

. these assumptions was that any of the standard sets of diffusion ecoefficient used algo a, is independent of wind speed. With these assumption ut diffusion coefficients found in most NRC computer codes, the revised building wa shown to result in better predictions of canterline concentrations in wakes than due largely to better prediction of concentrations at low w Commenting on the Atmospheric Knvironment article, Briggs, et al. (19p), poin increase in turbulence associated with building wakes should be a function pointed out that the improved predictioru of the updated model at low wind be related to better treatment of meander than of building wakes.

t In preparation for the peer review meeting, the updated wake model was tested

• assumptions. First e was assumed to be proportional to the wind speed. The result wa in predictive skill of the model because concentrations were over predicted conditions. However, the model was still better than previous models. The updated' also tested using a more state of the an parameterization for normal diffusion coe were when the model was applied with the original assu the peer reviewers.

Presentation of material on the updated wake model ended with a discussion of appl model in three computer codes: EXTRAN, RASCAL, and ARCON. The discussions of the EXTRAN and Irnplementation wasRASCAL implementations more detailed. of th model were brief; the discussion of the During the meeting the peer review panel capressed two related concems. They were about the use of straight line Gaussian models in the immediate vicinity of a release p building complex. They were also concerned that most (> 80%) of dats used for b anodel evaluation were farther downwind of thk release points than distances typically ofint control room habitability assessments. The peer review panel recommendations are:

[

3 I

, - - . _ - _ - . , , m,

, _,, , .- .e .. .

e  ;

1) 'Ihe turbulence increment generated by buildiras should be assumed to proponional to the

{

wind speed in accordance with accepted theory and physical reasoning.1

2) The effects of meander during low wind speed conditions should be treated explicitly in the apodel, but the treatnant should be separate from the treatment of building wakes.

3) Appropriate subsets of the available daa should be used to arvaluate the model after the suggested changes have been made.

4) An approach to determining concentrations other than straight-line Gaussian models should be considered when releases are from a building and receptors are on or near sne building. A distance equal to three building beights was offered as a reasonabic lower limit for the application of Gaussian models. A paper by Wilson and Britter (1982), and unpublished papers by Wilson and Chul, an8 Wilson and Lamb offer alternauve approaches.

5) Appropriate subsets of the available data should be used to evaluate approaches for deterrmrung the concentrations on or near buildings.

The current work statement for Task Order No. 3 " Atmospheric Relative Concentrations in Buildmg Wakes under

• Environmental Licensing and Regulatory Suppott' JCN J.2028 does not cover the changes to the model or the model evaluations recomrnended by the peer review panel. However, I have received a request for a proposal to modify the Task Order 3 work statement to cover these changes. I will submit a proposal in response to that request.

If you have any questions, please cal! me.

Si . erely.

Jarnes V. Ramsdell, Jr.

Senior Research Scientist Multimedia Exposure Assessment Group EARTH AND ENVIRONMENTAL SCIENCES CENTER JVR/lg G

4

.