ML20029B667
| ML20029B667 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 03/06/1991 |
| From: | Crawford A PUBLIC SERVICE CO. OF COLORADO |
| To: | Weiss S Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19310D318 | List: |
| References | |
| P-91084, NUDOCS 9103140056 | |
| Download: ML20029B667 (6) | |
Text
.
s, h Public Service' 2.th..
P.O. Box 840 1
Denver CO 80201 0840 2420 W. 26th Avenue, Suite 100-0, Denver, Colorado 80211 A. Clegg Crawford Vice Presdent i
March 6, 1991 Nu * 'epaa'on$
Fort St. Vrain Unit No. 1 P-91084 U. S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, 0.C.
20555 Attention: Mr. Seymour H. Weiss, Director Non-Power Reactor, Decommissioning and Environmental Project Directorate Docket No. 50-267
SUBJECT:
Natural Gas Wells in the Vicinity of Fort St. Vrain -
Contains Proprietary Information (Attachment 2)
REFERENCE:
PSC Letter, Crawford to Weiss, dated February-22, 1991 (P-91079)
Dear Mr. Weiss:
The referenced letter discussed natural gas wells in the vicinity of Fort St. Vrain and provided preliminary results of analyses of postulated natural gas leaks and subsequent explosions from FSV Well No. 11, the well closest to the Reactor Building.
These analyses, four in all, were performed by Westinghouse Electric Corporation, and have been completed. The purpose of this letter is to document the results of these analyses.
As discussed in the referenced letter, an initial flow rate of 1 million cubic feet per day (this.is standard cubic feet per day scfd) was considered to represent a conservative upper limit for the Producer pipe rupture.
The first analysis assumed a 90ntinuous natural gas flow rate of 1 million scfd from the ESV Well No. 11 wellhead, a wind speed of 5 mph in the direction - of the Reactor Building, and Pasquill Class F atmospheric stability, it was assumed that 100% of the natural gas consisted of methane and + :at methane has the same density as air (neutrally buoyant)..
This is an extremely. conservative assumption, given that methane has a specific gravity of 0.55, and rises rapidly in air.
The first analysis modeled the steady state methane plume resulting from the conditions stipulated above, and concluded that the lower flammability limit of-methane gas ~(4% methane in air) occurs at 108 feet from the gas flow
,,ou rce (wellhead),
in the direction of the Reactor Building.
The
. distance from the wellhead to one-half the lower flammability
- limit, in the direction of the Reactor Building, was determined to be 154 b b*Y 7
0
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P-91084
.=
.Page 2-
' March 6, 1991 The ' distance from the FSV Well No. 11 wellhead to the nearest corner of the Reactor Building (southeast corner) is '1184 -feet (survey measurement).
It is approximately 1060 feet from this wellhead to ~
the southeast corner of the Turbine Building, and approximately 930 feet from this wellhead to the nearest switchyard equipment item.
The first analysis also postulated that this cloud of methane gas detonated, with ignition occurring at a point on the outer edge of the. lower-flanriability limit nearest the Reactor Building.
An overpressure-of ').1 psi was computed to occur at the Reactor Building as a result of *.no postulated detonation, in the fonn of a shock wave travelling at the speed of sound.
This overpressure would not affect the strN tural integrity of the Reactor Building.
The Reactor Building is' designed to withstand a 300 mph horizontal wind velocity.
(correspondin9 to a positive static pressure of 1,44 psi) and maintain its structurcl integrity. to this letter identifies damage which would be expected to result from shock waves from blasts which produce various dynamic overpressures.
A.second -analyt was performed, also based on the assumptions described above, with the exception of wind speed which was conservatively assumed to_be 1 mile per hour in the direction of the Reactor Building.
The use of a 1 mile per hour wind speed, with Pasquill stability Class F, represents a more conservative assumption than the_1 meter per second (2.24 mile per hour) wind speed, again with _Pasquill stability Class F,
that the NRC typically uses for dispersion analyses.
This second analysis concluded that the greatest distance from the flow source 'to the lower flammability limit was 248 feet, and 359 feet to one half the lower flanunability L
limit.
Postulated detonation of the steady state methane plume in this second analysis produced an overpressure condition of 0.3 psi at the Reactor Building, again assuming the ignition source was located at the point in the plume at the' lower flammebility limit which -was nearest the Reactor Building. This.0.3 psi-overpressure would have l-no effect on the structural integrity of the Reactor Building.
L A third analysis was performed in which i_t was assumed that 100%
l methane flowed out of 'a postulated pipe rupture, at the _ location of the FSV No. 11 wellhead, at 1 million scfd under stagnant atmospheric l-conditions,_ with no dispersion.
The nwthane was again assumed to have neutral buoyancy in air.
Following one hour of leakage at this flow rate, detonation of the resulting gas cloud ~ was assumed to occur, with ignition of ali.the methane that escaped.
The resultant overpressure at the Reactor Building was. computed to be 0.6 psi.
This overpressure is sufficient to shatter windows, as identified in, but wnuid not affect the Reactor Building s tructu ral integrity.
These calculations were performed _using the Automated Resource for Chemical Hazard Incident Evaluation (ARCHIE), Version 1.00.
This IBM PC code was developed by the Environmental Protection Agency (EPA),
and the Federal Emergency Management Agency (FEMA).
This code is capable of performing a multitude of analyses for the release of potentially hazardous,.i.e. toxic or flammable, chemicals.
For this analysis, ARCHIE was used to estimate the atmospheric dispersion of
P-91084-x Page 3 _.
4 -
March 6, 1991 the-natural _ gas released and the potential effects from a-vapor cloud explosion.. Since this code has not undergone internal Westinghouse review for application to nuclear analysis, the code calculations were checked in the following manner.
The dispersion of methane gas for the first analysis, assuming a 1 million scfd gas release rate with a 5 nph wind, was repeated using the EPA SCREEN, Version 1.0, code. The results indicated sl-ightly less conservative results than the ARCHIE _ analysis; the flammability zone extended to approximately 90 feet, versus 108 feet for ARCHIE.
The blast effect calculations were checked by performing the " worst i~
case" calculations - by : hand, according to the methods described in "The SFPE Handbook of Fire Protection Engineering," Society of Fire
-l Frotection Engineers, National Fire Protection Association, First Edition, April 1990.
Since the release was treated as 100% methane (methane actuall comprises approximately 80% of the natural gas from FSV Well No.11)y an evaluation was performed to assess potential effects from the 10%
ethane in the flow stream, due to its higher density and lower flammability.
It was determined that the presence of ethane would not extend the distance from the wellhead to the lower limi t of g
. flamability in the dispersion analyses, and the assumption of 100%
methane. release is considered to be conservative.
Westinghouse Electric -Corporation has completed a fourth analysis involving a postulated explosion of natural gas. inside the measuri ng -
station, located approximately 300 feet to the west of the FSV Well No. 11 wellhead.
A stoichiometric mixture of methane in air was assumed to be present in a 512 cubic feet structure (the measuring station actually has a volume less than 200 cubic feet, and is vented to prevent-such an explosion), which was then detonated.
The pre-fab
- structure would collapse before pressures could reach 10 psig. At 10-psig, a missile, such as a plank' or a portion of the measuring station siding, could not be propelled to the FSV Security fence, a distance of about 250 feet.
The resultant overpressure at the Reactor Building was calculated to be less than 0.2 psi. _ Therefore, an explosion-driven missile and the resulting blast wave, from postulated explosion of the measuring station, would not affect the FSV Reactor Building. to this letter is the Westinghouse Electric Corporation Analysis MethodsSummary documenting the results of the computer runs and calculations for the analyses described above.
Information contained in Attachment 23 is considered.to be proprietary by Westinghouse Electric Corporation,' under the criteria set forth in 10 i:
CFR 2.790.
In accordance with the requirements of 10 CFR 2,790, the following documents are submitted with this letter:
l l
l I
l I
k w y,
P-91084 Page 4-March 6.11991 (1)-.One_ copy of_ an -Applicction for Withholding Proprietary Information froni Public Disclosure Attachment 3.
(2) One copy of the-proprietary information and. notice,.
-(3) One copy of an original affidavit, Attachment 5.
Calculation of the blast effects at various distances are estimates, and factors such as terrain, cloud shape, and detonation location can affect actual consequences but are difficult - to quantify with 4
existing technology. The analyses described above have incorporated much conservatism, by the assumptions'of neutrally buoyant gases, extremely stable meteorological conditions, and detonation locations nearest the Reactor Building.
Based on the results of the analyses described above PSC considers that postulated accidents involving releases of natural gas from FSV Well No. 11, the gas well nearest the FSV Reactor Building, would not pose a threat to nuclear safety.
In recent phone conversations ~, the NRC has noted a concern regarding injection of large volumes of high pressure fluids into the natural gas wells in the vicinity of FSV.
Except for occasional hydrofracing associated with possible recompletion of the gas wells near FSV, large volumes of high pressure fluids will not be injected into these wells for the purpose of enhancing oil or gas recovery.
Should you have any questions concerning this submittal, please contact Mr. M. H. Holmes at (303) 480-6960.
- Very truly yours,
$k A. Clegg Crawfor
-Vice President
-Nuclear Operations ACC/JRJ:dh Attachments cc: Regional Administrator, Region IV Mr. J.B. Baird
,3 Senior Resident-Inspector
. Fort-St.- Vrain Mr. Robert M..Quillin, Ofrector Radiation Control Division Colorado Department of Health 4210-East lith Avenue Denver, CO 80220
P-9108fl Roge'4 March 6, 1991 (1) One copy of an _ Application for Withholding Proprietary Information from Public Disclosure, Attachment 3.
(2) One. copy of the proprietary infonnation and notice.
(3).One copy of an original af fidavit, Attachment 5.
Ca'culation of the blast effects at variot.s distances are estimates, ar.d factors such as terrain, cloud shape, and detonation location can affect actual consequences but are difficuit-to quantify with existing technology.- The analyses described above have incorporated much conservatism, by the assumptions of neutrally buoyant gases, extremely stable meteorological conditions, and detonation locations nearest the Reactor Building.
Based on the results of the analyses described above, PSC con:iders that postulated accidents involving releases of natural gas from FSV Well No. 11, the gas well nearest the FSV Reactor Building, w ald nr+ pose a threat to nuclear safety.
In recent phone conversations, the NRC has noted a concern regarding injection of large volumes of high vressure fluids into tht: natural gas wells in the vicinity of FSV.
Except for cccasionel hydrofracing associated with possible. recompletion of the gas wells near Fi large volumes of high pressure fluids will not be injected into these wells for the purpose.of enhancing oil or gas recovery.
Should you have any questions concerning this submittal, please contact Mr. M. H. Holmes at (303) 480-6960.
Very truly yours,
(.7. Y pt YlU A. Clegg Cr.% ford Vice President Nuclear Operations ACC/JRJ:dh Attachments
.cc: Regional Administrator, Region IV Mr.-J.B. Baird Senior Resident Inspector Fort St. Vrain Mr. Robert M. Quillin, Director Radiation Control Division Colorado Department of Health 4210 East lith Avenue 9
Denver, CO 80220 Reviewed by:,1 %f.,
_.--3f5f9/
V
Marct) 6, 1991 P-91084 Explosion Overpressure Damage Estimates Overpressure *
(psig)
Expected Damage 0.03 Occasional breaking oflerge windows already under stress.
0.04 Loud noise (143 dQ); sonic boom glus failures.
0.10 Breakage of small windows under strain.
0.15 Typical pressure for glass failure.
0.30 Some dunage to house ceilings; 10% window glass breakage.
0.40 Limited minor structural damage.
0.50 1.0 Windows usually shattered; some window frame damage.
0.7 Minor damage to house structures.
1.0 Partial Demolition of houses; made uninhabitable.
1.02.0 Corrugated metal panels fail and buckle.
Housing wood panels blown in.
1.08.0 Range for slight to serious inkries due to skin lacerations from Dying glass and other missiles.
13 Stect frame of clad buuding slightly distorted.
2.0 Partial collapse of walls and roofs of houses.
2.03.0 Non. reinforced concrete or cinder block wallt, shattered.
23 Lower limit of serious structural damage.
2.4 12.2 Range for 190% eardrum rupture among exposed populadons.
2.5 50% desavetion of home brickwork.
3.0 Steel frame buUding distorted and pulled away from foundation.
3.0 - 4.0 Frameless steel panel building ruined.
4.0 Qadding of light industrial buildings ruptured.
5.0 Wooded udlity poles snapped.
5.0 - 7.0 Nearly complete destruction of houses.
7.0 Loaded train wagons overtumed.
7.0 - 8.0 8 12 in, thick non reinforced brick fail by shearing of flexure.
9.0 Loaded train box cars demolished.
10.0 Probable total building destruction.
15.5 - 29.0 Range for 199% fatalities among exposed populations due to direct blast effects.
- Dese are the peak pressures formed in excess of normal atmospheric pressu shock waves.
Source: Lees, F.P,tess Prevention In the Process Industries. Vol.1, Butterworths, Bostoo,1980.