ML17195A969
| ML17195A969 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 09/30/1985 |
| From: | Wojnarowski J COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 0706K, 706K, NUDOCS 8510080445 | |
| Download: ML17195A969 (12) | |
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_. *e CommonwAh Edison One First Nati.Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 Septerrber 30; 1985 Mr~ Harold R~ Denton, Director Office of Nuclear Reactor Regulation U~S~ Nuclear.Regulatory Commissioh Washington; DC 20555
Subject:
Dresden Station Units 2 and 3 Mobile Volume Reduction System
.LP Gas Storage_
NRC
- Elocket -Nos; ** 50... 237 -and** 5B"'"249
Reference:
Letter from B~ Rybak to H~.R. Denton dated December 4, 1984~
Dear Mr. Denton:
The referenced letter transmitted a proposed amendment to the Dresden Units 2 and 3 Technica~ Specifications *supporting use of a Mobile Volume Reduction System (MVRS).
During the'.course of your staff's review, questions were rais.ed regarding our plans for storage and handling of propane gas utilized by the MVRS.
In response to those questions, a copy of.
our Safety Evaluation for.the storage and handling of LP gas is enclosed~
Also enclosed is a diagram showing the.proposed storage configuration for the required eight; 250 gallon propane tanks~.
- We hope this information resolves your questions.* In order to support our current schedule for activation of the MVRS, we request your approval of the referenced Technical Specfficatidn amendments by November 1,.
1985~
If you have any questions regarding this *matter, please contact this
. office.
One signed original and thirty-seven (37) copies of this letter are provided for your use~ Ten (10) copies of the enclosures are also provided.
lm Enclosure Very truly yours;
'~,
~arowski Nuclear Licensing Administrator cc:
NRC Resident Inspector - Dresden M. Parker - State of Ill~
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10 CFR 50.59 SAFETY ANALYSIS FOR STORAGE AND HANDLING OF LP GAS FOR THE DRESDEN MVRS INTRODUCTION:
A safety analysis ofthe storage and handling of liquid propane required for the operation of the MobileVolume Reduction System (MVRS) has been made. System operational constraints, combined with site space limitations, have made it necessary to locate the MVRS and associated propane supply tanks within 300 feet of several safety related systems and components. The methodology described in Regulatory Guide 1.91," Evaluation of Explosions Postulated to Occur on Transportation Routes Near Nuclear Power Plants", has been used to determine whether or not the risk of damage to safety related structures, systems, or components due to an explosion during truck transport refill operations or during use of the propane supply system is sufficiently low to insure safe operation of the MVRS.
SUMMARY
RESULTS:
The results of the 10 CFR 50.59 safety analysis are summarized as follows:
- 1.
Per criteria in Regulatory Guide 1.91, the required safe separation distance for the stationary propane supply tanks from the nearest safety related structure/
system/component is 1, 150 feet. The actual separation distance from the nearest safety related structure/system/component (in this case, several equipment components/systems in the Unit 3 turbine bldg) to the propane tanks is approximately 300 feet.
- 2.
Per criteria in Regulatory Guide 1.91, the required safe separation distance from the nearest safety related structure/system/component for the propane transportation route is 1,300 feet. The refill truck will travel approximately 3000 feet while within this distance.
- 3.
The accident exposure rates for the propane supply tanks and the refill truck are both conservatively estimated to be 1.46 x 10-7. For transportation over public roads (which involves conditions that would yield a much higher likelihood of an accident), Regulatory Guide 1.91 has set 1 x 10-6 as the upper limit on accident exposure rate when using conservative assumptions, and 1 x 10-7 as the exposure rate limit when using re~listic assumptions.
- 4.
The propane concentration resulting from a tank rupture is, based on diffusion calculations, less than the concentration required for a flammable mixture by a factor of approximately 2.8.
1 - 1
CONCLUSIONS:
Since no information in the literature has been found that establishes criteria for calculating safe separation distances or accident exposure rates for onsite propane storage tanks at nuclear power plants, the criteria in Regulatory Guide 1.91 have been conservatively used as the basis for this analysis. Space availability at the Dresden Station has prevented the calculated safe separation distances from being met; however, in lieu of meeting this requirement, the accident probability rates
- for both the refill truck and stationary tanks have been conservatively shown to be sufficiently low to satisfy NRC acceptan~e criteria without the need to consider relocation of the system.
As an additional safety measure, the propane supply system {which, for operational reasons, is required to have a capacity of 2000 gallons) has been modified in accordance with NRC recommendations to consist of eight, 250 gallon tanks. These tanks will be located il"1 individual dikes that are designed to contain any spills to a controlled area, thereby ensuring that the propane concentration in any vapor cloud that would be created as a result of a spill or rupture will be kept within safe levels.
1 - 2
- 1.
PURPOSE DRESDEN MVRS 10 CFR 50.59 SAFETY ANALYSIS
SUMMARY
OF CALCULATIONS To determine, per criteria established in R.G. 1.91, the following:
- a.
The safe separation distance between any safety related structure, system, or comporient and either the eight tanks supplying propane to
- the MVR~ operation or a delivery truck used to refill these tanks.
- b.
The accident exposure rates associated with the hazards involved with the transportation of propane by refill truck to the designated supply
. tank area and with the storage ofthe propane in this area in order to show that the risk of damage due to explosions is acceptably low.
- c.
The vapor concentration of propane at the turbine building air intake louvers (North face) resulting from the rupture of a 250 gallon propane tank located approximately 300 feet NW of the louvers (certain equipment components/systems in this building are the closest safety related items to the propane tanks).
- 2.
REFERENCES
- 1.
Design Input Record Dl-5232-000 -"Dresden MVRS Site Interface"
- 2.
Reg. Guide 1.91 (1978) "Evaluations of Explosions Postulated to Occur on Transportation Routes near Nuclear Power Plants"
- 3.
llT Report J6405 "Accident Vapor Phase Explosions on Transportation Routes near Nuclear Power Plants" April 1977
- 4.
NUREG-CR-2650 - October 1982 - "Allowable Shipment Frequencies for the Transport of Toxic Gases Near Nuclear Power Plants"
- 5.
Gas Engineers Handbook - 1966
- 6.
NUREG-0570, "Toxic Vapor Concentrations in the Control Room Following _a Postulated Accidental Release", June 1979
- 7.
Reg. Guide 1.78, "Assumptions for Evaluating the Habitability of a Nuclear Power Plant Control Room During a Postulated Hazardous Chemical Release", June 1974 K
Gilbert Commonwealth Drawings 5232-0-360-006-001, Rev. 3; 5232-0-360-006-002, Rev. 4; 5232-0-360-006-003, Rev. 6; and, 5232-0-360-006-004, Rev. 6.
2 - 1
- e.
- 9.
"Handbook of Chemistry and Physics", 49th Edition
- 10.
Topical Report No. AECC-4-NP-A"Mobile Volume Reduction System,"
Aerojet Energy Conversion Company, November 9, 1984.
- 11.
NUREG-CR-1748, "Hazards to Nuclear Power Plants from Nearby Accidents Involving Hazardous Materials - A Preliminary Assessment",
April, 1981.
- 3.
COMPUTER PROGRAMS USED None
- 4.
ASSUMPTIONS
- a.
Maximum weight of propane per 250 g*allon tank is 875 lbs, based on a nominal filling density of 80 % of the tank volume (Ref. 5, Table 5-19).
- b.
The MVRS will operate at Dresden 3 months/year. Average DAW incineration rate will be 375 lbs/hr. Startup time required to bring incinerator to operating temperature is 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and consumes 900 lbs.
of propane. Cool down time to cold shutdown also requires 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> with zero propane consumption. Propane consumption during incineration is 12.5 lbs./hr. (Ref. 10)
- c.
- The explosion rate for a small propane refill truck is n = 8 x 10-9 explosions/kilometer (Ref. 3, page 9). Converting to English units:
n = (8 x 10-9)(1.6093 Km/mile)= 1.287 x 10-8 explosions/mile
- d.
Delivery of propane to the site will be limited to standard 2400 gallon (or less) sized delivery trucks.
- e.
Approximately 33 percent of the propane in a ruptured 250 gallon tank is.
instantaneously vaporized and released to the environment (Ref. No. 6).
This initial release is not considered in the propane concentration determination atthe turbine building vents.
- f.
The wind speed is 1 meter/sec. (3.28 ft/sec) from the NW direction, blowing directly at the turbine building air intake louvers.
- g.
Ambient temperature is 90°F.
- h.
Approximately 67 percent of the propane in a ruptured 250 gallon tank will be distributed evenly throughoufthe dike.
2-2
- 1.
The distance from the propane tank to the turbine building air intake louvers is approximately 300 ft. (Ref. No. 8).
J*
Stability Class F conditions exist as recommended per Reference No. 7.
- k.
Vaporization of the propane is due to absorption of heat from atmospheric radiation, solar radiation, convection of air and steel dike conduction. Reflection of radiation by the liquid surface and re-emission of radiation by the liquid body is ignored.
I.
The maximum expected atmospheric and solar radiation flux at the Dresden Site is approximately 350 BTUs/hr-sq. ft. or 264 calories/sec. - sq.
meter.
- 5.
CALCULATIONS Sa.
Safe Separation Distances From page 2 of R.G. 1.91:
R = KW 113, where:
R = Safe Separation Distance (feet}
W = equivalent weight of TNT (lbs)
K = 45 (ft!lbs3)
A TNT mass equivalence of 240% for substances subject to vapor phase explosions is an acceptable upper bounds when effective yields generated from test data do not exist.
For the storage tanks:
w = wt. of propane = (8)(875) = 7000 lbs; (for 8 tanks}
W = (7000)(2.4) = 16,800 lbs.
R = (45)(16,800) 113 = 1,152 ft For the refill truck:
w = (2400gallons)(4.24 lbs/gal) = 10, 176 lbs W = (2.4)(10, 176) = 24,422 lbs R = (45)(24,422) 1/3 = 1305 ft 2-3 USE1150ft USE 1300 ft
Sb.
Accident exposure Rates From data supplied by Aerojet Energy Conversion Company (Assumption B),
the MVRS, during its 3 month stay at the Dresden Station, will incinerate DAW for 89 days, since startup and cool down require a total of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The amount of propane required during this time is then:
Startup Heating Normal Operation = (89 days)(24 hrs/day)(12.S lbs/hr) 900lbs
= 26,700 lbs Cool Down
=
0 lbs Total Required
= 27,600 lbs Eight 2SO gallon tanks will be located near the MVRS pad to supply the required amount of propane for the incineration process. The propane gas.
supplier will bring in a refill truck whenever approximately 1000 gals of propane have been expended. The refill truck will contain a maximum of 2,400 gallons of propane. As calculated in Sa. above, the safe separation distance for the refill truck is 1300 ft, The entire delivery route must therefore be considered the exposure distance, since it is all within 1300 ft arcs swung from the nearest safety related structures/systems/components (see attached drawing). For the refill truck, the exposure distance is the distance traversed through the Dresden Station to the propane tank site, i.e., from point 11 A 11 to point 11 8 11
, which is approximately 3,000 feet.
Withdrawal of propane from a tank will be 80% of its full capacity of 87S lbs.
or 160 gallons (Reference 5). The number of refills per year (f) is then calculated as follows:
(8 tanks)(87S lbs/tk)(0.8) = 5,600 lbs/refill (27,600 lbs/90 days)(365 days/yr)/(5,600 lbs/refill) = 20 refills/yr From R.G. 1.91, the exposure rate (r) = (n)(f)(s), where:
n = explosion rate for the substance and transportation mode in question, in explosions per mile. In this case, n = 1.287 x 10"8 (Assumption C) f = frequency of shipment for substance in question, in shipments per year.
In this case, f is equivalent to the number of times the refill truck comes on site (20 times on a yearly basis).
s = exposure distance in miles = transportation route through Dresden Station to designated propane tank location = 3,000 ft (see attached drawing).
Then, for the refill truck:
r = (n)(f)(s) r = (1.287 x 10-8 )(20 refills/yr)(3000 ft)/(5280 ft/mile) = 1.46 x 10-7 2-4
- e.
This exposure rate is between the exposure rate upper limits of 10-6 and 10-7 established in RG 1.9 for conservative and realistic assumptions, respectively. While within the safe separation distance, the propane refill truck will be within the fenced site security area, where the speed limits are much lower than on public roads and the amount of traffic is also much lower.
Based on these conditions, it is justifiable to use the 10-6 exposure rate limit for the refill truck transport scenario.
Strictly speaking, the analytical approach used above is not applicable to the storage tanks because the tanks are stationary. However, since no other methodology could be found in the literature that would apply to these tanks, the accident exposure rate for the tanks is conservatively assumed to be the same as that for the refill tank. The justification for making this assumption is based on the following arguments:
- a. Since the tanks have a fixed, stationary location, they represent less of a hazard than a moving truck of propane. Collision accidents are highly
.improbable since the tanks are located on a trailer bed and are parked approximately 15 feet from the security road.. Therefore, the explosion rate (n) should be less than that for the case of the moving refill truck.
- b. The frequency (f) for filling the tanks is the same as the frequency of
- shipment of propane to the site by therefill truck.
- c. The exposure distance in this case is only the length of the tank skid, since it is only while a vehicle is passing the tanks that a collision could occur.
- d. The tanks contain less propane than the refill truck.
Sc.
Propane Diffusion Although the risk of damage due to explosions has been calculated to be sufficiently low to be discounted, a scenario was developed to determine the conditions that would be created as a result of a tank rupture and the subsequent release of propane to the atmosphere.
Under postulated worst-case accident conditions, it is assumed that the entire container of propane ruptures. Approximately 33 percent of the mass of the propane will instantaneously vaporize and form a puff release. It is assumed that the Instantaneous release will dissipate quickly enough such that concentrations at the turbine building vents are below flammability limits.
The remaining liquid will be distributed evenly throughout the steel dike and vaporize by absorption of atmospheric and solar radiation, convection of air and dike conduction.
A wind speed of 3.28 feet/sec. blowing from the NW direction and an ambient temperature of 90°F was assumed for conservative reasons. Under these 2-5
conditions, the concentration of propane at the turbine building louvers would be at a maximum level when considering the wind speeds and temperature ranges normally encountered at the site. Stability Class F
- atmospheric conditions were assumed to exist as recommended per Reference No. 7. The atmospheric/solar radiation flux was assumed to be 350 BTUs per square foot per hour, or 264 calories per square meter per second..
The propane concentration at the turbine building louvers, approximately 300 feet downwind of the ruptured tank, was calculated using the formulas contained in Reference No. 6 and standard* heat transfer equations:
- 1.
The mass of the instantaneously vaporized liquid propane released from the ruptured tank was calculated to be 1.31 x 105 grams, released as the initial puff.
Since the volatility of a substance is a direct function of its vapor pressure, and since propane has a sufficiently high vapor pressure when released to the atmosphere, the propane will instantaneously flash.
Approximately 33% of the propane in the ruptured tank is released instantaneously as a puff. The remaining 67% of the propane in the tank will be released at a slower rate and will vaporize by absorption of heat from atmospheric and solar radiation, air convection, and dike conduction.
The vaporization rate was determined utilizing the equations in Reference No. 6 by first calculating the heat transfer due to steel conduction (dike), forced convection of air, and atmospheric and solar radiation and then calculating the rate of total heat transfer. Although the vaporization rate decreases significantly over time, it was conservatively assumed that the strength of the continuous source is equal to the vaporization rate at one second after tank rupture.
- 2.
The diffusion equation for the continuous release of a vapor cloud with a finite initial volume and an elevated receptor point (Turbine Building Louvers) was used to calculate the down wind propane conce.ntration.
- 3.
The normal Pasquill-Gifford diffusion coefficients were altered to give credit for the finite initial size of the spill as suggested in Reference No. 6.
The concluding calculation resulted in a propane concentration of 5.3 x 10-4 lbs. of prop_ane per cubic foot of air at the turbine building louvers (Elevation 561.5'). This propane concentration was compared to the flammability limits of propane from Table 2.63 of Reference No. 5. at 90°F, which is a flammability limit of 2.055% propane in air. If the density of moist air at 90°F is 7.22 x 10-2 pounds of air per cubic foot (as determined from pages F-9 and F-10 of Reference l\\Jo. 9), the minimum concentration of propane which can be present in the air without exceeding the flammability limit is 1.48 x 10-3 pounds of propane per cubic foot. Since the concentration of propane 2-6
in air at the turbine building air intake louvers is less than 35 percent of the flammability limit, no explosion or flammable event will occur.
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