ML20247Q640
| ML20247Q640 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 05/31/1989 |
| From: | Cockfield D PORTLAND GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEIN-89-044, IEIN-89-44, NUDOCS 8906070002 | |
| Download: ML20247Q640 (10) | |
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Portland General BectricCoipany David W. Cockfield Vice President, Nuclear May 31, 1989 Trojan Nuclear Plant Docket 50-344 License NPF-1
" C. Nuclear P.egulatory Commission ATTN: Docuraent Control Desk Washingtcn DC 20555 Doar Sirs
- Nuclear Regulatory Commission (NRC) Information Notice No. 89-44, "Hydror.en Storar.e on the Roof of the Control Room" Portland General Electric (PGE) has completed its evaluation on the removal of the bulk hydrogen storage tanks from the roof of the control Building as committed to in our letter dated May 5,1989.
This evaluation is attached and is formatted to address the concerns outlined in the NRC Information Notice No. 89-44, " Hydrogen Storage on the Roof of the Control Room".
Each NRC concern and PCE's response is provided in the attachments to this letter.
Sincerely, 7
At taciunents c:
Mr. John B. Martin Regional Administrator, Region V
't N,b U.S. Nuclear Regulatory Commission bb gg Mr. William T. Dixon mo State of Oregon gy Departrent of Energy 00
$b Mr. R. C. Barr NRC Resident Inspector g
Trojan Nuc1 car Plant k9 I
0'. O WAG I I 121 S W 5drron SPoet Portard Oregon 97204
WC Y j,
" TrJJ2n NuclGer Plcnt Document Control Dark NT
. Docket 50-344 May 31, 1989 i! N7 License NPF-1 Attachment A i
Page 1 of 3 i
PORTLAND GENERAL ELECTRIC COMPANY'S (PGE) RESPONSE TO NUCLEAR REGULATORY COMMISSION (NRC)
INFORMATION NOTICE NO. 89-44, HYDROGEN STORAGE ON THE ROOF OF THE CONTROL ROOM NRC CONCERN i
1.
" Leakage of hydrogen gas from the storage facility in proximity to the air intakes to the control room ventilation and emergency pressuri-zation system may introduce a flammable or explosive gas mtxture into the control room. Because the hydrogen storage facility, containing four 8,000-sef hydrogen tanks at up to 2,450 psig is Seismic Category II, a seismic event may result in a hydrogen leak.
Further-l more, the pressure relief valves in the hydrogen facility exhaust downward to within six inches of the control room roof in the vicinity of the control room ventilation system air intakes.
It was also noted that six 8,000-sef nitrogen tanks were located in the vicinity of the control room air intakes. Nitrogen leakage and dispersion into the air intakes may lead to incapacitation of the control room operators."
PGE RESPONSE The hydrogen' storage facility, including the pressure control station, has been relocated to an area approximately 125 feet south of the I
cooling tower and 900 feet east of the control room. The new storage facility is mounted on a concrete foundation designed for the weight of-the tanks and skid assembly. The concrete slab, anchorage, and skid assembly are designed for Trojan specific Safe Shutdown Earthquake i
(SSE) ground accelerations. However, the installation will not be l
classified as a Seismic Class I structure per the guidelines of the Electric Power Research Institute's (EPRI) Special Report NP-5283-SR-A, j
" Guidelines For Permanent BWR Hydrogen Water Chemistry Installations, 1987 Revision."
The hydrogen distribution piping will be run in a buried trench from the new hydrogen storage facility to the southeast corner of the Turbine Building. Cathodic protection will be provided for the buried distribution piping to reduce the potential for pipe corrosion. Above ground piping will be routed up the south side of the Turbine Building roof, along the edge of the roof, and tied into the existing distribu-I tion piping to the volume control tank (VCT) and generator cooling system.
The new distribution system is designed to Seismic Category II requirements. All piping, tubing, fittings, and other materials conform to American National Standard Institute (ANSI) B31.1, " Power Piping", 1973 Edition.
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Trojan Nuc1 car Plant Document Control Desk Docket 50-344 May 31, 1989 License NPF-1 Attachment A Page 2 of 3 The design adequacy of the existing distribution piping is currently being reevaluated with respect to the lessons learned outlined in the NRC Information Notice No. 87-20 " Hydrogen Leak In Auxiliary Building." This reevaluation will be completed by July 14, 1989.
An analysis was performed to evaluate the potential for asphyxiation and fire associated with the release of hydrogen and nitrogen in the vicinity of the control room air intakes. A detailed description of this analysis is provided in Attachment B, and the results are summarized below.
Followin$ relocation of the hydrogen storage tanks, the closest hydrogen source to the control room air intakes is a 3/4-inch-diameter line located approximately 16 feet from the control room normal ventilation (CB-2) air intake. With flow limited by excess flow check valves, the hydrogen concentration at the CB-2 intake as a result of a pipe break will be below the maximum permissible concen-tration of 2 percent specified by Branch Technical Position (BTP)
Chemical Engineering Branch (CMEB) 9.5-1, " Fire Protection Program."
The six 8,000 standard cubic feet nitrogen tanks located on the roof of the Control Building were evaluated for impact on control room habitability.
The closest nitrogen source to the control room air intake is a 2-inch line on the roof of the control Building, located approximately 15 feet from the CB-2 air intake.
The flow from a break in the 2-inch line will be limited by two excess flow check valves. In addition, an arbitrary break in a 3/8-inch line in the tank header, located approximately 33 feet from the CB-1 intake, was evaluated. The analyses performed show that the postulated line breaks will not lower oxygen IcVels in the control room below 18 percent by volume as recommended by the American Conference of Governmental Industrial Hygienists document, " Threshold Limit Values and Biological Exposure Indices for 1988 and 1989."
Based on the above design features and supporting analyses, control room habitability will be assured in the event of hydrogen or nitrogen gas leaks.
NRC CONCERN 2.
"A detonation of a hydrogen storage tank (energy equivalent to 217 pounds of TNT) may structurally damage and affect performance of safety-related equipment on the control room roof, such as the ventilation system intake and exhaust structure, the emergency pressurization system, and equipment in the control room itself."
Trojan Nuclecr-Flant Document Control Dark Docket 50-344 May 31, 1989 License NPF-1 Attachment A Page 3 of 3 PGE RESPONSE The hydrogen storage facility is now located a minimum of 900 feet from any safety-related structures.
The 900 feet separation distance between a safety-related structure and the detonation of one hydrogen storage tank is within EPRI Special Report NP-5283-SR-A guidelines.
The location of the cooling tower between the hydrogen storage facility and the Plant will also prevent any damage to safety-related structures in the event hydrogen containers were tc become missiles.
Therefore, detonation of a hydrogen storage tank would have no impact on safety-related structures or equipment.
NRC CONCERN 3.
"An explosion of the hydrogen delivery truck that provides hydrogen to the facility through a fill line located at ground level on the wall of the Auxiliary Building may structurally damage safety-related component cooling water pumps and radwaste storage tanks located inside the Auxiliary Building and in the vicinity of the hydrogen fill line."
PCE RESPONSE The fill line to the hydrogen storage facility will be temporarily relocated to the new storage facility adjacent to the cooling tower.
An analysis has been performed to show that the detonation of a hydrogen storage tank would not adversely impact the integrity of the cooling tower basin or any safety-related structures, based on the criteria in the EPRI Special Report NP-5283-SR-A.
The risk of damage to safety-related structures from an explosion of the hydrogen gas tube truck while in transit through the Plant site was also evaluated. An analysis performed following the guidelines of Regulatory Guide 1.91, " Evaluations of Explosions Postulated to Occur on Transportation Routes Near Nuclear Power Plants", shows that the exposure rate for such an accident is acceptably low, i.e.,
less than lE-7 per year.
In the long-term, a permanent fill station will be installed approxi-mately 100 feet south of the cooling tower. The analyses referred to above, Which evaluate the detonation of a hydrogen storage tank at the storage facility and the exposure rate for a postulated explosion of the hydrogen gas tube truck While in transit through the Plant site, conservatively envelope the location of the permanent fill station.
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Trojen Nuclscr Pltnt Document C:ntrol Dsek Docket 50-344 May 31, 1989 License NPF-1 Attachment B Page 1 of 6 l
.ASPHYX1ATION AND FIRE ANALYSIS FOR NITROGEN AND HYDROGEN GAS LINE RUPTURES ON THE CONTROL BUILDING ROOF The following analysis evaluates the potential for asphyxiation associ-ated with the release of nitrogen in the vicinity of the control room heating, ventilating and air conditioning (HVAC) intakes and the potential for fire associated with the release of hydrogen from a pipe rupture on the roof of the Control Building.
Summary Three cases were evaluated:
1.
Double-ended sonic velocity discharge from an arbitrary 3/8-inch break in the nitrogen tank header.
2.
Nitrogen discharge from a 2-inch diameter broken pipe on the roof of the Control Building. Flow is assumed to be limited by two excess flow check valves arranged in parallel. A maximum discharge of 50 standard cubic feet per minute (sefm) at a point 15 feet away from the control room normal air (CB-2) intake was used in the analysis.
This case evaluates the nitrogen source closest to the control room air intakes.
3.
Hydrogen discharge from a 3/4-inch diameter broken pipe on the roof of the Control Building. Flow is assumed to be limited by two excess flow check valves arranged in parallel. A maximum discharge of 225 scfm at a point 16 feet away from the CB-2 intake was used in the analysis.
This case evaluates the hydrogen source closest to the control room air intakes.
The analysis found that in Cases 1 and 2, there was no discernible reduc-tion in the oxygen concentration at the control room emergency air (CB-1) intake and the CB-2 air intake.
In Case 3, the bounding concern was the flammability, rather than the asphyxiant potential.
The analysis found that the hydrogen concentration at the CB-2 intake will be below the maxi-mum permissib.1.e concentration of 2 percent allowed by Position C.S.d.(5) of Branch Technical Position (BTP) Chemical Engineering Branch (CMEB) 9.5-1, " Fire Protection Program."
A fourth case was also evaluated in this analysis.
During initial charging of the generator cooling system, flow will periodically be routed through a bypass line that is controlled by an excess flow check valve with a 600 scfm shutoff setpoint. Although this mode will be used infrequently, this condition was evaluated to determine potential consequences of a pips rupture during initial charging.
In this case, the consequences of a hydrogen pipe break during initial charging can be readily deduced from inspection of Case 3.
Should a pipe break during this mode, the hydrogen concentration at the CB-2 intake will be below the 2 percent limit Fpecified by BTP CMEB 9.5-1.
Trojtn Nucle?r Plant Document Control Dack Docket 50-344 May 31, 1989 License NPF-1 Attachment B Page 2 of 6 Methodology The dilution as a function of distance from the release point was determined assuming that the gas is released as a jet. ?he velocity of release was determined using sonic flow formulations from Reference 1, or obtained from the excess flow check valve limits.
The dilution of the I
jet was determined using the methodulegy outlined in Reference 2.
Four major zones can be distinguished Whan analyzing jets. They are roughly defined in terms of the maximum or centerline velocity existing at the cross section being considered:
Zone 1: A short zone, extending about four diameters or widths from the outlet face, in which the maximum velocity of the air stream remains practically unchanged.
Zone 2: A transition zone, extending to about eight diameters, over most of which maximum velocities vary inversely as the square root of the distance from the outlet.
Zone 3: A long zone in which the maximum velocity varies inversely with the distance from the outlet.
This is often called the zone of fully " established turbulent flow" and may be 25 to 100-diameters long, depending upon the shape and area of the outlet, the initial velocity, and the dimensions of the space into Which the outlet discharges.
Zone 4: A terminal zone in Which, as in confined spaces, the maximum velocity decreases at an increasing rate, or, in the case of large spaces free from wall effects, the maximum velocity decreases rapidly in a few diameters to the velocity below 50 feet per minute (fpm) which is usually regarded as still air.
Analysis 1.
Nitrogen at Tank Header - (Case 1)
For this case, it is assumed that a broken pipe at the tank header will release nitrogen at sonic velocity through a 3/8-inch double-ended break. Standard formulas were used to cr.lculate sonic velocity from the nitrogen tanks based on the following conditions:
I Pressure
= 2,450 psi Temperature
= 70*F Volume
= 51 ft3 Mol. Weight
= 28 lb/lb-mole 3
Gas Constant R = 10.73 psla-ft /lb-mole-R 3
Specific Volume = 0.082 ft /lbm Sonic Velocity = 1,148 ft/sec
, Trajtn Nuclagr Plcnt ;
Document Control Denk Docket 50-344 May 31, 1989 l,.
h License NPF Attachment B
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- Page 3 of 6.
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'Since all distances of interest (distances to the normal or' emergency _
air intakes) are within Zone 3, only Zone 3 parameters'were-calculated:
-Opening Diameter
= 0.49 inches Exhaust Velocity
= 68,873 fpm "i-Constant K.
= 6.20
-Constant K'
=17.01 Zone l'-; Zone 2 Boundary-(Bdry)
= 0.16 feet Zone 2 - Zone 3.Bdry-
= O.33 feet Nominal Oxygen Content
= 20.9. percent Distances 10xygen
. y jy j
(feet) x o-x o content 1.0
.2547 7.85 18.54%
2.0 '
.1274 15.70 19.65%
5.0
.0509 39.26.
20.38%
7.5
.0340 58.89
-20.55%
10.0
.0255 78.52 20.64%
20.0
.0127 157.04 20.77%
33.6
.0076 263.51 20.82%
46.3
.0055 363.86 20.84%
50.0
,0051 - 392.59 20.851-75.0
.0034 588.89 20.86%
100.0
.0025 785.19 20.87%
Where:
Vx = centerline velocity, fpm.
Vo = Initial velocity at discharge, fpm Qx e Total volume flow rate at' distance x from face of outlet, efm.
Qo = Discharge from outlet, efm.
K = Proportionality constant, with K' = 1.13 K (Reference 2).
As shown above, due to the high velocity through a small opening, the nitrogen quickly dissipates and mixes with the surrounding air, and-within a'few feet from the opening, the air concentrations are essentially normal.
From Reference 5, the minimum distance from a nitrogen tank to the CB-2 intake is approximately 46 feet. The minimum distance to the CB intake is 33.5 feet.
The oxygen concentrations at these distances are 20.84 percent and 20.82 percent, respectively. Therefore, negligible impact is-expected to the control room operators.
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- Tbojcn Eucisar Plint Document Control Dzak LO Docket 50-344
May 31,'1989 License.WPF-1 Attachment B Page 4 of 6 Fy 2.
Nitrogen Through' Check Valves - (Case 2)L-
_ i For this ' case, it is assumed that a broken pipe will release nitrogen
!1 15 feet east of the CB-2 intake. ' Flow wi13.be limited by,two excess flow check valves located in parallel (Reference 4)..
The shutoff setpoint is 19.7'sefm.
A conservative value of 50 scfm was used in the analysis.:
From Reference'4, the maximum line size carrying nitrogen is 2-inch pipe. From Reference 1, a Schedule 40,~2-inch pipe has a 2.067 inch inside diameter.
Opening Diameter
= 2.07 inches Exhaust Velocity
= 2,187 fpm Constant K
= 6.20 Constant K'
= 7.01 Zone 1 -~ Zone 2 Bdry.
= 0.69 feet Zone 2 -- Zone 3. Bdry
= 1.38 feet Nominal Oxygen Content-
= 20.9 percent Distance Oxygen.
y jy j
(feet) x-o x o content 1.0
.7120 2.81 15.41%-
2.0
.5340 3.75 16.50%
5.0
.2136 9.26 18.88%
7.5
.1424 14.05 19.51%
10.0
.1068 18.73 19.84%
15.0
.0712 28.09 20.18%
20.0
.0534 37.45
'20.36%
50.0
.0214 93.64.
20.68%
75.0
.0142 140.46 20.75%
100.0
.0107 187.27 20.79%
As shown above, due to the high velocity through a small opening. the nitrogen quickly dissipates and mixes with the surrounding air, and within a few feet from the opening, the air concentrations are essentially normal. At 15 feet, the oxygen concentration is 20.18 percent,'Which is within the normal air concentration range.
Therefore, a negligible impact is expected to the control room operators.
3.
Hydrogen Through Check Valves -- (Case 3)
For this case, it is assumed that a broken pipe will release hydrogen 16 feet east of the CB-2 intake. Flow will be limited by two excess flow check valves located in parallel. The shutoff setpoint is 75 scfm. A conservative value of 225 scfm was used in the analysis.
A e
Trhjtn Nucisar Plant Document Centrol Dask ji -
Docket 50-344-May 31, 1989 License NPP-l' Attachment B Page 5 of 6
'From Reference 4, the maximum line size. carrying hydrogen is 3/4 inch'
~
. pipe. However,-a more conservative 1-inch-line was used in the-analysis. From Reference l',
a Schedule 40 1-inch pipe has a.
,1.049 inch inside diameter.
Since all distances of interest, (distances to'the normal or emergency air intakes) are within Zone 3, only Zone 3 parameters were-J calculated.
Opening' Diameter
= 1.05 inchei:
Exhaust Velocity
= 38,210 fpm Constant K
= 6.20 Constant K'.
.= 7.01 Zone Zone 2 Bdry
= 0.35 feet Zone 2
. Zone.3 Bory
= 0.70 feet Distance Hydrogen s
y fy j
(feet) x o x o Content 1.0-
.5420 3.69 27.10%
5.0-
.1084-18.45 5.42%
7.5
.0723 27.68 3.61%
10.0
.0542 36.90 2.71%
16.0
.0339
-59.04 1.69%
20.0
.0271.
73.80 1.35%
25.0
.0217 92.25 1.08%
50.0
.0108 184.51
.54%
75.0
.0072 276.76
.36%
100.0
.0054 369.02
.27%
As shown above, the hydrogen concentration quickly dissipates, being below 2 percent at 16 fent away from the opening.
This concentration is below the flammability 3' limit for hydrogen. Therefore, no fire hazard is expected to the control room from a hydrogen line break.
Conclusions As shown above, release of nitrogen or hydrogen gas from breaks on the lines or ruptures near the nitrogen tanks do not adversely affect the control room habitability.
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't Document Control'Dask~
Trojen Euclear Plant o
pt J Docket 50-344 May 31, 1989
['
~ License NPF -Attachment B' t.
Page 6 of 6 e
,o-REFERENCES 1.
Flow of Fluids Through Valves. Fittings, and Pipe, Crane Technical
' Paper No. 410 Twentieth Printing - 1981.
1 2.
ASHRAE Handbook and Product' Directory. 1977 Fundamentals, American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., Fourth Printing.- 1980.
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3.
Nitrogen Tank Storage Drawing 6478-M78-1-4 (United States Steel Drawing No. 8KI2387U).
4 '.. Drawing M-232, Rev. 28, Miscellaneous Cas Supply System.
I
.5.
Drawing M-285 Sheet'2,'Rev. O, Heating, Ventilating, and Air-Conditioning, Control Building Plan of Roof.
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