ML20004E215
| ML20004E215 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/24/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8106110359 | |
| Download: ML20004E215 (8) | |
Text
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TENNESSEE VALLEY AUTHORITY CH ATTANC OG A. TENN ESSEE 37 201 400 Chestnut Street Tower II
/hE April 24, 1981
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k V% (g Q Ug7 IS Director of Nuclear Reactor Regulation C
Attention: Mr. A. Schwencer, Chief f
.Ah Licensing Branch No. 2
' #s \\y Division of Licensing
'u U.S. Nuclear Regulatory Ccanission Washington, DC 20555
Dear Mr. Schwencer:
In the Matter of
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Docket No. 50-328 Tennessee Valley Authority
)
Enclosed are revisions to TVA's responses to the questions for unit 2 of the Sequoyah Nuclear Plant which were transmitted by R. L. Tedesco's letter to H. G. Parris dated April 14, 1981. Wese questions address the technical issues on hydrogen control considered in the course of the recent public hearing on the McGuire Nuclear Plant.
Se initial TVA response was transmitted to you by my letter dated April 17, 1981. Revisions to quest ons 1, 4, and 9 are provided per the request of Mr. C. Tinkler of the Containment Systems Branch.
Very truly yours, TENNESSEE VALLEY Nmf0RITY hb L. M. Mills, Manager Nuclear Regulation and Safety Sworn to and subscribed before me this, 2 c G. day of /04] 1981
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Enclosure C
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. Mr. A. Schwencer April 24, 1981 cc (Enclosure):
Mr. K. C. Canaday, Manager Project Coordination & Licensing Duke Power Capany P.O. Box 33189 Charlotte, North Carolina 28242 Mr. Juan Castresan American Electric Power Service Co.
2 Broadway New York, New York 10004 l
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___, ENCLOSURE-i 1.
TVA does not believe that the lower compartment would be inerted with either steam or fog following a small break (S D-type) event 2
J during the time in which significant amounts of hydrogen could be released into containment. By definition, an inerted atmosphere would not be flamable for any concentration of hydrogen. For-example, Shapiro and Moffette showed that roughly a 65-percent concentration of steam by volume could effectively inert a hydh6 gen-rich atmosphere. However, a smaller steam fraction could prevent the combustion of a very low hydrogen concentration mixture that might -otherwise be flammable without steam simply by depressing the concentration below the lower flamability limit.
A mixture with a steam fraction less than approximately 60 percent by volume would not be inerted for concentrations of hydrogen above the lower flamability limit.
As explained in our response of December 1, 1980, to the NRC Request for Additional Information on the Sequoyah Interim Distributed Ignition System (IDIS), Volume 2, item ', the 4
concentration of steam during the long term following an S D2 l
event when hydrogen could be present is sufficiently low to have little effect on flamability limits and, therefore, the behavior l
of the igniters. When the air return fans are turned on at ten minutes after a phase B containment isolation signal, the lower i
compartment atmosphere is diluted with 80,000 cfm of air and l
rapidly deinerted. This occurs long before hydrogen generation l
would be expected.
(See attached figure 1-1 from our previous submittal.) TVA has been informally requested by the NRC to evaluate the consequences of extending this original degraded core i
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scenario (S D until approximately 75-percent metal-water reaction 2
occurs) to include the effects of reflood and any further hydrogen or steam releasas that could occur at that time. This extended scenario will be analyzed and the results provided as part of our overall submittal on the Permanent Hydrogen Mitigation System,
scheduled for October 1981. However, it is our prelidinary judgement that neither a significant release of hydrogen nor lower compartment steam inerting from the boiloff of water supplied by a safety injection pump would occur following S D reflood.
2 Similarly, the potential for significant fo6 formation after a small break would be low d' e to the relatively low steam u
concentrations that would be present when hydrogen could be released. In addition, experimental evidence of fog inerting was observed after a stepwise injection of steam followed by ambient cooling. During a small break, the superheated steam and hot hydrogen would be released into the lower compartment continuously during the event. Such continual injection of a high enthalpy mixture would reduce the tendency for fog formation due to the increased energy removal required before dropwise condensation could result. Further, experimentally observed fogging appeared to be due to a wil-cooling effect. D'at the Sequoyah lower l
compartment has a much smaller r:tio of surface area to volume i
than the experimental facility. Also, those surfaces would be prewarmed before a?ny release of hydrogen. thus reducing their potential for condensation. Finally, it is expected that continual and local fog formation could only occur at the interface betweer4 colder upper compartment air and warmer lower l
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compartment air during air return fan injection into the lower compartment. However, the cooler air from the upper compartment would terd to sink to the floor placing the localized interface away from the igniters and low in the volume where any fog would rain out to the water present at the floor.
Even if inerting was somehow postulated to occur in the lower comp &rtment. due to steam or fog, given the hydrogen release rates associated with the original S D scenario continuous or 2
semicontinuous burns would occur in the upper plenum, as stated in our response to question #2 of this submittal. The consequences of such upper plenum burning would be acceptable. Temperature effects are addressed in our responses to questions #4, 5-6, and 7, while pressure effects are addressed in response to #8.
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4.
TVA's September 4,1980, submittal from J. L. Cross to Robert L.
Tedesco provides the type, location, quantity, and encapsulating material for the polyurethane foam insulation in the Sequoyah ice condenser. See attached Table 4-1 for information from our
, previous submittal. The intermediate deck doors contain an additional 1500 pounds of urethane foam enclosed in galvanized steel. The top deck blankets contain 500 pounds of polyurethane-foe.m encapsulated above and below in stainless steel sheets.
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" cam in the wall panels was blown in place using CO behind~
2 h,11ayered steel sheets. The edges of inidividual layers of the wall _ sections are overlapped to effectively provide a solid surface over the foam throughout the ice condenser. The foam is bounded on-the bottom by the concrete flor. The top' of the foam is covered by at'least a foot of nonflammable fiberglass insulation (flasunability defined per USCG 46CFR 164.009) and capped with sheet steel. The multilayered construction of the wall panels precludes a supply of air to the foam which would permit; combustion should a hydrogen burn occur in the ice condenser.
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TABLE 4-1 ICE CONDENSER POLYURETHANE INSULATION SLHMARY' Containment Wa'.1 i
Type:,. Rigid urethane foam, "Chempol 30-1324/30-1426" (Freeman)
Conductivity: 0.21 BTU-in./hr ft - F 3
Density: 3 lb/ft 1
Approximately 26,000 lb.
Total Weight:
Encapsulation: Foamed-in-plade behind multilayer steel duct panel i
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9.
Removing electrical power to the ice condenser air handling units (IC AHU's) before possible hydrogen generation and release to the containment would stop forced circulation of air through the IC air ducts. The cooling function of the AHU's would not be required after a LOC; and was not assured in the original design.
Even after tripping the AHU's, however, the intake grilles of the AHU's and the roturn ducts would still be open to the-general upper plenum space. Two intake scilles are located on the front face of each AHU. The AHU discharge flows inLo a horizontal circumferential supply header, down into the vertical supply ducts, turns and flows up into the vertical return ducts, and then out into the upper plenum. Since the AHU intake grilles and associated return ducts are located within a few feet of each other around the upper plenum, they would be exposed to essentially the same pressure during an upper plenum burn. Thus, there would be no differential pressure mechanism to set up flow in the now-stagnant duct system which could induce significant j
quantities of either hydrogen or hot gas. Therefore, tripp? rr the IC AHU's would pr eclude hydrogen combustion in the duct system and l
appreciable foam heatup due to ingestion of hot gases into the l
duc ts.
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TVA will modify its emergency operating instructions for units 1 and 2 to remove power from the IC AHU's to prevent forced circulation of air 2
through the IC ducts during postulated hydrogen combustien events in the upper plenum. These changes will be complete before initial criticality of unit 2.
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