ML20002E372
| ML20002E372 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 01/22/1981 |
| From: | Cross J TENNESSEE VALLEY AUTHORITY |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8101270647 | |
| Download: ML20002E372 (5) | |
Text
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 374o1 500A Chestnut Street Tower II G
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L January 22, 1981 i:
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. cn Director of Nuclear Reactor Regulation 2
MN Attention:.Mr. A.'Schwencer, Chief Ti 3!
Licensing Branch No. 2 U
W a#2 Division of Licensing U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Schwencer:
In the Matter of
)
Docket No. 50-327 Tennessee Valley Authority
)
As requested by V. S. Noonan, Assistant Director for Materials and Qualification Engineering, during the site visit to Sequoyah Nuclear Plant on January 21, 1981, enclosed are discussions related to the following.
1.
Short Term Thermal Effects of a Hydrogen Burn on Equipment 2.
Assessment of Temperature Curves D and E for Equipment Survivability Evaluations If you have any questions, please get in touch with D. L. Lambert at FTS 857-2581.
Very truly yours, TENNESSEE VALLEY AUTHORITY
//d-J. L. Cross, Executive Assistant to the Manager of Power Subscribe worn t before 1981.
me this _
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Notary Public My Commission Expires Enclosure An Equal Opportunity Employer
ENCLOSURE 1 SHORT TERM THERMAL EFFECTS OF A HYDROGEN BURN ON EQUIPMENT The thermal effects of a hydrogen burn on equipment and structures located inside containment can be considered in two parts. There is a short term response due primarily to the presence of a flame and a longer term effect due to the residual energy in the atmosphere. An ultimate capability analysis of the short term temperature response of a transmitter' case was provided in our December 24, 1980, submittal.
The transmitter case has since been reanalyzed using more realistic assumptions and this analysis is discussed in the following paragraphs. As for the longer term thermal effects from a degraded core accident on equipment, these issues are discussed in Appendix B of the December 15, 1980, quarterly report on hydrogen and combustion and control at Sequoyah in our December 24, 1980, submittal, and in to our January 22, 1981, letter.
The transmitter case modeled is representative of the transmitters used in Sequoyah that are required for a degraded core event. The transmitter case modeled is a cylinder 7 inches in oiameter and 6 inches deep. The casing is 1/4 inch thick carbon steel. The interior of the case was modeled as dead air. The transmitters in the plant are located outside the crane wall in the dead ended regions on steel instrument racks or mounted to the wall. The walls end racks were conservatively neglected in the analysis. CLASIX resalts assumed a
. flame speed of 6 feet per second, which resulted in a burn time in the dead ended regions of two seconds. This value was used as the burn time in this short term analysis.
The Fenwal tests showed the ability of the igniters to initiate combustion of steam-air-hydrogen mixtures in which the hydrogen concentration was less than 10 volume percent (10 v/o). This data is supported by other tests and a considerable amount of published data.
It should be noted that the Fenwal tests also showed that for a test that modeled the small break LOCA hydrogen releases predicted at Sequoyah, the mixture burned when the hydrogen concentration react'd 5 v/o. Consequently, for this short term temperature analysis, a 10 v/o mixture was used to conservatively determine the flame temperature.
The adiabatic flame temperature of a dry air-10 v/o hydrogen mixture is 2350o F.
Flame temperatures are primarily a function of the fuel-air mixture. If a hydrogen concentration of 5 v/o was used, the adiabatic flame temperature would be around 13000 F.
The 23500 F value used is conservatively high es it neglects water vapor, disassociation, and heat transfer from the flame, all of which are present in the plant and which would result in lower flame temperature. Figure 1 provides the temperature profile used in the analysis.
O
Heat transfer from the flame and residual: gases to the transmitter was based on radiation and natural convection. The emissivity of the flame and residual gases was conservatively assumed to.be one. A time dependent heat transfer coefficient was used to account for the fact that the radiative heat transfer is dependent on the distance between the flame and the transmitter. The initial temperature of the transmitter was assumed to be 1600 F based on LOTIC calculations and the heat transfer coefficients were applied to all exterior surfaces of the transmitter simultaneously. The analysis showed that the exterior surface of the casing experienced a temperature increase of 300 F.
The interior surface of the casing increased 120 F.
The equipment will not experience any deleterious effects from temperature rises of this magnitude. Since this is a conservative analysis, we conclude that the equipment which may be subjected to a hydrogen burn environment and which is required for cold shutdown of the plant after a degraded core event and for prevention of breech of containment will not experience unacceptable degradation from the short term effects of a hydrogen burn.
l TEMPER ATURE PROFILE USED TO EV ALU ATE SHORT TERM EFFECTS ON EQUIPMENT 2500 23500F (MODER ATE LEVELS OF CONSERVATISM) l 2000 E
O w
W E
1500
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F i
Ew 0-1000 M 10000F 2
m F
500 M3OO OF l
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O 1
2 3
4 5
6 7
TIME (Sec.)
ENCLOSURE 2 ASSESSMENT OF TEMPERATURE CURVES D & E FOR EQUIPMENT SURVIVABILITY EVALUATIONS Temperature transient curve E is a by-product of the present CLASIX computer code which does not take into consideration. plant structural heat sinks. The present code was written to conservatively calculate the transient containment pressure during a postulated hydrogen burn event. As such, the disregard of structural heat sink would make the pressure calculations generally more conservative. The code was not intended to generate temperature transient curves for th9 purpose of equipment survivability evaluation. Because of the dir. egard of structural heat sinks, there is very ineffective removal of heat from the atmosphere in the lower compartment. If structural heat sinks are taken into consideration, there is insufficient energy in the atmosphere during and after the hydrogen burns to sustain the temperature profile depicted by curve E.
For this reasons, curve E grossly over-estimates the actual temperature transients and should not be used for equipment survivability evaluation.
A conservative calculation was made by TVA on the long term temperature rise in the plant heat sink during a postulated hydrogen burn event. The asymptotic (maximum) temperature was calculated to be approximately 2750 F (curve D). This curve was developed by putting all the energy in the post-H2 burn compartment ambient air into the steel heat sinks in the lower component. The concrete heat sinks were intentionally disregarded as an added conservatism.
If a multiple burn scenario is postulated, one would have a gradual temperature increase after each burn as the ambient air and the structural heat sinks approach thermal equilibirum between burns and eventually approact a value no higher than 275 F at the end of the last burn.
It should be noted that the 2750 F is bounded by the main steam line break temperature for Sequoyah.
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