ML20038C015
| ML20038C015 | |
| Person / Time | |
|---|---|
| Site: | Mcguire, Sequoyah, Cook, McGuire  |
| Issue date: | 12/01/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Adensam E Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19268A511 | List: |
| References | |
| NUDOCS 8112090421 | |
| Download: ML20038C015 (36) | |
Text
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TENNESSEE VALLEY AUTHORITY CH ATTAMOOGA. TENNESSEE 374ol 400 Chestnut Street Tower II December 1, 1981 f' m ; 1 PN g ;% '.
!T l Q s o, e y
-%y ISa g Director of Nuclear Reactor Regulation b
%% C/
Attention: Ms. E. Adensam, Chief s6 Licensing Branch No. 4 %
M Division of Licensing .
U.S. Nuclear Regulatory Commission Washingtcn, DC 20555
Dear Ms. Adensam:
In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 As requested by R. L. Tedesco in a letter dated July 8,1981 to H. G. Parris, we provided an initial response to the request for additional information on hydrogen control for our Sequoyah Nuclear Plant. The initial response was submitted on October 1, 1981 by letter from me to you and provided information on questions 1, 2, 4, and 5
, (transmitted in the July 8, 1981 letter).
Enclosure 1 contains our response to questions 3, 6, 7, 8, 11, 12, 13, and 14, as well as revised responses for questions 1 and 2.
Information for questions 9 and 10 is being reviewed by Duke Power and American Electric Power (AEP) as directed by the NRC in the July 8, 1981 letter. We expect to have a coordinated response provided to you for questions 9 and 10 on or before January 4,1982.
In response to your letter dated August 27, 1981 to H. G. Parris which requested information on equipment temperature response to hydrogen burns, we provided an initial response by my October 31, 1981 letter to you. Enchsure 2 provides the final response to questions A.1 through A.8 and B.1, regarding equipment suctivability and pctential secondary ,,
,bl fires. b phan Included as attachments for Enclosure 1 and Enclosure 2 are a M r.onproprietary topical report, OPS-036A31 (attachment 1) and a proprietary tqical report, OPS-07A35 (attachment 2) concerning the /
CLASIX Computer Code; the " Containment Response to Degraded Core O 'd-l Events" for the Sequoyah Nuclear Plant (attachment 3); and a #
nonproprietary version of the Equipment Survivability Report for the JH b* )(
0.q goW , ne d
N N eti2o90421 a112o1 PDR ADOCK 05000327 #p 'I 9 PDR OD An Equal Opportunity Employer j
Director of Nuclear Reactor Regulation December 1, 1981 Sequoyah Nuclear Plant dated November 16, 1981 (attachment 4). The applicable proprietary pages for the Equipment Survivability Report for the Sequoyah Nuclear Plant dated November 16, 1981 are provided in attachment 5.
Because attachments 2 and 5 contain infermation proprietary to Westinghouse Electric Corporation, the owner of the information, an affidavit (AW-76-3) signed by Westinghouse is also attached (attachment 6). The affidavit provides the basis on which the information may be withheld from public disclosure in accordance with 10 CFR Part 2.790. Therefore, we request attachment 2 and attachment 5 be withheld from public disclosure in accordance with 10 CFR Part 2.790.
Correspondence with respect to the proprietary aspects of this request for withholding from disclosure or the supporting Westinghouse affidavit should be addressed to R. A. Wieseman, Manager, Regulatory and Legislative Affairs, Westinghouse Electric Corporation, P.O. Box 355, Pittsburgh, Pennsylvania 15230. A letter authorizing the use of the proprietary report, OPS-07A35, by TVA is included ae attachment 7 Very truly yours, TENNESSEE VALLEY AUTHORITY 0N Lh M. Mills, Manager Nuclear Regulation and Safety Sworrg aud subs ibed efore me 1this/ day cA 1981 V
- Notary Public My Commission Expires N Enclosure
g - M-ENCLOSURE I RESPONSE TO R. L. TEDESCO'S REQUEST FOR INF0hMATION t REGARDING HYDROGEN CONTROL DATED JULY 8,1981 TO H. G. PARRIS SEQUOYAH NUCLEAR PLANT HYDROGEN CONTROL NRC Question No. 1 ,
Describe the permanent hydrogen igniter system installed inside containment. Provide and justify the criteria used for the system' design. Include in your discussion the proposed surveillance testing and technical specifications for the permanent system.
TVA Response (Revised)
The Permanent Hydrogen Mitigation System (PHMS) is designed to be a reliable system of distributed ignition sources capable of igniting hydrogen at low volumetric concentrations in a post-LOCA environment. -
The gradual addition of the helt of combustion due to the controlled burning of the hydrogen allows the active and passive containment heat sinks to reduce the overall impact and maintain a sufficient margin of safety below the containment ultimate capability. Descriptions are provided below of the PHMS and its design criteria, surveillance testing, and techn'.e.:1 specifications.
The principle of the controlled combustion concept selected for the PHMS is to ignite hydrogen at any containment location as soon as the concentration exceeds the lower flammability limit. To assure this, thermalg igniters capable of maintaining a minimum surface temperature of 1500 F were specified. Such igniters as the GM AC glow plug have been shown to reliably initiate combustion of hydrogen mixtures of 5- to 10-percent concentratieu. Other types of thermal igniters are still being examined as potential candidates.
To assure adequate coverage, a total of 64 igniters will be distributed throughout the major -egions of containment in which I hydrogen could be released or to which it could flow in significant quantities. There will be at least two igniters, powered from separate trained so'.rces, located in each of these regions. See figures 2 through 6 for igniter locations. Justification of those regions in containment for which igniters were not provided is included in the response to Question No. 2.
Following a degraded core accident, any hydrogen which is produced would be released from a break or the pressurizer relief tank into the containment in the lower compartment inside the crane wall. To cover this source region, there will be 22 igniters (equally divided between trains) located in the lower compartment inside the crane wall. Four of the igniters will be equally distributed around the interior of the crane wall below the ice condenser inlet doors at elevation 703'.
Four more igniters will be equally distributed around the exterior of the reactor cavity at elevation 703' . These eight igniters are so located to allow the partial burning that accompanies upward flame propagation at low (4-6 v/o) hydrogen concentratione. Two igniters will be located at the lower edge of each of the five steam generator and pressurizer enclosures at elevation 731'. A pair of igniters will 2
1
)
i be located in the top of the pressurizer enclosure at elevation 772'.
Another pair of igniters will be placed above the reactor vessel in the upper reactor cavity at elevation 730'.
Any hydrogen not burned in the lower compartment would be carried up -
through the ice condenser and into the upper compartment. To cover these regions, there will be 26 igniters (equally divided between ,
trains) located in the ice condenser and the upper compartment. Since '
steam world be removed from the mixture as it passed through the ice bed, thus concentrating the hydrogen, a nonflammable mixture in the lower compartment could become a flamable mixture in the ice condenser upper plenum. To provide controlled combustion in this region, 16 igniters will be equally distributed around the upper
~I plenum at approximately elevation 785'. A description and '
justification of the criteria used to determine the number and , .
location of upper plenum igniters is included in the response to '
t Question No. 14. Four igniters will,be located around the upper compartment dome at elevation 846 '. Four more igniters will be spaced i around the inside of the crane wall.below the upper plenum exit at elevation 787'. An "A" train igniter will be located above the "A"
- train air return fan at elevation 755' and a "B" train igniter will be ~
located above the "B" train fan at elevation 746'.
The two air return fans provide recirculation flow from the upper compartment through the accumulator rooms, pipe chase, and HVAC rooms (the sum of which are referred to as the " dead-ended" volume) and back /
into the main area of the lower compartment. To cover these regions, there will be 16 igniters (equally divided between trains) distributed throughout the rooms through which the recirculation flow passes. A pair of igniters will be located in each of the four accumulator rooms, the two HVAC rooms, the instrument room, and the heat exchanger s room between elevations 700' and 716'. (
The PHMS will be qualified environmentally and seismically. The components inside containment will be qualified to maintain their functional capability under the full range of main steam line break
! and post-LOCA temperatures, pressures, humidity, radiation, and chemical sprays present in the containment. These components of the system must survive the effects of multiple hydrogen burns and will be protected from containment spray impingement and flooding. All components of the system outside containment will be qualified to operate in the environment in which they are located. In addition, the PHMS will meet the requirements of seismic Category I. '
The igniters in the PHMS are equally divided into two redundant groups. Each group has independent and separate control, power, and -
igniter locations to ensure adequate coverage even in the event of a single failure. In addition,'the current PHMS design has 16 separate circuits per group with only two igniters on each circuit. This feature adds an extra degree of independence to the system.
Separate control of each group of igniters will be provided in the ,
main control room (MCR). Manual actuation capability for each group will be provided in the MCR, and the status (on-off) of each group will t e indicated there. Further details of system actuation are provided in the response to Question No. 4.
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, e.
Separato treina of c1:ctrical powcr will b3 providad for each group of PHMS igniters. Power is supplied from the 480V ac control and
. auxiliary building vent boards which are part of the Class 1E ao auxiliary power system and automatically would be loaded onto the
' diesel generators upon loss of offsite power. Group A igniters receive power from the train A diesels and group B igniters from the train'B diesels. Power from the 490-volt vent boards is routed to the 480/120V ao igniter transformers located in the auxiliary building and from.the transformers to the 120V igniter distribution panels, also ,
/ located in the auxiliary building. Power at each of the 120-volt 7
- distribution panels is monitored and alarmed in the main control room
, if an undervoltage condition is detected.. Also, the position of each of the 120-volt breakers is monitored and alarmed in the main control room if any breaker is not in the closed position. Each igniter
- assenbly is powered directly from the 120V distribution panel. Each
, 120-tolt circuit supplies power for only two igniters, making a total of 32 circuits (16 per group). A failure in one of the circuits of the group will not prevent the remaining circuits in that group from performing their function. In addition, the Class 1E auxiliary power system will be protected from failures in the PHMS.
Surveillance testing proposed for the PHMS is similar to the testing
- b. currently performed for the Interim Distributed Ignition System (IDIS) e Testing will consist of energizing the system from the main control room and taking voltage and current readings at the igniter distribution panels located in the auxiliary building. These voltage and current
- readings will be compared to readings taken at the -
distribut, ion panels during preoperational testing of the system. The comparison of the two readings will indicate whether or not all the ignitsrs on#each circuit are operational. If the readings do not compare favorably, then the igniters on that circuit will be checked visually for on-off status. Since the measured presence of the proper baseline voltage and current on a circuit assures that the igniters on s that circuit are operational at.the minimum temperature, there is no
,e need to measure the temperature of each igniter as part of the surveillance testing. In addition, access to some of the more remote igniter locations in close enough proximity to allow temperature f
measurements would be difficult.
The operability of at least 31 of the 32 igniters per train will maintain an effective coverage throughout the containment, providing
- any inoperable igniters are not on corresponding redundant circuits which provide coverage for the same region. The two trains of igniters should be operable during operational modes 1 and 2.
If one train of the PHMS should become inoperable, it should be restored to operable status within seven days or the surveillance interval to verify that the other train is operable should be reduced to at least once per week. If both trains of the PHMS shou!d become inoperable, at least one train should be restored to operable status (and its surveillance interval modified as above) or be in at least hot standby within the next six hours. At least once every 92 days, the PHMS should be demonstrated operable by energizing the igniters and verifying that at least 31 igniters per train are operable. If an -
inoperable igniter is detected, it should be confirmed that the cor-responding redundant circuit does not contain an inoperable igniter. ,
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KEY TO FIGURES 2 THROUGH 5'
- Denotes Hydrogen Igniter Location g
Igniter Identification Format: "X" - X is power train designation
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((.' - EL-XXX - Designates the vertical location of the igniter (elevation)
AZ-XXX - Designates the radial location of the igniter (azimuth)
NOTE: When the-azimuth is not specified, the radial location of the igniter shown in the figure is approximate.
' Note figure 1 is omitted intentionally.
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i NRC Ctestion No. 2 l
l List the rooms within containment for which there is no direct coverage by igniters and justify exclusion of these regions.
j TVA Response (Revised) i As stated in the response to Question No.1, the principle of the ,
- controlled combustion concept selected for the PHMS is to ignite '
hydrogen at any containment location as soon as the concentration exceeds the lower flammability limit. To assure adequate coverage, 64
- ~ igniters will be distributed throughout the major regions of
' containment which have potential hydrogen sources or transport mechanisms. All major regions within the containnent have at least
- two redundant igniters, except for the four steam generator enclosures, the circumferential pipe chase, and the reactor cavity a below the reactor vessel.
No hydrogen source exists in the steam generator enclosures since the reactor coolant inlet and outlet nozzles are located in the main lower compartment region at the bottom of the steam generators approximately 36 feet below the entrance to the enclosures. Any primary system leaks in the steam generator would be into the secondary side and not into the containment. No significant hydrogen transport path exists through the steam generator enclosures since any hydrogen released in l the main region of the lower compartment would have to bypass the pair l of redundant igniters located at the entrance to each of the enclosures at elevation 731' without being ignited. There is no concentrating mechanism within the enclosures themselves that would transform mixtures below the lower flammability limit into flammable j ones. Any nonflammable mixtures that enter any of the enclosures
?
simply would be transported up through the enclosure, out the top, and back to the main region of the lower compartment by the air return fans of the hydrogen skimmer system.
No primary system hydrogen source exists in the circumferential pipe chase at elevation 680' since no primary system piping is located in the region. No significant hydrogen transport path exists through the pipe chase since any hydrogen released in the main region of the lower compartment would have to pass first through the ice condenser and upper compartment and then bypass the pairs of redundant igniters located in the #3 and #4 accumulator rooms without being ignited before entering the pipe chase. There is no concentrating mechanism within the pipe chase itself that would transform mixtures below the lower flammability limit into flammable ones. Any nonflammable mixtures that enter the pipe chase would be transported around the pipe chase and up into the #1 and #2 accuculator rooms anu the two fan rooms which all contain redundant igniters. In addition, this region is below the expected flood elevation following a design basis LOCA, including ECCS inventory and ice melt.
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~ . . .
l l
No primary system hydrogen source exists in the lower reactor cavity, i discounting a break in the vessel or its nozzles. No significant hydrogen transport path exists through the lower reactor cavity following an accident in which hydrogen is released in the main region of the lower compartment. The reactor building fan coolers that
- ventilate the reactor cavity during normal operation will be shut off on a containment isolation cignal following the accident, making the lower reactor cavity relatively isolated from the rest of the lower compartment. In addition, this region is below the expected flood '-
elevation following a design basis LOCA.
1 I
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NRC Qu~stion No. 3 Discuss the effects of igniter operation in lean (0-4 v/o) hydrogen mixtures for sustained durations (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) on the ability of the igniter to subsequently perform its intended function. Describe the testing performed to evaluate the temperature effects of surface recombination and possible igniter degradation.
TVA Response ,
Tests hate been perforned at TVA's Singleten Laboratory to determine the effects of glow plug igniter operation in lean (4 vol %) hydrogen
, in air mixtures for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> on the ability of the igniter to subsequently perform its intended function. The 24-hour lean mixture exposure test was performed, and the igniter was subsequently demonstrated to initiate combustion in an 8 vol % mixture, cycled to j determine surface temperature characteristics, and examined visually for surface degradation. All three methods indicated clearly that exposure of the igniter for long periods to lean mixtures did not degrade its subsequent ability to perform its function.
Before the 24-hour test, the glow plug igniter was cycled on for five l minutes and off until it cooled to ambient. Three such cycles were j repeated at both 12 and 14V ac, while the igniter surface temperature was measured and recorded for comparison later after the 24-hour test.
.I D i
i The 24-hour lean mixture test was conducted in a combustica chamber fabricated from a four-foot section of ttur-inch diameter, schedule 40 l pipe. The tube was placed horizontally with the igniter mounted i through an end plate at the centerline. The lean mixture was l maintained at a constant 4 vol % hydrogen in air for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> by passing a 20-sofh stream of that concentration through a small mixing chadber, then into the combustion chamber above the glow plug near the end, and out the opposite end. The hydrogen concentration was established and monitored with a gas chromatograph that sampled the stream at the inlet to the combustion chamber. Then the igniter was energized at 14V ac for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, while its surface temperature, as well as the atmospheric temperature approximately one-inch above and below the plug, was recorded throughout the test.
Following the 24-hour lean mixture test, the test apparatus was allowed to cool to ambient t>aperature. Then, using the same technique as before, a combustible 8 vol % hydrogen in air mixture was passed through the combustion chamber. The igniter was reenergized for two hours, while the surface and atmospheric temperatures were recorded. The atmoJpheric temperatures observed both above and below the igniter in the 8 vol % test were higher than those ia the 4 vol %
test. In addition, the atmospheric temperature above the igniter exhibited a transient behavior that suggested periodic combustion, j The overall higher temperatures, coupled with the trarsient profile i observed above thc plug, indicate that the igniter was still able to initiate combustion following the 24-hour lean mixture test.
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Following the two-hour test, the igni',er was energized through the -
same three on-off cycles at 12 and 14i ao as before the 24-hour test.
~
Comparisons revealed only slight dif.'erences in the peak temperature (approximately 15) that were within the accuracy of the thermocouple used in the measurement. These retalts indicate that the igniter was still able to reach comparable peak surface temperatures following the 24-hour and two-hour tests.
After all other testing was completed, the igniter was removed from '.
the combustion chamber and visually inspected. Some discoloration and surface roughness was evident, neither of which inhibited the proper operation of the glow plug. Both the discoloration and surface roughness were removed by light sanding.
In conclusion, the tests have demonstrated that sustained exposure to lean hydrogen mixtures does not affect the subsequent ability of the igniter to perform its function.
O e
---p-,me r , , - - - -
NRC Question No. 6 Submit a topical report on the CLASIX code; in this regard:
g a) Describe in detail the version of the CLASIX code used to perform the revised analyses, including a discussion of models, methods for solution, assumptions and input parameters.
b) Describe the efforts and results to verify the revised CLASIX cod'e, i.e.,
- 1) Provide comparative analyses to show the effects of model changes from the initial version as described in the TVA Core Degradation Program Report, Vol. 2. As a minimum comparative calculations should be provided to isolate and identify the effects of adding heat sinks, upper plenum volume, fan head characteristics.
ii) Quantify the effects of incorporating the radiation heat transfer model and describe the results of analyses to verify this model in its application to containment heat transfer.
iii) Provide a discussion of the program to verify the revised CLASIX code against other containment codes and experimental da ta. Include a discussion of both the Fenwal and EPRI hydrogen test data. Comparison of CLASIX prediction of hydrogen combustion tests should also describe the code input parameters where used options may affect the comparison.
c) Discuss the treatment of hydrogen addition to a volume in which combustion is calculated to be taking place, d) Discuss in detail the treatment of the internadiate deck doors and the effect of the doors functioning as check valvec on upper plenum burning and downward flame propagation. Discuss modeling of vents around the doors.
e) Provide the results of calculations to determine the sensitivity to selection of timestep sizes.
[
f) Discuss initialization of the CLASIX code with results of LOTIC 1 analysis; i) Discuss application of LOTIC 1 to small break analysis especially prior to fan operation or for breaks without fan operation.
ii) Discuss use of LOTIC 1 for analysis of superhested atmosphere conditions, g) Provide the results of analysis to identify the effectiveness of the ice bed in removing heat from a highly superheated steam-air-hydrogen mixture. Provide figures showing ice bed heat transfer ,
coefficients, flow rates.
h) Discuss the potential for preferential flow to the ice bed (maldistribution)- during various accidents. What is the 1
7 probability and consequence of the break release point being C adjacent to the lower doors with the hydrogen-steam release point being ad jacent to the lower doors with the hydrogen-steam release jetting into 1 or 2 bays of the ice condenser rather than uniformly mixing in the lower compartment. Discuss the possible effects of partitioning the ice bed model in the circumferential direction as well as modeling the lower compartment as several subvolumes.
- 1) Describe any plans for future modification of the CLASIX code. '
TVA Response (a) Refer to sections II-VI of the Topical Reports No. OPS-07A35 (proprietary) and OPS-036A31 (nonproprietary) dated October 1981 concerning the CLASIX computer code.
(b) (i) Refer to Appendix E of the topical report.
(ii) Refer to Appendix F of the topical report.
(iii) Refer to section VIII and appendices A-C of the topical report.
(c) Refer to sections III, IV, and V.D of the topical report.
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(d) Refer to sections II, IV, V.A.1, V.D, and VI of the topical report and table 8 of the report, "Sequoyah Nuclear Plant: Containment Response to Degraded Cere Events," dated November 16, 1981 (attachment 3).
(e) Refer to sections IV-VI of the topical report.
(f) The CLASIX code is no longer initialized with results of LOTIC 1 since it runs from the tegirning of the transiant. Initial conditions are assumed te be those from the FSAR containment accident analyses.
(g) Refer to sections II, IV, V.C, and VI of the topical report.
(h) The original design of the ice condenser considered postaccident malaistribution problems from nonuniform ice melting, small breaks, and jet impingement on the lower inlet doors which could result in a channel being burned through the ice bed. At that time, Westinghouse performed various calculations to model possible nonuniform ice bed melting and showed that burnthrough was not a problem and that considerable margin remained in the ice bed. Independent of the Westinghouse efforts, Battelle Northwest Laboratories evaluated ice condenser performance after being commissioned by TVA and Duke Power and confirmed that no burnthrough would occur. The phenomena associated with potential maldistribution would be comparable for hydrogen-steam jets as for pure steam jets evaluated originally and j found to be acceptable.
In particular, the arrangement of the primary system piping well below the ice condenser inlet doors precludes the break release point being adjacent to those doors and should allow substantial mixing to occur in the lower compartment. The EPRI/ utility-sponsored research program at the Hanford Engineering Development Laboratory was designed to ,
model lower compartment mixing following a small break LOCA in an ice condenser plant. These tests should provide additional evidence that the lower compartment atmosphere is essentially uniform and that preferential flow to the ice bed is unlikely.
(i) Refer to the cover letter of the topical report (Offshore Power System letter PST-NE-359 dated October 27, 1981).
NRC Quintion No.7 Provide a discussion of the results of analyses of the S D transient using-the revised CLASIX code as discussed above addressing the fb11owing; a) Identify and providc the results of a base ' case reference analysis and -
discuss the rationale for selection of the base case, e.g. ,
representation of a best estimate or bonding calculation. Provide j, justification fv.' the characterization of this analysis. The resulta j should include plots of pressure, temperature and gas. concentrations for the various regions of the containment.
b) Provide the results of sensitivity studies to determine the 'effect of l operation of 1 or 2 trains of fans and sprays.
I i) combustion of lean hydroger. mixtures with partial combustion; l 11) complete combustion of hydrogen at various setpoints; j iii) the use of different combustion assumptions in separate regions of the containment; iv) combustion of hydrogen assuming various flame speeds; identify a best estimate and bounding value for -flame speeds; and l
I v) simultaneous ignition at multiple igniter sites.
d) Identify periods in the transient where hydrogen combustion is limited or precluded by the quantity of oxygen available in the compartment.
e) Identify the analysis (es) to be used as the biais for determining the maximum temperature response of essential equipment. Provide justification for the case (s) selected.
f) Where pressure effects are a major consideration in determining the survivability of equipment, such as the air return fans, idencify and justify the analysis used as the basis for assuring the equipment will function as intended.
g) Considering the capability of the containment shell, crane wall, and the operating deck perform an analysis to determine the maximum concentration of hydrogen which could be tolerated to burn to completion in the upper compartment considering multiple ignition sites and appropriate flame speeds.
h) Since the original S D 2 transient analyses did not mechanistically consider termination of the accident it is necessary to identify the i
effects of core recovery. Therefore, either demonstrate that various modes of core recovery do not adversely affect the hydrogen and steam release rates and therefore the containment pressure and temperature I
response or provide the results of analyses which address the more likely scenarios involving core recovery, i) Provide the fan head curve used in the CLASlX model. In order to demonstrate the effects of variable fan flow provide figures of fan flow as a function of time.
8
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J TVA Responsa
- }
3 (a)' Refer to section A of the report, "Sequoyah Nuclear Plant:
Containment -Response to Degraded Core Events," dated November 16, !
., 1981.
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') (b) Refer to section B of the containment response report and Figure 2. -
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(c)(1)
,, Refer to sections A and B of the containment response report and '
i' Figure 2.
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(d) Refer to section B of the containment resp'onse report.
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(e) An S2 D event with a one ft/s flame speed was used as the base
, case for evaluating the temperature response of equipment.
u Also, refe: to section A of the containment response report.
- l lj (f) The S2 D base cass' discussed in section A of the containment j response report was used to determine the pressure response of
', L - equipment to hydrogen burns.
I
~j (g) Refer to section E of the containment response report, dated U November 16, 1981 -
(h) Refer to section D of the containment response report, dated
. November 16, 1981.
(1) Refer to Append 3x E of the topical report and table 8 of the containment response report.
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NRC Quection No. 8 Identify the spectrum of accidents which you have conaidered in your evaluation of the distributed ignition system. Discuss the rationale for selection of the various accidents. Discuss the basis fbr assumptions regarding termination of the accident prior to core slump if applicable.
Provide the assumptions and results of CLASIX analyses performed to evaluate the containment atmosphere pressure and temperature results, similar to that provided for the S 2D transient, for the various accident sequences selected.
TVA Response Refer to section C of the containment responsa report NRC Question No._9_
Provide a quantitative evaluation of the probability and effects of forming a fog, comprised of water droplets, inside containment. This evaluation abould address the following items:
a) Identification of the range of droplet sizes and requisite volumetric density to preclude combustion of hydrogen or affect combustion characteristics such as flame propagation. Provide the basis, including experimental evidence, to support these conclusions.
b) Consideration of the probability and consequences of fog formation in the various regions of the conta*nment (e.g., lower compartment, ice condenser).
TVA Response Westinghouse and Acurex/ Factory Mutual are reviewing the resporise to the question. We expect to submit the coordinated response on or before January 4, 1982.
NRC Question No. 10 Provide a quantitative evaluation of the probability and effects of producing supersaturated steam conditions in the various containment compartments. Discuss the effects these conditions may have on igniter performance. Reference any test data used to support your conclusions.
TVA Response Westinghouse and Acurex/ Factory Mutual are reviewing the response to this question as directed by the NRC staff. We expected to provide the coordinated response on or before January 4,1982.
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NRC Quietion No. 11 The utility arguments presented to date on the issue of transition to detonation in the ice bed appear to be focused about two points:
- 1) The upper plenum igniters will burr U p-mixtures as they first become flammable, if richer mixtures begin td be formed the flame front will propagate downward in the ice bed where sufficient steam is condensed to support a flame; and .
S. .
- 2) The geometry of the ice condenser upper plenum is not conducive to producing detonations.
a) Please provide any references to supporting test data derived from a configuration which is analogous to the phenomena described in item 1.
b) It appears that the argument presented in item 1 relies upon a generally stable horizontal flame. Discuss the implications of localized downward flame propagation and consequential crossflow through the ice bed.
c) Discuss the applicability of the EPRI tests, designed to study transition to detonation, to the ice condenser geometry, d) Discuss the applicability of E?RI tests designed to study the effects of obstacles to the geometry of an ice conden*or plant.
e) Provide the L/D value applicable to the ice condenser region and evaluate the acceleration of burns initiated in the lower compartment -
which propagate through the ice condenser.
TVA Response -
(a) The following response was provided by- Dr. Bernard Lewis and Mr. Bela Karlovitz:
- "As soon as the mixture becomes flammable it will be ignited by glow
] plugs in the upper plenum and the flame will move downward into the j ice condenser along the boundary layers. The flame settles to a level
- where the mixture turns flammable owing to water vapor c'..ndensation.
If the mixture is already flammable in the lower compartment, it is ignited there by the glow plugs and only burned mixture passes through the ice condenser. The ice condenser is never filled 'with a strong H,-
air mixture where the H2 n entration approaches the detonable limit 7
" Measurements of detonation velocities in mixtures with various H concentrations show that the detonation limits are sharply defineb.
At the limits, the detonation velocity d velocity, creating a weak pressure wave.yops It off sharply follows to sound that outside of See, for example, Lewis and von Elbe " Combustion Flames and Explosions of Gases," 1961, Figure 279, page 530, and Figure 284, page 536. -
i
the detonable limits no tacisition to detonation is possible for any geometry of the system. Tc prove this statement, experiments at various geometries should always be carried with mixtures within and outside of the detonable range.
"Results obtained for transition to detonation under a given geometry of a system are applicable only to similar geometries; '
for example, values of L/D obtained in a smooth-bore tube are not applicable to a rough surface tube or to more complex systems.
The complex geometry of the ice condenser could not be simulated by a simplified test system."
(b) The following response was provided by Lewis and Karlovitz:
"The flame will spread in every direction from the glow plugs in the upper plenum. As the flame reaches the top of the ice condenser baskets, it will move downward in the boundary layer of the stream. Structural elements crossing the stream will act as flame holders and carry the flame across the stream. Ultimately, 5 flames will settle in a zone where sufficient water vapor is removed to render the mixture flammable.
" Flashback of flames into tubes was one of the earliest phenomena whic.4 has been studied extensively. - The experimental results are summarized by recognition of the fact that flashback is controlled by r,he gelocity gradient of the flow in the boundary layer at the wall. The velocity gradient of the flow in the boundary layer can be calculated from a diaggam which was originally published by Prandtl and Tietjens' an thePrincetonSeriesonHighSpeedAerodynamics.greprintedin
" Assuming equivalent diameter of 50 cm for the channels between the ice baskets and one foot (30 cm) average flow velocity, the Reynolds number of this flow is 11,000,jnd the velocity gradient in the laminar boundary layer is 42 see "Thic velocity gradient is to be compared with the critical boundary velocity gradient for flashback given on figures 93, 99, and 100 in reference 2 which show that for flur.es having a 2
Lewis and von Elbe ibid 1961 edition, pages 243-253 fPrandtlandTietjens"AppliedHydro-Aeromechanics,"McGraw-Hill.
High Speed Aerodynamics, Vol. II, " Combustion Processes,"
Princeton University Press,1956, page 359.
ltnin:r burning valocity of e. bout 40-50 c;/cto, tha critic 21 boundary velocity gradient is in the order of 400 to 600 sec-3 .
Accordingly, flames of even very weak hydrogen-air mixtures will flash back in the boundary layer of the flow in the ice condenser."
(c) The EPRI Whiteshell test plan, which wiu established in early March 1981 after extensive discussions among EPHI, AEP-Duke-TVA, Whiteshell-AECL and Ontario Hydro, reflects the soveral objectives that the group set out to realize. The details of the- ,
Whiteshell program have been related to the NRC through quarterly research reports and discussed with the staff in pm son on different occasions. Here, the key elements of the research program which are pertinent to the issue of hydrogen combustion are summarized.
The principal thrust of the Whiteshell effort is focused on providing confirmatory information in support of our selection and implementation of a distributed ignition system and in augmenting the current understanding of hydrogen combustion phenomena which are pert' pent to the application of that system.
We have maintained, based on the recommendations of Dr. B. Lewis ~
and Mr. B. Karlovitz and on careful evaluations of plant geometries, current literature er.d accident parameters, that the existing experimental data on transition from deflagration to detonation do not support as credible the possibility of its occurrence in un ice-condenser plant. It is within this reference frame that the Whiteshell pipe-sphere test configuration was conceived, that is with the intention of investigating flame acceleration and propagation in general.
The modeling of an ice-condenser geometry for transition from deflagration to detonation phenomenon was found to be complex and impractical. There is a general consensus in the technical community that data collected from reduced scale models or models which do not reproduce the exact configuration, including material surface roughness, initial temperature, etc. , of an ice condenser would not be conclusive. In view of this situation, a commitment was made to utilize the pipe-sphere configuration at Whiteshell as a best effort to acquire more fundamental knowledge on the phenomenon of transition to detonation and not to model the ice-condenser geometry specifically.
(d) As a part of the experimental effort at Whiteshell, described in the response to Question #11(c), the utilities have undertaken to study the effects of physical phenomena which result from the presence of obstacles in the event of hydrogen combustion. A series of experiments are being concluded in which cffects of turbulence generated by either a fan or the presence of gratings are being investigated.
e
It is our belief that under conditions which are prototypic of an S2 D type event, the aforemertioned Whiteshell turbulent l experiments will adequately address conditions similar to those i in an ice-condenser plant. Morecever, in calculations pertinent I
to the hydrogen mitigation and control system, conservative l' assumptions have consistently been applied whion would correspond to the existence or' turbulent effects upon the overall safety evaluation of the plant. The forthcoming results from ,
l Whiteshell chould confirm the validity of assumptions used. -
1 '
(e) The acceleration of a flame is generally recognized as a complex phenomenon. It is known that rapid flame acceleration requires strong turbulence which may be generated by interaction of flow ahead of the i flame with interior surfaces and obstacles. The turbulence generated l in a given situation and its effect on the flame acceleration process l 13 strongly dependent on the geometry among other factors such as heat
- transfer in the region of interest. There are no theories at present for quantitative prediction of flame acceleration. Experimental results obtained for a certain geometry are applicable to that geometry alone and cannot be extrapolated to other geometries. In particular, Lewis and Karlovitz have stated that "the L/D obtained from experiments in pipes is applicable only to pipes and is not applicable to the ice condenser."
f i
l Moreover, we maintain that the geometric ratio, L/D, is not necessarily a representative constant to be used to characterize the ice bed flow channels since they differ from a circular pipe for the purpose of flame propagation. The geometry of the ics bed is far less
, - constrictive than that of a closed pipe. The flow channel surrounded by each set of four ice baskets is actually open on all four sides between the baskets over their entire height. In fact, the ice basket design effectively allows crossflow between channels to prevent flow imbalances and maldistribution in ice melting raten. The melting of ice as the accident prograssed would only open up the ice basket flow paths even more. Therefore, the sideways confinement in the ice bed is limited and is unlike experiments in pipes with complete radial confinement and one-dimensional flame propagation.
Further, as stated in our response to Question #7 and in earlier submittals, the operation of the distributed ignition system will maintain the hydrogen concentration in the lower compartment below 8 v/o. Burning at such low concentrations would produce weak flames with very little potential for flame acceleration. Hence, based on the lack of one-dimensional confinement in the ice bed flow channels and the maintenance of low concentrations of hydrogen, we believe that combustion initiated in the lower compartment and propagating through the ice condenser is not expecced to be subscantially different from that occurring in other parts of the containment.
e
NRC Ouastion No. 12 Provide analysis to address the consequences of continuous or near continuous bu n;cg in the ice bed or upper plenam region. Describe the models, assumptions, and results of analysis to evaluate the decomposition or burning of materials in this region. Consider the effects of 2-3 dimensional heat transfer in the process. _ Address the likelihood of inadvertently supplying oxygen to support combustion of foam behind the wall panel ducts.
I TVA Response The following response was provided by Duke Power Company: "Of concern in consideration in hydrogen burning in the ice condenser is the possibility that the insulating foam in the ice condenser walls may decompose under heat and produce flammable decomposition products. The ignition of these products would then add to the energy release in containment and produce
, higher containment pressure. It is necessary, therefore, to analyze the heat transfer from flames residing in the ice condenser to the ice condenser wall materials and then to assess the possible adverse effects on the insulating foam.
"The large majority of foam is behind a double duct where cooling air cicculates under normal conditions. At the junction between ducts is a narrow area where the foam is more vulnerable, being protected by a steel flange. As a forcing function for the analysis, a band of flame one inch thick was assumed to occupy the entire ice condenser an?
remain at a constant level for 45 minutes. The axial location was chosen at the midgoint of the ice baskets. The flame temperature was chosen to be 1600 F, conservatively high for burning at 8.5%-9% hydrogen by volume. Hot gasses were assumed above the flame level, with the temperature of the gasses taken to be that behind a moving flame front at one ft/s; the temperature profile in the ice condenser as a function of .
height is shown in figure 12-1. All of these assumptions are considered conservative for the following reasons. Actual thickness of the flame band is likely to be less than 0.4 inch according to testimony by Bernard Lewis during the ASLB hearings on McGuire hydrogen control. A stationary flame imparts the maximum energy in a very small area, thus causing the maximum te=perature rise.
"Escaune of the conplex geometry and boundary conditions, it was j decided that the computer code HEATING 5 would be used for the solution to the heat transfer problem. The problem was modeled in three dimensions, using approximately 2700 nodes. Radiative and convective i heat transfer from the flame and hot gasses to the wall were modeled.
Heat conduction in solids, and radiative and convective heat transfer
] across gaps, were included in analyzing heat transfer tc and through the ice condenser wall.
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"The results of the analysis fbr ice condenser roam temperature rise due to heat input from a stationary flame and hot gasses is shown in figure 12-2 for the elevation coinciding with the level of the maximum foam tempergture. gThe maximum temperature reached in any part of the foam is 123 C (253 c';, substantially below the temperature at which pyrolysis of the foam would begin to occur. Figures 12-3 and 12-4, which show the temperature distribution at elevations above and below the flame, illustrate why the foam temperature remains low. .
Conduction of heat is very efficient in the axial direction up and down the wall in the gap between ducts, and thus the energy is conducted rapidly away from the fbam in the area where it is adjacent to the thick steel beam, by conduction in the steel. In areas where axial conduction is not as efficient where the fbam is adjacent to sheet metal, radial conduction into the wall is very inefficient becrluse of the double duct with two air gaps; therefore, the fbam temperature remains low all along its surface. Notealsoghatthg sheet metal in contact with the fcam remains less than 177 C (350 C),
thus precluding any buckling or degradation of the metal and preventing direct contact between the flame or hon gasses and the fbam. Therefore, because of the conservative assumptions used in the analynis, the tempera-ture rise of the fcam predicted in this analysis is considered to be an upper bound, and no degradation of the foam or release of gas from the foam will occur."
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RY.C Ouestion No. 13 Describe the testing performed to demonstrate Ubat upper plenum igniters will properly function in an environment of prolonged hydrogen burning.
TVA Response Refer' to.section 2.2 of the November 16, 1981, equipment survivabilit'y report for a discussion of upper plenum igniter box analysis in an environment of prolonged hydrogen burning.
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9 a
NRC Qu;~tiyn No 14 Describe and justify the criteria used to determi.ne adequate coverage of the ice condenser upper plenum region with igniters to insure combustion while minimizing exhaust of, unburnt gas to the upper compartment. Identify the minimum number of igniters needed to accomplish the intended objective.
TVA Response l -
{
i Coverage of the ice condenser upper plenum region with igniters is con-sidered adequate if combustion of the upward-flowing mixture can be assured such that exhaust of unburnt gas to the upper compartment is minimized. Complete combustion will be assured if each igniter is cap-able of initiating a flame in the flammable mixture as it passes, if the flame propagates spherically, and if the flames propagating from tha adjacent ignitars overlap before the mixture exits the upper plenum.
Considering the specific characteristics of the Sequoyah upper plenum geometry and expected flow conditions leads to an estimate of the minimum number of igniters required to accomplish the intended objective. Installation of the igniters is currently planned for approximately elevation 786' (or lower), which is 10.625 feet (or more) below the top of the upper plenum. Conservatively assuming that the flammable mixture is not ignited un'til it flows up past the igniters, the flames would have to propagate and overlap in the circumferential direction before the mixture had risen the remaining 10.625 feet and out into the upper compartment. Containment accident analyses have shown that a representative upward flow velocity through the upper plenum during the transient (except when accelerated briefly due to burning in the lower compartment) is one ft/sec. Assuming a conservatively low flame speed in this turbulent region of two ft/sec results in an igniter circuarerential spacing criterion of:
10.625 ft x 2 ft/see x 2 = 42.5 ft 1 ft/sec To adequately cover the approximately 300-foot circumferential dimension of tho upper plenum would require eight igniters. Therefore, a total of 16 igniters (eight per train) are adequate to ensure combustion in the upper plenum and minimize the exhaust of unburnt gas to the upper compartment.
Even though the igniters are located to assure complete coverage of the upper plenum by either train, we have evaluated the containment response due to partial coverage. Assuming that only 40 percent of the hydrogen burns at eight volume percent (instead of the base case assumption of 85-percent burn completeness) in the upper plenum and that the remaining hydrogen vents unburned to the upper compartment, the peak containment pressures and temperatures are essentially the same as in the base case.
More burns are predicted to occur in the lower compartment and upper plenum than in the base case. However, upper compartment burns are not predicted
, using base case assumptions for the other parameters. Therefore, while the i
' coverage is adequate to assure camplete combustion in the upper plenum, the containment response has been shown not to be particularly sensitive to -
exhaust of unburnt gas to the apper compartment.
e .s e ENCLOSURE 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION DATED AUGUST 27, 1931 EQUIPMENT SURVIVABILITY / POTENTIAL SECONDARY FIRE SEQUOYAH NUCLEAR PLANT NRC Question No. A.1 -
- a. Describe the specific criteria used for only discussing in the June 2, 1981 submittal certain of the equipment items identified in the Sequoyah SER as essential for safe plant shutdown. Justify that the results presented provide a bounding case for equipment required to survive the hydrogen burn environment; that is, show that the results apply to equipment of given type that is most sensitive to the temperature / pressure environment. Also demonstrate that the equipment response results are associated with modified CLASIX analysis which will result in the maximum temperature / pressure response of essential equipment; e.g., minimum- flame front velocity.
~
- b. In your submittal, you state that burns are not predicted to occur in the dead-ended or upper compartment. If the modified CLASIX aralyses used for limiting case equipment response indicates that burns in those regions must be considered, provide an evaluation that establishes that essential equipment in those regions can survive the resulting environment and perform its safety function.
- c. Provide analyses that demonstrate that the equipment temperature response to modified CLASIX results used in a. and b. above will not exceed the temperature rise of the same equipment when analyzed for exposure to the thermal environment profile used for qualifying the equipment. The equipment temperature analysis method should be the.
same for both exposures. Describe the assumptions made in modelling the equipment for analysis.
- d. To provide experimental verification of the equipment temperature response analysis method, submit the results of analyzing the temperature response of the cable containing Teflon insulation which was exposed in the Fenwal tests and exhibited some melting of the Teflon.
TVA Response No. A.1 (a) Results from the modified CLASIX analyses used for maximum equipment response are provided in Section 2.1 of the attached November 16, 1981, Equipment Survivability Report
( ES R) . Bases for equipment selection and analysis are provided in Section 2.2 of the ESR.
(b) Burns are not predicted by CLASIX to occur in the upper or dead-ended compartments. However, some equipment in those areas was analyzed using burn profiles for the lower compartment or '.ce condenser upper plenum. ,
(c) Refer to Sec, tion 2.2 of the ESR.
(d) Refer to Section 2.2 of the E3R.
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o ee NRC Question No. A.2 -
~
) ) For that equipment, e.g., transmitters, that must function during the burn, provide information that will assure that during a hydrogen burn, the equipment will not only retain its integrity, but also will perform
}v continuously its function.
TVA Response A.2 -
Refer to Sections 2.2 and 3 0 of the ESR.
NRC Question No. A.3 In order for the staff to perform independent thermal response analysis of essential equipment on a selected basis, provide drawings-(equipment dimensions and containment arrangement) and a detailed description of the design and materials of the equipment selected for survivability analyses and tests such as transmitter, igniter assembly, cable in conduit, exposed '
RTD and thermocouple cable.
TVA Response Nc. A.3 Refer to Sections 2.2 and 2 3 of the ESR.
NRC Question No. A.4 Singleton Tests - Explain how the thermal radiation from the cloud of burning gas was accounted for in calculatinst thermal energy exchange between the environment of burning hydrogen end the equipment. . What was the velocity and temperature of the flame and the basis for their selection? What view factors (geometrical factors) were used in these calculations?
TVA Response No. A.4 Refer to Section 2 3 of the ESR.
NRC Question No. A.5 Singleton Tests - Explain how the radiation from the flame was simulated or compensated for in the tests performed in Singlston Laboratory on thermocouplas. RTD and igniter cables.
TVA Response No. A.5 Refer to Section 2 3 of the ESR.
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u o NRC Question No. A.6 Singleten Tests - Describe in more detail the tests performed on igniter cables. Especially, specify the temperatures and the times of exposure usegduringthetests. Explain how the exposure to maximum temperature of 700 F would simulate hydrogen burn environment in the upper plenum where air temperatures were estimated to reach 1192 F- and where the cables wou,ld be exposed to radiant energy from the cloud of burning gas. '
TVA Response No. A.6 Refer to Section 2 3 of the ESR.
l NRC Question No. A 7 l Page 33 - Explain in more detail the reasons behind your statement that a
) PORV block valve could withstand hydrogen burn environment.
1 l TVA Response No. A.7 Refer to Section 2.3 of the ESR.
NRC Question No. A.8 At the 7/23/81 meeting between NRC and TVA/AEd/ Duke Power Co., it was indicated that the test chamber environments to which equipment was exposed was more severe than the predicted containment environment. Confirm that this is a correct understanding. Show that the equipment temperature response and functional behavior following exposure to the test chamber environments is more severe than that expected following exposure to the predicted containment environments. Explain the basis for nomparing test chamber results with equipment survivability predictions in the containment.
TVA Response No. A.8 Refer to Section 2 3 of the ESR.
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NRC Question No. B.1 -
Potential Secondary Fire Review the various types of cable (rafety or non-safety) in containment having insulation directly exposed to the hydrogen burn and provide information that demonstrates that there will be no cable fire initiatedL State which of this information is based on analysis or test results or both.
TVA Response No. B.1 TVA has conducted a design review and an onsite inspection of the various cables (safety and nonsafety) in containment and has
, confirmed that no cable fires would be initiated as a result of a hydrogen burn. The great majority of all cables is completely enclosed in conduit or ca'le u trays and is not directly exposed to the hydrogen burn. Those cables that have exposed insulation have been tested to ensure flame resistance, s The exposed incore thermocouple cables and the hot and cold leg RTD cables were tested at TVA's Singleton Laboratory as described in Section 2 3 of the ESR. The short segments of nonsafety-related cables between the containment penetration junction boxes and the conduit or cable tray located in the dead-ended or upper compartment have passed the Insu.lation Cable Engineers Association (ICEA) vertical flame test.
This test consists of five 15-second applications of a 1200-
! 1500 F flame with 15 seconds between burns. The segments of nonsafety-related cables in the vicinity of the reactor head are insulated with silicone rubber with an asbestos braid outer jacket and have passed the IEEE-383 vertical ; ray flame test.
This test consists of exposing the cables to 8.1500 F flame for 20 minutes.
In conclusion, due to the various flame test qualifications of the small amounts of exposed cable in the containment, we believe that no secondary cable fi.es would be initiated.
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