ML20028G017

Forwards Documentation of Results of Addl Tests on Tayco Igniter for Permanent Hydrogen Mitigation Sys & Supporting Basis for Util Belief That Sys Design Adequate

ML20028G017
Person / Time
Site:	Sequoyah
Issue date:	01/31/1983
From:	Mills L TENNESSEE VALLEY AUTHORITY
To:	Adensam E Office of Nuclear Reactor Regulation
References
NUDOCS 8302070321
Download: ML20028G017 (11)

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TENNESSEE VALLEY AUTHORITY CH ATTANOOG A, TENNESSEE 37401 400 Chestnut Street Tower II January 31, 1983 Director of Nuclear Reactor Regulation Attention: Ms. E. Adensam, Chief Licensing Branch No. 4 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Ms. Adensam:

In the Matter of ) Docket No. 50-327 Tennessee Valley Authority ) 50-328 As requested by the NRC in November of 1982, TVA performed additional testing on the Tayco igniter for our Permanent Hydrogen Mitigation System (PHMS). Information was subsequently provided to the NRC, on an informal basis, during telephone conversations and during the ACRS meetings of the conclusions of the test results. Enclosure 1 provides documentation of the results of the tests and the conclusions based on the test results.

Enclosure 2 provides formal documentation of information provided to the Nhc to support TVA's belief that the PHMS design was adequate.

If you have any questions concerning this matter, please get in touch with J. E. Wills at FTS 858-2683 Very truly yours, TENNESSEE VALLEY AUTHORITY L. M. Mills, Manager Nuclear Licensing

' Sworn d subs ibed before me thisi day of 1983

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Notary Pub'lic' My Commission Expires "I Enclosures (2) cc: U.S. Nuclear Regulatory Commission (Enclosures)

Region II Attn: Mr. James P. O'Reilly Administrator 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 8302070321 830131 i l PDR ADOCK 05000327 P PDR An Eaual Opportunity Emptover

. - ENCLOSURE 1 i ADDITIONAL TESTING PERFORMED ON TAYC0 IGNITERS SEQUOYAH NUCLEAR PLANT The obj ective of this submittal is to demonstrate that the Tayco igniter assemblies used in the Permanent Hydrogen Nitigation System at Sequoyah Nuclear Plant would op7 rate eff ectively in the spray environment of the upper compartment of the containment. Effective i operation is considered to be the igniters' ability to ignite mixtures of hydrogen, sir, and water near the lower flammability limit in the expected environment. Ignition depends on the capability of the igniter to transf er enough heat locally into the surrounding mixture to bring the mixture up to the ignition temperature. The approach taken in this submittal will be first to describe the design of the igniter assemblies f or the spray environment. Next, a number of laboratory-scale tests will be described where the igniter was subj ected to various spray environments while the igniter surf ace temperature was measured. Finally. the spray test environment will be compared to the expected upper comparteent conditions and the sustainable igniter surface temperatures will be related to the minimum surface temperature required for ignition in the upper compa r tment.

l Each of the igniter assemblies used in the upper compartment c'onsists of a Tayco igniter mounted through the end plate of a standard NEMA-type enclosure covered by a sheet metal spray shield. The dimensions of the igniter / shield configuration were allowed to vary slightly for ease of field installation. At a minimum, the shfeld extends four inches beyond the tip of the igniter coll;and six inches on both sides. At a maximum, the igniter is located ten inches below the shield. The design of the spray shield would prevent overhead impingement of the containment spray on the igniter. How ev er, intermittent local turbulence postulated to occur in the upper compartment could cause scue. indirect spray impingement. This indirect spray will be addressed in the remainder of this submittal.

Tests were performed by TVA at J ts Singleton'Naterials Engineering Laboratory to determine the effect of spray,on igniter surf ace temperature. Two basic groups of tests were conducted. The first group consisted of spray tests on an igniter assembly with a spray shield in an attempt to simulate the actual upper compartment environmental conditions. These tests used a single nozzle to spray l an igniter protected by a spray shield ten inches above the nozzle but *

! slightly smaller than the ones described previously. The second group consisted of spray tests on an igniter without a spray shield in an effort to determine the sustainable igniter surf ace temperature under various direct spray mass fluxes.

The first test of the first group was reported in a previous TVA submittal of November 1,1982. That test used a hollow cone spray nozzle located three f eet above the igniter with a flow rate of 3.5 gal / min. A large f an placed in front of the igniter was used to simulate a potentially turbulent upper compartment environment causing indirect spray impingement. The initial igniter surf ace temperature in this and the following tests varied between 17 00-173 0 *F. When the l spray and f an were activated, the igniter temperature dropped to L m l.__ m _~ ..~. . . . . - .. . . . _ _ ._ - ,

batvoca 1600-1635'F oithis five olestos and remmisod reintively .

stable for the remaining half hour of the test.

The second test of the first group used the some spray nozzle and flow rate, but located the nozzle only two feet above the igniter to provide the same spray mass flux as calculated for the Sequoyah upper c ompa r tment. Assuming uniform distribution of the 9500 gal / min from both trains of the containment spray system over the 10,400 f t* cross section of the upper compartment would yield a mass flux of 0.915 gal / min ft8 The f an was used again to promote turbulence and was moved to the side of the igniter. When the spray and f an were activated, the igniter temperature dropped to between 1650-1670*F and remained stable.

The third test of the first group used a solid cone spray nozzle located 25 f eet above the igniter with a flow rate of 10.5 gal / min.

The igniter was located on the periphety of the spray cone sach that the edge of the cone impinged on the centerline of the spray shield.

The overall mass flux at the igniter elevation equalled that of the upper compartment. The fan was located on the opposite side of the spray cone from the igniter. When the spray and fan were activated, the igniter temperature dropped to between 1525-1560*F. The sustained igniter surf ace temperatures determined in each of these three tests with a spray shield are well above the minimum required temperature that will be justified later in this submittal.

Since the environmental conditions (especially turbulence) cannot be accurately quantified at all locations in the , upper compartment and since reproducing these conditions exactly in a small-scale test is not possible, the second group of spray tests was conducted without a spray shield in order to obtain a simple correlation between the spray mass flux impinging directly on the ignit,er,and the igniter surface temperature. The solid cone nozzle was used for this group of tests at a number of elevations above the igniter to provide various mass fluxes ranging up to approximately the maximum direct upper compartment mass flux of 0.915 gal / min f t8 No f an was required to provide turbulence since the spray impinged directly on the igniter.

A series of four spray testiwas performed which, when the dry (initial) temp 9rature was included, yielded the curve in Figure 1, which relates the test to upper' compartmenkmass flux ratio and the average igniter surface temperature that could be sustained. The data

-shown in the figure is tabularized below.

Nozzle Heiaht Mass Flux Ratio

• Averaae Sustained Temperature 2.5 ' O.92 12758 F 3' O.64 1337' F 4' O.36 1440' F 6' '*0.16 1517' F

• Where a nozzle height of 2 4' would yield the u perpco pm artment mass flux of 0.915 gal / min /ft8 The sustainable igniter surf ace temperatures in the spray tests may be compared to the minimum igniter surface temperatures required to ignite hydrogen, sir, and water mixtures measured for the Tayco igniter at the Whiteshell Nuclear Research Establishment (WNRE). The results of the WNRE Tayco tests were submitted by TVA on June 14, 1982. One objective of the WNRE tests was to determine the igniter M b4 use 3 t.=eh.e' a-=.w- w ' --%.3

', , .strineo temperntgre required to ylsid a gss temperatere sufficient to ignite the test mixture. These experiments were performed in a 17 liter vessel with the Tayco igniter mounted horizontally near the center. Thermocouples welded to the igniter measured the surface temperature while an ionization probe was used to signal that ignition and flame propagation had occurred. A fan was activated in sane tests i to provide turbulence directly at the igniter. A number of tests were performed a't various concentrations of hydrogen and steam. No sprays were included. The results of the WNRE Tayco test series are shown in l Figure 2.

The WNRE Tayco test data is applicable to the Tayco igniter assemblies in the upper compartment at Sequoyah. Ile phenomenon of ignition is a local one that is based on transferring enough heat f rom the igniter into the immediately surrounding flammable mixture until it reaches a sufficient t empe ra t ur e. Once ignition occurs, the phenomenon of flame propagation may be affected by global conditions. H ow ev e r, since the phenomenon of ignition is local, it is demonstrable in a vessel of smaller scale than the upper conpartment as long as the smaller vessel does not impose unrepresentative boundary conditions. The WNRE vessel size was large enough, the f an flow was turbulent enough, and the time lag between igniter activation and ignition was short enough

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that no appreciable bulk heating of the mixture occurred before

! ignition. Since ignition occurred as soon as the igniter warned up i enough to transf er the required amount of heat into the local mixture i to promote ignition, the scale effects of the vessel size did not become important. The WNRE tests utilized a Tayco igniter of 'the same general configuration as the ones used in the. upper compartment a s semblie s. Since the ignition process is dependent on the heat transferred from the igniter to the local gas, it was important to have the same igniter temperature, surf ace area,; and geometrical configuration. The Tayco igniter has a relatively large surf ace area which promotes effective heat transfer. In addition, the Tayco coli configuration tends to create its own local turbulence and increase the residence time of local mixtures which enhances heat transfer.

The WNRE tests were performed with various concentrations of steam instead of spray. The effects of steam on ignition are more pronounced than spray, i.e.,' igniter surface temperatures required to heat a mixture with a high concentra tion of steam would be higher than those required for a typical spray mixtur'e' with more widely-dispersed drops. Accounting for the heat capacity effects of spray would probably yield results closer to the WNEE dry test conditions than q^

those of the high steam f raction tests shown in Figure 2. Note that the surf ace temperature shown in Figure 2 required to ignite the dry mixture was about 1200*F. The WNRE test conditions with f an flow and high st eam fraction should conservatively bound the heat transfer effects of turbulence and spray in the upper com.partment. Therefore. -

based on the WNRE test data f or the Tayco igniter in a turbulent, 40-p erce nt ste am enviro'nment (see Figure 2), we believe that 13258F represents a conservative minimum igniter surf ace temperature. For additional margin,1350*F will be employed as the minimum Tayco igniter surf ace temperature required for ignition in an environment typical of the upper compar tment. We do not believe that higher required surface temperatures that may be determined for other types of igniters are appropriate for use with the Tayco igniter because the Tayco igniter has its own unique combination of surf ace temperature, area, and configuration supported by test data specifically for that combination.

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expected spray mass fluxes due to local ~ turburence in th~e upper compa rtment. Of course, the mass flux ratio of 1.0'is'the maximum obtainable since it represents the direct overhead spray-impingement that would occur without any spray shield. The actual spray mass' flux ratio that might be expected to. impinge on the ignitors beneath their -

spray shields due to local turbulence would be significantly less.

There are six igniter assemblies located below the containment spray headers in the upper compartment.. Four .of these are mounted on the inside of the crane wall at elevation 784 and one on each of the ice condenser end walls at elevations 760 and 765. The boundary layer that would be associated with these walls in the upper compartment would tend to reduce the turbulence levels at the igniter locations  !

below bulk levels. In addition, the lowest igniter assembly is located well of f the operating floor where the spray-induced turbulence would be most pronounced. Furthermore, any local turbulence at the igniter locations would be intermittent and would -

not cause continuous spray impingement on the igniter. Employing the minimum igniter surf ace temperature of 1350'F justified above and referring to Figure 1, the corresponding mass flux ratio that could be tolerated is determined to be 0.6. Because of the presence of the spray shields above each of the igniters, their location in regions of reduced turbulence, and the intermittent nature of any local turbulence, we believe that the highest realistically achievable spray mass flux on the upper compartment igniters with spray shields would be less than this acceptable mass flux ratio of 60 percent of the maximum possible mass flux without the spray shields.

In summary, TVA has designed each of the PHMS " igniter assemblies in the upper compartment with spray shields to prevent overhead impingament by the containment spray. To account

• for any possible eff ects on igniter performance due to spray impingement induced by local turbulence, TVA has established 1350*F as the minimum igniter surf ace temperature required for ignition based on the WNRE test data and has conducted two groups of tests at its Singleton Laboratory to simulate expected environmental conditions in the upper compartment.

The first group of Singleton tests showed directly that the assembly with a spray shield would al'10w the igniter to remain above the minimum required surface temperature for ignition in an upper compartment spray environment. The secon'd' stoup of tests produced data that correlated various directly impinging spray macs fluxes with

-the sustainable igniter surf ace temperature. Based on the established minimum required surf ace temperature, the second group of te st s showed that the igniter could withstand direct spray mass fluxes higher than any spray mass fluxes that could be expected from local turbulence in the upper compartment. Based on our assessment of these test results, TVA has concluded that the Tayco igniter assemblies in the upper compartment would operate eff ectively in that spray environment.

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ENCLOSURE 2 4

ADDITIONAL INFORMATION ON ADEQUACY OF PENS SEQUOYAH NUCLEAR PLANT l TVA submitted a sammary report on. September 17, 1982, that concluded

! that the permanent hydrogen mitigation system (PHMS) was an adequate hydrogen control system for the Sequoyah Nuclear Plant (SQN) that would perform its intended function in a manner that would provide adequate saf e ty margins. TVA continues to believe that the present PEMS design is adequate.

We do not beliwve that modifications to the upper compartment portion of the system are of much benefit because it is highly unlikely that flammable'aistures would ever be present there. Since the potential sources of hydrogen would all be located in the lower compartment, such flammable mixtures in the upper compartment would have had to bypass all 22 lower compartment igniters and al1 16 ice condenser upper plenum igniters without being ignited and burned down to the lower flammability limit. Analyses with the CLASIX containment code sh ow that burns do not occur in the upper compartment unless the lower flammability limit is arbitrarily assumed to be lower there than in any other compartment. .

As stated in a previous informal submittal, TVA believes that data on

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minimum Tayco igniter surface temperature for ignition obtained at Whiteshell Nuclear Research Establishment (WNRE) is applicable for use in evaluating PHNS igniter performance in the' upper compartment.

These tests showed ignition of dry mixtures et a surf ace temperature of 1200'F, and ignition at high (40 percent) stcan concentrations at a temperature of 1350*F. As stated in the submittal, TVA proposed that 1350*F be used as the minimum Tayco igniter surface temperature required for ignition in the spray environment. The NRC staff has informally proposed a more conservative minimum temperature of 1500'F. Based on the modif red design of the igniter assembly spray shicid and on the recently-conducted spray tests reported in the previous informal submittal, it is TVA's judgment that the PHMS igniters in the upper compartment can be shown to maintain even this conservative temperature of 1500*F.

The bodified spray shield is designed to provide camplete coverage of the igniter surf ace f rom any spray droplets travelling at an angle up to 50' from the vertical (see attached figure). For an igniter located at the maximum distance of 10' from the shield, the, modified shield would be

• 22' deep and 26' wide. This would extend 13' beyond the front tip of the igniter and 121/2' on each side. It is our judgment that long-term spray-induced turbulence levels inside the upper compartment would not be great enough to cause significant prolonged spray impingement at greater than this severe angle (i.e., more horizontal than vertical). Again referring to the previous informal submittal, the igniters are located on walls f ar enough above the floor to avcid local turbulence from turning and f ar enough below the nozzles to avoid any horizontal component f rom the original traj ectory.

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• Tayco igniter has been demonstrated to maintain surface temperatures in excess of 1500*F even when subj ected to a direct (no spray shield) continuous spray of mass flux equivalent to 20 percent of that average flux calculated to f all throughout the upper compartment.

(Note that the igniter maintained a tamperature above 1350*F for a spray mass flux of 60 percent.) This data demonstrates that margin exists in the igniter temperature even for significant additional spray impingement under the shield from.an angle greater than 50' . Also, the spray tests were conducted at 120-V ac while the upper compartment Igniter should operate at slightly higher voltage levels which would correspondingly increase the tamperature margins.

t In summary, TVA believes that hydrogen combustion is unlikely to occur in the upper compartment. Even if flammable mixtures do occur there, the PENS igniter assemblies would be able to maintain sufficient temperatures for ignition even under severe postulated spray environments. The modified spray shields, supported by recent direct spray data, would allow even the conservative surf ace temperature of 150*F to be maintained. TVA believes that this hardware modification should satisfactorily resolve any spray effect concerns without requiring further analysis or testing.

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