ML20137H209

Suppl 3 to Preliminary Equipment Survivability

ML20137H209
Person / Time
Site:	River Bend
Issue date:	08/31/1985
From:	GULF STATES UTILITIES CO.
To:
Shared Package
ML20137H208	List: ML20137H209 RBG-21912, Forwards Suppl 3 to Preliminary Equipment Survivability, Per 850819 Request.Rept Includes Info Re Igniters & Cabling Located in Wetwell Region
References
NUDOCS 8508280223
Download: ML20137H209 (13)

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i Preliminary Equipment Survivability Supplement Three Gulf States Utilities Company 4

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August 1985 1

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INTRODUCTION The previously submitted Supplement Two (Reference 1) to the River Bend Station Preliminary Equipment Survivability Report (Reference 2) evaluated the thermal response of equipment located in the lower intermediate volume (between the HCU floor and Elevation 141 ft.) to deflagration type burning. The evaluation submitted in Supplement Two utilized the thermal profiles predicted by CLASIX-3 for the revised Stuck Open Relief Valve (SORV) base case as presented in Reference 1.

The following report considers the thermal response of equipment which is located in the wetwell volume.

MODELING AND ASSUMPTIONS The essential equipment located in the wetwell volume (between the suppression pool and the HCU floor) consists of_the hydrogen igniters and their associated electrical cable. The HEATING 6 model of the hydrogen igniter is the same as presented previously in Reference 2. As in the previous survivability analysis, no credit is taken for local shielding.or mounting details. Some shielding for the igniters will be provided by the pool swell shields. In addition, since six of the twelve wetwell igniters are located within the web of I-beams, these igniters will be further shielded from the wetwell burns. A conservatively high value of the emissivity for the hydrogen igniter was assumed with no credit taken for reduction in emissivity at lower temperatures. Likewise, heat transfer by forced convection was

3-conservatively assumed to be at a velocity of 12 ft/sec as previously discussed in Reference 3. This assumption is particularly conservative for igniters located within the I-beam webs. The only required cable in the wetwell volume is the cable to the hydrogen igniters. This cable is a two conductor number 12 AWG cable. Each conductor is enclosed in 30 mils of Ethylene Propylene Rubber (EPR) insulation and both conductors are enclosed by an outer jacket made of chlorosulfonated polyethylene (trade name Hypalon) with a thickness of 45 mils. The cable is routed through a thick wall galvanized steel conduit with a 3/4-inch inside diameter and a 0.113-inch wall thickness. The HEATING 6 model of the wetwell igniter cable includes both the cable and the conduit and conservatively assumes that the cable is in direct contact with the conduit.

ANALYSIS AND RESULTS Assessment of the wetwell hydrogen igniter survivability resulted in a peak predicted temperature of 410 F for the igniter case. This temperature occurred at the end of the transient. Comparing the predicted peak temperature with the equipment qualification temperature of 340 F indicates that survivability of the hydrogen igniters is not assurred. The qualification temperature of 340 F is reached at 16,000 seconds at which time 70% of the total hydrogen equivalent to 75% Mwr has been burned. Also, as noted previously, the effect of local shielding will be effective in reducing the thermal loading on the wetwell igniters. The main reason that equipment survivability for the wetwell hydrogen igniters has not been demonstrated is the overly u

conservative temperatures predicted by CLASIX-3 as compared to data from both the Nevada Test Site and the Hydrogen Control Owners Group (HCOG)

Quarter Scale Test Facility tests.

Review of data from the Nevada Test Site (NTS) indicates that CLASIX-3 may overpredict the deflagration temperature. In the RBS SORV transient, CLASIX-3 predicts temperature peaks of 1200 F based on assuming deflagrations are initiated at 8% with an 85% combustion completeness. Since the presence of energized igniters would never allow the hydrogen concentration to reach 8%, the hydrogen concentration would be closer to 5 to 6% at the onset of combustion. NTS data for deflagrations without sprays for initial hydrogen concentrations of 5 to 6% show that the resulting temperatures would be in the 500-600 F range. Therefore, the presence of energized igniters would reduce the temperature by 400-500 F compared to pre-mixed burns at 8% initial hydrogen concentration as predicted by CLASIX-3.

Another significant conservatism in the present analysis is the inclusion of the high reflood hydrogen releases in the CLASIX-3 analysis. As has been demonstrated during the HCOG Quarter Scale Test Program, release rates of this magnitude (5.125 lbm/sec peak) will provide diffusion flames anchored at the suppression pool, not serial deflagrations. Inspection of the thermal response of the hydrogen igniters shows that the initial series of burns produce a significant thermal loading. Exclusion of these burns corresponding to high I

hydrogen release rates may allow demonstration of igniter survivability, even for the overly conservative CLASIX-3 thermal profiles.

5-Tests completed at the Quarter Scale Test Facility by HCOG included 4 a test without sprays with a low hydrogen release rate (0.07 lbm/sec, full scale) out to approximately 31% Mwr. Although this test did not extend to 75% Mwr, inspection of the results shows.that the temperatures are not increasing, which indicates that if the test were extended, the final temperature would be approximately the same. This test (test S.10) indicated that serial deflagrations, as are predicted by CLASIX-3, do not occur even at relatively low hydrogen release rates. Also, the thermal environment is less severe than the environment predicted by CLASIX-3 as discussed below.

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Representative thermocouple traces from test S.10 for the hottest chimney, the 45 chimney, at the HCU floor, the floor above the HCU floor and at the top of the chimney are given in figures 1 through 3 respectively. These results indicate that the highest temperature reached in the." hot" chimney during the 0.07 lbm/see release rate was 230 F which is below the qualification temperature of any essential equipment. This should be compared to the 1200 F temperature peaks predicted by CLASIX-3 under the same conditions. It is also worth noting that the hydrogen release history used in this test was based on a 5000 gpm reflood to 30% core melt followed by a 0.07 lbm/sec release rate which has been presented by HCOG to be the most probable Hydrogen l

Generation Event (HGE). For HCOG scoping test S.10, the data for temperatures below the HCU floor was not conclusive because the temperatures recorded by T176 which is located in the 45 chimney below the HCU floor indicated that the temperature was only slightly above

. background during the constant release portion of the transient. To

provide an estimate of temperatures below the HCU floor, the results from scoping test S.11 are given in Figures 4 and 5 for thermocouple T176 and T178 respectively. This test was a 150 gpm reflood case producing 50% core melt followed by a 0.14 lbm/see tail out to 75% Mwr with sprays activated. Comparison of tests with and without sprays indicates that the effect of sprays is a reduction of temperatures in some areas and an increase in other areas due to improved mixing.

Therefore, these results provide a reasonable estimate of wetwell temperatures for RBS. These results show that the average temperature

, during the constant release portion of the HGE was 250-280 F, which is well below the equipmant qualification temperature of the wetwell hydrogen igniters and associated cable. From these test results, it can be concluded that equipment survivability for low constant release rates is not a concern since all temperatures are well below the equipment qualification temperatures.

4 The evaluation of the wetwell cable excluded the high hydrogen release portion of the transient since this release rate will produce diffusion type burning rather than deflagrations. The evaluation used I

- only the temperature profile attributed to the constant release rate beginning at 5000 sec for the original SORV base case (Reference 4).

The evaluation resulted in the cable reaching the qualification temperature of 450 F after 32 hydrogen burns. During these burns. 74%

of the total hydrogen equivalent to 75% Mwr is burned. As discussed above, CLASIX-3 does not predict a realistic thermal environment when compared to quarter scale test results. Comparison of the quarter scale test results for low hydrogen release rates with the cable qualification

7-temperature indicates that the igniter cable will survive the more f

realistic thermal environment resulting from low hydrogen release rates.

CONCLUSIONS I

Survivability of the wetwell hydrogen igniters and cable for the t

j entire hydrogen deflagration transient as predicted by the CLASIX-3 computer code is not assured. However, since the wetwell igniters and cable will survive at least 70% of the hydrogen release, there is reasonable assurance that they will survive the actual transient because i

of the conservative nature of the GSU preliminary analysis. In light of  ;

the quarter scale test results, as discussed above, the thermal y environment predicted by CLASIX-3 may be overly conservative. Review of the information available to date indicates that equipment survivability for deflagration type burns is not a concern. Since further analysis and RBS specific quarter scale testing are scheduled to be completed in the next several months, it is felt that the realistic thermal j environment will provide a basis for demonstrating equipment survivability.

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i REFERENCES

1. RBG-21,900 dated August 19, 1985 from Gulf States Utilities (J. E.

Booker) to Nuclear Regulatory Comission (H. R. Denton) 4

2. RBG-21,423 dated July 1, 1985 from Gulf States Utilities (J. E.

Booker) to Nuclear Regulatory Comission (H. R. Denton)

3. RBG-21,819 dated August 7, 1985 from Gulf States Utilities (J. E. L Booker) to Nuclear Regulatory Comission (H. R. Denton)

! 4. RBG-21,218 dated June 7, 1985 from Gulf States Utilities (J. E.

t Booker) to Nuclear Regulatory Comission (H. R. Denton) i J

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