ML20198P680

Provides Addl Info & Analysis of Potential for Dilution of Fuel Storage Pool in Response to NRC Questions.Revised Spent Fuel Pool Boron Dilution Analysis, Included

ML20198P680
Person / Time
Site:	Vogtle
Issue date:	01/16/1998
From:	Mccoy C SOUTHERN NUCLEAR OPERATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20198P685	List: ML20198P680 ML20198P696
References
LCV-0849-K, LCV-849-K, NUDOCS 9801220212
Download: ML20198P680 (8)

Text

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LCWO849.K Docket Nos. 50-424

$0 425 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555 Gentlemen: ,

VOGTLE ELECTRIC GENERATING PLANT l ADDITIONAL INFORMATION i/UEL STORAGE POOL BORQN DILUTION t

Southern Nuclear letter LCWO849.E dated August 8,1997, requested Technical Specifications changes that allow credit for the soluble boron concentration in the fuel storage pools. Enclosure 6 of that letter included an evaluation of the effects of potential fuel storage pool dilution. This letter includes additional information and analysis of the potential for dilution of the fuel storage pool.

The proposed Technical Specifications are based on analysis demonstrating that the fuel to be stored in the fuel storage pool will remain subcritical without credit for soluble boron. ,

Soluble boron credit is used 1o establich suberiticality margin by maintaining Kaless than the normal design value of 0.95. The criticality analyt.es show that La will be less than 1.0 on a 95/95 basis with the fuel storage pool filled with non borated water. The boron dilution analysis demonstrates that additional administrative requirements are not required to maintain the fuel storage pool suberiticality mergin, because it is not credible that such a dilution would go undetected.;The dilution study lists potentia! sources of pool dilution and provides conservative evaluations of the potential for dilution, and the time to reach the dilution point (concentration where La is F. cater than 0.95).

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The analyses of potential dilution events have been revised to assume that the two fuel storage pools are separated. This ciTectisely reduces the amount of water that is required to dilute a fuel storage pool and adds conservatism to the analysis. For the purposes of the dilution analysis, the boron concentration for maintaining Ke r s 0.95 was increased to 600 ppm from the value of 500 ppm in the dilution analysis submitted in LCV 0849 E. This is conservati : with respect to the criticality analyses for the current Vogtle rart a and is consistent with the c.iticality analyses f( .e planned placement of additional racks ir, the Unit I fuel storage pool. These additional racks were described in SNC letter LCV 0828 B dated November 20,1997. The effects of piping failures on dilution water sources have been revised to be in accordance with NRC Branch Technical Po.sition hiEB 3 1.

In the dilutloa analysis report a change was made to the description in section 2.8 regarding the status of administrative controls. The status description in LCV 0849 E stated that the controls "are in place". Some of the items are presently in effect, but a portion of them are planned to be in effect by implementatior. of the proposed revised Technical Specifications. The description was changed to state the controls "cither are in place or will be la place".

With the exception of the change to section 2.8 of the dilution analysis report, the above-described changes were discussed with the NRC staffin a telephone conference on November 24,1997, The incorporation of these changes into the analyses does not alter the Technical Specification changes requested in LCV 0849 E or in LCV-0828 H, and it decs not change the conclusions of the evaluations submitted in support of those requested changes.

Sincerely, C. K. hiccoy CKht/llWht/RJF Attachments:

1. Responses to Questions

2. Revised Spent Fuel Pool Boron Dilution Analysis

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. t U. S. Nuclear Regulatory Commise8on Page 3 l 4

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. xc: Southern Nuclear  !

Mr. J. H. Beasley, Jr.

Mr. M. Sheibani j l

. NORMS U. S. Nuctaar Raoulatorv Commission i Mr. L. A. Reyes,' Regional Administrator

._ Mr. D. H. Jaffe, Senior Project Manager, NRR .

Mr. J. Zeiler, Senior Resident Inspector, Vogtle i

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NTTACHMENT 1 ,

i RESPONSE TO NRC QUESTIONS ON DILUTION ANALYSIS ,

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. REhPONhi NRC OUESTIONS ON DILUTION ANALYSIS OF THE SPENT r FUEL POOL Question it s The boron dilution analysis (enclosure 6) states that the two spent fuel pools (SFPs) ai t  ;

normally connected via the cask loading area, which provides communication between the two SFPs. As a result, a combined volume of 772,000 gallons of water is used in the calculation for the boron dilution times and volumes. Equation 1 in the submittal is used for this calculation. llowever, to use Equation 1, timely through mixing between the two ,

pools is assumed. Provide, justification how the relatively narrow channel through the  !

i cask loading area (the channel appears in drawing AX4DD304 to be approximately 1/10th the wi.ith of the pools) supports the assumption of timely, through mixing to allow use of the combined water volume. (Alternatively, the boron dilution analysis may be completed for separate SFPs). 3 Responset The primary source of dilution water considered in enclosure 6 was from postulated broken pipes that spray water onto the surface of the spent fuel pool. Under these conditions the water level in the two pools will rise together until exceeding the elevation of the curb around the individual pools (approximately :levation 220' 6"). At this point <

water will flow along the surface between the two pools (also through or over the gates between the pools) as well as over the curb from both pools onto the floor of the fuel handling building. Thereafter, the primary source of unborated water is on to the surface of a pool and the flow of water fcorn the pools is from the surface of both pools. The flow of water from each pool will be approximately the same. Under these conditions the water flowing from the pools over the curb is expected to contain less soluble bomn than the average mixture in the two pools. Therefore, the assumption of fully mixed flow from the pools is believed to be consen ative.

The dilution analysis has been revised assuming that the gates between the two pools are

. closed. This analysis is attached.

Question 2: ,

. Given the use of a combined volume for the boron dilution analysis, clarify the statement that the SFPs are "normally" connected. When are the SFPs separated 7 Ilow long are they allowed to remain separated 7 What controls are in place to ensure that the SFPs are/ remain connected 7 KAvoO\RF.As\97VAA15Mol6060IX)C p w . - > .

Response

Itased on discussions with reactor engineering personnel, the pools hr,ve remained connected (the gates between the two pools are open) since the filling of the Unit 2 pool.

The Unit 2 pool contains 2098 fuel storage locations and the Unit 1 pool only contains 288 storage locations. This arrangement requires the transfer of fuel between the two pools which can only occur if the gates are open.

The gates would have to be closed during activities that require draining of the cask pit or draining of one of the SFPs. There are no scheduled activities requiring the draining of the cask pit. The placement of additional racks into the Unit 1 pool is expected to take place in 1998. This aedvity will include closing of the gates between the two pools. At some date in the future, shipment of spent fuel in spent fuel casks will occur. That activity may include periods of gate closure. There are no limits on the frequency or duration of gate closure and there are no requirements to maintain the gates open.

If a pool dilution event occurs while the gat:s are closed, the water level in the affected pool will rise until it over flows the gates. At that point water will flow into the other pool until both pools reach the same level. If the addition of water continues, the level of water will eventually reach the height of the curb around the pools and over flow on to the Fuel llandling Building floor from both pools. Nevertheless, as discussed in the response to questicn 1 the dilution analysis has been re-evaluated considering separate pools.

Question 3:

The boron dilution analysis states on Page 20 that the fire protection system (FP) flow rates range from 2l00 to 4800 ppm and that the most limiting scenario includes a FP fl w of 2300 gpm (seismic break of non-seismic piping). Why is 2300 gpm more limiting than 4800 gpm?

Response

The dilution of both pools as described in er. closure 6 requires over 1,070,000 gallons of water The combined fire protection water in both tanks is only 600,000 gallons.

Therefore, extraordinary assumptions are required to produce a dilution event capable of diluting the combined pools. Make up to the fire n atection tanks is available at a rate of about 650 gpm. By evah.ating the additional amount of water needed to dilute the pool, assuming that it is supplied by the make .,p water pumps, and that the fire protection tanks reach emptyjust as the required amount of water is supplied to the fuel storage pool, the optimum flow rate necessary to dilute the pools in the shortest amount of time can be determined. For greater flow rates the fire protection tanks will empty and the pumps will trip prior to supplying the 1,070,000 gallons necessary to dilute the pools.

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Lower flow rates will result in longer dilution times. This optimum flow rate was

. detennined to be about 2300 gpm.

The fire protection system has one electric oriven pump and two diesel driven pumps.

Pump flow at runout conditions is about 4800 gpm. For the analysis assuming dilution of both pools to 500 ppm, as described in enclosure 6,2300 gpm is the optimum flow rate to minimize the time for dilution of the pools. These assumptions were used to calculate limiting dilution times, however, no mechanisms have been identified that result in flows of these magnitudes.

These assumptions do not take credit for actual location or configuration of potential failures in fire protection piping. They do not take credit for the location of fire protection piping in the vicinity of the fuel storage pools.

All of the fire protection lines in the vicinity of the SFPs are seismically analyzed and supported even though they are not designated as seismic category 1 piping. For the purposes of flooding analyses, tiranch Technical Position MEll 3 1 requires the postulation of through wall cracks in moderate energy non seismic lines. There are 3 six inch fire protection lines in the vicinity of the Unit 1 pool and 3 in the vicinity of the Unit 2 pcol. The postulation of a through wall crack in accordance with IlTP. MEll 3 1 would result in postulated flows well below 2300 gpm.

Question 4:

Section 3.3: Evaluation ofinfrequent SFP Configurations. The boron dilution analysis states that the most limiting configuration is when the SFPs are separated. From a seismic event, a dilution could occur in 1.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. What, if any, controls are in place to assist the operators' " heightened awareness" of a SFP dilution following a seismic event?

Such as, a procedure for checking the plant's physical condition or alarms (other than SFP level)?

Response

Abnonnal Operating Procedure 18036-C "Scismic Event" provides operator response fallowing a seismic event. The procedure requires the initiation of a visual inspection of all accessible areas to determine damage. Following implementation of the revised Technical Specifications this procedure will be revised to include a specific reference to the possibility of dilution of the SFP due to pipe leaks.

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Question 5:

The boron dilution analysis states on page 20 that if offsite power is not available as a result of a seismic event it would take approximately 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to reach the dilution endpoint.1he sources and flow rates to reach this conclusion were not provided. Please provide this information.

Response: -

W8 a loss of electric power, the makeup pumps to the fire protection tanks are unavailable.1his significantly increases the amount of time to reach the dilution point following the emptying of the fire protection tanks.

- Flow rates of systems for broken lines (without offsite power) liire Protection: 4800 gpm (pump runout)-600,000 gal. limit.

Demineralized Water 120 gpm (for gravity fill)-for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> Normal Chilled Water: 300 gpm for 30 minutes (total water admitted is 9000 gallons)

Utility Water: 40 gpm for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> The calculation in attachn ent 2 has been revised to consider a single fuel storage pool and pipe leaks in accordance with MEB 3 1.

Question 6:

1he boron dilution analysis states on page 19 that certain pipes are assumed to remain intact during/afler a seismic event. Clarify that all such pipes are seismically qualified.

Response

This statement referred to non seismic piping outside the SFP area that feeds piping in the SFP area. It is necessary for that piping to remain intact in order to conduct water to -

the SFP area. .Thus the analysis inherently assumed that nonseismic piping outside the SFP are. mains intact while it fails in the SFP area.

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