ML20128G988

Application for Amends to Licenses NPF-68 & NPF-81, Eliminating Credit for Boraflex as Neutron Absorbing Matl in Fuel Storage Pool Criticality Analysis

ML20128G988
Person / Time
Site:	Vogtle
Issue date:	10/04/1996
From:	Mccoy C GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20128G993	List: ML20128G988 ML20128H020 ML20128H028 ML20128H049
References
LCV-0849, LCV-849, NUDOCS 9610090200
Download: ML20128G988 (20)

Text

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.. , Georg>a Power Cornpany 8

49 inverness Center Parkway Post offlce Box 1295 Birmingham. Alabama 35201 Telephone 205 877 7122 C.K.McCoy Vice Pre 9 dent. Nuclear Georgia Power Vogtle Project the southem eleCloc System October 4, 1996 LCV-0849 Docket Nos. 50-424 50-425 l

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

VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE In accordance with the provisions of 10 CFR 50.90 and 10 CFR 50.59, Georgia Power Company (GPC) hereby proposes to amend the Vogtle Electric Generating Plant (VEGP)

Unit I and Unit 2 Technical Specifications, Appendix A to Operating Licenses NPF-68 j and NPF-81. This revision to the Technical Specifications incorporates the requirements necessary to change the basis for prevention of criticality in the fuel storage pool. This change eliminates credit for Boraflex as a neutron absorbing material in the fuel storage ,

pool criticality analysis and supports the storage of fuel with enrichments up to and l including 5.0 weight percent U-235 rather than the current value of 4.5 weight percent U-235.

General Design Criterion 62 of Appendix A to 10 CFR Part 50 requires the prevention of criticality in the handling and storage of fuel. NRC guidance recommends a 5 percent suberiticality margin. Boraflex is currently used in the VEGP spent fuel racks as a nonproductive neutron absorber to reduce the reactivity of the fuel storage pool configuration. The current VEGP analyses take credit for the Boraflex to maintain the 5 .

percent margin. The proposed change will establish an alternative method for maintaining the margin without relying on the Boraflex.

Long term deterioration of Boraflex in fuel storage pool environments has been detected at plants utilizing Boraflex in their fuel storage pools. Consequently, the NRC issued Information Notice 95-38 and Generic letter 96-04 concerning Boraflex degradation.

L mgh Power Company has reanalyzed the criticality of the fuel storage pool without aig mdit for the Boraflex. The revised analyses were performed using the methodology developed by the Westinghouse Owner's Group and described in WCAP-14416 which is currently being reviewed by the NRC. This methodology allows credit for the soluble boron in the fuel storage pool for providing the 5 percent suberiticality margin.

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o GeorgiaPower1 U. S. Nuclear Regulatory Commission Page 2 i LCV-0849 l l

l The analyses established burnup and loading patterns for the spent fuel storage racks that will assure that the 5 percent margin is maintained without reliance on the Boraflex, for fuel that is enriched up to and including 5.0 weight percent U-235. The proposed Technical Specification changes incorporate the appropriate limiting conditions for operation and surveillance requi ements to assure that the fuel storage pool is maintained consistent with the analyses. Those aspects of the limits, such as loading patterns and boron concentration, that are subject to change following additional analyses, will be placed in the Core Operating Limits Report (COLR).

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The NRC has approved the implementation of the Improved Technical Specifications at l VEGP. The implementation date for the ITS will be prior to the expected approval date l of this request. Therefore, only revisions to the ITS are included in this application.

The proposed Technical Specifications relative to the control of baron concentration and loading patterns in the fuel storage pool are more restrictive than current VEGP l requirements. Georgia Power Company will implement these requirements administratively as a means of assuring compliance with both the requirements of GDC 62 i and the 5 percent subcriticality margin regardless of any Boraflex degradation that may i occur in the VEGP fuel storage pool. Deterioration of Boraflex is accompanied by elevated silica concentrations in the fuel storage pool. The higher silica levels are an operational concern but reduction of the silica levels is believed to increase the rate of l Boraflex degradation. Approval of this change will allow the reduction of silica levels and l the elimination of Boraflex coupon surveillance programs which represent operational benefits. Therefore, Georgia Power Company requests that the NRC approve the requested changes to the Technical Specifications by February 28,1997, which is l consistent with the NRC's schedule for review of the methodology of WCAP-14416.

l Enclosure 1 provides a description of the proposed changes to the ITS. Enclorure 2 provides the basis for a determination that the proposed change does not involve l significant hazards considerations. Enclosure 3 includes the marked up pages and instructions for their incorporation for the ITS. Enclosure 4 provides a conclusion concerning an environmental assessment of the proposed change. Enclosure 5 is the criticality analysis report for the VEGP Units I and 2 fuel storage pools. Enclosure 6 is an assessment of the probability of events that could result in a loss of soluble boron in the fuel storage pool, which concludes that it is highly unlikely for any combination of events l

to result in a loss ofboron to the extent that the 5 percent subcriticality margin would be

, exceeded. Enclosure 7 provides an example of the proposed COLR addition.

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.A GeorgiaPower1 4

l U. S. ' Nuclear Regulatory Commission 3 Page 3 LCV-0849 I

Mr. C. K. McCoy states that he is a Vice President of Georgia Power Company and is 3 authorized to execute this oath on behalf of Georgia Power Company and that, to the best of his knowledge and belief, the facts set forth in this letter and enclosures are true.

3 GEORGIA POWER COMPANY By: ,

C.K.M oy t

Sworn to and subscribed before me thish day of Och& .1996.

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j g W COMMfGSION CXPlRES  ;

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Enclosures:

1. Basis for Proposed Change

2. 10 CFR 50.92 Evaluation

3. Instructions for Incorporation and Revised Pages

4. Environmental Assessment

5. Criticality Analysis

6. Probability Assessment i 7. Proposed COLR addition 1

, c(w): Deorgia Power Company Mr. J. B. Beasley, Jr.

Mr. M. Sheibani NORMS U. S. Nuclear Regulatory Commission 4

Mr. S. D. Ebneter, Regional Administrator Mr. L. L Wheeler, Licensing Project Manager, NRR Mr. C. R. Ogle, Senior Resident inspector, Vogtle 4

State ofGeorgia Mr. L. C. Barrett, Commissioner, Department of Natural Resources

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l ENCLOSURE 1 L

o I

VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE BASIS FOR PROPOSED CHANGE Proposed Changes l

These changes to the Technical Specifications add two new Technical Specifications and j associated Bases, revise the Design Features and Administrative Controls sections, and i make the corresponding administrative changes necessary to credit soluble boron in the  ;

fuel storage criticality analyses. The proposed changes are described below:

J l

Revisions to the Proposed Improved Technical Specifications (ITS)

1. Revisions to the Table of Contents The Table of Coments is revised to include two additional Technical Specifications 3.7.17, l

" Fuel Storage Pool Boron Concentration" and 3.7.18, " Fuel Assembly Storage" that are '

being added to support crediting soluble boron in the fuel storage pool criticality analyses.

2. Revision to COLR definition l

The definition for COLR is revised to add the fuel storage pool limits to the report.

3. Add Technical Specifications 3.7.17 and 3.7.18 Two Technical Specifications 3.7.17, " Fuel Storage Pool Boron Concentration" and 3.7.18, " Fuel Assembly Storage' are being added to credit soluble boron in the fuel storage pool criticality analyses.

4. Specification 4.3.1.1 ,

I Design Features Section 4.3.1.1 is revised to reflect the increased maximum enrichment assumed in the fuel storage pool criticality analyses, change the 0.95 K a requirement if l

" fully flooded with unborated water" to " fully flooded with borated water," and add a 4 requirement to maintain K aless than 1.0 if fully flooded with unborated water, under maximum feasible conditions, and to add a reference to the COLR for fuel allowable storage configurations.

5. Specification 5.6.5 Section 5.6.5 is revised to add the fuel storage pool parameters to the COLR and add the WCAP containing the spent fuel rack criticality analysis methodology.

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l ENCLOSURE 1 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS C_REDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE

, BASIS FOR PROPOSED CHANGE (continued) )

6. Revisions to the Table of Contents (Bases)

The Table of Contents is revised to include two additional Technical Specification Bases. I 1 3.7.17, " Fuel Storage Pool Boron Concentration" and 3.7.18, " Fuel Assembly Storage" l that are being added to support crediting soluble boron in the fuel storage pool criticality analyses.

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7. Add Bases for Technical Specifications 3.7.17 and 3.7.18 Two Technical Specification Bases, 3.7.17, " Fuel Storage Pool Boron Concentration" and ,

3.7.18, " Fuel Assembly Storage" are being added to credit soluble boron in the fuel )

storage pool criticality analyses. These Technical Specification revisioas are attached with Enclosure 3. l Basis 1

The spent fuel rack criticality analyses have been performed taking credit for the soluble I boron contained in the fuel storage pool water and not taking any credit for the Boraflex poison contained in the racks. The analyses were performed for fuel enrichments up to and including 5.0 weight percent U-235. In the fuel storage pool criticality analysis, a storage configuration has been defined using maximum feasible La calculations to ensure that the spent fuel rack La will be less than 1.0 with no soluble boron under normal storage conditions and assuming nominal fuel assembly parameters and fuel rack ,

I dimensions. Soluble boron credit provides significant negative rcactivity in the criticality analysis which is used to offset uncertainties and tolerances and to provide subcritical margin such that the fuel storage pool Lais maintained less than or equal to 0.95.

New Technical Specification 3.7.17 establishes the new boron concentration requirements for the fuel storage pool water. The actual boron concentration limits will be contained in the COLR. Since the initial fuel load, soluble boron has been contained in the fuel storage pool, therefore, the new requirement will have little effect on normal pool operations and maintenance.

New Technical Specification 3.7.18 establishes the requirements for the fuel storage configurations. The actual fuel storage configuration limitations will be contained in the COLR. Since the new limitations are administrative, they will not have any significant elTect on normal pool operations and maintenance. Generic Letter 88-16 was issued to encourage licensees to prepare changes to Technical Specifications related to cycle-specific parameters. The generic letter provided guidance El-2

ENCLOSURE 1 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE BASIS FOR PROPOSED CHANGE (continued) for the relocation of certain cycle-dependent core operating limits from the Technical Specifications.

While fuel storage pool limits were not specifically addressed in Generic Letter 88-16, the .

Technical Specification changes associated with relocating the fuel storage pool limits to l the COLR are being submitted in accordance with the guidance provided in Generic Letter l 88-16 because they will be calculated with NRC-approved methodologies. The proposed changes reference the COLR for fuel storage pool limits and ensure that the fuel storage ,

pool is maintained within the limits of the COLR. The proposed changes to the l Administrative Controls section ensure that the calculation of the fuel storage pool limits proposed for inclusion in the COLR will be performed in accordance with NRC-approved .

methodologies.

1 The changes to the Technical Specifications are included in Enclosure 3. Enclosure 2 is an l evaluation in accordance with 10 CFR 50.92 to demonstrate that these changes to the j Technical Specifications do not involve any significant hazards considerations. i Due to degradation, Boraflex is being eliminated from the analytical basis for demonstrating compliance with General Design Criteria 62. This has been done by utilizing the methodology in WCAP-14416. The new criticality analyses assume enrichment up to and including 5.0 weight percent U-235. The VEGP new fuel storage area has already been analyzed for 5.0 weight percent U-235 fuel as documented in j section 9.1.1.3 of the VEGP Final Safety Analysis Report.

The new criticality analyses take limited credit for soluble boron in the fuel storage pool, checkerboard loading patterns in the spent fuel racks and the effects of burnup.

Therefore it is appropriate to estabFsh limiting conditions for operation and surveillance requirements in the Technical Specificaions to assure that spent fuel is stored in accordance with the analytical assumptions. The checkerboard patterns and bumup limits may be changed if new analyses are performed in accordance with the NRC approved methodology. Therefore the required methodology is being documented by referencing WCAP-14416 in the Technical Specifications and the checkerboard patterns and enrichment /bumup limits are being added as a new section of the COLR. Th, ised COLRs for Cycle 7 of Unit 1 and Cycle 5 of Unit 2 are included as Enclosure ,.

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ENCLOSURE 2 VOGTLE ELECTRIC GENER ATING PLANT l REQUEST TO REVISE TECHNICAL SPECIFICATIONS l CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE l

10 CFR 50.92 EVALUATION 1

Background

1 l

This submittal proposes to take credit for the soluble boron in the fuel storage pool water I to control the suberitical condition of the spent fuel assembly array. It also takes credit for fuel burnup and cheuerboard loading configurations in the spent fuel racks. The i

utilization of sohu twn, which is contained in the plant fuel storage pool, provides a simple, direct rrMho3 of osuring suberiticality. This control feature retains the necessary criticality safety recircants and has many benefits. Credit for soluble boron is currently used for Mode 6 reauhity control in the reactor vessel.

In order to obtain approval of this proposed license amendment, an alternative method of maintaining the 5 percent shutdown margin is being used. The current regulatory guidance documents (References 1,2, and 3) do not include credit for soluble boron. The proposed license amendment proposes limited use of credit for soluble boron in the fuel storage pool criticality analysis. The storage configurations have been defined using maximum feasible Kea calculations, as described in WCAP-14416 (Reference 4) and Enclosure 5, to ensure that the spent fuel rack K.g will be less than 1.0 with no soluble boron under normal storage conditions and assuming nominal fuel assembly parameters and fuel rack dimensions. Soluble boron credit is und to offset uncertainties, tolerances, and oft-normal conditions and to provide suberitical margin such that the fuel storage pool K.a is maintained less than or equal to 0.95. The Vogtle Units 1 and 2 spent fuel storage configurations were analyzed utilizing the Westinghouse Spent Fuel Rack Criticality Analysis Methodology described in WCAP-14416 (Reference 4).

The Vogtle Units 1 and 2 spent fuel racks have been reanalyzed to allow storage of Westinghouse 17x17 fuel assemblies with enrichments up to and including 5.0 weight percent U-235 in the allowable storage cell locations using soluble boron credit, burnup and checkerboard loading configuration. This analysis also ignores the presence of the spent fuel rack Boraflex poison panels.

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ENCLOSURE 2 l VOGTLE ELECTRIC GENERATING PLANT l REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued)

The analysis considered storage of fuel in all storage locations, 3-out-of-4 checkerboard and 2-out-of-4 checkerboard patterns. The enrichment for each storage pattern was determined and the required equivalent burnup for 5.0 weight percent U-235 fuel was determined. Burnup versus enrichment requirements for each checkerboard pattern were developed as described in Enclosure 5 and shown in enclosure 7. These took credit for soluble boron in accordance with WCAP-14416. The highest boron concentration required for maintaining K a <0.95 in the specified checkerboard arrangements was 550 ppm (Unit 1) and 450 ppm (Unit 2). An additional boron concentration was added to assure that the 0.95 limit would be met for a dropped or misplaced assembly, raising the concentration requirement to 1100 ppm (Unit 1) and 1250 ppm (Unit 2). The effective limit for boron concentration will be 1250 ppm because the two fuel storage pools are normally connected. The typical concentration of boron in the fuel storage pool is greater than 2400 ppm. Since a misplaced assembly and a dilution event are independent, conservative margin exists between the normal condition concentration and the concentration for maintaining K.a <0.95.

WCAP-14181, " Evaluation of the Potential for Diluting PWR Spent Fuel Pools" (Reference 5), was transmitted to the NRC by Westinghouse Owners Group Letter OG-95-076. This report identifies potential events which could dilute the soluble boron contained in PWR fuel storage pools and quantifies the frequency of those dilution events via a probabilistic risk assessment. This PRA was provided to the NRC as supporting information for the Westinghouse Owners Group boron credit program.

In WCAP-14181, a generic methodology was developed to identify potential events which could dilute the soluble boron contained in PWR fuel storage pools and to quantify the frequency of those events. This methodology utilized a probabilistic risk assessment (PRA) of a composite plant model to calculate the event frequency of a dilution event.

The results of the PRA concluded that the event frequency rem ined less than the NRC Safety Goal Policy Statement target risk objective oflE-6/ reactor year.

To account for differences in the potential sources of pool dilution bet.veen the composite plant described in WCAP-14181 and Vogtle, an individual analysis was made of the Vogtle pool. This analysis was conducted with methodology which closely paralleled that employed in WCAP-14181. The results, described in Enclosure 6, concluded that the frequency of pool dilution to the 0.95 K a boron concentration (1250 ppm) is on the same order of magnitude as that reported in WCAP-14181 and less than the NRC Safety Policy Statement criterion of 1.0E-6/ reactor year.

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ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued)

Deterministic calculations were also performed (Enclosure 6) in order to defme the dilution times and volumes for Vogtle. That data was then compared to analogous data for the composite plant utilized in WCAP-14181. The dilution sources availabl at Vogtle were also compiled and evaluated against the dilution volume calculated, to de* rmine the potential of a fuel storage pool dilution event. The deterministic evaluations si w that a large volume of water (more than 200,000 gallons for a single pool or 400,0( gallons when the pools are connected, which is the normal configuration) is necess' 3 dilute the fuel storage pool to a soluble boron concentration where a K,a of 0.95 wo. ;e approached in the Vogtle Units 1 and 2 fuel storage pools.

A dilution event large enough to result in a significant reduction in the fuel storage pool boron concentration would involve the removal of a large quantity of water from a dilution source and a significant increase in fuel storage pool level, which would ultimately overflow the pool. Such a large water volume turnover, and the likely overflow of the fuel storage pool, would be readily detected and terminated by plant personnel.

In addition, because of the very large quantities of water required, and the fuel storage pool level and sump alarms, any dilution of the fuel storage pool is expected to be detected and eliminated before a significant dilution could occur.

The evaluations in Reference 5 and Enclosure 6, which show that the dilution of the fuel storage pool is a low probability occurrence, combined with the maximum feasible K,g i calculation, which shows that the spent fuel rack K.g will remain less than 1.0 when l flooded with unborated water and assuming nominal fuel assembly parameters and fuel j rack dimensions, demonstrate a level of safety comparable to the conservative criticality l analysis methodology described in References 1,2, and 3.

The precedence of using soluble boron in water to provide criticality control aside from normal resctor operations has already been established. Credit for soluble boron in the fuel storage pool is currently permitted when considering abnormal or accident conditions.

Also, during refueling, soluble boron in the reactor vessel is the only direct control utilized to ensure that the reactor remains subcritical.

Proposed Change The proposed changes to the Technical Specifications are described in Enclosure 1, and the specific wording of changes are shown in Enclosure 3.

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ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued)

Safety Evaluation The design basis for preventing criticality in the fuel storage pool is that, including uncertainties, there is a 95 percent probability at a 95 percent confidence level that the K.g of the fuel storage assembly array will be less than 0.95 with full density moderation. This proposed license amendment includes an alternative to the current practice of assuming unborated water for demonstrating the 5 percent suberiticality margin. Compliance with GDC 62 without credit for soluble boron is demonstrated by assuring that the maximum feasible La is less than 1.0 assuming unborated water. The boron concentration is then determined to assure that La is less than 0.95 including uncertainties and including potentially dropped or misplaced assemblies. Actual boron levels are demonstrated to be sufliciently high that no reasonable combination of events will result in K.a less than 0.95, thus assuring that the 5 percent suberiticality margin recommended by the NRC will be maintained.

For the storage of fuel assemblies in the spent fuel storage racks, the acceptance criteria for criticality requires the efTective neutron multiplication factor, K.e ,be less than or equal to 0.95, including uncertainties. The criticality analysis performed for the Vogtle Units 1 and 2 spent fuel storage configurations shows that the acceptance criteria for criticality is met for the storage of 17x17 fuel assemblies under both normal and accident conditions with soluble boron credit, no credit for the spent fuel rack Boraflex poison panels, and the storage configurations and enrichment limits described in Enclosure 5.

The Vogtle Units 1 and 2 spent fuel storage racks were analyzed utilizing the Westinghouse Spent Fuel Rack Criticality Analysis Methodology described in WCAP-14416 (Reference 4). The analytical methods used in the analysis conform with ANSI N18.2-1973, " Nuclear Safety Criteria for the Design of Stationary Pressurized Water Reactor Plants", Section 5.7, Fuelllandling System; ANSI 57.2-1983, " Design Objectives for LWR Spent Fuel Storage Facilities at Nuclear Power Stations", Section 6.4.2; ANSI N16.9-1975, " Validation of Calculation Methods for Nuclear Criticality Safety", and the NRC Standard Review Plan, Section 9.1.2, " Spent Fuel Storage" The methodology uses an alternative method (relative to credit for the presence of soluble boron in the fuel storage pool) to that stated in ANSI 57.2-1983 (Reference 3) and the NRC position paper (Reference 7).

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ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS

. CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued)

While this License Amendment Request proposes use of credit for soluble boron in the fuel storage pool criticality analyses, storage configurations have been defined using l maximum feasible Lacalculations to ensure that the Krr will be less than 1.0 with no soluble boron under normal storage conditions and assuming nominal fuel assembly parameters and fuel rack dimensions. Soluble boron credit provides significant negative reactivity in the criticality analysis, which is used to offset uncertainties and tolerances, and to provide suberitical margin such that the fuel storage pool La is maintained less than or equal to 0.95. Soluble boron credit and storage configuration were also used to offset the reacthity increase when ignoring the presence of the spent fuel rack Borafiex poison panels.

New Technical Specification 3.7.17 establishes the new boron concentration requirements for the fuel storage pool water. The actual boron concentration limits will be contained in the COLR. Because soluble boron is normally contained in the fuel storage pool, the new requirement will have little efTect on normal pool operations and maintenance.  ;

New Technical Specification 3.7.18 establishes the requirements for the spent fuel storage l configurations. The actual fuel storage configuration limitations will be contained in the )

COLR. Since the pool storage configuration limitations are administrative, the new limitations will only have limited effects on normal pool operations and maintenance.

Fuel storage pool systems, instrumentation, and supporting systems are not modified as a result of the proposed license amendment. The operations involving fuel storage pool water cooling and cleanup do not change. The procedures related to the fuel storage pool will be upgraded as necessary to ensure that the pool boron concentration is formally controlled. The procedures will ensure that the proper provisions, precautions, and instructions exist to control the pool boron concentration and water inventory.

The Vogtle Units 1 and 2 spent fuel rack criticality analysis also addressed postulated accidents in the fuel storage pool. The accidents that can occur in the fuel storage pool and their consequences are not significantly affected by taking credit for the soluble boron present in the pool water as a major suberiticality control element.

Most fuel storage pool accident conditions will not result in an increase in La. Examples of such accidents are the drop of a fuel assembly on top of a rack, or between rack modules and the pool wall.

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ENCLOSURE 2 i

VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS C_REDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 1

l 10 CFR 50.92 EVALUATION (continued) l From a criticality standpoint, a dropped assembly accident occurs when a fuel assembly in its most reactive condition is dropped onto the storage racks. The rack structure from a criticality standpoint is not excessively deformed. Previous accident analysis with unborated water showed the dropped assembly which comes to rest horizontally on top of the rack has sufficient water separating it from the active fuel height of stored assemblies to preclude neutronic interaction. The rack continues to provide sufficient separation to prevent neutronic interaction even with the assembly enrichment increased to 5.0 weight percent U-235. For the borated water condition, the interaction is even less because the water contains boron, an additional thermal neutron absorber. The radiological consequences of a dropped assembly accident in the fuel storage pool are unaffected by l this proposed change to the Technical Specifications. I Two accidents can be postulated for each storage configuration which could increase reactivity beyond the analyzed condition. The first postulated accident would be a loss of the fuel pool cooling system. The second would be the mistoading of a fuel assembly into a cell for which the restrictions on location, enrichment or burnup are not satisfied.

The loss of normal cooling to the fuel storage pool water causes an increase in the temperature of the water passing through the stored fuel assemblies. This causes a decrease in water density which would normally result in an addition of negative reactivity.

However, since Boraflex is not considered to be present and the fuel storage pool water has a high concentration of boron, a density decrease causes a positive reactivity addition.

The fuel assembly misloading accident involves having restricted storage locations based on initial enrichment and burnup requirements. Administrative controls are placed on the loading of assemblies into these restricted locations. The misloading of an assembly constitutes not meeting the enrichment and burnup requirements of that restricted location. The result of the mistoading is to add positive reactivity, increasing La.

The amount of soluble boron required to offset each of these postulated accidents was evaluated for all of the proposed storage configurations. That evaluation established the amount of soluble boron necessary to ensure that the spent fuel rack Lawill be maintained less than or equal to 0.95 should a loss of fuel storage pool cooling or a fuel assembly mistoad occur. The amount of soluble boron necessary to mitigate these events has been included in the fuel storage pool boron concentration for maintaining K.g <0.95.

An event or sequence of events that reduces the amount of soluble boron in the fuel storage pool would add positive reactivity, thus increasing La. Significant dilution of the fuel storage pool requires two elements: (1) the inflow of a large volume of water from a l

source E2-6

ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS

, CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued) of water with a boron concentration less than that of the pool, and (2) a location or place to which the large volume of pool borated water goes when it is removed from the pool.

Deterministic calculations were performed (Enclosure 6) in order to define the dilution times and volumes for Vogtle. The dilution sources available at Vogtle were compiled 4

and evaluated against the dilution volume calculated, to determine the potential for a fuel storage pool dilution event. The deterministic evaluations show that a large volume of water is necessarj to dilute the fuel storage pool to a soluble boron concentration where the K.e would approach 0.95 (the calculation used 1250 ppm)in the Vogtle Units 1 and 2 spent fuel racks.

A dilution event large enough to result in a significant reduction in the fuel storage pool boron concentration will involve the removal of a large quantity of water from a dilution source and a significant increase in fuel storage pool !evel, which would ultimately result in pool overflow. Such a large water volume turnover, and the likely overflow of the fuel storage pool, would be readily detected and terminated by plant personnel. In addition, because of the very large quantities of water required, and the fuel storage pool level and sump alarms, any dilution of the fuel storage pool is expected to be detected and terminated before a significant dilution could occur.

Therefore, it is highly unlikely that any dilution event in the fuel storage pool could result in the reduction of the fuel storage pool boron concentration to less than 1,100 ppm (Unit

1) or 1,250 ppm (Unit 2).

In WCAP-14181, " Evaluation of the Potential for Diluting PWR Spent Fuel Pools" (Reference 5), a generic methodology was applied to identify potential events which could dilute the soluble boron contained in PWR fuel storage pools, and to quantify the frequency of those events. This methodology utilized a probabilistic risk assessment (PRA) of a composite plant model to calculate the event frequency of a dilution event.

The results of the PRA concluded that the event frequency remained less than the NRC Safety Goal Policy Statement target risk objective oflE-6/ reactor year.

DifTerences between the ccmposite plant described in WCAP-14181 and Vogtle relative to the potential sources of pool dilution have been addressed in an individual analysis of the Vogtle pool. This analysis was conducted with methodology which closely paralleled that employed in WCAP-14181. The analysis, found in Enclosure 6, concluded that the frequency of pool dilution to the 0.95 K.a boron concentration (1250 ppm) is on the same E2-7

ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE I

10 CFR 50.92 EVALUATION (continued) order of magnitude as that reported in the WCAP-14181 and less than the NRC Safety Goal Policy Statement criterion of 1.0E-6/ reactor year.

The results of these probabilistic evaluations demonstrate that the risk of exceeding a La of 0.95 in the fuel storage pool when taking credit for the soluble boron remains a very small contributor to the overall risk associated with the operation of the Vogtle plant.

Placing the fuel storage pool limits in the COLR has no impact upon plant operations or safety. No safety-related equipment, safety function, or plant operations will be altered as a result of the location of the limits. Because the Technical Specifications will require operation of the fuel storage pool within limits calculated by NRC-approved methodologies, the proposed location of the fuel storage pool limits is administrative in nature. Appropriate actions to be taken if the limits are violated will be contained in the Technical Specifications.

Conclusion The combination of the following provide a level of safety comparable to the conservative criticality analysis methodology required by References 1,2, and 3:

1. The maximum feasible K a calculation, which assumes normal storage conditions and nominal fuel assembly parameters and fuel rack dimensions, shows that the La will remain less than 1.0 when flooded with unborated water. l

2. The large volumes of water that are necessary to dilute the fuel storage pool and ample operator response times, assure that credible events will not result in dilution of the fuel storage pool to the boron concentration for K g of 0.95.

Therefore, Georgia Power Company believes there is reasonable assurance that the health and safety of the public will not be adversely atTected by the proposed Technical Specification changes.

Determination of Significant Hazards The proposed changes to the Operating License have been evaluated to determine whether they constitute a significant hazards consideration as required by 10 CFR 50, Section 50.91 using the standards provided in Section 50.92. This analysis is provided below:

1. The proposed change does not involve a significant increase in the probability or j consequences of an accident previously evaluated. l l

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ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued)

There is no increase in the radiological consequences of accidents previously evaluated in the Vogtle FSAR with the use of 5.0 weight percent U-235 fuel. Increasing the enrichment up to and including 5.0 weight percent U-235 affects the radiological source terms and subsequently the potential releases both normal and accidental. Evaluations performed (WCAP-12610-P-A, Reference 6) considered the source term, gap fraction, normal operating plant releases and the accident doses for a maximum fuel enrichment of 5.0 weight percent U-235. It was concluded that operating with and storing fuel with 5.0 weight percent U-235 enrichment may result in minor increases in the normal annual releases oflong half-life fission products that are not significant. Also, the radiological consequences of accidents are minimally affected due to the very small changes in the core inventory and the fact that the currently assumed gap fractions remain bounding.

The use of the slightly higher enrichment for VEGP fuel will not result in burnups in excess of those currently allowed for VEGP. The cycle _ design methods and limits will .

remain the same as are currently licensed. Therefore the use of fuel with the higher enrichment is not expected to result in operating conditions outside those currently allowed for VEGP.

There is no increase in the probability of a fuel assembly drop accident in the fuel storage pool when considering the presence of soluble boron in the pool water for criticality control. The handling of the fuel assemblies in the fuel storage pool has always been performed in borated water.

Fuel assembly placement will be controlled pursuant to approved fuel handling procedures and will be in accordance with the spent fuel rack storage configuration limitations in the COLR. The consequences of a misplaced assembly have been included in the analysis supporting this revision to the Technical Specifications. ]

I There is no increase in the consequences of the accidental mistoading of a spent fuel assembly into the fuel storage pool racks because criticality analyses demonstrate that the pool will remain subcritical following an accidental mistoading of an assembly even considering a dilution event. The proposed Technical Specifications and COLR limitations will ensure that an adequate fuel storage pool boron concentration will be maintained.

There is no increase in the probability of the loss of normal cooling to the fuel storage pool water due to the presence of soluble boron in the pool water for subcriticality control,  !

)

E2-9

ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL, STORAGE 10 CFR 50.92 EVALUATION (continued) because a high concentration of soluble boron has been maintained in the fuel storage pool water.

The loss of normal cooling to the fuel storage pool will cause an increase in the temperature of the fuel storage pool water. This will cause a decrease in water density which would normally result in an addition of negative reactivity. However, since Boraflex is not considered to be present, and the fuel storage pool water has a high concentration of boron, a density decrease causes a positive reactivity addition. The amount of soluble boron required to offset this postulated accident was evaluated for the allowed storage configurations. The amount of soluble boron necessary to mitigate these accidents and ensure that the Karwill be maintained less than or equal to 0.95 has been included in the fuel storage pool boron concentration. Because adequate soluble boron will be maintained in the pool water, the consequences of a loss of normal cooling to the fuel storage pool will not be increased.

Therefore, based on the conclusions of the above analysis, the proposed changes will not involve a significant increase in the probability or consequences of an accident previously

)

evaluated.

2. The proposed change does not create the possibility of a new or different kind of accident from any accident previously analyzed.

The potential for criticality accidents in the fuel storage pool are not new or different types of accidents. It has been reanalyzed in the Criticality Analysis report (Enclosure 5).

Because soluble boron has been maintained in the fuel storage pool water, the possibility of a fuel storage pool dilution has previously existed. Therefore, the implementation of Technical Specification controls for the soluble boron will not create the possibility of a new or different kind of accidental pool dilution.

, With credit for soluble boron now a major factor in controlling criticality, an evaluation of fuel storage pool dilution events was completed. A generic methodology was applied (Reference 5) to identify potential events which could dilute the soluble boron contained in PWR fuel storage pools, and to quantify the frequency of those events. This methodology utilized a probabilistic assessment of a composite plant model to calculate the event frequency of a dilution event. The results of the assessment concluded that the event frequency remained less than the NRC Safety Goal Policy Statement target risk objective oflE-6/ reactor year.

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i 2

ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICA.L SPECIFICATIONS 4

CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued) l

Differences between the composite plant described in WCAP-14181 and Vogtle relative to the potential sources of pool dilution were addressed in an individual analysis of the

. Vogtle pool. This analysis was conducted with methodology which closely paralleled that employed in WCAP-14181. That analysis, found in Enclosure 6, concluded that the i frequency of pool dilution to the 0.95 K.a boron concentration (1250 ppm) is on the same

order of magnitude as reported in WCAP-14181 and less than the NRC Safety Goal

- Policy Statement criterion of 1.0E-6/ reactor year.

2 l Proposed Technical Specifications 3.7.17 and 3.7.18 which ensure the maintenance of the i fuel storage pool boron concentration and storage configuration, do not represent new j concepts. The actual boron concentration in the fuel storage pool has been maintained at a higher value than the proposed limits for the Unit 1 and 2 fuel storage pools for refueling purposes. The criticality analysis (Enclosure 5) determined that a boron concentration of l

{ 1,100 ppm (Unit 1) and 1,250 ppm (Unit 2) results in a K.a < 0.95 including all the i

calculational uncertainties and additional margin to compensate for the possibility ofloss of cooling, or a "isplaced assembly.

There is no significant change in plant configuration, equipment design, or usage of plant equipment. The safety analysis for dilution accidents has been expanded; however, the criticality analyses assure that the pool will remain subcritical with no credit for soluble boron. Therefore, the proposed changes will not create the possibility of a new or different kind of accident.

3. The proposed change does not result in a significant reduction in the margin of safety.

I Proposed Technical Specifications 3.7.17 and 3.7.18 and the associated spent fuel boron concentration and storage limits in the COLR will provide adequate safety margin to assure that the stored fuel assembly array will always remain suberitical. Those limits are

. based on a plant specific criticality analysis (Enclosure 5) performed in accordance with l the Westinghouse criticality analysis methodology described in Reference 4.

While the criticality analysis utilized credit for soluble boron, a storage configuration has been defined using maximum feasible K a calculations to ensure that the spent fuel rack K.awill be less than 1.0 with no soluble boron under normal storage conditions and 4

4 E2-Il

I l

ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT I REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORQN AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued) assuming nominal fuel assembly parameters and fuel rack dimensions. Soluble boron credit is used to offset uncertainties, tolerances and off-normal conditions (such as a misplaced assembly) and to provide subcritical margin such that the fuel storage pool K,g is maintained less than or equal to 0.95.

The loss of a considerable amount of soluble boron in the fuel storage pool which could lead to exceeding a K,a of 0.95 during accidents and under adverse conditions has been evaluated and shown to be very improbable.

The combination of the probabilistic evaluation which shows that the dilution of the fuel storage pool is a low probability occurrence, the maximum feasible K,g calculation which shows that the K,g will remain less than 1.0 when flooded with unborated water and l

assuming nominal fuel assembly parameters and fuel rack dimensions, and the unavailability of the large volumes of water which are necessary to dilute the fuel storage ,

pool, provide a level of safety comparable to the conservative criticality analysis methodology required by References 1,2, and 3.

Therefore, the proposed changes in this license amendment will not result in a significant reduction in the plant's margin of safety.

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1 ENCLOSURE 2 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICHMENT INCREASE FOR FUEL STORAGE 10 CFR 50.92 EVALUATION (continued)

Conclusion Based on the evaluation above, and pursuant to 10 CFR 50, Section 50.91, Georgia Power Company has determined that operation of the Vogtle Electric Generating Plant in accordance with the proposed license amendment request does not involve any significant hazards considerations as defined by NRC regulations in 10 CFR 50, Section 50.92.

References

1. USNRC Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants, LWR Edition, NUREG-0800, June,1987.

2. USNRC Spent Fuel Storage Facility Design Bases (for Comment) Proposed Revision i

2,1981, Regulatory Guide 1.13. .

3. ANS, " Design Requirements for Light Water Reactor Spent Fuel Storage Facilities at Nuclear Power Stations", ANSI /ANS-57.2-1983.

4. WCAP-14416, " Westinghouse Spent Fuel Rack Criticality Analysis Methodology",

June,1995.

5. WCAP-14181, " Evaluation of the Potential for Diluting PWR Spent Fuel Pools", July, 1995.

6. WCAP-12610-P-A, " Vantage + Fuel Assembly Reference Core Report", April,1995.

7. Nuclear Regulatory Commission, Letter to All Power Reactor Licensees from B. K.

Grimes, OT Position for Review and Acceptance of Spent Fuel Storage and Handling Applications, April 14,1978.

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l ENCLOSURE 3 VOGTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS CREDIT FOR BORON AND ENRICIIMENT INCREASE FOR FUEL STORAGE l

INSTRUCTIONS FOR INCORPORATION l

l The proposed change to the Vogtle Electric Generating Plant Improved Technical j Specifications would be incorporated as follows.

Remove page Insert Page l

v and vi* v and vi*

1.1-l

• and 1.1-2 1.1-l

• and 1.1-2 3.7-39 3.7-40

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3.7-41 4.0-l

• and 4.0-2 4.0-1

• and 4.0 9 I 5.0-29* and 5.0-30 5.0-29* and 5.0-30 Changes to the Improved Technical Specification bases would be incorporated as follows: I l

Remove Page Insert Page iii* and iv iii* and iv B 3.7-92 through B 3.7-98 I

• Overleaf page containing no change.

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