ML20199A141
| ML20199A141 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 11/05/1997 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20199A145 | List: |
| References | |
| 97-647, NUDOCS 9711170073 | |
| Download: ML20199A141 (11) | |
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November 5, 1997 U.S. Nuclear Re0ulatory Commission Serial No. 97 647 Attention: Document Control Desk NL&OS/GSS R0 Washington, D.C. 20555 Docket Nos. 50-338 50 339 License Nos. NPF 4 NPF -7 Gentlemen:
YJRGINIAILECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 EROPOSED TEQHNLCAkSEEClflCATION CHANGES ALLQW SPENT FUEL PIT GATE MOVEMENT OVER IRRADIATED FUEL Pursuant to 10CFR50.90, Virginia Electric and Power Company requests amendments, in the forrn of changes to the Technical Specif; cations and to Facility Operating License Numbars NPF-4 and NPF 7 for North Anna Power Station Units 1 and 2, respectively.
The proposed char.gns will provide administrative controls in TS 3/4.9.7, Refueling Operations, Crane Travel- Spent Fuel Pit" to permit spent fuel pit gate movement over liradiatad fuel. A discussion of the proposed Technical Specifications changes is provided in Attachment 1.
The proposed Technical Specifications changes have been reviewed and approved by the Station Nue:sar Safety and Operating Committee and the Management Safety Review Committoo. It has been determined that the proposed Technical Specifications changes do not involve an unroviewed safety quoation as defined in 10CFR50.59 or create a significant hazards consideration as defined in 10CFR50.92. The proposed Technical Specifications changes are provided in Attachment 2. The basis for our determination that the changes do not involve a significant hazards consideration is provided in Attachment 3.
After the Spring 1998 Unit 2 refueling outage, a load path for movement of spent fuel pit gates over empty fuel storage cells will not be able to be established. Therefore, to ,
oormit maintenance
,' NC09 on the spent fuel pit gates during the Unit 1 Fall 1998 /
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, outage and subsequent refueling outages, we request NRC review and approval of the requested changes by July 1,1998.
If you have any further questions or require additionalinformation, please contact us.
Very truly yours, (t w & 8% ^-
' James P. O'Hanlon Senior Vice President Nuclear Attachments
- 1. Discussion of Changes
- 2. Proposed Technical Specification Chang (s
- 3. Significant Hazards Consideration Determination Oommitments made in this letter:
- 1. The commitments made in this letter are as Indicated in the proposed Technical Specification changes.
cc: U.S. Nuclear Regulatory Commission Region ll Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303 Mr. M. J. Morgan NRC Senior Resident inspector North Anna Power Station Commissioner Bureau of Radiological Health Room 104A 1500 East Main Street Richmond, VA 23219
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4 COMMONWEALTH OF VIRGINIA )
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COUNTY OF HENRICO )
The foregoing document was acknowledged before me, ir; and for the County and Commonwealth aforesaid, today by J. P. O'Hanlon, who is Senior Vice President - Nuclear, of Virginia Electric and Power Company. He has affirmed-before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of his knowledge and belief. ;
Ackrowledged before me this d day of ,bVI mh'r ,,19 07. t My Commission Expires: March 31,' 2000.
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ATTACHMENT 1 :
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Diccussion of Proposed Technical Specification Change Movement of Spent Fuel pit Transfer Gate over irradiated Fuel i
North Anna Power Station Units 1 and 2
Discussion af Changes intraduttinn Pursuant to 10CFR50.90, Virginia Electric and Power Company requests changes to Technical Specifications 3/4.9 Refueling Operations, " Crane Travel - Spent Fuel Pit,"
Limiting Condition for Operation 3.9.7, Surveillance Requircment 4.9.7, and Bases Section 3/4.9.7 for North Anna Power Staticn Units 1 and 2. The current Technical Specifications requirements prohibit loads in excess of 2500 pounds from traveling over irradiated fuel assemblies in the spent fuel pit. The proposed changes will exempt these requirements for the movement of the spent fuel gates provided specific administrative controls are satisfied.
Due to the number ofirradiated fuel assemblies currently stored in the spent fuel pit over years of operation, additional flexibility is needed to accomplish the movement of the spent fuel pit gates during refueling activities and to reduce fuel handling activities in preparation for refueling outages. In order to perform gate seal maintenance prior to each outage, a gate is moved across the irradiated fuel storage rea to the cask handling area where it can be lifted out of the spent fuel pit. When a clear path of empty fuel storage cells cannot be established (North Anna 1998 Fall outage) seal maintenance cannot be perfonned unless relief from the current LCO is granted. Therefbre, Virginia Electric and Power Company is proposing changes to the North Anna Power Station Technical Specifications to permit movement of the spent fuel gates over irradiated fuel assemblies.
The proposed Technical Specifications changes will preserve the existing load restrictions of prohibiting loads in excess of 2500 pounds from travel over irradiated fuel assemblies in the sreat fuel pit, with the specific exception of the three spent fuel pit gates. The gates are located at each unit's transfer canal and one at the spent fuel cask separating wall. These gates will be permitted to be carried over irradiated fuel provided administrative controls are in place to limit the gate lift height, attach redundant safety cables to support the gate should a hoist failure occur and to ensure that the gate is not carried over irradiated fuel which contains a rod control cluster assembly. The administrative controls will be specified in station procedures.
The proposed changes do not involve any physical modifications to the plant 0:
modification in the methods of plant operation which would cause an : cnt or event of a different type than previously analyzed. Gate rigging and m sent is currently allowed over empty fuel storage cells and is controlled by NUREU 0612 heavy loads procedares. Commitments to NUREG 0612, as clarified in Attachment 2 of Virginia Electric and Power Company's May 13,1996 letter responding to NRCB 96-02, do not require that a load drop be postulated or analyzed, llowever, since the gate will be moved over irradiated fuel, additional actions were deemed prudent: (1) use of redundant rigging to prevent a load drop, (2) structural analysis of the effects of a direct impact caused by a gate drop and (3) administrative controls which maximize prot (ction for irradiated fuel, t
T'wo load handling accidents were considered:
- 1. Direct gate impact on a single fuel storage cell in order to confinn that the cell protects irradiated fuel from gate impact load
- 2. Direct gate impact on the fuel pool floor to confirm its structural integrity The existing UFSAR fuel handling accident analysis is not altered and the margin of safety fo- design basis accidents remains unalTected by the prooosed changes.
lhek Mtnund Years of operation have resulted in a large number of irradiated fuel assemblies being stored in the spent fuel pit. In order to reduce fuel handling activities in preparation for refueling outages, additional flexibility is needed to move the gates over irradiated fuel assemblies. Under the existing Technical Specification restrictions, gate movements over the fuel racks were preceded by fuel shuflies in order to prepare a load path of empty storage cells. As the number of empty storage cells has been reduced, it has become more difficult and complex to shufile fuel and establish a load path over empty cells.
Gate movement over the fuel storage area is needed so that seal maintenance can be perfonned near the cask handling area. Upon implementation of the proposed changes, only those assemblies containing rod control cluster assemblies will be subjected to such moves prior to movement of the spent fuel pit gates. Although fuel handling activities are conducted in a safe manner in accordance with station procedures, this elimination of unnecessary fuel movements will reduce the overall probability of a fuel handling accident in the spent fuel pit.
Design and Licensing Ilasis The Spent Fuel Pit System consists of the spent fuel pit seismic class I structure and its cooling subsystem which provide a safe storage location to hold spent nuclear reactor fuel assemblies from both reactors. The speat fuel pit is located between the two containments in the Fuel lluilding. The pit consists of a shipping cask area, a fuel storage area, and two transfer canal areas. There are stainless steel fuci storage racks in the pit that can accommodate a total of 1737 fuel assemblies. A dividing wall separates the spent fuel pit with one end designated as the fuel shipping cask area and the other end designated as the fuel storage area. A slot in the dividing wall has a removable gate which allows movement of the fuel assemblies to the shipping cask area.
The existing Technical Specifications requirements were established to ensure that a load handling accident in the spent fuel pit did not result in unacceptable consequences when considering radioactive release and criticality. Specifically, the Technical Spe:ifications requirements were imposed based on two considerations in the event of a load weighing less than 2500 pounds was dropped:
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a the radioactivity released as a result of a dropped load would be limited to that contained in a single fuel assembly (all the fuel rods in one fuel assembly were assumed to fail); consistent with the design basis fuel handling accident, and
- b. the fuel storage racks will not distort into a critical array.
The 2500 pound criteria was taken as a conservative upper limit for the weight of an irradiated fuel assembly including a control rod assembly and the fuel handling tool.
Discussion North Anna Power Station Technical Specification Limiting Condition for Operation (LCO) 3.9.7 states that loads in excess of 2500 pounds shall be prohibited from travel over irradiated fuel assemblies in the spent fuel pit. The travel path for the spent fuel pit gates is prohibited by Technical Specifications LCO 3.9.7 from movement over irradiated fuel assemblies since the gate's weight in air is approximately 4200 pounds. Due to the number of irradiated fuel assemblies currently stored in the spent fuel pit and the anticipated inability to prepare a path of empty starage cells prior to the North Anna 1998 Fall ouiage, additional flexibility is needed for spent fuel pit gate movement in order to perform seal maintenance.
Gate rigging and movement is currently allowed over empty fuel storage cells and is controlled by NURl!G-0612 heavy loads procedures. Commitments to NURl!O-0612 (as clasified in the response to NRCil 96-02) do not require that a load diap be postulated or analyzed. Ilowever, since the gate will be moved over irradiated fuel, additional actions were deemed prudent. The gates will be double rigged to prevent a load drop :nduced by hoist failure. For additional assurance, a structural analysis of the effects of a direct gate impact on the storage rack <md pit floor was perfonned to verify that the basis of the existing Technical Specifications would not be violated.
A calculation checked the adequacy of all rigging components between the gate and the crane superstructure and found there is no credible suigle mode failure which could lead to a gate drop. In addition, it demonstrated that even if a postulated gate drop of either the transfer canal gates or the gate at the cask handling separating wall were to occur, it would not result in the potential for unacceptable consequences when considering the structural efTects of an impact upon the spent fuel storage racks and the spent fuel pit floor. it was concluded that the gates may be lilled and moved over irradiated fuel assemblies in the spent fuel pit as long as the following administrative controls are satisfied:
- 1. A gate lif1 height restriction is imposed whi'h permits a maximum lif1 of 39 inches (15 inches above the top of the platform crane deck support beam)
- 2. Safe load paths are established so any of the three gates may be lifted and moved over irradiated fuel which contains either no inserts or inserts of any type except rod 3
t control cluster assemblics. Lifling any gate over fuel containing a rod control cluster
' assembly is prohibited regardless of the lift height.
- 3. When any gate is lifled over the spent fuel cask handling area, irradiated fuel is excluded from the cask area and, therefore, there is no restriction on the gate lin height.
- 4. llefore moving the gate over irradiated fuel, redundant safety cables are attached to the gate and the gate lowered to remove slack in the redundant cables.
The same evolution will be used to move the cask area gate or the canal gates under these procedures. The gate will be lilled by the crane hoist, connected to redundant safety cables, lowered to remove slack and then moved laterally over the racks along a path where rod control cluster assemblies are excluded. Redundant gate rigging serves two functions: (1) the safety cable length with no slack ensures the gate lift height complies with the Technical Specincations, and (2) the rigging will support the full weight of the gate in the event the hoist were to fail. ,
r Gate impact was conservatively applied to a single fuel storage cell. The acceptance criteria was to preclude fuel damage and maintain a subcritical configuration. These criteria are bounded by the design fuel handling accident which assumed damage to one fuel assembly. Speci0cally, the spent fuel storage rack was treated as a target and its ability to prevent fuel damage by limiting the gate penetration into the rack was assessed.
Additionally, the ability of the rack to maintain fuel spacing and the structural integrity of the sper.t fuel pit Door were assessed.
Oate penetration into the ra:k considered the physical length of a storage cell and the '
overall lengths of the various fuel plus insert combinations. The top of the storage cell includes a 1" tall Dared section that was conservatively neglected. Dimensions ofinserts with spring mounted hubs were based on the fully compressed spring connguration. An available crush zone was determined by subtracting the fuel / insert length from the cell length. This zone dictated the maximum allowable gate penetration into the rack before loads were presumed to impact the fuel assembly and cause damage. The gate maximum lin height was seketed based on maintaining at least a 6" vertical clearance over the tallest obstruction in the pool, the opening in the wall to the spent fuel cask handling area.
The proposed Technical Specincation controls the gate lift with reference to a convenient datum, the movable platfonn deck support beam. The gate was analyzed as a rigid missile uid was not allowed to absorb any impact energy via displacement. Only the rack was allowed to distort. Gate penetration into a single storage cell was evaluated using the cell physical and material properties. The calculation found that regardless of the gate drop height, fuel damage was likely if the gate hit a cell containing fuel and a control rod assembly. All other fuel assembly combinations are short enough to avoid impact by a dropped gate provided the gate lift height is controlled. 4 4
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The calculation predicted fuel storage cell strain due to impact and compared it to the acceptance criteria of one half ultimate strain. Predicted strains are significantly less than the acceptance value. The calculation used this approach to conclude that a gate drop would not cause inadvertent criticality.
The calculation considered a gate drop over the spent fuel cask handling area from the high hook position. The redundant rigging system is not used and there are no lif1 height restrictic.4s during this 1111. 'lhe spent fuel pit floor structural integrity was verified. This analysis is bounding for postulated gate drops over other areas of the spent fuel pit except over the transfer canals. There is no need to carry the gates over the transfer canals, beyond the gate installed positions, and such movement will be prohibited by procedure.
Sntdik Changes The following changes are applicable to bo:h Units I and 2:
- 1. P.evisc Technical Specifications 1.imiting condition of Operation 3.9.7 to add the fbliowing exception with specific administrative controls:
3.9.7 1.oads in excess of 2500 pounds shall be prohibited from travel over irradiated fuel assemblies in the spent fuel pit. This does not apply to movement of any spent fuel pit gate provided each of the following is satisfied:
- a. the top of the gate (excluding lifting lugs) is no higher than 15 inches above the top of the moveabic platform crane deck support beam w hile over irradiated fuel,
- b. the gate is rigged to slack free safety cables while over irradiated fuel,
- c. Irradiated fuel containing Rod Control Cluster Assemblics are excluded along the load path where the gate is moved, and ,
- d. Irradiated fuel is prohibited in the cask area when the gate is lifted mer the spent fuel cask handling area. There is no restriction on lift height.
The first sentence remains unchanged in order to maintain the existing general restriction applicable to loads over spent fuel. The exception which follows identifies the gate handling restrictions which ensure that the gate will not be dropped and therefore the fuel handling accident remains bounding for gate movement. Existing applicability and Action Statement remain unchanged.
- 2. Revise Technical Specifications Surveillance Requirement 4.9.7 to read as noted below in 4.9.7.1 and add new Surveillance Requirement 4.9.7.2:
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' 4.9.7.11.oads other than the spent fuel pit gates shall be verified to be less than [
2500 pounds prior to movement over irradiated fuel assemblies in the spent fuel pit. !
4.9.7.2 For movement of any of the spent fuel pit gr.tes:
- a. gate lift height and slack free redundant rigging shall be verified prior to moving over irradiated fuel
- h. load oaths shall he verified not to have irradiated fuel with Rod Control Cluster Assemblics present in the gate load path
- c. the spent fuel cask handling area shall be verified to have no irradiated fuel present prior to moving a gate over the area.
- 3. The existing liases section for 3/4.9.7 will be changed to add new paragraph and to read as follaws:
3/4.9.7 CRANIIlitAVEL - SPLINT FUEL MI ,
The restriction on movements of the spent fuel pit gates over irrad8ated fuel ensure that redundant rigging will be used in order to prevent a gate drop caused by hoist failure. As shown by calculation, in the event the 'nad is dropped (1) the spent fuel storage racks limit -
gate penetration rnd prevent the impact load from being applied to stored fuel, (2) fuel spacing will not he changed, and (3) impact loading to the spent fuel pit structure is acceptahic.
The restrictisn on movement of other loads ;n excess of the nominal weight of a fuel and control rod assembly and associated handling tool over other fuel assemblies in the storage pool ensures that in the event this load is dropped. (1) the activity released will be limited to that contained in a single fuel assembly, and (2) any possible distortion of fuel in the storage racks will not result in a critical array. This assumption is also consistent with the activity release assumed in the accident analyses.
The first paragraph describes the design basis for carrying the spent fuel pit gates over irradiated fuel. The second paragraph is essentially retained from the existing basis with the clarification that it is applicable to loads "other" than the gates.
Saicty Slenificance l
Virginia Electric and Power Company has reviewed these proposed Technical Specifications changes and determined that the changes would not involve an unreviewed safety question.
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- 1. 'Ihe proposed changes would not increase the probability of occunence or the consequences of an accident or malfunction of equipment important to safety :
previously evaluated in the safety analysis report.
The accident in question is a fuel handling accident in the spent fuel pit. The safety analysis report does not postulate a drop of the spent fuel pit gate. The proposed ;
changes will reduce the probabil!ty of a fuel handling accident based on the fact that i only those assemblies containing rod control cluster assemblies will be subjected to '
such moves prior to rigging the gates. Previously, fuel assemblies were cleared as necessary to create a load path of empty storage cells. Each fuel assembly movement presents a finite risk for a fuel handling r.ccident. With the proposed Technical Specifications changes, the number of fuel assembly movements would be reduced. A calculation checked the adeqtney of all rigging components between the gate and the crane superstructure and found there is no credible single mode failure which could lead to a gate drop. Furthermore, even though the double rigging system makes a load drop due to a hoist failure an incredible event, a calculation was performed to determine the effects of a :iirect impact load on a single fuel storage cell or the SFP stnicture. The calculation concludes that there will be no adverse consegui ices to either irradiated fuel or the SFP structure with the established administrative controls in place.
- 2. The proposed changes would not create the possibility for an accident or malfunction of a difTerent type than any evaluated previously in the safety analysis report. This change revises the Technical Specifications to allow movement of the spent fuel pit gates over irradiated fuel. The proposed Technical Specifications and administrative controls will assure that the gates will not be dropped on the racks or pit floor.
Therefore, no new type of accident or malfunction will be created.
- 3. The proposed changes would not reduce the margin of safety as defined in the basis for any Technical Specifications. The existing basis section ensures ti. a , ostulated load drop over irradiated fuel in the spent fuel pit will not (1) exceed the radioactive release of a single fuel assembly which is consistent with the design basis and (2) that the storage rack geometry will not be deformed into a critical array. The proposed changes and administrative controls for the 1111 height, redundant rigging, and RCCA restrictions will prevent the degradation of the existing margin of safety. Therefore, no margin of safety as delined in the basis for any technical specification has been reduced, llased on the above evaluation, the proposed changes to the Technical Specifications will not rJversely afTect the safe operation of the plant. The changes were evaluated against the station licensing and design basis for preventing accidental criticality and radioactive ulcases in the spent fuel pit due to a fuel handling accident.
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