ML070380169

Response to Request for Additional Information, License Amendment Request to Delete Reference to Banked Position Withdrawal Sequence (BPWS)

ML070380169
Person / Time
Site:	Peach Bottom
Issue date:	02/05/2007
From:	Cowan P Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML070380169 (17)

Text

Exelon Nuclear 200 Exelon Way www.exeloncorp.com Nucl ear Kennett Square, PA 19348 10 CFR 50.90 February 5,2007 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Peach Bottom Atomic Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-44 and DPR-56 NRC Docket Nos. 50-277 and 50-278

Subject:

Response to Request for Additional Information License Amendment Request to Delete Reference to Banked Position Withdrawal Sequence (BPWS)

Reference:

Letter from P. B. Cowan (Exelon Generation Company, LLC) to U. S.

Nuclear Regulatory Commission, dated June 8, 2006 In the referenced letter, Exelon Generation Company, LLC (Exelon) requested an amendment to Appendix A, Technical Specifications, of the Renewed Facility Operating Licenses DPR-44 and DPR-56. The proposed change modifies Technical Specifications (TS) 3.1.3, Control Rod OPERABILTY; TS 3.1.6, Rod Pattern Control; TS 3.3.2.1, Control Rod Block Instrumentation; TS 3.10.7, Control Rod Testing -

Operating, and; TS 3.10.8, SHUTDOWN MARGIN (SDM) Test - Refueling. The proposed change would replace the current references to Banked Position Withdrawal Sequence (BPWS) with references to the analyzed rod position sequence. is our response to a request for additional information as discussed in a conference call with the U. S. Nuclear Regulatory Commission staff on December 18, 2006. Enclosure 2 contains updated PBAPS, Units 2 and 3 Bases pages associated with this License Amendment Request that reflect re-insertion of a reference to NEDO-21231, Banked Position Withdrawal Sequence, January 1977, as requested by Question 5.

Response to RAI re LAR to Delete Reference to Banked Position Withdrawal Sequence (BPWS)

February 5,2007 Page 2 No new regulatory commitments are established by this submittal.

If any additional information is needed, please contact Tom Loomis at (610) 765-5510.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 5thof February 2007.

Respectfully, Pamela B. Cowan Director, Licensing & Regulatory Affairs Exelon Generation Company, LLC

Enclosures:

I) Response to Request for Additional Information - License Amendment Request to Delete Reference to Banked Position Withdrawal Sequence (BPWS)

2) Revised Bases Pages to Reflect Re-Insertion of Reference to NEDO-21231 cc: S. J. Collins, Administrator, USNRC Region I J. Shea, Project Manager, USNRC F. Bowers, USNRC Senior Resident Inspector, PBAPS

ENCLOSURE 1 Response to Request for Additional Information License Amendment Request to Delete Reference to Banked Position Withdrawal Sequence (BPWS)

Response to Request for Additional Information License Amendment Request to Delete Reference to BPWS Question 1:

Some plants, which exclusively rely upon the RWM for enforcement of the control rod sequence, perform several Technical Specifications surveillance requirements to verify that the RWM is functionally operable prior to startup. For instance, these tests include: 1) Performance of the Rod Worth Minimizer diagnostic test; 2) Selection of out of sequence control rods in each distinct RWM group to verify that the selection error annunciator alarms; and 3) Withdrawal of an out-of-sequence control rod no more than three notches to verify the rod block function.

Presently, PBAPS Technical Specifications SR 3.3.2.1.2 requires a channel functional test of the RWM to be performed, within one hour after startup, by only attempting to withdraw a control rod not in compliance with the prescribed sequence and verifying a control rod block occurs. This test may be insufficient in that it is performed after startup and it does not test the RWM overall system functional operability whereas some function of the system could be in a degraded state and the system still perform the single rod block function. Also, the RWM is single channel and, with the removal of the BPWS, makes the TS requirements less restrictive.

Therefore, additional requirements should be included in the LAR to provide additional safety.

Provide justification of not including the above tests in LAR.

Response

The subject License Amendment Request (LAR) proposes that, in lieu of exclusive use of BPWS, cycle specific analyses may also be performed to develop startup/shutdown control rod sequences. These sequences will minimize incremental control rod reactivity worth and will be developed in accordance with the General Electric Standard Application for Reactor Fuel, NEDE-24011-P-A-15 (GESTAR-II), and U. S. Supplement, NEDE-24011-P-A-WUS, September 2005, which incorporates NRC-approved methodology, and will be reviewed and approved in accordance with the 10 CFR 50.59 process. New analyzed sequences will not adversely impact the results of the rod drop accident as described in the UFSAR. This change will allow the implementation of startup/shutdown sequences in addition to those allowed by the general requirements of the BPWS and will result in an overall reduction in unnecessary reactivity manipulations and associated operational challenges. The margin to safety will not be reduced by this change. The existing Rod Worth Minimizer (RWM) design, operating procedures and surveillances will not be affected by the proposed change.

This change does not impact TS SR 3.3.2.1.2. Surveillance Test ST-0-62A-210-2(3) is performed to meet the TS requirement that an out-of-sequence rod withdrawal will result in the proper RWM alarm and block functions. As discussed in the current SR 3.3.2.1.2, the TS permit 60 minutes for performing the described testing. The proposed TS change does not alter this basis. Safety will not be reduced as a result of this change. Changes outside those described in the Improved Technical Specifications are not necessary.

Page 1 of 3

Response to Request for Additional Information License Amendment Request to Delete Reference to BPWS Question 2:

The control rod sequence is based upon the control rod drop accident (CRDA) results utilizing plantkycle specific data. Since this analysis is fuel and reactivity related, which could result in fuel damage from an incorrect rod sequence error, sufficient controls should be in place to assure that cycle-specific rod sequence results are maintained and accessible for implementation and review. Since the RWM will be the only system to detect a rod sequence error, please provide justification on why the cycle-specific results of the rod sequence is not included in the COLR.

Response

TS 5.6.5 defines the contents of the COLR. The Core Operating Limits Report contains cycle-specific fuel thermal operating limits and cycle specific rod block setpoints. Rod Sequence patterns do not fall within the category of information currently specified by Technical Specifications for incorporation into the COLR. The Exelon Nuclear engineering change process utilized at Peach Bottom Atomic Power Station is used to control the development, approval and documentation of analyzed control rod sequences. This is consistent with existing process controls used in the development of BPWS compliant sequences. All sequences will continue to be documented in an Engineering Design Analysis and issued as a calculation in an Engineering Change Request (ECR) package. Placing the sequences in the COLR provides no advantage over the existing Exelon Nuclear engineering change process. Existing administrative controls will continue to provide a back-up methodology to the Rod Worth Minimizer in assuring compliance with analyzed sequences.

Question 3:

Since the RWM will be the sole monitoring system, review of administrative controls of relevant procedures, related forms and quality control should be conducted to assure the RWM process is effectively controlled. Provide a discussion of the present RW M administrative controls and any anticipated changes to the administrative controls as a result of this LAR.

Response

No changes to administrative controls associated with the RWM are occurring as a result of this change. The Exelon Nuclear engineering change process utilized at Peach Bottom Atomic Power Station continues to be used to control the development, approval and documentation of analyzed control rod sequences. The sequences will be documented in an Engineering Design Analysis and issued as a calculation in an Engineering Change Request (ECR) package. Rod Worth Minimizer enforcement of startup/shutdown sequences will remain unchanged.

The subject LAR proposes that, in lieu of exclusive use of BPWS, cycle specific analyses may also be performed to develop startup/shutdown control rod sequences. These sequences will minimize incremental control rod reactivity worth in a manner consistent with BPWS, and will be developed in accordance with the General Electric Standard Application for Reactor Fuel, NEDE-24011-P-A-I 5 (GESTAR-II), and U. S. Supplement, NEDE-24011-P-A-I 5-US, September, 2005, which incorporates NRC-approved methodology, and will be reviewed and Page 2 of 3

Response to Request for Additional Information License Amendment Request to Delete Reference to BPWS approved in accordance with the 10 CFR 50.59 process. New analyzed sequences will not adversely impact the results of the rod drop accident as described in the UFSAR. This change will allow the implementation of startupkhutdown sequences in addition to those allowed by the general requirements of the BPWS and will result in an overall reduction in unnecessary reactivity manipulations and associated operational challenges.

Question 4:

The LAR TS submittal replaces the term "Banked Position Withdrawal Sequence (BPWS)" with the term "analyzed rod position sequence" to reflect cycle-specific control rod sequence based on plant specific information. There is insufficient Bases discussion regarding the use of the term "analyzed rod position sequence." Provide a discussion on how this term is determined.

Response

The term analyzed rod position sequence is intended to indicate that the sequence, regardless of the use of BPWS, will meet the same CRDA technical requirements as BPWS, will be developed using the same NRC approved methods as those used to develop BPWS, and will be implemented in a manner equivalent to those used in the implementation of BPWS compliant sequences. No Bases change is necessary.

Question 5:

In the TS Bases Section A.l, A.2, A.3, and A.4, reference 5 was removed from the last sentence which stated Even with the postulated additional single failure of an adjacent control I'

rod to insert, sufficient reactivity control remains to reach and maintain MODE 3 conditions (Ref. 5)." It seems that the reference referred to an analysis that demonstrated sufficient reactivity control. Provide a discussion why a new reference or explanation in the bases to support this statement is not needed.

Response

The reference to the 1977 BPWS analysis will be re-included into the Bases. Enclosure 2 contains updated PBAPS, Units 2 and 3 Bases pages associated with this License Amendment Request that reflect re-insertion of a reference to NEDO-21231, "Banked Position Withdrawal Sequence," January 1977.

Page 3 of 3

ENCLOSURE 2 Revised Bases Pages to Reflect Re-Insertion of Reference to NEDO-21231 Unit 2 Unit 3 B 3.1-17 B 3.1-17 B 3.1-18 B 3.1-18 B 3.1-21 B 3.1-21 B 3.1-35 B 3.1-35 B 3.1-38 (change deleted as shown) B 3.1-38 (change deleted as shown)

Control Rod OPERABILITY B 3.1.3 BASES ACTIONS 1. A.2. A .3. and A.4 (continued) stuck position and the highest worth OPERABLE control rod assumed to be fully withdrawn.

The allowed Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to verify SDM is adequate, considering that with a single control rod stuck in a withdrawn position, the remaining OPERABLE control rods are capable of providing the required scram and shutdown reactivity. Failure to reach MODE 4 is only likely if an additional control rod adjacent to the stuck control rod also fails to insert during a required scram. Even with the postulated additional single failure of an adjacent control rod to insert, sufficient reactivity control remains to reach and maintain MODE 3 conditions (Ref. 5).

L l With two or more withdrawn control rods stuck, the plant must be brought to MODE 3 within 12hours. The occurrence of more than one control rod stuck at a withdrawn position increases the probability that the reactor cannot be shut down if required. Insertion of all insertable control rods eliminates the possibility o f an additional failure o f a control rod to insert. The allowed Completion Time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> i s reasonable, based on operating experience, to reach W E 3 from full power conditions in an orderly manner and without challenging plant systems.

C.l and C.2 With one or more control rods inoperable for reasons other than being stuck in the withdrawn position, (including a control rod which is stuck in the fully inserted position) operation may continue, provided the control rods are fully inserted within 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and disarmed (electrically or hydraulically) within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Inserting a control rod ensures the shutdown and scram capabilities are not adversely affected. The control rod is disarmed to prevent inadvertent withdrawal during subsequent operat ions. The control rods can be hydraulically disarmed by closing the drive water and exhaust water isolation valves. The control rods can be electrically disarmed by disconnecting power from all four directional control valve solenoids. Required Action C.1 is modified by a Note, which allows the RWM to be bypassed if required to allow insertion of the inoperable (continued)

PBAPS UNIT 2 B 3.1-17 Revision No. 2

Control Rod OPERABILITY B 3.1.3 BASES ACTIONS C,1 and C . z (continued)

..

control rods and cont inued operat ion. LCO 3 3 2.1 provides additional requirements when the RWM i s bypassed t o ensure compliance with the CRDA analysis.

The allowed Completion Times are reasonable, considering the small number o f allowed inoperable control rods, and provide t i m e t o i n s e r t and disarm the control rods i n an orderly manner and without challenging plant systems.

l2Luuud Out o f sequence control the p o t e n t i a l tions, including the r e inoperable control rods d not separated by a t action must be taken t o restore the control rods t o s modified by a Note s not applicable when not required t o be followed scribed i n the Bases f o r LCO 3.1.6. The allowed Completion Time o f 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> i s acceptable, considering the low p r o b a b i l i t y o f a CRDA occurring ,

I f any Required Action and associated Completion Time o f Condition A, C, o r 0 are not met, o r there are nine o r more inoperable control rods, the p l a n t must be brought t o a MODE i n which the LCO does not apply. To achieve t h i s status, the plant must be brought t o MODE 3 w i t h i n 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. This ensures a l l insertable control rods are inserted and places the reactor i n a condition t h a t does not require t h e active function ( L e o , scram) o f the control rods. The number o f control rods permitted t o be inoperable when operating above 10%RTP (e.g., no CRDA considerations) could be more than the value specified, but the occurrence o f a l a r g e number o f (continued1 PBAPS UNIT 2 8 3.1-18 Revision No. 2

Control Rod OPERABILITY B 3.1.3 BASES SURVEILLANCE SR 3.1.3.5 (continued)

REQUIREMENTS t o the " f u l l out" position during the performance o f SR 3~1.3.2. This Frequency i s acceptable, considering the low p r o b a b i l i t y t h a t a control rod w i l l becom uncoupled when i t i s not being mved and operating expertence related t o uncoupl i n g events.

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REFERENCES 1. UFSAR, Sections 1.5.1.1 and 1.5.2.2.

2. UFSAR, Section 14.6.2.

3. UFSAR, Appendix K,Section V I .

4. UFSAR, Chapter 14.

5. NEW-21231, "Banked Position Withdrawal Seauence.

Section 7.2, January 1977.

A PBAPS UNIT 2 Revision No. 0

Rod Pattern Control BASES APPLICABLE SAFETY ANALYSES (cont i nued) 9

• c rods are required to-be moved i n arouDsFwith a l l control rods assigned t o a specifi I

s e f ed banked positions he banked posit imm incremental control rod worth without bein 1ant operat i on. dS*/

demonstrated that not be violated during a e o f operation, The so evaluates the effect o f 1 rods not i n compliance ited number (i.e., efght)

Onoperable control rods.

Rod pattern control satisftes Criterion 3 o f the NRC Policy

- A r.rrr.+

control rods i n the APPL ICAB I L ITY In MODES 1 and 2, when THERMAL POUER is s 10% RTP, the CRDA is a Design Basis Accident and, therefore, compliance w i t h the assumptions o f the safety analysis i s required. When THERMAL POWER i s > 10% RTP, there i s no credible control rod configuration t h a t results i n a control rod worth t h a t could exceed the 280 cal/gm fuel damage l i m i t during a CRDA (Ref. 2). In MODES 3, 4, and 5, since the reactor is shut down and only a single control rod can be withdrawn from a core cell containing fuel assemblies, adequate SDM ensures t h a t the consequences o f a CRDA are acceptable, since the reactor will remain subcritical wlth a single control rod withdrawn.

(continued)

PBAPS UNIT z B 3.1-35 Revision No. 0

Rod Pattern Control B 3-1.6 BASES REFERENCES 60 NEW-21778-A, "Transient Pressure Rises Affected (cont inoed) Fracture Toughness Requi rements for Boi 1ing Water Reactors, " December 1978.,

7. ASME, Boiler and Pressure Vessel Code.

8. NU#)-21231, "Banked Position Withdrawal Sequence, "

January 1977.

r PBAPS UNIT 2 B 3.1-38 Revision No. 0

Control Rod OPERABILITY 6 3.183 BASES ACTIONS A e l m A.21. A .3. and A . 4 (continued) stuck position and the highest worth OPERABLE control rod assumed to be ful l y withdrawn .

The allowed Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to verify SDM is adequate, considering that with a single control rod stuck in a withdrawn position, the remaining OPERABLE control rods are capable of providing the required scram and shutdown reactivity. Failure to reach MODE 4 i s only likely if an additional control rod adjacent to the stuck control rod also fails to insert during a required scram. Even with the postulated additional single failure of an adjacent control rod to insert, sufficient reactivity control remains to reach and maintain MODE 3 conditions (Ref. 8

>)

aa With two or more withdrawn control rods stuck,. the plant must be brought to MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The occurrence of more than one control rod stuck at .a withdrawn position increases the probability that the reactor cannot be shut down if required. Insertion o f all insertable control rods eliminates the possibility of an additional failure o f a control rod to insert. The allowed Completion Time o f 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is reasonable, based on operating experience, to reach MODE 3 from full power conditions in an orderly manner and without chall enging pl ant systems .

C . 1 and C.2 With one or more control rods inoperable for reasons other than being stuck in the withdrawn position (including a control rod which is stuck in the fully inserted position) operation may continue, provided the control rods are fully inserted within 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and disarmed (electrically or hydraulically) within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Inserting a control rod ensures the shutdown and scram capabilities are not adversely affected. The control rod is disa.rmed to prevent inadvertent withdrawal during subsequent operations. The control rods can be hydraulically disarmed by closing the drive water and exhaust water isolation valves. The control rods can be electrically disarmed by disconnecting power from all four directional control valve solenoids. Required Action C m I is modified by a Note, which allows the RWM to be bypassed if required to allow insertion o f the inoperable PBAPS UNIT 3 8 3.1-17 Revision No. 2

Control Rod OPERABILITY B 3.1.3 BASES ACTIONS C.1 and C . 2 (continued) control rods and continued operation. LCO 3.3.2.1 provides additional requirements when the RWM i s bypassed t o ensure compliance with the CRDA analysis. The allowed Completion Times are reasonable, considering the small number o f allowed inoperable control rods, and provide time t o i n s e r t and disarm the control rods i n an o r d e r l y manner and without challenging p l a n t systems.

0.1 and 0.2 CZI i s modified by a Note i n d i c a t i n g t h a t the Condition i s not applicable when

> 10% R l P , since t h # m s not required t o be followed under these conditions, as described i n t h e Bases f o r K O 3.1.6. The allowed Completion Time o f 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> i s acceptable, considering the low p r o b a b i l i t y o f a CRDA occurring I f any Required Action and associated Completion l i m e o f Condition A, C, o r D are not met, or there are n i n e or more inoperable control rods, the p l a n t must be brought t o a MODE i n which the LCO does not apply. To achieve t h i s status, the plant must be brought t o MODE 3 w i t h i n 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. This ensures a l l insertable control rods are inserted and places the reactor i n a condition t h a t does not require the active function (i.e., scram) o f the control rods. The number o f control rods permitted t o be inoperable when operating above 10% RTP (e.g., no CROA considerations) could be more than the value specified, but the occurrence o f a l a r g e number o f (Continued)

PBAPS UNIT 3 8 3.1-18 Revision No. 2

Control Rod OPERABILITY B 3.3-3 BASES SURVEILLANCE SR 3.1.3.5 (continued)

REQUIREMENTS t o the "full out" position during the performance o f SR 3 o I m 3 o 2 . This Frequency i s acceptable, considering the low probability that a control rod w i l l become uncoupled when i t i s not being moved and operating experience related t o uncoupf ing events.

REFERENCES 1, UFSAR, Sections 3.5,lml and 1.5.2o2m

2. UFSAR, Section 14.6.2, 3, UFSAR, Appendix K,Section V I .

4, UFSAR, Chapter 14.

5, NEDO-21231, "Banked Position Withdrawal Sequence, Section 7.2, January 1977,

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..

PBAPS UNIT 3 8 3.1-21 Revision No. 0

Rod P a t t e r n Control (i BASES equired t o be ~IK) ned t o a s p e c i f i banked positions Rod pattern control s a t i s f i e s C r i t e r i o n 3 o f t h e NRC Policy Statement.

LCO Compl iance w i t h the prescribed control r o d sequences minimizes the potential conseque the i n i t i a l conditions t o those This LCO only applies t o OPERABL inoperable control rods requtred requirements are specified i n LC OPERABILITY," cons control rods i n t h APPLICABILITY I n MODES 1 and 2, when THERMAL POWER i s s 10% RTP, t h e CRDA i s a Design Basis Accident and, therefore, compliance w i t h the assumptions o f the safety analysis t s required. When THERMAL POWER i s > 10%RTP, there i s no c r e d i b l e control rod configuration t h a t r e s u l t s i n a control rod worth that could exceed the 280 cal/gm f u e l damage l i m i t during a CRDA (Ref. 2). I n MODES 3, 4, and 5, since t h e reactor i s shut down and only a single control rod can be withdrawn from a core c e l l containing f u e l assembligs, adequate SDM ensures t h a t the consequences o f a CROA are acceptable, since the reactor w i l l remain s u b c r i t i c a l with a s i n g l e control rod withdrawn.

(continued)

PBAPS UNIT 3 B 3.1-35 Revision No. 0

Rod Pattern Control 6 3.1.6 BASES REFERENCES 6. NEDO-21778-A, "Transient Pressure Rises Affected (cont inued) Fracture Toughness Requirements f o r B o i l ing Water Reactors, " December 1978.

7. ASME, Boiler and Pressure Vessel Code.

80 NEW-21231, "Banked Position Withdrawal Sequence,"

January 1977.

I PBAPS UNIT 3 B 3.1-38 Revision No. 0