ML051960435

Proposed Technical Specification Changes Correction to Equation for Overtemperature T Function Allowable Value

ML051960435
Person / Time
Site:	North Anna
Issue date:	07/14/2005
From:	Hartz L Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
05-420
Download: ML051960435 (15)

Text

VIRGlNIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 July 14, 2005 U.S. Nuclear Regulatory Commission Serial No.05-420 Attention: Document Control Desk NL&OS/ETS RO Washington, D.C. 20555 Docket Nos. 50-338/339 License Nos. NPF-4/7 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 PROPOSED TECHNICAL SPECIFICATION CHANGES CORRECTION TO EQUATION FOR OTAT FUNCTION ALLOWABLE VALUE Pursuant to 10 CFR 50.90, Virginia Electric and Power Company (Dominion) requests amendments, in the form of changes to the Technical Specifications to Facility Operating Licenses Numbers NPF-4 and NPF-7 for North Anna Power Station Units 1 and 2, respectively. The proposed changes will correct two errors in the units of measure used to determine the Overtemperature AT Function Allowable Value. A discussion of the proposed Technical Specifications changes is provided in Attachment

1. The marked-up and proposed Technical Specifications pages are provided in Attachments 2 and 3, respectively.

We have evaluated the proposed Technical Specifications changes and have determined that they do not involve a significant hazards consideration as defined in 10 CFR 50.92. The basis for our determination that the changes do not involve a significant hazards consideration is included in Attachment 1. We have also determined that operation with the proposed changes will not result in any significant increase in the amount of effluents that may be released offsite and no significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed amendment is eligible for categorical exclusion as set forth in 10 CFR 51.22(~)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment is needed in connection with the approval of the proposed changes. The basis for our determination that the changes do not involve any significant increase in effluents or radiation exposure is also included in Attachment 1.

The proposed changes have been reviewed and approved by the Station Nuclear Safety and Operating Committee, as well as the Management Safety Review Committee. Approval of the proposed changes is requested by April 2006 with a 30-day implementation period.

Serial No.05-420 Docket Nos. 50-338/339 Page 2 of 4 If you have any questions or require additional information, please contact Mr. Thomas Shaub at (804) 273-2763.

Very truly yours, c, I Vice President - Nuclear Engineering Attachments Commitments made in this letter:

1. No regulatory commitments are made in this letter.

cc: U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303 Mr. J. E. Reasor, Jr.

Old Dominion Electric Cooperative lnnsbrook Corporate Center 4201 Dominion Blvd.

Suite 300 Glen Allen, Virginia 23060 Commissioner Bureau of Radiological Health 1500 East Main Street Suite 240 Richmond, VA 23218 Mr. J. T. Reece NRC Senior Resident Inspector North Anna Power Station

Serial No.05-420 Docket Nos. 50-338/339 Page 3 of 4 Mr. R. E. Martin NRC Lead Project Manager - North Anna and Surry U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. S. R. Monarque NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 8-H12 Rockville, MD 20852 Mr. J. Honcharik NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Rockville, MD 20852

Serial No.05-420 Docket Nos. 50-338/339 Page 4 of 4 COMMONWEALTH OF VIRGINIA )

)

COUNTY OF HENRICO 1 The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Leslie N. Hartz, who is Vice President - Nuclear Engineering, of Virginia Electric and Power Company. She has affirmed before me that she 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 her knowledge and belief. A Acknowledged before me this / # G a y of ) 2005.

My Commission Expires (SEAL)

Attachment 1 Serial No.05-420 Discussion of Changes North Anna Power Station Units 1 and 2 Virginia Electric and Power Company (Dominion)

Discussion of Changes Introduction Pursuant to 10 CFR 50.90, Virginia Electric and Power Company (Dominion) requests changes to Note 1: Overtemperature AT in Technical Specifications Table 3.3.1-1, Reactor Trip System Instrumentation. While preparing the Improved Technical Specification (ITS) compatible expanded cycle specific Core Operating Limits Reports (COLRs), two errors regarding units of measure were noted in Note 1 of Table 3.3.1-1 for the equation fl(A1) used to determine the Overtemperature AT function Allowable Value. The proposed changes will correct the unit in the equation for fi(A1) = 0% of RTP, whereby the unit designation % of RTP will be deleted since the fi(A1) function is dimensionless; and in the equation for fl(A1) = [*I {

[*I % - (qt - qb) }, whereby the percentage designation % will also be deleted. These proposed changes are consistent with the equations for fl(AI) specified in the original Technical Specifications, Core Operating Limit Report for Units 1 and Unit 2, and WCAP-12159.

Desigaicensing Bases The Overtemperature AT trip function is provided to ensure that the design limit DNBR is met and also limits the range over which the Overpower AT trip function must provide protection.

The inputs to the Overtemperature AT trip include pressurizer pressure, coolant temperature, axial power distribution, and reactor power as indicated by loop AT assuming full reactor coolant flow. The Overtemperature AT trip function is calculated for each loop as described in Note 1 of Technical Specifications Table 3.3.1-1. This function uses each loops AT as a measure of reactor power and is compared with a setpoint that is automatically varied with the following parameters:

Reactor coolant average temperature - the trip setpoint is varied to correct for changes in coolant density and specified heat capacity with changes in coolant temperature; Pressurizer pressure - the trip setpoint is varied to correct for changes in system pressure; and Axial power distribution - fl(A1) -the trip setpoint is varied to account for imbalances in the axial power distribution as detected by the NIS upper and lower power range detectors. If axial peaks are greater than the design limit, as indicated by the difference between the upper and lower NIS power range detectors, the trip setpoint is reduced in accordance with Note 1 of Technical Specifications Table 3.3.1-1.

Discussion While preparing the ITS compatible expanded Core Operating Limits Reports for the North Anna operating cycles NlC16 and N2C15, two errors in the equation fl(A1) used to determine the Overtemperature AT function Allowable Value were identified. These are: (1) the % sign 1

should be deleted within the first equation for fl(A1) in Note 1 of Table 3.3.1-1 and (2) the unit designation of % of RTP should be deleted in the second equation for fl(A1). The first error does not occur in the Standard Technical Specifications (NUREG-1431), while the second error relating to the unit designation has been carried over from the Standard Technical Specifications.

The following discussion supports the proposed changes and provides clarification:

Dimensions of f 1m The Overtemperature AT trip function is calculated for each loop as described in Note 1 of Table 3.3.1-1. In the Overtemperature AT setpoint equation, fl(A1) is a dimensionless quantity since the expression within the braces has zero dimension. fl(A1) can be expressed as follows, using a general notation :

In the above expressions, C1 and C2 define the three ranges of AI. Graphically, A and B represent slopes of f1 as a function of AI. The terms qt and qb are % RTP in the upper and lower halves of the core, respectively.

The numerical values of the four constants, A, B, C1 and C2, have been moved to the cycle-specific Core Operating Limits Report (COLR). It should be noted that C1, C2 and A1 are in units of normalized power [% RTP], while A and B are in corresponding inverse units of [/ % RTP] or

[% RTPI-. Thus fI(A1) is a dimensionless number.

For North Anna, the numerical values of the four constants are:

A = 0.0165 [% RTP1-l B = 0.0198 [% RTPI-C1 = -35%RTP C2 = +3 % RTP Substituting the numerical values in the expressions for fi(AI), we get (1) fl(A1) =0.0165{-35 -(qt-qb)} when (qt - qb) c -35 % RTP (2) =O when -35 % RTP 5 (qt - qb)< +3 % RTP (3) = 0.0198 {( qt - qb)-3} when (qt - qb) > +3 % RTP Equation (2) applies in the middle range, where the fl(A1) penalty is zero. Away from the middle range on both sides, fl(A1) is non-zero and positive.

2

The errors corrected in the above expressions are:

1. The middle expression, f1 = 0, has no units, since fl(A1) is dimensionless.

2. There should be no % sign next to -35 within the braces in the first expression.

It is understood from the context that when numerical values with the proper units and algebraic signs are substituted in the equations, fi(A1) comes out to be a dimensionless number.

History of the fl(A1)Equation Change Traveler WOG-ED-29 documents previous attempts at corrections to the f l (AI) equation concerning (i) overlapping end points in defining ranges of the axial flux difference, and (ii) confusion as to the magnitude and sign of the rate coefficients A and B. The proposed changes refer to the current equation presented in the North Anna Technical Specifications.

The rate coefficients A and B are given in the original Technical Specifications as a percentage per % RTP, representing a fractional change (in the AT setpoint) for each % RTP that A1 is away from the end points of the middle region. In one version (NUREG-1431 Rev 1, WOG STS dated 4/7/95), the coefficients appear as 100 times their true value and are corrected in the Change Traveler. Probably, at that time fi(A1) was expressed as a %, not a fraction; thus, the coefficients were input as percentages.

In the 1977 Westinghouse version of the OTAT equation specified in WCAP-8746, the fl(A1) function had the dimension of temperature, and the K constants were in special units such as %

of full power AT/OF. These units were confusing and may have contributed to the present situation wherein some subtle errors were left behind in the equations.

In later documents such as WCAP-14483-A, the equation was normalized so that the effect of changes from nominal conditions could be expressed in terms of dimensionless quantities - a development conductive to a better understanding of the physical phenomenon. It is the latter formulation that is adopted by the North Anna Improved Technical Specifications.

Precedentloperating Experience In the initial response to resolve these errors, the WOG ITS Working Group agreed to revise NUREG-143 1 to eliminate the errors from the Improved Standard Technical Specifications.

WOG had agreed to make these changes as part of Rev 3 to NUREG-1431 as part of their efforts to correct editorial errors in the NUREG. The proposed changes were made part of a TSTF Standard Technical Specification Proposed Change presented at the 2002 December WOG meeting whereby changes were considered editorial and were to be incorporated into Rev 3 of NUREG-1431. However, based upon the 2004 status report obtained from Excel Services, Inc.,

the NRC did not consider the changes as editorial, and indicated that a plant specific change request package would be required. These proposed changes represent the plant specific changes for the North Anna Technical Specifications.

3

Proposed Changes The proposed changes will correct the Note 1 equation within Table 3.3.1-1: for fi(A1) = 0% of RTP, the unit designation "% of RTP" will be deleted since the fl(A1) function is dimensionless; and for fi(A1) = [*I { [*I % - (qt - qb) }, "%" will also be deleted.

Table 3.3.1-1 Note 1: Overtemperature AT Delete "%" in first equation for fl(A1)

From:

fi(A1) = [*I [*I% - (qt - qb)) when (qt - qb) < [*I% RTP when (qt - qb) < [*I% RTP Delete "% of RTP' in second equation for fi(A1)

From:

fi(A1) = 0% of RTP when [*I% RTP _< (qt - qb) 5 [*I% RTP To:

fi(A1) = 0 when [*I% RTP 5 (qt - qb)< [*I% RTP Safety Considerations The proposed changes do not have any impact on equipment operability. The errors only relate to the unit designations for the fi(A1) equation that were incorrectly assigned. These errors do not affect the value of the variable, or the way in which the plant or equipment is operated.

Significant Hazards Consideration Determination Dominion has reviewed the requirements of 10 CFR 50.92 as they relate to the proposed changes and determined that a significant hazards consideration is not involved. The proposed changes correct two errors in the unit designations in the fi(A1) equation used to determine the Overtemperature AT function allowable value as specified in Note 1 of Technical Specifications Table 3.3.1-1. The errors are in the units in the equations. For fi(A1) = 0% of RTP the unit designation "% of RTP" will be deleted since the fi(A1) function is dimensionless; and for fl(A1)

= [*I { [*I % - (qt - qb) }, the "%" will also be deleted. The following is provided to support the conclusion that the proposed changes do not involve a significant hazards consideration.

1. Do changes involve a significant increase in the probability or consequences of an accident previously evaluated?

4

The proposed changes do not significantly increase the probability or consequences of an accident previously evaluated in the UFSAR. The proposed changes correct errors in the unit designations used in the fl(A1) equation. The actual numerical values of fi(A1) calculated by the equation remain the same, only the units applied to the value are changed. The Overtemperature AT function allowable values are utilized by the Reactor Trip System (RTS) instrumentation to prevent reactor operation in conditions outside the range considered for accident analyses. The proposed changes will not alter the allowable values used by the RTS instrumentation. The Overtemperature AT allowable value is not an initiator to any accident previously evaluated. As a result, the probability of any accident previously evaluated is not significantly increased. As the Overtemperature AT allowable value is not changed, the probability or consequences of an accident previously evaluated is not significantly increased.

2. Do changes create the possibility of a new or different kind of accident from any accident previously evaluated?

The proposed changes do not create the possibility of a new or different lund of accident from any accident already evaluated in the UFSAR. The proposed changes correct errors in the unit designations used in the fl(A1) equation. Changes do not introduce a new mode of plant operation and do not involve any physical modifications to the plant. The changes will not introduce new accident initiators. Therefore, the proposed changes do not create the possibility of a new or different kind of accident from any accident previously analyzed.

3. Do changes involve a significant reduction in the margin of safety?

The proposed changes do not involve a significant reduction in a margin of safety. The proposed changes correct errors in the unit designations used in the fl(A1) equation. This will eliminate the possibility of an error resulting from incorrect interpretation of the equation and potential subsequent errors in the application of the equation. The allowable value of the Overtemperature AT function is unaffected. Therefore, the proposed changes will not significantly reduce the margin of safety as defined in the Technical Specifications.

Based upon the above, Dominion concludes that the proposed changes involve no significant hazards consideration under the standards set forth in 10 CFR 50.92(c).

Environmental Review 10 CFR 51.22(~)(9)provides criteria for the identification of licensing and regulatory actions eligible for categorical exclusion for performing an environmental assessment. A proposed amendment to an operating license for a facility does not require an environmental assessment if operation of the facility in accordance with the proposed Amendment would not (1) involve a significant hazards consideration, (2) result in a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, and (3) result in a significant increase in individual or cumulative occupation radiation exposure.

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By reviewing the proposed changes it has been determined that they meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(~)(9). Therefore, pursuant to 10 CFR 5 1.22(b), no environmental impact statement or environmental assessment is required to be prepared in connection with the issuance of the proposed license amendment. The basis for this determination is as follows:

1. The proposed amendment involves no significant hazards consideration.

As described in the significant hazards consideration evaluation, the proposed changes do not involve a significant hazards consideration.

2. There is no significant change in the type or significant increase in the amounts of any effluents that may be released offsite.

The proposed changes do not involve the installation of any new equipment, or the modification of any equipment that may affect the types or amounts of effluents that may be released offsite. Therefore, there is no significant change in the types or significant increase in the amounts of any effluents that may be released offsite.

3. There is no significant increase in individual or cumulative occupation radiation exposure.

The proposed changes do not involve plant physical changes, or introduce any new mode of operation. Therefore, there is no significant increase in individual or cumulative occupational radiation exposure.

References The following references support the proposed Technical Specification changes and the evaluation of these changes.

1. NUREG-143 1, Rev 1, Standard Technical Specifications Westinghouse Plants, April 1995; Improved Technical Specification 3.3.1, Reactor Trip System (RTS) Instrumentation, with supporting Bases

2. Original North Anna Technical Specifications 3.3.1, Reactor Trip System (RTS)

Instrumentation 6

Attachment 2 Serial No.05-420 Mark-up of Unit 1 and Unit 2 Technical Specifications Changes North Anna Power Station Units 1 and 2 Virginia Electric and Power Company (Dominion)

RTS Instrumentation 3.3.1 Table 3.3.1-1 (page 4 of 5)

Reactor Trip System Instrumentation Note 1: Overtemperature AT The Overtemperature AT function Allowable Value shall not exceed the following nominal trip setpoint by more than 2.0% of AT span.

Where: AT is measured RCS AT, OF.

ATo is the indicated AT at RTP, OF.

s i s the Laplace transform operator, sec-l.

T i s the measured RCS average temperature, OF.

T ' is the nominal Tavg at RTP, I [*]OF.

P i s the measured pressurizer pressure, psig P ' i s the nominal RCS operating pressure, L [*I psig Where qt and qb are percent RTP i n the upper and lower halves o f the core, respectively, and qt + qb is the total THERMAL POWER in percent RTP.

The values denoted w i t h [*] are specified in the COLR.

North Anna Units 1 and 2 3.3.1-16 Amendments 231/212

Attachment 3 Serial No.05-420 Proposed Unit 1 and Unit 2 Technical Specifications Changes North Anna Power Station Units 1 and 2 Virginia Electric and Power Company (Do minion)

RTS I nstrumentation 3.3.1 Table 3 . 3 . 1 - 1 (page 4 o f 5)

Reactor Trip System Instrumentation Note 1: Overtemperature AT The Overtemperature AT Function Allowable Value shall not exceed the following nominal trip setpoint by more than 2.0% o f A T span.

Where: AT i s measured RCS AT, OF.

A T o is the indicated AT at RTP, "F.

s i s the Laplace transform operator, sec-'.

T i s the measured RCS average temperature, "F.

T' i s the nominal Tavg at RTP, I [*]OF.

P is the measured pressurizer pressure, psig P' i s the nominal RCS operating pressure, 2 [*] psig z1 1 [*] sec z2 5 [*I sec Where qt and qb are percent RTP in the upper and lower halves o f the core, respectively, and qt + q b i s the t o t a l THERMAL POWER in percent RTP.

The values denoted with [*] are specified in the COLR.

North Anna U n i t s 1 and 2 3.3.1-16