ML20086J020
| ML20086J020 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 12/05/1991 |
| From: | Tuckman M DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9112100249 | |
| Download: ML20086J020 (9) | |
Text
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DUKE POWER December-5, 1991 U.
S.
Nuclear Regulatory Commission Attn:
Document Control Desk Washington, D.C.
20555
Subject:
Catawba Nuclear Station Docket Nos. 50-413 and 50-414 Supplement to Technical Specification Amendment Table 2.2-1 I
i Please find attached additional information regarding the subject amendment request which was originally submitted in a letter dated November 20, 1991.
The original Technical Justification has been marked up, and the additional information provided as an insert.
This information is Attachment I of this submittal.
Attachment II contains additional justification for the exigency of this amendment.
This additional information is in regards to the work done by Westinghouse between October 24, 1991 and the time Duke Power received the proposed changes to the Technical Specifications from Westinghouse.
Duke Power believes that this amendment meets the requirements to be processed on an exigent basis, according to 10 CFR 50.91(a) (6).
Catawba Unit 2 is currently scheduled to start up i
from refueling on December 14, 1991 and this amendment is needed at that time.
Very truly yours, R, S, ke M.
S. Tuckman, Vice President
~
Catawba Nuclear Generation Department 9112100249 91120" PDR ADOCK 05000413 l
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U.
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Nuclear Regulatory Commission December 5, 1991
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Page 2-xc:
Mr.
S.
D.-Ebneter Regional Administrator, Region II U.-S.
Nuclear Regulatory Commission 101 Marietta Street, NW, Suite 2900 Atlanta, GA-30323 Mr. Heyward Shealy, Chief Bureau of Radiological Health South Carolina Department of Health &
Environmental Control 2600 Bull-Street Columbia,'SC 29201 f
American_ Nuclear Insurers c/o Dottie Sherman,-ANI Library The Exchange, Suite 245 270 Farmington Avenue Farmington, CT 06032 M & M Nuclear.onsultants Suite 1500 1100 Circle 75-Parkway Atlanta, GA 30339 Mr. W.
T.
Orders NRC Resident Inspector Catawba Nuclear Station Mr. R.
E.
Martin
' Office of Nuclear Regulation U.
S.
Nuclear' Regulatory Commission one White' Flint: North, Mail-Stop 14H25 Washington, D.C.
20555
U.-S.
Nuclear.-Regulatory Commission December 5, 1991 Page 3 bxc: R.
C.
Futrell R.
L. Gill
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P. Harrall G.
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Swindlehurst M.
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Proposed Revision to Technical Specification Table 2.2-1 This proposed Technical' specification r2 vision changes the slope value for the positive wing of the axial offset band, which was determined to be potentially nonconservative for Catawba Unit 2, such that it will conservatively provide the necessary margin to DNB.
In addition, the unit specific values for Total Allowance, Z, S and Allowable Value are added since a new, more restrictive, Allowable Value was calculated for Unit 2.
Technical Justification The overtemperature AT (OTAT) reactor trip is designed to protect the reactor core from DNB over a range of temperatures and pressures.
The setpoint for the OTAT trip is variable depending upon RCS temperature, pressurizer
- pressure, and axial flux difference.
Due to a potential nonconservatism discovered in the methodology used to calculate the F-Delta I (f(AI)) reset portion of the OTAT trip function, it was determined that the positive side of the axial offset band w&s non-conservative for Catawba Unit 2.
The f(AI) reset portion of the trip function is designed to lower the trip setpoint when axial flux dif ferences exceed predetermined limits.
Since the limiting margins to DNB occur as the result of highly skewed power distributions, a slope change to the positive wing on the axial offset band is necessary in order to prevent the DNB limits from being exceeded.
Therefore, an evaluation was performed using the Improved Thermal Design Procedure to determine l
a now value for the slope of the positive side of the axial offset l
band which conservatively bounds this operating region.
This new l
slope value will be included as a Catawba Unit 2 specific value in the Technical Specifications.
- sJor Catawba Unit 2, Westinghouse calculates the O'IAT f( AI) ret >e t fitnction, which is presented in the Technical Specificati,ons,, based l
on asial of f set limits and core thermal limits.
current methodolobN'he Improved Thermal Design Procedprc'/rhe j
t uses a linear extrapolation beyond 118% power to generat6 the f(AI) reset function.
However> since (depp ling on tti5 DNB correlation used)
L,. - the axial offset limitii' ate not.ndepch, dent of power (the deadband and slope of an 118% power 'curat,e,afInot similar to those of an 80%
c) to power curve), that calcula MnW, be non-conservative for some C plants.
Specifically,3h calculate'd' slope of the positive wing of the f(AI) reset fupeflon may not be ab gh as it would be if calculations wefet,erformed using actual axia c(iMot fset limit data at
'C the higher -p~ower levels (the negative wing adversely 1 af fecte -t,ecause of the typically large negative AI b'And and since s
T th.
ial power shapes with negative axial offsets are fypically
.t limiting).
N Since the positive wing slope provides the gain values for the f(AI) setpoint penalty, an uncertainty in this penalty would be multiplied by this gain to translate it into an uncertainty in the K
term of the OTAT setpoint.
Therefore, the change in the 1
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positive-wing of the _ axial of f set band necessitates a change to the Allowable Value and Z value for Catawba Unit 2.-
Also included in the Z value - change isf an increase in the uncertainty associated-i with the;incore flux map accuracy.
The previous value used for this uncertainty was il.2%AI. span;{however, as a result of recent re-calculations the new value for this uncertainty was determined to be slightly higher at il.3%AI span.
This now flux map accuracy uncertainty of il.3%AI span-has been included in Z along with the change resulting from the increased positive wing slope of the axial offset band.
A new, more restrictive, Allowable Value was calculated as a-result of the change in the positive axial offset wing slope.
The Total Allowance, Z and S_ values are also changed as the result of-the use of Westinghouse methodology, which includes the AI uncertaintics in the K term of the OTAT setpoint 2
as. opposed-to leaving-the uncertainty allowances out-of K and t
._ using them to adjust the f( AI) trip reset function breakpoints.
Therefore, the Total Allowance, Z, S and Allowable value are to be given as unit specific values to replace the dual unit values in the current Technical Specifications.
In summary, the Technical Specification changes described above are required to ensure adequate DNB protection for the Catawba Unit 2 reactor core during ' plant operation.
These changes are Catawba Unit 2 specific and do not affect the, values for Unit 1 since the uncertainty allowances for Unit 1 were determined using an approved non-Westinghouse methodology.
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Insert-1 For - Catawba Unit-2, Westinghouse calculates the OTAT fAI reset
- function. presented in the ~' Technical Specifications by using the axial _ of f set limits, sce page 4-7 of WCAP-8745, and - the core-thermal limits, see 'page 4-4 of WCAP-8745. _ The core thermal limits are - converted - _f rom _ power versus - T n1.e to AT versus Toyo to i
determine'the gains (K1, K2, K3) of the OTAT equation (the OTAT setpoint is a function of the AT and Toyo along with pressure and axial, flux difference).
The axial of f set limits identify how much the power-(AT) must_bc reduced as the axial offset limits (and AI)
.is increased or decreased from a zero axial offset.
The axial offset limits art used to generate "new" core thermal limits based
- on the core thermal limits for large positive and negative. AIs.
These "new" core limits are plotted on_the AT versus Toyo curvo, see-page C-6 of WCAP-8745, and a "new" OTAT K1 gain is determined.
The i amount that K1 changes for the _ subject AI defines the fAI-penalty'for that AI.
- Because the axial of f set curve is_ a power reduction -curve, the core thermal _ limits were linearly-extrapolated to higher power levels than-permissible.
_This - was donc so-that when the power (AT)
- reduction was: applied to_the-extrapolated core thermal limits-for large AIs,.:the "new" power (AT) versus T yo core thermal limits were in - the range of permissible operation.
It is this linear
- extrapolation _of-the core thermal limits _ and_ the application of _the power-reduction from the axial offset limits that is the issue.
ForLcertain DNB correlations, this approach is valid because the power. reduction is essentially independent of power.
However, for other DNB correlations this approach may not be valid and may result - in a potentially. non-conservative fAI for some plants.
Specifically,-the calculated slope of the' positive wing of the fAI reset-function'is notLadversely affected because of the typically large 1 negative AI band and because the axial power shapes with negative axial-offsets are typically not limiting.
- The core thermalklimits and axial of fset limits (see -pages 4-4 and
~4-7 of WCAP-8745) used to calculate the fAI roset function remain valid _and are not-affected'by this issue. -It is the metnodology that was used to calculate the f4I roset-function that is the issue.
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Additional: Justification for Exigent TS Change This submittaliis being made to provido additional explanation of the work done by Westinghouse in the time period between October 24 and the time Duke Power received the proposed changes to the TS on November-14, 1991.
Westinghouse began work on the_new analysis on October 25.
This..
i
-work involved several different groups at Westinghouse. There were
'several iterations between the. Transient Analysis group and the Thermal. Hydraulics group to ensure that a conservative statepoint had been.provided.
When their work-was complete. values for-the Overtemperature AT, Total Allowance, Z, and Sensor Error had to-be verified.-
It is important to note that none of the work could be-done in parallel..
Information was provided informally between
- groups before calculations were finalized to speed up the process as much as possible, since the information provided by each group was.needed for the next to begin work.
This work was. completed by Westinghouse on an expedited schedule.
The normal schedule for-work of this-type would be a month, and the completed TS package was roccived by Duke on November 14.
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