ML18227C701

Letter Proposed Amendment to Facility Operating Licenses Re Effects of Fuel Rod Bowing on the DNBR Margin

ML18227C701
Person / Time
Site:	Turkey Point
Issue date:	04/04/1977
From:	Robert E. Uhrig Florida Power & Light Co
To:	Stello V Office of Nuclear Reactor Regulation
References
Download: ML18227C701 (11)

Text

F IlOM:

Florida Power

& Light Company Miami, Florida Mr. Robert E. Uhrig TO:

Mr. Victor Stello IVilCI u<<M 1iJb

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DATF. OF DOCUMENT 4/4/77 DATE <<ECEIVEO 4/7/77 lit!LETTE R BfotIIGINAL QcopY DESCRIPTION C3NOTORIztn

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~i Amdt. to OL/cha rige to Apperidix A tech specs concerns the effects of fuel rod bowing with attached report. entitled "Margins in Turkey Point Units 3, 4

Safe'ty Analysis to Offset, the Effects.'f Fuel Rod Bowing'el /Q~g~f PLANT NAME Turkey Points Units. 3 & 4 RJL SAFETY ASSXGNED AD:

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J FLORIDAPOWER & LIGHTCOMPANY April 4, 1977 L-77-106 Office of Nuclear Reactor Regulation Attention:

Mr. Victor Stello, Director Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C.

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Dear Mr. Stello:

Re:

Turkey Point Units 3 and 4

Dockets No. 50-250 and 50-251 Proposed Amendment to Facility 0 crating Licenses DPR-31 and DPR-41 In our letter of August 19, 1976 (L-76-300) we described the options available at Turkey Point Units 3

& 4 for offsetting an increased rod bow penalty.

Since then, FPL has performed analyses which account for the effects of fuel rod bowing on the DNBR margin of the Turkey Point nuclear units, and which are in conformance with the DNBR penalties promulgated by the NRC for the type of fuel (Westinghouse LOPAR) currently in the cores of the Turkey Point units.

However, instead of taking the rod bow penalty in terms of a reduction in F<

we show in the attached safety analysis that sufficient plant specific DNB margin exists to absorb the entire penalty due to the low power level at which the units are operating.

This margin is available because the setpoints and transient thermal-hydraulic analyses are based on a considerably higher enthalpy rise hot.

channel factor than the one under which the plants are now operating.

Only the curves of reactor core thermal and hydraulic safety limits for normal operation shown in the Technical Specifications need be revised, as the new curves are based on the current enthalpy rise hot channel factor.

As this fact is not, reflected in the basis of the Technical Specification, the basis needs revision also.

Therefore, in accordance with 10 CFR 50.30, three (3) signed originals and forty (40) copies of a request to amend Appendix A of Facility Operating Licenses DPR-31 and 41 are hereby submitted for your review.

The proposed changes are described below and shown on the accompanying Technical Specification pages bearing the date of this letter in the lower right hand corner.

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Office of Nuclear Reactor Regulation Page Two Fi ure 2.1-1 This is the replacement figure for the thermal and hydraulic safety limits and includes the rod bow penalty.

Pa e B2.1-1 The values for F and F<

are changed to reflect the current N

N values.

A stateQent is added that the safety limits have been reduced to account for rod bow.

Page B2.1-2 The statement on the reactor control and protection system is expanded to indicate that. tgis system is based on the original design values of F and F>H, which therefore leads to highly conservative setp8ints.

This proposed amendment has been reviewed by the Turkey Point Plant Nuclear Safety Committee and the Florida Power a Light Company Nuclear Review Board.

They have concluded that the proposed amendment does not involve a significant hazards consideration and should not involve prenoticing pursuant to 10 CFR 2.105.

Until such time as this change is approved, the administrative procedures with regard to DNB margin, detailed in our letter of August 19, 1976, will be continued.

Very truly yours, Robert E. Uhrig Vice President REU/RDH/MAS/cpc Attachment cc:

Mr. Norman C. Moseley, Region II Robert Lowenstein, Esquire

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640 P = 2400 psia 630

'P ='250 psia 620 a

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Figure 2. l-l. Reactor Core Tharr.".of apd Hydraufic Sofety Limits Three le) Operant~

4/4/77

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B2.1 BASES FOR SAFETY LIMIT,.REACTOR CORE To maintain the integrity of the fuel cladding and prevent fis-sion product release, it is necessary to prevent overheating of the cladding under all operating conditions.

This is accomplish-ed by operating within the nucleate boiling regime of heat

~ansfer, wherein the heat transfer coefficient is very large

.and the clad surface temperature is only a few degrees Fahrenheit above the coolant saturation temperature.

The upper boundary of

.the nucleate boiling regime is termed departure from nucleate boiling (DNB) and at this point there is a sharp reduction of the heat transfer coefficient, which would result in high clad temperatures and the possibility of clad failure.

DhB is 'not,

however, an observable parameter during reactor operation.

Therefore, the observable parameters; thermal power, reactor

~woolant temperature and pressure; have been related to DNB-through the 8-3 DNB correlation.

The >l-3 DNB correlation has been developed to predict the DUB flux and the location of DNB

'for axially uniform and non-uniform heat flux distributions.

The local DNB heat flux ratio (DNBR), defined as the ratio of the heat flux that would cause DNB at a particular core location Co the local heat flux, is indicative of the margin to DNB.

She curves in the Specification represent'the loci of points of thermal power, coolant system pressure and average temperature which ensure that the design limits on mini,mum DNBR are not exceeded.

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The cv'rves are based on the following nuclear hot channel factors:

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~ 2.41 q

F

~ 1.55 N

hH B2.1-3.

4/4/77

'These limiting hot channel factors are higher than those cal-culated at full power for the range from all control rods fully withdrawn to maximum allowable control rod insertion.

The con-trol rod insertion limits are covered by Specification 3.2.

Slightly higher hot channel factors could occur at lower power levels because additional control rods are in the core.

Bow-ever, the control rod insertion limits dictated by Figure, 3.2-1 ensure that the DNBR is sways greater at partial power

.than at full power.

Me hot channel factors are also sufficiently 1arge to account for the degree of malpositioning of part-length rods that is a1lowed before the reactor trip set points are reduced and

" mod withdrawal block and load runback may be required.

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Rod

('2) withdrawal block and load runback occur before reactor trip setpoints are reached.

The Reactor Control and Protection System is designed to prevent any anticipated combination of transient. conditions that would result

-in exceeding DNBR design limits.

t The setpoints are based on the original values of F and FAH in the FSAR. 3.13 and 1.75 N

N respectively, and. represent conservative values even with the rod bow penalty included.

I References (1)

FPL report NAD-QR-25 (2)

FSAR 3.2.2 32.1-2 4/4/77

STATE OF FLORIDA

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COUNTY OF DADE

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st Robert E. Uhrig, being first duly sworn, deposes and says:

That he is a Vice President of Florida Power 6 Light Company, the Licensee herein; That he has executed the foregoing document; that the state-ments made in this said document are true and correct to the best of his knowledge, information, and belief, and that he is authorized to execute the document on behalf of said Licensee.

Robert E. Uhrig Subscribed and sworn to before me this day of OTARY PUBLIC, in and for the County of Dade, State of Florida ROTARY PUSUC STATE OF KORIDA"ATIAAF MYCohVAISSIOM EXPIRES NOV. 30 1979 qjission expires-

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