ML17317A910
| ML17317A910 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 01/24/1979 |
| From: | Tillinghast J INDIANA MICHIGAN POWER CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| AEP:NRC:00136, AEP:NRC:136, NUDOCS 7902020258 | |
| Download: ML17317A910 (10) | |
Text
INDIANA R MICHIGAN POWER COMPANY P. O. BOX 18 Bo WLI N G G R E EN STAT ION NEW YORK, N. Y. 10004 January 24, 1979 AEP:NRC:00136 Donald C.
Cook Nuclear Plant Unit. 1 Docket No;. 50-315 License No:.
DPR-58 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Denton:
On January 18, 1979, we learned that a reanalysis based on the February 1978 Westinghouse ECCS Evaluation Model for 15 x 15 Westinghouse fuel used in a,Nuclear Plant (Plant X) with a NSSS design similar to Cook',
had resulted in a lower Fq peaking factor limit.
Since one.third o'f the Donald C.
Cook Nuclear Plant, Unit
-1 core is fueled with 15 x 15 Westinghouse fuel, concern arose as to
~
whether a similar penalty should be imposed in the Donald C.
Cook Nuclear Plant Unit 1 resulting in an F limit below the 1.90 presently in effect This.letter and its enclo ures address those concerns and demonstrate that the present Donald C.
Cook Unit 1 limit re-mains valid.
The present value of 1.90 was established on the basis of an NRC staff order issued upon a review of an analysis performed by the Westinghouse Electric Corporation.
The analysis was performed to evaluate the effect of correcting a logic inconsistency discovered in the previous evaluation model.
The new analysis was performed using the same blowdown and reflood hydraulic transients of the earlier sub-mittal.
However, the rod heat-up portion of the calculation (LOCTA-IV) was redone.
In this calculation the error in the zirconium-water re-action calculation was corrected and the new 15 x 15 FLECHT coefficients were employed.
A worst break condition, the double ended cold leg guillotine break, with a discharge coefficent Cq of 0.8 was assumed.
The discussion, below demonstrates the conservatism of the interim value of 1.90 in relation to the results of a final reanalysis employing the
, February 1978 model.
'Rp(UI IIn'n
. copY(
Nr. Harold R. Denton, Director AEP:NRC:00136
- First, a similar interim calculation was performed for Plant X.
The only major difference between the Cook and the Plant X analyses was thatthe margin in as-built pellet temperatures was used in the Plant X
analysis.
- Second, the interim calculation performed for Plant X resulted in an Fq of 2.02 for a CD = 0.6 break.
A reanalysis was performed for Plant X following the NRC approval of the February 1978 model.
This re-analysis resulted in a preliminary decrease in the Fq limit of 0.16 for a
CD = 0.8 break.
The shift of worst break condition from CD = 0.6 to CD = 0.8 was caused by the fact that the 0.6 break received a large bene-fit resulting from the changes in the SATAN-VI code.
Neither break re-ceived significant benefit from the improved reflood heat transfer model since the Peak Cladding Temperature (PCT),which peaks a few seconds into reflood, occurred at the burst location.
Third then, the following considerations give the reasons why the Cook 1 limit of 1.90 is unaffected by results for Plant X.
(1)
Some of the Fq reduction for Plant X was caused by the removal of the margin in as-built fuel temperatures.
As mentioned before no advantage of this margin was taken in any of the Cook analyses.
(2)
The interim Cook analysi's i'ndicated a
PCT locati'on three feet aboye the burst locati;on.
Fi'gure 1 i'llustrates the difference in the clad temperature time histori'es between the burst and the PCT locations, The figure indicates a 500oF difference between the two locations which is quite different from the Plant X situation in which the PCT occurs at the burst location.
There are two important points to be made in this regard:
a)
The Cook Plant ice condenser containment performance during a
LOCA is quite different from that of a dry containment (Plant X) in that the former design leads to lower reflood rates.
The low backpressure during a
LOCA in an ice condenser containment causes the PCT to occur late in the reflood period
( '300 seconds) and at an upper axial location.
b)
The February 1978 model includes an improved steam cooling model which would have given Cook significant benefit due to the low reflood rate nature of the ice condenser transient.
- Also, even though the entire new 15 x 15 FLECHT correlations were ap-P<<ved by the NRC for the February 1978 model, a penalty of 0.03 was imposed by the NRC on the interim calculations as additional margin.
~
~
E I
j Jl
Nr. Harold R. Denton, Director AEP:NRC:00136 (3)
The Westinghouse fuel is near the end of its third cycle.
The lowest assembly average
- burnup, as of the date of this letter, is above 27,000 MWD Therefore, the maximum steady state pellet temperature MTU is approximately 500 F lower than that used in the interim analysis.
This is equivalent to an increase in the limit Fq limit of approximately
- 0. 41.
Finally, we should note (see Figure 2) that the present maximum Fp peaking factor measured in the Westinghouse fuel is roughly 1.41 (with APDNS penalty applied) and that during Cycle 3 the Westinghouse maximum Fq value (penalized) has never exceeded 1.65 at 1005 power.
On the basis of all the facts presented, it is clear that the present F
limit of 1.90 remains a conservative value applicable to the WestinghoIIse fuel in the D.
C.
Cook Unit 1 core until its final removal during the April 1979 refueling outage.
Very truly yours, 0
n has 1ce Press ent Sworn ari$ subscribed bo before me this W4 day of January, 1979 in New York County, New York Notary Pu i
GREGORY l>>l. GIIRICAH Notary Public, State of New York No. 31-4643431 Qualified In Nevi York CountV><
Commission Expires March 30, 19'~
cc:
R.
C. Callen P.
W. Steketee R. Walsh R. J. Vollen D. V. Shaller-Bridgman R.
W. Jurgensen G.
Char noff
~
l, lg J
)
4 4 I I
~
L I
W
~l
~.
E
D.C. COOK-UNIT I '- CY.CLE 5 MAXIMUMFg IN REGION 5.
- WESTINGHOUSE FUEL, C
SO O-MAX 1.5
'(100Ã Power }
CD fDA O
BURNUP t GWD/MTU)
FIGURE 2 Plo
~ ~
C)
~ ~
C)
CD CA Ch
fr I