ML20058A150

Forwards Responses to First Round Questions Re Cycle 5 Reload Application

ML20058A150
Person / Time
Site:	Fort Calhoun
Issue date:	10/31/1978
From:	Short T OMAHA PUBLIC POWER DISTRICT
To:	Reid R Office of Nuclear Reactor Regulation
References
NUDOCS 7811070099
Download: ML20058A150 (3)

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.y Omaha Public Power District 1923 MARNEY e O M A M A. NESRASMA 68102 a TELEPHONE S 3 6. AOOO ARE A CODE A02 October 31, 1978 Lirector of 'luelear Reactor Regulatien Ari:

Mr. Ecbert W. Reid, Chief Operating Peactors Branch :To. k U. S. Iluelear Pegulatory Commission Washington, D. C.

20555 7 '-

Reference:

Docket !io. 50-285,'

Gentlemen:

V The 0.aha Public Power District received a first round of questions in regard to the Fort Calhoun Station Unit Tio.1 Cycle 5 Reload Application, dated August, 1978, frc: the Cc:=tission on October 5, 1978. Accordingly, please find attached responses to these questions.

Sincerely, (20

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T. E. Shcrt Divisica Manager Production Operations TES/KTi/PJd:J::::

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cc: LeBceuf, Lamb, Leiby & MacRae 1757 "i" Street,ii. W.

Washingten. D. C.

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1 RESPONSES TO FIRST ROUND OF QUESTIONS ON FORT CALHOUN CYCLE 5 RELOAD i

I APPLICATION

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Question 1 Refer to paragraph 3.7.3.3 on page C-12.

Here a very brief description I

is given of the use of ROCS in place of fine mesh PDQ in the reload

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safety analysis. Please describe in detail how ROCS was used in the

?

I safety analysis. In particular, formulate a list of all core power distributions computed in the analysis and indicate whether the distri-j bution was computed using ROCS and PDQ.

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Response

Fine mesh PDQ calculations continue to form the basis of the safety analysis as was the case for Cycle 4.

However, as discussed in Paragraph 3.7.3.3, ROC 5 was used to supplement the PDQ calculations in the Cycle i

5 safety analysis.

Specifically:

1. ROCS was used to survey a variety of core conditions and to compute i

various safety-related parameters._ PDQ was then used to investigate I

the limiting conditions and parameters.

2. Two-and three-dimensional ROCS calculations were used in conj nction l

with two-dimensional PDQ calculations to obtain best estimate core parameters.

3. ROCS was used to determine the impact of the three-dimensional gross power distribution on reactivity parameters.

Power distributions calculated with ROCS were used to scope various core conditions as described in Item 1 above and to weight the relative importance of fine mesh PDQ planar power and burnup distributions in the l

determination of three-dimensional and integrated core power and burnup r

distributions. One-pin peaking factors and CECOR coefficients were cal-culated with fine mesh PDQ.

Question 2 f

Refer to paragraph 3.7.4 on page C-12.

There is a table here of the Cycle 4 and Cycle S assumed uncertainties in peaking factors.

The sta!! accepts-the Cycle 4 values and does not accept the lower Cycle 5 values. It is the staff's understanding that there may be credits in other parts of 1

the safety analysis to offset the difference between the Cycle 4 and Cycle 5 values.

Please identify the credits available to you and show that the i

credit in all four of the table entries is at least equal to the di!!er-I ence between the Cycle 4 and Cycle 5 values.

i

Response

There are conservatisms in both the DNBR and kw/ft LCO and LSSS used in the i

safety analysis. These conservatisms are sufficient to offset the differ-l-

ences between the Cycle-4 and Cycle-5 values.

Response to Question 2 (Continued)

There are two areas in which conservatisms are known to exist in the DNBR related limits.

In the first of these, the degree of conservatism is kr,own, since comparisons with a more exact model have been performed.

In the latter, the degree of conservatism has not been explicitly deter-mined; however, it is clear that it is conservative.

In the DNB limit analysis, the assumed uncertainties in various measured parameters are not combined in a single equation, but are factored into i

functional relationships as biases at various points in the analysis.

This biasing of functional relationships throughout the analysis is equiva-lent to adding the relative power uncertainties equivalent to the un-certainties in the various measured parameters and applying the total power uncertainty to the best estimate calculation. The specific uncertainties along with their equivalent power uncertainties are given below.

Parameter Measurement Uncertainty Relative Power Equivalent _

ASI 0.06 ASIU

>2.2%

Pressure 22 PSI s.8%

Temperature 2 DEGF s.9%

Flow 4% FLOW 55.0%

Power 5% POWER (LSSS) 53.5%

2% POWER (LCO)

'1.4%

The sum of these uncetainties is 12.4% for LSSS,10.3% for LCO. Treating these measurement uncertainties as statistically independent, the proper method for combining them is RSS. The RSS combination yields 6.6% for LSSS, 5.8% for LCO, giving a net conservatism in the analysis of 5.8% for LSSS, 4.5t for LCO. This is more than sufficient to compensate for the 2.9%

difference in LCO allowances and 4.9% difference in LSSS allowances between the Cycle-4 and Cycle-5 analyses.

In the multiplicity of QUlX axial flux shapes used, more severe shapes are calculated than are expected to occur during actual operation. This results in conservatism.

l With respect to the kw/ft LSSS, there is conservatism in the way ASI limit curve is constructed. The Technical Specification ASI Trip Test is con-structed to lie below the actual Trip Tent. The construction contains at least 5t conservatism and is sufficient to offset the 4.2% difference be-tween the Cycle-4 and Cycle-5 allowances.

Sufficient margin exists in the LOCA monitoring limit of 14.7 kw/ft to offset concerns regarding uncertainties in the kw/ft LC0 allowances. The current limit of 14.7 kw/ft is bt;ed upon the characteristics of the previous cycles' low density fuel. The limit would be greater than 16 kw/f t based on the high density fuel present for Cycle 5.

Therefore, there is excess of 5%

conservatism in the current LOCA limit which is the Technical Specification kw/ft LCO limit of 14.7 kw/ft and is sufficient to offset the 2.2% differ-3 ence between the Cycle-4 and Cycle-5 allowances.

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