ML19317D728
| ML19317D728 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 08/23/1972 |
| From: | Thies A DUKE POWER CO. |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 7912100496 | |
| Download: ML19317D728 (3) | |
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Q ll, Mr. Angelo Giambusso
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Deputy Director for Reactor Projects Directorate of Licensing W-United States Atomic Energy Commission C
Washington, D. C.
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Re: Oconee Nuclear Station Docket No. 50-269
Dear Mr. Giambusso:
In response to Mr. R. C. DeYoung's letter of July 26, 1972, the following information is provided.
The ability of the out of-core detector system to indicate radial tilts has been reevaluated by Babcock & Wilcox. This review shows that the limits in technical specification 3.5.2 provide an adequate indication of a potential for exceeding power distribution limits.
Significant radial tilts are not expected ti,ccur.
Potential causes of tilts include dropped rods, rods out-of-sequence, xenon oscillations, enrichment variations, misloaded fuel, and inlet temperature mismatch.
The effects of enrichment variations are discussed in FSAR Section 3.2.3.
l 2.2.
Hisloading of fuel is discussed in FSAR Section 3.2.2.2.l(g). Xenon stability is discussed in FSAR Section 3.2.2.2.2.
Of the remaining potential causes of radial tilts, misalignment control rods are most significant.
The reactor control system includes several systems to detect misaligned control rods and has both alarm and power runback provisions. Control rod position is indicated by two separate methods at the control console as discussed in FSAR Section 3.2.4.3.2(j).
In addition, an alarm is sounded when a control rod deviates more than a preset value from the group and power it run back when a deviation occurs as indicated in technical specifications 3.5.2 and 4.7.1.
Indications are also provided for control rods in the fully inserted or withdrawn position.
An additional provision is available for detection of misaligned control rods through radial tilt indication by out-of-core detectors. Present j
limits in technical specification 3.5.~2 specify that if radial tilt exceeds l
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Mr. Angelo 'tambusso Page 2 August 23, 1972 10 percent, power shall be limited to 80 percent; and if radial tilt exceeds 20 percent, power shall be limited to 60 percent. During normal operation, these limits prev.at exceeding design thermal-hydraulic criteria and the ECCS criteria of 17.4 Kw/ft for unpressurized fuel. The most limiting criterion is the ECCS criteria of 17.4 Kw/ft. During normal equilibrium operation at 2568 MW(t) the maximum expected linear heat rate is 14.24 Kw/ft. This gives a margin of 22.2 percent to the ECCS criteria.
The relationship of increased peaking and radial tilts has been investigated for various conditions and plants.
Figure 1 presents results for increased peaking as a function of quadrant tilt as indicated by out-of-core detectors for dropped rods and single and multiple rods out of sequence. The magnitude of a radial tilt as indicated by out-of-core detectors depends on the relationship of tilt axis and the out-of-core detectors. A maximum in-i dication is obtained when the tilt axis is aligned with the out-of-core detectors. A minimum indication is obtained when the tilt axis is at an extreme from the out-of-core detector. An uncertainty of 23 percent is included in tilt indication in Figure 1 to account for the potential difference between nominal quadrant tilt and a minimum indication. Figure 1 is then a pint of peaking increase as a function of indication for a minimum indication by out-of-core detectors. The data were determined with "3D" thermal-hydraulic feedback analyses (PDQ-7) with the exception of the dropped rod cases which are from "2D" PDQ-7 analysis. The data are limited by a line with a slope of 1.84 A(Kw/ft.%). Use of this slope would A(Indic %)
then require a minimum margin of 18.4 percent at the 10 percent radial tilt indication limit during normal operation. The ECCS criteria could be exceeded at a quadrant tilt indication of 12.2 percent.
The minimum system of incore detectors as specified in technical specification 3.5.4 has been investigated for the same perturbations. The limiting slope is 1.59 A(Kw/ft. %) requiring a minimum margin of 15.9 percent to the ECCS A(Indic. %)
criteria of 17.4 Kw/ft in normal operation. The ECCS criteria could potentially be exceeded at an incore indication of 13.9 percent.
Either the out-of-core detector system or the minimum system of incore detectors provide an adequate indication of a potential for exceeding safety limits at the present technical specification limit of 10 percent.
Please advise if you require further information.
Very truly yours, A. C. Thies ACT:vr
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10 12 14 16 Til t Indicated Tilt at out of Core Detector PERCENT CH ANGE IN PE AK POWER VS PERCENT CH ANGE IN R ADI AL TILT Figure i
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