ML19317D225

Requests Changes to Tech Spec 3.5,incorporating Control Rod Position & Axial Imbalance Limits to Period After 100 Plus or Minus 10 Effective Full Power Days.Forwards Proposed Tech Spec,Justification for Change & BAW-1477.B&W Rept Not Encl

ML19317D225
Person / Time
Site:	Oconee, Crane
Issue date:	01/23/1978
From:	Parker W DUKE POWER CO.
To:	Case E Office of Nuclear Reactor Regulation
Shared Package
ML19317D226	List: ML19317D225 ML19317D227
References
NUDOCS 7911190612
Download: ML19317D225 (11)

Text

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DISTRI3UTION AFIER ISSUANCE OF' ERATEIG LICriSE u.s.Nuct.24n rsout.Arony ceuwis..cn occx t suusen NaC scru tw fd - 2. b h

74 3 Ni'C OISTRIBUTION =on PART 50 DCCKET MATERIAL l

FROM.

cars op occuusar To: Mr. E/ son G. Case Duke Power Co.

01/23/78 Charlotte, N. C.

28242 3,7,,,e,y o

William O. Parker, Jr.

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ssceirT:cN License No. DPR-39 Appi for Amend:

tech specs proposed change concerning control rod position ar.d axial imbalance limtis applicabl to the period after 100110 EFPD...Notorized 01/23/78...w/att BAW - 1477 en'itle.4 "Oconee

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Mr. Edson G. Case, Acting Director T)

Office of Nuclear Reactor Regulation

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U. S. Nuclear Regulatory Ccemission Washington, D. C. 20555 JAN 2 61978"* :-

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Oconee Unit 1

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Dear Mr. Case:

By letters dated October 4, 1977 and November 9, 1977, Duke Power Ccepany submitted proposed revised Technical Specifications limits pertaining to quadrant power tilt and control rod positions.

The revised limits were proposed in order to accomodate the quadrant pcwer tilt observed at the beginning of Cycle 4 and to provide additional conservatisms in the con-trol rod position limits, based on power peaking, ej ected rod worth and shutdown margin consilerations, in the wake of the observed quadrant tilt.

The NRC approval of the revised Technical Specification limits was granted by your letter of November 23, 1977.

However, the control rod position and axial limits applicable to the period after 100 1 10 EFPD vere excluded from the revised set of limits in order to factor actual core performance with the tilt into the analyses used to escablish the control rod position and imbalance limits. These analyses have now been performed, and attached (Attachment 1) are proposed replacement pages to the Oconee Nuclear Station Technical Specifications that would include the control rod position and axial imbalance limits for operation of Oconee Unit 1 after 100 t 10 EFPD.

Pursuant to the provisions of 10CFR50.90, an amendment to the Oconee Nuclear Station Technical Specifications is requested in order to incorporate the control rod position and axial imbalance limits applicable to the pericd after 100 i 10 EFPD.

As in the case of the beginning of cycle limits, the proposed limits are established assuming a quadrant power tilt of 6.03" and the unrodded node of operation. Attachment 2 describes the manner in which the effect of the assumed quadrant tilt on limiting power peaks, ejected rod vorth limits, and shutdown =argin limits are conservatively accounted for in the proposed Technical Specification limits.

In view of the existance of a quadrant tilt in this core, the core perfor-mance in this cycle has been and is being closely monitored.

As indicated in our letter of Dece=ber 14, 1977, it is possible that the observed tilt in Cycle 4 could have been caused by a s=all tilt that existed in Cycle 3 ce=bined with the cross-core shuffling of once and twice burned fuel for the Cycle 4 design.

Calculations have been done simulating burnup mismatches in selected burned fuel assemblies in order to validate this hypothesis.

780270022

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Mr. Edson G. Case Page 2 January 23, 1978 These calculations showed that a quadrant tilt of the order of 1-2% in Cycle 3 could create a tilt of the magnitude seen in Cycle 4.

Further-more, the observed reduction of tilt with cycle burnup is consistent with a beginning of Cycle 4 burnup asymmetry in selected fuel assemblies. of this letter (BAW-1477) includes detailed discussions of efforts to resolve the tilt behavior and provides a summary of the measured core performance up to 60 EFPD.

It is seen that the core performance is satisfactory and that the proposed Technical Specifications limits are conservative limiting conditions of operation and provide acceptable margins of safety.

Oconee Unit 1 has now attained approximately 75 EFPD's of cycle burnup.

To enable timely implementation of the limits and continued operation of the unit, it is requested that approval of the proposed Technical Specifi-cations limits be granted by February 15, 1978.

Forty copies of this request, including five copies of BAW-1477, are submitted.

Vertruly yours, Nms. c./

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William O. Par er, Jr.

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'Page 3 January 23, 1978 VILLIAM 0. PARKER, JR., being duly sworn, states that he is Vice President of Duke Power Company; that he is authorized on the part of said Company to sign and file with the Nuclear Regulatory Comission this request for amendment of the Oconee Nuclear Station Facility Operating Licenses DPR-38, DPR-47, and DPR-55; and that all statements and matters set forth therein are true and correct to the best of his knowledge.

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f (J u - [b, cw William O. Parker, Jr., R1,c) President Subscribed and sworn to before me this 23rd day of January, 1978.

ubt b C/'ltrew Notary Public My Commission Expires:

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j ATTACHMENT 2 OCONEE 1, CYCLE 4 JUSTIFICATION FOR OPERATION FROM 100 (110) EFPD TO EOC IN AN UNRODDED MODE l

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Justificatien fer Operction from 100 (110)EFPD to EOC with Unrodded Mode of Operation Power Peaking Conservatisms The power peaking analysis for Oconee I cycle 4 operation from 100 (110) EFPD to EOC in the unrodded mode was performed assuming the existence of a 6% real quadrant tilt at all power levels.

This tilt was determined to cause 1 9% in-crease in local peaking, based on two factors:

(a) this represents a conservative relationship between peaking and tilt established by many full-core PDQ and FLAME cal-culations with tilt induced by various means, and (b) the comparison of calculated and measured power distribu-tions shown in Figures 1 and 2 (attached) at full power and at 56.6 EFPD shows that a factor of 1.09, in conjunction with the standard total and radial nuclear uncertainty factors would be conservative.

All other peaking penalties normally included in the generation of Technical Specifications operating limits were included in this analysis.

The present cycle 4 RPS limits, Technical Specification Figure 2.1 - 2A, were shown to be valid under the above conditions.

Operation in the unrodded mode was found to provide reduced total peaks during the fuel cycle at all times after 4EFPD compared to rodded operation.

Table 1 (attached) provides a comparison of the total peaks calculated during each time step of the fuel cycle from 100 EFPD to EOC. This table clearly shows that the peaking for the unrodded core is lower than for the rodded core for normal operation after 100 EFPD.

Since the base peaking is lower for the unrodded cores the perturbed peaking is also lower. This is especially true when Bank 7 is confined to the range of 300% to 274% WD at full power, as restricted by Technical Specification Figure 3.5.2 - 1A2.

Operating in the unrodded mode provides a means to restrict power peaking to nominal values.

This protection is gained at the expense of operational flexibility. With this mode of operation the plant has a greatly reduced maneuvering capability. However, as stated above, the usual peaking factorc due to xenon changes induced by normal maneuvering were included in the analysis, providing additional conservatism.

Ejected Rod Limits The ejected rod worth insertion limits were determined in an extremely con-servative fashion, again using the correction factor of over 50% based on the measured, beginning-of-cycle, hot zero power data.

The HFP ejected rod worth limits were based on projected EOC data and were still found to be less limiting than the shutdown margin insertion limits. At HZP the 0-100 EFPD red insertion limits were adjusted based on a projected slight increase in the maximum ejected rod worth at EOC.

The resulting rod insertion limits were less limiting than shutdown margin criteria at all power levels above zero pwoer.

Thus only che zero power limit (64% withdrawn) is based on ejected rod criteria.

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Shutdown Rod Insertion Limits The shutdown rod insertion limits were determined using standard techniques based on symmetric conditions and adjusting these calculations to account for the tilt. The calculated stuck rod worths were increased 10%. This un-certainty has been shown to be conservative by many FLAME 3 calculations in which stuck rod worths were determined with and without the existence of a quadrant tilt.

The result of this procedure is the conservative shutdown rod insertion limits shown in Technical Specification Figures 3.5.2 - lA2 and 3.5.2 - 2A2.

Discussion The net effect of all these conservatisms is the core is restricted in operating flexibility but allowed to operate at full power in a safe manner.

The APSR position limits, Technical Specification Figure 3.5.2 - 4A3, originally approved for operation after 235 + 10 EFPD should be observed after 100 + 10 EFPD. The imbalance limits, Technical Specification Figure 3.5.2 - 3A1,that are currently in force for 0 to 100 EFPD are more restrictive than necessary for the proposed mode of rods-out operation from 100 EFPD to EOC, and can thus be retained. This represents another conservatism in the analysis. The rod position limits were determined based on the super-position of the most conservative calculated and measured data.

The limits are clearly conservative. Operation of Unit 1 under these limits from 100 EFPD to EOC will insure that no initial condition criteria are exceeded, l

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ATTACHMENT 3 OCONEE 1, CYCLE 4 QUADRANT POWER TILT Report BAW-1477