ML20207B259
| ML20207B259 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 07/25/1988 |
| From: | Morris K OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| LIC-88-620, NUDOCS 8808020284 | |
| Download: ML20207B259 (5) | |
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l Omaha Pubilc Power District 1623 Harney Omaha. Nebraska 68102 2247 402/536 4000 July 25, 1988 LIC-88-620 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Station P1-137 Washington, DC 20555 References :
1.
Docket No. 50-285 2.
Letter from 0 PPD (K. J. Morris) to NRC (Document Control Desk) dated July 1, 1988 (LIC-88-577)
Gentlemen:
SUBJECT:
Cycle 11 Setpoint Errors The purpose of this letter is to provide an update and to correct inaccurate information previously provided in Reference 2.
The inaccurate information was in reference to the information placed in the Shift Supervisor Log as referenced in Paragraph 4 of Reference 2.
More accurate information concerning that log entry is contained in paragraph 4 of this letter.
The information in Reference 2 is included here, in that this letter reflects the content of Reference 2, as corrected. Changes from Reference 2 are denoted by a vertical line in the right hand margin.
During performance of the Cycle 12 Reload Analysis at OPPD, discrepancies in the Cycle 11 Setpoint Analysis were discovered.
A meeting was held on June 28, 1988 to discuss these discrepancies.
Based on the results of this meeting, it was confirmed that errors existed in the current Cycle 11 Setpoint Analysis.
The impact of these errors was not quantified, but the errors were known to affect Technical Specification Figure 1-3 for the Thermal Margin Trip Setpoint and Technical Specification Figure 2-6 for the Excore Monitoring Linear Heat i
Rate (LHR) Limiting Condition for Operation (1.C0).
Following the meeting on June 28, 1988, several interim corrective actions were initiated to ensure conservative plant operation during the period in which the j
discrepancies were being quantified.
The Reactor Engineer contacted the Shift Supervisor and discussed with him the conservative actions to be taken until the errors could be quantified.
The Shift Supervisor was instructed that if any situation arose that necessitated the use of the excore linear heat rate LCO, the unit would be brought to 80Y.
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l U. S. Nuclear Regulatory Commission LIC-88 620 Page Two power and not the 90% power level as identified in Technical Specification Figure 2-6.
Given the action statement in Technical Specification 2.10.4(1)(b), Figure 2.6 would not have been entered under any circumstances that night.
In addition, instructions were provided that the unit was to be held at 90% power and the core inlet temperature maintained at 541*F until the situation was resolved, in order to prevent any reactivity changes which might have the potential for initiating a transient event which could challenge the
- RPS, After this discussion, the Reactor Engineer called the Manager-Fort Calhoun Station and apprised him of the at,ove described events.
They discussed the i
applicability of entering an LC0.
This was not done because the error in the TM/LP trip had not been quantified.
After this conversation, the Plant Manager called the Shift Supervisor to confirm that upon entry into Figure 2 6, that an immediate power reduction to 80% would be initiated.
Based on the Manager -
Fort Calhoun Station's recommendation, the Reactor Engineer also called the Manager Administrative & Training Services to discuss the situation.
The Manager Administrative & Training Services communicated with other management personnel. The Reactor Engineer called the night Shift Supervisor to fully brief him on the circumstances related to the information contained in the Shift Supervisor's Log.
On June 29, 1988, the Reactor Engineer was notified that the Thermal Margin Pvar equation used in the RPS trip units was nonconservative by approximately 80 psi based on preliminary calculations which remained to be independently reviewed.
It would take several hours to perform the analysis verification and confirm the exact value needed to place the TM/LP trip units back in a conservative condition.
The Plant Manager and his staff were immediately brought up to date on this latest development.
At 0920 although the exact degree of nonconservatism had not been identified, the station was placed in a 12 heur LCO per Technical Specification 2.15(3).
The TM/LP trip units were declared inoperable and recalibration was initiated.
The Plant Manager also stipulated that, at four hours into the LCO, if signi-ficant progress had not been made on recalibration of the trip units, a shutdown would be initiated.
A conservative value of 100 psia was chosen such
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that it would bound the analytical result determined by the engineering staff.
Per 10 CFR 50.72, at 1230, a four hour report was made to the NRC.
By 1730 the recalibration and the operability surveillance tests were completed and the four trip units had again been declared operable.
The root cause of the errors was determined to result from procedural omissions in training by Combustion Engineering and a misunderstanding between CE and the OPPD Staff during the training.
This training was provided to permit conver.
sion from hand calculation methods of setpoint generation to a less time cons'iming computer aided technique, which also reduces the probability of analysis uncertainties or calculational errors.
During the training, the CE Instructor assumed the OPPD Staff would incorporate a temperature dependent radial peaking factor penalty into the analysis, while the OPPD Staff assumed that all inputs were nxplicitly identified by the code and procedure. As a j
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8 U. S. Nuclear Regulatory Commission LIC-88-620 Page Three result, the penalty factor was not incorporated into the Cycle 11 Setpoint Analysis, which affected Technical Specification Figure 1-3.
A second error occurred for the same reasons with respect to use of transient analysis and LOCA required overpower margins (ROPM's) for Technical Specification Figure 2-6.
Failure to identify the error during verification of the analysis i
resulted from turnover of experienced staff and the necessity to use a qualified but less experienced independent reviewer.
After the June 28, 1988 meeting, the CE setpoint expert was instructed to completely and independently reanalyze the required Cycle 11 setpoints and determine the degree of nonconservatisms in any part of the analysis performed by 0 PPD, No other nonconservatisms, other than those already identified, were found to exist which would affect Technical Specifications.
A verification of j
the CE Setpoint expert's analysis was performed.
Results of the reanalysis
- 3 were reported to the Manager-Fort Calhoun Station and the Reactor Engineer j
after completion of the reanalysis on June 30, 1988.
The reanalysis showed nonconservatisms of less than 79 psia in the Pvar equation of Technical j
Specification Figure 1-3 and 4% power in Technical Specification Figure 2-6 at the maximum permissible power.
In addition, verification of the applications l
of the previous cycle's (i.e., Cycle 10) setpoint methods were reviewed and i
found to be correct by CE.
To prevent this error from occurring in the future, Combustion Engineering is revising the analysis procedure for use of the computer aided setpoint gener-ation code. At the time the analysis error occurred, both the analyst and the analysis reviewer had recently been trained by CE to perform the computer aided analysis and thus had the same misconceptions regarding the analysis methods.
Since Cycle 11 additional personnel have been trained and qualified in setpoint analysis. OPPD Staff qualified to perform setpoint analyses have now been informed of the appropriate analysis methods and it is unlikely that even with-out the analysis procedure correction that the same error could again occur.
In addition, OPPD has committed to having CE perform analysis verification of any portion of a reload analysis when sufficiently experienced OPPD personnel y
are not available.
To ensure continued safe operation for the remainder of Cycle 11, which is expected to end on approximately September 2,1988, the following operations analysis evaluations have been performed and/or the corrective measures have i
been or are being taken:
1.
As discussed above, the RPS Thermal Margin Calculator Setpoints have been adjusted by 100 psia to conservatively account for the 79 psia nonconser-l vatism identified in the reanalysis.
This 79 psia corresponds to a 2.63%
nonconservatism in the total integrated radial peaking factor (FR) which resulted from a failute to apply the penalty factor.
l 2.
It has been determined that Cycle 11 operations have not resulted in a full 1
power total integrated radial peaking factor in excess of 1.70 (e.g. actual i
maximum has been 1.68).
The Technical Specification limit for this para-l 9 =1.80 yielding an additional Cycle 11 operating margin of 5.56%
i meter 1 i
1.70) or approximately a 180 psia conservatism to the l
(for Fp ThermaT Margin Pvar equation.
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o U. S. Nucle.r Regulatory Commission LIC-88-620 Page Four It has been concluded that prior to revising the Thermal Margin trip 3.
setpoints in (1) above that at no time during Cycle 11 operation had the setpoint margin requirements been exceeded.
4.
Should loss of the incore monitoring ability combined with lack of a valid power distribution within the last seven days (per Technical Specification 2.10.4(1)(b) result in the use of the excore monitoring LHR LC0 (e.g.,
1 Technical Specification Figure 2-6) versus the normally used incore monitoring DNB LCO (Technical Specification Figure 2-7), power shall be i
immediately reduced to 80% of rated power.
The most current valid power distribution was placed in the Control Room Log on Friday June 24, 1988.
It is significant to note that, throughout the maintenance of 90% power, the excore LHR LCO could not be entered into until at least Friday July 1, 1988 (assuming the loss of the incore monitoring system) and that under no circumstance would the Technical Specification Figure 2-6 (Excore LHR LCO) have been entered on Tuesday night, June 28, 1988.
Revisions to the Technical Data Book Figures III.16.b, III.16.b.1, III.16.b.2, cnd III.16.c have been prepared and implemented into the Operating Manual, Volume I.
It should be noted that use of the excore monitoring LHR LC0 has not been j
required within at least the previous twelve years of operation and that use of this LCO is not expected to be required during the remainder of Cycle 11 operation, j
Review of Technical Specification 2.10.4(1) was conducted with the NRC l
Senior Resident Inspector, Mr. P. H. Harrell and it was concluded that this Specification was being appropriately applied.
It was identified that clarification of the text for entering the excore LHR LC0 would be appro-priate.
This change will be included in the Cycle 12 Reload Application and Technical Specification changes.
5.
It has been concluded that onculd use of the excore monitoring LHR LCO have l
been necessary during Cycle 11 operation, sufficient nargin would have exis}edduetomarginbetweentheactualtotalplanarradialpeakingfactor (FXY ) and the Technical Specification limit of 1.85 to hav9 prevented l
exceeding any of the required LHR margins.
The maximum Fyy occurring i
i during Cycle 11 to date has been 1.72 which yields a margin of 7.0%.
6.
An Operations memo has been issued notifying Operations to utilize the Technical Data Book figures in lieu of Technical Specification Figures 13 i
and 2 6.
l In conclusion, OPPD discovered two errors in the Cycle 11 setpoint analysis and has taken appropriate and timely corrective act!ons to ensure continued safe operation through changes of RPS Thermal Margin trin setpoints, administrative l
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U. S. Nuclear Regulatory Commission LIC-88 620 Page Five i
restrictions on core inlet temperature and power to prevent transient reactivity-induced conditions which could potentially challenge the RPS, and i
revision of Technical Data Book Figures related to the excore monitoring LHR l
LCO, as well as corrections to OPPD setpoint analysis methods.
l Sincarely,
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orris j
Division Manager l
Nuclear Operations j
KJM/me c:
LeBoeuf, Lamb, Leiby & MacRae R. D. Martin, NRC Regional Administrator 4
- 1. F. Westerman, Chief, Project Section 8 - Region IV J. E. Gagliardo, Chief Reactor Projects Branch - Region IV P. D. Milano, NRC Project Manager P. H. Harrell, NRC Senior Resident Inspector T. Reis, NRC Resident Inspector i
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