ML19340A795
| ML19340A795 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 07/21/1977 |
| From: | Bolger R COMMONWEALTH EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML19340A794 | List: |
| References | |
| NUDOCS 8009030833 | |
| Download: ML19340A795 (6) | |
Text
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C:mmsnwraith Edison
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one fernt National M.va. Chicago, Ilknois Address Reply to: Post Othee Box 767 Chicago, Ilknois 60690 1,.
July 21, 377 k
i Mr. James G. Keppler, Director i
Directorate of Inspection and
. Enforcement - Region III U.S. Nuclear Regulatory Commission l
799 Roosevelt-Road Glen Ellyn, IL 60137
Subject:
Dresden Station Units 1, 2, and 3 Response to IE Inspection Report Nos. 50-10/77-16, 50-237/77-15, and 50-249/77-15 NRC Docket Nos. 50-10/237/249 l
Reference (a):
G. Fiorelli letter to Byron Lee, Jr.,
. dated Junc 30, 1977.
]
Dear Mr. Keppler:
1 Attached to t his letter is Commonwcalth Edison's response to the items of noncompliance noted in Appendix A of l
Reference (a).
Please direct any additional questions concerning this matter to this office.
Very truly yours,
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R. L.
Bolger Assistant Vice President Attachment l
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JUL 2 W7 2
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Commonwealth Edison NRC Docket Nos. 50-10 50-237 Attachment 50-249
, Infraction 1:
Contrary to 10 CFR 50, Appendix B, criterion XVI, and the licensee's Quality Assurance Program, inadequate corrective action to preclude repetition was taken when the licensee determined that the Unit 2 APRH/RBM flow bias indication exceeded 100%
on both channels, resulting in a nonconservative flow bian scram setpoint.
This condition was reported to the NRC in February, 1977 (LER 237/77-02), and again in April, 1977 (LER 237/77-19).
Criterion XVI states, "In the case of significant conditions adverse to quality, the measures shall assure that the cause of the condition is determined and corrective action taken to preclude repetition."
Discussion:
On January 28, 1977, it was observed during normal opertilon that, with the core ficw at 100% as measured through the jet punps, the APRM/RBM flow bias indication exceeded 1005 on both reactor protection system (RPS) channels A and B.
The flow bias is derived from measurements of recirculation loop flows.
At 100% core flew, the APRM scram setpoint would not have been exceeded; however, at reduced ficw rates, the flow bias scram setpoint would have been nonconservative by several percent from the Technical Specification linit.
Even though nonconservative, however, none of the analyzed abnormal operational transients could have violated the fuel safety limits, since the analyses do not consider the additional margin provided by a flow biased scram.
The APRM/RBM flow converters were immediately readjusted to read 100% at 100% total core flow and an investigation was begun to determine the cause of the deviation.
The investigation initially focused on setpoint drift as was pointed out in our LER 50-237/77-02 dated February 9, 1977.
The intended long-term corrective action to prevent recurrence was to include a periodic check or surveillance of the APRM/RBM flow converter correlation to total core flow.
As the investigation proceeded, it was realized that this correlation varied both during the operating cycle as a function of power level and void condition, for example, and from cycle to cycle because of changing friction factors across the core.
The resulting delay in implementing a surveillance occurred in spite of our best efforts to promptly and adequately evaluate all the parameters j
involved, and not as a result of any disregard on our part for implementing corrective action as required by 10 CFR 50, Appendix B, j
Criterion XVI of our Quality Assurance Program.
l
C:mmon vaalth Edison
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NRC Docket Nos. 50-10 50-237 i 50-249" 1
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l On April 25, 1977, Dresden Unit 2 was at full core flow for,the first time following a short outage during which the i
flow converters were recalibrated in accordance with. procedure DIS 700-1.
Once again with core flow at 100%, the APRM/RBM 4
flow bias indication exceeded 100% on both RPS channels A.and B.
The flow converters were again readjusted.
The subsequent j
investigation now clearly revealed that the deviation reoccurred
.as a result of following a calibration procedure which contained the original flow converter correlation to total core flow and I
not the current correlation.
We now believe this to have been the cause of the original deviation rather than instrument drift and, as pointed out in LER 50-237/77-19, dated May 9, 1977, we are revising our procedure to ensure that only the current correlation or a conservative substitute for it is used to calibrate the flow l
converters.
i corrective Action, Corrective Action to Prevent Recurrence, and Date of Full Comoliance:
i In each instance in which th3 APRM/RBM ficw bias indication was identified as exceeding 100% indication at 100%
total core flow, the flow bias converuers were immediately J
readjusted to 100%.
To prevent future recurrence, the instrument calibration procedure, DIS 700-1, which must be performed once each refueling outage, is being revised to remove the original correlation between total core flow and recirculation drive flow.
j It will be replaced with a correlation which will be conservative l
for future operation.
In additior, a new procedure will be written to adjust the flow bias converters to the most current correlation (with the participation of the nuclear engineers), after startup from the refueling outage, and after jet pump calibration has been perfomr.ed.
The most current correlation will be obtained as needed during startup testing or during routine data acquisition.
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This corrective action will be completed by September 15, 1977.
j In addition, a weekly surveillance has been implemented to verify that the APRM/RBM flow bias flow converters are not exceeding the' total ~ core flow which they should properly indicate.
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t Commonwealth Edison NRC Docket Nos. 50-10 50-237
- 50-249
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Infraction 2:
Con'trary to Technical Specifications, Section 1.0.CC.a and b, surveillanc,e intervals for 5 specific surveillances conducted j
on Units 2 and 3-were exceeded in February, 1977.
(
Reference:
LER's 50-237/77-06 and 50-249/77-06)
Technical Specification 1.0.CC requires :
(a) a maximum allowable extension not to exceed 25% of the surveillance interval and (b) a total maximum combined interval time for any 3 consecutive intervals not to exceed 3.25 times the specified surveillance interval.
Discussion:
As stated in LER's 50-237/77-06 and 50-249/77-06, the intervals between completion of five routine surveillances conducted on Units 2 and 3 were exceeded in February, 1977.
Three of these discrepancies resulted from exceeding the allowable "three interval" extension permitted by the Technical Specifications and were computed from the date the three surveillances had been completed in November, 1976.
These five surveillances, however, were a very small fraction of the surveillances that were satisfactorily completed during that month.
Station surveillances are scheduled and updated on a computer, and it has been difficult to incorporate the necessary flexibility, offered by Technical Specification definition 1.0.CC regarding surveillance interval extensions, into the computer program.
Definition 1.0.CC became effective in May, 1976; in December, 1976, a management audit revealed some misunderstanding of the definition and the interpretation of the existing computer program output'necessary to ensure compliance with it.
Corrective action taken to resolve those difficulties was outlined in LER's 50-237/76-71 and 50-249/76-36 in December, 1976.
It included reprogramming the computer to schedule surveillances based on the last date it was performed.
Prior to December, surveillances were scheduled for completion on one fixed date each month, regardless of when it had been proviously completed.
Secondly, a base date was established for each regularly scheduled surveillance to provide a stable reference point for its completion.
This base date, unfortunately, did not permit the ficxibility required by the Technical Specification definition 1.0.CC.
Implementation of a monthly review of the surveillance program was also described in those reports to permit prompt i
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Comm:nw alth Edis:n NRC Docket Nos. 50-10 50-237
. 50-249 t
identification of future discrepancies.
The monthly review conducted in February identified five additional surveillance interval discrepancies.
However, since the December, 1976 review had i
indicatea an average of approximately 17 late surveillances per month prior to the December changes, the apparent frequency decline to 2 or 3 per month by February seemed to be no more than a residual from the earlier misinterpretations.
Continued personnel acquaintance with the new definitions was expected to further reduce the incidence of later surveillances.
Thus, no additional corrective action seemed necessary at that time and the corrective action indicated in December was expected to resolve the February discrepancies also.
Corrective Action, Corrective Action to Prevent Recurrence, and Date of Full Comcliance:
As a result.of additional late surveillances identified in the May, 1977 review of the surveillance programm, additional software programming changes have been requested from the Commonwealth Edison Computer Systems Department.
These changes will result in listing both a " preferred date" for ccmpletion of the surveillance, based on the last date it was performed, and a latest completion date which includes the minimum of the two different interval extensions permitted by the Technical Specification definition.
Additional corrective actions have been taken this year.
,The Operating Department now receives an updated list each week of surveillances scheduled for the next two weeks to allow advanced awareness of upcoming surveillances.
The Instrument Mechanic Department now receives weekly and monthly lists of forth-coming surveillances.
As an interim corrective action, integrated charts have been prepared for manually recording surveillance histories throughout the year in order that the allowable interval extensions can be calculated.
The monthly review which identified these interval violations will also be continued to ensure prompt correction of any errors.
Although infrequent personnel errors may still occur, their incidence should continue to be reduced to even more insig-nificant levels and the Station believes full compliance will be achieved upon completion of the software program revisions by the Computer-Systems Department.
The revisions are scheduled for completion by October 1, 1977.
Commonwealth Edison NRC Docket Nos. 50-10 50-237
, r0-249 Deficiency:
Contrary to Technical Specifications Section 6.6.B.2.b, a condition leading to a plant shutdown (on Unit 3) required by a liniting condition for operation was not reported within the required 30-day time requirement.
The Unit 3 reactor was shutdown on April 6, 1977, as a result of excessive-leakage in the primary containnent.
Discussion:
At 0035 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br /> on April 6, 1977, with the unit at approx-imately full power, the Unit 3 reactor operator received panel alarms indicating that the 3A recirculation pump seal leakage may have increased above normal; however, primary containment coolant leakage remained below the allowable limits specified in Section 3.6.D o f the Technical Specifications.
At 0235 hours0.00272 days <br />0.0653 hours <br />3.885582e-4 weeks <br />8.94175e-5 months <br />, with primary containment coolant floor drain leakage near allcaable limits, plant management initiated a controlled plant shutdown.
At 1504 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.72272e-4 months <br /> the reacter mode switch was placed in the shutdown mode and a cold shutdown operating condition was achieved at 1830 hours0.0212 days <br />0.508 hours <br />0.00303 weeks <br />6.96315e-4 months <br />.
While taking prudent action by proceeding with a plant shutdown and at approximately 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> prior to achieving cold shutdown, the allowable Technical Specification limits for primary containment coolant leakage were exceeded.
Since the reactor was in the cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of exceeding allowable primary containment coolant leakage, section 3.6.D of the Technical Specifications was complied with satisfactorily.
Corrective Action:
The Station believes that adequate corrective action was taken by plant personnel in that a reactor shutdown was initiated in advancc of exceeding Technical Specification allowable primary containment coolant leakage limits.
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Corrective Action to prevent Recurrence:
In order to prevent a recurrence of this type of noncompliance item, future reporting of similar events has been discussed within l
the Station.
Date of Full Comoliance:
The Station believes that full compliance has been ach:.eved.