ML20005A679
| ML20005A679 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1981 |
| From: | Case E Office of Nuclear Reactor Regulation |
| To: | Zach J AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML20005A678 | List: |
| References | |
| NUDOCS 8106300599 | |
| Download: ML20005A679 (3) | |
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UNITEO STATES NUCLEAR REGULATORY COMMisslON
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t!r. James J. Zach 2731 - 42 Street Two Rivers, tlisconsin 54241
Dear !!r. Zach:
Your letter to Chairman Hendrie dated !! arch 30, 1978, which expressed a belief that reports by power reartor licensees of high coolant activity or instrument setpoint drift are nuisance recorts, was referred to me
-for response.
You also suggested that the fluclear Regulatory Commission (i4RC) should evaluate these reports and perhaps delete the reautrements for them.
Requirements for licensees to report infonnation to the NPC are, as you know, contained in Title 10 of the Code of Federal Requiations onn in the facility license (usually in the apoended Technical Specifications).
Information submitted by licensees pursuant to these requirements is reviewed and its usefulness is periodically evaluated. At the present time, we are evaluating all required reports and records and may codify our report reouirements as a result of this evaluation.
tle do not agree with_ you that the two types of reports you describe as nuisance reports should be deleted at this time.
The concentration of radioactive iodine in the coolant is of safety significance. Experience has shown that changes in power level, not necessarily associated w.'th shutdown, can cause a significant increase in the measured concentration of iodine activity. Based on measurements reported to date, these concentrations have been low enough to permit the plant to continut.
operating safely during these temporary increases in coolant activity.
However, we rely upon the coolant activity as stated in some Technical Specifications to remain below conservatively established limits to assure that potential exposures to the public due to a costulateo steam line failure or steam generator tube failure will be within apprcoriate exposure guidelines. Contrary to this experience, sorce licensees and nuclear steam supoly system ver.dcrs believe that the lii.iits we have set are too restrictive and may affe.ct plant availability.
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i1r. -James J. Zacn The surveillance requirements and reporting requirements are necessary to provide us with an adequate data base to detemine whether the existing limits should be relaxed or tightened.
The surveillance data we have seen to date indicates that more frequent sampling during a spike may be necessary to determine the actual increase in iodine levels. Also, monitoring coolant activity, with a report whenaver an activity limit is exceeded, is one of the few techniques available to detect possible core degradation during plant operation.
In view of the above, we believe it is prudent to continue case-oy-case reporting of specific events to detemine that no safety hazard existed and that no corrective action was required for each case where the Technical Specification limit for Iodine activity has been exceeded.
With respect to your second area of concern, we agree with your observation that a large number of licensee event recoets involve instrument drift.. In fact,
.tpoint drift is one of the largest sources of reportable occurrences. He have been encouraging licensees and nuclear vendors to provide error analyses rslated to trip settings.
Such analyses would include detft and all other significant factors of instrumentation bias and imprecision; instrument drift, hwever, apoears to be an overriding factor.
He believe that such error analyses coula provide a better basis for establishing with greater confidence an aoprooriate oistribution of the spread between nomal operation and trip seti.irg and the spread between the trip setting ano the Technical Specification limit.
In some cases, to minimize unwanted trips, licensees have selected trip setooints nearly coincident with the Technical Specification setpoint limit. While this orovides least risk of an unwanted trip, in many cases it has not provided adequate scread between the setting and the Technical Specifications limit.
Thus, when the instrument is checked, the setting has actually drifted beyonc the allowed limit and a violation of the Technical Scecifications has occurred.
In your letter you state that when a setpoint drift exists there are "usually two other channels" that would have r,erformed satisfactorily.
It is important that there be a high degree vf assurance that both of these "two other channels" are functioning properly (not out of
' limits because of drift or failed because of an unrelated cause) to T
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!!r. James J. Zach have assurance that the protection to be provided by the redundant instruments is not lost. Therefore, knowing the cause or causes of the excessive in'trument drift and whether one channel or more than one channel is affected, is important.
If the frequency of unacceotable instrument drift occurrences is to be reduced, it must be accomplished through corrective actions (change allocation of spread, reduce drift, increase frequency of checking setpoint or some combination of these).
It will not be corrected by eliminating the reouf rement to report violations of Technical Specification safety system limits.
We hope you find the above discussion infonnative. We also are enclosing for your infonration, selected pages taken from our
" Nuclear Power Plant Operating Experience" HUREG-0366 which describes some of the NRC staff's asessment of infonnation being obtained from licensee event reports.
Sincerely,
,Q l..
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A Edson G. Case, Acting Director Office of Nuclear Reactor Regulation
Enclosure:
Pages from NUREG-0366 i
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