ML17252A589

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Ack Receipt of Proposing Deletion of Manual Trending of APRM Errors Per Commitment to 1974 Violation. Concurs W/Proposal
ML17252A589
Person / Time
Site: Dresden  Constellation icon.png
Issue date: 08/10/1988
From: Wright G
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To: Reed C
COMMONWEALTH EDISON CO.
References
NUDOCS 8808160300
Download: ML17252A589 (3)
v • d • e


Text

Docket No. 50-237 Docket No. 50-249 Commonwealth Edison Company ATTN:

Mr. Cordell Reed Senior Vice President Po~t Office Box 767 Chicago, IL 60690

  • Gentlemen:.. *..

"U.G'.' 1 o 1988.

~

.;c I Thank you for your letter 6f August 3, 1988 proposing ~eletion of manual trending of APRM errors which was a commitment to a 1974 Notice of Violation.

We have reviewed the letter, including the "Bases for Deletion of APRM Drift Trending," and concur with your proposal.

Attachment:

Bases For Deletion of APRM Drift Trend_i ng cc w/attachment:

B. L. Siegel, Project Manager, NRR

.s~. G.- *DuPont, SRI..

  • Dresden

.PaDaRos160300 *esos1*0 Q

ADQC1.1 "' 05000237 PNU Sincerely,

.O~~~~.~~~.~L~~-~:. :~~.FEOtrnEt C. WRIGH.t

  • -***-*-*----...... ~*.

Geoffrey C. Wright, Chief Operations Branch

ATl'Atmmfl BASES FOR DELETION OF APBM DRIFT TRENDING Based on the results of AEC inspections conducted in October, 1973, the AEC issued a Notice of Violation to Commonwealth Edison citing activities at Dresden Station (Reference (a)).

Among the activities considered to be in

.. violation of the Technica_l Sp4!cifications was. the practice of allowing Average Poller Range Moliito*r (APRM) Gei'n** Adjustment *Factors (GAF) to _drift until. the

  • APRM's were reading up to 8' non-conservative.

This non-conservatism in APRM readings would have resulted in.the scram and rod-block functions being initi-ated at a non-conservative power level.

In a March, 1974 letter (Reference (b)), Commonwealth Edison committed to several corrective actions to prevent recurrence of the violation.

These

  • corrective actions included the following:

L Revision. of the inst.rwnent calibration procedure _to reduce. APRM rod block and scram trip points by 3' t~ provide margin for variation in APRM accuracy. "(DIS 700-7, APRM Flow Biased Scram; Rod Block, and Downscale Calibration.)

  • 2.

Revision of operating procedures to include:

(a) *A schedule of daily surveillance of the GAF by the Nuclear Station Operator (NSO).

(DOS 500-6, APRM Gain Adjustment)'

(b). An action level. of 2' APRM.error for the NSO and Shift Engineer

  • Surveillance.

(DOS 500-6,* APRM Gain Adjustment.)

.3.

Incorporation of APRM error. trending into weekly Technical Support Surveillance.

(DTS 700-1, Technical Staff Surveillance of Unit 2/3

.

... -'.,..,,... *-*........ _....... ~is _,\\f~luat_i_qn _d,iscuss.e~. the bases for* the deletion of *Item 3, APRM
    • ~ * *., *.*:** -:~rro*r. -~~e.~11~*I19"~'.:**trom~.*~e*
  • 1ie*etii!*:-recl1htc8i.. s*~i?p*o*~*~--~ siir_~~i1tl!nc:~_ei*~*:*:'*....,.,: -* **r...... *-****. ***

At the time of the 1973 ~i~i.atio~,*

  • wo,:,.ld drift significantly at constant power.

The noticable drift in APRM signals has been attdbuted to a* *spike in one or more of* the Local Power* Range Monitor (LPRM) signals feeding the corresponding APRM.

The spike in the LPRM chamber and LPRM cable. -The effects of this LPRM fail~re mode have been minimized by improving the LPRM design. 'Recent plots of APRM errors confirm that improved LPRM designs have reduced the frequency and severity of APRM drifting.

With no specific trend detectable, weekly trending of APRM errors provides little information in the determination or prevention of APRM drifting.

  • .. *.~: ;.

2 -

'l'he primary intent of the.corrective actions was to prevent a recurrence of APRM Gain Adjustment Factors (AGAF's) that would result in non-conservative scram and rod block functions.

As discussed above, the third corrective action, APRM error trending, has become ineffective as a method for preventing recurrence of non-conservative AGAF's.

However, as a supplement to the corrective actions delineated in the 1974 commitment, Dresden now has a process computer progream (OD-76) which calculates AGAF's every 5 minutes for all 6 APRM's.

When the calculated AGAF.ezceeds 2' of the nominal value a

  • mess~ge is, i:outed to.. the alarm typer and t,o the unit.NSO' s alarm CRT stating that the AGAF action llmit has been.-esceeded*. 'Tiiis aiam 1fhen coupled with an operating procedure mentioned above, helps ensure that action will be taken to bring the AGAF's back into specifications.

This methodology will identify drifting APRM's regardless of the cause (LPRM failure, zenon redistribution, etc.).

Today*, APRM drifts at constant power with equilibrium zenon are relatively rare and primarily due to the component LPRM's drifting.

Trending of these APRM drifts has not revealed any discernable trend.

However, a detect.ion. of the. LPRM drifts has been facilitated by. the implementation of a drift diagnostic moqule, in the.POWERPLEX:core.monitoring system that provides messages when LPRM. drifts are detected *. These messages are printed on the control room typer for the Prime computer.

In conclusion, of the three corrective actions specified in Reference (b), the only action being proposed for deletion is the weekly trending of APRM errors.

The deletion of trending of APRM is justified by the following arquments:

1.

No trend is detectable in APRM errors following the replacement

  • of old style LPRM's with a new improved LPRM design which has greatly reduced the number and magnitude of LPRM drifts.
2.

The detection of APRM errors has been aided by the addition of a.process*computer*pi:ogram.which calculates A~AF's every.

5 minut~s and alarms if the nominal value is ezceeded by2,.

,,.... *.~*""**.. ;

n*;

  • .... **:."*.. ?,..... /:*.. :**.-*.***.. ** 1:

~*

  • ~:* *.,', ** :. ** '._.* ** -:~.***;.,,*.'-,:~::*:~."':.~:': ** ** ** **.*.~~.** :: ** ~.:*'.>'"**.~*'.,f.,.:...... :;:... ;_;.,.*t***.,, <*
  • 3.

The detectiQn of LPRM drifts which contribute* to *APRM. drifts..

  • 1186 *. bee~:... ai*d~C!* by,.the* aCiaidon***.e:>! *a PcMERPt£x* modure* which..
  • prints a message*upon detecting LPRM drifts.

Based upon the above review, CECo believes that relief from the AGAF trending is appropriate and will allow more productive utilization of the site nuclear engineering resources.

4975K

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