ML20084T425

AO 08-73:on 730806,while Analyzing in-core Scan Data from Primary Data logger,in-core Scans Discovered Improperly Updated.Caused by Failure of in-core Detector Alarm. Operators Instructed to Check Hourly Data Logger Output

ML20084T425
Person / Time
Site:	Palisades
Issue date:	08/16/1973
From:	Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-08-73, AO-8-73, NUDOCS 8306230187
Download: ML20084T425 (2)

Text

. .,

Q y$W-LYh flW/ A Y,

.e m fr Qf"e[QQ Gy l=l .

Con"'lmBTS

\

, . k i bO'.23[

8 \.\ 005)207 NZ/

hl ome.u con.,.i =* ..nnl6uicnia.n avenu.. a.a.on, uicm aan 492oi . Are. Cod. Si7 780-0S50 August 16, 1973 c

Mr. John F. O' Leary, Director Re: Docket 50-255 Directorate of Licensing License DPR-20 United States Ata=ic Energy Co= mission A0-08-73 Washington, DC 20545

Dear Mr. O' Leary:

This letter is written to report an abnormal occurrence involving the primary data logger at the Palisades Plant which was discovered on August 6, 1973.

On August 6, while enalyzing in-core scan data from the primary data logger, it was discovered that the in-core scans had not been properly updated between 3:00 PA August 3,1973 and 8:45 AM August 6. The system progres was restarted on August 6 at 8:45 AM for other reasons. This restart caused in-core scan program to start functioning properly.

Appendix B to the operating license requires the in-core detector alarms, generated by the data logger, to be properly opera-tional if the linear heat generation rate is in excess of 85 percent of the muimum allowable value. Calculations taken prior to the in-core scan failure indicated the in-core detector alarm settings were approximately 21 percent higher than obcerved linear heat generation rate, including uncertainty, engineering and augmentation factors.

During the interval when the in-core scan was not funceioning, power level and control rod position vere maintained essentially constant.

Therefore, it is not likely that the maximum allowable linear heat generation ~ rate limits were exceeded.

Section 3.11 of the Technical Specifications requires that readings be obtained for at least 10 individual detectors per quad-rant if the data logger in-core scan is not operable and power is above 75 percent rated. These readings were not obtained because the failure of the in-core scan was not detected until after it was

.again operating properly.

l To ensure a similar occurrence vill not go undetected, op-erators vill be instructed to check each hourly data logger output to verify that at least one in-core detector reading is different from the previous hour's data logger output. Hourly ta logger in-core fSNSOC?oS$88fj, g \(g con sg335ruscion / ~ s-

._. _ . --- . . _ _ _ - - - ~ - - - -

. M' e .

s' Mr. John F. O' ary, Diractor 2

l Docket 50-255 License DPR-20 A0-08-73 l

August 16, 1973 .

scan readings vary slightly at constant power levels with no control rod motion. Observation of these differences vill provide confima-tion that updating is occurring.

The primary data

• logger is provided with equipment, " watch ,

dog timer," that checks continuously to ensure that the analog scan program is executed every 30 seconds. In this particular case, the

" watchdog" did not go off because at least a portion of the scan was being done. Although the same program scans all of the analog inputs, it appears that in this case it somehow skipped or failed to save in

, memory a large block of inputs (including the in-cores). Since the program was reloaded before the problem was discovered, it is not pos-sible to locate the exact problem area; however, it is postulated that the program in cosputer memory was inadvertently changed through computer operator error, input device malfunction, or computer memory error. If the problem reoccurs it vill be noted promptly by the operator's hourly check and will be investigated in detail at that time. Operator check-ing vill continue until such time as the problem is resolved.

Yours very truly, *

'e .

RBS/ce Ralph B. Sevell Nuclear Licensing Administrator i

a

.