ML19350C199

Discusses Calibr of Regulating Control Rod for Core VI & Safety Amplifier Response to Noise Transients.Calibr Performed on 810119 Due to Extended Period of Maint.On 810130,two Safety Control Rods Scrammed

ML19350C199
Person / Time
Site:	Texas A&M University, 05000128
Issue date:	02/05/1981
From:	Feltz D TEXAS A&M UNIV., COLLEGE STATION, TX
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
NUDOCS 8103310542
Download: ML19350C199 (2)

Text

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TEXAS ENGIN E ERING EXPE RI.\t ENT STATION THE TEXAS A&M UNIVERSITY SYSTEM

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CCU.EGE STATICN. TEXAS 77843 f"

3 February 1981

~M i NUCLEAR SCIENCE CENTER 713/845-%

qh 3 ' g, g l ! S, f Mr. Kari V. Seyfrit /S gf [(~f('rlt

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.U.S. Nuclear Regulatory Commission fy ,,,,

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611 Ryan Plaza Drive, Suite 1000 h 3 x N1m.'-! .

Arlington, Texas' 76012- $$%

Dear Mr.'Seyfrit:

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Nufr-9' ois v The following-information-is provided in reference to two. items that oc e

. discussed by telephone with your of fice. The first was a report to Mr.

Aneshansley on.1-22-81 concerning calibration of the NSCR regulating rod.

The second was a report to Mr. Madsen on 2-2-81 concerning characteristics of the NSCR safety amplifier when a detector experiences high voltage arcing.

The findings are not considered by the staff of the'NSC to be reportable occurrences but we do want to update youlon'our evaluations, actions and results'.

Calibration of the'Re2ulating Control Rod'for Core VI-

' Annual reactor =aintenance of the NSCR is sche'duled, each January and calibration

.of Core VI control rods were scheduled -to be performed within- a three or four week period.- Due to our operating schedule it was.necessary-to schedule Fridays and'in some cases Monday mornings'for reactor maintenance. The Tech Spec's state that:all rods will be calibrated at one year intervals but. not to exceed

14. months. Due to this extended-period of maintenance the regulat'ing rod was

calibrated:on'l-19-81. The previous: calibration was performed on ll-12-79.

,This raises'a question-ofJ he t interpretation'of-the'14' month interval for L

, control' rod. calibration. It is~our-interpretation that-calibration of.'the regulating rod'within -the' month of lJanary (the.14th month) satisfies the

- .intentiof-the Tech Spec'.s. ' All other control rods"were calibrated within the -

-one year. period. The regulating rod calibration of 1-19-Sl~resulted in a-total reactivity. worth of'44 centsias compared to a value of 48 cents obtained'

• on-11-12-79. .The

NSC will establish a program to. review-reactor maintenance

'on' a- quarterly " basis - to insure reactor maintenance is performed prior to dead-

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line dates.

M, o.-

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T ~ RESEARCH AND DEVELOPMENT FOR MANKIND

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, lir. Karl V. Seyfrit Page 2 Safety Amplifier Response to Noise Transients on 1-30-81 during operation of the NSCR at a power level of 300 Kw a loss of detector high voltage and channel 1 high power indication were received on the safety amplifier resulting in the scram of two safety control rods. The remaining two safety control rods did not scram. Also there was no safety amplifier scram indication on the reactor console panalarm. All other power measuring channels indicated there was no change in reactor power just prior to the scram. The cause for these events was found to be noise transients introduced by high vcitage arcing of the channel 1 detector. This was verified by switching the inputs of channel 1 and channel 2 detectors resulting in the transfer of the problem to channel 2. The instrument response raises two questions:

1. Why did only two control rods scram?

2. Why was there no safety amplifier scram indication on tne reactor console panalarm?

The safety amplifier circuitry was studied to determine the response to a noise transient introduced by detector high voltage arcing. The high voltage and high power scram alarms are monitored by SCR circuits that respond to very short signal durations. The transient signals produced these alarm indications. The control rod scram circuit involves mechanical relays that due to their time response did not latch during the transient signal. However, during the transient there was a momentary reduction in magnet current suf ficient to drop the two rods. The safety evaluation conducted by the NSC staff indicates there was not a f ailure of the safety amplifier and there was redundant monitoring by safety channel 2 in the event a power increase occurred. As stated earlier other safety measuring channels indicated there was no reactor power increase just prior to the scram. The review of the safety amplifier circuitry and functions will be presented by lecture to the NSCR operations staff to insure adequate understanding of its design performance.

Sincerely,

,- *ys**

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D. E. Felti '-

Associate Director DEF/ym cc: Dr. Robert R. Berg,. Chairman Reactor Safety Board

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