ML20003G497

Responds to IE Bulletin 80-17,Suppl 4, Failure of Control Rods to Insert During Scram at Bwr. Submits Monitoring Sys Description,Including Schematic of Apparatus & Associated Electronics.Provides Calibr Criteria & Data

ML20003G497
Person / Time
Site:	Cooper
Issue date:	01/27/1981
From:	Pilant J NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
IEB-80-17, LQA8100052, TAC-13212, NUDOCS 8104290676
Download: ML20003G497 (6)

Text

.

COOPER NUCLEAR STATION

' ' ' 5""

Nebraska Public Power District 9'A*e"#'o*O%f"".^11 LQA8100052 To ADM/DM8:

January 27, 1981 POR LPDR NSIC GDM/TIDO Mr. Karl.V. Seyfrit, Director ADM/RSB U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV .

9 Q 611 Ryan Plaza Drive 6 [

Suite 1000 U -

p Arlington, Texas 76011

/jpg 2 4 j

2

Subject:

Response to IE Bulletin 80-17, supplement 4 -

- u,%ge,193 '

O Failure of Control 2ods to Insert },

During a Scram at a BWR ** -E

'P

Dear Sir:

un This response is being submitted in accordance with the requirements of the subject bulletin. The areas of concern with regard to system in-sta11ation have not been a particular problem at Cooper Nuclear Station due to the design of this system and the operability checks performed after its installation.

Item 1 - Bench Test of CMS (a) System description including a schematic of the apparatus and asso-ciated electronics.

The enclosed schematic shows the apparatus and associated elec-tronics. As previously transmitted, the monitoring system at Cooper Nuclear Station is an adaptation of existing equipment on the c:arket used to measure fluid depths in open channels. Four independent sensing circuits constantly monitor the header through.

the installed sensors. The analog output is continuously displayed by local meters. The outputs to the recorder are monitored by that apparatus and the recorder will start automatically when a signal corresponding to 1.5" water level is received. The recorder is located in the control room along with an alarm that initiates after a 10 second time delay. The digital comparator initiates a local alarm after a 16 second time delay. At this point, operating procedures dictate required operator action.

E104 290(py(p

Mr. Karl V. Seyfrit January 27, 1981 Page 2.

The depth computing circuitry is all-digital logic. Each time a signal is emitted from the transducer, a digital count is begun.

When the echo return is sensed, counting stops. The resulting count corresponds to the liquid depth, normalized to full scale.

This measurement is updated every five seconds.

(b) Type of sensing device and characteristics (include response characteristics versus temperature).

The sensing circuit utilizes an ultrasonic transducer that prop-agates a sound wave through the pipe wall into the water. When the sound wave reaches the water surface, the majority of the energy is reflected back towards the transducer. The returning pulses strike the transducer and are converted back to electrical energy.

The operating frequence is 1 MHz resulting in a relatively short wave length. The short wave length gives a good echo, even with turbulent or choppy water surfaces. Reliability is further en-hanced by the short duty cycle. With the 5 microsecond transmit 7, period every five seconds, the transducer is actually operating less than one minute per year.

The measurement is affected by changes in the speed of sound in the measured liquid, the most significant factor being temperature.

The depth meter corrects for liquid temperature changes by mon-i itoring a thermistor embedded in the sonic transducer; monitoring is done between depth measurements, using the same transducer cable.

i (c) Calibration criteria, including transmission losses.

Until more operational data is obtained, an initial calibration criteria of ti" deviation in output versus water level has been adopted. This-criteria was taken into account when determining the l required action steps outlined in operation procedures.

Another concern of the NRC is transmission losses. The transducer cable is impedsuce matched which reduces transmission losses to an insignificant level.

(d) Training and testing of personnel performing the calibration test.

l Personnel performing the calibration test and the installation were

given guidance and instruction by the vendor. No specific testing

! of personnel is required by the vendor to be able to perform such l calibration.

I t

I

Mr. Karl V. Seyfrit January 27, 1981 Page 3.

Extensive testing was performed prior to installation 'tsing a mock-up of the header. At that time, installation procedures and calibration procedures were verified. As a result of these tests, the acceptance criteria for installation was generated. Tests included simulating various flows, within the limitations of the mock-ups, to verify no loss of signal, determining maximum variation of transducer orientation to the pipe before signal loss would occur, and verification of a linear output by the sensing circuit.

Item 2 - Ooerabilitv Test of CMS An operability test was performed af ter installation of the CMS on the Scram Discharge Header during a plant outage. This test was performed after calibration of the individual sensing circuits. The vendor's recommendation did not include an independent verification measurement.

. The design of the system is such that as long as the signal is received, the indication will be correct. This is based on the above discussion on the design of the system.

The test consisted of filling the Scram Discharge Header and assuring a response was received from all transducers. Level indication wac con-sistent and all alarm functions and the recorder checked out satisfac-torily. Additional testing as outlined by Item 4 of the subject bul-letin, will be performed during our next scheduled. outage slated for late April 1981.

Item 3 - Interim Manual surveillance Inasmuch as the operability test, noted in Item 2, was completed to the satisfaction of the vendor, =anual surveillance will not be performed.

l Item 4 - Full test of CMS to be conducted during a planned outage As noted in Item 2, a full test of the CMS will be performed during our scheduled April outage. This test will meet the requirements of Item 4 We would like to express our concern as to whether it is realistic to expect a consistent and reliable depth indication during a full scram.

l The original intent of the system was to monitor header level to provide i

sufficient warning of loss of free volume. This loss of free volume could only be due to scram outlet valve luakage or failure, that would exceed the capacity of the header's ability to drain. Tests run at

! Cooper Nuclear Station as a result of IE Bulletin 80-17 indicate the

=ax1=u= flow rate to be approximately 60 gym, this was from a header with 125 psig pressure after the scram test. This would indicate that

i l

Mr. Karl V. Seyfrit January 27, 1981 Page 4.

during operation, flow in the header would be -small resulting in an insignificant amount of turbulence as compared with that associated with full scram testing. Consider 1ug the above, it is realistic to expect a momentary loss of signal due to the turbulence and other phenomena of a full scram.

Itens 5 and 6 - Operability of CMS during reactor operation and operating procedures Surveillance procedures have been prepared to assure continued oper-ability of the CMS. These procedures censist of the following:

(a) Quarterly functional check of the sensing circuit and alarm func-tion using a calibration standard and prior to startup after a scras.

(b) Quarterly visual inspection of the transducer mountings.

(c) Annual calibration check of the sensing circuit and alarm functions using the scram discharge header as the source of :he water level.

Calibration will consist of an independent verification of the instrument output. This will be performed during our scheduled refueling outage. This test will not be performed se=1 annually as reques:ed by Ite= 5 of the subject bulletin for the following reasons:

1) Testing shows scras testing of individual rods will not put sufficient amounts of water into the header to allow neas-uresent.

2) Testing also shows the duration of ti=e the water is in the header is very short making =anual verification nex to in-possible.

3) Present scram testing of individual control rods is done in conjunction with rod swaps to min 4m4:e the power shocks the

! fuel is subjected :o as a result of control rod movenents.

The locations of the control rods which are scrammed as par:

of the rod swap control rod =anuevers are not necessarily the same control rod 1ccations that vould persi: the injection of sufficient amounts of water to the individual headers to

, per=it an adequate level seasurement. It is possible to scram

=ultiple rods so as :o sari =1:e the possibility of obtaining sufficient water level in the headers to permit measurements

Mr. Karl V. Seyfrit January 27, 1981 Page 5.

for surveillance purposes. This, however, has some poten-tially severe drawbacks.in regards to potential fuel damage.

The control rods scrammed in as part of the rod swap are carefully selected considering potential power shocks to the fuel and to limit the control rod movements to only those control rod movements that are absolutely necessary to swap from one control rod sequence to another. Selecting control rods to be scrammed solely for the purpose of measuring water level in the headers would violate the above logical selection of control rods. Additionally, if the control rods are not scrammed in based upon the above criteria, the possibility exists that a limiting control rod pattern might be developed during the subsequent withdrawal of the scrammed control rods.

For the above reasons, multiple scram testing of rods for verification of CMS operability will not be performed.

(d) A functional check will be performed prior to startup as described in -(a) above when maintenance activities in the area of the CMS would have affected its operability.

The limiting conditions for operation as defined in Item 5 of the sub-ject bulletin will be adhered to except for the use of a hand held UT device for manual checks of the SDV. In lieu of this method, an: air test, previously approved for use by the NRC, will be used to verify that there isn't a significant amount of water in the SDV.

Approximately 30 manhours were expended in the preparation of this report.

If there are any additional questions concerning the above statements, please contact the originator.

Sincerely, M

J. M. Pilant Director of Licensing and Quality Assurance JMP:PFD:cg Attach.

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