ML20045B633
| ML20045B633 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/07/1993 |
| From: | Denton R BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-88-17, TAC-M69731, NUDOCS 9306180182 | |
| Download: ML20045B633 (3) | |
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/~ BALTIMORE GAS AND l
ELECTRIC 1650 CALVERT CLIFFS PARKWAY. LUSBY, MARYLAND 20657-4702 ROBcRT E. DENTON Vic[ PRE $lDENT June 7,1993 NUCLEAR ENERGY (410) 260 4e55 U. S. Nuclear Regulatory Commission Washington,DC 20555 A'ITENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No. 2; Docket No. 50-318 Generic Letter 88-17, " Lass of Decay Heat Removal" Change to Completion Date for Narrow Rance Level Instrument Modification fTAC No. 69731)
REFERENCES:
(a)
Letter from Mr. G. C. Creel (BG&E) to NRC Document Control Desk, dated June 11, 1991, Generic Letter 88-17, " Loss of Decay Heat Removal" (b)
Letter from Mr. D. G. Mcdonald, Jr. (NRC) to Mr. G. C. Creel (BG&E), dated May 28, 1991, Programmed Enhancements For Generic Letter 88-17," Lass of Decay Heat Removal" Gentlemen:
In Reference (a), we described our plans to install new wide-range and narrow-range RCS level instruments to provide continuous control room indication of RCS level during shutdown operations invohing reduced reactor coolant inventory. For Unit 2, we committed to install both of these instruments during the spring 1993 refueling outage, which is currently ongoing. In Refcance (b),
you requested written notification of any significant schedule change to the estimated completion date for hardware modifications related to Generic Letter 88-17. 'Ihe purpose of this letter is to inform you that, due to hardware problems, we have not been successfulin placing the narrow-range instrument in service. As a result, we are deferring completion of this item.
As you are aware, the wide-range instrument consists of a stilling well with heated and unheated continuous resistance temperature detectors (RTDs) with a measurement range from approximately eleven feet above the reactor vessel flange down to approximately six inches below the bottom of the hot leg. A gauge glass is provided in parallel with the stilling well inside containment to provide local indication of water level.
The narrow-range instrument consists of' an ultrasonic system with a transducer installed on the bottom of an RCS hot-leg pipe. The range of measurement is from the top of the hot leg down to approximately four inches above the bottom of the hot leg.
These instruments complement the already existing refueling pool level indicator, w hich functions to provide water levelindication down to the bottom of a hot leg when the reactor vessel head is vented, and the Reactor Vessel Level Monitoring System (RVLMS), which functions to provide an
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Document Control Desk June 7,1993 Page 2 approximate indication oflevel when the reactor vessel head is installed. Additionally, a tygon tube level indication is connected to the same tap as the Refueling Level Indicator and provides local (in-containment) indication of RCS level. Permanent instrument tubing is installed from the RCS to the containment wall where tygon tubing is fastened and elevations are marked.
Following narrow-range instrument installation and during acceptance testing, random noise developed and testing was stopped. Troubleshooting was performed, but we were not successful in identifying the source of the noise. A similar instrument is operating satisfactorily on Unit 1.
Troubleshooting continued until this activity began to adversely impact the outage schedule (reflooding the refueling pool in preparation for refueling the reactor). Troubleshooting was terminated and the refueling pool was filled. Our decision to defer placing the narrow-range instrument in service is based on the following:
a.
The instrument would not be utilized during the remainder of this outage since no additional mid-loop operations were planned. 'Ihe instrument would not be useful until the next outage involving mid. loop operations.
b.
This instrument is only one of several independent and diverse means for monitoring level as we approach and enter mid-loop operations. Other means include the RVLMS, the reactor vessel refueling pool level indication, and the new wide-range reactor vessel level instrument.
The potential economic costs of extending the outage exclusively to troubleshoot and repair c.
this instrument, whose near-term use was not expected, was not justified in view of the fact that' existing instrumentation is sufiicient to assure safe operations with reduced RCS inventory.
When the decision was made, the problem had been narrowed down to the signal processor and/or a possible grounding or shielding problem. Subsequently, the processor was replaced and the noise was eliminated. Even though the problem was corrected, the acceptance test will not be completed this outage. We were able to perform some testing after the signal processor was replaced. From this testing, we can conclude that the system should perform adequately from the top of the hot leg to approximately the hot leg centerline. However, the limiting factor for completing all testing is that the narrow-range system is an ultrasonic device and requires a water surface in the pipe for the system to operate. Therefore, we will complete the acceptance test of the narrow range instrument during the next outage of sufficient duration that involves entry into mid-loop operations with levels within the measurement range of this instrument.
Should you have any questions regarding this matter, we will be pleased to discuss them with you.
Very trulyyours, i
N RED /JMO/jmo/bjd/dlm
Document Control Desk June 7,1993 -
Pa.c3 D. A. Brune, Esquire cc:
J. E. Silberg, Esquire R. A. Capra, NRC D. G. Mcdonald, Jr., NRC T. T. Martin, NRC P. R. Wilson, NRC R. I. McLean, DNR J. II. Walter, PSC l
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