ML20202H449
| ML20202H449 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 12/04/1997 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-88-17, NUDOCS 9712100285 | |
| Download: ML20202H449 (2) | |
Text
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C H c a.rs li. Octet:
Itzhimore Gas r.nd filectric Compmy Vice President Cah en ClifIs Nuclear Power Plant Nutleur EnerFy 1650 Calvert Clif h l'arLway 1.usby, Mary land 20657 410 495-4455 December 4,1997 U. S. Nucfear Regulatory Commission Washington, DC 20555 A'ITENTION:
Document Control Desk SUILIECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50 318 Chance in Method of Reactor Coolant System Ltvel Detection
REFERENCE:
(a)
Letter from G. C. Creel (BGE) to Document Control Desk (NRC), dated June 11,1991, Generic Letter 88-17. " Loss of Decay lleat Removal" (TAC Nos. 69730 and 69731)
Generic Letter 88-17 put fonvard the Nuclear Regulatory Commission position that the Reactor Coolant System (RCS) level had to be monitored during shutdown conditions and that two independent level I
indications must be provided. Optimally, the level indications were to be tapped into the RCS at different points to ensure that blockage of a piping penetration did not affect both instruments. The l
generic letter also allowed, as an alternative, the use of a common tap if provisions were made to detect blockage of the tap.
in Reference (a), Baltimore Gas and Electric Company described compliance with the RCS level M-monitoring requirements of Generic Letter 8817, in that letter, we committed to providing a wide-range h
level detector connected to a tap on the bottom of an RCS hot-leg and an ultrcsonic transmitter installed g'
on the bottom of an RCS hot-leg as the narrow range detector. Both of these instruments were gg' subsequently put into service. Due to the regulatory sensitivity concerning shutdown operations, we feel g
it is prudent to notify Nuclear Regulatory Commission that we have changed the commitment in g
Reference (a) by adding the refueling level indicator to the instruments used to detect RCS level during g,
shutdown conditions.
The wide range level detector is connected to a tap on the bottom of an RCS hot leg. The instrument consists of a stilling well with heated and unheated continuous resistance temperature detector probes.
The range of the wide range level detector is from the bottom of the hot leg to above the reactor vessel flange.
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The ultrasonic transmitter is attached to the bottom of an RCS hot leg on the outside of the pipe. The b
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transmitter emits a signal up through the RCS water. The signal reflects off the surface of the water and returns to the transmitter. The time between the emission of the signal and the retern indicates the height 9712100295 971204 PDR ADOCK 05000317 P
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Document Control Desk December 4,1997 Page 2 of the water surface above the bottom of thn hot leg. He range of the level indication is from the top of the hot leg to approximately four inches from the bottom of the hot leg. Because the ultrasonic transmitter only measures the depth of water in the hot leg, it is only used when the hot leg is less than full.
la addition to the wide-range level detector and the ultrasonic transmitter used to comply with Generic Letter 88 :",.. refueling level indicator is used to show the depth of water in the refueling pool. He refueling level indicator is attached to the same hot leg tap as the wide range level detector. It uses a differential pressure sensor to measure the height of water above the bottom of the hot leg. Because the refueling pool is usually Ulled to a level above the reactor vessel Cange, and the instrument is tapped off of the bottom of the hot leg the range of the refueling level indicator includes the range of both of the other instruments. The refueling level indicator has been verified to meet all the requirements for reduced inventory RCS level indication specified by Generic Letter 88 17.
In conditions of high flow rates with the hot leg less than full, the ultrasonic transmitter sometimes gives I
inaccurate readings. liigh flow rate on shutdown cooling is needed when the unit is at reduced inventory
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and a high level of decay heat is present. This is an infrequent occurrence. The reason for the inaccurate
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readings is that high flow rate produces laminar disturbances that give brief false indications of RCS level. During these occasions, the true level is always known because the wide range level detector is not affected by the high flow disturbances. The refueling level indicator, like the wide-range level detector, uses water head pressure as opposed to the ultrasonic transmitter's dependence on sound reflected off the water's surface so the high flow rate disturbances do not affect the reading As noted above, the refueling level indicator is installed on the same RCS hot leg tap as the wide-range level detector. Generic Letter 88-17 allows use of two instruments on the same tap if the tap can be checked for blockage. The common tap for the wide-range level detector and the refueling level indicator is provided with a drain. The dral. will be opened to assure there is flow prior to relying on the refueling level indicator. Continuing flew with no decrease in water in the indicators will provide assurance that the tap is not blocked.
Therefore, since the refueling level indicator covers the same range as the wide range detector and the ultrasonic transmitter, and the refueling level indicator performs more consistently under high flow rate conditions, Baltimore Gas and Electric Company has changed the commitment for measurement of RCS level during shutdown. This way, at least two instruments will be available under all RCS level and flow conditions.
Should you have questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours,
/
CllC/EMT/bjd cc:
R. S. Fleishman, Esquire
- 11. J. Miller, NRC J. E. Silberg, Esquire Resident inspector, NRC Director, Project Directorate 1 1, NRC R. L McLean, DNR A. W. Dromerick, NRC J. II. Walter, PSC I
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