ML20246J896
| ML20246J896 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/25/1989 |
| From: | Michael Ray TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-88-17, NUDOCS 8909050295 | |
| Download: ML20246J896 (3) | |
Text
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~,, ma TENNESSEE VALLEY AUTHORITY -
CHATTANOOGA. TENNESSEE 37401
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'AUS 251989 U.S. Nuclear Regulatory Commisston ATTN: Document Control Desk Washington, D.C.
20555 Gentlemen:
In the' Matter of
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Docket Nos. 50-327 Tennessee Valley Authority-
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50-328 SEQUOYAH NUCLEAR PLANT (SQN)
GENERIC LETTER 88-17, LOSS OF DECAY HEAT REMOVAL'
Reference:
.TVA letter to NRC dated February 2, 1989, "TVA's 90-Day Response to Generic Letter 88-17, Loss of Decay Heat Removal, for the Sequoyah and Hatts Bar Nuclear Plants"
-In the referenced letter, TVA committed to provide a description of the
. planned instrumentation system, including the results of the residual heat removal (RHR) alarm function evaluation, to NRC.
This submittal provides the required Information.
For reactor coolant system (RCS) level indication, the reactor vessel level indication system (RVLIS) will provide wide-range indication. An ultrasoisic level measurement system will provide a more accurate narrow-range indication
-when RCS level is in the range of the RCS hot leg pipe diameter. A 11guld level gauge will provide redundant level indication for both the wide-and narrow-range systems.
The existing RVLIS is adequate for wide-range indication to facilitate RCS drain-down.
It provides indication and trending from the top of-the reactor
'to the hot leg and from the hot leg to the vessel bottom. The water level in the reactor vessel is inferred from sensing the differential pressure, corrected for specific weight, across a transmitter.
The instrumentation in the reactor vessel has a temperature variation capability of 0 to 700 degrees Fahrenheit (F) and a pressure variation capability of 0 to 3000 pounds per square inch gauge (psig). The basic level measurement has two ranges: full range and dynamic range.
The full range is a level measurement over the full height of the reactor. vessel with all reactor coolant pumps stopped. The dynamic range channels indicate a differential pressure across the reactor vessel with reactor coolant pumps in operation.
The. ultrasonic level measurement system will provide continuous RCS water level indication as well as high-and low-level audible and visible alarms in the. main control room.
The transducer will be seismically mounted on the loop 4 hot leg near the RHR suction point and will remain in place during plant operation. This will eliminate the installation cost, personnel exposure, and reliability problems associated with repeated installations.
This discrete level' measurement device senses the level of water by means of l
horizontally propagating ultrasonic waves. The pulse can be generated and the water surface echo received by a single ultrasonic transducer coupled to the bottom of the pipe. A strap-on arrangement is being considered for the 8909050295 890825 b0 ADOCK 0500 7
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, AUS 251989 U.S. Nuclear Regulatory Commission-mounting'of th'e transducer. The holder assembly and straps are made of stainless steel,-which will maintain ~the same coefficient of thermal expansion as the pipe'and will prevent loosening with thermal. cycles. The basic components of the ultrasonic level measurement system are:
(1) the ultrasonic transducer, which acts as both a transmitter and receiver of ultrasonic waves; (2) the electronic unit, which interfaces with the transducer and provides an output proportional to the ultrasonic wave travel time in the water and steel; and (3) associated electrical cables and transducer mounting hardware.
The liquid level gauge will provide an overall indication range of 144 inches from elevation 693 feet 8 inches to elevation 705 feet 8 inches. The indication should be continuous over the span of the gauge. The gauge will be totally enclosed and fitted with a magnetic flag indication for an accurate,
. plainly visible readout. Additionally, the gauge will have legend placards mounted on one side of the gauge to provide information useful to the operator (e.g., hot leg centar11ne, vortex threshold, normal _ operating band, etc.).
The level gauge will be tapped into a thimble guide tube as the sensing point. This use of a. guide tube will eliminate gauge level errors that are due to reactor vessel differential pressure during RHR system operation.
The gauge column will be located as close as practical to the sensing point to reduce the~ length of. tubing runs. The tubing will be continuously sloped upward to provide adequate venting and to eliminate bubble entrapment.
It will be stainless steel of suitable bore and will be rigidly mounted.
The gauge will be vented to the pressurizer through appropriate valves and a flanged spool piece. The gauge column will be seismically. mounted, and the column and its associated connecting tubing would be considered permanent plant equipment. Removable spool pieces, flanges, and appropriate valves will be incorporated in the design to allow the gauge to be drained and disconnected during reactor operation at power. Materials for the gauge column, tubing, and other associated hardware will be compatible with reacter coolant chemistry requirements. The operating conditions of the gauge system will be less than 200 degrees F and less than 50 psig.
At SQN, TVA will use two existing incore thermocouple to provide continuous temperature indications. These indications are representative of the core exit conditions when the RCS is in a mid-loop condition and the reactor vessel head is located on top of the reactor vessel. Because of SQN's design, the incore thermocouple must be disconnected just prior to head removal.
These temperature indications will be visibly and audibly alarmed in the main control room either by the plant computer or a centrally located display.
.TVA has completed an evaluation of RHR parameter monitoring capabilities in the main control room. Currently, SQN has RHR pump flow rate, pump motor current, and pump discharge pressure indications. There is also an alarm for i
high RHR pump discha'rge pressure or a miniflow condition.
Past licensee event
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reports for SQN, the Control Room Design Review, and the Safety Parameter
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9 U.S.' Nuclear Regulatory Commtssion AUS 251989 l
Display System, as well as input from the Operations organization, have been evaluated. Additionally, monitoring plans for other utilities have been reviewed. It has been determined that the present monitoring capabilities of the RHR system in conjunction with the enhanced RCS level indication scheduled for implementation are adequate.
As stated above, diverse indicators and' alarms will be provided.for monitoring each RCS level indication system, and a supplemental shared two-pen recorder
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is being considered for trending.
Indications for RCS level and core temperature will be visibly and audibly alarmed in the main control room either by the plant computer or a centrally located display. RHR pump performance parameters are currently available, and a high pump discharge pressure or miniflow condition alarm is provided in the main control room.
No additional RHR indicators or alarms are planned. -
No commitments are contained in this submittal.
Please direct questions concerning this issue to Kathy S. Whitaker at (615) 843-7748.
Very truly yours.
TENNESSEE VALLEY AUTHORITY
,d Manage, Nuclear L[ censing and Regulatory Affairs cc: Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. B. A. Wilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 l
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