ML20046C871
| ML20046C871 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/09/1993 |
| From: | Fenech R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9308120342 | |
| Download: ML20046C871 (8) | |
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rennessee Vaney Authonty, Post Ofhte Box 2000, Soddy Daisy, Te itessee 37379 2000 Roben A. Fenech Wr,.e President. Saquoyah Nuclear Plant August 9,.1993 I
U.S. Nuclear Regulatory Commission 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 i
SEQUOYAH NUCLEAR PLANT (SQN) - USE OF DATA LOGGER.FOR RESISTANCE i
TEMPERATURE DETECTOR (RTD). CALIBRATIONS This letter provides NRC with additional information on the use.of a single data logger connected to.the four protection sets for reactor coolant system resistance temperature detector (RTD) calibrations.-'A concern was expressed with this process based on the possibility that sufficient isolation between the protection sets may not exist. NRC.
representatives' Jerry Mauck and' Paul Loeser met with Westinghouse'
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Electric ~ Corporation and TVA personnel at the Westinghouse Process Controls division offices in Pittsburgh, Pennsylvania on January 26, 1993, to discuss ~this concern. As a result of.this meeting, NRC requested that TVA formally' submit the information discussed regarding
.the isolation ~ capabilities of:the Eagle 21 system that' supports the acceptable isolation of protection sets during the RTD c&librations. The enclosure to this letter provides.the requested information.
If you'have any questions concerning the enclosed information, ple'ase contact Keith C. Weller at (615) 843-7527.
I Sincerely, 1
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1 Robert.A; Fenech j
Enclosure.
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'U.S. Nuclear Regulatory Commission Page 2 August 9, 1993 Enclosure cc (Enclosure):
Mr. D. E. LaBarge, Project Manager
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U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike
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Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee. 37379-3624 r
J Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta. Street, NW, Suite 2900 Atlanta, Georgia' 30323-0199 P
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1 Enclosure EVALUATION OF DATA LOGGER USE AT SEQUOYAH NUCLEAR PLANT FOR RESISTANCE TEMPERATURE DETECTOR CALIBRATIONS 1
4 Sequoyah performs a reactor coolant system (RCS) resistance temperature detector (RTD) cross-calibration test in Modes 3 and 4 during unit heatup after refueling outages. This test is accomplished by connecting a data logger to the field terminals of the Eagle 21 process protection system.
The data logger is connected to all four protection channel sets at the same time.
Because the data logger is not a qualified isolator, a concern has been raised that the protection channel set independence, as required by Institute of Electrical and Electronic Engineers (IEEE)
Standard-279, IEEE Standard-338, and Regulatory Guide 1.118, may be violated by this test configuration.
The RTD resistance measurements are made by measuring the voltage across the RTD (VRTD) at the field terminal blocks using the data logger and by measuring the RID excitation current (IRTD) at the Eagle 21 test panel using a digital multimeter..The VRTD measurements are made with the RTD connected to the Eagle RTD input (ERI) circuit board.
The data logger is powered f rom 120-volt alternating current (VAC) that is procedurally controlled and does not generate any internal voltages larger than 120 VAC.
Therefore, the worst-case postulated fault that the data logger could inject into the Eagle 21 System, would be a 120-VAC (nominal value) fault in either the common mode or the transverse mode inputting simultaneously into the RCS RTD channels in all four protection sets.
Sequoyah does not plan to use the data logger to obtain IRTD readings.
i Instead, the IRTD tcensurements are taken with a digital multimeter at the I
beginning of the test and reverified at the end of the test.
l The RTD inputs monitored as part of RTD cross-calibration are inputs to the overpower and overtemperature protection function. This function is not needed during Modes 3 and 4 when the test is being performed.
The steam generator lo-lo level trip time delay function also monitors the same RTD inputs. Trip time delay is procedurally set to zero before the stnrt of the test to eliminate any potential adverse impacts during calibration. The remaining concern is that other instrument loops residing in the same rack, which are needed to be operational in Modes 3 and 4. may be adversely affected by the data-logger fault.
The ERI board acts as a qualified isolator in this configuration. A simultaneous 120-VAC fault into all RTD inputs under test will not affect other instrument loops residing in the same rack. Also, the ERI board will withstand a 120-VAC fault without damage. The following paragraphs describe analysis and testing that support these statements.
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- The ERI board is designed to withstand a 125-volt direct current (VDC) or 125-VAC fault applied at the field terminals (VRTD and IRTD) continuously.
without damage. Westinghouse Electric Corporation has performed testing,
" Hardware Verification Test for Eagle Series RTD Input Board," ES-6604, Revision 1, dated July 6, 1992, that proves this capability.
This documentation-is Westinghouse Proprietary Class 2 and has not.been submitted to NRC; however, the applicable portions.have been summarized in the following discussions. The RTD voltage input circuitry for each channel is independent, including the power supply as shown in Figure 1.
The RTD excitation current circuitry for each channel is conpletely independent as shown in Figure 2.
Figures 3 and 4 show the test connections for the tests performed by Westinghouse.
The ERI board uses an Analog Devices 289 isolation amplifier (see Figure 1) to isolate the field signal from the microprocessor. This device is the same device that was qualified as an isolator as part of the Appendix R current-loop input and RTD input boards for the Qualified Display Processing System (QDPS) installed at South Texas Project.
These tests are documented in Westinghouse Commercial Atomic Power (WCAP) 11341, dated November 1986 that was submitted to NRC as part of the QDPS licensing process.
Fault voltages of 250 VDC and 580 VAC were applied to the Appendix R boards. These tests further support the isolation capabilities of the ERI board.
Thus, a 120-VAC fault applied simultaneously to all four channel sets will only affect the RTD inputs being faulted. All other' functions in the rack will remain fully operational. During the final RID readings in Mode 3, an overlap channel check will be performed between the data logger and the Eagle 21 man' machine interface (MMI) terminal ~.
This test will confirm output temperature data is consistent between the data logger and Eagle-21 software. As a verification check after the final readings are taken in Mode 3 and disconnecting the data logger test' leads from the protection sets, a channel check will be performed by comparing temperature readings taken f rom the Eagle 21 MMI terminal. This will ensure that the data logger has not damaged the RTD or the ERI input circuitry.
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( TEST PANEL VRTD DATA l
LOGCER MONITORING l
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AMPLIFIER
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O REPRESENTS FIELD TERMINALS SWC REPRESENTS SURGE WITH STAND CIRCUITRY NOTES:
- 1. EACH RTD INPUT VOLTAGE IS MONITORED BY A SEPARATE ISOLATED CIRCUIT.
2.
+/- 15V IS SUPPLIED BY SEPARATE ISOLATED POWER SUPPLIES.
4.
ANALOG DEVICES 289. ISOLATION AMPLIFIER ISOLATION RATED VOLTAGE IS 2500 VRMS AND ISOLATION IMPEDANCE ARE SXIOIO OHMS AND 20 PICOFARADS.
FIGURE I
VRTD MONITORING SIMPLIFIED SCHEMATIC ERI VOLTAGE ~ INPUT CIRCUIT
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O REPRESENTS FIELD TERMINALS SWC REPRESENTS SURGE WITH STAND CIRCUITRY l
NOTES:
- 1. EACH RTD INPUT VOLTAGE IS MONITORED BY A SEPARATE ISOLATED CIRCUIT.
2.
+/- 15V IS SUPPLIED BY SEPARATE ISOLATED POWER SUPPLIES.
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ISOLATION RATED VOLTAGE IS IOOOV DC AND ISOLATION IMPEDANCE ARE 10 GIGA OHMS AND 6 PICOFARADS.
- 5. TEST POINT RESISTER FOR READING IRTD IS A 50 OHM RESISTER
(+/- 0.01% TOLERANCE) RATED AT O.33 WATTS.
FIGURE 2 IRTD MONITORING SIMPLIFIED SCHEMATIC ERI EXCITATION CIRCUIT l.
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