ML19260C868
| ML19260C868 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 02/01/1980 |
| From: | Peoples D COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8002060295 | |
| Download: ML19260C868 (7) | |
Text
Commonwealth Edison One Firs: National Plaza. Chicago. Illinois Address Reply to: Post Office Box 767 Chicago Illinois 60690 February 1, 1980 Dr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Zion Station Units 1 and 2 Additional Information on Subcooling Criterion NRC Docket Nos. 50-295 and 50-304 Reference (a) :
December 27, 1979 letter from D.
F.
Ross, Jr. to Cordell Reed
Dear Dr. Denton:
Reference (a) requested Commonwealth Edison Company to provide documentation showing the errors used to develop its subcooling criterion and how the errors were combined. to this letter provides the requested information.
This attachment contains calculations which indicate that over the applicable range of safety injection termination the the subcooling meter has an accuracy of 110 F under normal operating conditions and 1300F under post accident conditions.
Reference (a) also requested Commonwealth Edison to install instrumentation and readout devices that will ensure 20 F of actual subcooling.
At Zion Station, the Emergency Operating Procedures (EOPs) allow safety injection termination with greater than 50 F indicated subcooling and reinitiation if indicated subcooling drops below 350F, This assures at least 5 F subcooling at all times.
Increasing the subcooling criteria an additional 15 F to meet the 20 F request of Reference (a) is not possible with current instru-mentation.
Commonwealth Edison intends to replace the pressure transmitters used in the determination of saturation temperature with more accuratg transmitters.
When this modification is completed, the 20 F subcooling criterion should be met.
Although extensive lead times are required for obtaining environmentally qualified pressure transmitters, Commonwealth Edison will make every effort to expeditiously complete this modification by the January 1, 1981 date specified in Reference (a).
5
//)
JADD*
93g ies H. DENTbH I
i 1933 129 3 o oeo e o e>!7Js~~
Commonwealth Edison NRC Docket Nos. 50-295 and 50-304 Dr. Harold R. Denton Page 2 February 1, 1980 Please address any additional questions that you might have concerning this matter to this office.
Very truly yours, D.
L.
Peoples Director of Nuclear Licensing DLP:WFN: rap Attachment i933 130
.Subcooling Meter System Accuracy Description of Subcooling Meter System:
RCS pressure is obtained from the average of 4 narrow range pressure channels between 1750 and 2500 psig and from a single wide-range pressure channel. for all other pressures between 0 and 3000 psig.
The P-250 proces computer converts the pressure to a saturation temperature and then subtracts from it the core exit temperature as obtained from the average of the 10 highest indicating thermocouples to give the degrees subcooling which is displayed on a control board meter.
The attached diagram shows the components in the subcooling meter system.
Note:
The accuracy of the subcooling meter is of concern when used to determine if adequate subcooling exists to allow termina-tion of Safety Injection actuation.
Since one of the other criteria for terminating SI actuation is RCS pressure above 2000 psig, and the pressurizer safety valves should keep RCS pressure below 2500 psig at all times, the range of RCS pressure of concern is the range covered by the narrow range pressure channels.
I.
Errors in Saturation Temperature as Calculated frcm the Narrow Range Pressure Channels A.
Loop Power Supply Accuracy Hagan Model 121
= + 5% of 46 volts 4111085-001
= T 2.3 volts (per Westinghouse Instrument Bulletin IB-137-121)
Note:
This is within the acceptable range of input voltage (39 to 49 volts) to the pressure transmitter per the Fisher Porter Instruction Manual and therefore does not enter into the overall loop accuracy.
B.
Pressure Transmitter Accuracy Fisher Porter Model 50EP106
= + 0.5% of 800 psi (per Fisher Porter Instrument
= + 4 psi Bulletin 50EP1000-C Rev. 2 pg.2) 0 Ambient temperature effect on
= + 0.5% / 50 F transmittec lpec Fisher Poccee
= T C.5% ot 800 psl Instrument Bulletin 50-EP1000-C
= I 4 psi Rev. 2 pg. 2)
}g33 Note: This assume's no greater than a 50 F change from the ambient temperature at which the device was calibrated under normal operating conditions.
. Block Diagram of Subcooling Meter Loop (Using Narrow Range Pressure Channels) Pow GR Go P P L'{ Co0 TMart tai Bo oa b.4R Y ~T*HGAm o Co o f t-G S NARCou/ RAA W RGFGR5ncli PREscoRG gyg ey,y YMTR Bog V Sic,9AL 150 l-A-fc R A-P 2.fo CotA P O TG A \\[ CONTRo G BoARP M572R Note: One of four narrow range pressure channels shown, One of si::ty five thermocouple inputs shown. Calibration device accuracy (per Zion Instrument Maintenance Dept.) Heise Gauge = 1 0.1% of 3000 psi = 1 3 psi Digital Volt Meter = 1 0.1% of 800 psi = + 0.8 psi I to V Module = +0'.01% of 800 psi - 0.1 psi = C. Signal Isolator Accuracy Hagan Model 110 = + 0.5% of 800 psi 4111083-002 = + 4.0 psi (per Zion Instrument Maintenance Dept. ) D. I to V Module Accuracy (per Zion Instrument = 1 0.01% of 800 psi Maintenance Dept.) = + 0.1 psi E. P-250 Computer Input Accuracy Analog to Digital Instrument = 1 0.025% of 800 psi Accuracy (Characteristic of = + 0.2 psi Analog to Digital Converter) Accuracy of conversion from = 1 0.1 psi pressure to saturation temperature (per comparison with steam stables) Tota] error in narrow range = 3 (4) 2+(3) 2+(. 8) 2+2 (.1) 2+ (. 2 ) 2'+1 Pressure under normal ambient environment = 1 7.7 psi At 2000 psi this converts to = + 0.6 F an error in saturation temperature Note: Since the above errors are random and '.ndependent (except for the computer conversion uuuuracy) they can be combined statistically by taking the square root of the sum of the squares. F. Pressure Transmitter Accuracy Under Post-Accident Environment (per Franklin Institute Report = + 10% of test pressure pg. A-16 contained in NCAP = + 10% of 2030 psi 7410-L Vol. I of II. Unit 3 = + 203 psi of Test 1 is within + 100) ~ }93)
. At 2000 psi this converts to an error = + 13.8 F in saturation temperature Total error in narrow range pressure = normal + environmental under post,-accident environment error = 0.6 + 13.8 = _+ 14.4 F II. Errors in Corc Exit Temperature as Calculated from the Core-Exit Thermocouples A. Thermocouple Accuracy (per In-Core Thermocouple Equipment = + 0.4% of actual F Specification No. 676511) = T 0.4% of 670 F 0 = _T 2.7 F Note: 670 F corresponds to saturation temperature at 2500 psi B. Reference Junction Box Accuracy (per Whittaker Thermocouple Reference = + 0.3 F Junction Instruction Manual) C. P-250 Computer Accuracy 0 Calibration Accuracy = + 1.0% of 670 F 0 (Comparison of process computer = I 6.7 F thermocouple curve to the "K" calibration curve) Analog to Digital Instrument Accuracy = + 0.025% of 2250 F (Characteristic of Analog to Digital = T 0.6 F Converter) Total error in cora exit temperature ='Y(2.7) 2+(.3) 2+(.6) 2 ' + 6.7 under normal ambient environment = _+ 9.5 F Note: Since the above errors are random and independent (except for computer conversion of the "K" calibration curve) they can be combined statistically by taking the square root of the sum of the squares. D. Reference Junction Box Accuracy Under Post-Accident Environment (per Whittaker Thermocouple Reference = error equivalent to Junction Instruction Manual) two junction boxes 0 = _+ 6.0 F Total error in core exit temperature = normal + environmental error under post-accident environment = 9.5 + 6.0 = _+ 15.5 F III. " Total Error in Indicated Degrees Subcooling A. Accuracy of Control Board Meter (per Zion Instrument Maintenance Dept.) = + 1.5% of scale = + 1.5% of 100 F = { l.5 F B. Maximum Indicator Reading Error (standard estimate of one half ot = + 0.5 times 2 F smallest meter division) = { l.0 F (. 6) 2+ (2. 7) 2+ (. 3) 2+ (. 6) 2+1. 5) + (1. 0 ) 2'+ 6.7 Total error in decrees = subcooling under normal ambient environment = + 10.1 F Total error in degrees subcooling = normal + environmental error under post-accident environment = 10.1 + 13.8 + 6.0 = 29.9 F 4 Y}}