ML20045C636
| ML20045C636 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/17/1993 |
| From: | TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20045C634 | List: |
| References | |
| NUDOCS 9306240103 | |
| Download: ML20045C636 (14) | |
Text
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6 ENCLOSURE 1 PROPOSED TECHNICAL SPECIFICATION CHANGE ;
SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 (TVA-SQN-TS-93-08)
LIST OF AFFECTED PAGES Unit _1 2-5 Ullit_2 2-5 9306240103 930617 ((
- ADR-P ADOCK 05000327 pon {5
TABLE 2.2-1 REACTOR TRIP SYSTEH INSTRUHENTATION TRIP SETPOINIS FUNCTIONAL LH4IT TRIP SETP0lltT ALLOWABLE VALUES L 11anual Reactor Trip Not Applicable liot Applicable c- 2. Power Range, Neutron Flux Low Setpoint - < 25% of RATED
{
TilERMAL POWER -
Low Setpoint TilERMAL POWER
$ 27.4% of RATED R145 liigh Setpoint 5109% of RATED liigh Setpoint - < 111.4% of RATED R 14."
TilERHAL POWER TilERMAL POWER
- 3. Power Range, Neutron Flux, 5 5% of RATED TilERMAL POWER with liigh Positive Rate < 6.3% of RATED TilERHAL POWER a time constant 1 2 second with a time constant 1 2 second
- 4. Power Range, Neutron Flux, 5 5% of RATED TilERMAL POWER with liigh NeDative Itate < G.3% of RATED TilERHAL POWER a time constant 1 2 second wi
~aie constant 1 2 second 7
- 5. Intermediate Range, Neutron '/S. 20 Yo Fiux 5 25% of RATED TilERMAL POWER 5 30% of RATED lilERHAL POWER
- 6. Source Range, Neutron Flux .t. YS 5 10 counts per second 0 5 M x 10 counts per second
- 7. Overtemperature AT See Note 1 u
See Note 3 gg 8. -Overpower AT .See Note 2 See Note 4
.h $
-< q 9. Pressurizer Pressure--Low 2 1970 psig 2 1964.8 psig M f*
mN 10. Pressurizer Pressure--liigh 5 2385 psig 5 2390.2 psig R145
$CD ^
- 11. Pressurizer Water Level--Ili0h $ 92% of instrunent span 5 92.7% of instrustent span
^
- 12. Loss of Flow > 90% of design flow > 89.4% of design flow
~
per loop
- per loop *
- Design flow is 91,400 gpia per loop.
TABLE 2.2-1 '
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8 REACTOR TRIP SYSTEM INSTRUMENTATION TRIP SETPOINTS j FUNCTIONAL UNIT TRIP SETPOINT ALLOWABLE VALUES
- 1. Manual Reactor Trip Not Applicable E Not Applicable Z 2. Power Range, Neutron Flux Low Setpoint - 125% of RATED m Low Setpoint 1 27.4% of RATED TilERMAL POWER TilERMAL POWER lR13
- liigh Setpoint 1 109% of RATED High Setpoint TilERMAL POWER 5 111.4% of lR132 a RATED THERMAL POWER
- 3. Power Range, Neutron Flux, 5 5% of RATED THERMAL POWER with
-liigh Positive Rate 5 6.3% of RATED THERMAL POWER R36 a time constant 1~2 seconds with a time constant 1 2 seconds
- 4. Power Range, Neutron Flux, < 5% of RATED THERMAL POWER with liigh Negative Rate < 6.3% of RATED THERMAL POWER a time constant 1 2 seconds wi a R36 e constant 1 2 seconds u 5. Intermediate Range, Neutron W.2OIo di Flux 5 25% of RATED TilERMAL POWER 5 30T of RATED THERMAL POWER
- 6. Source Range, Neutron Flux 5 10s -counts per second .L W 5 .kT x 105 counts per second j 7. Overtemperature AT See Note 1 See Note 3'
- 8. Overpower AT -
See Note 2 See Note 4
-9. Pressurizer Pressure--Low 3 1970 psig 1 1964.8'psig
- 10. Pressurizer Pressure--High R132
< 2385 psig 5 2390.2 psig o k C3 E .11. Pressurizer Water Level--liigh ' 5 92% of instrument span-5 92.7% of instrument span 1 . ---I 5 12. Loss of Flow i- % 3 1 90% of design flow per loop
- 1 89.4% of design flow per loop *
- si.
g
- Design flow is 91,400 gpm per loop.
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1 ENCLOSURE 2 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 (TVA-SQN-TS-93-08)
DESCRIPTION AND JUSTIFICATION FOR REVISION OF REACTOR TRIP ALLOWABLE VALUE FOR INTERMEDIATE-RANGE NEUTRON FLUX 1
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Description of Change TVA proposes to modify the Sequoyah Nuclear Plant (SQN) Units 1 and 2 technical specifications (TSs) to increase the allowable values for the intermediate-range and source-reactor-range reactor trip setpoints. For the intermediate range, the change will be from less than or equal to 30 percent rated thermal power (RTP) to 45.20 percent RTg. For the source range, the change will be from less than 1.3 x 10 counts per second (CPS) to 1.45 x 105 CPS. This change affects the information in TS Table 2.2-1, Items 5 and 6, for the allowable values column.
Reason for Changa During the Cycle 4 refueling outages for both units, TVA installed Gamma-Metrics intermediate- and source-range detectors to replace the original Westinghouse Electric Corporation detectors. The new intermediate-range detectors have a ten-decade range as compared with only eight decades for the Westinghouse detectors. The additional two decades in range were provided at the expense of some decreased accuracy for the channel. In addition, TVA has reevaluated the demonstrated accuracies for the intermediate- and source-range channels using a more conservative summing technique with the uncertainty results being applied logarithmically. This logarithmic application is a more accurate method for applying these uncertainties than presently being used. These changes indicate the need to increase the allowabic values for intermediate- and source-range reactor trip setpoints to be consistent with design capabilities of the instrumentation. At the present time, additional and excessive functional checks of the intermediate-range channels are required to ensure TS limits are not exceeded. This change should allow these checks to be performed at the normal TS-required intervals without compromising TS compliance.
Justification for Change The overpower protection provided by the out-of-core nuclear instrumentation consists of three discrete but overlapping levels.
Continuation of start-up operation or power increase requires a permissive signal from the higher-range instrumentation channels before the lower-range icvel trips can be manually blocked by the operator. The following is a description of the nuclear instrumentation system trips provided in the SQN design for start-up or power escalation. These trips are discussed in Sections 7.2 and 15.2.1 of the SQN Updated Final Safety Analysis Report (UFSAR).
The power-range high neutron flux trip circuit tripe the reactor when two of the four power-range channels exceed the trip setpoint. There are two independent bistables per channel, one with a high cetting and one with a low setting, and a total of four channels. The high trip setting (109 percent RTP) provides protection during normal power operation and is always active. The low trip setting (25 percent RTP), which provides protection during start-up, can be manually bypassed then two out of the four power-range channels read above the permissive at approximately 10 percent power (P-10). Three out of the four channels below 10 percent automatically reinstate the trip function.
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4 The intermediate-range high neutron flux trip circuit trips the reactor l when one out of the two intermediate-range channels exceed the trip setpoint. This trip, which provides backup protection during reactor start-up, can be manually blocked if two out of four power range channels are above P-10. Three out of the four power-range channels below this value automatically reinstate the intermediate-range high neutron flux trip. The intermediate-range channels (including detectors) are separate from the power-range channels.
The source-range high neutron flux trip circuit trips the reactor when one of the two source-range channels exceeds the trip setpoint. This trip, which provides protection during reactor start-up and plant shutdown, can be manually bypassed when one of the two intermediate-range channelgreadsabovetheP-6setpointvalue(greaterthanorequalto 1 x 10- percent RTP) and is automatically reinstated when both intermediate-range channels decrease below the P-6 value. This trip is also automatically bypassed by two out of four logic from P-10.
The source-range trip function can also be reinstated below P-10 by an l administrative action requiring manual actuation of two control board j mounted switches Each switch will reinstate the trip function in one of' the two protection logic trains. The source-range trip is set between the P-6 setpoint and the maximum source-range level (1 x 10 6CPS). The channels can be individually blocked at the nuclear instrumentation racks to permit channel testing at any time under prescribed administrative procedures and under the direction of authorized supervision. This blocking action is annunciated on the control board.
The power-range low setpoint trip and the intermediate- and source-range ,
trips described above are designed to protect the reactor-core against l power excursions during reactor start-up or low-power operation. The 1 intermediate- and source-range trips provide redundant protection to the i low setpoint trip of the power-range neutron flux channels for the ;
Condition II fault for an uncontrolled rod cluster control assembly bank l withdrawal from a suberitical condition as described in Sections 7.2 and 15.2.1 of the UFSAR. In this analysis only the power-range low setpoint trip of 25 percent RTP is assumed to actuate to mitigate the accident. Actuations of the intermediate- or source-range trips are not assumed in the SQN safety analysis for this or any other design basis accident. The SQN TSs bases for the intermediate- and source-range trips state that "No credit wec taken for operation of the trips associated with either the Intermeolate or Source Range Channels in the accident analyses; however, their functional capability at the specified trip ;
settings is required by this specification to enhance the overall l reliability of the Reactor Protection System." '
TVA installed the Gamma-Metrics intermediate- and source-range detectors at SQN during the Cycle 4 refueling outages to meet environmental qualification requirements for accident monitoring instrumentation.
These enhancements were necessary to meet the recommendations of Regulatory Guide 1.97 for instrumentation in harsh environments required to operate during postaccident conditions. The original Westinghouse intermediate- and source-range detectors could not meet the requirements for harsh environments necessitating the change to Gamma-Metrics detectors. The new detectors provide equivalent operation with the
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! 4 exception of the intermediate range now having a ten-decade range instead of eight decades. This increase in range results in larger relative inaccuracies because of applying the instrumentation errors to a larger span.
l l The intermediate- and source-range inaccuracies were applied to an l improved setpoint methodology by TVA. The TVA setpoint methodology utilized for the proposed intermediate- and source-range reactor trip allowable values continues to utilize rack inaccuracles for allowable value determinations as in the original Westingnouse setpoint methodology. The TVA setpoint methodology generates a rack accuracy of 2.76 percent of span value for the source range and a 2.57 percent of l span value for the intermediate-range channels. These values were l
developed by using a square root of the sum of loop component errors l squared as shown in Enclosure 4. The previous methodology summed the l rack calibration, bistable, test equipment, and drift terms, squared the l result and added this to the square of the rack temperature effect before taking the square root of the total. This resulted in a less conservative channel accuracy. If the previous summing method had been used, the rack accuracies would be 3.75 percent of span value for source range and 3.61 percent of span value for intermediate range. Therefore, TVA has implemented a more conservative method for determining percent of sr.a rack accuracy and subsequently a conservative allowable value for these trip functions.
Another significant change in the methodology was implemented that is considered by TVA to be essential to properly determining allowable values for instrumentation that operates in logarithmic ranges. The previous methodology applied the percent of span accuracy values for intermediate-andsource-rangeghannelslinearlytotherangesof0to 120 percent RTP and 0 to 1 x 10 CPS, respectively. This method resulted in overly conservative allowable values for the intermediate- and source-range channels for a given channel accuracy. By applying the accuracies this way, allowable values more restrictive than the design capabilities of the instrumentation were assigned. This could and has required excessive calibration checks more frequently than required by the TS to ensure compliance. TVA has applied the accuracies for intermediate and source ranges logarithmically, which is more appropriate ;
since these instrumentation channels operate in this mode. The l power-range channels, by contrast, operate in the linear mode. All of l the accuracy terms in the TVA setpoint methodology are based on percent which is 0 to 10 volta direct current. This oftotalchannelspag, represent CPS (6decadeslogarithmic)forthesourcerange
- anda10ga1to10to 100 percent RTP (10 decades logarithmic) for the intermediate range. The following equations apply:
Source-Range Volts (output) = 1.667 (LOG CPS)
Intermediate-Range Volts (output) = LOG percent RTP + 8 The above equations describe the relationship between the voltage output and the process variable. Their use is integral to the proper calibration, setup, and operation of the source- and' intermediate-range channels. Since the TS trip and allowable values are in-process terms of CPS and percent RTP, the total rack error that is in volts must be properly converted into the associated process terms.
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The net result of applying the accuracy logarithmica withtheconservativesummingmethod,isa0.15x10 gly,whenconsidered CPS increase for the source-range TS-allowable value. This SQNTSvalue;however,itisonly0.05x10gsaslightincreaseforthe CPS above the value in the latest version of the improved standard TSs (NUREG-1431). The calculated allowablevagueforthesource-rangereactortripneutronfluxsetpoint is 1.45 x 10 CPS as shown in Enclosure 4. The net change in percent RTP for the intermediate-range allowable value is of a greater magnitude.
The magnitude of this change is the result of the previous methodology applying the errors over a 0 to 120 percent linear span as opposed to a ten-decade logarithmic span. The difference in this application is significant as can be seen in the change from 30 percent RTP to 45.20 percent RTP allowable value for the intermediate range. The change in the source-range allowable value was less in magnitude because the-previous methodology applied the error over a 0 to 1 x 106 span that correlates much closer to a six-decade logarithmic span. The calculated allowable value for the intermediate-range reactor trip neutron flux setpoint is 45.20 percent RTP as shown in Enclosure 4.
The proposed changes are justified based on the use of a more conservative summing of loop component inaccuracies than previously used and properly applying these loop inaccuracies logarithmically to the setpoint to determine the appropriate allowable values. These changes do not affect any SQN safety analysis conclusions because the intermediate-and source-range neutron flux trips are not taken credit for in the SQN design for design basis accidents. The equivalent trip function that is assumed in the SQN safety analysis is the low setpoint power-range reactor trip. This instrument loop spans approximately two decades and therefore provides a much more accurate capability for initiating a reactor trip for start-up excursion events than the ten- and six-decade ranges utilized by the intermediate and source ranges, respectively. The proposed change will implement realistic values for the intermediate- and source-range TS-allowable values based on the design capabilities of the instrumentation.
The reliability of the reactor protection system (RPS) has not been decreased because the source-range-allowable value continues to be well }
below the power-range setpoint of 25 percent RTP.
For the intermediate range, the increase in allowable value does not impact the overall reliability aspects for the RPS because the uncontrolled rod withdrawal analysis in Section 15.2.1 of the UFSAR indicates a very rapid neutron ,
flux increase such that the actuation time for a reactor trip is )
essentially the same for setpoints up to approximately 100 percent RTP. l Therefore, reactor trip actuation at 35 percent RTP as assumed in the I accident analysis by the power range or 45.20 percent RTP by the l
intermediate range will result in the same accident response and thereby 4 l maintain the overall RPS reliability provided by the intermediate range. j With the proposed allowable values, plant Maintenance personnel will be able to perform calibration checks for these instrument loops on a frequency consistent with TS-required frequencies. The proposed change
) I will not adversely affect SQN safety functions and will ensure the use of I appropriate allowable values for maintaining the trip functions for the l
intermediate- and source-range neutron flux instrumentation.
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Environmen_tal Impact Evaluation The proposed change request does not involve an unreviewed environmental question because operation of SQN Units 1 and 2 in accordance with this change would not:
- 1. Result in a significant increase in any adverse environmental impact previously evaluated in the Final Environmental Statement (FES) as modified by NRC's testimony to the Atomic Safety and Licensing Board, supplements to the FES, environmental impact appraisals, or decisions of the Atomic Safety and Licensing Board.
- 2. Result in a significant change in effluents or power levels.
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- 3. Result in matters not previously reviewed in the licensing basis for '
SQN that may have a significant environmental impact..
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Enclosure 3 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 (TVA-SQN-TS-93-08)
DETERMINATION OF NO SIGNIFICANT HAZARDS CONSIDERATION l
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. Significant Hazards Evaluation TVA has evaluated the proposed technical specification (TS) change and has determined that it does not represent a significant hazards consideration based on criteria established in 10 CFR 50.92(c).
Operation of Sequoyah Nuclear Plant (SQN) in accordance with the proposed amendment will not:
- 1. Involve a significant increase in the probability or consequences of an accident previously evaluated.
The proposed change increases the allowable value for the intermediate- and source-range neutron flux reactor trip functions.
These trips are not taken credit for in the safety analysis, but do provide additional reliability for the reactor protection system.
These trips are provided for accident mitigation purposes and are not considered to be the source of any accident. Therefore, there is no-increase in the probability of an accident because no plant functions have been changed and the increase in the associated allowable values has no impact on accident generation. The mitigation functions for the intermediate- and source-range trips are not assumed in the analysis, but are backups to the power-range neutron flux low setpoint trip. The power-range low trip is assumed in the analysis for uncontrolled control rod withdrawal from a suberitical condition but is not affected by the proposed change. Therefore, mitigation functions assumed in the SQN safety analysis have not been affected by the proposed change and the consequences of an accident, including offsite dose levels, will not be increased.
- 2. Create the possibility of a new or different kind of accident from any previously analyzed.
The trip functions affected by the proposed change are utilized for accident mitigation purposes though not taken credit for in the safety analysis. No plant functions have been changed as a result of this change, only the allowable values for intermediate- and source-range reactor trip setpoints. Since previously analyzed trip functions remain unchanged and no new or different functions have been introduced, the possibility of a new or different kind of accident has not been created.
- 3. Involve a significant reduction in a margin of safety.
3 The trip functions affected by the proposed change are not assumed for any accident in the SQN safety analysis and therefore are not an input to the TS margin of safety. The TS margin of safety for the l
low-power excursion event is provided by the power-range low setpoint
- trip function in the safety analysis. As described in Enclosure 2 l the overall reliability of the reactor protection system is not reduced because the source-range-allowable value remains well below the power range trip setpoint and the intermediate-range-allowable value, while higher, will still provide the same accident response because of the rapid increase in neutron flux for low-power excursion events. Therefore, the proposed change will not result in a reduction in the margin of safety or overall reactor protection system reliability.
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A Enclosure 4 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 (TVA-SQN-TS-93-08)
DEMONSTRATED ACCURArY FOR INTERMEDIATE-AND SOURCE-RANGE LOOPS l
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o DEMONSTRATED ACCURACY FOR INTERMEDIATE RANCE LOOP 0% 0.5 % 1.0% .22%
1 1 1 .
5 5 5 AMP OPTICAL AUCTIONEER BISTABLE ISOLATOR TEST GENERATOR (RCSa) l RACK CALIBRATION ACCURACY (RCa) l DETECTOR ,_ -I The optical isolator (0I) has an accuracy of 0.5%. The auctioneer / test generator (AU/TG) has an accuracy of 1.0%.
Rack Calibration (RCa) = (OI 2 + AU/TG 2 )1/2 = (0.52 + 1,o2)l/2 = 1.1180%
Rack bistable (RCSa) is a combination of resource accuracy (Re) and bis table drif t (De) for the first 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> of operation, therefore RCSa = (Re2 + De 2 )l/2
= (0.1 2 + 0.2 2)l/2 = 0.2236%
Rack test equipment (RMTe) accuracy is based on the use of a frequency counter with an accuracy level of 0.1% or better and a digital multimeter with an accuracy of 0.1% or better producing an overall RMTe of 0.1414%.
RMTe = (0.1 2 + o,12 )1/2 ,o,ising Rack temperature ef fect (rte) = 0.04%/'C, the worst case temperature range experienced by this equipment is 50*F-110*F. This equates to a AT of 33.33*C using the equation of, *C = ('F - 32)(5/9):
(110*F = 43.33*C and 50*F = 10*C)
Therefore, rte = (0.04)(33.33) = 1.3332%
l The rack drif t (Rd) is 0.5%/6 months, however te parallel the plants l outage schedule of 18 months plus an additional 25% to allow for possible l l extension, this calculation uses a drift value for the period of l 22.5 months. Therefore, 0.5%/6 x 22.5 = 1.8750% or Rd =1.3750%.
l Note To calculate the total rack accuracy (rat) this calculation uses l
square root sum of squares methodology:
rat =
GRCa2 + RMTe2 + RCSa2 + Rd2 + g7e2
=
}1.11802 + o,14142 +0.22362 + 1.87502 + 1.33322
= 2.572% of span Tech Spec Allowable Value = Setpoint + rat
= 9.398 VDC '(25%) + .2572 VDC (2.572% x 10V)
= 9.6552.VDC t
l = 45.20% RTP I
+
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i DEMONSTRATED ACCURACY FOR SOURCE RANGE LOOP
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- 0% 0.5 % 1.0% .22%
_J- __F- __F-i AMP OPTICAL AUCTIONEER BISTABLE l ISOLATOR TEST GENERATOR (RCSa)
RACK CALIBRATION ACCURACY-(RCa)
DETECTOR The optical isolator (0I) has an accuracy of 0.5%. The auctioneer / test generator (AU/TG) has an accuracy of 1.0%. '
Eack Calibration (RCa)' = (OI 2 + AU/TG 2
)l/2 = (0.5 2 + 1,0 2)1/2 = 1.1180%
Rack bistable (RCSa) is a combination of resource accuracy (Re) and bistable drift (De) for the first 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> of operation, therefore, RCSa = (Re2 , pe2 )l/2
= (0.1 2 + 0.2 2)l/2 = 0.2236%
Rack test equipment (RMTe) accuracy is based on the use of a frequency counter with an accuracy level of 0.1% or better and a digital multimeter with an accuracy of 0.1% or better producing an overall RMTe of 0.1414%.
RMTe = (0.1 2 + 0.12 )l/2 , o,1414; l Rack temperature effect (rte) = 0.05%/*C, the worst case temperature range experienced by this equipment is 50*F-110*F. This equates to a 6T of 33.33*C using the equation of, *C = (*F - 32)(5/9):
(110*F = 43.33*C and 50*F = 10*C)
Therefore, rte = (0.05)(33.33) = 1.6665%
The rack drift (Rd) is 0.5%/6 months, however to parallel the plants outage schedule of 18 months plus an additional 25% to allow for possible extension, this calculation uses a drift value for the period of 22.5 months. Therefore, 0.5%/6 x 22.5 = 1.8750% 'or Rd =1.8750%.
Note To calculate the total rack accuracy (rat) this calculation uses square root sum of squares methodology:
rat =
fRCa2 + RMTe2 + RCSa2 + Rd2 + rte 2
=
yl.11802 o,14132 +0.22362 + 1.87502 + 1.66652
= 2.759% of span Tech Spec Allowable Value = Setpoint + Pat
= 8.33 VDC + 0.2759 VDC (2.759% x 10V)
= 8.6059 VDC
-= 1.45 x 105 CPS
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