ML20082C132
| ML20082C132 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 04/04/1995 |
| From: | Barkhurst R ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20082C135 | List: |
| References | |
| W3F1-95-0058, W3F1-95-58, NUDOCS 9504060173 | |
| Download: ML20082C132 (31) | |
Text
_ _ _ - _ _ _ _ _ _ _ _ _ _ _ - _ _
c Entergy Operations,Inc.
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Ross P. Barkhurst n.
W3F1-95-0058 A4.05 PR April 4, 1995 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555
Subject:
Waterford 3 SES Docket No. 50-382 License No. NPF-38 Request for Enforcement Discretion Technical Specification 4.1.1.3.2, 2/3 Core Life Moderator Temperature Coefficient Surveillance Test Exigent Technical Specification Change Request NPF-38-165 Gentlemen:
This submittal constitutes the Waterford 3 request for enforcement discretion from a Technical Specification (TS) Surveillance Requirement.
The enforcement discretion is requested to exclude the Moderator Temperature Coefficient (MTC) test prescribed by TS 4.1.1.3.2.c for a period of 23 days, or until approval of the enclosed TS change, whichever occurs first. This 23 day period is proposed to provide the necessary time for the staff to process and issue the attached exigent TS change submitted pursuant to 10 CFR 50.91(a)(6). The estimated due date for TS 4.1.1.3.2.c is midnight April 5,1995. Therefore, the enforcement discretion would be in place until midnight April 28, 1995.
of this submittal is the Waterford 3 Request for Enforcement Discretion and Enclosure 2 is Exigent TS Change Request NPF-38-165. The determination that these requests have no adverse impact on the public health and safety is provided herein. This submittal has been reviewed by the Waterford 3 Plant Operations Review Committee, approved by the General Manager-Plant Operations and approved by the Safety Review Committee.
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Request for Enforcement Discretion Technical Specification 4.1.1.3.2 MTC 2/3 Core Life Test Exigent Technical Specification Change Request NPF-38-165 W3F1-95-0058 Page 2 April 4,1995 Should you have further questions concerning the attached information, please contact D.W. Vinci at (504) 739-6370.
Very truly yours, EoA e
3, A
R.P. Barkhurst Vice President, Operations Waterford 3 RPB/PLC/ssf Attachments:
Affidavit NPF-38-165
Enclosures:
Request for Enforcement Discretion Description of Safety Analysis cc:
L.J. Callan, NRC Region IV C.P. Patel, NRC-NRR R.B. McGehee N.S. Reynolds NRC Resident Inspectors Office Administrator Radiation Protection Division (State of Louisiana)
American Nuclear Insurers I
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1 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the matter of
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Entergy Operations, Incorporated
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Decket No. 50-382 Waterford 3 Steam Electric Station
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A_FFIDAVIT a
1 D.R. Keuter, being duly sworn, hereby deposes and says that he is General Manager Plant Operations - Waterford 3 of Entergy Operations, Incorporated; that he is duly authorized to sign and file with the Nuclear Regulatory Commission the attached Request for Enforcement Discretion - Exigent Technical F
Specification Change Request NPF-38-165; that he is familiar with the content thereof; and that the matter:: set forth therein are true and correct to the best of his knowledge, information and belief.
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D.R. Keuter General Manager Plant Operations -
4 Waterford 3 i
STATE OF LOUISIANA
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Subscribed and sworn to before me, a Notary Public in and for the Parish and 4
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l Waterford 3 Request for Enforcement Discretion Technical Specification 4.1.1.3.2 Moderator Temperature Coefficient SPECIFIC REQUIREMENTS THAT WILL NOT BE MET l
Technical Specification (TS) Surveillance Requirement (SR) 4.1.1.3.2.c requires the Moderator Temperature Coefficient (MTC) to be determined within 7 Effective Full Power Days (EFPD) of reaching 2/3 of expected core burnup.
The MTC surveillance test lasts approximately 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, requires a power reduction, an artificial increase in Reactor Coolant System cold leg temperature (Teoio), and cycling of the primary and secondary systams to achieve a temperature swing of at least 8 F.
The relative severity of this test and the artificial conditions it imposes, combined with problems associated with the n;ain turbine thrust bearing trip device, increases the i
potential for a reactor trip. A sound technical basis, provided in Enclosure 2, substantiates End of Cycle (E0C) MTC to be well within the TS limits; l
therefore, performing the 2/3 cycle MTC surveillance in Cycle 7 would be contrary te plant safety.
l CONSEOUENCES 1
l The estimated due date for TS surveillance 4.1.1.3.2.c is no later than midnight April 5, 1995.
Pursuant to TS 4.0.3 failure to perform the specified surveillance will constitute a failure to comply with OPERABILITY requirements for the Limiting Condition for Operation (LCO). ACTION for the MTC LCO states i
that "With the moderator temperature coefficient outside any one of the above i
limits, be in at least HOT STANDBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />."
MTC DESIGN REQUIREMENTS According to General Design Criteria 11, the reactor core and its interaction with the Reactor Coolant System (RCS) must be designed for inherently stable power operation, even in the possible event of an accident.
In particular, the net reactivity feedback in the system must compensate for any unintended reactivity increases.
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The MTC relates a change in core reactivity to a change in reactor coolant temperature. A positive MTC means that reactivity increases with increasing moderator temperature; conversely, a negative MTC means that reactivity decreases with increasing moderator temperature. The reactor is designed to operate with a negative MTC over the largest possible range of fuel cycle operation. Therefore, a coolant temperature increase will cause a reactivity decrease, so that the coolant temperature tends to return toward its initial value.
Reactivity increases that cause a coolant temperature increase will thus be self limiting, and stable power operation will result.
MTC values are predicted at selected burnups during the safety evaluation analysis and are confirmed to be acceptable by measurements.
Both initial and reload cores are designed so that the beginning of cycle (B0C) MTC is less positive than that allowed by the LCO. The actual value of the MTC is dependent on core characteristics such as fuel loading and reactor coolant soluble boron concentration. The end of cycle (EOC) MTC is also limited by the requirements of the accident analysis.
Fuel cycles that are designed to achieve high burnups or that have changes to other characteristics are evaluated to ensure that the MTC does not exceed the EOC limit. MTC values are bounded in reload safety evaluations assuming steady state conditions at BOC and E0C.
A middle of cycle (M0C) (2/3 expected core burnup) measurement is conducted at conditions when the RCS baron concentration reaches approximately 400 ppm.
The measured value may be extrapolated to project the E0C value, in order to confirm reload design predictions.
MTC is one of the controlling parameters for core reactivity in accidents that result in both overheating and overcooling of the reactor core.
Both the most positive value and most negative value of the MTC are important to safety.
Accidents that cause core overheating, either by decreased heat removal or increased power production, must be evaluated for results when the MTC is i
positive. The most limiting event with respect to a positive MTC is a CEA withdrawal accident from zero power, also referred to as a startup accident.
The M0C measurement acts as a confirmatory check of the most negative MTC value. The measurement is performed so that the projected E0C MTC may be evaluated before the reactor actually reaches the EOC condition.
Accidents that cause core overcooling must be evaluated for results when the MTC is most negative. The event that produces the most rapid cooldown of the RCS, and is therefore the most limiting event with respect to the negative MTC, is a steam line break (SLB) event.
0 CIRCUMSTANCES SURROUNDING THE SITUATION On Saturday March 25, 1995, Waterford 3 intended to perform TS surveillance 4.1.1.3.2.c (2/3 Core cycle MTC test).
During MTC testing the Primary and Secondary Systems are cycled to achieve specific plant conditions.
Steam flow is strictly regulated to control temperature while measurements are taken of specified core parameters. Therefore, the Steam Bypass Control System (the SBCS allows the avoidance of a reactor trip upon a turbine trip) and the Reactor Power Cutback System (that receives inputs from the SBCS) are disabled during the MTC test. To compensate for the absence of these protective systems the reactor trip on turbine trip feature is engaged.
The plant performed a normal down power to approximately 93%. Tcoio was artificially increased from its normal 545 F to 553 F when the pretrip alarm from the Turbine Thrust Bearing Wear Trip device sounded. The turbine rotor moved approximately 0.0015" during the down power and another 0.0010" during the increase in Tcoia. Thrust bearing oil pressure was at 55 psig and spiking to 60 psig. The turbine thrust bearing pretrip alarm setpoint is 60 psig and the turbine trip setpoint is 75 psig.
Reactor operators stopped all MTC test related activities and returned the plant to its pretest configuration and power levels. As load was placed back on the turbine and reactor power increased, turbine bearing trip oil pressure decreased to its pretest levels.
The following data was obtained subsequent to the MTC test:
PRE TEST MTC TEST POST TEST GOV.VLV.1 Position 100% Open 32.9% Open 100% Open GOV.VLV.4 Position.
25.4 Open 0%
Open 25.4 Open Mwe 1180 1095 1180
% Power 100%
93%
100%
Tcoio 545 F 552.5 F 545 F 1st Stage Pressure 583 534 583 MS Pressure
- 820 890 820 HP Position 6.280 6.295 6.280
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Thrust Pressure 34 psig 55 psig 35 psig Pressure Spike 36 psig 60 psig 37 psig Thrust Temp.
152 153 154
- Note: Main steam pressure rose from 820 to 850 psi during the down power prior to the increase in Tcoie.
Primary temperatures were constant. Main steam pressure rose to 890 during primary temperature increase while turbine output was maintained at 93%.
1st stage pressure did not change between down power and primary increase.
l l
Additional discussion and technical description of key turbine components related to this event are required to fully understand the above observations and their potential ramifications. This discussion follows.
Main Turbine Thrust Bearing In order to maintain axial position of the turbine rotor, a thrust bearing is located on the High Pressure Turbine end of the Low Pressure Turbine 2.
The type of turbine thrust bearing used is an automatic leveling plate.
This type of bearing is constructed with babbitt faced steel sh,es that are mounted to leveling plates that are supported by retaining rings.
The leveling plates position the babbitted shoes against a t5 rust collar machined on the turbine rotor by means of a rocking motion. lhis type of arrinownt ensures equal loading of the babbitt shoes so each shoe carries an equ i share of the thrust.
Each side of the turbine thrust collar is provided with this arrangement. Thrust from either direction is absorbed and axial position of the rotor is maintained. Oil under pressure normally completely floods the thrust bearing ensuring a film of oil between each shoe and the thrust collar.
See attached simplified drawing Figure A.
Thrust Bearing Wear Trip Device The thrust bearing trip device is a protective feature that is designed to provide a warning if the thrust bearing shoes wear down a predetermined amount.
Further wear trips the turbine before serious damage can occur to other turbine parts. The device consists of two nozzles which receive Auto Stop 011 and distribute it to either side of a ring mounted on the turbine rotor. There is a slight clearance between each nozzle tip and rotor mounted ring face.
During normal operation, these clearances are nearly constant and j
the backpressure in the nozzles is constant. This backpressure opposes a spring pushing downward on the thrust bearing wear trip diaphragm, but cannot overcome it.
The spring pushes the diaphragm downward, pulling the trip plate with it, rotating the trip plate counter-clockwise, closing the trip valve.
If thrust bearing wear causes the thrust bearing to move to either side, the reduced clearance on that side will increase the backpressure inside the affected nozzle. The upward force against the spring-loaded diaphragm will begin increasing.
When this pressure rises to the pretrip setpoint, a pressure switch will annunciate an alarm.
If the thrust bearing continues to wear, the pressure will further increase until the trip setpoint is reached and the pressure will overcome the spring force, pushing the diaphragm upward, rotating the trip plate clockwise, opening the trip valve. See attached simplified drawing Figure B.
The attached Figure C provides a simplified illustration of the clearance settings that are associated with the turbine rotor, thrust bearing and trip mechanism. The relationship between rotor movement in inches and turbine thrust bearing trip oil pressure can be seen on attached Figure D.
With a properly positioned rotor, movement of 0.0015" to 0.003" (as observed during the MTC test), is probably normal and of little consequence to thrust bearing trip oil pressure. However, as indicated on Figure D, the thrust bearing trip device is highly non-linear. Once oil pressure starts to rise, it takes very little change in rotor movement to go into alarm or trip.
Since the beginning of the current cycle Waterford 3 has experienced higher than normal thrust bearing trip oil pressure (approximately 30 to 40 lbs).
This pressure has been closely monitored, especially when performing activities that may affect rotor movement such as turbine valve testing.
Turbine valve testing requires a reactor down power to approximately 90%.
In September 1994, the thrust bearing pretrip alarm setpoint was increased from 35 psig to 60 psig, due to intermittent sounding of the pretrip alarm during turbine valve testing.
Waterford 3 has considered increasing the trip setpoint. This would require removing the cover of the Mechanical Turbine Trip Mechanism, that houses several other turbine trip devices, and making adjustments. Any adjustments or activity in this area poses a significant increase in turbine trip risk.
HISTORICAL EVENTS Maintenance was performed on the main turbine thrust bearing during Rgfuel 6 (April 1994). This required the disassembly of the thrust bearing, trip nozzles and Turbine Supervisory thrust position sensors.
The turbine thrust bearing was reassembled to its as-found condition. Total float (thrust bearing clearance) was measured at 0.019".
During assembly, the turbine rotor is set at a predetermined position.
Westinghouse designates this position "K" (see Figure C). This position allows the. rotor to thermally expand to its normal running position.
At this point, the thrust bearing and the thrust nozzles are locked into place. The Supervisory instrumentation is locked in place after the rotor is repositioned to the center of the thrust bearing. Also, during assembly, it was determined that an as-found rotor position reading was not taken. This reading is used to help validate the rotor position during setting of the thrust bearing.
Initially, after startup, a rotor position shift of 0.027" towards the generator was indicated via Turbine Supervisory instruments.
Correspondingly, thrust bearing trip oil pressure increased to approximately 25 - 30 psig.
Between the initial shift during Refuel 6 start-up and November 1994, a 0.007" drift toward the generator has been seen. During that time, the thrust bearing trip oil pressure range increased to approximately 30 - 40 psig.
No trendable movement since November has been experienced. Thrust trip oil pressure currently indicates approximately 30 - 40 psig.
During the entire cycle, thrust bearing trip oil pressure has fluctuated.
Thrust bearing trip oil pressure oscillations are normal; h; wever, these oscillations are larger due to the present operating point on the thrust bearing trip oil pressure curve (see Figure D).
EVALUATION L
The initial indicated rotor shift after Refuel 6 could have been caused by several events. These include: 1) a phenomena described as a " sling-shot" effect, 2) not properly locking down or mispositioning of the thrust bearing,
- 3) initial mispositioning of the thrust nozzles and Supervisory position probes.
r 1)
The " sling-shot" affect occurs when stresses are built up in the l
turbine rotors prior to going on turning gear. Westinghouse has not j
determined the cause of the " sling-shot" effect. Once the turbine is l
placed on turning gear and started up, the rotors " sling-shot" to a new position to relieve this stress. Westinghouse has indicated that rotor position shifts of 0.020" due to the " sling-shot" effect have been experienced previously at Waterford 3.
Additionally, shifts of 0.020" -
i O.030" have been experienced at other nuclear plants. This causes an actual movement of the thrust bearing. However, after the initial movement no significant additional movement is expected.
2)
The entire thrust bearing cage, if not locked down properly, could shift position. However, the cage is contained in a rabbit fit joint.
If this movement was experienced, the thrust bearing cage would eventually l
bottom out in the rabbit fit. This can explain the initial drift and subsequent stabilization of rotor position.
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Initial thrust bearing misposition is possible and could have exaggerated the effects of the " sling-shot".
Cycle 6 as-found rotor position / thrust bearing position data was not taken.
Even though the thrust bearing was set at the "K" position, the as-found position data could have provided additional assurances of the correct position of the thrust bearing prior to start-up.
3)
Turbine Supervisory instrumentation indicates a position consistent with the thrust bearing trip oil pressure.
If supervisory instrumentation and the thrust nozzles pressure coincide, then both must be installed in
.the correct position, or.both must be mispositioned by the same amount.
It is possible that they both were mispositioned since both reference the rotor and thrust bearing for their settings.
After the initial shift in position, the rotor continued to drift until' November. Current position-indicates approximately 0.034".
This drift could be caused by several factors: 1) movement of the turbine supervisory J
instrumentation and thrust nozzles, 2) movement or wear of the thrust bearing.
1)
Movement of the supervisory instrumentation and thrust nozzles is not probable since the thrust trip oil pressure tracks indicated position.
This would require that the thrust nozzles and electronic position 3
indicators move in unison. They are mounted separately.
2)
The final possibility is a combination of actual thrust bearing wear and thrust bearing components movement. Slight movement can be expected and is attributable to the settling in and positioning of the thrust bearing components.
Thrust bearing wear indication is provided by three 1
additional indicators besides thrust bearing trip oil pressure.
These include: thrust bearing oil drain temperatures, thrust bearing metal temperatures and the presence of wear metals in the turbine lube oil 3
analysis. The thrust bearing oil drain temperatures have remained normal through the cycle. The thrust bearing metal temperatures will increase if the oil wedge is lost during operation. The oil is used to cool and lubricate as well as position the rotor.
Thrust bearing metal temperatures have not indicated wear.
Lube oil analysis is performed monthly. Wear metal particle count is one analysis that is performed.
There have been no abnormal amounts of wear metals.found in any turbine lube oil analysis. This is a positive indication that no appreciable wear is occurring on the turbine thrust bearing.
The oscillations of the thrust bearing trip oil pressure has been a normal occurrence. When the thrust bearing and nozzles are set in their normal operating position, the thrust bearing trip oil pressure curve is very flat. Any normal rotor position variations will cause a very small and at times non-detectable change in thrust bearing trip oil pressure.
The order of magnitude expected is 1 - 2 psig. However, at our current operating position the thrust bearing trip oil curve is very steep (see Figure D).
For the same small change in position the thrust bearing trip oil pressure can change by up to 10 psig.
ROOT CAUSE The initial rotor position shift was most likely caused by a combination of the " sling-shot" effect and an initial mispositioning and/or shift in position of the thrust bearing. The drift seen during the subsequent months is due to a settling of the thrust bearing and turbine, and potentially some movement of the thrust bearing components. The thrust nozzles and supervisory instrumentation are believed to be indicating a correct position and pressure.
The variation in oil pressure as read by the gage is normal. This indicates the normal float this rotating machine has during operation.
The indicator, thrust bearing trip oil pressure, is exaggerated since we are operating on the steepest portion of the curve shown in Figure D.
The most probable cause of events have been outlined. However, these cannot be verified until a visual inspection of the thrust bearing, trip nozzles and supervisory instrumentation is accomplished.
It is important to note that Westinghouse, the turbine manufacture, has been consulted and informed of the determinations and evaluations discussed above.
The manufacture agrees with Entergy that operating the turbine in its current condition does not place the machine in danger.
The current operating position of the rotor is 0.034".
SAFETY SIGNIFICANCE OF PROPOSED DEVIATION As previously stated, the 2/3 end of cycle MTC test, TS Surveillance Requirement 4.1.1.3.2.c, acts as a confirmatory check of the most negative MTC value.
TS 3.1.1.3 requires that the most negative MTC value for this cycle must be less negative than the Core Operating Limits Report (COLR) specified value of
-3.3 X 10" delta k/k F.
Waterford 3 has determined that the most negative i
MTC value for the current cycle is -2.88 X 10" delta k/k F.
This value is well within the TS limit including applicable uncertainties.
provides a proposed exigent TS change submitted pursuant to 10 CFR 50.91(a)(6). The proposed change would amend the TS to allow a one time deviation not to perform Surveillance Requirement 4.1.1.3.2.c in Cycle 7.
A determination has been made that the proposed change does not involve, an unreviewed safety question, a significant hazard, or adverse consequences to the environment. The basis for these determinations are included in Enclosure i
2 under title headings Safety Analysis and Environmental Consequences.
Therefore, there is no potential for detriment to the public health and safety.
POTENTIAL FOR REDUCTION IN PLANT RELIABILITY Waterford 3 has considered the potential for other plant transients either known or unknown that may have an impact on turbine steam flow and consequently thrust bearing trip oil pressure. Certainly turbine valve testing is a concern because this test also involves a reactor down power and manipulation of the turbine governor valves. The turbine valve test interval is quarterly.
Based on the current schedule valve testing will be required at least once and possibly twice (May & August) between now and the end of Cycle 7.
For several reasons, Waterford 3 feels confident that these valve tests l
can be performed without a substantial increase in turbine trip risk.
- First, I
turbine valve testing has been conducted through out the cycle at monthly interval s. Only recently (License Amendment 103 dated March 2,1995) was the test interval increased to quarterly.
Second, while increases in thrust bearing trip oil pressures have been observed, the pretrip alarm has not locked in during valve testing since the setpoint adjustment was made in September 1994. Third, plant perturbations and disruptive steam flows associated with the MTC test are not seen during turbine valve testing or i
other planned reactor down powers. During valve testing the governor valves i
are in a full arc opening sequence vs. the MTC test where the governor valves are in sequential sequence. The sequential sequence appears to aggravate steam flow to the extent that rotor position is affected.
There may be other plant transients that may affect turbine thrust bearing trip oil pressure. However, there is no increase in the potential for an offnormal event. Additionally, should a transient occur, protective features such as the Steam Bypass Control System and/or the Reactor Power Cutback System would be available and of significant benefit.
COMPENSATORY MEASURES Waterford 3 has placed daily instructions in the control room that identify the precautions associated with turbine thrust bearing trip oil pressure.
In addition Operations shift personnel will have been instructed on the limiting event including adverse consequences associated with a more negative MTC at this point in core life.
As a check on the accuracy of the core physics predictions, the TS surveillance on core reactivity will be performed on a weekly basis during the period of enforcement discretion. Additionally, a check of predicted vs.
l actual critical boron concentration as a function of core burnup is and will be performed on a weekly basis. These checks will provide confidence in the accuracy of overall core physics predictions.
CONCLUSION Based on the above the request for enforcement discretion is justified.
Considering the TS MTC surveillance interval of 2/3 expected core burnup, the period of discretion i.e., 23 days will have no significant impact on safety.
l This time period is proposed to provide the necessary time for the staff to process and issue the attached exigent TS change.' Thus, the duration for the noncompliance is justified.
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ENCLOSURE 2 l
NPF-38-165 l
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DESCRIPTION AND SAFETY ANALYSIS
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0F PROPOSED CHANGE NPF-38-165 The proposed change modifies the Waterford 3 Technical Specification on Moderator Temperature Coefficient. The footnote tied to MODE 1 is deleted.
A new footnote is added and tied to Surveillance Requirement 4.1.1.3.2.c.
The proposed change constitutes a one time deviation not to perform the two-thirds end of cycle moderator temperature coefficient test for Cycle 7.
Existina Specification See Attachment A l
Proposed Specification l
See Attachment B Discussion The proposed change removes a footnote tied to MODE 1 of TS Limiting Condition for Operation 3.1.1.3, Moderator Temperature Coefficient (MTC). The deleted footnote was only valid for Cycle 2 and its removal is purely administrative.
l A new footnote is added to surveillance 4.1.1.3.2.c that proposes a one time deviation not to perform the specified 2/3 end of cycle (E0C) MTC test for Cycle 7.
TS 3.1.1.3 requires that the most negative MTC value for this cycle to be less negative than the Core Operating Limits Report (COLR) specified value of -3.3 X 10'd delta k/k F.
Waterford 3 has determined that the most negative MTC value for the current cycle is -2.88 X 10'd delta k/k F.
The MTC i
for Waterford 3 Cycle 7 has been determined to be well within the TS limit including applicable uncertainties.
The determination of sufficient margin for the E0C MTC is based on four points:
a.
Accuracy of the calculational methodology used to predict MTC's l
for the Waterford 3 plant.
b.
Predicted margin between the best estimate E0C temperature coefficient and the Technical Specification limit.
c.
Simihrity in design between the current cycle and past cycles for which the E0C measurements were included.
d.
Calculations demonstrating that the measured MTC's at the beginning of cycle (B0C) 7 satisfy all criteria for eliminating the EOC MTC measurement according to the methodology of Reference 2 which is currently under review by the NRC.
A.
Accuracy of the Calculational Methods The Physics design and subsequent prediction of Physics parameters such as MTC for Waterford 3 make use of the NRC approved coarse mesh diffusion theory code ROCS, and of cross sections generated by the multigroup transport theory assembly code DIT (Reference 1). The ROCS code provides an explicit calculation of fuel isotopic depletion coupled with thermal-hydraulic and xenon feedback, and the flexibility of the cross section treatment provides a detailed account of local and global temperature effects.
The accuracy of the ROCS methodology for predicting MTC's has been substantiated by numerous benchmarks to measurements at both BOC and E0C. A large data base of temperature coefficients has been analyzed and a Topical Report was submitted to the NRC in support of a change in Technical Specification MTC Surveillance Requirement 4.1.1.3.2.c i
(Reference 2). The result of the data base analysis is summarized in l
Figure 1, which shows the difference between measured and calculated isothermal moderator temperature coefficients, together with a linear fit to the data, and confidence and prediction intervals.
Figure 1 contains data from several units and cycles under various conditions of power, temperature and boron concentration. The data base is very consistent, and indicates that the temperature coefficients can be predicted with a 95/95 confidence level of 0.16 X 10" delta k/k/*F.
Most of the uncertainty is likely due to random variations in the measurements. Additional data points specific to the Waterford 3 reactor have been added to this data base, leading to the results given in Figure 2.
The Waterford 3 data points are highlighted and are shown to fit very well within the larger data base. Tolerance and prediction intervals are not changed by the inclusion of more Waterford 3 data.
The thirteen data points from Waterford 3 cover Cycles 4 to 7, and are summarized in Table 1.
l 4
l.
I *.
I I
l 4
i Taken by itself, the Waterford 3 data base defines a slightly bigger tolerance interval because of the smaller data base, but would still provide sufficient margin against the TS limit, as shown later. The l
Waterford 3 data base is given in Figure 3.
l l
i I
j i50 THERMAL TEMPERATURE COEFFICIENT BlAS (Meas-Calc) (E-4/F) 0.2 0.1 -
Prediction Interv.
O O
0\\
O R
n 0- 0 D
i Fit U
S 0
0 0
knfiDergeIntery.
O i
- 0.1 -
O O
O O
O O
-0.2 -
0 0
0 0
0 o
-0.3 -
1
-0.4 -
-0.5 0
0.2 0.4 0.6 0.8 1
1.2 1.4 1.6 1.8 2
(Thousands)
Baron Concentration (PPM)
Figure 1
I I50 THERMAL TEMPERATURE COEFFICIENT BI AS i
(Meas-Calc) (E-4/F) 0.2 0.1-Prediction Interv.
0 0 0 I
(" tb n
n 0
Fit 0
E 0
0 E a
V O
O
-0 ^1 -
'EU g
I J
Confidencgint 0
i 0
2 u
O 0
0
%0 f
-0.2 -
0 0
E i
0 l
f D
o
-0.3 -
'f i
-0.4 -
l i
-0.5 O
0.2 0.4 0.6 0.8 1
1.2 1.4 1.6 1.8 2
l (Thousands)
Ekron Concentration (PPW) l R Waterford-3 Data a 0ther CE Plants Figure 2
Table 1 WATERFORD-3 ISOTHERMAL TEMPERATURE COEFFICIENTS Core Avg Core Avg PWR Tmod ITC ITC M-C Cycle Enrich Burnup PPM
(%)
(F)
MEAS CALC (10 % i r)
(10 % /4 )
(10 *ap/*F) 4 3.82 14074 1540 0
545
-0.074 0.065
-0.139 4
3.82 14211 1077 92 582
-0.957'
-0.855
-0.102 4
3.82 25206 370 95 582
-2.114
-2.049
-0.065 5
3.91 14898 1530 0
545
-0.097 0.003
-0.100 5
3.91 15040 1066 91 582
-0.912
-0.913 0.001 5
3.91 25907 404 93 582
-2.119
-2.017
-0.102 6
3.95 15524 1647 0
545
-0.114 0.173
-0.287 6
3.95 15524 1411 0
545
-0.600
-0.383
-0.217 6
3.95 15638 1131 90 578
-0.830
-0.726
-0.104 6
3.95 27465 444 96 580
-1.982
-1.875
-0.107 7
3.95 14974 1741 0
S45 0.160 0.253
-0.093 7
3.95 14974 1471 0
545
-0.435
-0.305
-0.130 7
3.95 16199 1162 94 578
-0.707
-0.666
-0.041 i
e u.
i WATERFORD TEMPERATURE COEFFIClENT BIAS (Meas-Calc) (E-4/F) 0.2 0.1 -
4 n
0 --
I E
v O
I
- 0.1 -
a E
E O
$v
-0.2 -
?
o
-0.3 -
t
-0.4 -
l
-0.5 i
i i
i i
i i
i i
i i
i i
i i
i i
i i
0 0.2 0.4 0.6 0.8 1
1.2 1.4 1.6 1.8 2
(Thousands)
Bcron Concentration (PRI)
Figure 3
If only the Waterford 3 data base were used to define an MTC design margin, it would require that the calculated MTC be less negative than the TS limit-by 0.25 X 10'd delta k/k/*F.
This criterion'is satisfied for Cycle 7.
From the data presented above, it can be concluded that the calculational models provide a very accurate prediction of the MTC under any operating conditions, and the accuracy of_the Waterford 3 predictions is quite comparable to that of other_ plants.
B.
Predicted Margin to _E0C Technical Specification Limit Current design predictions using ROCS. indicate that for Waterford 3 Cycle 7 the most negative E0C MTC is -2.88 X 10'd delta k/k/*F, relative to a TS limit of -3.3 X 10'd delta k/k/*F. This value is actually more negative than the best estimate E0C' MTC since it '
includes a 26 EFPD extension beyond the actual end of full power reactivity.
The margin to the TS limit is thus 0.42 X 10'd delta k/k/*F, much larger than the conservative uncertainty of 10.25 X 10'd delta k/k/*F based on the Waterford 3 data base alone.
+
C.
Similarity in Designs Between the Current and Past Cycles.
The similarity in designs between Cycles 4 to 7 results in the same trend of the measured temperature coefficients vs soluble boron concentration. Slight variations in core' average burnup, and the presence of 92 fresh assemblies in Cycle 7 vs 84 fresh assemblies in the previous cycles have a second order effect.
Figure 4 gives the change in measured moderator temperature coefficient with boron concentration. The data label on Figure 4 represent the cycle number.
It is clear that the data correlates well with boron concentration, and that the. slight variations in recent Waterford 3 cycle design have little impact on the MTC. This data indicates that the E0C-7 (0 PPM) MTC, based solely on past measurements, is expected to have a value of -2.59 X 10'd delta k/k/*F, which.is again well-within the current TS limit of -3.3 X 10~4 delta k/k/*F.
I i
- ~.-
e, 1
I l
1 WATERFORD-3 Measured Wderator Teno. Coefficients O.5 7
i 0
E Sh 8
l
-0.5 -
0 4 uv u
- 1. 5 -
]
6 h
45 m e 3
i
-2.5- -
Tech. SoeC
-35 0
0.2 0.4 0.6 0.0 1
1.2 1.4 1.5 1.8 CThousards)
Ekron Concentration CPFM) r 1
I Labels indicate Cycle Number Figure 4 l
I
l l
D.
Conformance to the Combustion Engineering Owners Group E0C MTC Measurement Elimination Criteria.
In 1993, ABB Combustion Engineering (CE) developed the methodology and criteria that ABB CE plants could utilize to eliminate the near l
end of cycle MTC measurement currently required by the TS
-Surveillance Requirements. This work, that was produced on behalf of the CE Owner's Group (CE0G), resulted in a Topical Report (Reference
- 2) that was submitted by Waterford 3 in December 1994 to the NRC for review. Although NRC approval of the CEOG Topical is not expected until 1996, the application of the methodology to the present _
evaluation further substantiates the previous arguments that the 2/3 expected. core burnup MTC measurement is not required.
The underlying concept of this methodology is that if the B0C HZP and HFP measured MTC's show sufficient agreement (to 0.16 X 109 delta i
k/k/*F) with the predicted values, then the near E0C MTC measurement can be eliminated since the accuracy of the E0C prediction 1:
guaranteed.
In the case of Waterford 3 Cycle 7, the HZP and HFP l
measured MTC's both. met this criterion (See data in Table 1).
l Therefore, if the CEOG methodology were currently approved, the 2/.1 i
expected core burnup measurement would not be performed.
Conclusions Waterford 3 and ABB CE believe that there is sufficient justification for the elimination of the near end of cycle MTC measurement for Cycle '7.
This conclusion is based on the following considerations:
a.
Present methodology used to predict MIC's for Waterford 3 is highly accurate.
b.
There is substantial margin in the best estimate E0C-7 MTC to current TS limit.
c.
The Waterford 3 cycle 7 design is sufficiently similar to previous cycles so that the expected MTC based solely on past measurements is well within the TS limit.
d.
If the methodology of Reference 2 were applied to Waterford 3 Cycle 7, then the near 2/3 expected core burnup MTC measurement would not be required.
0 Safety Analysis The proposed change described above shall be deemed to involve a significant hazards consideration if there is a positive finding in any of the following areas:
1.
Will operation of the facility in accordance with this proposed change involve a significant increase in the probability or consequences of any accident previously evaluated?
Response
No Waterford 3 is currently analysed for a E0C limitimg value of -3.3 X 10'd delta k/k/ F.
Under the proposed change, compliance with this TS f
Limit is assured by supporting data and arealysis. The analysis demonstrates that the predicted E0C 7 best estimate MTC value is
-2.88 X 10~d delta k/k/ F.
This is a conservative value because it includes a 26 EFPD extension beyond the actual end of full power 1
reactivity. The margin to the TS limit is :hus 0.42 X 10'd delta R/k/ F.
The probability and consequences of an accident previously evaluated will not be increased because this change does not modify any assumptions used in the input to the safety analyses. The current safety calculations will remain valid because the allowed range of MTC values will not change. Therefore, the proposed change will not involve any increase in the probsbility or consequences of any accident previously evaluated.
2.
Will operation of the facility in accordance with this proposed change create the possibility of a new or different type of accident from any accident previously evaluated?
Response
No Plant operation and plant parameter TS limits will remain unchanged.
There are no new changes in plant design nor are any new failure modes introduced. Therefore, the proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated.
s,.
3.
Will operati_on of the facility in accordance with this proposed change involve a significant reduction in a margin of safety?
Response
No The margin of safety will not be reduced because the range of allowed.
temperature coefficients will not be changed. The surveillance program consisting of beginning-of-cycle measurements was not affected.
Explicit End-of-Cycle 7 MTC predictions have ensured that the MTC.is and will remain within-the range of specified values.
t Therefore, the proposed change will not involve any reduction in a margin of safety.
Safety and Sionificant Hazards Determination 1
Based on the above safety analysis, it is concluded that:
(1) the proposed l
change does not involve an unreviewed safety question (USQ) (2) the proposed change does not constitute a significant hazards consideration as
' defined by 10CFR50.92; and (3) there'is a reasonable ' assurance that the health and safety of the public will not be end...gered by the proposed change; and.(4) this action will not result in a condition which significantly alters the impact of the station on the environment as described in the NRC final environmental statement.
Environmental Consecuences
~
This request involves the use of facility components located within the restricted area, as defined in 10 CFR part 20, and changes a surveillance requirement.
Entergy Operations Incorporated, has determined that this request does not involve:
(1)
A significant hazaN /nsideration, as described above; (2)
A significant change in the types or significant increase in the j
amounts of any effluents that may be released offsite; 5
(3)
A significant increase in individual or cumulative occupational radiation exposure.
i Accordingly, this request meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9)
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepa.ad in connection with this request.
j 1
i
References:
1.
"The ROCS and DIT Computer Codes for Nuclear Design". CENPD-266-P-A, April, 1983.
2.
" Analysis t,f Moderator Temperature Coefficients in Support of a Change in tha Technical Specification End of Cycle Negative MTC Limit".
Ct.'-NPSD-911, March, 1993.
.