ML20154P777
| ML20154P777 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 05/19/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20154P768 | List: |
| References | |
| NUDOCS 8806060074 | |
| Download: ML20154P777 (10) | |
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UNITED STATES y
g NUCLEAR REGULATORY COMMISSION 5-1l WASHINGTON. D. C. 20555 i
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\\***# /SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0. 84 TO FACILITY OPERATING LIC5NSE NPF-9 AND AMENDMENT N0. 65 TO FACILITY,0PERATING LICENSE NPF-17 T
DUKE POWER COMPANY DOCKET NOS. 50-369 AND 50-370 MCGUIRE NUCLEAR STATION, UNITS 1 AND 2 INTRODUCTION 1
By letter dated October 29, 1985 and supplemented by letters dated August 25, 1986, May 26, 1987 and January 19, 1988, Duke Power Company (the licensee) requestad amendments to Facility Operating License Nos. NPF-9 and NPF-17 for the McGuire Nuclear Station, Units 1 and 2.
The' proposed amendments would revise the Technical Specifications (TS) due to changes in the reactor trip system and engineered safety features response times to accommodate the removal of the Resistance Temperature Detector (RTD) bypass system and the installation of repiscement RTDs in thermowells located s-directly in the hot leg and cold leg piping.
This system will use narrow range fast response RTDs.
This design modification is desired by the licensee because of problems with the existing RTD bypass sp, tem due to leakage from valve packing or mechanical joints.
These problems reduce system reliability and result in high radiation doses during the performance of. maintenance around the RTD bypass system.
f Tne substace of the changes noticed in the Federal Register on September 10, 1986 and the proposed No Significant Hazards determination were not affected by th licensee's letters dated May 26, 1987 and January 19,.1988, which clarified cercain aspects of the request.
j EVALUATION
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Present System 9escription Currently, the hot and cold leg temperatures of each steam generator are measured by RTDs inserted into reactor coolant bypass loops.
A bypass loop from upstream of tre steam generator to downstream of the steam generator is used for the hot leg RTDs and a bypass loop from downstream of the reactor coolant pump to upstream of the pump is used for the cold leg RTDs.
The RTDs are located in manifolds in the bypass loops and are directly inserted into the reactor coolant flow without thermowells.
Each RTD manifold (one hot leg and one cold leg manifold per reactor coolant loop) contains two narrow range RTDs:
one for protection and control system inputs and one as a spare.
Flow into each hot bypass is provided by three scoops located at 120 intervals around the hot leg pipe perimeter to take account of temperature variation across the pipe due to hot leg streaming.
The action of the coolant pump provides well mixed coolant in the cold leg bypass manifold from a single tap into the cold leg.
0806060074 080519 PDR ADOCK 05000369 P
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w Each loop's pair of RTDs (one in the hot leg and one in the cold leg) is used to provide inputs for protection system functions based on the average loop temperatures Tavg = (T HOT COLD)/2 and the loop differential temperature, delta T =T
-T Protection functions based on these HOT COLD.
inputs are:
overtemperature delta T and overpower delta T reactor trips with their associated (non protection) rod stop and turbine runback actions, low Tavg main feedwater isolation, and low-low Tavg (P-12) steam dump block signals.
Each loop's pair of RTDs is also used to provide inputs for control system functions based on the average loop temperature and the ioop differential temperature.
Control functions based on these inputs are:
turbine loading stop from auctioneered low Tavg; rod, steam dump and pressurizer level control from auctioneered high Tavg; and rod insertion limit alarms from auctioneered high delta T and Tavg.
Modified System Description In the proposed modified system, after removal of the bypass loops, the hot leg temperature inpui.s from each reactor coolant loop will be developed from three fast response narrow range RTDs mounted in thermowells located within the three existing RTD bypass manifold scoops.
An outlet port will be provided at the end of each scoop and the thermowell will be positioned so that the RTD sensing element it ated near the middle inlet hole of the scoop.
The objective of this dei to ensure that the temperature sensed by the RTD is close to that of evious scoop flow.
One RTD per loop will be mounted in a thermowell located at the existing penetration for the bypass loop into the cold leg downstream of the coolant pump.
Additionally, a new penetration will be added to each cold leg for a spare thermowell-mounted, narrow range RTD.
The RTDs are placed in thermowells to allow replacement without draindown.
The thermowells, however, increase the response time.
Each hot leg temperature input for protection system functions will be developed by electronically averaging the signals from the three new fast response, narrow range RTDs.
This averaged input will replace the single input from the currently installed hot leg RTD.
Each cold I?g input for protection system functions will be provided by the new fast response, narrow range RTD which replaces the currently installed cold leg RTD.
In the event of a hot leg RTD failure, the electronics allow a bias developed from historical data for the failed RTD to be manually added via a potentiometer to the remaining two RTD signals in order to obtain an average value comparable to the three-RTD average prior to failure of one RTD.
If a cold leg RTD fails, the spare cold leg RTD can be used instead.
The failure of an RTD would be detected by the Tavg or delta T deviation alarm.
Inputs for the control system functions will be provided, through isolators, from the average loop temperatures and loop differential temc:ratures calculated by the protection system.
This aspect of the design has not been changed; only the use of three hot leg RTDs instead of one per loop to provide an average hot leg temperature is different.
Effect of Modifications on Overall RTD Response Time In the existing bypass system, the overall RTD response time of 10.0 seconds consists of 2.0 seconds for the RTD bypass piping and thermal lag, 0.5 second for the RTD response time, 6.0 seconds for the RTD filter time constant and 1.5 seconds for the electronics delay.
In the licensee's January 19, 1988 submittal, the overall response time of the new thermewell RTD hot leg temperature measurement system is also given as 10.0 seconds, and consists of 6.5 seconds for the RTD-thermowell combination, a 2 second electronic filter time constant and 1.5 seconds for the electronic delay.
Recent testing at another plant aftcr completion of a similar RTD bypass system removal modification has resulted in response times slightly greater than ant.cipated.
Also, as noted in NUREG-0809 (Reference 1), extensive RTD testing has revealed degradation of RTD response tire with aging.
In accordance with the guidance in NUREG-0809, the licensee in its January 19, 1988 submittal revised Technical Specification (TS) 4.3.1.2 to provide for response time testing of all RTDs once per 18 months.
The testing method specified is the Loop Current Step Response (LCSR) method, which is the approved in-situ method for measuring RTD response time.
Effect of Modifications on Temperature Measurement Uncertainty With regard to the effect of the proposed plant modification on the uncertainty of the temperature measurements, the new method of measuring each hot leg temperature with three thermowell RTDs manufactured by the RdF Corporation, used in place of the RTD bypass system with three scoops, has been analyzed to be slightly less accurate.
The measurement uncertainty of the RTDs manufactured by the RdF Corporation is slightly greater (by about 0.5 F) than that of the existing Rosemount RTDs.
Also, the new thermowell measurement may have a small streaming error relative to the former scoop flow measurement because of the temperature gradient over the 5-inch scoop span.
On the other hand, the modified system eliminates hot leg temperature uncertainties due to unbalanced scoop flows.
Hot leg temperature uncertainties are further decreased because of the statistical advantage of using three RTDs rather than the single RTD used in the bypass method.
Because of these compensating factors, the overall effect of the modifications on Tavg and delta T values is small, and the current values of nominal setpoints for the McGuire TS would remain valid for the modification.
There will be no change in the present RTD temperature deviation alarms which include both a Tavg and a delta T deviation alarm.
This alarm system compares the Tavg or delta T signals to a pre-set threshold value.
This value is nominally set to + or - 2 F and is adjusted during startup and subsequent operation such that it is just beyond the range of normal operating variations.
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4 RTD Drift Literature studies (References 1 to 4) have indicated some tendency for long-term drift in RTD readings.
The licensee will compensate for drift by calibrating the RTDs at each refueling.
The calibration method is the Westinghouse-recommended RTO cross-calibration method at heatt.ps af ter each refueling.
This procedu.e requires multiple measurements at thise or four different temperatures.
To date, Westinghouse has evaluated the ca t from over 400 RTDs using this technique, and several repeat tests performed one to three years apart have not shown any indication of drift in only one ditaction.
The results of the tests indicate that the RTDs drift less than was assuned for uncertainty calculations for the protection system.
The procedure sens -
i tivity is sufficient to discern a random drift of less than 1.0 F by one or several RTDs.
If a drift is noticed, either the calibration of the resistance to voltage converter for the affected RTD would be adjusted to account for the shift, or if the drift is appreciable, the RTO would be declared inoperable and wou' be replaced.
Comparison of Delta T Readings Before and After Modifications Since both the old and the new methods of coolant temperature measurements have an inherent streaming inaccuracy, accounted for in the staff's safety analyses, it is not appropriate to compare the new method to the old method and declare any differences as errors.
It is possible, however, to compare the normalized full power delta T measured before and after the modifications.
It is expected that the delta T readings will be very similar once any secondary side measurement errors, such as feedwater flow, have been factored into the power calculation.
If there were any significant differences between the two delta T readings, it would indicate that a problem existed with one of the measurement methods.
The licensee will perform a comparison of the temperature indications after the modification with measurements prior to the modifications.
The NRC will be notified of the results of this comparison including an explanation of any variations larger than expected.
Effect of Modifications on RCS Flow Measurement Uncertainty The RCS flow measurement uncertainty after the RTD system modifications e analyzed by the licensee using the methodology in letter NS-EPR-2577 dated March 31, 1982 from E. P. Rahe, Jr. of Westinghouse to C. H. Berlinger of NRC.
The methodology is based upon use of a calometric procedure to determine PCS flow.
This analysis used data from the plant-specific instrumentation of the McGuire plant.
l As mentioned abov1, RTO system modification will result in a slightly increased uncertainty in individual RTD readings and in the individual hot leg temperature determination for each loop.
However, in using the calometric procedure to determine RCS flow, the temperatures in all four loops are considered.
The RCS temperature uncertainties are reduced because data from the cross-calibration of the RTDs in all four loops during heatups before power operation are used.
Because of this statistical advantage, the RCS flow measurement uncertainty remained the same as the current value of 1.7%
(not including a 0.1% penalty for feedwater fouling allowance),
the staff reviewed this analysis and finds that the flow measuremert uncertainty will not be increased by the RTO system modifications and re, mains acceptable.
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l Effect of Modifications on Non-LOCA Accident Analyses Non-LOCA accident analyses which rely on overtemperature and overpower delta T (0 TDT and OPDT) reactor trips can potentially be affected by RTD modifications, primarily through their effect on RTD response time.
These events include (1) Uncontrolled Rod Cluster Control Assembly (RCCA) withdrawal, (2) Uncontrolled Boron Dilution at Power, and (3) Steamline Rupture at Power.
Since the overall RTD response time in the modified system (10.0 seconds) will remain the same as in the present bypass system, there is no impact on the FSAR Chapter 15 non-LOCA accident analyses, and the conclusions presented in the FSAR and our SER remain valid.
Effect of Modifications on LOCA Accident Analysis The replacement of the RTD bypass system will impact the uncertainties associated with RCS temperature and flow measurement.
The effect of these uncertainties on the LOCA evaluation has been considered.
The magnitudes of the uncertainties in the RCS inlet and outlet temperatures, thermal design flow rate and the steam generator performance data used in the LCCA analyses are such that the conclusions of the existing analyses are not affected.
Past sensitivity studies concluded that the inlet temperature effect on peak clad temperature is dependent on break size.
As a result of these studies, the LOCA analyses are performed at a nominal value of the inlet temperature without consideration of small uncertainties.
The RCS flow rate and staam generator secondary side temperature and pressure are also determined using the loop average temperature (Tavg) output.
These nominal values used as inputs to the analyses are not affected by the RTD modifications.
We find that the replacement of the bypass system ty the in-line thermowell RTDs will not affect the LOCA analyses input, and hence the results of the analyses remain unaffected.
Therefore, the plant design changes due to the RTD bypass replacement are acceptable from a LOCA analysis standpoint.
Effect of Modifications on Plant Instrumentation and Controls The staff has evaluated the effect of the proposed modification upon the plant's instrumentation and control system based upon Sections 7.2 and 7.3 of the Standard Review Plan (SRP).
Those sections state that the objectives of the review are to confirm that the reactor trip and engineered safety features actuation system satisfy the requirements of the acceptance criteria and guidelines applicable to the protection system and will perform their safety function during all plant conditions for which they are required.
Since the staff's review indicates that the modified system does not functionally change the reactor trip and engineered safety features actuation systems (except three hot leg RTDs are utilized instead of just one), the staff's existing evaluation conclusions for these systems, as documented in Section 7 of the SER for McGuire Units 1 and 2 (NUREG-0442), remain valid.
Based on this and the licensee's statement that the new hardware for the RTD bypass elimination has been qualified to WCAP-8587, "Methodology for Qualifying Westinghouse WRD Supplied NSSS Safety Related Electrical Equipment," the staff finds the plant modifications to eliminate the RTD bypass manifold and to install fast response RTDs directly in the reactor coolant system hot and cold legs to be acceptable.
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. Changes to McGuire Technical Specifications As a result of the proposed plant modifications to remove the existing RTO bypass manifolds and replace them by in-line RTDs, the following changes to the McGuire TS have been requested L,y the licensee:
Change 1 -
In Table 2.2-1 under Functional Units 7 and 8, add "**" to the entries under Allowable Value to reference a new footnote (see Change 2).
Change 2 -
On page 2-5 add a new footnote "** Prior to removal of each unit s RTO bypass manifolds, Note 3a is applicable."
Change 3 -
In Table 2.2-1 under Functional Unit 8, revise the entry under Allowable Value from "Note 3" to "Note 4."
Change 4-In Table 2.2-1 under Functional Unit 12, revise the entry under Allowable Value from "89%" to "88.8%."
Change 5 -
On page 2-8 revise the value for T from " 16 sec." to 3
1 sec."
2 Change 6 -
On page 2 9 revise the value for T from " <6 sec." to " <2 sec."
6 Change 7 -
On page 2-11 revise the allowable value in hote 3 from "2%" to "3.6% of Rated Thermal Power."
Change 8 -
On page 2-11 add the following new footnote:
"Note 3a:
The channel's maximum trip setpoint shall not exceed its computed trip setpoint by more than 2%."
Change 9 -
On page 2-11 add the following new footnote:
"Note 4:
The channel's maximum trip setpoint shall not exceed its computed trip setpoint by more than 4.2% of Rated Thermal Power."
Change 10 -
Add new page B 2-4a which is equivalent to old page B 2-5 with tne phrase "(WITH RTD BYPASS SYSTEM INSTALLED)" added to the title "BASES."
Change 11 -
On page B 2-5 add the phrase "(WITH BYPASS SYSTEM REMOVED; RTDs IN THERM 0 WELLS)" to the title "BASES."
Change 12 -
On page B 2-5 under "Overtemperature aT," delete the words "piping transit delays from the core to the temperature detectors (about 4 seconds)" and substitute "thermal delays associated with the RTOs mounted in thermowells (about 5 seconds)" in the first sentence.
, Change 13 -
On page B 2-5 under "Overpower AT", delete the words, "for piping delays from the core to the" and substitute "for instrumentation delays associated with the" in the second sentence.
Change 14 -
On page 3/4 3-9, change the footnote identified as "*"
to footnote "(1)."
Change 15 -
In Table 3.3-2 for Functional Units 2, 4, 7 and 8, under Response Time, reference footnote "(1)" in lieu of footnote HA H Change 16 -
In Table 3.3-2 change the response time for Functional Units 7 and 8, Overtemperature oT and Overpower AT, from "8.0" to "10.0."
Change 17 -
In Table 3.3-2 for Functional Units 7 and 8 under Response Time, reference a new footnote "(2) The <10.0 second resoonse time includes a 6.5 second delay for the RTDs mounted in thermowells" which is added to the page.
Change 18 -
In Table 3.3-2 for Functional Units 7 and 8 under Response Time, reference a new footnote "(3) The
-<10.0 second response time is applicable to each unit only after the RTD byp' ass manifold is removed; until then the value
<8.0 sec.
Change 19 -
On page 3/4 3-1, add a new Surveillance Requirement:
"4.3.1.3 The response time of RTDs associated with the reactor trip system shall be demonstrated to be within their limits (see Note 2 to Table 3.3-2) at least once per 18 months."
Changes 1, 2, 3, 8, 10, 11, 12, 13, 14, 15, 17, and 18 above are editorial changes necessary to c1 compass the removal of the RTO bypass manifold and the situation where remova' of the bypass has been completed on only one of the two units.
On the basis that these changes add clarity and conciseness to the technical specifications, we find them acceptable.
Changes 4, 7, and 9 above are new values based on revised instrumentation uncertainties resulting from the bypass manifold elimination.
These new values were calculated using essentially the Westinghouse setpoint methodology as previously approved by the staff for generic use (see NUREG-0717, SER for Virgil C. Summer Nuclear Station) as documented in the licensee's letter dated May 26, 1987.
The staff finds these changes acceptable.
Changes 5, 6, and 16 above are new values based on revised individual component response times resulting from the bypass manifold elimination.
Since the new individual response times produce a total response time for the two reactor trips which were previously approved by the staff (see the staff's SER related to Amendment 42 to Facility Operating License NPF-9 and Amendment 23 to Facility Operating License NPF-17), we find these changes acceptable.
Change 19 provides a means to detect RTD drift and make appropriate adjustments before allowable limits are exceeded.
This change is therefore acceptable.
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, Mechanical Safety Evaluation The staff has reviewed the fabrication and inspection methods described in the licensee's letter dated October 29, 1985 for the replacement of the RTD bypass system with the new RTD thermowell system.
This change requires modifications to the hot leg scoops, the crossover leg bypass return nozzle, the cold leg piping and the cold leg bypass manifold connection.
The new thermowells, caps cnd penetrations will be fabricated in accordance with the ASME Code,Section III.
The welding will be by approved procedures and inspected by penetrant testing per the ASME Code Section XI.
In accordance with Article IWA-4000 of Section XI, a hydrostatic test of the new pressure boundary welds will be performed.
The staff finds that the mechanical aspects of the proposed RTD thermowell system, fabricated, examined and tested as described above, are acceptable.
Radiological Safety Evaluation The licensee has estimated the occupational radiation exposure for the RTD bypass modification in the submittals of October 29, 1985 and August 25, 1986.
The estimate is based on anticipated stay times for each major subtask and estimated dose rates.
The estimates per loop and per unit are given in the table below.
Manhour Oose Estimate Subtask Estimate (Person-Rem)
(1) Preparation for RTD 33 1.09 bypass modification (2) Shielding Installation /
64 9.6 Removal (3) Remove / Replace pipes, 417 11.1 hangers, electrical interferences, etc...
(4) Modify the RTDs 120 12.0 Total per loop BT4 3I79 Total per unit 2536 135.16 (4 loops) man-hours person-rem Specific measures to keep doses as low as is reasonably achievable (ALARA) will include preplanning of mechanical operations, use of temporary shielding and special tooling, familiarization of workers with the work area, and close supervision of the work in process by nealth physics technicians and ALARA personnel.
The licensee will adhere to administrative limits for occupational exposure to individual workers at McGuire which are lower than the NRC limits in 10 CFR 20.101 (for example the licensee's administrative whole body dose limit is 1.0 Rem per quarter, which is less than the 10 CFR 20.101(b) dose limit of 1.25 Rem per quarter).
Therefore, the licensee's administrative limits for individual workers, as applied to the RTD mo'difications, are acceptable.
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After replacement of the RTD bypass manifold system, present occupational exposures associated with valve and manifold maintenance, in-service inspection and snubber inspection would be avoided.
Over the life of the plant, the licensee estimates this dose would be approximately 1250 person-rem per unit.
The net occupational exposure savings would therefore be approximately 1115 person-rem per unit.
No significant liquid or gaseous radioactive wastes are expected to be generated as a result of the RTD replacement implementation activities.
Therefore no increases in liquid or airborne effluents (and related offsite doses to the public or maximum individuals) are expected 3s a result of the modifications.
Some solid radwaste will be generated, and the licensee has specifically identified the radioactive materials slated for disposal (typically valves, hangers, and possible decontamination materials).
This waste will be shipped to an appropriate land burial site, or scrapped if decontamination is feasible.
The solid radwaste volume will be about 13.6 cubic meters, containing an estimated 8.4 curies of radioactivity.
This is only about 8% of the average annual volure of radwaste shipped from the McGuire station, and less than 2%
of the average volume of radioactive waste shipped per PWR in recent years (729 cubic meters per PWR per year, 1980 - 1984).
The licensee has identified dose rates and contamination levels which fall into the typical ranges of such wastes.
The types, volumes and activities of these wastes as characterized are well within the parameters of normal operations evaluated for radiological impact in the FES and SER for McGuire 1 & 2.
On the basis of the above considerations, and the licensee's radiation protection programs previously found to be acceptable in the SER, the staff corcludes that the radiological and ALARA aspects of the proposed RTD replacement are acceptable, and that the proposed modification will result in an overall reduction in occupational exposure.
ENVIRONMENTAL CONSIDERATION l
These amendments involve changes to the installation or use of facility com-ponents located within the restricted area as defined in 10 CFR Part 20 and changes in surveillance requirements.
The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational exposures.
The NRC staff has made a determination that the amendments involve no significant hazards consideration, and there has been no public comment on such finding.
Accordingly, the amendments meet 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 i
prepared in connection with the issuance of these amendments.
CONCLUSION The Commission made a proposed determination that the amendments involve no significant hazards consideration which was published in the Federal Register (51 FR 32266) on September 10, 1986.
The Commission consulted with the state of North Carolina.
No public comments were received, and the state of North Carolina did not have any comments.
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10-We have concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public.
REFERENCES (1) NUREG-0809, Safety Evaluation Report, Review of Resistance Temperature Detector Time Response Characteristics, August 1981.
(2) NUREG-CR-4928, Degradation of Nuclear Plant Temperature Sensors, June 1987.
(3)
K. R. Carr, An Evaluation of Industrial Platinum Resistance Thermometer Temperature - Its Measurement and Control in Science and Industry, ISA publication, Vol. 4, Part 2, 1972, pages 971-982.
(4)
B. W. Mangum, The Stability of Small Industrial Platinum Resistance Thermometers, Journal of Research of the NBS, Vol.
89, No.
4, July-August 1984, Pages 305-350.
Principal Contributors:
S. Kirslis, POII-3/0RPI/II
- 0. Hood, POII-3/0RPI/II F. Burrows, DEST /SRXB H. Balukjian, DEST /SRXB Dated: May 19, 1988 l
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'May 19. 1988 DATED:
AMENDMENT NO. 84 T0 FACILITY OPERATING LICENSE. hPF McGuire Nuclear' Station, Unit 1.
' AMENDMENT NO 65 TO FACILITY OPERATING LICENSE NPF McGuire Nuclear Station Unit 2 DISTRIBUTION:~
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