ML20134J171
| ML20134J171 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/23/1985 |
| From: | Wilson R GENERAL PUBLIC UTILITIES CORP. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| 5211-85-2135, GL-83-28, RFW-0591, RFW-591, NUDOCS 8508290198 | |
| Download: ML20134J171 (2) | |
Text
,
GPU Nuclear NQQIgf 100 Interpace Parkway Parsippany. New Jersey 07054 201 263-6500 TELEX 136-482 Writer's Direct Dial Number:
August 23, 1985 5211-85-2135 REW-0591 Office of Nuclear Reactor Regulation Attn: John F. Stolz, Chief Operating Reactors Branch No. 4 Washington, D. C. 20555
Dear Mr. Stolz:
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 Response to NRC Request for Additional Information Generic Letter 83-28, Item 4.5.3 On November 8, 1983, GPUN provided a response to Generic Letter 83-28,
" Required Actions Based on Generic Implications of Salem /ATWS Events,"
defining the degree of TMI-l conformance as well as plans and schedules for upgrades to conform with the positions of the Generic Letter. On April 3, 1985, the NRC requested additional information on Items 2.1, 2.2 and 4.5 of the Generic Letter. GPUN provided information on Items 2.1 and 2.2 on August 5, 1985. This letter provides information on Item 4.5 and completes our response to the NRC's request for additional information.
Item 4.5.3 concerns the reliability of the Reactor Trip System (RTS) based upon the current Technical Specification required on-line functional testing interval. As indicated in our November 8, 1983 response, GPUN was participating in the Babcock & Wilcox Owners Group (BWOG) program to demonstrate that the current on-line test interval for the RTS is consistent with high RTS availability. The NRC requested a description of the program, a discussion of the results and plant specific information regarding how the results will be implemented at TMI-1.
The BWOG has completed its program and evaluation and concludes that the current one month surveillance test interval is consistent with high reliability. The evaluation (Attachment 1) was submitted to the NRC on h820198850823 p
DOCK 05000289 AoSC GPU Nuclear is a part of the General Public Utilities System
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5211-85-2135 August 23, 1985 April 8, 1985.
Section 4.5, Reactor Trip System Reliability (System Functional Testing), provides the information requested by the NRC. GPUN has reviewed the evaluation and concurs.
Note the two equipment upgrades discussed in the section Configuration Features of Importance have been implemented at THI-1.
S re y, W. H1) y-R.
son Director Technical Functions RFH:gpa 2231f/001-2 Attachment cc: R. Conte T. Murley J. Thoma i
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Working Together to Economically Provide Reliable and Safe Electrical Pow aprii e, nea Suite 220 7910 Woodmont Avenue Bethesda, Maryland 20814 (301)951 3344 ICAN648504 Mr. Thompson Division of Licensing Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, DC 20555
SUBJECT:
B&W Owners Group - ATWS Committee-Amended Resoonse to GL 83-28 Gentlemen:
83-28 dated November 5,1983. Attached is Amendment 1 :o the B&W O actions to date and future activities relative to these item e
discussed with your staff during recent meetings.The infor significant interaction with your Ctaff during the formulation and There has been implementation of these resolutions.
the development of sound and thorough resolutions.We believe this was most helpfu Should you have questions with regard to the Owners Group activities, p contact me.
Very truly yours, J. Ted Enos, Chairman BWOG ATWS Committee JTE: ds s
cc:
BWOG ATWS Committee E. C. Simpson FPC J. H. Taylor B&W t
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4.1 REACTOR TRIP SYSTEM RELIABILITY (VENDOR-R The original response to this Item (November 1983) indicated that no Vendor related modification had been recommended fo Trip Breakers (RTB).
In February 1984, the B&W Owners Group determine long term actions to improve r(eliability of the RTBsBWO particular the Undervoltage (UV) trip device.
This program was, in during presentations by the BWOG to the NRC on Jun October 10, 1984.
21, 1984 and The long term Improvement Program evaluated two general types of
+
improvements:
Replace GE AK Breakers with a different device; and Modify existing GE AK Breakers.
A number of alternatives were identified in each category as follows:
Replacement Alternatives W 05-206 Breaker with UV-and shunt W DS-416 Breaker with UV and shunt ITE K600 Breaker with UV and shunt ITE K1600 Breaker with UV and shunt Contactor/ Molded Case Breaker combination Solid State Device Modification Alternative Replacement of bearings with Mobi! 28 lubricated bearings and shunt trip.
Replacement of front frames and a shunt trip boosted UV device and a shunt tripReplacement of bearin Replacement of bearings with Mobil 28 lubricated bearings and 2 shunt trips.
It was recognized that many parameters and concerns existed which must be evaluated against each option to determine the one that best improved long term performance in e reasonable and economic manner assist in determining the best alternative.such, the Kepner-Treg As This technique is a Amendment 1 - April 8, 1985 q_
systematic process for thorough consideration of objectives, alternatives, and risks in selection of a course of action and it proved very valuable in our application.
To accomplish the review, a comprehensive list of system " Requirements" and "Desirables" were established.
Requirements to be considered acceptable.An alternative had to meet all Following this, the Desirables were " weighted" by relative importance and each alternative was assigned a numerical score based on its capability to meet the Desirable.
which represented its ranking as an alternative.The final result w are listings of the Requirements and Desirables. and 2 The first round KT evaluation clearly indicated that Modification alternatives were superior to Replacement Alternatives.
A second KT evaluation was conducted on the Replacement alternatives all the Requirements) in an effort to fine tune the e clearly distinguish between the alternatives.
The entire program was oriented toward identifying the root cause of previous UV performance problems and identifying the most cost effective resolution of those problems.
A substantial amount of data was gathered and evaluated w'nich indicated conclusively that the root cause was two fold:
Improper Maintenance Practices; and Aging of bearing lubricant.
This, combined with the results of the evaluation program lead conclusively to the following necessary modifications to resolve long term reliability concerns.
Improved Maintenance and Surveillance Practices Incorporation of Screening and Operability Criterion Installation of DC shunt trip Replacement of Trip Shaft bearings with Hobil 28 lubricated bearings Followup effort to verify fix.
This solution was chosen by the BWOG for the following reasons.
It meets all of the evaluation requirements.
The results of maintenance improvements made in 1983 were very positive.
Amendment 1 - April 8, 1985 i
rt.,)
It results in a breaker unreliability rate of less than 10E-3 per demand.
The overall Reactor Trip System Unreliability (failure to trip) is extremely small.
The shunt trip to be added has a proven high reliability.
GE lubrication testing indicated approximately lubricant.
It is a cost effective solution that technically resolves the concerns.
The BWOG has recommended that all applicable GE and B&W service advisories for RTB Maintenance be incorporated into the individual plant procedures.
and/or superceded during the evolution of this issue, the BW directed B&W to provide a Comprehensive Service Advisory which previous advisories. encompasses all currently valid advisory information be provided to the individual utilities.Upon completion of this work, the a
-The BWOG has recommended that each utility incorporate a scr The Screening Criterion (nominally 50 msec) is a me at a point where the RTB is still operable. response time which The Operability Criterion Analysis) beyond which the RTB is not Operable.(nomin The BWOG has recommended that each utility install a DC shunt t existing GE AK RTBs.
The BWOG has recommended that each utility adopt the 12 month preventative maintenance interval recommended by GE and B&W.
The BWOG has recommended that each utility replace trip shaft and roller bearings (in existing RTBs) with bearings lubricated with Mobil
- 28. In addition, the BWOG has recommended Mobil 28 lubricated be used exclusively in GE AK RTBs.
The BWOG has implemented a data gathering effort to evaluate the effectiveness of these modifications.
continue for approximately 2 years.
This program is expected to 4.2 for further details.)
(See Amendment 1 response to Item Amendment 1 - April 8, 1985
EVALUATION CRITERIA ALL OPTIONS REQUIREMENTS CapabilitytoInterrupth2KA@600V o
Trip Capability from RPS o
Reliability Greater than 10 E-3 o
500 Amp Continuous Current Rating o
Response Time Less than 80 msec o
Seismic Qualification (IEEE 344) o Compliance with GDCs o
Diverse From SCRs (ATWS Rule) o I
1 Amendment 1 - April 8, 1985
EVALUATION CRITERIA ALL OPTIONS DESIRABLES Minimize Responso Time o
2/1 Trip Force Over Required o
Parts Available Thru 2006 o
Minimize Maintenance Required o
o Minimize Cost Maximize Expected Life o
Maximize Maintenance Interval o
Minimize Implementation Schedule o
Capability To Provide Trip Confirm o
t Amendment 1 - April 8, 1985 U
O e
4.2 Reactor Trip System Reliability (Preventive Maintenance and Surveillance Program for Reactor Trip Breakers).
Item 1:
A Planned Program of periodic maintenance, including lubrication, housekeeping, and other items recommended by the equipment supplier.
Our Amendment 1 response to Item 4.1 describes the BWOG recommendatio for periodic maintenance.
Item 2:
Trending of parameters affecting operation and measured during testing to forecast degradation of operability.
Our November 3, 1983 response described in some detail a proposed program for trending RTB performance to forecast degradation.
program was originally proposed at a time (1983) when actual This performance degradation of RTB performance was being observed over a
', <,v relatively short time.
As such, it was expected that a trending program could predict a need for maintenance over a short period (e.g.
months).
The degradation in performance is now understood and attributed to aging problems with the lubricant used in the RTB bearings.
discussed in our Amendment I response to Item 4.1, the BWOG.has '
As with Mobil 28 lubricant. recommended that the RTB bearings be replaced with Extensive testing by General Electric has indicated that a similar aging problem with Mobil 28 should not occur for well in excess of 40 years.
This testing is substantiated by the fact that the test data predicted aging problems with the old lubricant at a time very consistent with field data.
lubricated with Mobil 28, short term performance degradation is notWith a expected.
Given this, the monitoring program has been reoriented to provide a
" proof of fix."
The program collects data from the B&W Operating Owners on key performance parameters notably UV response time, trip shaft torque, and UV device pick up and drop out voltage.
As the maintenance parameters (e.g., insulation resistance, etc being collected.
Data from these performance parameters is provided to the BWOG Availabilit> Committee for trending ano analysis.
Provicea no unexpected results are obtained, we anticipate this program to complete in approximately two years.
In addition to the lubrication change, the BWOG has recoe~ ended the incorporation of screening criteria in the maintenance / surveillance an Operability limit. procedure (s), which would result in RTB maintenance prior The BWOG has recommended that Preventative Maintenance be performed on GE RTB's, at a 12 month interval.
Field experience with Mobil 28 Amendment 1 - April 8, 1985 i
lubricated bearings, to date, has shown essentially no RTB performance degradation between maintenance intervals.
Item 3:
Life testing of the breakers (including the trip attachments), on an acceptable sample size.
The BWOG has evaluated this concern and the circumstances surround the Westinghouse RTBs at Salem, which prompted the concern.
Substantial input has been obtained from General Electric and B&W in the course of this evaluation as well as the field experience of the RTB users.
It is the conclusion of the BWOG that the design of the GE AK RTBs is such that the breaker and its tripping devices are not susceptible to a wear related failure as are the Westinghouse RTBs.
GE does not recommend replacement of any trip related parts (due to wear related concerns) for the life of the breaker.
in years and number of trips both of which are beyond actual serviceB projected to be seen in actual RTB service.
As such the BWOG has concluded that life cycle testing of a GE RTB would produce no useful information to predict wear related failures as there are no mechanistic means for wear to produce a failure.
therefore,. does not recommend performance of a life cycle test.
The BWOG Please refer to the BWOG Amendment 1 response to Item 4.5.3 for further analysis of breaker wear.
Item 4:
Periodic replacement of creakers or components consistent with demonstrated life cycles.
The BWOG recommends that GE RTBs be maintained and/or replaced consistent with existing Ganeral Electric and B&W guidance.
Amendment 1 - April 8, 1985-4 L
L
- 4. 5 REACTOR TRIP SYSTEM RELIABILITY (System Functional Testing)
I Item 4.5.3 Existing intervals for on-line functional testing required by l
Technical Specifications shall be reviewed to det availability when accounting for considerations such as:
1.
uncertainties in component failure rates 2.
uncertainty in common mode. failure rates 3.
reduced redundancy during testing 4.
5.
operator errors during testir,g component " wear-out" caused by the testing" determine appropriate test intervals as described abo to existing required intervals for on-line testing as well as the Changes intervals to be determined by licensees currently not performing on-line testing shall be justified by information on the sensitivity of reactor trip system availability to parameters such as the test intervals, component failure rates, and common mode failure rates.
Our November 3, 1983,- response indicated that the BWOG had an evaluation underway to address this item.
That evaluation has been completed and the results demonstrate the current one month surveillance test interval for the Reactor Trip System is consistent with high reliability.
The following is a summary of the evaluation and conclusions.
Configuration Features of Imoortance The investigation performed is generic to all plants with B&W NSS equipment including 177 and 205 fuel assembly plants.
be accounted for by the reliability evaluation of the R Only two ane month test interval (or for longer intervals).
Consequently two separate models have been constructed.
For this project all 177 fuel assembly plants exce configuration (0conee group);pt Davis Besse are represented by one Fuel Assembly plant are the other configuration (Davis BesseDavis group).
The fundamental differenr.e between the two configurations is:
l Oconee group:
Safety rods (groups 1-4) are tripped by the Control Rod Drive Control System (CROCS) using the O.C.
Shunt and A.C. undervoltage trip devices of each A.C. or 0.C. breaker.
Regulating rods (groups 5-7) are tripped by the electronic trip (SCR's) portion 0.C. shunt and A.C. undervoltage trip devices.of t Amendment 1 - April 8, 1985 i
Davis Besse All rods are tripped by either the CRDCS using f..C.
group:
breakers or the electronic trip (SCR trip).
breaker is tripped by 0.C. shunt and A.C. undervoltage Each trip devices.
breakers are backed by the electronic trip (SCR tr electronic trip reduces the possibility of common mode failures The Trip actuation features of these two groups of plants are very 1
similar.
inputs are virtually the same.The Reactor Protection System (RPS) an Anticipatory Reactor Trip System (ARTS) that senses loss ofThe feedwater and signals reactor and turbine trip.
of the ARTS arrangement exist between the two groups of plants Minor differences to the electronic trip, two important equipment up in progress (or have been completed) to reduce the potential fo now common mode failure of the breakers.
r exist for the purpose of this evaluation. changes will be in 1.
Chance of trio shaft bearirc-iubricant to Mobil 28 from Lucriko, the original trip snaft bearing lubricant.
Accelerated aging tests by General Electric indicat~e that Mobil 28 has an expected lifetime in excess of approximately 1 x 106 lifetime of 1 x 105 hours0.00122 days <br />0.0292 hours <br />1.736111e-4 weeks <br />3.99525e-5 months <br /> (s100 years) as compared to the Lubriko operating temperature of 40*C. hours (s10-11 years) at an expected associated with lubricant stiffening are expected to beThus the pa diminished considerably for the remainder of plant life particular the common mode failure contribution to RTS In unavailability that has largely been attributed to breaker shaft bearing stiffness resulting in slow response when the by the lubricant change.undervoltage device is actuated is expact The BWOG has recommended each with Mobil 28 lubricant (see Amendment 1 to Item 2.
Addition of an RPS trio sional to the D.C. Shunt trio devic This cevice operates on a cifferent principle than the A C _
~
undervoltage trip device.
Whereas the A.C. device is released by removal of power to the coil and uses the power cevice uses the power obtained by energizing a c the trip shaft to the " breaker open" pssition.
l The f
undervoltage device can apply about 30 oz. in of torque, but the shunt device can apply approximately 200 oz. in of torque.
Thus the O.C. shunt trip provides a diverse mechanism from the A.C. undervoltage device and would be expected to cause shaft rotation even with frozen bearings.
Amendment 1 - April 8, 1985
Methods and Aoproach The modeling methods use Reliability Block Diagrams (RBD's) for The PACRAT code (developed by B&W was used dependent unavailability of equipment for the one-month on-line test intervals.
It is similar to FRANTIC II and has been used for other evaluations of the RPS previously submitted to the NRC (see i
topical report BAW-10085P, " Reactor Protection System " Vol Rev. 6, April 1979.
. 2, and Davis Besse gro)ups include sensors and process equ providing signals to the Reactor Protection System (RPS), the RPS trip module outputs, the sensors and processing equipment l
associated the Anticipatory Reactor Trip System (ARTS), the ARTS and the CRDCS Electronic Trip (SCR's). outputs, the control The analysis addressed automatic RTS operation and omitted credit for the additional advantages of operator action for manual trips and operator action to " power drive" the rods in using the CRDCS in manual All of the five issues raised by question 4.5.3 were addressed by
~the evaluation.
Ranaam and common mode equipment failure rates were accounted for and operating experience was used to suppert the evaluation wherever,possible.
Data from LER's was used foh
' sensors and inst,rument strings a'nd B&W operatin'g experience data was relied upon to provide random and common mode breaker failure rates and was updated to show the effects of the lubricant changes.
evaluated to obtain failure modes and frequencies for theH individual breaker components.
CE operating experience was used to provide failure rates for the shunt trip device and both B&W and CE experience provided data to support the U.V. device failure rates.
the U.V. device actuation, the expected future performa accounted for by crediting the breaker data base operating experience for those past events for which failure would not have occurred had the new lubricant been installed.
Generic data sources were used to provide failure rates for quantification for and instrument strings. electrical components of the RTS otner than t Wearout caused by test cycling and aging was evaluated for all components ano emphasis was placed on the breakers since they are most affected by testing.
The breakers are designed for 12,500 cycles and the lubricant change will virtually eliminate aging concerns.
It was concluded tnat wearcut is a relatively unimportant concern, nowever possible effects were simulated by a sensitivity analysis using the RBD's.
Amendment 1 - April 8, 1985
The effects of testing on RTS availability included the influence of operator errors during testing and considered test and maintenance errors that could contribute to breaker failure to trip.
The effect of reduced system redundanc., due to channel i
bypass during testing was also evaluated.
Tna tests of importance are the monthly single channel RPS and ARTS instrument string, the trip module, and breaker tests.
Time dependent point estimate values for the RTS unavailability I were determined using best estimate data to establish a base line and the sensitivity analysis was performed to indicate the influence of uncertainties for the five considerations of question 4.5.3.
The sensitivity analysis was based on a 95% upper bound distribution and provided insights for the effects of uncertainties.
Amendment 1 - April 8, 1985
l Summarv of Results and Conclusions 1.
The results of the best estimate and sensitivity analyses are:
Average System unavailability using best estimate data Davis-Besse class Oconee class Base Case Best estimate time average system 6 x 10 7/ demand 6 x 10 7/ demand Average System unavailability using best-estimate data Davis-Besse class Oconee class Sensitivity to Uncertainties in random component failure rates 7 x 10 7/ demand 2 x 10 8/ demand (slightly (moderately sensitive) sensitive)
Uncertainties in common mode
-failure rates / operator errors-9 x 10 6/ demand 6 x 10 8/ demand (highly.
(highly sensitive) sinsitive)
Reduced redundancy during test 9 x 10 7/ demand 6 x 10 7/ demand (channel bypass)
(slightly (slightly sensitive) sensitive)
Breaker wearaut caused by testing (not sensitive)
(not sensitive) 2.
The RTS configuration of both the Oconee and Davis Bessee groups have several features that contribute to the high reliability such as:
a)
The Electronic Trip (SCR trip) provides a' diverse method of trip actuation that is separate from the CROCS mechanical breakers.
Thus the potential for failure to trip due to common mode failure of the breakers is significantly reduced.
b)
The common mode failure potential of the breakers is considerably reduced by the addition of the shunt trip device which provides diversity from the undervoltage device.
The reliability of trip actuation by the undervoltage device is improved by the lubricant change.from Lubriko to Mobil 28.
c)
The RPS and ARTS are configured with four channels.
3.
The wearout evaluation indicated that the RTS components are not susceptible to wearout caused by testing.
components affected by test cycling and the GE AK-2 breaker has aThe bre design cycle objective of 12,400 cycles.
Aging of the trip shaft i
Amend.nent 1 - April 8, 1985 o
bearing lubricant is virtually eliminated as a concern when the Mobil 28 lubricant is installed.
mode failure due to wearout is not a significant source of RTSTh unavailability.
indicate that wearaut is a concern.Other components do not exhibit historie 4
Reduced redundancy caused by testing does not significantly contribute to RTS unavailability.
testing of the RPS and ARTS sensor strings which has the e Other on-line tests (breakers, electronic trip, trip mo performed with the channel tripped and therefore in a " fail safe" condition that does not affect unavailability.
5.
The evaluation of the RTS reliability and demo addresses the concerns of Generic Letter 83-28 Item 4.5.3.
necessity of further evaluation to determine a different surveillance The incorporated in their overall evaluation of Tech Spec Amendment 1 - April 8, 1985 8
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