ML20237J092
| ML20237J092 | |
| Person / Time | |
|---|---|
| Issue date: | 08/19/1987 |
| From: | Novak T NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Arlotto G NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML19318E953 | List: |
| References | |
| RTR-REGGD-01.106, RTR-REGGD-1.106 NUDOCS 8708250310 | |
| Download: ML20237J092 (8) | |
Text
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AUG 111'987.
1
%.c MEMORANDUM FOR:
Guy ' A. Arlotto, Director,
~
Division of Engineering, RES l
l FROM:
' Thomas M. Novak, Director Division of. Safety Programs, AE00-
SUBJECT:
COMMENTS ON PROPOSED REVISION 2.TO REGULATORY. GUIDE 1.106 l
The purpose of this. memorandum is to provide. comments in response to your request of July 14, 1987 concerning proposed Revision'2, Draft I to Regulatory
-[
Guide 1.106, " Thermal Overload Protection for Motor Operated Valves:for Nuclear!
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- Power Plants," dated July 1987.
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Since AE0D has.-rec $mmended review of thernal overload (TOL) devige use and Regulatory Guide 1.106 in at least three reports (AE00/C203, May 1982; AE0D/
<l 5503, September 198S; and AE0D/C603, December 1986), we. support this effort-to.
= revise Regulatory Guide.'I.106.. We do, however, have'several concerns 'about
' issuance at this: time.and with the proposed emphasis and direction. The issues
- of.. concern are applicability to operating plants as well as new plants; com-pletion.of on-going efforts by the Generic Issues Branch, RES, addressing TOL devices.(conducted in response to an AE0D request); and specific problem areas and emphasis of the guide. Therefore, ws suggest that the proposed regulatory guide revision effort should be delayed until September or October 1987, when the results of the Generic Issues Study would be defined.so the staff can meet to discuss various options.
Further discussion of our concerns is provided in the enclosure.
4 The proposed _ regulatory guide was reviewed by Earl J. Brown of my staff.
If you have questions, conta_ct Mr. Brown at x24491.
Original Signed By f
Thomas M. Novak l
1 Thomas M. Novak, Director i
Divison of Safety Programs, AE0D Enclosure.
' As stated I
cc w/ enclosure:
L. C. Shao j
E. L. Jordan DISTRIBUTION DCS RBaer, RES JJp ee, NRR I
ROAB.RF FCherny, RES Mggarwal, RES MChiramal ORothberg, RES MVagins, RES JRosenthal CBerlinger, NRR FRosa, NRR j
MWilliams RKiessel, NRR JJohnson, EDO KBlack Plam JRaines87-134 CHeltemes GLanik RSingh EBrown
- SEE PREVIOUS CONCURRENCES
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- JRosenthal : T ovak
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.' C ENCLOSURE Comments on proposed revision 2, draft 1 to Regulatory Guide 1.106.
" Thermal Overicad Protection for Motor Operated Valves for Nuclear Power Plants," dated l
July 1987.
1.
The review request indicates the proposed guide would not apply to operating
^
plants. We believe this issue should be reconsidered for several reasons. As a result of the Davis Besse event in June 1985, IE Bulletin 85-03 was issued for action on MOVs in certain systems.
Further, AE0D has issued Case Study C603 that recommends extending IE Bulletin 85-03 to all safety related valves.
In addition, the ED0 has requested that NUMARC take the lead for industry action on the AE0D recommendations. Thus, NRC guidance on TOLS should be timely, appropriate, and applicable to all plants.
2.
In response to an AE0D recomenda, tion, the Generic Issues Branch has been investigating TOL device use and problems for some time and the effort is nearing completion. Also, investigation subsequent to an AE0D study (AE0D/
E702) on hydraulic lockup of M0Vs has provided information rele.tive to other options for use of TOLS. We believe the results of the Generic Issues Branch effort as well as recent information should be utilized in the revised regulatory guide.
3.
The final area of concern involves emphasis of the guide together with the options as related to operating plants. The statements about concern that TOL devices "should not needlessly prevent the motor from performing its safety function," and " experience has shown that indiscriminate application of TOL protection devices could result in needless hinderance to successful completion of safety function" are oversimplifications that are not discernible from our reviews of operating data.
Furthermore, this emphasis in proposed position C.3 has resulted in oversizing to the point that little if any overheating protection is available for MOV motors during inservice testing or other operation. There are similar concerns about proposed position C.2 in that position (a) has resulted in destruction of the motor (actual event) and position (b) for automatic bypass would generally require considerable modification to implement for operating plants. We believe the single most important issue is recognition that correct sizing is essential before the TOL can be successfully utilized in either an alarm function (as proposed in position C.1) or a protection function. The proposed regulatory guide should build on this issue and then provide options for alarm and/or protection.
t k
e May 1988 Revision 2 (Draft 2)
Contact:
S. K. Aggarwal (301) 492-3829 l
REGULATORY GUIDE 1.106
. THERMAL OVERLOAD PROTECTION FOR MOTOR-0PERATED VALVES FOR NUCLEAR POWER PLANTS A.
INTRODUCTION Criterion 1, " Quality Standards and Records" of Appendix A " General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, " Domestic Licensing of Production and Utilization Facilities," requires, in part, that components important to safety be designed, fabricated, erected, and tested to quality standards commens" rate with the importance of the safety functions to be performed.
Criterion 4, " Environmental and Missile Design Basis," of Appendix A to 10 CFR Part 50 requires, in part, that components important to safety be designed to accommodate the effects of, and be compatible with, the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents, including loss-of-coolant accidents.
Criterion 13, " Instrumentation and Control," of Appendix A to 10 CFR Part 50 requires that instrumentation be provided to monitor variables and systems over their anticipated ranges for normal operation and for postulated accident conditions and that controls be provided to maintain these variables and systems within prescribed operating ranges.
Criterion XI, " Test Control," of Appendix B, " Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to 10 CFR Part 50 requires, in part, that a test program be established to ensure that systems and components perform satisfactorily and that the test program include opera-tional tests during nuclear power plant operation.
This regulatory guide describes a method acceptable to the NRC staff for complying with the above criteria with regard to the application of thermal overload protection devices that are integral with the motor starter for electric motors on safety related motor-operated valves.
B.
DISCUSSION Thermal overload protection devices are used in normal plant operation to preclude the possibility of valve motor burnouts. Motor-operated valves with thermal overload protection devices for the valve motors are used in safety systems.
Improper application of thermal overload protection devices to these valve motors can result in needless hindrance to successful completion of safety functions.
Thennal overload protection devices are designed primarily to protect continuous-duty motors while they are running, rather than during starting.
Use of overload protection devices to protect intermittent-duty motors may, 5
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l la therefore, result in undesired actuation of the devices if the cumulative effects i
of heating caused by successive starts at short intervals are not taken into l
l account in determining the overload trip setting.
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It is generally very difficult to design and apply any thermally sensitive device to approximate adequately the varying thermal characteristics of an intermittent-duty motor over its full range of starting and loading conditions.
l This is mainly due to the wide variations in motor heating curves for various i
sizes and designs and also by the difficulty in obtaining motor heating data to I
an acceptable accuracy.
1 Since the trip function in a thermal overload protection device is dependent on temperature, the degree of overload protection provided is affected by changes in ambient temperature at both the motor and starter locations. This aspect becomes more complex in nuclear power plant applications, where, in some cases the motor to be protected is inside the containment and the overload protection devices are outside the containment.
In such a situation, the temperature difference between the motor and the overload protection device l
could be as high as 200 F under design basis conditions. Thus, the selection i
of an appropriate trip set point for such a valve motor should take into con-l sideration operation of the valve under various temperatures for both normal and postulated accident conditions, including loss-of-coolant accidents. The I
recommendations of the motor operator manufacturer in sizing of thermal overload
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protection devices should also be considered.
It is not the intent of this
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guide that motors be operated with thermal overload devices removed from the motor starters, or that the trip points of the devices be set beyond the bounds of reasonable uncertainties so as to preclude operation of the devices.
The accuracy obtainable with the thermal overload relay trip generally varies from -5% to 0% of trip setpoint. Since the primary concern in the application of overload protection devices is to protect the motor windings against excessive heating, the above negative tolerance in trip characteristics of the protection device is considered in the safe direction for motor protection.
l However, this conservative design feature built into these overload protection devices for motor protection could interfere in the successful functioning of a safety-related system; i.e., the thermal overload protection device could needlessly trip and remove power from a motor before the safety function has been completed or even initiated.
In nuclear power plant applications, the criterion for establishing an overload trip setpoint should be to complete the safety function (i.e., drive the valve to its proper position to mitigate the effects of an accident) rather than merely to protect the motor from destructive heating.
In some nuclear power plants, the thermal overload protection device contacts are bypassed during accident conditions. The bypass initiation circuitry is considered to be part of the protection system.
In the past few years, a number of valve operator motor burnouts, approximating one per reactor-year of plant operation in the U.S., have been reported.
In some cases, the burnouts have gone undetected for extended l
periods. Since burnout, as well as many lesser motor overload conditions, 1
would be accompanied by the tripping of a properly sized thermal overload j
protection device, it is reasonable that thermal overload devices be installed
{
and that their tripping be indicated to warn of the potential nonfunctioning i
DRAFT 7/6/88 2
REG GUIDE 1.106 REV. 2 (Draft 2)
J
l' 2
condition of the valve motor operator, and of possible damage to the motor itself.
It is not the intent of this guide that each thermal overload device trip be alarmed individually in the control room. Group alarms are acceptable.
j i
C.
REGULATORY POSITION In order to ensure that safety-related motor operated valves will perform their function, the following regulatory positions constitute an acceptable method for meeting the Commission's requirements with respect to the application of thermal overload protection devices that are integral with the motor starter i
for electric motors on safety-related motor operated valves.
I 1.
Motor starters that actuate safety-related motor operated valves should be equipped with thermal overload devices, and thermal overload device j
trip should be alarmed in the control room.
Group alarms are acceptable.
2.
The trip setpoint of the thermal overload protection devices should be established with all uncertainties resolved in favor of completing the j
safety function. With respect to those uncertainties, consideration should be given to (a) variations in the ambient temperature at the installed location j
of the overload protection devices and the valve motors, (b) inaccuracies in motor heating data and the overload protection device trip characteristics and (c) setpoint drift.
In order to ensure continued functional reliability and the accuracy of the trip point, the thermal overload protection devices should be periodically tested.
3.
Provided that the completion of the safety function is not 1
jeopardized or that other safety systems are not degraded, the thermal overload protection device contacts that are usually in force during plant operation to protect the motor should be automatically bypassed under accident conditions.
D.
IMPLEMENTATION The purpose of this section is to provide information to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.
Except in these cases in which the applicant or licensee proposes an acceptable alternative method for complying with the specified portions of the Commission's regulations, the methods described herein will be used in the evaluation of applications of thermal overload protection devices for nuclear power plants as follows:
1.
Plants for which the construction permit is issued after the issue date of the final guide, 2.
Plants for which the operating license application is docketed 6 months or more after the issue date of the final guide, and 3.
Plants for which the applicant or licensee voluntarily commits to the provisions of this guide.
3 REG GUIDE 1.106 REY. 2 (Draft 2)
DRAFT 7/6/88 t
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DRAFT VALUE/ IMPACT STATEMENT
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BACKGROUND Thermal overload protection devices protect valve operator motors from damage due to overheating by tripping and disconnecting the motors.
However, a thermal overload protection device could trip and remove power from the motor before the safety function has been completed or even initiated.
In nuclear power plant applications, the criterion for establishing an overload trip setpoint should be to complete the safety function; i.e., driving the valve to its proper position to mitigate the effects of an accident rather than merely to protect the motor from destructive heating. The regulatory positions in R.G. 1.106, Rev.1, dated March 1977, delineate such criteria and pennit, for example, the bypassing of the thermal overload protection devices under certain conditions.
However, the proposed Rev. 2 permits the bypassing of the thermal overloed protection devices only under accident conditions. Also, it is not the intent of this guide that motors be operated with thermal overload devices removed from the motor starters, or that the trip points of the devices be set beyond the bounds of reasonable uncertainties so as to preclude operation of the devices.
An NRC AE0D study (AE0D/5503, dated September 1985) identifies more than 200 valve operator motor burnouts that had occurred within the past 5 years.
Vhat is especially disturbing about these events is that many have gone undetected for extended periods.
In retrospect, this circumstance follows from what the staff perceives as a deficiency in Regulatory Guide 1.106 Rev. 1; specifically, there is no provision to alarm tripping of the thermal overload protection devices. Since motor burnout, as well as many lesser motor overload conditions, would be accompanied by tripping of thermal overload protection devices, it seems essential that such tripping should be alarmed to warn of the potential or actual nonfunctioning condition of the valve operator. The trip alarm would also alert the plant operator to the possible nonoperability of the motor starter itself. Regulatory Position C.1 (Rev. 1) has been deleted to lessen the probability of undetected motor burnouts.
VALUE While the conditions that cause overload, such as faulty limit switches, excessive friction, and undersized valve operators, cannot be corrected by this regulatory guide, the staff believes that thermal overload protection device trip alarm would make a contribution to safety by removing the observed class of undetected failures which has obvious common-cause failure, as well as random I
failure, implications.
)
l Therefore, an appropriate regulatory position C.1 has been added.
l IMPACT This regulatory guide applies to future nuclear power plants and has no backfit provisions. Thus, this regulatory guide does not impose any new I
requirements or costs on current licensees or applicants. Use of the guide by the current licensees or applicants is voluntary.
l DRAFT 5/18/88 4
REG GUIDE 1.106 REV. 2 (Draft 2)
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