ML20151S860
| ML20151S860 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 08/11/1988 |
| From: | Sears P Office of Nuclear Reactor Regulation |
| To: | Randazza J Maine Yankee |
| References | |
| TAC-59110, NUDOCS 8808160135 | |
| Download: ML20151S860 (11) | |
Text
.
August 11,19C3 t
Docket No. 50-309 t
Mr. J. B. Randazza President Maine Yankee Atomic Power Company 83 Edison Drive Augusta, Maine 04336
Dear Mr. Randazza:
SUBJECT:
MAINE YANKEE: 10 CFR 50.62 (ATWS RULE) REVIEW REQUEST FOR INFORMATION (TAC NO. 59110)
The ATWS Rule (10 CFR 50.62, "Requirements for Reduction of Risk from Anticipated Transients Without Scram [ATWS) Events for Light-Water-Cooled Nuclear Power Plants") requires improvements in the design and operation of commercial nuclear power facilities to reduce the likelihood of failure to shutdown the reactor following anticipated transients and to mitigate the consequences of an ATWS event.
The requirements for Combustion Engineering plants such as Maine Yankee are to provide a diverse scram system (DSS),
diverse auxiliary feedwater system (AFYS) actuation, and diverse initiation of turbine trip. Paragraph (c)(6) of the Rule requires that infonnation sufficient to demonstrate compliance with the requirements be submitted to the Office of Nuclear Regulation (NRR).
Yankee Atomic Power Company provided information concerning implementation of i
the ATWS Rule requirements at Maine Yankee by letter MN-85-141 dated July 31, 1985. However, the information provided is not sufficient to allow for the 1
review to be completed. Therefore, it is requested that the information i
delineated in the enclosure be submitted. A schedule for submittal will be i
negotiated with the Project Manager Maine Yankee after your review of the enclosure.
Sincerely.
Odginal signe'd @
Patrick M. Sears, Project Manager Project Directorate I-3 i
Division of Reactor Projects I/II i
Enclosure:
As stated i
cc: See next page Distribution:
Docket File, NRCPDR, local PDR, PDI-3 r/f, 0GC SVarga, BGrimes. EJordan, PSears, MRushbrook, ACRS (10), 7, d, BBoger,.g, Rg 5. Ve k'%Y
[^
@[
PDI-3/DIR MRushrook PSears:ek RWessman
/
88 y/g/88
/
88 qf/rf/88 b
g0 I 8809160135 080011 PDR ADOCK 05000309 4
I i
P PNU n
A Mr. J. B. Randazza Maine Yankee Atomic Power Company Maine Yankee Atomic Power Station i
CC:
John B. Randazza, President Mr. P. L. Anderson, Project Manager Maine Yankee Atomic Power Company Yankee Atomic Electric Company 83 Edison Drive 1671 Worchester Road Augusta, Maine 04336 Framingham, Massachusetts 07101 Mr. Charles B. Brinkrian Mr. G. D. Whittier, Manager j
Manager - Washington Nuclear Nuclear Engineering and Licensing Operations Maine Yankee Atomic Power Company i
Combustion Engineering, Inc.
83 Edison Drive 7910 Woodmont Avenue Augusta, Maine 04336 Bethesda, Maryland 20814 John A. Ritsher, Esquire Ropes & Gray 225 Franklin Street Boston, Massachusetts 02110 State Planning Officer Executive Department 189 State Street Augusta, Maine 04330 Dr. E. T. Boulette, Plant Manager Maine Yankee Atomic Power Company P. O. Box 408 i
Wiscasset, Maine 04578 Regional Administrator, Reg 10n i U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, Pennsylvania 19406 First Selectman of Wiscasset j
Municipal Building V.S. Route 1 i
Wiscasset, Maine 04578 i
Mr. Cornelius F. Holden Resident Inspector c/o U.S. Nuclear Regulatory Comission P. O. Box E Wiscasset, Maine 04578 4
1 1
~n e
ENCLOSURE MAINE YANKEE 10 CFR 50.62 (ATWS RULE) i REQUEST FOR INFORMATION j
TAC NO. 59110 INTRODUCTION AND DISCUSSION On July 26, 1984, the Code of Federal Regulations (CFR) was amended to include the ATWS Rule (Section 10 CFR 50.62, "Requirements for Reduction of Risk from Anticipated Transients Without Scram [ATWS] Events for Light-Water-Cooled Nuclear Power Plants"). An ATWS is an expected operational transient (such as loss of feedwater, loss of condenser vacuum, or loss of offsite power), which is accompanied by a failure of the reactor trip system (RTS) to shutdown the reactor. The ATWS Rule requires specific improvements in the design and operation of connercial nuclear power facilities to reduce the likelihood of failure to shutdown the reactor following anticipated transients and to mitigate the consequences of an ATWS event.
Paragraph (c)(6) of the Rule requires th t information sufficient to demonstrate compliance with the requirements of the Rule be submitted to the Director, Office of Nuclear Reactor Regulation. The ATWS Rule requirements for Combustion Engineering (CE) plants such as Maine Yankee are to provide a diverse scram system, diverse (from the existing reactor trip system) auxiliary feedwater system (AFWS) actuation, and a diverse (from the existing reactor trip system) initiation of turbine trip.
Infonnation in addition to that provided in Yankee Atomic Power Company letter MN-85-141 dated July 31, 1985 is needed to allow the staff to detennine whether Maine Yankee complies with the hardware diversity, electrical independence, and I
reliability and testability at power requiren"ents of the ATWS Rule. The information identified below is required by the staff to complete the review of implementation of the ATWS Rule requirements at Maine Yankee.
l 3
' 1.
The Maine Yankee diverse scram system (OSS) design uses existing reactor coolant system (RCS) pressure transmitters that were purchased and installed as Class 1E equipment. These transmitters are not part of the
]
existing reactor trip system (RTS). The output signals from these
]
transmitters will be used in a 2-out-of-3 logic matrix to develop a high RCS pressure trip signal which is set between the existing RTS high pressure trip and below the lowest pressuri2er safety valve setpoint.
This signal will opan the existing Control Element Drive System (CE05) motor-generator (MG) set output contactors which are located between the motor-generators and the reactor trip breakers. Opening these contactors will interrupt the motor-generator set output power to the control rod drives and initiate a reactor scram. This alterndte trip system will be designed so that no single failure will result in an inadvertent reactor scram. On-line testability will also be designed into the system to allow testing of all equipment except the final output contactors.
It is the staff's understanding that the DSS circuitry from the sensors, through the logic, up to and including the final actuation devices (MG set outpt t contactors) will be designed, procurred and installed as safety-related Class 1E equipment.
a.
Is the staff's understanding correct?
If not, please explain.
b.
Please provide electrical schematic /elementar.y diagrams for the OSS that clearly show all instrument channels (including bistables) logic, actuation circuits, test circuits, interlocks, bypasses, alarms and indications. Also, provide electrical one-line diagrams showing the CEOS MG sets and DSS actuated output contactors and power distribution to the RTS and 055, including vital buses, inverters, batteries and chargers, etc.
4 0
3-c.
Using circuit breakers from different manufacturers is generally not considered sufficient to provide the required diversity for interruption of control rod power.
In general, circuit breakers from different manufacturers are considered susceptible to common mode failures (CMF) because of connon design features such as mechanical linkages (consisting of springs, pivots, latches, pins, cams, etc.) that are subject to binding / malfunction from a number of causes (e.g., dirt, corrosion, improper lubrication, etc.) as has been demonstrated through operating experience. Please provide information that demonstrates physical hardware diversity of the CEDS MG set output contactors from the reactor trip breakers actuated by the RPS.
d.
For all DSS, diverse turbine trip (DTT) initiation and diverse auxiliary feedwater (DAFW) initiation instrument channel components (excluding sensors and signal conditioning equipment upstream of the bistables) and logic channel components, and DSS actuation devices, provide information sufficient to demonstrate compliance with the ATWS rule diversity requirements. The infonnation should include a diversity comparison of the DSS and DTT components with the components used in the existing RTS, e.g., manufacturer, model number, design principle (electromechanical, solid state, etc.) mode of operation (energize /
deenergize to actuate), power source (AC/DC), etc. The similarities and differences in the physical and operational characteristics'of i
these components must be analyzed to determine the potential for common mode failure (CMF) mechanisms that could disable both the RTS and ATWS prevention / mitigation functions. The evaluation of the adequacy of the diversity provided must be perfonned at a detailed level to include hardware design considerations and diversity aspects that might at be apparent from a cursory / audit review.
For example, two electromechanical relays from the same manufacturer and having the same voltage / current ratings and energize-to-actuate /deenergize-to-actuate trip status, and therefore, which appear to be unacceptable for satisfying the diversity requirements of the ATWS rule, may
4 actually be acceptable if different materials and different manufacturing processes are uwd. Conversely, two printed circuit cards from different manufacturers, and therefore, which appear to be acceptable for satisfying diversity requirements of the -ule, may not be acceptable if they both use identical components.
Some information concerning diversity between the RTS and the DAFW initiation circuits was provided in CEN-315. "Sumary of the Diversity Between the Reactor Trip System cnd the Auxiliary Feedwater Actuation System for CE Plants." Additiemi information should be provided that specifically addresses diversity between the General Electric (GE) relays used in the RTS and the GE relays used in the AFWS, as discussed in the staff's evaluation of CEN-315 (letter dated August 4, 1986 from D. Crutchfield, NRC to R. W. Wells, Combu;cion Engineering OwnersGroup).
e.
Provide information to explain how the DSS and DTT functions will remain operable on a loss of off site power.
f.
Explain in detail the indications and alarms used to alert the control room operators to DSS and DTT inoperable and bypassed conditions (e.g.,
when a channel is taken out of service for testing or maintenance).
Also include a discussion of any operational bypasses, automatic or manual, used in conjunction with the DSS or DTT.
g.
Explain the specific operator actions required to manually initiate the DSS and DTT protective actions.
Once initiated, is the protective action sealed in such that the system function goes to completion?
2.
The ATWS rule requires that the equipment / systems installed to prevent and/or mitigate the consequences of ATWS events be electrically independent of the existing RTS to minimize the potential for CHFs that could affect both RTS and ATWS circuits. Electrical independence of the DSS from the
=
5 existing RTS should be provided from the sensor outputs up to and including the final actuation device.
Electrical independence of the DAFW and DTT -
circuits from the existing RTS should be provided from the sensor outputs up to the final actuation davice.
]
The staff has allowed exceptions to the electrical independence requirements for DSS, diverse DAFW actuation and DTT circuits where the circuits are designed, procured, installed and maintained as fully redundant safety related (Class 1E) circuits, and it has been demonstrated that CMF of the j
shared power sources will not result in loss of both RTS and ATWS prevention / mitigation functions as discussed in item a below.
l a.
Identify all DSS, AFWS and DTT system components that receive power from sources that are also used to provide power to the existing RTS.
If RTS power supplies are used, information must be provided to demonstrate that:
- 1) faults within the DSS, DAFW actuation or DTT circuits cannot degrade the reliability / integrity of the existing RTS below an acceptable level, and 2) that a comon mode failure affecting the RTS power distribution system (including degraded voltage and/or degraded frequency conditions, e.g., overvoltage and undervoltage; overfrequency and underfrequency; the effects of degraded voltage j
and/cr frequency conditions over time must be considered if such conditions can go undetected) cannot compromise both the RTS and ATWS prevention / mitigation functions.
If alarms are relied on 'o provide early detection of degraded voltage / frequency conditions, the infomation should include the specific alam(s) and their setpoint value(s), and the limiting steady state altage/ frequency values for which the affected circuits / components nave been analyzed / demonstrated to still be capable of perfoming their intended functions. A discussion of the periodic surveillance / testing performed to verify operability of the alam circuits should also be provided.
l
b.
Electrical independence of nonsafety-related ATWS circuits from safety related circuits is required in accordance with the guidance provided in IEEE Standard 384, "IEEE Standard Criteria for Independence of Class 1E Equipment and Circuits," as supplemented by Regulatory Guide
)
1.75, Revision 2. "Physical Independence of Electrical Systems."
If the Maine Yankee DSS, DTT or DAFW circuits use non-Class 1E (nonsafety-related) components, information must be provided to i
demonstrate the adequacy of all isolation devices used to protect the integrity of safety related circuits from nonsafety-related l
ATWS DSS, DTT and DAFW circuits.
The required information is identified in Attachment 1.
If the isolation devices are identical to isolation devices used in other applications (e.g., to isolate l
the safety parameter display system from safety related circuits),
j and the requested information has been previously submitted for j
staff review, and the isolation devices have been approved for their applications, the related correspondence should be referenced, and no additional information need be provided.
3.
The equipment required by 10 CFR 50.62 to reduce the risk associated with an ATWS event must be designed to perform its functions in a reliable manner. The DSS, DAFW actuation circuitry, and DTT circuits must be designed to allow periodic testing to verify operability while at power.
All bypass conditions should be automatically and continuously indicated
)
in the main control room.
a.
Describe the scope and intent of the various surveillance tests (e.g., sensor / channel checks, instrument channel functional tests, logic channel and actuation device tests, channel / system calibrations, overall system functional tests, etc.) that Maine Yankee Atomic Power Company intends to use to periodically verify operability of the DSS and DTT equipment / circuitry installed at Maine Yankee.
Indicate the frequency for which each surveillance
7 1
4 test is conducted. Also discuss the controls / programs (e.g.,
technical specifications) to be used to ensure that the equipment / circuitry installed in accordance with the ATWS Rule will be properly tested and maintained in an operable condition. The controls / programs should provide reasonable assurance that the ATWS equipment / circuitry will perform its design functions when required, and therefore, satisfy the reliability requirements of the ATWS Rule.
b.
Please indicate whether the test procedures involve undesirable practices such as installing jumpers, lifting leads, pul. ling fuses, tripping breakers, blocking relays, or other circuit alternac'ons.
4.
During the life of a comercial light-water-cooled nuclear power plant many components reach their end of life and must be replaced, including components installed in the RTS, AFWS, DSS, and DTT system. Provide a description of the measures / programs implemented at Maine Yankee to assure tha( the equipment diversity provided in accordance with the ATWS Rule will be maintained during component repair. splacement.
modifications and/or design changes etc. throughcut the life of the plant.
5.
Discuss how good human factors engineering practices are incorporated into the design of ATWS prevention / mitigation system components located 1
in the control room.
l 4
i I
l
\\
4 I
ATTACHMENT 1
I ISOLATION DEVICE REQUEST FOR ADDITIONAL INFORMATION 1
Each light-water-cooled nuclear reactor shall be provided with a systes for the prevention and/or mitigation of the effects from anticipateo transient without scram (ATWS) events. The Commission-approved requirements for the prevention / mitigation of ATWS events are definec ;a the Code of Federal i
Regulations (CFR) Section 10 paragraph 50.62. Tne staff has determined that the isolation devices used within ATWS prevention / mitigation system: (to provide isolation between Class IE and non-Class 1E circuits or between redundant Class IE circuits) will be reviewed on a plant-specific basis, ibe following additional information is required to continue and complete the i
, plant-specific isolator review:
Isolation Devien Please provide the following:
a.
For the type of device used to accomplish electrical isolation, describe the specific testing perfonned to demonstrate that the device is acceptable for its application (s). This description should include elementary diagrams, when necessary, to indicate the test configurhtion and should describe how the maximum credible faults were applied to the devices.
l I
b.
Data to verify that the maximum credible faults applied during the test were the maximum voltage / current to which the device could be exposed, and define how the maxitum voltage / current was determined.
l
. l J
)
c.
Data to verify that ti.e maximum credible fault was applied to tha non-Class 1E side of the device in the transverse mode (between signal t
andreturn)andthatotherfaultswereconsidered(i.e.,openandshort circtits).
l d.
Define the pass / fail acceptance criteria for each type of device.
l l
e.
A comitment that the isolation devices comply with the environmental qualifications (10 CFR 60.49) and seismic qualifications that were the basis for plant licensing.
)
f.
A description of the measures taken to protect the safety systems from j
electrical interference (i.e., Electrostatic Coupling. EMI, Coninon Mode and Crosstalk) that may be generated by the ATWS circuits.
1 g.
Information to verify that the Class 1E isolator is powered from a Class IE source.
l j
I 4
1 i
4 J
- - - - - - - - - - - - - - - - - - - - - - -. --