ML20151A460
| ML20151A460 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/11/1988 |
| From: | Mroczka E NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| A07296, A7296, TAC-59114, NUDOCS 8807200003 | |
| Download: ML20151A460 (9) | |
Text
.,
,. e MEAST UTILITIES cenerai orrices. seiden street. Beriin. connecticui C
t j
) 5 July 11, 1988 Docket No. 50-336 A07296 Re: 10CFR50.62 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.
20555 Gentlemen:
Millstone Nuclear Power Station, Unit No 2 ATWS Modifications (TAC #59114)
In a June 8, 1988 letter,II) the Staff requested that Northeast Nuclear Energy Company (NNECO) provide responses to a number of questions regarding proposed ATWS modifications at Hillstone Unit No.
2.
These responses were to be submitted to the Staff within 15 days from receipt of the June 8,1988 letter.
However, discussions with the Project Manager for Millstone Unit No. 2 on June 10, 1988 resulted in a mutually agreeable due date of 15 days after the June 10 telephone discussion for approximately one-half of the required responses, with the remainder being due by July 12, 1988.
Since the agreed 27,1988.gd upon due date fell on a weekend, approximately one-half of the reque material was submitted on the first business day following; June Enclosed are responses to questions 1.c; 4, 5, 6, and 7 of the Staff request for additional information on ATWS modifications at Hillstone Unit No.
2.
These responses constitute the remainder of the total amount of information requested by the NRC Staff.
NNEC0 trusts this information will be adequate to support Staff review of planned ATWS modifications of Millstone Unit No. 2.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY
/
SeniorVicePr/
E.W Mr'odzka esident 1
(1)
D. H. Jaffe letter to E. J. Mroczka, "Millstone Nuclear Power Station, Unit No. 2, Request for Additional Information," dated June 8, 1988.
(2)
E.
J.
Mroczka letter to U.S.
Nuclear Regulatory Commission "ATWS Modifications (TAC #59114)", dated June 27, 1988.
I 8807200003 880711 4
i PDR ADOCK 05000336 P
U.S. Nuclear Regulatory Commission A07296/Page 2 July 11, 1988 cc:
W. T. Russell, Region I Administrator D. H. Jaffe, NRC Project Manager, Millstone Unit No. 2 W. J. Rayniond, Senior Resident Inspector, Millstone Unit Nos.1, 2 and 3
\\
Docket No. 50-336 A07296 k
Millstone Nuclear Power Station Unit No. 2 Responses to Questions on ATWS Modifications 4
July 1988 1
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' ' Attachment 1 A07296/Page 1 July 11, 1988 Ouestion 1.c NNEC0 proposes to install a DSS at Hillstone, Unit 2, that receives inputs from the existing reactor protection system (RPS) pressurizer pressure sensors.
The pressurizer pressure signals are processed by newly installed instrumentation consisting of bistables and logic circuitry arranged in a two-out of-four energize-to-actuate logic to trip the RPS Hotor Generator (MG) set output contactors upon detection of conditions indicative of an ATWS event.
Provisions will be included to allow the bypass of any one sensor input thus converting. the logic to two-out-of-three to allow for maintenance of the sensors.
For all DSS and DTT 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 infor-mation should include a diversity comparison of the DSS and DTT components with the components used in the existing RPS, 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 these components must be analyzed to determine the potential for common mode failure (CMF) mechanisms that could disable both the RPS and ATWS preven-tion / mitigation functions.
The evaluation of the adequacy of the diversity provided must be performed at a detailed level to include hardware design considerations and diversity aspects that might not be apparent from a cursory / audit review.
Fnr 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 actually be acceptable if different materials and different manufacturing processes are used.
Conversely, two printed circuit cards from different manufacturers, and therefore, which appear to be acceptable for satisfying diversity requirements of the rule, may not be acceptable if they both use identical components.
Response
Comparison of design principles and instrument components between RPS and DSS is shown in the matrix Table 1, which demonstrates compliance with the ATWS diversity rule.
Each component is compared at detailed levels of manufactur-er, model number, design principle, mode of operation, DC power supply model, AC power source, etc.
It should be noted that the initiation relays and the actuation devices of both RPS and DSS are from the same manufacturer, GE, but above components are of different models.
Furthermore, the design principle and the operation mode of above components are all compliant with the diversity requirement.
Question 4 During the life of a commercial light-water-cooled nuclear power plant many components reach their end of life and must be replaced, including components installed in the RTS, DSS, and DTT system.
Provide a description of the
'Att'achment 1 A07296/Page 2 July 11, 1988 measures / programs implemented at Millstone Unit 2 to assure that the equipment diversity provided in accordance with the ATWS Rule will be maintained during component repair, replacement, modifications and/or design changes etc.
throughout the life of the plant.
Response
NNEC0 will keep spare parts available for all DSS /AMSAC components.
The spare parts for components repair, replacement and modification use the same model number as the original design, which equires diversity, throughout the plant life. Plant procedures in effect at hillstone Unit 2 ensure that appropriate replacement parts are used when necessary.
Any design changes to the installed DSS /AMSAC equipment will follow the design QA procedures.
Question 5 Discuss how good human factors engineering practices are incorporated into tSe design of ATWS prevention / mitigation system components located in the control room.
Response
The diverse scram is not a manual initiation but an automatic instantaneous trip (Response to Question 1.f).
Good human factor engineering practices are incorporated in the design by utilizing standards and conventions established as part of the control room design review.
This includes the use of key locked switches and the utilization of administrative procedures.
Good human-factor practices are also implemented by the location and standard acronyms and abbreviations for the control-board annunciators (Response to Question 1.e).
The fully functional test for DSS /AMSAC will confirm the existing AFAS functionality with DSS either bypassed or on-line.
Question 6 By letter dated August 4, 1986 (from D. Crutchfield, NRC to R. Wells, CE Owners Group), the staff provided its evaluation of CEN-315 "Summary of the Diversity Between the Reactor Trip System and Auxiliary Feedwater Actuation System for CE Plants."
Based on the review of CEN-315, the staff concluded that the Millstone, Unit 2 AFAS design has sufficient diversity to satisfy the requirements of the ATWS Rule with the possible exception of the GE initiation relays used in both the RPS and the AFAS.
Please provide information similar to that request in item Ic of this document so that a determination of the level of diversity can be made.
[
Resoonse Comparison between RPS and AFAS is shown in Table 2, which is excerpted and revised from Ref. 1.
The initiation relays of RPS and AFAS are from two manufacturers:
GE and Amerace.
The final actuation devices of both systems are from GE, but of different models.
Further diversities in design principle and power source are also compliant.
' ' Att'achment 1 A07296/Page 3 July 11, 1988 Ouestion 7 i
o,With the implementation of the DST at Millstone, Unit 2, the diverse turbine trip requirement will also be satisfied.
The existing RPS initiated turbine trip is accomplished by Undervoltage relays monitoring the 240 VAC reactor trip bus voltage.
While the turbine trip in an ATWS event is accomplished by the same undervoltage relays, the initiation of the undervoltage condition is diverse from the RPS.
Please assure that the information request in item 2b above is supplied as Class 1E to non-Class IE interfaces exist-for this system.-
Resoonse Fig. 5 in our June 27, 1988 letter shows the diverse scram path with compo-nents diverse from the RPS.
As detailed in response to Question 1.c, the final actuation devices for the RPS are the trip breakers (model # AK-25),
while those for DSS are the MG trip contactors (model # IC 28112Bil3).
Therefore, the.DTT function of DSS /AMSAC via undervoltage relays meets the diversity requirement.
In our response to Questions 1.a and 2.a, the DSS /AMSAC is designed as Category lE equipment.
Electronics for instrumentation and isolation are qualified to IEEE-323 (1983) and IEEE-344 (1975) criteria.
In response to Question 2.b, the Category lE electronics are analyzed to demonstrate isola-tion from the RPS.
Further protection from field faults is also provided by the DS relays as isolation devices, which actuate the MG trip contactors as well as DTT.
References:
1)
Results from CE0G Program to comply with 10CFR50.62 Task 494 Subtask 1-3, Final Report, July 1986, CE NPSD-319.
(
o Table 1 A07296/Page 1 July 11, 1988 Table 1 Design Design Component Description RPS DSS Diversity Bistables Manufacturer Electro-Mechanics Foxboro Yes Model No.
Assy 6822-34860 N-2AP-ALM-AR Yes Schematic 6822-34868 Design Buffered input compared with Buffered input compared with Yes Principle Setpoint. Trip deenergizes Setpoint. Trip energizes matrix relays.
matrix relays.
DC Power Supply Power Mate, 15 VDC
- Foxboro, 15 VDC Yes AC Power Source Vital Buses VA10, VA20, Vital Buses fused separately Yes VA30, VA40 VA10, VA20, VA30, VA40 Matrix Logic Manufacturer Douglas Randall Foxboro Yes Relays Model No.
378907 N-2A0-L2C-R Yes Design Principle Electromechanical relays Contacts of electro-Yes constitute six sets of matrix mechanical relays constitute relays from 2/4 trip paths six trip paths as a logic of logic matrices (Fig. 7) matrix (Fig. 2)
DC Power Supply Power Mate, +28VDC Diode Coupled Foxboro, +15VDC Yes AC Power Source VA10, VA20, VA30, VA40 VA10, VA20, fused separately Yes
Table 1.
A07296/Paji2 July'll, 1988 1
Table 1 (Continued)
Design Design y
Component Description RPS DSS-Diversity l
Initiation Manufactuer General Electric (GE)
.GE No j
Relays Model No.
12NGV13AIA HFA Yes Design Principle.
NC contacts of matrix N0 contacts of matrix relays Yes relays keep the initiation keep the initiation relays relays energized, which deenergized, which control control the trip circuit the MG contractors and AFWS breakers.
initiation.
Power Supply and 120VAC Vital Buses VA10, 125VDC, LCS-B-120 of LAMDA Yes Sources VA20, VA30, VA40 by VA10 and VA20 Final Manufacturer GE GE No Actuation Devices Model No.
Trip Breaker AK 2-25 MG Contactor IC28112B113 Yes Design Mechanical Latch Trip on Contactors open on coil Yes Principle Under-Voltage and Shunt Trip deenergized Coils Power Supply and 125VDC Vital Buses 240 VAC across two wires Yes Source VD10, VD20, VD30, VD40 of MG output
Table 2 A07296/Page 1 July 11,1988 Table 2
-l Design Design Component Description RPS DSS Diversity Initiation Manufacturer General Electronic (GE)
Amerace
.Yes Relays Model No.
12NGV13AIA EGPD001 and E7012AF Yes Design NC contacts of matrix relays EGPD001 relays are energized Yes Principle keep the initiation relays by matrix contacts to energized, which control the initiate E7012AF timing trip circuit breakers.
relays. E7012AF timing out then initiate HFA relays.
Power Supply 120VAC Vital Buses VA10, VA20, 125VDC, 2CS-B-120 of LAMDA Yes and Source VA30, VA40 powered by VA10 and VA20 Final Manufacturer GE GE No Actuation Devices Model No.
Trip Breaker AC 2-25 HFA Yes Design Mechanical Latch Trip on Under-HFA relays are energized Yes Principle Voltage and Shunt Trip Coils by initiation relays to switch contacts Power Supply 125VDC Vital Buses VD10, VD20, 120 VAC Vital Buses VA10 Yes and Source VD30, VD40 and VA20
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