ML19330B480
| ML19330B480 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 07/23/1980 |
| From: | Naughton W COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8008040072 | |
| Download: ML19330B480 (7) | |
Text
,
o, O one First Nabonal Piaz'. Chicago. Illinois Commonwealth Edison Address Reply to: Post Office Box 767 Chicago, Illinois 60690 July 23, 1980 Mr. Harold R. Denton, Director Of fice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Zion Station Units 1 and 2 Schedule For Completion of ATWS Modifications NRC Docket Nos. 50-295 and 50-304 References (a):
June 19, 1980 letter from Steven A.
Varga to D. Louis Peoples (b):
April 28, 1980 letter from D.
L. Peoples to H. R. Denton
Dear Mr. Denton:
Reference (a) requested Commonwealth Edison Company to re-evaluate its proposed schedule for completing ATWS modifications at Zion Station as outlined in Reference (b).
In addition, the NRC Staff requested that Commenwealth Edison improve upon the schedule required of other plants due to the risk the Staff believes tnat Zion Station represents.
Commonwealth Edison does not concur with the NRC Staff that Zion Station represents an additional risk over and above other plants especially with regard to its Alternate Mitigating Systems Actuation Circuitry (AMSAC) installation schedule.
On February 20, 1980 Commonwealth Edison in conjunction with the Power Autnority of the State of New York and Consolidated Ediscn Company presented the results of their 60 day study on mitigation of severe accidents to tne NRC Sta f f.
This study was docketed for Zion Station on June 9, 1980 per a D. L. Peoples to H.
R. Denton letter.
The results of this study revealed that, due to additional features incorporated in the initial design of the Zion units, these reactors do not pose the risk stated by the Staff in its comparison to the Wash 1400 plant.
Subsequent meetings involving technology exchanges with the NRC Staff, as part of our detailed probability risk analysis work for [O}i Zion Station, have continued to support Commonwealth Edison's 3
j position.
Currently, a review team is being formed under Mr.
S.
///
Israel of your Staf f to review our ongoing work in greater detail.
Therefore, Commonwealth Edison has concluded that improvement on the schedule requireo of other plants for completion of ATWS modifications is not necessary for Zion Station.
8008040 g 9 2 THIS DOCUMENT CONTAINS g
P0OR QUAUTY PAGES
Commonwealth ECson Mr. Harold R. Denton, Director July 28,-1980 Page 2 With regard to the schedule contained in Reference (b) for the design, procurement and installation of AMSAC at Zion Station, the completion dates are realistic and are based on a schedule that includes-the necessary front end lead time to provide adequate.
interaction between Commonwealth Edison and other parties, such as, Architect-Engineers, Westinghouse and the NRC.
Also expected during tnis engineering phase was the NRC final generic input regarding the AMSAC design.
Such an interaction at the early stage is necessary to su/ficiently define the AMSAC scope of work.
As indicated in
-Reference (b), the schedule provided for normal preparation of equipment specifications, competitive bidding, QA reviews, component development, qualificaton activities, production, and installation consistent with planned refueling outages.
In Commonwealth Edison's view this proposed schedule is very realistic considering the fact that the Westinghouse AMSAC concept still has not received NRC concurrence.
However, in discussions at a May 13, 1980 meeting with the Westinghouse ATWS Owner's Group, the NRC Staf f indicated informally their position with regard to diversity and tne single failure criterion for AMSAC.
Based on Commonwealth Edison's understanding of the Staff positions, a revised schedule for Zion Station is possible, provided an expeditious agreement can be reached with the Staff on the system design details described in Attachments 1, 2 and 3 to this letter.
This system operates independent of the reactor protection system by initiation of auxiliary feedwater and turbine trip when an impending loss of heat sink is detected via the steam generator level monitors.
The twelve existing steam generator level instrumentation channels are utilized to develop the AMSAC trip signal.
The proposed system utilizes isolators to separate the AMSAC input signal from the reactor protection input signal to elminate the possibility of interaction between the two systems.
Existing actuation devices for auxiliary feedwat~er and turbine trip are utilized.
The balance of the AMSAC system is separate and independent of the reactor protection system (RPS) and to the extent practicable meets the original plant seismic design requirements.
This system also satisfies requirements for diversity from the RPS by virtue of the variety of other parameters which are input to that system and which initiate reactor trip.
Utilization in AMSAC of the design criteria depicted in Attachments 1, 2, and 3, results in a system-that can be procured and' installed on a much more expeditious schedule than that-1
Commonwe:lth Edison Mr. Harold R. Denton, Director July 28, 1980 Page 3 delineated in Reference (b).
The proposed system significantly decreases the quantity of hardware to be procured and installed at the sensor level, simplifies the design, reduces. channel separation within AMSAC (thus improving cable installation time), minimizes plant down time to accommodate installation, decreases engineering efforts, and reduces considerably the system cost while achieving the same design objectives.
The proposed system provides for a reliable and redundant backup to the existing RPS and also provides for the analytical results contained in the December 30, 1979 Westinghouse. letter (NS-TMA-2182).
The system, which increases plant safety for the low probability ATWS event, is appropriate for Zion Station because it can be expeditiously procured and readily installed in an operating plant.
In order to begin procurement activities and expenditures in pursuit of a January 1, 1982 completion date, prompt NRC approval of the AMSAC design contained in Attachments 1,2 and 3 is essential.. To that end, Commonwealth Edison's engineering personnel will be available at Staff's convenience to meet or discuss with the Staff the proposed design.
Please address any questions that you might have concerning this matter to this office.
One (1) signed orginal and thirty-nine (39) copies of this letter and seven (7)~ copies of the attachments are provided for your use.
Very truly yours, H
- L William F. Naught Nuclear Licensing Administrator Pressurized Water Reactors Attachments (3) 5566A L
Commonwealth Edison NRC Docket Nos. 50-295 50-304 PROPOSED DESCRIPTION OF-ANTICIPATED TRANSIENTS WITHOUT SCRAM MITIGATING SYSTEM ACTUATION CIRCUITRY (AMSAC)
There are three independent level transmitters provided for each of the four steam generator loops.
Loss of any one of the three sensors associated with a respective loop will not jeopardize initiation of a low-low level signal under said conditions.
A high degree of reliability is accomplished by the two out of three logic integrated into the circuit design of each loop.
Since these existing sensors also generate Reactor Protection System (RPS) signals, to separate the AMSAC signal from the RPS signal, isolators are provided in the auxiliary electrical equipment room.
Downstream of each isolator a signal comparator provides an auxiliary relay contact closure resulting in a two out of three logic of the low-low level sensors as per the control schematic.
This capability is provided for each steam generator loop.
A combination of any two auxiliary relay contact closures of the four steam generator loops (2 out of 4 logic) and the P-8 power level permissive greater than 60%, will initiate AMSAC to start auxiliary feedwater and trip the turbine.
Operator Indication is provided for P-8 Power level less than 60%, P-8 Power level greater than 60%, AMSAC blocked and AMSAC initiated in the Control Room.
The logic cabinet for the AMSAC signal will employ solid state devices and will be separate and independent from the Reactor Protection System logic cabinets.
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