ML20002C997
| ML20002C997 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 02/09/1970 |
| From: | Haueter R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Morris P, Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20002C998 | List: |
| References | |
| NUDOCS 8101150705 | |
| Download: ML20002C997 (4) | |
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General Offices: 212 West Michigan Avenue. Jackson, Michigan 49201. Area Code 017788-05S0 FEBiIu;a'g D
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%4 Dr. P. A. Morris, Director Division of Reactor Licensing United States Atomic Energy Commission Re: Docket 50-155 Washington, DC 205h5 DPR-6 ZEK
Dear Doctor Morris:
Attention:
Mr. D. J. Skovholt This letter is written in response to your letter of December 30, 1965, requesting Consumers Power Company to review the Big Rock Point emergency core cooling provisions to determine if there exists a need for additional provisions to maintain containment intcc;rity in the event of a major rupture of the primary coolant system. As noted in our letter of September 1,1967, we engaged a consultant, General Electric Company (GE), to perform the loss-of-coolant accident analysis.
GE sub-mitted their completed report to us in November 1967, and we have since reviewed it and initiated a design of a redundant core spray system.
The following is a report of our findings and the course of action we intend. to pursue as a result of the fi.idings:
I.
Sum =ary of Anal,ses (Complete Analysir, Attached as Attachment A)
The lor,8-of-coolant analyses perfomed by GE covered a spectrum of pipe rupture break sizes at various locations in the primary coolant system. This was done to establish the limiting break size which the ex-isting reactor system could sustain without melting of fuel cladding.
In all casee, instantaneous, complete pipe ruptures were assumed to occur.
For ease in categorizing the results of the analyses, the primary coolant system was divided into two regions - above and below the core. Analyses of pipe breaks were performed accounting for important effects peculiar to each region.
The results of the analyses show that:
1.
W'.th core spray available, the Big Rock Point reactor can sustain, without melting any fuel cladding, a rupture above the core of any pipe, even one as large as that equivalent to the complete, instan-taneous severance of a 17-inch downcomer, the largest pipe above the Core.
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Dr. P. A. Morris 2
Re: Docket 50-155, DPR-6 ZEK February 9, 1970 2-For a rupture below the core and with core spray avail-90ck Point reactor can sustain, without melting any fuel able, the Bib cladding, a rupcure equivalent to the complete, instantaneous severance of any pipe greater than about two inches in diameter, even the sever-ance of the 20-inch recirculation'line, the largest pipe below the core.
3 For _ small breaks.below the core, equivalect to about 0.02 to 0.03 ft of flow area (about a two-inch pipe), feed-water addition is required to maintain fuel eladding abon the melting point because the primary coolant system pressure does not Jacay fast enough to allow-adequate core spray cooling.
II. Planned Action As a result of the loss-of-coolant analyses, Concuters Power Company has concluded that the existing single core spray system should be augmented by a second, separate and redundant, core spray systec. To this end, a design study has been conducted on the addition of a second, independent core spray system. This study shows that such an addition is feasible for the Big Rock Point Plant.
The preliminary design calls for the backup core spray line to enter the reactor vessel head through a 10-inch access port located on the reactor vessel axial center line. The line would extend down through the access port nozzle, intt the steam dome and then terminate in a single water spray nozzle at the erntral opening in the steam taffle above the core. The spray nozzle would be aimed to deluge the entire top of the reactor core. The
.th of the backup core spray line from the reactor vessel head access port to the fire system water supply would carry it throuth a bend for flexibility, thence through the reactor shield plug to the backup enclosure spray line. The bend in the backup spray line would provide enough flexibility for it to maintain its integrity for vertical movement of at least six inches. The final design of the Big Rock Point emergency core cooling system, including the backup core spray system, is expected to be in conformance with single failure cri-teria as applied to active components. The final design was initiated in the second quarter of 1968 and should be completed by the fourth quar-ter, 1970.
Installation of the carbon steel components of the backup core spray system should be completed during the first quarter of 1970.
In-stallation of the stainless steel components, including the spray nozzle, should be completed during the first quarter of 1971. The stretching out of the above design, procurement and installation schedule is attributed to the difficulty in engaging experienced nuclear designers and the prob-lems in obtaining small lots of nuclear grade piping and valves on any-thing but a long delivery schedule.
Attachment B contains a detailed description of the proposed redundant core spray system, a statement of the design criteria, a list of modifications to be made to existing systems and a failure analysis of the system. Also included is a piping diagram to give an idea of the routing.
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Dr. P. A. Morris 3
Re: Docket 50-155, DPR-6 ZEK February 9 1970 Attachment C contains a description of the conceptual design of the spray nozzle installation in the reactor vessel.
It is our in-tention to proceed on the bases outlined in Attachments B and~C.
-It is our belief that installation of the backup core spray system will eliminate the need for the temporary core flooding system installed for the centermelt fuel program and this temporary system will be removed at that time.
We believe that the addition of this redundant core spray system will make Big Rock Point equivalent to BWR plants currently authorized for construction, with respect to loss-of-coolant accidents. We would, there-fore, like your concurrence in the approach we are taking, as illustrated in Attachments B and C.
With your concurrence, we will proceed with in-stallation of the carbon steel components of the system at the next re-fueling outage in early 1970, and the completion of the design of the stainless steel components in mid-1970. Prior to putting the system into operation, we intend.to prepare a Technical Specifications change relative to the operation, testing and surveillance of the redundant core spray system.
The other area pertinent to the loss-of-coolant analyses con-cerns off-site power for operation of the reactor feed pumps. During a refueling outage at Big Rock Point, a second source of outside power was installed. This second source was operable by March 15, 1968. Now, there are two power lines feeding the plant from two different directions.
We consider the two power lines, a 46 kV and a 138 kV line, as independent sources because they come from different points on our system. We do not consider as crea2ble the assumption that Big Rock Point would sustain the loss of both outside power sources coincident with a pipe rupture or a maximum credible accident. This assumption is generally made in current loss-of-coolant analyses where the plant size is a subt.tantial fraction of the power system capacity and the loss of the large plant toy cause the electric system to become unstable. Big Rock Point at 71 MWe repre-sents less than two percent of Consumers Power Company's total installed capacity of 3,600 MWe. The loss of a unit of this sine on our syatem has very little measurable effect.
III. Conclusions As a result of our review of the loss-of-coolant analyses per-forced by GE, our review of feasible plant modifications and a careful i
consideration of plant and system operating characteristics, we have concluded that:
1.
A separate, independent and redundant backup core spray system added to the Big Rock Point Plant will bring its emergency core cooling system up to current criteria.
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Dr. P. A. Morris 4
Re: Docket 50-155, DPR-6 ZEK February 9,1970 2.
Two outside power sources supplying station power for feed pump operation provide ample backup to cover emergency situations.
3 With the separate, independent and redundant core spray systems, being controlled by the electric and diesel fire pumps, coupled with the two sources of power to operate feed pumps, the Big Rock Point reactor could sustain a pipe rupture of any size without endangerir:g the health and safety of the public.
In addition to the modification of the emergency core cooling system, a number of other modifications have been made to the Big Rock Point Plant or will be made in the near future:
1.
The inetallation of the 46 kV backup power line was com-pleted by March 15, 1968.
2.
The installation of a fast-acting d-c isolation valve between the turbine bypass valve and the condenser was completed by March 15, 1968. This additional isolation valve insures our ability to quickly terminate any inadvertent blowdown caused by a bypass valve malfunction.
3 Material and components for the control rod thimble support structure have been procured. Installation will be accomplished in.the first quarter of 1970, during the upcoming refueling outage.
All of the above modifications resulted from our continuing review of means to guarantee the safety and operability of all our power plants.
Yours very truly, l,
-L GJW/ map Robert L. Haueter Electric Production Attachments A, Superintendent - Nuclear B and C CC:
GFlorelli, USASC EBrunner, USABC l
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