ML20033B704
| ML20033B704 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 11/23/1981 |
| From: | Randazza J Maine Yankee |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| FMY-81-171, GL-81-21, NUDOCS 8112010654 | |
| Download: ML20033B704 (2) | |
Text
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(207) 623-3521 November 23, 1981
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FMY-81-171 Lhited States Nuclear Regulatory Commission gg Washington, D.C.
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( ft Attention: Office of Nuclear Reactor Regulation I
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Mr. Robert A. Clark, Chief h NOV3 019BMo.v@
Operating Reactors Branch 3 E
Division of Licensing
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Reference:
(a) License DPR-36 (Docket 50-309)
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(b) USNRC Generic Letter 81-21 dated May 5, IMb
Subject:
Natural Circulation Cooldown
Dear Sir:
Maine Yankee has, as requested in reference (b), "revie ved plant operations in light of the St. Lucie Unit 1 event". We have " implement (ed),
as necessary, procedures and training which will enable operators to avoid (if possible), recognize and properly react to reactor vessel voiding during natural circulation cooldown".
Maine Yankee has conducted two special natural circulation cooldown tests, one in 1979, and one in 1980 under conditions representative of expected operating conditions.
The 1979 test, a cooldown from 532 F to 360 F, 0
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achieved a maximum cooldown rate of 23 F/hr, The 1980 test, a cooldown from 0
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500 F to 190 F achieved a ccoldown rate of 60 F/hr.
An evaluation of the data taken during these tests indicates voiding did not occur. We have demonstrated that our procedures for natural circulation cooldown can be executed without undue risk of primary system voiding.
Maine Yankee has sufficient fresh water on site to support natural circulation cooldown even if the cooldown is conducted extremely deliberataly.
In addition to the condensate storage tank which normally contair-a minimum of 100,000 gal, of condensate, there are other sources of feed including the condenser hotwell, the primary water storage tank with 150,000 usable gallons, over 1.5 million gal, of fresh water available in the on-site fresh water reservoir, and fresh water replenishment at will from an offsite reservoir.
Fresh water from these sources can be used to restore condensate tank level in such a variety of ways that interruption of makeup capability is inconceivable.
The Maine Yankee training program covers the following concepts which relate to this issue:
how voiding can occur where it can occur what effect voiding has on core cooling and primary I
p p I system operation q
8112010654 811123 0
PDR ADOCK 05000309
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M AIP4E YANKEE AYOMIC POWER COMPANV lhited States Nuclear Regulatory Commission November 23, 1981 Attention:
Mr. Robert A. Clark, Chief Page 2 how to recognize the trend toward voiding and the occurrence of voiding how to prevent or mitigate voiding.
This subject gets considerable attention in training.
Maine Yankee procedures governing cooldown under natural circulation conditions caution the operator about void formation, instruct the operator to achere to the minimum pressurization and temperature (MPT) curve, instruct the operator to restrict cooldown rate to 200F/hr. A recent procedure addition cautions the operator to observe the temperature of reactor coolant under the vessel head.
The reactor coolant temperature under the vessel head is monitored through a thernowell installed in a head instrument stalk which projects into the
-reactor coolant. This monitor was installed during the last refueling outage to aid in control of voidirc by allowing observation of the temperature of fluid under the head and comparison of the fluid temperatura with the saturation temperature for the system pressure. The monitor provides information through the plant computer to the control room.
The operating procedures discussed above retain the elements of the conservative natural circulation cooldown strategy employed prior to the installation of the head fluid temperature sensor. Future revisions will take advantage of the ability to monitor head liquid subcooling by relaxing the cooldown rate limit.
We trust this information is satisfactory.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY
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John B. Randazzu Vice President J8R/p1b STATE OF MAINE
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)ss COUNTY OF KENNEBEC)
Then personally appeared before me, John B. Randazza, who, being duly sworn, did state that he is a Vice President of Maine Yankee Atomic Power Company, that he is duly authorized to execute and file the foregoing request in tha name and on the behalf of Maine Yankee Atomic Power Company, and that the statements therein are true to the best of his knowledge and belief.
1 huaW kw 0./'mt Notary Public /
,<s.
. Amis MAY 1,1988