ML20058K573
| ML20058K573 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 01/12/1973 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Dienhart A NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 9102120503 | |
| Download: ML20058K573 (4) | |
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UNITED STATES
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WASrilNGTON, D.C. 20545 j
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January 12, 1973 a
Docket No. 50-263 l
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i Northern States Power Company i
ATTN:
Mr. Arthur V. Dienhart Vice President of Engineering 414 Nicollet Mall l
Minneapolis, Minnesota 55401
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Gentlemen:
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Tests of drywell vacuum breakers in.some E'R plants have demonstrated l
.- t ha t these devices failed to perform properly and did not have accurate valve position indication in the control room.
In addition, technical i
I specifications for operability checks and leakage surveillance have been inadequate to assure that the vacuum breakers will not compromise the function of the suppresrion pool and will fulfill their function as an engineered safety system.
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As a result of this experience, it is requested that the following actions regarding the drywell vacuum breakers be taken for your nuclear power staticn:
I=ediate Action:
1.
Check the position of each vacuum breaker by direct visual inspection, i
if possible, or by position indicators.
2.
Close those vacuum breakers that arc open. If the position cannot be ascertained to be closed, take i=ediate remedial action to assure closure.
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Within 60 days provide the Cc=ission with a report that includes:
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Information regarding the plant vacuum breakers, including:
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Number installed.
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Location cf the installed vacuum breakers.
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Size of each.
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d.
Design differential pressure to open, the test methods used to verify opening of the vacuum breakers and the test results.
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Manufacturer, model number, ratings, and modifications, if l
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any, of the vacuum breakers and position switches.
f.
Installed assembly drawing, including testing equipment and 4
position switches.
Materials used in the vacuum breaker and position switch, g.
including seals, seats, bearings, lubricant, body and oper-
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ating pa-ts.
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Position indicators and alarm locations, design criteria,
. l surveillance requirements, and redundancy of position l
switches, circuits, indicators and alarms.
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Capability of parts and their design life in the most severe i
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suppression chamber operational transient and accident environ-l Discuss possible deleterious effects of chemicals l
ments.
present during the surf ace preparation and application of the suppression chamber coating and of nitrogen on vacuum breaker system materials. Advise what tests have been performed on the vacuum breakers and their position indication system in i
a simulated accident environment.
2.
For the tests performed on each vacuum breaker system, provide a brief description of acceptance criteria and test results, including:
"f Preoperation and periodic surveillance tests.
a.
b.
Other tests and reasons for the tests.
A description of corrective action taken to remedy any f ailure of 3.
the vacuum breakers or their position indication system, including a discussion of the cause of the failure.
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4.
A description of the station procedures or checks used to assure that the vacuum breakers:
Function properly prior to startup.
a.
b.
Are closed af ter completion of pre-startup functional checks.
Are maintained properly.
c.
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~3-January 12, 1973 rl; 5.
A curve showing total allowable drywell to torus bypass area, in terms of equivalent orifice area, as a function of various
>l primary system break areas for containment design and test l
pressures and indicate the fraction of this total bypass area that is allowable for the vacuum breakers. Show the limiting condition of operation for vacuum breaker bypass area on this ll graph.
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6.
A discussion, based on the information provided in item 5, of the l
allowable distance in inches the vacuum breaker can be off its seat and the degrees away from the closed position with the pivot point as the apex.
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The flow vs area characteristics of the vacuum breaker and a curve showing vacuum breaker bypass area vs degrees the vacuum breaker is open from closed to full open.
I 8.
An analysis of the capability of the drywell sprays and the suppression chamber sprays to accommodate primary system break areas, including a curve of break areas vs total bypass area within sprays' capability.
Include a discussion of the avail-ability of sprays, considering interlocks, during a LOCA.
9.
Additional equipment and systems and/or modifications to existing equipment and systems proposed to assure that malfunction of vacuum breakers can be detected reliably and appropriate action can be taken.
10.
Proposed technical specifications for limiting condition of oper-ation and surveillance requirements with bases regarding the I
drywell vacuum breakers.
,i During the next refueling outage:
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Perform the following tests and submit the results to the Commission I
in the subsequi it semiannual report:
Presnurize the drywell to an appropriate pressure above the a.
suppression chamber pressure and determine the leakage rate to the suppression chamber over a suf ficient period of time to assure reliability of leakage data, compensating for i
temperature difference. If the leakage rate exceeds the allowable, as determined in item 5 of the 60-day report, take the appropriate corrective measures and retest until the total leakage rate is acceptable.
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b.
Test each vacuum breaker to assure that it will open with a j
specified suppression chamber pressure above drywell pressure i
to prevent drywell failure due to external pressure.
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Check and adjust each vacuum breaker position switch to assure j
that an alarm in the control room will be actuated at the time j
or before the vacuum breaker is opened to the amount specified as a limiting condition of operation.
d.
Determine that both the opened and closed positions, within allowable limits, of each vacuum breaker are properly indicated In the control room.
l Three signed originals and thirty-seven copics of your submittals are l
l required.
l Sincerely.
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Donald J< Skovholt j
Assistant Director for l
Operating Reactors l
Directorate of Licensing cc: Gerald Charnoff I
Shaw, Pittman, Potts, Trowbridge & Madden i
910 - 17th Street, N. W.
Washington, D. C.
20006 Environmental Library of Minnesota 1222 S. E. 4th Street l
Minneapolis, Minnesota 55414 i
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