ML19329B083: Difference between revisions
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. . . : . , ' 9_.r:.; . . | . . . : . , ' 9_.r:.; . . | ||
Serial No.131 '.~' '. # | Serial No.131 '.~' '. # | ||
, Docket No. 50-346 . . | , Docket No. 50-346 . . | ||
... ' ',a. .. . . | ... ' ',a. .. . . | ||
Line 42: | Line 41: | ||
c | c | ||
.- s. | .- s. | ||
.' Mr. James G. Keppler li - . | .' Mr. James G. Keppler li - . | ||
~ | ~ | ||
Line 72: | Line 70: | ||
the gate current of the shunting SCR's (silicon controlled rectifiers) was in the medium to upper range of the specification limits. With . | the gate current of the shunting SCR's (silicon controlled rectifiers) was in the medium to upper range of the specification limits. With . | ||
these two conditions existing, the thermal rating of the diode is ex-ceeded, which may lead to failure of the zener. | these two conditions existing, the thermal rating of the diode is ex-ceeded, which may lead to failure of the zener. | ||
8001300 | 8001300((h | ||
. . v. . | . . v. . | ||
n . | n . | ||
Line 104: | Line 102: | ||
'ational testing of the devices prior to station operation assures that - - - | 'ational testing of the devices prior to station operation assures that - - - | ||
the health and safety of the public are not jeopardized. . . . | the health and safety of the public are not jeopardized. . . . | ||
~:,;= . | ~:,;= . | ||
.Yo.urs very truly. | .Yo.urs very truly. | ||
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w i . | w i . | ||
~. . . . .: s. .. . . | ~. . . . .: s. .. . . | ||
pc/29 - | pc/29 - | ||
- -~ - | - -~ - | ||
._ .};:,..{,'', [ . | ._ .};:,..{,'', [ . | ||
cc: .. | cc: .. | ||
,Dr. Ernst Volgenan, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D. C. 20555 . | ,Dr. Ernst Volgenan, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D. C. 20555 . | ||
, .i . | , .i . | ||
1 ' | 1 ' | ||
y | y |
Latest revision as of 01:15, 16 March 2020
ML19329B083 | |
Person / Time | |
---|---|
Site: | Davis Besse ![]() |
Issue date: | 10/19/1976 |
From: | Roe L TOLEDO EDISON CO. |
To: | |
Shared Package | |
ML19329B081 | List: |
References | |
131, NUDOCS 8001300674 | |
Download: ML19329B083 (2) | |
Text
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TOLEDO
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. EDISON
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. um ese.sa<a October 19, 1976 '- .
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Serial No.131 '.~' '. #
, Docket No. 50-346 . .
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.' Mr. James G. Keppler li - .
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- y. Regional Director, Region III .
.Dir'ectorate of Regulatory Operations -
C
. ., U.S. Nuclear Regulatory Commission ,
\ "
el 799 Roosevelt Road J.. . "-
's-Glen Ellyn, Illinois
. 60137 -
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Dear Mr. Keppler:
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' Th'is letter is submitted in accordance with 10 CFR 50.55(e) as a con-
.. .* smnmation of the Interim Report dated August 6,1976 regarding defi-
. ciencies in the Davis-Besse Nuclear Power Station Unit No. 1, General
. Electric, type AK-3-25 and AK-3-50 480 volt AC circuit breakers, power sensors and supplies. ., . ,
.. c .,
Description of the Deficiency
.~ --
General Electric identified a failure mode of the zener diode in the power supply circuit. Diode failure could occur when simultanecusly the~ '
' breaker load current was less than 15-20% frame size current rating and 5 '
the gate current of the shunting SCR's (silicon controlled rectifiers) was in the medium to upper range of the specification limits. With .
these two conditions existing, the thermal rating of the diode is ex-ceeded, which may lead to failure of the zener.
8001300((h
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n .
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. Corrective Aceion .
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General Electric redesigned the power supply circuit t:o eliminate the - -
stated failure mode. The Applicant has arranged to replace all subject
- ** power supplies and power sensors at Davis-Besse Unit I and is presently -- --
" . having General Electric rework the breakers. Each reworked breaker will,
. be required to pass pre-operational testing under the Applicant's test
. program before being considered acceptable for use.
Safety Implications '
- 5 .'.'"': ~.A. . .
~ ~ ~
- If the above conditions had gone uncorrected, the zener diode coulci have .
- " failed.
- If the diode had shorted, insufficient trip voltage would have ~
- .j
.been available. The consequence would have been failure to protect t
associated essential electrical equipment during an electrical fault.
With the diode opened, excessive control voltage would be available in e the power supply and power sensor circuits. In this latter c.ase, no *
- immediate safety consequence would have necessarily occurred, however electrical fault protection of associated essential electrical equipment
- could have been adversely affected should the high voltage have caused the power sensor to fail. .
, ,,.7 A The scheduled repair of the affected breakers and acceptable pre-oper-
'( ,
'ational testing of the devices prior to station operation assures that - - -
the health and safety of the public are not jeopardized. . . .
~:,;= .
.Yo.urs very truly.
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,Dr. Ernst Volgenan, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D. C. 20555 .
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