ML20244C935
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NAY I 51934 MEMORANDUM FOR: Gus C. Laines, Assistant Director for Operating Reactors, DL L. S. Rubenstein, Assistant Director FROM:
for Core and Plant Systems, DSI DAVIS-SESSE - THE OPERABILITY OF AN AC VITAL SUBJECT :
INSTRUMENT BUS WHEN POWERED FROM A NON-CLASS 1E P0lER SOURCE IN LIEU OF AN INVERTER (TAC NO. 54262 TIA 64-15)
Per TAL No. 54262 (TIA B4-15), the Power Systems Branth has reviewed the operability requirements for ac vital instrument buses of the Davis-Besse pl ant.
Our evaluation is as follows:
We recognize that the technical specification requirement to the current. tandard technical specifications) are somewhat vague in
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that the 120V ac vital buses can be energized from a non-Class 1E power supply for en extended period of time when an inverter is out for repairs.
of these plants do not limit the time that these vital buses may beEnergizing energized from a source other than battery / inverter com The generic would be interrupted in the event of loss of offsite power.
safety concern srises from the si.tuation where power In some designs with two vital is lost due to an assumed single failure.
In other designs, buses deenergized, spurious safety act a tions will occur.
the loss of power on two buses can prevent automatic there is a potential for plants with these types of designs to be operating for extended periods of time outside their origint! licensing basis, i.e.,
in violation of the single failure criterion.
Cecause of the above concern the standard technical specifications revised to require the licensee to 1E de bus through an associated inverter within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or proceed to j
shutdown the plant, While a few plants have this LCO requirement, a majority of the operatj
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plants do not have such requirements.
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i ps_, - MAY 151384
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to other operating plants, this issue is currently being studied by the NRR statf under Generic Issue 48, " Operational Restrictions for Class 1E 120V AC Vital Instrument Buses,* in accordance with HRR Office Letter Number 39.
As part of the proposed resolution of this issue we anticipate recommending vital bus may be energized from a source other than a Cla For regulatory consistency, subject to approval of the proposed requirement by CRGR, it will be a backfit on all operating plants (including an inverter.
Our current projection for completion of this generic task Davis-Besse).
This completes our action on TAC No. 54262 and TIA 84-15.
is early 1986.
odlua (C L. Si ubenstein, Assistant Director for Core and Plant Systems Division of Systems Integration
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R. Mattson M. Srinivasan J. Stolz A. DeAgazio J. Knight A. Ungaro
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