ML20037D209

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Forwards Info Providing Before/After Sketches of Circuit Changes Planned for Valves PCV-521,HCV-480,HCV-481-HCV-484, HCV-485 & AC Sequencer Circuit SI-2 in Response to 810423 & 27 Discussions
ML20037D209
Person / Time
Site: Fort Calhoun 
Issue date: 05/15/1981
From: William Jones
OMAHA PUBLIC POWER DISTRICT
To: Clark R
Office of Nuclear Reactor Regulation
References
IEB-80-06, IEB-80-6, NUDOCS 8105220251
Download: ML20037D209 (11)
v • d • e


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'.T-A Omaha Public Power District 1623 HARNEY OMAHA. NESMASMA 68102 TELEPHONE S36 4000 AREA CODE 402 kp ~! '

May 15, 1981 k

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Mr. Robert A. Clark, Chief l

MAY 211981*

U. S. Nuclear Regulatory Coumission

,, wee Office of Nuclear Reactor Regulation e

coawamm n

Division of Licensing Operating Reactors Branch No. 3 g,%,, -

Washington, D.C.

20555 4 oy,, -

Reference:

Docket No. 50-285

Dear Mr. Clark:

The attached information is provided in response to discussions between Messrs. C. Trammell and P. Bender of your staff, Mr. D. Hackett of EG&G, and Messrs. T. Patterson, R. Mehaffey, and D. Flegle of Omaha Public Power District on April 23, 1981 and April 27, 1981.

In response to IE Bulletin 80-06 regarding resetting of ESF components, the District determined a need to modify certain circuits to preclude repositioning or resequencing of several components that are actuated by emergency safeguards signals. Valve circuits for valves PCV-521, HCV-480, 481, 484, and 485 will be modified to remain in their accident position upon reset of the safeguards actuation signals. AC sequencer circuit SI-2 will be modified to prevent load shedding of safeguards buses upon reset of the offsite power loss signal lockout relays. As an interim measure, the Emergency Procedure (EP-35) has been revised to ensure operator awareness of the effects of resetting the ESF actuation signals.

l The attached information provides before and after sketches of the l

circuit changes planned for valves PCV-521, HCV-480, HCV-481, HCV-484, HCV-485, and AC sequencer circuit SI-2.

A verbal description of the changes to the sequencer circuit and the revisions to EP-35 are also p rovided.

Sincerely, 1

~'. -f W. C. Jones Division Manager Production Operations WCJ/KJM/TLP:jmm

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3.

General Description of Sequencing Circuit Upon receipt of an Offsite Power loss Signal (0PLS) the following will happen (refer to Figure 5):

1.

Relay 27 TIS /lA3 is energized closing the contact in Figure 5.

2.

Contact 86A/0PLS opens.

nisyg3, cettAT 3.

Diesel Generator circuit breaker auxiliaryr. remains closed.

This contact stays closed until the circuit breaker spens <scu, 4.

Relays 27-1/SI-2 and 27-lX/SI-2 are energized. The contact outputs frnm these relays will reset the sequencer timing re-lays. This action will load shed the 4160 V safeguard buses thus preparing the buses for the diesel generator.

5.

The diesels accelerate up to running speed with the proper voltage established at its tenninals. The diesel generator circuit t eaker closes and contact 52b/ LAD 1 opens, thereby de-energizing 27-1/SI-2 and 27-1X/SI-2. The sequencing timers are beginning to time out and safeguard loads begin to be loaded.

A few items need to be understood at this time:

1.

OPLS is actuated by two independent channels.

2.

Either of these OPLS channels (86A/0PLS and 86B/0PLS) or both.

can energize relay 27 TIS /lA3.

Upon reset of the OPLS lockouts, the following can happen:

(

Assume that the 86A/0PLS lockout is reset before the 86B/0PLS l.

lockout is.

2.

Contact 86A/0PLS in Figure 5 will close.

3.

Contact 27 TIS /lA3 remains closed as 86B/0PLS keeps the relay 27 TIS /1A3 energized.

4.

Relays 27-1/S1-2 and 27-!X/S1-2 are energized. The contact outputs from these relays will reset the sequencer timing re-lays. This will again loadshed the safeguard buses which is the undesirable feature of this scheme.

Presently, this problem is being addressed administratively in EP-35 for the interim process. Test switches in series with the 86A/C9LS and 86B/

l l

OPLS contacts that energize 27 TIS /1A3 relay will be opened prior to the 0PLS lockout reset. This will ensure that the 27 TIS /1A3 contact will be opened, thereby eliminating any possibility of picking up relays 27-1/

r SI-2 and 27-lX/SI-2. As a permanent solution, the District is looking into removing contact 86A/0PLS from the sequencer scheme.

The original l

intent of cdntact 86A/0PLS being in this control circuit would be to arm the sequencer circuit while the diesel generator is being tested in its monthly surveillance test. The Architectural Engineering firm of Stone -

and Webster is employed by the District in preparing a safety analysis for the removal of the OPLS contact.

It should be noted that a favorable safety analysis is required before final approval to remove the contact will be made.

l I-

EP-35 Su,5 mary In order to assure operator awareness of the fact that certain of the Fort Calhoun Station Engineering Safety Features (ESF) equipment will change state on reset of the ESF initiating lockout relays (designated

86) Emergency Procedure EP-35 has been modified.

EP-35 is the station's step-by-step procedure which provides for the or-derly and safe resetting of the initiating signals. Under the EP a step-by-step procedure is provided for resetting the 86 lock out relays.

Accompanying these step-by-step procedures are tables which identify all equipment special features, and functions.

The District has included reset information wherever most applicable.

OPLS information is in the step-by-step section. Valve information is provided in the table. Since reset occurs after the accident transient has been stabilized, the District feels that no safety problem will be encountered during the interim until modification is completed in the fall 1981 refueling outage.

After the modifications are completed, the District plans to revise EP-35 to reflect the as built status of circuits.

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