ML20213D775
| ML20213D775 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 11/03/1986 |
| From: | Hunsader S COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 2359K, NUDOCS 8611120227 | |
| Download: ML20213D775 (6) | |
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'7 Address Reply to: Post Omce Box 767
\\, d Chicago, Illinois 60690 - 0767 November 3, 1986 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC. 20555
Subject:
Byron Station Unit 2 Review of the Reactor Head Vent Valves for Spurious Operation
Reference:
September 22, 1986 A.D. Miosi letter to H.R. Denton Dear Mr. Denton The purpose of this letter is to provido you with the results of our review of spurious operation of the Reactor Head Vent Valves for Byron Station Unit 2.
The analysis of the Head Vent valves is completed.
Attached are changes to the Fire Protection Report which account for that analysis.
Based on this analysis changes will have to be made to the Control Room Inaccessibility procedure (PRI-5) at Byron Station.
We anticipate that these changes to the PRI-5 procedure can be completed prior to exceeding 5% power pending your comments.
Please contact us should you have any questions concerning this matter.
One signed original and fifteen copies of this letter and enclosure are provided for your review.
Very truly yours, S.C.
Hunsader Nuclear Licensing Administrator
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L. Olshan encl.
2359K 8611120227 861103 PDR ADOCK 05000455 F
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BYRON-2 2.4.2.73 Unit 1 Fire Zones Containing Equipment and/or Cables Used for. Unit 2 Safe Shutdown As shown in Table'2.4-4, Unit 1 Fire Zones 3.1-1,'3.2A-1, 3.2B-1,
-3.2C-1, 3.2D-1, 3.2E-1, 3.3B-1, 3.3C-1, 3.3D-1, 3.4A-1, 5.1-1, 5,2-1, 5.6-1, 11.5-1, 11.5A-1, 11.6-1, 11.7-1, and 18.5-1, contain equipment and/or cables associated with the auxiliary building HVAC exhaust _ system and/or the "O" component cooling pump.
In any of these zones, a fire could result in the loss of, at most, 2 of the 4 exhaust fans.
Additionally, Table 2.4-4 shows that cables and equipment serving the control room HVAC system are present in Fire Zone 18.4-1, and cables serving this system are present in zones 3.1-1, 3.2A-1, 3.2B-1, 3.2C-1, 3.2E-1, 3.3A-1, 3.3B-1, 3.3C-1, 3.3D-1, 3.4A-1, 5.1-1, 5.2-1, and 5.6-1.
However, cables from only one electrical division are present.
In summary, a fire in any of these Unit 1 zones would not affect the ability to safely shut down Unit 2.
2.4.3 Identification and Analysis of High-Low Pressure Interfaces 2.4.3.1 Indication of High-Low Pressure Interfaces A thorough review of all interfaces of the RCS with other plant systems has identified six high-low pressure interfaces that I
utilize redundant electrically controlled devices for isolation of the primary coolant pressure boundary.
Two >f the interfaces consist of the two motor-operated valves in series in each of the RHR pump suction lines.
Two addition:e1 interfaces consist of.the I
two power-operated relief valves (POT / 's) and their associated motor-operated block valves.
The other two interfaces consist of the two pairs of solenold-operated reactor head vent valves.
l 2.4.3.2 Evaluation of High-Low Pressure Interfaces 2.4.3.2.1 RHR Pump Suction Lines 2.4.3.2.1.1 Interface Description The two RHR pump suction lines are as follows:
1.
MOV RH8701A-1 a'nd RH8701B-2 in RHR suction line from RC loop A.
2.
MOV RH8702A-1 and RH8702B-2 in RHR suction line from RC loop C.
These valves are interlocked by diverse pressure instruments as described in FSAR Subsection 7.6.4 and are shown in FSAR Figure 6.3-2 (P&ID M-62).
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it BYRON-2 For the containment, the PORV cables (2RY246 and 2RY252) will be routed individually in conduit from their respective penetrations to the opening at the top of the pressurizer enclosure.- Thus, if a fire damaged the conduit and the PORV cable insulation, a hot short would not occur since there are no cables in direct contact with either PORV cable.
2.4.3.2.3 Reactor Head Vent Valves-2.4.3.2.3.1 Interface Description The four reactor head vent valves are as follows:
1.
Valve 2RC014A in series with' valve 2RC014C (Train A);
2.
Valve 2RC014B in series with valve 2RC014D (Train B).
The arrangement of these valves is shown in FSAR Figure 5.1-1, Sheet 1.
All four valves are d-c solenoid-operated and are closed (de-energized) during normal operation.
Each valve is controlled through a separate circuit from a 2-position (CLOSE and OPEN) switch at main control room panel 2PMllJ.
Power is supplied to each solenoid directly through the control cabling.
The Train A valves are powered from 125-Vdc non-safety-related Division 21 distribution panel 2DC05EB and the Train B valves are powered from 125-Vdc non-safety-related Division 22 distribution panel 2DC06EB.
Table 2.4-15 lists the cables serving the head vent valves.
2.4.3.2.3.2 Assumptions and Information Spurious opening of a head vent valve due to a two-wire d-c hot short in the cabling is considered.
There are no interlocks in the valve control circuits, however, fire induced failures of the control switches are considered.
2.4.3.2.3.3 Failure Modes Two fire induced failure modes are postulated.
Failure Mode 1 - Control Switch Contact closure Train A:
Fire causes closure of control switch contacts at panel 2PM11J for valves 2RC014A and 2RC014C.
Circuits are energized and both valves open.
Train B:
Fire causes closure of control switch contacts at panel 2PMllJ for valves 2RC014B and 2RC014D.
Circuits are energized and both valves open.
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BYRON-2 Failure Mode 2 - Two-wire d-c Hot Short to Control Cable Train A:
A two-wire hot short occurs due to contact of. energized d-c conductors with cable 2RC620, 2RC621, or 2RC622 for valve 2RC014A, or with cable 2RC626, 2RC627 or 2RC628 for valve 2RC014C.
Train B:
A two-wire hot short occurs due to contact of energized d-c conductors with cable 2RC623, 2RC624, or 2RC625 for valve 2RC014B, or with cable 2RC629, 2RC630, or 2RC631 for valve 2RC014D.
2.4.3.2.3.4 Evaluation and Results Failure mode 1 could occur as a result of a fire in the control room (zone 2.1-0) only.
In the event of a fire in this zone, evacuation may be required.
Therefore, to preclude inadvertent opening of the head vent valves, the PRI-5 procedure will be revised to require that, upon evacuation of the control room during a fire, the circuits for the non-safety-related head vent valves will be deenergized.
Failure mode 2 could occur as a result of a fire in any of the
.following zones:
Valve 2RC014A or Valve 2RC014B or 2RC014C Opens 2RC014D Opens 2.1-0 2.1-0 3.2E-2 3.2A-2 3.3C-2 3.2B-2 3.'3D-2 3.2C-2 3.4A-2 11.6-2 11.5-0 Containment ll.5A-2 11.6-0 Containment For any of the above zones, a fire could only open one of the valves.
Spurious opening of valves A and C or B and D would l
require two simultaneous two-wire d-c hot shorts in the control cabling.
This is not postulated to occur.
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DYRON-2 TABLE 2.4-15 CABLING FOR REACTOR HEAD VENT VALVES VALVE 2RC014A 2DC166 Power from 2DCOSEB (Division 21) to control panel 2PMllJ 2RC620 Valve to_ reactor head connector plate 2RC0lR-A 2RC621 Reactor head connector plate to penetration 2LV01E 2RC622 Penetration to control panel 2PMllJ VALVE 2RC014B 2DC167 Power from 2DC06EB (Division 22) to Control Panel 2PMllJ 2RC623 Valve to reactor head connector plate 2RC0lR-A 2RC624 4
Reactor head connector plate to penetration 2LV03E 2RC625 Penetration to control panel 2PMllJ i
VALVE 2RC014C 4
2DC166 Power from 2DC05EB (Division 21) to control panel 2PMllJ 2RC626 Valve to reactor head connector plate 2RC0lR-A 2RC627 Reactor head connector plate to penetration 2LV01E 2RC628 Penetration to control panel 2PMllJ VALVE 2RC014D 2DC167 Power from 2DC06EB (Division 22) to Control Panel 2PMllJ l
2RC629 Valve to reactor head connector plate 2RC0lR-A i
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. TABLE 2.4-15 (Cont'd) 2RC630 Reactor-head connector plate to penetration 2LV03E 2RC631 Penet' ration to control panel 2PMllJ 4
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