ML20207D907
| ML20207D907 | |
| Person / Time | |
|---|---|
| Issue date: | 12/24/1984 |
| From: | Parr O NRC |
| To: | NRC |
| Shared Package | |
| ML20151H089 | List:
|
| References | |
| FOIA-88-92 NUDOCS 8808160203 | |
| Download: ML20207D907 (5) | |
Text
_-_ _ - - _--___
\
i e
.. - . . . . . . . . . . - . . . . . . . . . . . . . . . . . . _ . _ l
/ ,, UNITED STATES
.E e NUCLEAR REGULATORY COMMISSION g WASHING TON, D. C. 20666 s , l l
%., ' " * * /
- occ 241984 1
1 NOTE TO: ASB Reviewers FROM: Olan D. Parr
SUBJECT:
REVISION TO FIRE PROTECTION REVIEW GUIDANCE As a result of additional infonnation received on the subject of current '
transfomers and multiple high-impedence faults, I am providing the attached revisions to those pages discussing these subjects. The changes reflect present staff positions and are noted by bars in the right hand margin, j
b . A '
Olan D. Parr J cc: R. Bernero ,
L. Rubenstein j l
l l
l I
JONESBO-92 .
I
- \
l 3 - Revision 1 I acceptability of the design. Since issuance of that guidance, there i have been several expansions on associated circuits. In particular, the patential for multi-high impedence faults in AC power circuits could result in the loss of power to safe shutdown equipment.
Figure 1 contains a sketch of circuit designs which could result in - -
the loss of needed power to safe shutdown equipment. As can be seen -
in Figu*e 1, redundant divisions of safe shutdown cables are properly l separated in accordance with Appendix R criteria. However, a fire in fire area A would result in loss of Division A safe shutdown equip-ment and cause damage to nonsafe shutdown cables associated with the Division 8 bus. Further, the individual fault current resulting from the fire damage in the nonsafe shutdown cables may not be enough to trip the individual breakers (8 and 8 7), but the sum of the faults 3
may be sufficient to trip the main breaker B . If this were to occur,theDivisionBbusandthecorrespondi$gredundantDivisionB safe shutdown equipment would be lost.
1 The ASB reviewer should, therefore, request an analysis by each applicant which confirms that the above situation does not occur for postulated fire (high impedence faults) in all AC power cables in each fire area containing one or more safe shutdown divisions. Some newer plants may be able to show that no division A and 8 cables are located in a single fire area. This would be acceptable. If the analysis indicates that this condition could occur, then either some number of cables should be protected from fire damage (additional cable wraps or relocation from the fire area of concern) in order to reduce the total fault current below the setting for breaker 8 3, or, the applicant may provide an appropriate procedure for reestablTshing power to a faulted bus powering safe shutdown loads (i.e., identifying the failure to the operator to that he can strip the faults from the bus, and close breaker B3 to reestablish shutdown train B).
Another area of concern is the spurious operation of equipment for the case of three-phase AC and non-grounded two-wire DC power circuits. For the three-phase AC circuit, the possibility of getting a hot short on all three circuits in the proper phase to cause spurious operation of a motor is considered an impropable event. Therefore, utilities can be granted relief from analyzing this case. For non-grounded DC circuits, cable-to-cable faults and wire-to-wire faults are postulated to occur, Hence, these types of faults must be considered during the review.
However, if the utility can demonstrate that non-grounded cable-to-cable DC shorts are impropable, relief can be granted. Hot shorts in three-phase AC and non-grourded DC circuits must be analyzed and corrected for spurious operation of H1/Lo pressure interfaces.
During the Fitzpatrick review, the staff did not require that the licensee pursue the three-phase and DC circuit issue discussed above.
However, for the DC circuits, the licensee was required to request an exemption from Section III.G.2 of Appendix R. The review of the exemption is performed by pSB.
, _ . -r
v 4 - Revision 1 2.2.3 Transfer Switch Isolatian _Ci_rcuitry DurindafireprotectioninspectionattheWolfCreekGenerating Station, it was discovered that for a fire in the control room, - .
isolation transfer switches for certain hot shutdown systems /com-ponents had to be switched to the alternate or isolated position prior to damage occurring to these circuits. If this were not accom plished in time, uses would have to be replaced in order to make the system / component operable. This situation existed because the transfer switches did not place new/ redundant fuses into the control power circuit, but left the existing (assumed blown) set of fuses in the circuit. For most of the transfer switches the situation did not cause a problem since the desired effect after isolation was the deenergization of power. In other instances where the system / component had to be operable or where operation might be required to override a spurious actuation (such as a motor operated valve) replacement of fuses would be required if blown.
At the Wolf Creek facility, the transfer switches at the remote shut-down panel had redundant fusing so that only transfer switches at other local stations (which were designed / installed after those on the remote shutdown panel) that mainly involved support systems operability or correction of spurious operations were identified as a concern. Wolf Creek either modified the existing switches nr installed new switches for certain components such that redundant fusing does exist with a new (different) set of fuses switched into the circuit when the switch is placed in the isolated mode. Alternate shutdown procedures were also modified such that shutdown could be achieved assuming imediate evacuation of the control room and possible control room circuit damage with possible spurious operation of equipment prior to isolation outside the control room.
This situation may exist at other facilities and may involve other areas of the plant that require alternate shutdown capability and could include the switches on the alternate / remote shutdown panel. The reviewer should ensure that the utility has reviewed its safe shutdown circuitry and has taken any applicable corrective action necessary to ensure that the isolation transfer switches required for post-fire safe shutdown capability do not rely on the continuity of fuses that may be blown due to control room (or other area) circuit fire damage. The following are possible courses of action to be taken by the utility.
- 1. Review the electrical design drawings for the existing isolation transfer switches to detennine where and if this situation exists.
- 2. Provide modifications to wisting switches and/or install new isolation switches where r.acessary to provide redundant fusing such that a blown fuse will not require replacement to achieve and maintain hot shutdown, and
- 3. In the interim, ensure that sufficient replacement fuses are available in the event a fire were to blow fuses and thereby disable a required function / operation for alternate shutdown.
l t
4A 2.2.4 Current Transformers inOedober1982.BNLidentifiedaproblemwithopen-circuitoperationof current transformers (CT) which could exacerbate the consequences of a - -
centrol room fire. The concern stems from the fact that a control '
room fire could result in a breakdown of the power feeder insulation and cause a second fire. Attachment 7 contains the detailed descrip-tion of the problem along with the applicant response to a PSB question on the subject. The Power Systems Branch has reviewed this concern and ;
concluded that the BNL concerns were overly conservative and recommended no further action on this issue. Therefore, the ASB reviewer should be aware of this concern; however, no other action is required. Attach-ment 9 is the PSB evaluation. ;
l i
l
. - . . _ . - _ v_. . . _ _ __ . _ __% _ . , - . . , . _ , -
I FIGURE l - "" " '
FIRE AREA 2
! FRE AREA l FIRE i
.i NON SAFE SHUTDOWN ,
DIVISDN B I
4 -SAFE SHUTDOWN >
) )) DIVISION A DVISDN B ))) B1) )B2 I
4
)
)B3
? ,
i ...
b _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - _ _ _ - _ _ _ _ - - - _ - _ _ .
_ _