ML20078B881
| ML20078B881 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 09/22/1983 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Adensam E Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8309270295 | |
| Download: ML20078B881 (8) | |
Text
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- ,,-y TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 37401 400 Chestnut Street Tower II September 22, 1983 Director of Nuclear Reactor Regulation Attention:
Ms. E. Adensam, Chief 1
Licensing Branch No. 4 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Ms. Adensam:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 By my letters to you dated September 17, 1982 and July 1, 1983, we requested changes to the technical specification 3 6.19 to support operations for unit 1 and 2 at our Sequoyah Nuclear Plant. As requested in telephone conversations with Carl Stahls of your staff, enclosed is a probabilistic risk assessment (PRA) study to support our request for a revision in the technical specifications. This PRA study was performed to i
quantify the effect on containment isolation failure probability if more than one set of containment purge lines is open during modes 1, 2, 3, and 4.
If you have any questions concerning this matter, please get in touch with Jerry Wills at FTS 858-2683 Very truly yours, TENNESSEE VALLEY AUTHORITY
. M. Millo, Manaiger Nuclear Licensing Sworn t ga d subscr be before me this _
- day of '
1983 Y1 b
Notary Public d
My Commission Expires / "
~
Enclosure cc:
U.S. Nuclear Regulatory Commission (Enclosure)
Region II Attn:
Mr. James P. O'Reilly Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30303
[d 8309270295 830922 l
, f1 PDR ADOCK 05000327 I
P PDR
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j 1983-TVA 5OTH ANNIVERSARY An Equal Opportuni+y Employer
i ENCLOSURE Probabilistic Rick Assessment for Containment Purge System Sequoyah Nuclear Plant Units 1 and 2 g tainment Purge System
===.
Background===
The containment purge system at Sequoyah is used during normal operation to reduce radiation levels inside containment and to control containment pcessure, temperature, and relative humidity. During containment purge, an open path exists between the containment and the environment. In order to limit the risk due to an inability to isolate containment purge, the technical specifications (TS 3 6.1.9) permit only one pair (one supply line and one exhadst line) of purge lines to be open in modes 1, 2, 3, and 4.
The following analysis will determine the effect on containment purge isolation of the proposed change to TS 3.6.1 9 which would allow the simultaneous operation of 3 sets of purge lines during normal operation.
Configuration As shown in Figure 1, five sets,of containment purge supply and exhaust lines penetrate containment. Each of these lines has two isolation valves which are normally closed except during containment purging through that line. During purge operation, these valves are energized open. Isolation capability is provided by train A and train B containment vent isolation signals which energize a relay to open a set of contacts in the solenoid circuit of the valve. The relays arc designed to " latch in" and maintain the solenoid circuit in the deenergized state in the event that the isolation signal is lost. All of the valves are air-operated and are designed to " fail closed" on loss of air or control power to the solenoid circuit. '
g
- D*ta The probability of failure to isolate was calculated for both the present and proposed operating configurations using data from existing probabilistic risk analyses:
Failure of SSPS to generate containment vent isolation signale (one train) = 3.56 x 10-3/ demand (Zion PSS) a D
Failure of~SSPS to generate containment vent isolation signals (both trains) = 2.72 x 10-6/ demand (Zion PSS)
Failure of air-operated valve to transfer to the failed position = 2.66 x 10-4/ demand (Browns Ferry)
Single Line Ooeration Assuming the configuration shown in Figure 1, a failure to isolate containment is dominated by the following events:
1.
FCVs 30-14 and -56 remain open due to failure of train A containment vent isolation signal coupled with a hardware failure of FCV 30-15 or -57.
2.
FCVs 30-15 and -57 remain open due to failure of train B containment vent isolation signal coupled with a hardware failure 'of FCV 30-14 or -56.
3.
Failure of both train A and train B containment vent isolation signals. _._
[ Tha pecb bility of fcitura dua to cy:nts 1 through 3 in giv:n by:
3.56 x 10-3(2.66 x 10-4 + 2.66 x 10-4) +
3.56 x 10-3(2.66 x 10-4 + 2.66 x 10-4) +
2.72 x 10-6 Failure to isolate = 6.51 x 10-6 Two Line Operation
^
Again referring to Figure 1, it is now assumed that FCVs 30-7,
-8, -50, and
-51 are also open. Failure to isolate containment is dominated by the following events:
1.
FCVs 30-7, -51, -14, and -56 remain open due to failure of train A containment vent isolation signal coupled with & hardware failure of FCV 30-8, -50, -15, or -57.
2.
FCVs 30-8, -50, -15, and -57 remain open due to failure of train B containment vent isolation signal coupled with a hardware failure of FCV 30-7, -51, -14, or -56.
3.
Failure of both trains A and train B containment vent isolation signals.
The probability of failure due to events 1 through 3 is given by:
3.56 x 10-3(2.66 x 10-4 + 2.66 x 10-4 + 2.66 x 10-4 + 2.66 x 10-4) +
3.56 x 10-3(2.66 x 10-4 + 2.66 x 10-4 + 2.66 x 10-4 + 2.66 x 10-4) +
2.72 x 10-6 Failure to isolate = 1.03 x 10-5
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- si Three Line Operation We now assume that FCVs 30-7,
-8,
-9,
-10, -14, -15, -50, -51, -52, -53,
-56, and -57 are open. Failure to isolate containment is dominated by the following events.
1.
FCVs 30-7, -10. -14, -51. -52, and -56 remain open due to failure of trainAcontainm$ntventisolationsignalcoupledwithahardware failure of FCVs 30-8,
-9, -15
-50, -53, or -57.
2.
FCVs 30-8,
-9,
-15, -50, -53, and -57 remain open due to failure of train B containment vent isolation signal coupled with a hardware failure of FCVs 30-7, -10, -14, -51, -52, or -56.
3 Failure of both trains A and B cottainment vent isolation signals.
The probability of failure due to events 1-3 is given by:
(6)(3.56 x 10-3)(2.66 x 10-4) +
i (6)(3 56 x 10-3)(2.66 x 10-4) +
E.72 x 10-6 Failure to isolate = 1.41 x 10-5
. e.... :..
_ Conclusions The probability of failure to isolate three pairs of purge lines using containment isolation valves is n~ factor of 2.23 higher-than for the case where only one pair is open. Even at 1.41 x 10-5, h, wever, the isolation capability is quite reliable,'and this event is not a significant contributor to risk. The Reactor Safety Study (WASH-1400) found that sequences involving containment isolation failure were low in probability.
5 In addition, secondary containment isolation valves also close upon receipt of either train containment vent isolation signal and provide an additional way to isolate flow through the purge lines.
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e, Solenoid Circuit Power Source Supply Containment "ent 125V de Battery Bd Manual Exhaust Valve Isolation Sishal, Unit 1(Unit 2)
Control Valve FCV 30-2 TRA,TRB(buffered)
I(III)(a)
HS 30-2 FCV 30-5 TRA,TRB(buffered)
- -L(III)(b)
HS 30-5 FCV 30-7 TRA I(III)
HS 30-7 FCV 30-51 FCV 30-8 TR3 II(IV)
HS 30-8 FCV 30-50 FCV 30-9 TRE II(IV)
MS 30-9 FCV 30,
FCV 30-10 TRA I(III)
,TRA I(III)
HS 30-14 FCV 30-56 FCV 30-15 TRE II(LV)
HS 30-15 FCV 30-57 FCV 30-16 TRB II(IV)
HS 30-16 FCV 30-17 TRA I(III)
HS 30-17 TRB II(IV)
HS 30-37' FCV 30- 37 i
TRA I(III)
- HS 30 40 FCV 30-40 FCV 30-19 TRA II(IV)(?
H!! 30-*19 leCV 3 58 FCV 30-20 TRA I(III)-
US 30--20 Fev 30-59 TRA,TRB(buffered)(a)
I(III)
HS 30-61 FCV 30- 61 TRA,TRB(buffered)(a)
I(III)
HS 30-62 I?CV 30-62 All FCV listed deenergize to close.
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All FCV fail closed on lors of tir or control power to the ralve solenoid circuit.
Containment vent isolation signals train A and train B energize a relay to open a contact in valve solenoid circuit.
(a) FCV 30-2,
-5, -61, -62 receive two isolation signals:
(1) a train A containment vent isolation signal which energizes a relay to open a contact in the valve solenoid circuit and (2) a train B (buffered) containment vent l-isolation signal which has a train A power source and deenergizes a miay l
to open a contact in the valve solenoid circuit. l
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