ML20059M123

Ei Hatch Nuclear Plant Evaluation of Failure of Time Delay Relays in RWCU Differential Flow High Instrumentation During Design Basis Events

ML20059M123
Person / Time
Site:	Hatch
Issue date:	05/31/1989
From:	Chi L, Sozzi G GENERAL ELECTRIC CO.
To:
Shared Package
ML20059M119	List: HL-1122, Application for Amends to Licenses DPR-57 & NPF-5,changing Tech Specs Re Protective Instrumentation ML20059M120 ML20059M123
References
EAS-24-0489, EAS-24-489, NUDOCS 9010030169
Download: ML20059M123 (7)

Text

. - .. . .- . _

t.  :

ENCLOSURE 4 EAS 24 0489-3 DRF A00 03470 l MAY 1989 1 I

1 4

. EDVIN I. HATCH NUCLEAR FIANT t'

EVALUATION OF THE FAILURE OF THE TIME DEIAY REIAYS IN THE RWCU DIFFERENTIAL FIAV HIGH .

INSTRUMENTATION DURING DESIGN BASIS EVENTS J.L. Jscobs i

.t Reviewed by:

i L.L. Chi, Principal Engineer Plant Performance Engineering f ,

/.pproved by: D A t G/L. Sozzi' ManWgf6r Plant "erformance Engineering l

l 6 GENuclearEnergy i

? 175 Cunw Annw SonJose. CA 95125 l 9010030169 900921 fDR ADOCK 05000321 PDC

=

li- .= i l-l (-

l

- IMPORTANT NOTICE REGARDING CONTENTS OF THIS REPORT ,

l I

!l' L PLEASE READ CAREFULLY ,

l The only undertakings of General Electric Company respecting

( information in this document are' contained -fn. the contract-  !

between Georgia Power Company (GPC) and General Electric Company,

= as identified in the= purchase order for this report and nothing ,

t contained in 'this document shall be construed ins ' changing the-contract.. The use of this information by anyone _ other ' than GPC '

or for any purpose other than that for which it is intended, is not authorized; and with: respect to any unauthorized use, General Electric Company makee no representation or warranty, and assumes-no .iability as to the completeness, accuracy, or usefulness of the information contained in this document.

l The information contained in this report is_ believed by General [

Electric to be an accurate and true representation of the facts known, obtained or provided to General Electric at the time this report was prepared.

t i

i 1

=

( .

EAS 24-0489

,( , l '. INTRODUCTION l

The Reactor Water Cleanup (RWCU) system for Plant Hatch contains I two isolation' valves that are part of the Primary l Containment Isolation O System (PCIS). The two valves, C31 F001 and C31 F004, are members of'

(

Isolation Group.5. The following signals isolate the Group 5 valves:

Reactor Vessel Water Level Low Low (14 vel 2)

T -

RWCU equipment room temperature high RWCU equipment room ventilation differential temperature high. ,

RUCU differentia 1' flow high  !

Actuation of Standby Liquid Control System (C31-F004 only) -1

( -

High Temperature following non regenerative heat exchanger (C31-F004 only) ,

The RWCU differential flow high signal will initiate an automatic

, isolation after a 45 second time delay provided by two relays, 031-R6160 and D. This evaluation considers the common mode failure of these time-delay relays in the RWCU differential flow instrumentation. Failure cf

l. these relays results in the failure of ~ the differential flow signal ,

high. Therefore, leakage in the RWCU system piping that'would normally.

be detected by this signal must now be . detected - by other ' isolation signals during design basis events. It should be . noted however, that failure of the time delay-relays will not. prevent an alarm annunciation on RWCU high differential. flow in the reactor control room-(for Unit 1).

Although this evaluation takes no credit for operator action to achieve isolation during a RUCU line break, the operator would be alerted to the high differential flow signal and the potential for RWCU system leakage.

This evaluation demonstrates that other instrumentation' would isolate-the RWCU system -during design basis Loss-of-Coolant Accident (LOCA) and High Energy Line Break (HELB) events; therefore the failure . of the relays in RWCU differential flow-instrumentation would have-no impact on these design baais events.

t 1

9 - - , - , . - - - - _ ~ , . . . . .

t

\i '.

EAS-24-0489 J'

(- 2. EVALUAf10N .

J The purpose of the RWCU high differential flow signal is to detect' significant leakage in the RWCU system by means . of a flow- comparison

(

between system inlet and outlets. Flow instruments C31 N012 G31-NO36, and 031 N041 indicate system outlet flow to the condenser /radwaste, , ;

inlet flow from the reactor, and outlet- flow to the reactor, respectively. When the difference between the inlet and outlet flows y exceeds the trip setting, an isolation signal 'is generated after a 45 second time delay (G31-R6160,D delay isolation for the inboard Land i outboard isolation valves respectively). This timer is provided to override the isolation signal during any pump and valve surge conditions to avoid unnecessary isolations. The RWCU system leakage can = also be  !

detected by reactor water level, area temperature, and area differential temperature. The trip settings for these RWCU isolation; signals, as

, identified in Table 3.2-1 of the Unit 1 Technical-. Specifications - and Table 3.3.2-2 of the Unit 2 Technical Specifications, are listed below:

Unit 1 Unit 2 Instrument Trin Settina Trio Settine' Reactor Vessel Water Level Low Low (Level 2) 2 47 inches 2 -47 inches-l Reactor Water Cleanup System Differential Flow 20 to 80 gpm 5 79 gpm Reactor Water Cleanup Area Temperature 5 150 F ,

s 150 F c..

Reactor Water Cleanup Area Ventilation  !

Differential Temperature s 67 F $ 63 F i

The objective of this evaluation is to -demonstrate that isolation of the RWCU system during design basis IDCA and HELB events can be 2-

_ _ _ _ _ _ _ - _ _ _ _ _ _ - . __ .. - . _ _ _ . _. -. . _ . . . _ . ~-

7

, y t.

s.

EAS-24-0489-lc _ achieved ' with ' signals other than the differential flow' signal. In-E particular, the area temperature instrumentation is most- likely to l isolate the RUCU system first during a break outside containment. This ,

_ instrumentation includes six temperature elements, three for each of the

(' isolation valves. For example, the RWCU room _ outlet area temperature elements G31 N062 A, E, and J monitor outlet temperature in the RWCU

-heat exchanger room,-pump room and phase separator room respectively for -

the inboard isolation valve 1G31-F001. 14akage in'the piping cbntained

(

in - these three rooms, which would be detected by the differential ~ flow ,

high instrumentation, can also be detected by the area-temperature high instrumentation. The design basis events under consideration are RWCU lin-' breaks inside the conta'inment (IhCAs) and outside the containment.

3 (HELBs). _These events are discussed separately be bw.

The first event to be considered -is a RWCU line ' break inside containment. The break itself cannot be isolated by any signal since it t

is assumed to occur before the inboard isolat' ion valve. Therefore, inventory lost during a postulated break of .- the RWCU line is not affected by the postulated failure of the .high differential flow instrumentation, and the IDCA analysis design basis ; is not - affected.

Furthermore, primary containment isolation for Group- 5 valves during a s i -

RWCU line break would eventually be achieved via reactor water level low

low signal (Level 2) . Thus, failure of-the time delay relays in the r

l

' high differential flow instrumentation has' no impact on a-RWCU line

! break inside the containment. ,

4 l

Appendix N of the Unit 1 FSAR and 15A'of the Unit 2 FSAR contain ,

f I

l the HELB evaluation for breaks outside the containment. The - RWCU 'line break in the HELB evaluation is a single ended break of a 6 ' inch 4

l diameter high energy line with concurrent loss of offsite power. The ,

diesel generators (D/Cs) start immediately on loss of offsite power and :I are up to speed at approximately 13 seconds. The break is assumed to be isolated at 43 seconds. This is based on a 30 second valve stroke time plus the 13 seconds for D/G start time (necessary to power the inboard isolation valve). Thus the RWCU HELB analysis assumes that an isolation 4

1

._ -_ _ _ _ _ _ ___ _ _ ~ ._ ,_.

c . , ,

EAs-24-0489 signal will be received within the first 13 seconds of the. event. The g ~

blowdown data and isolation valve closing time fo,r this event are shown- "

in Table N.5 1 of the FSAR. The temperature profiles for the~RWCU heat exchanger room and RWCU pump room (Reference 1)~during this event ~

indicate that the ambient temperature in both rooms exceed the high area

(

temperature setpoint of 150'F within' the first 2 seco'nds of. the event.

Therefore, the RWCU "RLB is independent of the high differential flow >

isolaticn.

(

For smaller HELBs (but with leakage > 80 gpm), it is likely that the high differential flow signal would initiate isolation earlier than the area temperature signal. Reference 2 shows. temperature profiles for Unit 2 (also applicable to Unit' 1) in the RWCU equipment rooms for 25 gpm leaks occurring in the winter . time. - Since an 80 gpm break would produce a faster temperature rise ant.' thus an earlier, isolation, these-profiles can be conservatively applied to- an 80 gpm break to estimate ,

the mass and energy release associated with a break isolated on high area' temperature. At the time the 25 gpm profiles show the area temperature exceeding the trip setpoint, the mass *and energy ' release from an 80 gpm break would still be nell below that. postulated in the  ;

limiting RWCU break event. Break sizes in between the limiting. RWCU line break and an 80 gpm leak will also result in less mass and' energy release than the design basis event. Therefore,- even if the : time delay relays for the high differential . flow instrumentation fail, the single ended break of the 6 inch diameter pipe is still the limiting RWCU HELB.-

l' It is important to note that in addition to not taking credit for the time delay relays, this evaluation assumes an arbitrary single failure.

The limiting single failure is a failure which would affect the outboard isolation valve (DC powered). Thus, break isolation is dependent on the C operation of the high area temperature instrumentation' for the inboard l isolation valve in the room in which the break occurs. Therefore, that l particular trip channel must be operable. Based on the above, common mode failure of the time delay relays in the high differential flow i instrumentation has no impact on the RWCU HELB analysis presented in the FSAR.

1

~4-a.

= g - - . - - - - . . . , - , . . . - - , . . - - (, _.

,. m .

(- -,

.i

, EAs.24-0409 +

1 In addition to the safety concerns discussed above, an electrical It '

l' failure analysis should be performed to confirm tpat failure of- the time '

delay ::elays cannot result in. any damage to other essential components in the leak detection system. It should also be noted that the possible failure of the time delay- relays for the high differential flow I'

instrumentation increases the dependency on other isolation signals, particularly the area temperature instrumentation, n

3. CONCLUSION t  ;

I Based on the discussion above, failure . of the time delay relays C31 R616 C and D in the RWCU high differential flow instrumentation has no impact on the design basis IDCA and HELB events for Plant Hatch Units 1 & 2. It dbes however increase the dependency on other leak detection  !

instrumentation.

4. REFERENCES -

1. "High Energy Line Break Evaluation for Edwin I. Hatch Nuclear Power Station", General Electric Company,'NEDO 24873. Revision"1, October..

1980.

2. Letter from R. A. Glasby (Bechtel)' to D. W. Diefenderfer -(CE),

" Analog Transmitter Trip System", dated September 28,_1982. j t

I-(

5