ML19305B285

Forwards Summaries of PWR & BWR Pressurizer Relief Sys. Drawings & Tables Also Encl

ML19305B285
Person / Time
Issue date:	08/17/1979
From:	Stampelos J Advisory Committee on Reactor Safeguards
To:	Advisory Committee on Reactor Safeguards
References
ACRS-SM-0159, ACRS-SM-159, NUDOCS 8003190455
Download: ML19305B285 (17)

Text

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NUCLEAR REGULATORY COMMISSION o

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WASHINGTON, D. C. 20665 g

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August 17, 1979 ACRS Members ACRS Staff

SUMMARY

OF REACTOR COOLANT RELIEF SYSTEMS IN OPERATING U.S. LWRs Based on previous operating history, the probability of a small break LOCA due to activation of a power-operated relief valve (with its block valve open) is 0.1 per reactor year for B&W PWRs (NUREG-0560).

Sixty inadvertent blowdowns have occurred in BWRs..The BWR main steam pressure relief systems do not have block valves. This report contains a general description and operating history of these systems.

John G. Stampelos ACRS Fellow Attachments:

1.

Summary of PWR Pressurizer Relief Systems 2.

Sumary of BWR Main Steam Relief Systems cc: ACRS Fellows 9

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4 e

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SLM%RY OF PWR PRESSURIZER RELIEF SYSTEMS The pressurizer pressure relief system (Figure 1) consists of from two to three spring-loaded backpressure compensated safety valves (Figure 2) and up to three (generally one or two) power-operated relief valves (Figure 3).

The safety valves are required for overpressure protection by the ASME Boiler and Pressure Vessel Code.. The power-operated relief valve does not contribute to the required relieving capacity cf the reactor system but enhances plant availability. The power-operated relief valves limit the lifting frequency of the safety valves and are used to provide overpressure protection during operation at low temperatures. The setpoint of the safety valve is nominally 2500 psig. The setpoint of the power-operated relief valve is nominally 2450 psig.

The safety valves (Figure 2) operate against the force of spring pressure.

A water loop seal is provided to minimize valve leakage.. The power-operated relief valve (Figure 3) is a pilot-operated valve. This valve can be operated either manually or automatically by a mode selectic, switch located in the control room.. Reactor coolant system pressure from chamber I (in Figure 3) leaks pass the valve disc guide into chambers II, III, and IV.

The valve disc (#2) is held shut by this pressure and the force of the valve spring.(#4). When actuated, the solenoid lifts the pilot valve disk

(#13) which vents the reactor coolant system pressure in chamber II through chamber IV and into the. atmosphere. The main valve disc (#2) moves down and opens. A block valve is provided upstream of the power-operated. relief valves in case of failure. Leakage of the power-operated relief valves may be indicated by temperature detection on the valves exhaust pipe, valve position indication detectors, and quench tank level and pressure. The position indicator only indicates whether the solenoid is energized. The safety valves do not have block valves.

The operating history of the spring-loaded safety valves has been unremark-able. The history of the power-operated relief valves is surrnarized in NUREG-0560 for B&W plants (Table 1). A review (NUREG-0560) of the LERs dealing with feedwater types of transients bas. indicated that three events have occurred in B&W plants in which these valves have stuck.open.. There has been about 150 occasions in which pressurizer relief xalves have actuated in B&W plants yielding a failure rate of 2 x 10-' per event and a probability of a small break LOCA of about 0.1 per reactor-year if the block valve is not closed. The control circuits for relief valves are currently not single failure proof. A single failure in the control circuits can result in a small break LOCA.

The setpoint pressure of power-operated relief valves has been changed from 2255 psig to 2450.psig because of TMI-2. This should reduce the actuation rate of these valves. The setpoint for the other vendors was.around 2450 psig before the TMI-2 experience. The reactor trip setpoint varies from 2300 psig to 2385 psig depending on the vendor.

. Attachments:

As sta,ted

1 AUTO r__________7_,

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POWER OPERATED 2, 84 3) j RELIEF VALVE TE CODEN3)

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@ VALVES

[DISCHARGETO REACTOR SAFETY r

COOLANT DRAIN TANK (QUENCH TANK)

DISCHARGETO REACTOR COOLANT DRAIN TANK

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(QUENCH TANK)

MOTOR-OPERATED BLOCK VALVE LccP SEAL PRESSURIZER LEGEND:

@- PANEL MOUNTED IN CONTROL ROOM PSV - PRESSURE RELIEF VALVE FHS - FLOW HAND ACTUATED SWITCH PS - PRESSURE SWITCH TE - TEMPERATURE ELEMENT TS - TEMPERATURE SWITCH ADA PrED FROM NUREG-0S60 f/60KE I:

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MATERIALS 2C tracket Stud Not ASMt $A194 Cr. 4 la tower Base ASME SA182 8316. Stainless Steet 21 Lever ASTM A216 WCB CarDon Steel, ginc PlateO I tese AssembPy is too riange A5Mt sA1:2 m6. siamies stee 22 te.er Pin Careen sieet (Caemium Piatesi IC Case ASTM A351 CA15 CFSM 23 Adlusting Screw A151 416. Staintess Steet, ginc PlateO 10 Tube f asert ASME SA162 r316. Stainless Steet 24 tocsnut Carton Steet. (Zanc PlateO 2 Disc ASTM A565 Cr. 416. stainless sieet. Condit en T 25 tracset Cover Alst 302. 5tamiess s'eet 3 Ptsten iting Alli 420. Mareenes Stamiess Steel 26 Solenoid Plate Alsa C1019, gas PlateO 1

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2 2

2 2

2 Spring-loaded

. Type Sprin0-loaded Spring-loaded Spring-loaded Spring-loaded Suring-lee 64 same 2 s-31739A 2%-31739A i

Model no.

3-31759A 2 - 31739A

3XHIX6, 2 -31739A Type H886 Size 3" x 6" 2%" x 6" 4" x 6" 2%" x 6" 2 " x 6" 2%" x 6" Relief cap.

311,733 f/hr 311,733 dhr 311,973 f/hr 317,973 f/hr 280,000 f/hr f

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2500 psig 2500 psig 2500 psig 2500 psig 2500 psig

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2375 2375 2450 2475 j

(approx.)

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(significant)

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1 1

1 1

1 1

Model no.

31533vX-30 Same Electromatic Electromatic flectroostic Electroniatic Type Electroostic Electromatic 31533vX-30 31533VX-30 HPV-ST 31533 VM-30 Slie 25" x 4" 2%" x 4*

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pre Malf. date 9/1/74 None 9/24/77 None None June 1975 June 1978 None 3/29/78 Ressat press.

(significant)

Boric acid Valve leakage Oe-energfred -

cause Improper Steam pilot vital bus crystal bulldup, venting valve system bent lever on pilot valve Fall position Closed Closed (IE)

Closed (non-Closed (non-Closed Position Ind.

Yes (Pliot-Yes (open-Yes (on pilot-Yes (open-No Pilot-red (Class IE) 1E)

IE) -

(non-1E) red / green) closed) red / green closed) green Ilghts)

Thermocouple ind..Yes (computer) Yes (computer) Yes (computer) Yes (computer)

Yes (computer) Yes and alarn Thersecouple type, strap-on

' kell /sSD ft Strap-on/

5 trap-on/6 Strap-on/40 ft c.nd location froe valve

+1 f t 7 ft downstreas from valve Block Valve Mfg.

Velen Dresser Yslan Westinghouse same same Velan Motor-operated Motor-operated Same Type Motor-operated Motor-operated Motor-operated Motor-operated fall position As-is (non-1E) As-is (TE)

As-Is (non-1E) As-is (non-lE)

As-is (non-1E) -

Pos. Indication Yes Yes Yes Yes Yes Yes SovRc2 : NdREG 0560 eul2ETW 77-OS6 D

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FOIA Exemption (b)5 SLM4ARY OF BWR MAIN STEAM RELIEF SYSTEMS The main steam pressure relief system (Table 1) for U.S. BWRs include a total combination of from 6 to 22 safety / relief valves (SRVs), spring-loaded safety valves (SVs), and/or power actuated relief valves (PARVs).

Valve Setpoints 1.

spring-loaded safety valves (SVs) 1225 psig 2.

power actuated relief valves (PARVs) 1130 psig 3.

safety / relief valves (SRVs) 1025-1155 psig*

• depends on the plant and the total number of valves employed in the system A specific number of PARVs or SRVs, in addition to providing overpressure protection, are utilized in the automatic depressurization system (ADS).

The ADS is part of the Emergency Core Cooling System. Generally, the ADS.is actuated on the simultaneous receipt of a high drywell pressure, reactor vessel low water level, and indication of output pressure from one low pressure core j

injection or core spray pump signal.

Most SVs discharge directly to the containment drywell whereas the PARVs and the SRVs discharge to.the suppression pool. The pressure relief system valves do not have blocking valves. The safety valves (Table 1) are required to provide overpressure protection by the ASME Boiler & Pressure Vessel Code.

The relief system valves have leakage indication and alarms via temperature monitoring devices located near the valve exhaust tail pipes. The older design SRVs have a bellows leakage alarm for their pilot stage.

A typical spring-loaded SV (Figure 1) actuates when reactor coolant pressure exceeds the spring pressure. A typical PARV is shown in Figure 2.

Main steam in chamber A passes upward around the disk. guide into chamber B.

In addition, main steam normally pressurizes chamber C via.a clearance space between the main valve disc and disc guide. The main valve spring and the steam pressure PARV. actuation is acco711shed by

. in chamber C hold the main valve disc. shut.

energizing.the solenoid in the pilot valve which vents the steam in chamber C The subsequent. differential pressure (between chamber C to the atmosphere.

and chamber B) forces the main valve disc to drop down and open the valve.

Most BWR plants employ the older 3-stage The SRVs are typically of two designs.

SRV design (Figure 3).. The main valve disk is held in the closed position by the force of the main valve preload spring and main steam pressure acting on the main valve piston.(the chamber behind the main valve piston is pressurized through the main valve. piston orifice). The main valve disc opens when the second stage piston moves down allowing main steam pressure to bleed from The.second stage piston moves down when main behind the main valve piston.

steam pressure is sufficient to move the pilot stage, piston disc to the right This and pressurize the chamber imediately above the second stage piston.

3-stage SRV has had a.significant number of inadvertent blowdown events (Table 2 and Table 51.

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The major cause of spurious openings or failures of the 3-stage SRV to reseat has bee.' excessive pilot valve leakage. The principal strategy to assure that pilot leakage is minimized involves increasing the simmer margin, per-forming more frequent valve maintenance, and replacement with the new 2-stage SRV design.

(The simmer margin is the differential pressure between normal system operating pressure and the valve setpoint.) The new 2-stage design (Figure 4) has an improved pilot section design and no second stage piston.

As of April 12, 1979, twenty 3-stage valves have been replaced with the new 2-stage design and ten more are committed to be replaced. Hatch Unit 1, Fitzpatrick, and two of the reactors at Browns Ferry have replaced.some of their 3-stage valves with the new design. There have been no inadvertent blowdowns to date with the new 2-stage design..In addition to the mechanical failures associated with the 3-stage valves, several failures of the pneumatic diaphragm operator have occurred. Excessive heating caused by extended service life and improper thermal insulation were the cause. Yearly diaphragm replace-ment should correct the problem.

The NRC, as part of its continuing program for monitoring safety / relief valve performance, has requested all BWR licensees to provide.an operations and maintenance history for each of their safety / relief valves manufactured by Target Rock Corp. The response of the licensees is due September 16, 1979.

Attachments:

As stated e

g___-____

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TABLE 1 VALVE COMPLEMENT POWER-ACTUATED BWR TYPE FACILITY SAFETY / RELIEF VALVES SAFETY VALVES RELIEF VALVES 16 6

2 Nine Mile Point 16 5

2 Oyster Creek 3

Dresden 2 1

8 4

3 Dresden 3 1

8 4

3 Millstone 1 6

3 Monticello 7

3 Pilgrim 1 4

2 3

Quad Cities 1 1

8 4

3 Quad Cities 2 1

8 4

4 Browns Ferry 1 11 2

4 Browns Ferry 2 11 2

4 Browns Ferry 3 11 2

4 Brunswick 1 11 4

Brunswick 2 11 4

Cooper 8

3 4

Duane Arnold 6

2 4

Fitzpatrick 11 '

4 Hatch 1 11 4

Peach Bottom 2 11 2

4 Peach Bottom 3 11 2

4 Vemont Yankee 4

2 SouRct : N OR E G.- o % E

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TABLE 2_

E Inadvertent Blowdowns Events _

1969 1970 1971 1972 1973 1974 1975 1976 1977 1978__

i 8

b 2

2 1

2 S

ns Ferry 1 2

1 k

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f ms Ferry 2 3

3

[ns Ferry 3 l

/

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F-4 nswick 1 2

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esden 2 I

esden 3 1

I 3

Iane Arnold 3

l itzpatrick 1

1 3

f j

1 1

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5 atch 1 1

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1 j

2 Y

s-tillstone 1

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7 bnticello j

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I 7

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Oyster Creek 3

1 2

1 1

3 Peach Bottom 2 2

/

8 Peach Bottom 3 1

2 1

Pilgrim 1 Quad Cities 1 2*

l 2,

y Quad Cities 2 TOTAL 0

0 2

4 2'

11 8

10 10 fc 3

j Vormont Yankee i

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TAB' E 3 Failures to Ooen Properly on Demand

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1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 ToSL I_M Browns Ferry 1

==

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Browns Ferry 2 Browns Ferry 3 Brunswick 1

.=.

Brunswick 2 1._

Cooper

=

Dresden 2 3*

2*

1*

6 f.

=:

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1*

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=

Duane Ar'nold 1

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f Fitzpatrick

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2 2

Hatch 1 2.

Millstone 1 Monticello 2

1 3

g.

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p Nine Mile Point 1*

Oyster Creek 1*

1*

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Peach Bottom 2 1

P2ach Bottom 3 2-f.

I Pilgrim 1 4

1*

1*

2 4/

Quad Cities 1 1*

2*

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1. /

Quad Cities 2 Vermont Yankee 1

1 2

3 i

TOTAL 1

3 0

2 2

4 2

4 9

• Power Actuated Relief Valve TO IU'1' lI 'I E SouRc2 : A/UREG-C'fG2 (TulY /Y'72), orparED

TABLE 4 Potential Failures to Open Proper 1v I

1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 /177 W T4 L I

Browns Ferry 1 1

Browns Ferry 2 Browns Ferry 3 Brunswick 1 Brunswick 2 1

/

2.

1 1

2.

Cooper Dresden 2 Dresden 3 Duane Arnold

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1 1

2.

1

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Fitzpatrick 1

1 8.

Hatch 1 Millstone 1 1

/

2.

Monticello Nine Mile Point 1*

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Oyster Creek Peach Bottom 2 1

2 1

Y

/

/

Pgach Bottom 3 Pilgrim 1 Quad Cities 1

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Quad Cities 2 Vermont Yankee 2

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TOTAL 0

0 0

2 2

2 3

3 4

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60 Blowdowns Failures to

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