ML20074A489

Rev 0 to Improved Dynamic Vacuum Breaker Valve Response for Vermont Yankee

ML20074A489
Person / Time
Site:	Vermont Yankee
Issue date:	05/11/1983
From:	Bilanin A CONTINUUM DYNAMICS, INC.
To:
Shared Package
ML20074A488	List: ML20074A487 ML20074A489
References
82-20, AR-830511, GL-83-08, GL-83-8, NUDOCS 8305130104
Download: ML20074A489 (20)

Text

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C.D.Io TECH NOTE NO. 82-20 j

IMPROVED DYNAMIC VACUlfi BREAKER VALVE RESPONSE FOR VERMONT YANKEE REVISION O PREPARED FOR GENERAL ELECTRIC COMPANY 175 CURTNER AVENUE SAN JOSE, CALIFORNIA 95125 UNDER PURCHASE ORDER NO. 205-XJ102 BY CONTINUUM DYNAMICS, INC.

P.O. BOX 3073 PRINCETON, NEW JERSEY 08540 i

APPROVED BY l -

, [W .bl

! ALAN J. BILANIN PRINCIPAL INVESTIGATOR i

$00'$S0c0#o !$0SN1 P r'R

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i DISCLAIMER OF RESPONSIBlWTY This document was prepared by or for the General Electric Company. Neither the General Electnc Company nor any of the contributors to this document:

A. Makes any warranty or representation, express or implied, with respect to the accuracy, completeness. Or usefulness of the information containedin this docu.

ment. Or that the use of any information disclosed in this document may not ininnge privately owned rights; or B. Assumes any responsibility for liabokty or damage of any kind which may result from the use of any information disclosed in this document.

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SLNMARY Improved plant-unique expected and design vacuum breaker impact velocities have been calculated for the Vermont Yankee plant.

i The valve displacement time history was predicted using a valve dynamic model which takes credit for the reduction of hydrodynamic torque across the vacuum breaker as a consequence of valve actuation. As a result of this study the vacuum breakers in the Vermont Yankee plant are predicted to not actuate during the chugging transient.

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SIMMARY OF TlIE METHODOLOGY USED TO DEFINE PLANT-UNIQUE WETWELL TO DRYWELL MARK I VACUUM BREAKER FORCING FUNCTIONS FROM FSTF DATA During the Mark I FSTF test series, wetwell to drywell vacuum breaker actuation was observed during the chugging phase of stern blowdowns. As a result of this observation, a metho-

'dology was developed which can be used to define the loading function acting on a vacuum breaker during chugging (Ref.1) .

The methodology developed uses FSTF pressure tbne history data and adjusts the vent system and wetwell pressures to account for plant-unique geometry. For plants with internal vacuum breakers, the most critical parameter controlling the magnitude of the vacuum breaker forcing function is the drywell volume per vent area. Vacuum breaker forcing functions are specified as a time history of the differential pressure across the valve disc.

The steps taken in the development of the plant-unique forcing function model are shown in Figure 1. Step 1 involves the development of analytic dynamic models for the unsteady motion in the steam vent system (see Figure 2), at the steam water interface (see Figure 3) and in the suppression pool (see Figure 4) assuming that the condensation rate at the steam water interface is known. The dynamics in the vent system are assumed to be governed by one-dimensional acoustic theory and jump con-ditions across the steam water interface are the Rankine-Hugoniot relations. A one-dimensional model of the suppression pool was l

developed which accounts for compression of the wetwell airspace 2

STEP Develop a dynamic model of the vent system,leteam water inter-I foce and coo slosh with the condensotlon rote of the inter-

face unknown.

o 2 Use measured drywell pressure to determine the condensation rate.

p With the condensation rate 3 determined, predict unsteady 4

pressures a t other vent locations to validate the model.

u Use the condensation source of the vent exit to drive dynamic 4 models of Mark I plants to determine unique vacuum breaker forcing functions.

i Figure 1. Steps in determining plant unique vacuum breaker forcing functions.

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10 - Drywell External Vacuum -__

Breaker Piping -__

9 - Jet Deflector Plate

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Main Vent l is Header x . . ... ..... . . ..

7 Wetwell l 6 l 5 l 4 12 Airspace -- -- --

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Downcomers Figure 2. Schematic model of the vent system depicted by 12 dynamic components.

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Steam Side

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Steam Water l

n InferYoci ~

-u c

uW I dh, Water Side dt l

Figure 3. Details of the steam water interface.

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jWetwell Airspace a f i +-A p q -- , Pool u A t

H h, n a

u, hw o

u u o u= 0 Figure 4. Details of the pool dynamic model j around each downcomer.

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with the lowering of the steam water interface in the downcomer.

Assuming a unit condensation source in frequency space, a trans-fer function is then developed between the condensation source and the pressure in the drywell. Once this transfer function has been established, the condensation time history at the steam water interface can be extracted from a measured drywell pressure time history which is step 2 in Figure 1.

The model developed permits validation (step 3 in Figure 1) provided that an additional pressure time history, at another location in the suppression system, is available. With the con-densation rate determined at the vent exit using a pressure time history from the drywell, the pressure history in the ring header was predicted and compared against measured data. The comparison was very favorable (Ref. 1).

In order to predict plar:-unique vacuum breaker forcing functions, the key assumption is made that the condensation rate is a facility independent quantity. This assumption is supported by the observation that the condensation rate is fixed by local conditions at the vent exit; i.e., steam mass flow rate, non-condensibles and thermodynamic conditions, and that these local l conditions vary slightly between plants. Using this condensation rate, the forcing function parameters given in Table 1 were used to compute expected and design loads across the Vermont Yankee plant vacuum breakers (Ref. 1).

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TABLE 1 Forcing Function Parameters for Vermont Yankee Value Used Pa'ameter r . In Computation

• Vent / pool area ratio 0.045 Drywell volume / main vent 411,96 ft area ratio Main vent area /downcomer area 0.99 Main vent length 37.32 ft Header area /downcomer area 1.47 Header length 15.0 ft Downcomer area 3.01 ft2 Downcomer length 10.8 ft Submergence head 4.29 ft water Distance along main vent from drywell to external line 6,7 ft Length of main vent side external line 26.9 ft Length of wetwell side external line 7.7 ft External line area 1,767 ft 2 4

f

• The modeled plant is FSTF.

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S W MARY OF THE METHODOLOGY OF Tile MARK 1/ MARK II VACUUM BREAKER VALVE MODEL (INCLUDING HYDRODYNAMIC EFFECTS)

During the Mark I shakedown tests, the vacuum breaker displacement time history was recorded. Use of a simple single-degree-of-freedom valve model resulted in large overly conserva-give predictions of the resulting valve dynamics. In an effort to reduce the conservatism in this test series, and additionally to relax the prediction of valve impact velocities in expected Mark II downcomer-mounted applications during chugging, a metho-dology was developed which uses the differential forcing function across the vacuum breaker (computed by the vent dynamic model) but includes the effect of torque alleviation as a consequence of valve flow (Ref. 2). With the valve in an open position, the pressure difference across the valve is not the pressure dif-ference felt by the valve disc, because of flow effects across the open valve disc. This reduction in hydrodynamic torque is estimated by the following:

1. A linear analysis of the pressure field on either side of the closed valve permits the solution for pressure and velocity in the vicinity of the valve disc without i flow.

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2. The flow effect is modeled as a mathematical source /

sink around the circumference of the open valve.

3. The local pressure and velocity fields permit evaluation I of the strength of the flow source / sink.

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4. The response of the valve to both flow and up and downstream pressure transients is computed as a super- l position of these influences. In all cases flow tends to reduce the pressure load felt by the disc.

The 18" A&M valve characteristics for Vermont Yankee are shown in Table 2.

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1 TABLE 2 Vacuum Breaker Characteristics for Vermont Yankee Vacuum breaker type '

18" A&M External System moment of inertia (1b-in-s 2) 38,46 System moment arm (in) -

3,586 Disc moment arm (in) 11.375

! System weight (ib) 106.1 2

Disc area (in ) 283.5 System rest angle (rad) 0.4124 Seat angle (rad) 0.33 Body angle (rad) 1,32 J

Seat coefficient restitution 0.8 -

Body coefficient rcstitution 0.6 11

RESULTS The pressure time history shown in Figure 5 was used to drive a valve dynamic model with/without flow effects for the A&M valve with characteristics given in Table 2. Table 3

,su==arizes the vaive impact data for the expected response.

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valve actuation is predicted for this valve during the chugging transient.

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TIME (SECJ Figure 5.a. Pressure time history predicted across a vacuum breaker located on the l external line in Vermont Yankee. Submergence head has not been added.

0 - 10 seconds.

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a n; J r h I W m jf 4 b 0 '. rII' o

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10 12 14 16 18 20 TIME (SEC) .

Figure 5.b. Pressure time history predicted across a vacuum breaker located on the external line in Vermont Yankee. Submergence head has not been added.

10 - 20 seconds.

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20 22 24 26 28 30 TIME (SEC)

Figure 5.c. Pressure time history predicted across a vacuum breaker located on the external line in Vermont Yankee. Submergence head has not been added.

20 - 30 seconds.

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Figure 5.d. Pressure time history predicted across a vacumn breaker located on the external line in Vermont Yankee. Submergence head has not been added.

30 - 40 seconds.

TABLE 3 Vacuum Breaker Valve Response for Vermont Yankee Maximum Impact Number Maximum Opening Velocity .

of Angle (rad /sec) Impacts (2) (rad)(3)

Expected Loading Function (l)

No flow effects 0.0 0 0.0 Flow effects 0.0 0 0.0 3

(1) Submergence head is taken as 1.859 psi.

Vacuum breaker assumed to be mounted on an external line with characteristics given in Table 1.

(2) Seat impacts above 1 rad /sec. .

l (3) The valve does not actuate.

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REFERENCES

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1. " Mark I Vacuum Breaker Dynamic Load Specification, Revision 3," C.D.I. Report No. 80-4, February,1980.

2. " Mark I Vacuum Breaker Improved Valve Dynamic Model -

Model Development and Validation," C.D.I. Tech Note No. 82-31, August 1982.

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