ML20072E982

Rev 1 to Improved Dynamic Vacuum Breaker Valve Response for Brunswick Plant

ML20072E982
Person / Time
Site:	Brunswick
Issue date:	09/30/1982
From:	CONTINUUM DYNAMICS, INC.
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ML20072E980	List: ML20072E976 ML20072E982 ML20072E995
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NUDOCS 8306270226
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C.D.I. TECH NOTE NO. 82-22 IMPROVED DYNAMIC VACulN BREAKER VALVE RESPONSE FOR THE BRUNSWICK PLANT REVISION 1

! 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 l

APPROVED BY l

( _A[/AE ALAN J. BILANIN

! cao6270226 830623 p SEPTEMBER, 1982 QM ADOM 05000W

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f DISCLAIMER OF RESPONSIBILITY .,

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Neither the General Electric Company nor any of the contributors to this document l makes any warranty or representation (express or implied) with respect to the accuracy, completeness, or usefulness of the information contained in this document or thac the use of such information may not infringe privately owned rights; nor do they assume any responsibility for liability or damage of any kind which may result from the use of any of the information contained in this document.

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4 SUtiARY 1mproved plant-unique expected and design vacuum breaker impact velocities have been calculated for the Brunswick

, plant.

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. Expected vacuum breaker actuation velocities are reduced by 17% over a prediction which does not take credit .

for hydrodynamic torque reduction.

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SUMMARY

OF THE METHODOLOGY USED TO DEFINE PLANT-UNIQUE WETWELL TO DRYWELL MARK I VACUUM BREAKER FORCING FUNCTIONS FROM FSTF DATA l

During the Mark I FSTF test series, wetwell to drywell vacuum breaker actuation was observed during the chugging phase of steam 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 usen FSTF pressure time 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 l 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 developed which accounts for compression of the wetwell airspace 2

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l STEP

Develop a dynamic model of the vent system,l steam water inter-I face and poo slosh with the condensation rate at the inter-f ace unknown.

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

v With tha condensation rote 3 determined, predict unsteady pressures a t other vent locations to validate the model.

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

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

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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 tune 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 plant-unique vacuum breaker forcing functions, the key assumption is made that the condensation rate is a facility independent quantity. This assumption is supported l

by the observation that the condensation rate is fixed by local conditions at the vent exit; i.e., steam mass flow rate, non-l i

condensibles and thermodynamic conditions, and that these local conditions vary slightly between plants. Using this condensation l

l rate, the forcing function parameters given in Table 1 were used f to compute expected and design loads across the Brunswick plant vacuum breakers (Ref. 1).

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TABLE 1 Forcing Function Parameters for Brunswick Value Used -

Parameter In Computation

• Vent / pool area ratio 0.045 l

Drywell volume / main vent area ratio , 532.87 ft**

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 3.0 ft wate 4

• The modeled plant is FSTF

• • Group 2 value used even though Brunswick is 591.03 ft.

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SUMMARY

OF THE METHODOLOGY OF THE MARK I/ 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-tive 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 flow.

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 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-position of these influences. In all cases flow tends to reduce the pressure load felt by the disc.

The 18" GPE valve characteristics for Brunswick are shown in Table 2.

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TABLE 2 Vacuum Breaker Characteristics for Bruns' rick Vacuum breaker type 18" GPE Internal 2

System moment of inertia (1b-in-s ) 24.0 System moment am (in) 11.172 Disc moment arm (in) 11.47 System wei.ght (lb) 49.8 9

Disc area (in") 375.85 System rest angle (rad) 0.0698 Seat angle (rad) 0.0698 Body angle (rad) 1.256 Seat coefficient restitution 0.6 Body coefficient restitution 0.6 Magnetic latch set pressure (psi) 0.25 1

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RESULTS The pressure tLme history shown in Figure 5 was used to

, drive a valve dynzmic model with/without flow for the GPE valve with characteristics given in Table 2. The response of the valve for displacement and angular velocity are-given.in Figures 6 and 7. All results shown are for the expected pres-sure loading function with flow. Table 3 summarizes the valve ,

l impact data for both expected and design loading response.

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REFERENCES

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.

3. General Electric Company letter MI-G-43, July 9, 1982 -

Mark I Containment Program - Task 9.5.1, Architect Engineer Question Reply No. 315.

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