ML20072H162

Rev 1 to Improved Dynamic Vacuum Breaker Valve Response for Peach Bottom

ML20072H162
Person / Time
Site:	Peach Bottom
Issue date:	09/30/1982
From:	CONTINUUM DYNAMICS, INC.
To:
Shared Package
ML20072H155	List: ML20072H151 ML20072H162
References
82-10, 82-10-R01, 82-10-R1, NUDOCS 8303290305
Download: ML20072H162 (21)

Text

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,- - C.D.~I. TECH NOTE NO. 82-10

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IMPROVED DYNAMIC VACUUM BREAKER VALVE RESPONSE FOR PEACH BOTTOM Revision 1 Prepared by CONTINUUM DYNAMICS, INC.

for GENERAL ELECTRIC COMPANY September 1982 l

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l 8303290305 830325 PDR ADOCK 05000277 P PDR

. C.D.I. TECH NOTE NO. 82-10 l

IMPROVED DYNAMIC VACulN BREAKER VALVE RESPONSE FOR PEACH BOTTOM .

REVISION 1 PREPARED FOR GENERAL ELECTRIC COMPANY ,

175 CURTNER AVENUE

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SAN JOSE, CALIFORNIA 95125 UNDER PURCHASE ORDER NO. 205-XJ102 BY _

CONTINUUM DYNAMICS, INC.

P.O. B0X 3073 PRINCETON, NEW JERSEY 08540 APPROVED BY b^_xb Lx_

ALAN J. BILANIN PRINCIPAL INVESTIGATOR SEPTEMBER, 1982

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

l kind which may result from the use of any of the information contained in this document.

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SUMMARY

1mproved' plant-unique expected and design vacuum breaker impact velocities have been calculated for the Peach Bottom 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 Peach Bottom are predicted to not actuate during the chugging transient.

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Revision 1 1

SLNMARY OF THE METHODOLOGY USED TO DEFINE PLANT-UNIQUE WETWELL TO DRYWELL MARK I VACULM 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 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 uses 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 motion in the steam vent system (see Figure 2), at the steam l

l water interface (see Figure 3) and in the suppression pool (see Figure 4) assuming that the condensation rate at the steam water l

interface is known. The dynamics in the vent system are assumed to be governed by one-dimensional acous tic theory and jump con-i 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 l condensation raic of the inter- -

f ace unknown.

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

U With the condensation rate 3 predict unsteady determined, pressures a t other vent locations to validate the model.

o Use the condensation source of the vent exit to drive dynamic 4 models of Mark I plants to determine unique vacuum l

breaker forcing functions.

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

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Breoker Piping

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

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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 tLme 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 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 thenmodynamic conditions, and that these local l

conditions vary slightly between plants. Using this condensation rate, the forcing function ptrameters given in Table 1 were used to compute expected and design loads across the Peach Bottom plant vacuum breakers (Ref. 1).

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TABLE _1 Forcing Function Parameters for Peach Bottom

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Value Used Parameter In Computation

• Vent / pool area ratio 0.045 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 4.0 ft water

• The modeled plant is FSTF.

< ** Group 2 value used even though Peach Bottom is 549.75 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 alleiiation as a consequence

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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 4 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 Peach Bottom are shown in Table 2.

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TABLE 2 Vacuum Breaker Characteristics for Peach Botton Vacuum breaker type 18" GPE Internal System moment of inertia (1b-in-s 2) 20.08 System moment arm (in) 10.854 Disc moment arm (in) 11.468 System weight (1b) 49.84 2

Disc area (in ) 375.83 System rest angle (rad) . 0.0 Seat angle (rad) 0.0698 Body angle (rad) 1.391 Seat coefficient estitution 0.6 Body coefficient restitution 0.6 Magnetic latch set pressure (psi) 0.5 l Revision 1 11

RESULTS The. pressure time history shown in Figure 5 was used to drive a valve dynamic model with/without flow for the GPE valve with characteristics given in Table 2. Table 3 summar-izes the valve impact data for the expected response. No -

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

1 Revision 1 12

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TABLE 3 (REVISION 1)

Vacuum Breaker Valve Response for Peach Bottom Maximum Impact Number Maximum Opening Velocity of Angle -

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

Expected Loading Function (1)

No flow effects 0.0 0 0.0 Flow effects 0.0 0 0.0 (1) Submergence head is taken as 1.73 psi.

Vacuum breaker assumed to be mounted at the main vent-header junction.

(2) Seat impacts above 1 rad /sec.

(3) The v'alve does not actuate f

I Revision 1 17 l

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l REFERENCES

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

2. " Mark 1 Vacuum Breaker Improved Valve Dynamic Model -

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

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