ML20117M127

Rev 0 to Mark I Wetwell to Drywell Differential Pressure Load & Vacuum Breaker Response for Peach Bottom Atomic Power Station Units 2 & 3

ML20117M127
Person / Time
Site:	Peach Bottom
Issue date:	01/31/1985
From:	Bilanin A CONTINUUM DYNAMICS, INC.
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ML20117L850	List: ML20117L847 ML20117M127
References
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.

2850009500 C.D.I. TECH NOTE NO. 84-14 W

MARK I WETWELL TO DRYWELL DIFFERENTIAL PRESSURE LOAD AND VACUUM BREAKER RESPONSE FOR THE PEACH BOTTOM ATOMIC POWER STATION UNITS 2 & 3 Revision 0 Prepared by CONTINUUM DYNAMICS, INC.

P.O. BOX 3073 PRINCETON, NEW JERSEY 08540 Prepared under Purchase Order No. 306820 for PHILADELPHIA ELECTRIC COMPANY 2301 MARKET STREET

P.O. BOX 8699 PHILADELPHIA, PA. 19101 Approved,by I

L A44 V ( -

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8505160515 850514 " Al*"/*811*"I".

PDR ADOCK 05000277 January 1985 P PDR I

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2850009500

SUMMARY

Mark I wetwell to drywell vacuum breaker (VB) ac'tuation velocities during the chugging phase of a postulated loss of coolant accident (LOCA) are predicted. Data collected during the full scale test facility (FSTF) test series is used to conservatively predict the differential pressure load across the VB. Adjustment is made for plant-unique drywell volumes with a vent dynamic model validated against FSTF test data. The predicted differential pressure load is used to drive a valve dynamic model with the plant-specific VB valve characteristice. The valve dynamic model, validated against full scale test data, conservatively predicts actuation velocities. These velocities are predicted on a plant-unique basis, and presented in this report.

Application of the above methodology to the Peach Bottom Atomic Power Station Units 2 and 3 results in a negative differential pressure peak of 0.65 psid, applied across installed 18-inch GPE internal vacuum breakers, and a predicted maximum closing impact velocity of 0.70 rad /sec.

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TABLE OF CONTENTS Section Page Summary i 1- Introduction 1-1 2 ~ Forcing Function Methodology 2-1 3 Vacuum Breaker Methodology 3-1 4

4 References 4-1 af 6

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2850009500

1. INTRODUCTION The Mark I long term containment program included the construction of a -

. full scale test facility (FSTF) modeling a 1/16th sector of a Mark I torus and -

ring header, with eight downcomers.- A series of tests simulating a loss of coolant accident (LOCA) demonstrated a chugging phenomenon occurring at the ends of the downcomers. Continuum Dynaries, Inc. (C.D.I.) was requested to examine the FSTF geometry and develop a vent acoustic rodel for predicting'the differential pressure across wetwell to drywell vacuum breakers during the chugging phenomenon. Concurrently, C.D.I. developed a valve dynamic model

+ that includes the hydrodynamic effects of pressure alleviation across the valve disc when the valve is partially open. These two efforts are summarized in Sections 2 and 3, respectively, of this report.

These methodologies have recently been reviewed and accepted by the

-Nuclear Regulatory Commission (Ref. 1). This report documents the application of these methodologies to the Peach Bottom Atomic Power Station Units 2 and 3 (hereafter referred to as Peach Bottom).

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2850009500

2. FORCING FUNCTION HETHODOLOGY This section of the report summarizes the methodology used to define -

plant-unique wetwell to drywell Mark I vacuum breaker differential pressure forcing functions from FSTF data. Additional details of the analysis may be found in Ref s. 2 and 3.

During the Mark 1 FSTF test series, wetwell to drywell vacuum breaker actuation was observed during the chugging phase of a postulated LOCA. This observation lead to the development of a methodology defining the plant-unique pressure loading function acting across a vacuum breaker during the chugging

! phenomenon. The methodology idealized the FSTF as an interconnection of simple acoustic elements and modeled the chugging phenomenon as a condensation process occurring at the. exit of each downcomer across the steam water interface. The FSTF drywell airspace pressure time history data was used with i a vent dynamic model to compute the consistent condensation source velocity time history during chugging. The FSTF ring header pressure time history data

< was then used to validate the methodology.

For plant-unique applications the most important parameter controlling the 2 magnitude of the vent pressure oscillations (and hence the VB forcing

- function) was determined to be the ratio of the drywell volume to main vent area. These forcing functions are specified as time histories of the

• differential pressure across the valve disc, using the time segment of actual FSTF data that generated the most conservative condensation source strength.

.o The steps taken in the development of the plant-unique forcing function

{

model are shown in Figure 2-1. Step 1 involves the development of analytical 1

models for: the unstear!f motion in the steam vent system (characterized as shown in Figure 2-2); the dynamics of condensation across the steam water interface (schematically shown in Figure 2-3); and the dynamics of the suppression pool and the wetwell airspace (idealized as shown in Figure 2-4). In the analysis the condensation source is a velocity time history representing the transport of steam into water at the steam water interface.

2-1

2850009500 STEP -

1 UEVELOP A DYNAMIC MODEL OF THE VENT SYSTEM, STEAM WATER INTER-

', FACE AND POOL SLOSH' WITH THE CONDENSATION RATE AT THE INTER-FACE UNKNOWN.

2 USE MEASURED DRYWELL PRESSURE TO DETERMINE THE CONDENSATION RATE.

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• 3 WITH THE CONDENSATION RATE DETER MINED, PREDICT UNSTEADY PRESSURES AT OTHER VENT LOCATIONS TO VAll-DATE THE MODEL.

4 USE THE CONDENSATION SOURCE AT THE VENT EXIT TO DRIVE DYNAMIC MODELS OF MARK l PLANTS TO DETERMINE PLANT-UNIQUE VACUUM BREAKER

. FORCING FUNCTIONS.

Figure 2-1. Steps in determining plant-unique vacuum breaker forcing functions.

2-2 I

2850009500

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2850009500 i

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-u oW dh, Water Side di Figure 2-3. Details of the steam water interface. '

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2850009500 For the purposes of step 1, this velocity time history is assumed to be unknown. The steam dynamics in the vent system are governed by one-dimensional , acoustic theory (in the configuration used here, element 3 in s ,

Figure 2-2 is nulled). Jump conditions across the steam water interface are the Rankine-Hugoniot relationships. A one-dimensional model of the

. suppression pool (assigning an equal share of the wetwell airspace volume and I

pool area to each downcomer) was developed to account for the compression of the airhace with the lowering of the steam water interface in the downcomers.

For plants with external lines connecting the vacuum breakers to the main vent and the wetwell airspace (elements 11 and 12 in Figure 2-2), additional i

analysis and bounding linearized loss coefficients obtained from subscale

/ acoustic tests (Ref. 4) are included in the vent model to conservatively predict the differential pressure across the VB disc. Internal vacuum breakers are attached at the main vent intersection with the ring header, element 7 of Figure 2-2. The same condensation source velocity time history is assumed to act at the end of each downcomer.

$ top 2 involves determining the condensation source velocity time history by using the FSTF measured drywell pressure time history data during the period of most severe chugging.

step 3 involves validation of the model in the FSTF by using the ,

condensation source velocity time history determined in step 2 to predict the pressure elsewhere in the FSTF. A prediction of the ring header pressure time

, history was made and compared with experimental data. To bound the negative pressure peaks , a load factor of 1.06 was used to multiply the predicted results to match the largest pressure data' spike. To identify the origin of the nonconservatism in the vent dynamic model, the input parameters to the model were varied by wide margins without altering the results (Ref. 5). The origin of the nonconserva tism appears to result from the assumption of applying an averaged condensation source of each downcomer exit. This assumption was required because sufficient independent data ' sets do not exist to determine the condensation source at the exit of each downcomer independently.

2-6 ,

2850009500 Step 4 applies the modified condensation source velocity time history to the plant-unique vent dynaalc model. The key assumption is made that the cordensation source at the end of a downconer is plant independent. The amount of steam condensed per chug per, downconer is assumed to be the same

/

between the FSTF and Mark I plants.

This assumption is supported by the observation that the condensation rate is fixed by local conditions at the I

vent exit, such as steam mass flow rate, noncondensibles, and thermodynamic conditions. These local conditions will vary only slightly between plants.

i The only plant characteristics which are changed ir. s plant-unique calculation are the ratio of drywell volume to sair. vent area and the pool submergence. All lengths, areas and system flow and pool parameters are retained at their FSTF values in a plant-unique calculation. Thus, gross

( depressurization, controlled by drywell volume, is corrected on a plant-unique basis, while high frequency ring out at the vent natural frequency is not plant-unique and is essentially 'taken to be that of the FSTF. The plant drywell may be treated as a capacitance or as an acoustic volume composed of two right circular cylinders standing and to end. The acoustic volume model results in a more conservative forcing function for Peach Bottom.

The plant characteristic parame ters given in Table 2-1 were used to compute the differential pressure time history across the vacuum breakers in Peach Bottoa. Figure 2-5 shows the resulting differential pressure time histcry, without addition 'of the pressure resulting from the submergence head.

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. . . 2850009500 TABLE 2-1 3 ,

Plant Characteristic Parametera '

for Peach Bottos Atomic Power Station U. nits 2 & 3 FSTF Parameter d

{ Hain vert area /downcomer area ratio 0.99 4

Main vent length 37.32 ft Header area /downcomer area ratio 1.47

( Header length 15.0 ft Downconer area 3.01 ft 2 Downcomer length . 10.8 ft

)

Vent / pool area ratio 0.045 Plant-Specifie Parameter Drywell volume / main vent area ratio 548.23 it

. submergence head 4.0 ft water tower drywell volume length 50.21 ft Lower drywell volume area 2522.2 ft2

, Upper drywell volume length 51.90 ft Upper drywell volume area 580.5 ft2

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2850099590

3. VACUUM BREAKER HETHODOLOGY

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j This section of the report summarizes the methodology used to construct

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the Mark I vacuum breaker valve dynamic model including hydrodynamic effects. Additional details of the analysis may be found in Ref. 6.

During the Mark I shakedown tests, the vacuum breaker displacement time history was recorded. A methodolohy was developed that uses the differential 9

j pressure forcing function across the VB (computed by the vent dynamic model) j and includes the effect of torque alleviation as a consequence of fluid flow o

through the opened valve. With the valve in an open position, the differential pressure acting across the valve disc is less than the applied pressure, because of flow across the face and around the edges of the open disc. The purpose of the analysis is to take credit for the reduction of static pressure across the valve disc as a consequence of flow.

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Hydrodynamic torque reduction is estimated using the following procedure:

4 1 1) A linear analysis for the flow fielti on either side of an arbitrarily

,'. moving disc pamits the solution for the local pressure and velocity L .

r 4 in the vicinity of the valve disc.

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2) The flow is modeled as a mathemat.ical combination of sources and

. sinks around the circumference of the open disc, with the local pressure obtained in step 1 used to evaluate the strength of the ij sources and sinks. **

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, 3) The complete response of the valve to this resulting flow and to the I d

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applied differential pressure obtained from the vent dynamic model is then calculated. In all cases, the inclusion of the hydrodynamic torque tends to reduce the actual dif ferential pressure and hence load acting on the valve disc.

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2850009500 Comparison, of the valve dynamic model with Mark 1 FSTF test data from blowdown SDA allows validation of the valve dynamic model (Ref

. 6) since both valve disc di,splacement and differential pressure across the valve disc measured.

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The characteristics of the VB valve in Peach Bottom are given in Table 3-1.

An application of the valve dynamic model with these characteristics and the differential pressure forcing function determined in Section 2 r esults in the computed valve response shown in Figure 3-1 for valve disc angle and Figure 3-2 for valve disc velocity.

3-2. A summary of results appears in Table

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2850009500 l TABLE 3-1 l

"1 .

,' 1 Vacuum Breaker Valve Characteristics for Peach Bottom Atomic Power Station Units 2 & 3 l

Vacuum breaker type 18" GPE internal

! System moment of inertia 20.08 in-lb-sec2

' i System weight 49.84 lb

.{ System moment arm 10.85 in

, Disc moment arm 11.47 in k- Disc area 375.83 in2 System rest angle 0.0 rad Seat angle 0.07 rad Body angle 1.39 rad Seat coefficient of restitution 0.6

(, Body coefficient of restitution 0.6

, Magnetic latch set pressure 0.5 psid 9

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i. Valve angle response to the. differential pressure time history shown in j Figure 2-5 for the vacuum breaker in Peach Bottom. a) 15 - 20 seconds (no response below'15 seconds).

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Figure 3-2. Valve velocity response to the differential pressure time history shown in Figure 2-5 for the vacuum breaker in Peach Bottom. a) 15 - 20 seconds.

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l 2850009500 l TABLE 3-2 ii Vacuum Breaker Valve Response for Peach Bottom Atomic Power Station Units 2 & 3

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F Haximum closing impact velocity 0.70 rad /sec f

Maximum opening angle 0.0027 rad l'

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4. REFERENCES l

1. Safety Evaluation by the Office of Nuclear Reactor Regulation on the Acceptability of the Analytical Model for Predicting Valve Dynamics,

< i issued by F. Eltavila, NRC, December 24, 1984.

2. " Mark I Containment Program; Mark I Wetwell to Drywell Vacuum Breaker Functional Requirements," General Electric Company Report No. NEDE 24802,

• i April 1980.

1

3. " Mark I Wetwell to Drywell Vacuum Breaker Load Methodology, Revision 0,"

Continuum Dynamics, Inc. Report No. 84-3, February 1984.

i

! 4. " Mark I Experimental Determination of External Line Losses for Definition

{ of External Vacuum Breaker Loads, Revision 2," Continuum Dynamics, Inc.

i Report No. C1-2, September 1984.

7 5. " Responses to NRC Request for Additional Information on Mark I Containment Program Wetwell to Drywell Vacuum Breaker Load Methodology, Revision 0,"

Continuum Dynamics, Inc. Technical Note No. 84-11, October 1984.

6. " Mark I Vacuum Breaker Improved Valve Dynamic Model, Revision 0,"

Continuum Dynamics, Inc. Technical Note No. 82-31, August 1982.

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