ML20141N087

Forwards Request for Addl Info Re Mod of Vacuum Breakers on Mark I Containments (Generic Ltr 83-08),per Util 830429 Evaluation of wetwell-to-drywell Vacuum Breakers.Response within 45 Days of Ltr Receipt Requested

ML20141N087
Person / Time
Site:	Cooper
Issue date:	02/14/1986
From:	Long W Office of Nuclear Reactor Regulation
To:	Pilant J NEBRASKA PUBLIC POWER DISTRICT
References
GL-83-08, GL-83-8, NUDOCS 8603030545
Download: ML20141N087 (3)

Text

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Doctet No.: 50-238 RB 1 $ 'SS6 ,

Mr. J. H. Pilant Technicel Staff Marager >

Nuclear Power Group i Nebrasta Public Fower Uf strict 1 P. O. Box 499 Columbus, Nebraska 68(41 '

SUBJECT:

5GIFIr.ATION OF VACWM BRERERS ON MARK I CCHTAINMENTS (CEhERIC LETTER 83-08)

Re; Cooper vclear 3tatfor, f By letter dated April 29, 75'83 you provided an evaluation of the ilof;per '

floclear Station Netwell-to-Urywelt Vacuum Breakers. A'e are continuing the review and find that we need the information re0sted in the escitsurc  ;

to this letter in order to coinple.?,e our review regarding .the var.uum bwaken. t Please respond to this request within 45 days from receic a , of this letter. =

This request for infonnation was approved by the Cffice of Management and Budget under clearance W. 3150-0011. C m nts en buraan and duplicetion -

uay be directed to the Office of Maasknent and @dget. Reports Manager;>nt. _ .

Room 3208, !!ew Executive Office Buriding, Washincon,' O.C. 2050h

• Cincerely  ;

S$gtnaleign,3,g William O. Long, Project Manager DVR Project Directorate #2 Divk kn of 3% Licar.cin,o '

Enclosure:

DIS _TPED JTIO1(:- '

As stated T DBEW F 'TTaf ~ Gray File i flRC PDR Franklin Petearch Center cc w/ enclosure: Local POP l See next page (Dr.VoCon) i PDP2 P/F RBernero i

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' OFFICIAL RECORD COhY

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. l Mr. J. M. Pilent Nebraska Public Power District Cooper Nuclear Station

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Mr. G. D. Watson General Counsel Nebraska Public Power District P. O. Box 4999 Columbus, Nebraska 68601 Mr. Arthur C. Gehr, Attorney Snell & Wilmer 3100 Valley Certcr .

Phcenix, Arizona 85073 '

Cooper Nuclear Station ATTN: Mr. Paul Thomason. Division Panager of Nuclear Operations P. O. Box 98 Brownville, Nebraska 68321 Director Nebraska Departmer.t of Environmental Control P. O. Box 94877

. State House Station Linccin, Nebraska 68509 Mr. William Sittert, Commissioner Nemaha County Board of Commissioners Necaha County Ccurthouse Auburn, Nebraska 62205 Resident Inspector

• U.S. Nuclear Regulatory Commission P. O. Box 218 Brownville, Nebraska 68321 .

Regicnal Administrator Region IV U.S. Nuclear Regulatory Commission

, 611 Ryan Plare Drive, Suite 1000 Arlington, Texas 76011

H. Ellis Simcons, Director L

Division of Radiological Health Department of Health 301 Centennial Mall, South P. O. Box 95307 Lincoln, Nebraska 63509

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V Reouest for Additional Information ,

Related to the tiodification of Vacuum Breakers on Mark 1 Containment ,

r f Cooper Nuclear Station- ,

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The results of the staff review of the Cooper Nuclear Station torus-to-drywell vacuum breaker evaluation identified several areas where further information is needed before the staff can comolete its review. These 2

areas sunnarized below were delineated in the staff's generic evaluation

• of the methodology prooosed to predict vacuun breaker valves opening and closino irpact velocities, letter from D. Vassallo to H, Pfefferlen,

] dateddecember 24, 2984 (copy attached).

I 1. Is the chugging source rate used in the evaluation the same as the one develooed in CDI Report (#E4-3)? If not the same, orovide the chuaning i source rate with the supporting justification.  ;

2. Did the calculation aoply the 1.07 load factor to account for the uncertainty in calculating the underoressure (See Section IV of tha t

{ attachedevaluation).

j 3. Did the calculations use the drywell podel which results in the rest i conservative prediction (See Section V of the attached evaluation)?-

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'/ h n umT O STATES NUCLEAR RECULATORY COMMISSION I

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i Mr. H. C. Pfefferlen, Manager BWR Licensing Procrams General Electric Company 175 Curtner Avenue, MC 682 San Jose, California 95125

SUBJECT:

EVALUATION OF MODEL FOR PREDICTING DRYWELL TO WETWELL VACUUM BREAKER VALVE DYNAMICS

. The staff issued Generic Letter 83-08 dated February 2, 1983, to all applicants and licensees of plants with Mark I containments reouesting .

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submittal of information related to a potential failure mode of the  !

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drywell-to-torus vacuum breakers during the chugging and condensation 1 oscillation phases of a Loss-of-Coolant Accident (LOCA). As stated in the (

oeneric letter, this issue was discovered at the time the generic phase of l the Mark I Containment Long-Term Program was near ccepletion, however, the j

-, Mark I Owners Group connitted to resolve this issue although not necessarily as part of the NUREG-0661 Long Term Program. )

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i To resolve the generic aspects of this issue the following reports were j prepared by Continuum Dynamics Inc. (CDI) for the General Electric Company ,

and the Mark I Owners Group: 1 CDI TECH NOTE B2-31, ' Mark 1 Vacuum Breaker Improved Dynamic Model - l Model Development and Validation" transmitted by your letter dated l October 28, 1982 '

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CDI Report No. 84-3, ' Mark I Wetwell to Drywell Vacuum Breaker Load Methodology" transmitted by your letter dated March 2,1984 These reports describe the models to'be used to compute the vacuum breaker valve response to chugging' and condensation events in Mark I plants.

Based on our review of these reports and the additional information provided in your letters dated September 26,1984 and November 6, 1984, we haya concluded that the valve dynamic model conservatively predicts the opening and closing velocities for the valve and, therefore, is acceptable for use in the analyses and/or qualiffcation of Mark I wetwell-to-drywell

9 Mr. H. C. Pfefferlen - 2-vacuumireaker valves subject to the restrictions set forth in Section V of the enclosed Safety Evaluation (SE).

SinEarely, nic 8. Vassallo, Chief Operating Reactors Branch #2 Division of Licensing

Enclosure:

As stated i

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3AFETY FVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ON THE ACCEPTABilf 7Y OF THE ANALYTICAL MODEL 00R PREDICTING VALVE OYNAMICS l

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1. Introduction  :

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Mark I containments are equipped with simple check valves to serve as vacuum breakers to equalize any overpressure of the wetwell air space region relative to the drywell so that the reverse direction differential pressure will not

- exceed the design value. In general, the vacuum breakers will swing open when the wetwell eir space pressure is 0.5 psi (or more) greater than the vent. header pressure. Typical vacuum breaker arrangements for the Mark I plants are shown in i

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Figure 1. As shown, internal vacuum breakers are located on the vent pipes, E and external vacuum breakers are located in a supplementary piping system.

- Following the onset of a loss-of-coolant accident (LOCA) and during the chugging phase, caused by the rapid condensation of the steam at the vent exit, the vacuura breaker may be called upon to function in a cyclic manner. This is due t3 the fact that the chugging phenomenon is repeate'd on the average every two seconds causing strong dynamic underpressure conditions in the vent pipe, which depending on the chug strength may open the vacuum breaker with high velocity. The underpressure condition which normally lasts for about 5 msec is followed by a dynamic overpressure condition, which again depending on the strength of the chug, may close the vacuum breaker with high velocity. l Failure of a vacuum breaker to reclose could result in a pathway for steam bypass of the pool, thus , jeopardizing the ' integrity of the coritainment.

II. Backgr6und

During the Mark I Full Scale Test Facility (FSTF) containment loads program, a GPE wetwell to drywell vacuum breaker was observed to cycle. Inspection of the valve after Test MI, which had the highest opening velocity, revealed that ,

the pallet hinge was bent, the latching magnet was broken and indentation was 4

observed in the valve casing which suggested that the pallet opened fully during the test. In other tests, there also was observed damage but it was licited to i ((' the pallet sealing gasket. MI was the only test in the FSTF test series which i

had fully opened the vacuum breaker. Having presented the test results it she'uld be noted that the actuation velocities sustained in the FSTF test program are not considered to be prototypical. The results are considered very conservative

/ because the drywell volume in ths FSTF is much smaller than any domestic l- Mark I plant. For this reason, it was concluded in CDI report #84-3, that opening impacts and hence the vacuum breaker damage observed in test MI, are not anticipated in domestic Mark I plants.

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j III. Summary of the Topical Reports Report CDI #82-31 describes the methodology used to predict the drywell to wetwell vacuum breaker cycling velocities, particularly when and if the valve i disk strikes the full open stop or seat. Since the location of vacuum l breakers vary from plant to plant, a need exists to quantify the ring header /wetwell pressare fluctuations for plant unique application.$ CDI report

1. 84-3 describes an analytical model to extract condensation source time l

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- 3-histories ffom the FSTF test f acility. After transferring these condensation sources to a model of an actual Mark I plant, the analytical model would compute the pressure time history across the' disk of the vasvum breaker.

Figure 2, extracted from CDI report 84-3, provides the steps followed to i detemine the plant unique vacuum breaker forcing functions.

111.1 Valve Dynamic Model Verifiestio3 7 The dynamics of the vacuum breeker, described in COI report 82-31, is simulated in tenns of the hydrodynamic torque about the valve shaft. This torque is as a consequence of a differential pressure across the valve disk.

g., During run tS-DA of the F5TF tests, the vacuum breaker was !nstrumented such a

that the valve displacement and pressure differential across the valve disk were recorded. This information was used to verify the valve dynamic model as i .

l follows. By driving tne valve dynamic model with the seasu.*ed differential pressure across the valve from test f5-DA, predictions of valve displacement versus time were made and compared against the measured data from the same FSTF run #5-DA. 1 l

't The results of this comparison indicated that the predicted impact velocities i

were greater than the experimental values by an average factor of more than

21. This extreme conservatism was attributed to the fact that the valve l dynamic model did not account for the reduction 'in the hydrodynamic torque as l a result of the reduced static pressure across the valve disk due to l flow computations. A parametric study was perfomed to reduce this 4

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conservatism. The result was the development of a conservative yet realistic valve dynamic model described in CDI report #82-31. Comparison of the predicted valve impact velocities based on the improved model still bounded all test impact velocities with approximately a 12% margin.

It was, therefore, concluded in the CDI report #82-31 that the valve dynamic model is appropriate for the analysis and/or qualification of Mark I wetwell to drywell vacuum breaker.

III.2 Vent Dynamic Model Verification r, The model descri. bed in CDI report #84-3 was developed to allow the development b #

4-of unsteady condensation rate at the vent exit from the reasured FSTF drywell pressure. A transfer function was developed which translates the condensation soprce at the vent exit to a pressure at any location in the vent system.

, The pressure time history measured in the drywell was used with the transfer function to deduce the condensation rate at the vent exit. This source was then used with the transfer function to predict the unsteady pressure at a location in the vent header where measurements were taken. The comparisons

_ between the measured and predicted pressures were favorable and, therefore, it was concluded that the transfer function model contains the essential elements  ;

required to predict pressure oscillations in Mark I steam vent systims. Since  !

.. l the condensation rate is fixed by local conditions at the vent exit, i.e.,

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l 5-5 steam mass flow rate, noncondensibles and thermodynamic conditions, these conditions would only vary slightly between plants and, therefore, the 4

condensation rate / source thus developed can be used in any Mark I facility to predict the unsteady pressure at the prescribed location of the vacuum breaker.

III.3 Selection of the Condensation Source The FSTF test data were screened to determine the chugging events that produced the most severe actuation of the vacuum breaker, i.e., large impact velocities. Over 1000 seconds of chugging data were recorded in which 400 distinct chug events actuated the vacuum breaker 179 times. Three runs were

{5 noted to have significant chugging: runs MI, M4 and M9. Data from these runs

. were used to drive the vacuum breaker valve described in Section III.1 to

, detemine the maximum impacts of the valve disk on the body and the seat of the valve. It was determined by CDI that the time interval 65.9-105.9 seconds of run MI would bound all FSTF data including those that caused the valve damage in test M1; therefore, the 65.9 to 105.9 seconds time interval was chosen to determine the condensation rate as described in Section 111.2 IV. Plant Unique Application The transfer function discussed in Section III.2 is modified for plant unique l 3 application by inputting the 1) drywell volume / total vent area, 2) ~ pool submergence and 3) damping due to external piping length (for the six .'tark I plants that have external va uum breakers). The condensation rate discussed

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. i in Section 111.3 is used with the plant unique modified transfer function to compute the pressure on the vent side of the vacuum breaker disk and the wetwell air space pressure. A ' sensitivity study of the vent dynamic model demonstrated that the wetwell air space pressure is insensitive to the wetwell air space volume. (Pool pressure coefficient in response to question 4 1

represents the wetwell air space volume in the sensitivity study). Therefore, this volume is not considered as a plant unique input in the model.

These two pressures are then subtracted, multiplied by a load factor of 1.07 (to account for uncertainty in calculeting the underpressure) and applied across the vacuum breaker valve dynamic model discussed in Section 111.1 to obtain disk actuation velocities.

_ V. Staff's Evaluation and Recomendation During the review of the infomation presented in the CDI reports, the staff '

expressed concern on weather the damage sustained to the valve installed on the

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FSTF could occur in domestic Mark I plants. The' staff also expressed concern that using the methodology, no opening impacts were anticipated in

Mark I plants even though the valve that was installed on the FSTF had an opening impact during test M1.

In response to these concerns, CDI stated that the vacuum breaker response in the FSTF was not prototypical and is very conservative. This is due to the fact that the drywell volume / total vent area ratio in the FSTF is asch smaller

than any domestic Mark I plant. CDI contends that this ratio has a significant e

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influence on the pressure oscillation in the ring header and in turn,,an '

influence on the load across the vacuum breaker. To illustrate this point, CDI provided the results of analyses which sho.ed that the vent pressure monotonically decreases with increasing drywell volume / vent area ratio. The calculated load across the vacuum breaker would also decrease as this ratio increased. Based .

on the above, CDI concluded that the large opening impact velocities and valve damage experienced during the FSTF test M1 are unlikely to occur in any domestic Mark I plant.

4 Based on our review of the methods and assumptions described in the CDI reports, and the response to the request for additional infonnation (RAI),

we conclude that the valve dynamic model conservatively predicts valve opening .

and closing velocities and, therefore, is acceptable for use in the analysis and/or qualification of Mark I wetwell to drywell vacuum breakers subject to the following restrictions:

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1. The plant unique loads 'are to be computed using one of two drywell models which result in the most conserfative prediction. One model examined by

. CDI represents the drywell by a capacitance in the vent dynamic model as i

discuss 6* in Section 111.2. The other model divides the drywell into two i

cylinders; treating each volume as an acoustic circuit in the vent dynamic model; I ..

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2. The salue of all plant unique parameters inputted to the models to obtain plant' Jnique wetwell to drywell vacuum breaker load definitions should be provided with the results; and

3. Any plant-unique deviations of the methodology and/or assumptions that were found acceptable in this report should be identified. Additionally, the rationale and justification for the proposed alternative method and/or assumptions should be provided. Justification should include the

_ identificationoftheconservatismassociatedwiththedeviation.

Principal Contributor: F. E1tawila Dated: December 24, 1984 (I, -

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REFERENCES 1s CDI TECH NOTE 82-31. " Mark I Vacuum Breaker Improved Dynamic Model -

Model_ Development and Validation."

2. CDI Report No. 84-3 " Mark I Wetwell to Drywell Vacuum Breaker Load Methodology,."

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l Tigore i Mark I Vaccus Breaker Location

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STIP Develop a dynamic model of the

vent system, stes= water inter-1 face and peal slosh with the condensation rate at the int.er-face unknoun.

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Vse measured drywell pressure to 2 determine the condensation rate. -

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F- With the condensation rate i J deter =ined,~~ predict unsteady k 3 pressures at other vant locations

.- to validate the model.

y Use the condensation source at the vent exit to drive dyna =ic 4 models of Mark I plants to determine unique vacuum breaker forcing functions.-

1 Tigure 2 steps in determining plant unique vacuum breaker forcing functions l

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