ML20137M410

Forwards Request for Addl Info Re 830513 Response to Generic Ltr 83-08 Re Mod of Vacuum Breakers on Mark I Containments

ML20137M410
Person / Time
Site:	Pilgrim
Issue date:	01/23/1986
From:	Zwolinski J Office of Nuclear Reactor Regulation
To:	Harrington W BOSTON EDISON CO.
References
GL-83-08, GL-83-8, NUDOCS 8601280260
Download: ML20137M410 (3)

Text

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January 23, 1986 Docket No. 50-293 Mr. William D. Harrington Senior Vice President, Nuclear Boston Edison Company 800 Boylston Street Boston, Massachusetts 02199

SUBJECT:

MODIFICATION OF VACUUM BREAKERS ON MARK I CONTAINMENTS (GENERIC LETTER 83-08)

Re: . Pilgrim Nuclear Power Station By letter dated May 13,-1983 you responded to Generic Letter 83-08 dated' February 2,1983. We are continuing the review and find that we need the information requested in the enclosure to this letter in order to complete our review regarding the vacuum breakers. Please respond to this request on a schedule to be negotiated with your project manager. I would like to see this issue fully resolved as expeditiously as possible and therefore recommend you provide a timely response.

This request for information was approved by the Office of Management and Budget under clearance No. 3150-0011. Coments on burden and duplication -

may be directed to the Office of Management and Budget, Reports Management, Room 3208, New Executive Office Building, Washington, D.C. 20503.

Sincerely, p .u..on John A. Zwolinski, Director BWR Project Directorate #1 Division of BWR Licensing

Enclosure:

As stated cc w/ enclosure:

See next page

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DISTRIBUTION Docket EJordan NRC PDR BGrimes Local PDR JPartlow PD #1 RDG- PLeech 9601280260 e60123~

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Mr. William D. Harrington

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Boston Edison Company Pilgrim Nuclear Power Station cc:

Mr. Charles J. Mathis, Station Mgr.

Boston Edison Company RFD #1, Rocky Hill Road Plymouth, Massachusetts 02360 Resident Inspector's Office U. S. Nuclear Regulatory Commission Post Office Box 867 Plymouth, Massachusetts 02360 Mr. David F. Tarantino Chairnan, Board of Selectman 11 Lincoln Street Plymouth, Massachusetts 02360 Office of the Commissioner Massachusetts Department of Environmental Quality Engineering One Winter Street Boston, Massachusetts 02108 Office of the Attorney General 1 Ashburton Place 19th Floor Boston, Massachusetts 02108 Mr. Robert M. Hallisey, Director Radiation Control Program Massachusetts Department of Public Health -

150 Tremont Street Boston, Mhssachusetts 02111 Regional Administrator, Region I U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406 Mr. A. Victor Morisi Boston Edison Company 25 Braintree Hill Park Rockdale Street Braintree, Massachusetts 02184 l

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Request for Additional Information Related to the Modification of Vacuum Breakers on Mark I Containment Pilgrim Nuclear Power Station The results of the staff review of the Pilgrim Station torus-to-drywell vacuum breaker modification identified several areas where further information is needed before the staff can complete its review. These areas summarized below were delineated in the staff's generic evaluation of the methodology proposed to predict vacuum breaker valves opening and closing impact velocities, letter from D. Vassallo to H. Pfefferlen, dated December 24, 1984 (copy attached).

1. Is the chugging source rate used in the BSEP evaluation the same as the one developed in CDI Report (#84-3)? If not the same, provide the chugging source rate with the supporting justification.

2. Did the BSEP. calculation apply the 1.07 load factor to account for the uncertainty in calculating the underpressure (Section IV of the staff's generic evaluation).

3. Have the BSEP calculations used the drywell model which results in the most conservative prediction (Section V of the generic evaluation)?

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'/ (g UNITED STATES NUCLEAR REGULATORY COMMISSION a wAsunciow. o. c. 20sss

}' \...../ December 24, 1984 A'TTACHMENT T0 REQUEST FOR ADDITIONAL INFORMATION i

a Mr. H. C. Pfefferlen, Manager BWR Licensing Programs 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 .

submittal of information related to a potential failure mode of the

. drywell-to-torus vacuum breakers during the chugging and condensation oscillation phases of a loss-of-Coolant Accident (LOCA). As stated in the generic letter, this issue was discovered at the time the generic phase of the Mark I Containment Long-Term Program was near completion, however, the

1. Mark I Owners Group comitted to resolve this issue although not necessarily as part of the NUREG-0661 Long Tem Program.

To resolve the generic aspects of this issue the following reports were

' prepared by Continuum Dynamics Inc. (CDI) for the General Electric Company and the Mark I Owners Group:

CDI TECH NOTE 82-31 " Mark I Vacuum Breaker Improved Dynamic Model -

Model Development and Validation" transmitted by your letter dated October 28, 1982 -'

l l 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 infomation provided in your letters dated September 26, 1984 and November 6, 1984, we have 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 qualification of Mark I wetwell-to-drywell 99 1

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, 1 4 . o Mr. H. C. Pfefferlen i l

vacuum breaker valves subject to the restrictions set forth in Section V of i the enclosed Safety Evaluation (SE). l Sincerely, l

l omenic B. Vassallo, Chief Operating Reactors Branch #2 Division of Licensing

Enclosure:

As stated D

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ON THE ACCEPTABILITY OF THE ANALYTICAL MODEL FOR PREDICTING VALVE DYNAMICS

1. Introduction

' 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 air 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

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Figure 1. As shown, internal vacuum breakers are located on the vent pipes, 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 s

vacuum 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 i

seconds ca'using 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 msee is followed by a dynamic overpressure condition, which again depending on the strength of the chug, may close the vacuum breaker with high velocity.

Failure of a vacuum breaker to reclose could result in a pathway for steam bypass of the pool, thus jeopardizing the integrity of the con}tainment.

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1 I II. Background 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 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 limited to

[ the pallet sealing gasket. MI was the only test in the FSTF test series which

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had fully opened the vacuum breaker. 'Having presented the test results it should 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 the FSTF is much smaller than any domestic 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 i

not anticipated in domestic Mark I plants.

III. Sundary 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 disk strikes the full open stop or seat. Since the location of vacuum breakers vary from plant to plant, a need exists to quantify the ring l

header /wetwell pressure fluctuations for plant unique application. ..CDI report

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

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histories from the FSTF test facility. 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 vacuum breaker.

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

III.1 _ Valve Dynamic Model Verification 7 The dynamics of the vacuum breaker, described in CDI report 82-31, is simulated in terms 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 #S-DA of the FSTF tests, the vacuum breaker was instrumented such I

b that the valve displacement and pressure differential across the valve disk were recorded. This information was used to verify the valve dynamic model as follows. .By driving the valve dynamic model with the measured differential t

pressure across the valve from test iS-DA, predictions of valve displacement

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versus time were made and compared against the measured data from the same FSTF run #S-DA.

The results of this comparison indicated that the predicted impact velocities 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 dynamic model did not account for the reduction in the hydrodynamic torque as I

a result of the reduced static pressure across the valve disk due to flow computations. A parametric study was performed to reduce this

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- 4-I conservatism. The result was the development of a conservative yet realistic i

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 .

The model descri. bed in CDI report #B4-3 was developed to allow the development (rk- -

_ of unsteady condensation rate at the vent exit from the measured FSTF drywell pressure. A transfer function was developed which translates the condensation source at the vent exit to a pressure at any location in the vent system.

The pressu*re 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 c'ntains the essential elements required to predict pressure oscillations in Mark I steam vent systers. Since the condensation rate is fixed by local conditions at the vent exit, i.e.,

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i steam mass flow rate, noncondensibles and thermodynamic conditions, these conditions would only vary slightly between plants and, therefore, the 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 vacuuti breaker, i.e., large impact

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velocities. Over 1000 seconds of chugging data were recorded in which 400 distinct chug events actuated the vacuum breaker 179 times. Three runs were

'{ noted to have significant chugging: runs M1, M4 and M9. Data from these runs

,~ were used to drive the vacuum breaker valve described in Section 111.1 to  ;

determine the maximum impacts of the valve disk on the body and the seat of i the valve. It was detennined by CDI that the time interval 65.9-105.9 seconds j of run M1 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 III.2 IV. Plant Unique Application i

The transfer function discussed in Section 111.2 is modified for plant unique application by inputting the 1) drywell volume / total vent area, 2) ' pool submergence and 3) damping due to external piping length (for the six Mark I i

plants that have external vacuum breakers). The condensation rate discussed i

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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 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 calculating the underpressure) and applied across the vacuum breaker valve dynamic model discussed in Section III.1 to obtain disk actuation velocities.

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I V. Staff's Evaluation and Recommendation During the review of the information presented in the CDI reports, the staff expressed concern on weather the damage sustained to the valve installed on the 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 much smaller than any domestic Mark I plant. CDI contends that this ratio has a significant

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. 7-l 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 showed 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.

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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 p1 ant unique loads 'are to be computed using one of two drywell models which result in the most conservative prediction. One model examined by i

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

discussed in Section 111.2. The other model divides the drywell into two l

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

model;

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2. The value of all plant unique parameters inputted to the models to obtain plant-unique 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 identification of the conservatism associated with the deviation.

Principal Contributor: F. Eltawila Dated: December 24, 1984 r -

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REFERENCES

( 1s CDI TECH NOTE S2-31. " 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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INTERNAL M" VActMN TO DRMELL

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i Tigure 1 Mark I Vactus Breaker Location n.-- . , , . , , , _ , , - . , , - - . - - - - _ , . - - _._,7, , , , , , , , _ _ _ . _ _ . - - _ - _ _ - ___._a,.,,- . . , , ,---e , ,,., .,,, ,,,- ._ w..

o STEP Develop a dynamic model of the vent system, steam water inter-1 face and pool slosh with the condensation rate at the inter-face unkncun.

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Use measured dryvell pressure to 2 determine the condensation rate. -

o With-the condensation rate l ( l, 3 deter =ined, predict unsteady L pressures at other vant locations to validate the model.

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1 Use the condensation source at the vent exit to drive dyns=ic 4 models of Mark I plants to

• determine unique vacuum -

breaker forcing functions.

. Figure 2 steps in determining plant unique vacuum braaker i forcing functions I

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