ML20140D093
| ML20140D093 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 01/17/1986 |
| From: | Rooney V Office of Nuclear Reactor Regulation |
| To: | Capstick R VERMONT YANKEE NUCLEAR POWER CORP. |
| References | |
| GL-83-08, GL-83-8, NUDOCS 8601290136 | |
| Download: ML20140D093 (3) | |
Text
1 January 17, 1986 Docket No. 50-271 DISTRIBUTION Docket File NRC PDR Local PDR Mr. R. W. Capstick PD#2 Reading Licensing Engineer RBernero Vermont Yankeee Nuclear Power Corporation VRooney 1671 Worcester Road SNorris Framingham, Massachusetts 01701 EJordan BGrimes
SUBJECT:
MODIFICATION OF VACUUM BREAKERS ON MARK I JPartlow CONTAINMENTS (GENERIC LETTER 83-08)
ACRS (10)
OELD Re:
Vermont Yankee Nuclear Power Station Gray File W L-o r4 3 By letter dated May 11, 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 within 45 days from receipt of this letter.
This request for information was approved by the Office of Management and Budget under clearance No. 3150-0011.
Coninents 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, Original signed by/
Vernon L. Rooney, Pro.iect Manager RWR Project Directorate #2 Division of BWR Licensing
Enclosure:
As stated cc w/ enclosure:
See next page 0
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l Mr. R. W. Capstick Vermont Yankee Nuclear Power Corporation Vermont Yankee Nuclear Power Station cc:
Pr. W. F. Conway President & Chief Executive Officer W. P. Murphy, Vice President &
Vermont Yankee Nuclear Power Corp.
Manager of Operations R. D. 5, Box 169 Vermont Yankee Nuclear Power Corp.
Ferry Road R. D. 5. Box 169 Ferry Road Brattleboro, Vermont 05301 Brattleboro, Vermont 05301 Mr. Donald Hunter, Vice President Vermont Yankee Nuclear Power Corp.
Mr. Gerald Tarrant, Comnissioner 1671 Worcester Road Vermont Department of Public Service 120 State Street Framingham, Massachusetts 01701 Montpelier, Vermont 05602 New England Coalition en Nuclear Pollution Hill and Dale Farm R. D. 2. Box 223 Public Service Board State of Vermont Putney, Vermont 05346 120 State Street Mr. Walter Zaluzny Chairwen, Board of Selectman Post Of' ice Box 116 Vermont Yankee Decommissionirg Alliance Vernon, Vermont 05345 Box 53 J. P. Pelletier, Plant Manager Montpelier, Vermont 05602-0053 Vermont Yankee fluclear Power Corp.
Post Office Box 157 Resident Inspector Vernon, Vermont 05354 U. S. Nuclear Regulatory Commission Raymond N. McCandless Post Office Box 176 Vernon, Vernont 05354 Vermont Division of Occupationti A Radiological Health Admini tration Building Vermont Public Interest t
10 Baldwin Street Research Group, Inc.
43 State Street Montpelier, Vernont 05602 Montpelier, Vermont 05602 Honorable John J. Easton Attorney General Thomas A. Murley State of Verwent Regional Adninistrator 109 State Street Region I Office U. S. Nuclear Reculatory Conmission Montpelier. Vermont 05602 631 Park Avenue John A. P,itscher, Esquire King of Prussia, Pennsylvania 19406 Ropes & Gray 225 Franklin Street Boston, Massachusetts 02110
Request for Additional Information Related to the Modification of Vacuum Breakers on Mark I Containment Vermont Yankee Nuclear Power Station The results of the staff review of the Vermont Yankee Nuclear Power Station (VY) 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 VY evaluation the same as the one developed in CDI Report (#83-3)? If not the same, provide the chugging source rate with the supporting justification.
2.
Did the VY 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 VY calculations used the drywell model which results in the most conservative prediction (Section V of the generic evaluationi?
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UNITED STATES
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December 24, 1984 Mr. H. C. Pfefferlen, Manager BWR Licensing Proorams General Electric Company 175 Curtner Avenue, MC 682 San Jose, California 95125
Dear Mr. Pfefferlen:
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-Tenn Program was near completion, however, the Mark I Owners Group consnitted to resolve this issue although not necessarily as part of the NUREf-0661 Long Tenn 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
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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 infonnation 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
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Mr. H. C. Pfefferien vacuum breaker valves subject to the restrictions set forth in Section V of the enclosed Safety Evaluation (SE).
Sincerely, l
omenic B. Vassallo, Chief Operating Reactors Branch #2 Division of Licensing
Enclosure:
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ON THE ACCEPTABILITY OF THE ANALYTICAL MODEL FOR PREDICTING VALVE DYNAMICS I.
Introduction Mark I containments are equipped with simpla check valves to serve as vacuum breakers to equalize any overpressure of t'se 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 Figure 1.
As shown, internal vacuum breakers are located on the vent pipes,
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I and external vacuum breakers are located in a supplementary piping system.
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Following the onset of a lossi-of-coolant accident (LOCA) and during the chugging phase, caused by the rapid condensation of the steam at the vent exit, the 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 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 nomally lasts for about 5 msec is followed by a dynamic overpressure con b ion, 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 containment.
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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
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the pallet sealing gasket. MI was the only test in the FSTF test series which had fully opened the vacuum breaker. Having presented the test results it sho'uld be noted that the actuation velocities sustained in the FSTF test program are Cj.
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 not anticipated in domestic Mark I plants.
III.
Sumary 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 rtng header /wetwell pressure fluctuations for plant unique application. CDI report
- 84-3 describes an analytical model to extract condensation source time
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histories from the FSTF test faciltty. After transferring these condensation sources to a model of an actual Mt.rk I plant, the analytical model would compute the pressure time history across the disk of the vacuum breaker.
Figure 2, extracted from CDI report S4-3. provides the steps followed to detennine the plant unique vacuum breaker forcing functions.
III.1 Valve Dynamic Model Verification
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The dynamics of the vacuum t,reaker, described in CDI report 82-31, is simulated in tenns of the hydrodynamic torque about the valve shaft. This
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torque is as a consequence of a differential pressure across the valve disk.
During run tS-DA of the FSTF tests, the vacuum breaker was instrumented such that the valve displacement and pressure differential across the valve disk were recorded. This infonnation was used to verify the valve dynamic model as
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follows. By driving the valve dynamic model with the measured differential pressure across the valve from test fS-DA, predictions of valve displacement 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 a result of the reduced static pressure across the valve disk due to flow computations. A parametric study was performed to reduce this a
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 CLI report #84-3 was developed to allow the development k'
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 pressure time history reasured in the drywell was used with the transfer
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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 systems. Since the condensation rate is fixed by local conditions at the vent exit, i.e.,
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steam ness flow rate, noncondensibles and thermodynamic conditions, these conditions would only vary slightly between diants 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 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 f"'s 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 111.1 to determine 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 M1 would bound all FSTF data including those that caused the valve
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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 The transfer function discussed in Section III.2 is modified for plant unique application by inputting the I) drywell volume / total vent area, 2) pool submergence and 3) damping due to external piping length (for the sex Mark I plants that have external vacuum breakers). The condensation rate discussed 4
. 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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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 MI.
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
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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
i 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.
Based on our review of the methods and assumptions described in the CDI reports, and the response to the request for additional infornation (RAI),
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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 conservative prediction. One model examined by CDI represents the drywell by a capacitance in the vent dynamic model as discussed in Section III.2. The other omdel divides the drywell into two cylinders; treating each volume as an acoustic circuit in the vent dynamic model; Se
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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 lC
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REFERENCES is CDI TECH NOTE 82-31
" Mark I Vacuum Breaker Improved Dynamic Model -
Model Development and Validation."
2.
R{p{rt No. 84-3. " Mark I Wetwell to Drywell Vacuum Breaker Load l
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EXTERNAL VAcuuu SAEAltfR i
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INTERNAL vAcuw TO DRYWELL 8RIAKER MAIN VENT
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Tigure i Mark I Vact um Breaker Location l
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o-SIIP Develop a dynamic model of the vent system, steam water inter-1 face and pool slosh with the condensation rate at the inter-
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face unknown.
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Use measured drywell pressure to 2
detemine the condensation rate.
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With the condensation rate deceded, predict asteady 3
pressures at other vent locations to validate the nodel.
9 Use the condensation source at.
the vent exit to drive dyna =ic 4
models of Piark I plants to deterzine unique vacuu:n breaker forcing functions.
i Tigure 2 Steps in determining plant unique vacuu:n braaker forcing functions e.
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