ML20134A731

Forwards Request for Addl Info Re Mod of Vacuum Breakers on Mark I Containments,Per Generic Ltr 83-08.Response Requested within 45 Days of Ltr Receipt

ML20134A731
Person / Time
Site:	Brunswick
Issue date:	11/05/1985
From:	Vassallo D Office of Nuclear Reactor Regulation
To:	Utley E CAROLINA POWER & LIGHT CO.
References
GL-83-08, GL-83-8, NUDOCS 8511070562
Download: ML20134A731 (3)

Text

{{#Wiki_filter:. --. _ . -- November 5,1985 Docket Nos. 50-325/324 DISTRIBUTION Docket, File na NRC POR Local POR ORB #2 Reading Mr. E. E. Utley HThompson Senior Executive Vice President SNorris Power Supply and Engineering & Construction MGrotenhuis Carolina Power & Light Company WLong Post Office Box 1551 ELJordan Raleigh, North Carolina 27602 BGrimes JPartlow

SUBJECT:

MODIFICATION OF VACUUM BREAKERS ON 0 ELD MARK I CONTAINMENTS (GENERIC LETTER 83-08) ACRS (10)

Gray File i Re: Brunswick Steam Electric Plant, Units I and 2 By letter dated June 23, 1983 you responded to Generic Letter 83-08 dated 3

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. The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L. 96-511. Sincerely, Original signed by/

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

Enclosure:

As stated cc w/ enclosure: See next page 1 ORB p#2.0L ORB #2:0L OEB#2:DL ORB #2:DL 1 SNoYris:rc MGrotenhuis WLong DVasjsllo 4 10/JI/85 10/61/85 10/S /85 g/3 /85 ft h p og g g g PDR g4

I Mr. E. E. Utley i Carolina Power & Light Company Brunswick Steam Electric Plant; Units 1 and 2 l cc: Richard E. Jones, Esquire J. Nelson Grace Carolina Power & Light Company Regional Administrator 336 Fayetteville Street Region II Office Raleigh, North Carolina 27602 U. S. Nuclear Regulatory Comission 101 Marietta Street, Suite 3100 4 George F. Trowbridge, Esquire Atlanta, Georgia 30303 Shaw, Pittman, Potts and Trowbridge

   ,     1800 M Street, N. W.                          Dayne H. Brown, Chief Washington, D. C. 20036                       Radiation Protection Branch Division of Facility Services Mr. Charles R. Dietz                         Department of Human Resources Plant Manager                                 l'ost Office Box 12200 Post Office Box 458                          Raleigh, North Carolina 27605 Southport North Carolina 28461 Mr. Franky Thomas Chairman Board of Comissioners Post Office Box 249                                                                -

. Bolivia, North Carolina 28422 Mrs. Chrys Baggett State Clearinghouse Budget and Management 116 West Jones Street 4 Raleigh, North Carolina 27603

• Resident inspector U. S. Nuclear Regulatory Comission Star Route 1 Post Office Box 208 Southport, North Carolina 28461

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t Request for Additional Information Related to the Modification of Vacuum Breakers on Mark I Containment Brunswick Steam Electric Plant Units 1 and 2 The results of the staff review of the Brunswick Steam Electric Plant (BSEP), Units 1 and 2, torus-to-drywell vacuum breaker modification identified several areas where further information is needed before the staff can complete its review. These areas sunmarized 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 staff's generic evaluation . underpressure (Section IV of the

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

                    /p no UNITED STATES I          o*?.\            NUCLEAR REGULATORY COMMISSION
                 ;;          -p                          WASMNGTON, D. C. 20555
                    %y ,,, #                                    December 24, 1984 Pr. H. C. Pfefferlen, Manager BWR Licensing Proorams General Electric Company 175 Curtner Avenue, MC 682 San Jose, Califors% 95125

SUBJECT:

EVALUATION OF MODEL FOR PREDICTING DRYWELL TO WETWELL VACUUM BREAKER VALVE DYNAMICS l 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-Tmn Program was near completion, however, the Mark I Owners Group committed to resolve this issue tithough not necessarily as part of the NUREG-0661 Long Term 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 ' 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 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 k ApW .

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Mr. H. C. Pfefferlen vacuum breaker valves subject to the restrictions set forth in Section V of the enclosed Safety Evaluation (SE). t Sincerely, omenic B. Vassallo, Chief Operating Reactors Branch #2 Division of Licensing

Enclosure:

As stated

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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 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 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 vacuum breaker may be called upon to function in a cyclic manner. This is due t'6 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 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 containment. f '

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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 , observe'd 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 had fully opened the vacuum breaker. 'Having presented the test results it should

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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 not anticipated in domestic Mark I plants.

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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 ring , header /wetwell pressure fluctuations for plant unique application. CDI report j #84-3 describes an analytical model to extract condensation source tin s S

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i histories from the FSTF test facility. After transferring these condensation l 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 detennine the plant unique vacuum breaker forcing functions. J

           .       III.1 Valve Dynamic Model Verification

[ The dynamics of the vacuum breaker, 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 fS-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 information was used to verify the valve dynamic model as follews. By driving the valve dynamic model with the measured differential i l pressure across the valve from test #S-DA, predictions of valve displacement , versus time were made and compared against the measured data from the same FSTF run #S-DA. i 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 gf the reduced static pressure across the valve disk due to flow computations. A parametric study was performed to reduce this g

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l l l i , conservatism. The result was the development of a conservative yet realistic j valve dynamic model described in t'DI report #82-31. Comparison of the predicted , nlve impact velocities based on the improv:d model still bounded all test impact 4 velocities with approximately a 12% margin. It was, therefore, concluded in the CDI report #82-31 that the valve dynamic l 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 described in CDI report #84-3 was developed to allow the development ( 4 t of unsteady condensation rate at the vent exit from the measurea FSTF drywell pressure. A transfer function wa: developed which translates the condensation 1 Sotree at the vent exit to a pressure at any location in the vent system. ' i 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 j then used with the transfer function to predict the unsteady pressure at a j i location in the vent header where measurements were taken. The comparisons between the measured and predicted pressures were favorable and, therefore, it I 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., l______. _- _ _ . _ _ - _ . _ _ _ ._

1

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steam mass flow rate, noncondensibles and thennodynamic conditions, these conditions would on13 vary slightly between plants and, therefore, the condensation rate / source thus developed can be used in any Mark I facility to i predict the unsteady pressure at the prescribed location of the vacuum breaker. III.3 Selection of the Cor.densation Source 4 f I

- The FSTF test data were screened to determine the chugging events that produced q the most severe actuation of the vacuum breaker, i.e., large impact '

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

( roted to havt significant enugging: runs M1, M4 and M9. Data from these runs j were used to drive the vacuum breaker valve described in Section III.1 to ! determine the naximum impacts of the valve disk on the body and the seat' of i

!                             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 damage in tesEM1; therefore, the Eb.9 to 105.9 seconds time interval was chosen to detennine the condensation rate as described in Section III.2

IV. Pla-{,Unioue Apelication '

The traiter fenction discussed in Section III.2 is modified for plant unique I appli:ation by inputting the 1) drywell volume / total vent area, 2) pool - submerge:.ce an.13) damping due to external piping length (for the six Mark I I plants th: have external vacuum breakers). The coredensation rate dis ussed i

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I i j 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 coeff'icient 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 i (to account for uncertainty in calculating the underpressure) and applied l t

• across the vacuum breaker valve dynamic model discussed in Section III.1 to j obtain disk actuation velocities.

l I ( V. Staff's Evaluation and Recenenendatie.n - i During the review of the inforra. tion presented in the CDI reports, the staff expressed concern on weather the damage sustained to the valve installed on the

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F5TF could occur in domestic Mark 1 plants. The' staff also expressed concern that using the methodology, no opening impacts were anticipated in t Mark I plants even though the valve that was installed on the FSTF had an ope.ning impact during test M1. i 1 In response to these concerns, CDI stated that the vtcuum breaker response in ! the FSTF ws: not pmtotypical and is very conservative. This is due to the i i fact that the drywell volume / total vent area ratio in the FSTF is much smaller i than any domestic Mark I plant. CDI contends that this ratio has a significant i.

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( influence on the pressure oscillation in the ring header and in turn,,an c 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 a t decreases with increasing drywell volume / vent area ratio. The calculated load 4 across the vacuum breaker would also decrease as this ratio increased. Based on the above, CDI concluded that the large opening impact velocities and i 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 information (RAI), ( we ccnclude 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: ' 4 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 model divides the drywell into two cylinders; treating each volume as an acoustic circuit in the vent dynamic l model; e I. N

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2. The value of all piant unique parameters inputted to the models to obtain plant-unioue wetwe,11 to drywell vacuum breaker load definitions should be provided with the results; and l 9 <

3. Any plant-unique deviations of the methodology and/or assumptions that were found acceptable in this report should be; identified. "Jditionally,

                                               ,        the rationale and justification for the proposed alternative method and/or
                                                     ' assumptions should be provided. Justification should include the
                                ;            ,t identification of the conservatism associated with the deviation.

Principal Contributor: F. Eltawila . Dated: December 24', 1984

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REFERENCES t' is COI TECH NOTE 82-31. " Hark I Vacuum Breaker Improved Dynamic Model - Model Development and Validation."

2. R rt No. 84-3. " Mark I Wetwell to Drywell Vacuum Breaker Load b

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k EETERNAL VACUWM BAEACER R _% IedTEMNAL # VAcuuw 70 DRYWELL _ SMEAICER

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                                                                                                        ~                                                                                  M COMERS SUPMLESSION POOL TORLJ i

i l ( Tigure i Hark I Vacrum Breaker Location -

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e ( . I STEP Develop a dynamic model of the vent system, steam wat'er inter-1 face and pool slosh with the

condensation rate at the inter-face unkncun.

q 2 Use measured dryvell pressure to  ! deter =ine the condensation rate. - r i f With the condensation rate ( 3 deter =ined, predict unsteady pressures at other vent locations  ! to validate the model. v

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

l Figure 2 Steps in determining plant unique vacuum breaker

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                        -   forcing functions 4

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