ML20101H297
| ML20101H297 | |
| Person / Time | |
|---|---|
| Site: | 05200001 |
| Issue date: | 05/22/1992 |
| From: | Saxena U GENERAL ELECTRIC CO. |
| To: | Chang Li, Poslusny C NRC |
| References | |
| NUDOCS 9206290282 | |
| Download: ML20101H297 (18) | |
Text
FAY 22 '92 01:2#ti c, C !U' LEAR PLM J
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- ATTACRMENT A GE Desponse to DSER Questions I
Identified and Discussed in May 6, 1992 GE/NRC Mootings ISBUE:
GE has not provided a detailed description of how the ABWR drywell volumes and the unique vont system are modoled in the code and how air carryover from the drywell volumes to the wetwoll is treated in the code.- What is the difference, if any, betwoon the hydrostatic forco due to venting betwoon the Mark III and ABWR designs.
RESPONSE
ABwR Vent System conf f euratiqn In the ABWR-design, as described in SAR, the cylindrical RPV pedestal which is connected rigidly to the diaphragm floor separates the lower drywell from the wetwell, as shown in Figure 1. The pedestal is a ,
prefabricated stool structure filled with concrete after erection.
Ten drywell connecting vents (DCVs) are built into the RPV pedestal and connect the UD and LD. The DCVs are extended downward via 1.2M inside diameter steel pipes, each of which has three horizontal 0.7M diameter vent outlets into the supprossion pool.
The drywell-to-wotwell connecting vent system features in the ABWR design are similar to the Mark III vant system features, as shown in Figuro 2. The diameter, length, and vertical spacing of horizontal vents are same as that in Mark III design. Vertical vents total area in ADWR corresponds to vent annulus area in Mark-III. Horizontal vents and vertical vents total aron ratio in ABWR is comparable with the norizontal. vents and vont annulus total = area ratio in Mark III.
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. Hydraulic diameter of vent annulus area in Mark III is comparable with the vertical vents diamator in ABWR.
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In view of vont system configuration nimilarity betwoon ADWR and Mark III, it is expected that vent clearing process in the AUWR design will ,
be hydrodynamically similar to that observed for the Mark III design.
Vent clearing process for the Mark III vont system design has boon well investigated through extensive test programs and analytical studies performed by GE over a number of years, and this phenomenon is now well understood.
In view of geometrically almilar ADWR and Mark III vent systems, both ABWR and Mark III are expected to be subjected to quite similar hydrostatic pressuro loading conditions (on the structure housing the vont system) due to venting. However, considering that-the ABWR vont system is well encased incide the RPV pedestal (see Figure 1),
pressure loading on the overall vent system due to venting should be of no significant structure concern. The portion of horizontal vent extending into the pool, in the ABWR design, is designed for structural adequacy against pressure loading conditions due to venting Containment Pressure /Tomoerature Response to LOCA ABWR containment pressure and temperature transient-following a loss-of-coolant accident (LOCA) were determined using approved analytical methods (described in NEDO-20533). These analytical methods, which have boon developed based on extensive horizontal vent test data, describe the pressure / temperature transient and the attendant containment system inventorios due to a primary system pipe rupture. Therefore, these analytical methods are considered to be
, appropriato-for modeling and analyzing ADWR containment prossure/temperaturo response due to LOCA. Presence of discreto vertical vents connecting to horizontal vents in ABWR, compared to l
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- vent annulus connecting to horizontal vents in Mark III, is not expected to produce vent clearing process significantly different than that expected for Mark III. Slight geometrical differences, if any, are expected to produce second order or negligiblo effects on the '
overall vent clearing process. Furthermore, given that for the ABWR design the containment peak pressure occurs substantially later in time after the vont clearing process is complete, as seen in Figure 3, any slight geometrical differencos should be of no practical significance.
Those analytical methods permit modeling multi-node drywell featurn of the ABWR design. However, for conservatism, the drywell in SAR calculations was modeled as a single node representing upper drywell volume plus 50% of the lower drywell volume. This credit for transfer of 50% of the lower drywell contents into the wetwell is considered to be a conservative approach. Because of the ABWR unique containment configuration feature of separate upper and lower drywells, the inert atmosphere in the lower drywell would not transfer to the wetwell airspace region until the peak pressure in the drywell is achieved.
Because the lower drywell is connected to the upper drywoll via connecting vents, no gas can escape from the lower drywell until the peak pressure in the drywell is attained. For this situation lower drywell can be compared to a bottle whose opening is exposed to an atmosphere with increasing pressure.
In order to confirm conservatism in the singlo-node drywell modeling approach as employed in SAR calculations, containment pressure transient calculations were done modeling upper drywell and lower dryvell as separate nodes, using the same analytical methods as that used for SAR calculations. The calculated drywell pressuro response due to a feedwater line break modeling upper drywell and lower drywell l
l as separate nodes is shown in Figuro 4. When compared with the SAR single-node model results (shown in Figure 3), it is evident that the simplified singlo-node model (UD plus 50% of LD) approach used in SAR O I -
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. calculations produces conservative containnont response.
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ISBUE:
Provide detailed information on the vacuum breakers.
How can we verify that the vacuum breakers and containment will perform as predicted following a LOCA?
RESPONSE
The ABWR containment design requires provision of a total of eight (20-inch) vacuum breakers, which includes one valve for single f ailure (valvo fail to open) criterion. These vacuum breakers are intended to be simple swing check type valves, similar to that used on earlier BWR plants. These valves will open passively due to a negative differential pressure (WW airspace greater than the DW pressure) across the valve disk and close by gravity, thus requiring no external pcwor to actuate them. Consistent with the vacuum breaker sizing analysis assumptions, vacuum breaker valve will be required to start opening at a negativo pressure differential of 0.1 psi and fully open at a negativo pressure differential of 0.5 psia. Figure 5 shows key features of a typical simple swing check type valve.
Vacuum breaker valves are installed horizontally locating in WW airspace, one valve per penotration (through pedestal wall) opening into lower drywell. Position locations of those valves, both axially and azimuthally, are identified in Figures 1.2-3C and 1.2-13K in SAR, and they are reproduced here in Figures 6 and 7. The Amendment 6, vertical position location of these valves precludes them from being subjected to direct pool swell impact loading (valves position wo)1 above expected maximum pool swell height. Also, appropriate design '
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. features (shield etc.,) protecting theaa valveu from possible froth impact loading condition will be provided.
Connistent with the requirementn defined for earlier DWR designa, ADWR design will require periodic inspection and testing os vacuum breakers during plant outage, in order to assure that they will perform as intended when challenged to actuate during a given drywell deprenourization event. Valve dink will be manually tested for ita freedom to move and functionality. Also, vacuum breakern will bo equipped witn position switches f acilitating monitoring of valve ~
open/close position inside the control room.
ISSUE:
Resolve the discrepancies between the drywell and wetwell pressure and temperature plots at various break sizen and peak valuca shown in Table 6.2-1 of SAR.
RESPONSE: .
Drywell and wetwell pressure / temperature plots in SAR which correspond [
to the peak valuun shown in Table 6.2-1 of SAR are identified below.
Design Design Calculated Referenco Earagoter value va_lue Figure
- 45 poig 39 psig Figure 6.2-6
- 1. Drywell pressure 3400F 3380F Figure 6.2-13
- 2. Drywell temp.
Wetwell pressure 45 psig 26 psig Figure 6.2-6 3.
! W ZZ '92 01:ICori G E ILCLEM ELD J
. p y -3(r -g Wetwell temp. 2190F 2070F Figure 6.2-8 4.
(+) 16 Figure 6.2-6
- 5. Drywell-to- (+) 25 Wetwell differ. paid psid
(-) 1.5 Figure 6.2-17 presnuro (-) 2
(*: Figures correspond to those in SAR)
ISSUE:
~
Provide additional information concerning the subcompartment analysis (This inforcmation has been provided and is being reviewod) n In May 6, 1992 meeting, GE identified and described analytical rtthods and ant,umptions unod in performing the SAR subcompartment analynAs, and NRC identified and described a couple of inconsistencies observed in the subcompartment analysis results presented in SAR. In conclusion, GE agreed to
- 1. make available mass and energy blowdown data used in the subcompartment analysis to NRC;
- 2. chock SAR analysis jnput data and calculation results, and [
explain and clarify the inconsistencies observed by NRC;
- 3. provide a detailed description of computer program used for the subcompartment pressurization analysis; and
- 4. address SRP requirement for a 40% design margin in the calculated peak pressure values.
RECPONSE:
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7 The following paragraphs provido status and response to the items identified as above.
- 1. _B_ lowdown Datn Mass and energy blowdown data for all break cases which were considered and analyzed in the SAR subcompartment analyson were mado available to !!RC ( Chang-Yang Li/Chet Ponluony ), faxed on May 11, 1992.
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- 2. SAR Results In 5/19/92 GE/NRC phone call, GE cxplained the SAR input data, annumptions and results, noted that the SAR results are consistent with the analysis input data, assumptions and interconnection paths among subcompartment nodes. GE explained and provided clarification for the inconsistencies identified by NRC in 5/6/92 meetings. IfRC understood GE explanation and clarification of the SAR analysis results.
- 3. Subcompartment Analysis __ Method The following paragraphs provide a description of GE engineer compu*.er program, Subcompartment Analysis Method (SCAM), which was used in performing the subcompartment prescurization analyses prosented in SAR. Subcompartment pressurization analyses for Mark III standard plant were based on SCAM. This computer program, SCAM, has boon checked out against NRC specified 13 subcompartment standard problems, and overall SCAM meets the critoria for subcompartment analysis set forth by;the NRC.
SCAM is a transient, thermal-hydraulic digital computer program for uso in calculating thermodynamic conditions ir containment subcompartments after a loss-of-coolant accident. This program
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permita calculation of multiple nodo cases with user-def ine d flow paths between nodes, a self-choking compressible flow model, and modeling of momentum effects in inter-compartmental flow at the beginning of the problem.
SCAM integrates mass and onergy for each of the flow components in ,
each subcompartment through each timo step. Thena are known at each time step and are used to determine the temperature and pressure of each subcompartment as a function of time. The transient thermodynamic model is given the mass and energy present in each ~
compartment and required outputs are the temperature and pressure of
?ach compartment. Liquid is treated as a separate thermodynamic system in SCAM, and flow of liquid between subcompartments is }
proportional to entrained volume. The flow model used in SCAM for inter-compartmental flow is same vent flow model as that used in GE M3CPT computer code. Extensive verification of the model with experimental results has been conducted, as described in document NEDO-20533.
The key assumptions embedded in the code are:
- a. No heat transfer in calculated between the flowing components
-and the subcompartment walls. _
- b. Homogeneous mixing of air and water vapor is assumed in the subcompartmonts and in the flow paths,
- c. No gravitational potential energy is included in the flow energy equation,
- d. Initial compartment components are_ assumed to be air and water vapor.
- e. Air is treated as an ideal gas.
4
t%Y II *?2 01:27FM G E rU: LEAR ELDG J F .10 ' :. .
- 4. 40% Mar 91D As noted in 5/19/92 phone call, SAR analysis results will reflect ,
40% design margin in calculated values, ccnoistent with SRP .
requirements.
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f%Y 22 '92 01:29Pf1 G E f D'LEM ELIG .T P.1E - 1 E (mh PRIMARY CONTAINMENT PRESSURE RESPONSE FEEDWATER LINE BREAK l
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DRYWELL PRES $URE ST ARTS DECREASING DUE TO COLD F EEDWATER D RYWELL PR ESSUR E (psial 40 -
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MARK ill CONFIGURATION ABWR CONFIGURATION "[
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E VENT GEOMETRICAL CONFIGURATION -- MARKill AND ABWR i
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Elevations relative to RPV invert EL. 0.0.
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