ML20087K657

Blind Analysis for Geraffe Helium Tests H1 - H4

ML20087K657
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Site:	05200004
Issue date:	08/31/1995
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,

BLIND ANALYSIS FOR GIRAFFE IIELIUM TESTS HI- H4 August, 1995 A J lilich (GENE) 9508240069 950818 PDR ADOCK 05200004 A PDR

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. TABLE OF CONTENTS . _l j

1.'0 INTRODUCTION-

,, 2.0. TRACG MODEL AND NODALIZATION 3.0' COMPARISON TO THE SBWR NODALIZATION t-4.0 RESULTS OF BLIND CALCULATIONS 5.0 DISCUSSION

6.0 REFERENCES

s E

1.0 INTRODUCTION

A blind analysis was conducted to predict the results of a series of four tests conducted at the GIRAFFE facility in Kawasaki, Japan. The facility is described in Ref. I and a schematic of the plant is shown in Fig 1. This is part of a validation effort for the TRACG code for application with the SBWR. The model described in this report was originally developed by the TOSHIBA corporation. Modification were made at GENE for application to the GIRAFFE helium test configuration.

This report is divided into two main portions. The first provides a detailed description of the GIRAFFE TRACG model; the second presents the results of the analysis for the four tests. A brief description of the four helium tests is included in the introduction. A more detailed description along with a discussion ofinstrumentation, shakedown, data acquisition, and test control is found in Ref 2 GENE document 25A5677, Revl GIRAFFE HELIUM TEST SPECIFICATION dated May 10,1995.

The test objectives of the GIRAFFE / Helium Test Program are:

1. Demonstrate the operation of a passive containment cooling system with the presence of a lighter-than-steam non-condensable gas, including demonstrating the process of purging noncondensables from PCC condenser. (Concept Demonstration)

This test objective addresses phenomena DW3, PC8, and XC6, as defined in Table 6.1-1 of the TAPD.

2. Provide a database for computer codes used to predict SBWR containment system performance in the presence of a lighter-than-steam noncondensable gas, including potential systems interaction effects (IntegralSystems Tests)

This test objective addresses phenomena XC6, as defined in Table 6.1-1 of the TAPD.

3. Provide a tie-back test, which includes the appropriate Quality Assurance documentation to repeat a previous GIRAFFE test, thereby reinforcing the validity of the previous GIRAFFE testing.

This test objective validates earlier GIRAFFE data; additionally it provides data that may be used to address phenomena DW3 and PC8 as defined in Table 6.1-1 of the TAPD.

The four helium tests conducted and analyzed are:

- Test H1 The purpose of this test is to provide a base case with initial conditions for the SBWR containment at one hour from the initiation of a LOCA caused by a rupture of the main steam line. At the start of this test, the drywell will contain a mixture of steam and ,

nitrogen. This case will demonstrate the operation of the PCCS system without the presence of helium.

- Test H2 The purpose of this test is to demonstrate the effects of a lighter than steam non-condensable gas on the operation of the PCC system. The test is a repeat of H1, but with helium replacing the total volume of nitrogen in the drywell. The results from this test .

can be compared to H1 results in order to determine the effects of a lighter than steam non-condensable gas on the PCCS system.

- Test H3 The purpose of this test is to demonstrate the effects of a high concentration of a lighter than steam non-condensable gas on the operation of the PCCS system. This test will confirm the efficacy of the PCCS system for conditions resulting from result of a significant amount of metal water reaction. For this test an estimated initial bounding concentration of hydrogen is postulated; the initial mass of helium in the dry well is based on assuming that approximately 20% of the hydrogen generated by a 100% SBWR metal-water reaction is initially in the drywell.

- Test H4 The purpose of this test is to confirm the assumption that the hydrogen generated by the metal water reaction will not permanently build up in the PCCS condensers. In order to confirm this, helium will be continuously injected into the upper drywell for the first hour of the test until the total amount of helium equal to that used for H3 is reached.

The remainder of this report deals with a brief comparison of the SBWR modeling with the GIRAFFE nodalization and a discussion of the results of this analysis.

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2.0 TRACG MODEL AND NODALIZATION The foremost feature of the GIRAFFE TRACG input deck model is the use of a single three dimensional VSSL component which models the reactor pressure vessel (RPV), the suppression chamber (S/C), upper portion of the dry well (D/W), the passive containment cooling (PCC) pool, the gravity driven cooling system (GDCS) and a portion of the PCC unit. The model is illustrated in Fig 2. The three dimensional components are connected together by a series of one dimensional components listed in Table A at the end of this section. These one dimensional components are represented by a combination of TEES, VALVES, and PIPES. The major similarities and differences between the GIRAFFE modeling and that of the SBWR are discussed in Section 4. Differences in nodalization are in part due to the historical origin of the two decks and the fact that there are inherent differences between the configurations.

2.1 3-D VESSEL The GIRAFFE wetwell, upper drywell, PCC and GDCS pools and a portion of the PCC unit are represented as three dimensional components. The VSSL01 component has seventeen levels, three rings and one azimuthal sector. The first seven levels in ring 1 of the VSSL01 component are used to model the GIRAFFE RPV. The first four levels in rings 2 and 3 represent the wetwell. Level 5 rings 2 and 3 along with levels 6 and 7 in ring 2 are dummy cells. Levels 14 to 17 in rings 2 and 3 are also not used in the model.

The upper dry well is level 6 and 7 in ring 3; the remainder of the drywell containment is modeled using 1-D components. The PCC pool is composed of 2 rings in levels 8 through 13. These same levels are utilized in ring 3 for the GDCS pool. Figure 3 shows a correspondence between the physical layout of the various components in the GIRAFFE facility and the TRACG representation. The PCC headers are also modeled with the 3-D vessel component as shown in Fig 4. The steam and water box have multiple connections modeled taking advantage of the VSSL flexibility.

2.2 RPV and Associated Piping The RPV in GIRAFFE is modeled with a combination of TEE components, and the electric heaters are modeled with a CHAN component; both are within the vessel described in the above section. TEE 16 is used to model the chimney while TEE 34 simulates the bypass flow. The chimney extends from the top of the heater to the bottom oflevel 4. CHAN08 is used to model the bundle with electric heaters in the vessel with four heated cells. The heaters transfer heat to the fluid in CHAN08 resulting in two phase flow. Also connected to the RPV are VLVE02 and VLVElI which simulate the main steamline break to the drywell and the depressurization valve. A final connection is the VLVE40 in level 2 which represents the condensate return piping from the GDCS.

2.3 PCC The PCC unit is used to transfer the decay heat into the PCC pool. The pool itself consists of two rings and six levels with the fluid volumes representing the actual available cooling water and steam regions.

The PCC heat transfer unit is more complicated and is illustrated in Fig 3. It consists of a steam box which acts as the receptor for the mixture ofincoming (via VLVE03) steam and non-condensable gas. From this box, extending vertically downward, are three 1.8 meter tubes ( represented by PIPE 54, PIPE 55, and PIPE 56 ) that are connected to the  :

water box. In addition there is BREK21 and VLVE13 assembly attached to the steam box. It represents a potential capability to flush the PCC unit in a simulated pretest. The ,

valve is set to close at the time zero and is not employed in this analysis. From the water box, two lines are attached; VLVE05 is the non-condensable gas vent line which connects to level 2 of the wet well. The other is VLVE04 which is the condensate drain line to level 9 of the GDCS. These are shown in Figure 3.

The upper steam box is modeled with 2 vessel levels ( 16 and 17 ) in ring 1. The lower  ;

water box is more involved. The upper portion of this box consists of two levels ( 14 and 15 ) in ring 1. Vessel representation is needed to accommodate the multiple junctions from the three tubes and two pipes. The lower portion of the of the water box is simulated by PIPal5. A one dimensional component was selected so that heat transfer could be modeled between the water box and PCC pool. The upper steam box is insulated. All volumes have been appropriately accounted for.

The pool water boils, inducing natural circulation in the pool, with the up-flow in the inner ring and the down-flow in the ring 2. The steam formed from the pool is vented to BREK09 via PIPE 16 at the top of the pool in level 13 as shown in Figure 3.

I 2.4 Main Vent and Vacuum Breaker l

The main LOCA vent in the GIRAFFE model is represented by PIPE 06 (Figure 3) which l starts at the upper drywell (level 6 ) enters the top steam portion of the wetwell (level 4), l and is submerged in the supression pool. Flow through this pipe will occur only when j the drywell pressure exceeds the wetwell pressure by more than the hydrostatic head )

corresponding to the submergence of the vent in the supression pool.

There is a single vacuum breaker VLVE07 (Figure 3 ) in the GIRAFFE model connecting level 6 of the dry well with level 4 of the wetwell. The valve will open when the dry well pressure falls below a set point and will close when a second set point is reached. These set points are discussed under initial conditions.  ;

i l

2.5 Component Heat Loss and lleat Capacity The heat losses from the GIRAFFE vessels (as shown in Fig 3) and piping to the i environment or to other components have been included in the GIRAFFE input model. l Component to component heat transfer is accounted for between the components used to represent the PCC and other containment components. As noted earlier, heat transfer between the PCC unit and the PCC pool is modeled. Also taken into account are losses from PCC vent and drain piping along with the main LOCA vent. Additional piping losses to the ambient include the PCC steam / gas supply line, main steam line break line, and the DPV line.

For most vessel heat losses, the double-sided heat slab in TRACG is used to model the metal wall of the vessel. The insulation and outside film resistance are combined into an overall outside heat transfer convective coefficient and the outside ambient temperature is speciDed. The same is done for the one dimensional components losing heat to the environment. For component to component heat transfer (e.g. the PCC tubes), the inside and outside heat transfer coefficients are determined by TRACG.

l 2.6 Decay lieat To represent the decay heat in the GIRAFFE TRACG input model, the decay heat curve from previous GIRAFFE tests was used. The decay rate is established from the May-  ;

Witt decay heat curve. It became necessary to establish only the initial power which is specified as part of the initial conditions. TRACG modeling does not allow ambient losses from inner rings. Specifically, the RPV power, which had a measured 8 kW heat loss, is simulated by adjusting the initial power by a minus 8 kW. Other adjustments are ,

summarized in the initial conditions.

2.7 InitialConditions ,

I Ref 2 describes the state of the GIRAFFE facility prior to the Helium series of four runs. I GENE is developing a modified version of TRACG that is capable of handling multiple  ;

non-condensable gas species. For the blind analyses, however, the standard TRACG l version was employed. For the post-test analysis, it is planned to use both versions.

This standard version does have a non condensable gas option which provides the l capability to account for air in the presence of steam; additionally, it provides the l

flexibility to change two properties (i.e. R - Gas Constant, Cv - Specific Heat at Constant Volume) which are used in the gas computations. This feature was used to represent the gas in the system. For H1, the properties of nitrogen were used; for H2 the properties of helium were used; for H3 a weighted average of 80% helium and 20% nitrogen was used.

The 114 analysis represents the weighted gas average used in H3; though it is noted that using pure helium for this case iesulted in insignificant differences for the results presented in this report.

In addition to the GIRAFFE facility geometry, the initial thermodynamic conditions in the system prior to initiation of the transient tests must be part of the TRACG input model. For the long term cooling phase of the LOCA transient, the GIRAFFE tests begin approximately one hour afler the accident initiation. Conditions at this time in the transient were derived from SBWR TRACG calculations for the case of a guillotine rupture of one of the steam lines. The SBWR calculations show that the thermodynamic conditions throughout the system are relatively stable at this time in the LOCA transient.

The RPV blowdown is complete, the GDCS pools have dumped a major portion of their inventory to the RPV, the decay heat has overcome the subcooling introduced by the injection of GDCS water, and steaming due to boil-off has resumed. The pressure difference between the RPV and the DW is sufficient to push the boil-off steam through the flow path provided by the break and the open depressurization valves. ,

The specified initial pressures and temperatures for the individual vessels were established in the model by long (i.e. 2000 second) steady state runs.

The initial conditions that are to be incorporated can be divided into two categories.

First, those conditions which apply to all four tests (Table B); second, those conditions which are germane to the individual tests (Table C). For purposes of completeness, the two tables from Ref 2 which define in detail the two sets of conditions are included as part of this section.

The last value to be established in the initial conditions is that ofinitial power. During the actual test runs, the facility employed microheaters in an attempt to balance heat losses to the ambient. Despite the microheaters, heat losses were significant. Values for the heat losses were obtained from Ref 3. as follows:

Vessel Heat losses (kW)

RPV 8 D/W 12 GDCS 7 S/C 0 The test was specified with an initial RPV power of 93 kW to compensate for the heat losses. As mentioned in Sect 2.6, TRACG does not allow for ambient heat losses from inner rings of the vessel; therefor, the initial 93 kW loss adjusted to 85 kW to account for the RPV heat loss.

The adiabatic conditions in the wetwell were simulated by setting all the double sided heat slabs (DSA) in levels 1 to 4 to zero. These areas are used in the calculations for heat loss to the ambient. The convective heat transfer coefficient for the remainder of the vessel was chosen such that the upper drywell lost an appropriate amount of heat

corresponding to its surface area; the effective heat transfer area (DSA) for the GDCS pool was adjusted to match its appropriate heat loss.

The final adjustment was to the TRACG control system which regulates the vacuum breaker. Contained within the control system logic are two constants which represent the set points for opening and closing. The valve will open when the wetwell pressure is 3240 Pa higher than drywell; the valve will close when the pressure difference is less than 2060 Pa These set point values were incorporated.

n 9

l 1

TABLE A l 1 - D COMPONENT LIST COMP # DESCRIPTION 2 VLVE - main steamline break 3 VLVE - Upper DW to PCC steam box 4 VLVE - Drain line from bottom of water box to GDCS 5 VLVE Gas vent line from top of water box to WW 6 PIPE - Main LOCA 7 VLVE - Vacuum breaker 8 CIIAN - Fuel channel simulating electric heaters 9 BREK - Pressure boundary to ambient for pipel2 11 VLVE - Depressurization line 12 PIPE - Steam vent line from PCC tank to ambient 13 VLVE - Pre test valve for PCC unit. NOT used in this analysis 15 PIPE - Bottom of water box 16 TEE - Chimney 21 BREK - Pressure boundary for unused VLVE13 30 TEE - Annulus of DW 31 PIPE - DW portion connecting annulus with lower DW 32 PIPE - Lower DW 33 FILL - Zero velocity fill 34 TEE - Channel bypass flow 35 FILL - Zero velocity fill 40 VLVE - Condensate return from GDCS to Level 2 of RPV 41 VLVE - Equalization line between upper DW and Level 12 of GDCS '

54 PIPE - PCC tube #1 55 PIPE - PCC tube #2 56 PIPE - PCC tube #3 88 FILL - Zero velocity fill '

77 FILL - Gas injection to upper DW. ONLY MODELED IN II4

- ' M U GENuclearEnergy GIRAFFE He Integral Systems Tests Initial Conditions Parameter Value Tolerance RPV Pressure (KPa) 4(,m 295 6KPa Initial Heater Power (Kw) [4 peat loss compensation 1Kw RPV Water Level (m)* 12.0 0.150m -

Drywell Pressure (KPa) 294 4KPa Wetwell Pressure (KPa) 285 14KPa Wetwell Nitrogen Pressure (KPa) 240 4KPa GDCS Gas Space Pressure (KPa) 294 14KPa  ;

GDCS Nitrogen Pressure (KPa) 274 4KPa Suppression Pool Temperature (K) 352 2K PCC Pool Temperature (K) 373 2K GDCS Pool Temperature (K) 333 2K GDCS Pool Level * (m) .

Suppression Pool Level * (m) 3.25 0.075m  !

PCC Pool Collapsed Water Level * (m) 23.2 0.075m PCC Vent Line Submergence (m) 0.95 0.075m Referenced to the Top of Active Fuel (TAF).

GDCS poollevel should be positioned in hydrostatic equilibrium with the RPV level  !

(including an appropriate adjustment for temperature difference).

i i

TABLE B  :

L) GENuclearEnergy .

i GIRA' le Integral Systems Test Matrix i

DrywellInitial Partial Pressures (KPa) ( 2KPa)

GIRAFFE Helium Test No. Injection Rate Nitrogen Steam Helium  ;

(Kg/sec)

H1 0 13 281 0 j H2 0 0 281 13 H3 0 13 214 67 l

H4 0.00027 13 281 0 i

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3.0 COMPARISON TO THE SBWR NODALIZATION l i

ideally, the nodalization for the GIRAFFE model should be similar to the existing SBWR  !

nodalization. However, there will be differences related to the differences in physical '

• configurations. The nodalization is similar in the upper DW, WW, and PCC which are _

considered crucial to the purpose of the GIRAFFE helium tests. A brief one on one l comparison is best shown in tabular form.

]

Component GIRAFFE SBWR RPV VSSL - 7 levels VSSL - 8 levels I ring 2 rings .

GDCS VSSL - 6 levels VSSL - 2 levels I ring 2 rings PCC pool VSSL - 6 levels VSSL - 6 levels 2 rings 2 rings WW VSSL - 4 levels VSSL - 4 levels 2 rings 2 rings  !

DW  !

Upper VSSL - 2 levels VSSL - 4 levels I ring 2 rings Annulus 1 - D, 6 cells VSSL - 5 levels 2 rings Lower 1 - D, 3 cells VSSL - 1 level .

2 rings and 1 - D,3 cells 1

PCC tubes 1 - D, 8 cells 1 - D, 8 cells The GIRAFFE RPV has one ring compared to two rings in the SBWR. It is felt that the +

one ring design is sufficient to model the RPV flow since TEE 34 models the guide tube .,

and bypass regions along with two leak holes between the channel. l

b GIRAFFE represents the upper DW as part of the 3-D VSSL (same as SBWR) and the remainder as 1-D. The three 1-D components (TEE 30, PIPE 31, and PIPE 32) were nodalized such that the cell numbers would come close to matching cell numbers in SBWR. The mid and lower sections of the DW in GIRAFFE are long and one dimensional and are represented as 1-D components.-

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1 4.0 RESULTS i x

Four plots for each test are presented

• ~

Total pressure of DW and WW.- ..

• Noncondensable gas Pressures in upper DW -

• PCC heat transfer and decay heat

• Noncondensable gas pressure for various DW elevations-Two plots for comparison

• DW pressures HI - H4

• WW pressures HI - H4-I' I

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HI -I I D/W PRESSURE 2 W/W PRESSURE 4.00E+05 iiiiiiii, iiiiiiiii siiiiiiii iiiiiiiii iiiiiiiii gigiiiiii iiiiiiiii iiiiiiiii iiiiiiiii siiiiiii, 3.40E+05 - -

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H2-1 1 2 W/W PRESSURE D/W PRESSURE 4.00E+05 iiiiiiiii iiiiiiiii siiiiiisi iiiiiiiii iiiiiiiiisiiiiiiiigigigiiiigiiiiiiiiiiiiiiiiiiiiiiiiiii 3.40E+05 - -

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i 5.0 DISCUSSION i The transient sequences depicted in all of the plots in section 3 can be described as follows. At the start of the transient, steam flows from the RPV to the DW and mixes  !

with the particular gas already in the DW. The drywell pressurizes and forces flow of the mixture through the PCC to the wetwell.' Initially, some of the steam is condensed in the heat exchanger unit , but the PCC is basically operating in a purge mode. Uncondensed ,

steam and gas are transported from the DW to the WW. The transfer of gas to the WW  !

gas space increases the WW pressure. Both the DW and WW pressure rise to a l maximum in approximately one hour. The time of these peak pressures is determined by the amount of time it takes to purge the gas from the upper DW. The WW pressure then decreases slightly due to heat transfer from the gas to the liquid. With the upper DW essentially purged of gas, and the heater power declining, the PCC is able to remove more ,

energy from the DW than is being added by the RPV steam. This coupled with the heat losses from the DW results in the pressure starting to decrease. The final drywell - ,

pressure will be bounded by the wetwell pressure plus the static head of water i corresponding to the PCC vent submergence. l 1

In all cases there is an accumulation of a portion of the non-condensable gases in the lower portion of the DW. This region has the highest rate of heat transfer rate due to inaccessibility of micro heaters. Condensation of steam in the bottom of the drywell l induces a downward velocity in the lower drywell in all cases. In the 1-D drywell,  !

buoyancy is not a factor (i.e. as steam moves downward, any gas in that fluid cell will  !

travel with it).

i i

For the base case H1, the drywell pressure falls below the pressure in the wetwell. The pressure difference exceeds the value of the set point resulting in the opening of the vacuum breaker. A burst of gas / steam is injected into the upper drywell. The DW pressure rises immediately and begins to fall again as the PCC is able to handle the heat i load with the nitrogen that reenters the tubes. The vacuum breaker opens and closes three times in the 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> with the DW pressure staying close to the WW pressure. The associated bursts of nitrogen can be seen in the plot of the upper DW gas pressures.

For 112, the vacuum breaker valve opens only once during the analysis. The substitution of helium appears to induce a sufficient degradation of the PCC heat transfer efficiency j such that the DW pressure rises above the wetwell pressure and remains slightly above it. q For 113, the vacuum breaker valve does not open since the DW pressure does not fall below the pressure in the WW. The higher concentration of the simulated helium / nitrogen mixture results in still further degradation of the PCC units. The peak j

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i pressure is higher; this corresponds to the higher amount of non condensable gas in the drywell initially.

For H4, the DW and WW pressures reach the highest peaks of the four tests because helium is injected into the drywell in addition to the steam generated by decay heat.

Unlike H3, the DW pressure begins a more rapid decline and approaches the WW pressure towards the end of the analysis.

The last two plots show comparisons of the four wetwell and drywell total pressures.

They all have similar responses; the greater concentrations of non condensable gases exhibiting the higher peak pressures.

Conclusions The four GIRAFFE / Helium series of tests (H1-H4) have been analyzed with TRACG.

These are blind predictions for which the analyst had no knowledge of the exact test initial conditions or the test results.

The predictions show that:

1.) The maximum drywell and wetwell pressures for H1 and H2 (with Helium replacing Nitrogen) are very similar. The pressure histories also track closely 2.) Test H3 and H4 with much higher amounts of helium show no anomalous behavior.

The PCC clears the helium / nitrogen mixture (as used in the TRACG calculations) 3.) While the vacuum breaker behavior is different in the various cases, this has little impact on the integrated heat removal and the overall pressure history of the DW and WW.

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6.0 REFERENCES

i-  ;

I. . 1. K. M. Vierow, " GIRAFFE Passive Heat Removal Testing Program", NEDC-32215P J ,

f REV 0 Class 3 June 1993  !

l  !

2. GIRAFFE HELIUM TEST SPEC, May 10,1995. GENE 25A5677, REV 1  ;

l_  !

L- 3. Shakedown Test Series, May 1995. TOSHIBA TOGE110-T18 l'  ;

I i -

l 4

l l

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