17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

Advanced Analysis of the CEA-NEA/OECD VVER-1000 Coolant Transient Benchmark with the Coupled System Code ATHLET/BIPR-VVER

S. Nikonov 1 , M. Lizorkin 1 , S. Langenbuch 2 , K. Velkov 2 1 RRC KI, 123182 Moscow, Russia 2 GRS mbH, 85748 Garching, Germany

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

CONTENT

 Introduction  ATHLET/BIPR-VVER reactor pressure vessel model - mixing at assembly head  Exercise 1 of Phase 2 of the CEA-NEA/OECD VVER-1000 Coolant Transient Benchmark  Thermocouple correlation  Further developments  Summary

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

INTRODUCTION

 The nodalization of the RPV and a correct description of the mixing phenomena in the RPV plays a very big role on the accuracy of the predicted local core parameters which are needed to check the acceptance critera.  Recent studies proved that additional modelling of the assembly outlets by the coupled code ATHLET/BIPR-VVER is necessary in order to take into account the fluid mixing phenomena at the thermocouple location  Correlation based on measured thermal necessary for correct comparison couples‘ values at core outlet (for VVER-1000) with the real coolant temperatures at those positions are  In order to meet all these additional requirements, new models have been included in the coupled code ATHLET/BIPR-VVER and an international Benchmark problem based on experimental data is recalculated

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

DW_CAM-010 DW_CAM-001

NODALIZATION OF THE REACTOR VESSEL (OPTIMAL nodalization schema)



16 down comers

modelled with 16 parallel thermal-hydraulic channels (PTHC) with

cross flows (CF).

•

16x7= 112 bottom plenums

(2 levels) modelled with 118 PTHCs with

CFs

which describe the volume of the reactor bottom part with the perforated elliptical bottom plate up to the fuel assembly support plate  163 + 163 = 326 PTHC in the core (2:1) – 2 PTHC per assembly – – 163 for the assembly flow 163 for the control rod guide tube flow  3 different types of guide tube channels – – – Empty Burnable absorbers Control rods

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

158(14) 159(14) 160(14) 161(14) 162(14) 163(14) 149(15) 150( 0) 151( 3) 152( 0) 153( 9) 154( 0) 155( 4) 156( 0) 157(13) 139(15) 140( 4) 141( 0) 142( 7) 143( 1) 144( 2) 145( 8) 146( 0) 147( 3) 148(13) 128(15) 129( 0) 130( 8) 131( 0) 132( 0) 133( 5) 134( 0) 135( 0) 136( 7) 137( 0) 138(13) 116(15) 117( 9) 118( 2) 119( 0) 120(10) 121( 0) 122( 0) 123(10) 124( 0) 125( 1) 126( 9) 127(13) 103(15) 104( 0) 105( 1) 106( 6) 107( 0) 108( 0) 109( 6) 110( 0) 111( 0) 112( 6) 113( 2) 114( 0) 115(13) 89(15) 90( 3) 91( 7) 92( 0) 93( 0) 94( 6) 95( 0) 96( 0) 97( 6) 98( 0) 99( 0) 100( 8) 101( 4) 102(13) 76( 0) 77( 0) 78( 0) 79(10) 80( 0) 81( 0) 82( 5) 83( 0) 84( 0) 85(10) 86( 0) 87( 0) 88( 0) 62(16) 63( 4) 64( 8) 65( 0) 66( 0) 67( 6) 68( 0) 69( 0) 70( 6) 71( 0) 72( 0) 73( 7) 74( 3) 75(12) 49(16) 50( 0) 51( 2) 52( 5) 53( 0) 54( 0) 55( 6) 56( 0) 57( 0) 58( 5) 59( 1) 60( 0) 61(12) 37(16) 38( 9) 39( 1) 40( 0) 41(10) 42( 0) 43( 0) 44(10) 45( 0) 46( 2) 47( 9) 48(12) 26(16) 27( 0) 28( 7) 29( 0) 30( 0) 31( 6) 32( 0) 33( 0) 34( 8) 35( 0) 36(12) 16(16) 17( 3) 18( 0) 19( 8) 20( 2) 21( 1) 22( 7) 23( 0) 24( 4) 25(12) 7(16) 8( 0) 9( 4) 10( 0) 11( 9) 12( 0) 13( 3) 14( 0) 15(12) 1(11) 2(11) 3(11) 4(11) 5(11) 6(11)

(0) – empty guide tubes; (1-10) – control rod group numbers; (11-16) – burnable absorbers. Location of the different types of guide tube channels in the core

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

 48 bypass THC  24 axial nodes in the active core  2 upper plenums and 1 reactor head  163 +163 = 326 heat structures (HS) in the core – – 163 HS for the fuel assemblies 163 HS for the guide tubes  Neutronically the core is modelled 1:1 (1 node per assembly in X-Y plane)  All other details concerning nodalization and modelling of the primary and secondary loop can be seen in:

S. Nikonov, Lizorkin M., Kotsarev A., Langenbuch S., Velkov K.,

Optimal Nodalization Schemas of VVER-1000 Reactor Pressure Vessel for the Coupled Code ATHLET-BIPR8KN, 16th Symposium of AER, Bratislava, September 2006.

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

TRANSIENT:

Isolation (closure of SIV-1 and FW valve) of SG-1 at reactor power of 9.36% Pnom (Benchmark V1000CT – Phase 2, Exersice 1)

 Comparison of the cold and hot legs’ temperature agree very well with the measurements. The maximum differences are 1.8 K. These differences are small considering the reported measurements’ error of 2.0 K

.

 The differences in the predicted local coolant temperatures at the begin and at the end of the transient compared with the measured one are small. At t=0 s the maximum assembly coolant temperature deviation is 1.4 K, and at the end of the transient – 5.8 K.

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

558,0 556,0 554,0 552,0 550,0 548,0 546,0 544,0 542,0 540,0 0 544,0 543,5 543,0 542,5 542,0 541,5 541,0 0 COMPARISON WITH MEASUREMENTS – LOOPS‘ COOLANT TEMPERATURES

COMPARISON OF COLD LEG 1 TEMPERATURE HISTORIES COMPARISON OF HOT LEG 1 TEMPERATURE HISTORIES

558,0 556,0 554,0 6 DC 16 DC 24 DC 34 DC 48 DC MEASURED 552,0 Loop #1 550,0 548,0 200 200 546,0 400 600 800 1000

TIME [S]

1200 1400 1800 2000 544,0 0 400 600 800 1000

TIME [S]

1200 1400 1600

COMPARISON OF COLD LEG 2 TEMPERATURE HISTORIES

1600 6 DC 16 DC 24 DC 34 DC 48 DC MEASURED 2000 Loop #2 548,5 548,0 547,5 547,0 546,5 546,0 545,5 545,0 544,5 544,0 0 1800 200 200 400 600 800 1000

TIME [S]

1200 1400 1600

COMPARISON OF HOT LEG 2 TEMPERATURE HISTORIES

1800 2000 400 600 6 DC 16 DC 24 DC 34 DC 48 DC MEASURED 6 DC 16 DC 24 DC 34 DC 48 DC MEASURED 800 1000

TIME [S]

1200 1400 1600 1800 2000

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

543,0 542,8 542,6 542,4 542,2 542,0 541,8 541,6 541,4 541,2 541,0 0

COMPARISON OF COLD LEG 3 TEMPERATURE HISTORIES

543,0 542,8 542,6 542,4 542,2 542,0 541,8 541,6 541,4 541,2 541,0 0 6 DC 16 DC 24 DC 34 DC 48 DC MEASURED 200 400 600 800 1000

TIME [S]

1200 1400 1600 1800 2000

COMPARISON OF COLD LEG 4 TEMPERATURE HISTORIES

Loop #3 6 DC 16 DC 24 DC 34 DC 48 DC MEASURED Loop #4 200 400 600 800 1000

TIME [S]

1200 1400 1600 1800 2000 547,0 546,5 546,0 545,5 545,0 544,5 544,0 0 547,0 546,5 546,0 545,5 545,0 544,5 0

COMPARISON OF HOT LEG 3 TEMPERATURE HISTORIES

200 400 600 800 1000

TIME [S]

1200 1400 6 DC 16 DC 24 DC 34 DC 48 DC MEASURED 1600 1800 2000

COMPARISON OF HOT LEG 4 TEMPERATURE HISTORIES

6 DC 16 DC 24 DC 34 DC 48 DC MEASURED 200 400 600 800 1000

TIME [S]

1200 1400 1600 1800 2000

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

OUTLET COOLANT TEMPERATURE AT ASSEMBLY #64 OUTLET COOLANT TEMPERATURE AT ASSEMBLY #79

282 276 280 275 278 274 276 273 274 ASSEMBLY 272 ASSEMBLY 272 G. TUBE 271 G. TUBE 276 270 0 275 274 273 272 271 270 269 0 200 200 400 600 800 1000

TIME [S]

1200 1400 1600

OUTLET COOLANT TEMPERATURE AT ASSEMBLY #80

1800 2000 400 270 0 200 400 600 800 1000 1200 1400 1600

TIME [S] OUTLET COOLANT TEMPERATURE AT ASSEMBLY #89

1800 2000 274 ASSEMBLY G. TUBE 273,5 273 272,5 272 271,5 271 270,5 ASSEMBLY G. TUBE 600 270 800 1000 1200 1400 1600 1800 2000 0 200 400 600 800 1000 1200 1400 1600

TIME [S] TIME [S]

Comparison of outlet coolant temperature histories for different types of assemblies with different guide tube channel usage 1800 2000

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

Experiment Assemblies Guide tubes 10% mixing 20% mixing 30% mixing 40% mixing 50% mixing 60% mixing 70% mixing 80% mixing Mean ( o C)

275.08

275.86

275.06

275.13

275.19

275.24

275.29

275.33

275.36

275.39

275.41

Max ( o C) Min ( o C)

285.50

270.40

288.26

271.00

286.97

270.35

287.09

270.41

287.19

270.46

287.27

270.50

287.34

270.54

287.40

270.57

287.45

270.60

287.50

270.63

287.54

270.65

16.80

16.83

16.85

16.80

16.90

Max Min ( o C)

15.10

17.26

16.62

16.68

16.73

16.76

Maximum Deviation (

6.40 ( 51) 5.69 ( 51) 5.75 ( 51) 5.80 ( 51) 5.85 ( 51) 5.89 ( 51) 5.92 ( 51) 5.95 ( 51) 5.98 ( 51) 6.00 ( 51)

o C) (Assembly #) Minimum Deviation (

-3.49 ( 31) -4.12 ( 31) -4.06 ( 31) -4.02 ( 31) -3.98 ( 31) -3.94 ( 31) -3.91 ( 31) -3.88 ( 31) -3.86 ( 31) -3.84 ( 31)

o C) (Assembly #) SIGMA

4.0259

3.4922

3.4809

3.4805

3.4867

3.4968

3.5091

3.5225

3.5364

3.5505

Comparison of different flow mixing relations on the model accuracy for the end of the experiment

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

THERMOCOUPLE CORRELATION

(interpretation of the TC measurements) T TC = (T GT + C M * T ASS ) / ( 1 + C M ) T TC

- thermocouple temperature

T GT

- guide tube coolant flow temperature

T ASS

- fuel assembly coolant flow temperature

C M

- mixing coefficient (0.2)

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

FURTHER DEVELOPMENTS

 Confirmation of the TC correlation for nominal and intermediate reactor power (in preparation )

COOLANT TEMPERATURE AT THC #89

274 273 The TC correlation is derived from 272  data set with a heat up of only 3 o C 271 270 and reactor power of 9.4 % P nom 269 INLET OUTLET 268 0 200 400 600 800 1200 1400 1600 1800 1000

TIME [S]

Dependence of the mixing coefficient at assembly head from the type of the guide tube application (empty, inserted rods, CRs insertion depth, burnable absorbers) 2000  Study the influence of different coolant temperature in the guide tubes on the accuracy of the microscopic cross section generation and homogenization procedures

17th Symposium of AER, Yalta, Crimea, Ukraine, Sept. 24-29, 2007

SUMMARY

 A method is developed which allows to take into account the correct interpretation of the TC measurements (still subjected to validation)  Additional modelling in the coupled code ATHLET/BIPR-VVER is developed to meet the requirements of the correct description of the fluid mixing phenomena at the places where the TCs are located (additional PTHC introduced)  The Exercises of Phase 2 of the CEA-NEA/OECD VVER-1000 Coolant Transient are recalculated introducing the new TC correlation and the data are compared with the old ones  The coupled system code ATHLET/BIPR-VVER is able to predict the coolant temperature at the assembly outlet within a rather high accuracy even though ATHLET system code is based on 1-D thermal-hydraulic pipe models