XT-ADS Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety”

Forschungszentrum KarlsruheTechnik und Umwelt

IRS /FzK W.M.SchikorrEUROTRANS WP1.5 Safety Meeting : Madrid, Nov 13-14. 2007 1

XT-ADS Transient AnalysisXT-ADS Transient Analysis

M. Schikorr, E. BubelisM. Schikorr, E. Bubelis

EUROTRANS: DM1 WP1.5 : “Safety”

Madrid , 13-14 November 2007



1. Design Criteria for XT-ADS

2. XT-ADS design Data for Transient Analysis

3. Some XT-ADS results to the ULOF transient

Topics:



1. Neutron Flux sufficiently high ( ~ 2.0E15 n/cm2/s ) to allow XT-ADS to operate as an irradiation facility (i.e. for MA sub-assembly testing).

2. Operate XT-ADS at k_eff ~ 0.95 - 0.97 with several (8?) test rig positions. Design currently optimized by Task Force (Struwe).

3. Design core and primary system in such a manner to allow sufficient natural convection flow rate especially to sustain a ULOF transient for at least 30 minutes without „large number“ of pin failures (i.e. via gas blowdown. Note: this does not mean clad melting !!)

1. Some important XT-ADS Design Criteria:



Assure a sufficiently large natural convection flow rate ( > 25 % nominal flow) under ULOF conditions.

This implies :

1. keep pressure drop across the core „low“ (~< 0.75 bar) by selecting an appropriate fuel pin / subassembly design

2. minimize pressure losses throughout the primary / DHR system such that total system pressure loss <~ 1.0 – 1.1

bar

3. assure a height differential between the core midplane and the heat sink midplane of at least ~ 2.00 m

XT-ADS ULOF Design Criteria requires :



1. Select an appropriate pin / sub-assembly design by optimizing the pin diameter, pin pitch, wrapper dimensions etc.

2. Minimize the number of grid-spacers and optimise design (reduce grid spacer thickness to a minimum: 0.25 mm from currently 0.50 mm)

3. Keep the length of the fuel pin low

4. Optimize inlet and outlet support structures to keep pressure drops small

Keeping P_core in the XT-ADS Design low:



Most current XT-ADS Design Data: 580mm Lower Gas Plenum

Thermal power 56.85 MW

Average Linear Power 146.1 W/cm

Axial Form Factor f_ax 1.257Radial Form Factor f_rad_hot_SA 1.312

f_peak_pin 1.048f_rad_tot 1.375f_tot_hot_SA 1.649f_tot_peak_pin 1.728

580

Fuel Bundle and Pin Design

Dimensions UnitsNumber of pins 91Number of anchoring SS pins per SA 1Active Fuel Heights 60.0 cmPitch to Diameter Ratio 1.410Pin diameter 6.55 mmPitch 9.24 mmAnnulus diameter 1.6 mmNumber of Pin rows in SA 5Clad Thickness 0.475 mmCold Gap between clad and fuel 0.100 mmPellet diameter 5.400 mmAvailable inter-pin gap for spacers 3.8 mmSpace pin - inner wrapper 1.3350 mmWidth over inner flats 89.20 mmThickness Wrapper 2.00 mmGap between SA´s 3.00 mmWidth over outer flats (wrapper) 93.20 mmWidth over unit cell (includes Sgap) 96.20 mm

Number Fuel Subassemblies 72Number of SA spallation zone 3Number Grid Spacers 3



Peak Burn Up 100 MWd/kgiHM

For MOX Fuel use Philipponneau Correlation for thermal conductivity

BOC EOCO/M 1.975 2Porosity 5% 7.50%

580

Other XT-ADS Data Inputs:

580mm Lower Gas Plenum

Heights difference core / heat sink 2.00 m

T_in 300 °CT_out 400 °CFlow Rate 3854 kg/s

Current Grid Spacer Design :

Proposed Grid Spacer Design:

Calc. Prim. System Pressure Drops: 4 Spacers @ 0.50mm thickness 0.604 barCore Inlet/Outlet 0.117 barFlow Friction 0.413 barTotal Core 1.134 barTotal Prim. System 1.564 bar

Assumed Zeta Factor (Ratio of Prim.System/Core Pressure Drop)

1.38

Calc. Prim. System Pressure Drops: 4 Spacers @ 0.25mm thickness 0.178 barCore Inlet/Outlet 0.117 barFlow Friction 0.413 barTotal Core 0.708 barTotal Prim. System 0.977 barAssumed Zeta Factor (Ratio of Prim.System/Core Pressure Drop)

1.38



XT-ADS Nominal Conditions at BOC :

BOC Axial Temperature Profile Average Pin, 146 W/cm and no oxide layer

383.6

350400

419

1025

823

928

621668

1189

300

400

500

600

700

800

900

1000

1100

1200

1300

-30 -20 -10 0 10 20 30Axial Core Position [cm]

Te

mp

era

ture

s [

°C]

Cladding

Coolant

Center Fuel

Surf Fuel

Avg Fuel

BOC Axial Temperature Profile Peak Pin, 201 W/cm and no oxide layer

414.6

369438

463

1263

9731098

684 731

1470

300

500

700

900

1100

1300

1500

1700


Te

mp

era

ture

s [

°C]

Cladding

Coolant

Center Fuel

Surf Fuel

Avg Fuel

Note: using Ushakov (Zhukov-bundle) instead of Subbotin will reduce clad temps by about 9 °C

XT-ADS :

Pin = 6.55mm OD

T_in = 300 °C

4 Grid Spacers @ 0.50 mm



XT-ADS Nominal Conditions at EOC :

Oxide Layer = 30 um

At 1 [W/m/K] oxide layer thermal conductivity

EOL Axial Temperature Profile, Avg Pin 146 W/cm and 30 um Oxide Layer

405

350400

438

918

753

866

588648

1084

300

400

500

600

700

800

900

1000

1100

1200


Te

mp

era

ture

s [

°C]

Cladding surf

Coolant

Center Fuel

Surf Fuel

Avg Fuel

EOL Axial Temperature Profile, Peak Pin 201 W/cm and 30 um Oxide Layer

444

369438

489

1175

928

1081

680756

1408

300

500

700

900

1100

1300

1500


Te

mp

era

ture

s [

°C]

Cladding surf

Coolant

Center Fuel

Surf Fuel

Avg Fuel

XT-ADS :

Pin = 6.55mm OD

T_in = 300 °C

4 Grid Spacers @ 0.50 mm

At EOC (~ 100 MWd/kg peak burnup):

Fission Gas Pressure in peak pin ~ 38.4 bar

Degraded thermal fuel conductivity (Philiponneau)



XT-ADS :

Pin = 6.55mm OD

T_in = 300 °C

No Oxide Layer

XT-ADS ULOF-ss

at BOC :

BOC ULOFss Temperature Avg Pin, 146 W/cm and no oxide layer

571.8

520

744

767

1191

980

1118

768

890

1378

300

500

700

900

1100

1300

1500


Te

mp

era

ture

s [

°C]

Cladding

Coolant

Center Fuel

Surf Fuel

Avg Fuel

Clad Failure Time ~ 240 hrs

BOC ULOFss Temperature Peak Pin, 201 W/cm and no oxide layer

638.4

572

848

878

1450

1152

1315

8541007

1677

300

500

700

900

1100

1300

1500

1700

1900


Te

mp

era

ture

s [

°C]

Cladding

Coolant

Center Fuel

Surf Fuel

Avg Fuel

Clad Failure Time ~ 0.5 hrs4 Grid Spacers @ 0.50mm thickness

H (core-HX) = 2.0 m

P_primsystem = 1.56 bar

Conclusion:

At BOC ULOFss Clad Failure Time of ~ 0.5 hrs for Peak Pin is acceptable !!

Current Spacer design:



XT-ADS ULOF-ss

at EOC :

EOL ULOFss Temperatures , Peak Pin 194 W/cm and 30 um Oxide Layer

660

566

837

881

1366

1111

1300

857

1009

1618

300

500

700

900

1100

1300

1500

1700

-30 -20 -10 0 10 20 30

Axial Core Position [cm]

Te

mp

era

ture

s [

°C]

Cladding surf

Coolant

Center Fuel

Surf Fuel

Avg Fuel

Clad Failure Time ~ 0.13 hrs

EOL ULOFss Temperatures , Avg Pin 146 W/cm and 30 um Oxide Layer

593

520

744

778

1113

932

1087

751

880

1314

300

500

700

900

1100

1300

1500

-30 -20 -10 0 10 20 30


Te

mp

era

ture

s [

°C]

Cladding surf

Coolant

Center Fuel

Surf Fuel

Avg Fuel


XT-ADS :

Pin = 6.55mm OD

T_in = 300 °C

Oxide Layer = 30 um

4 Grid Spacers @ 0.50mm thickness

H (core-HX) = 2.0 m


Conclusion:

At EOC ULOFss Clad Failure Time of ~ 0.13 hrs for Peak Pin is somewhat less than the 0.5 hrs design goal!!

Current Spacer design:



XT-ADS :

Pin = 6.55mm OD

T_in = 300 °C

No Oxide Layer

XT-ADS ULOF-ss

at BOC :


H (core-HX) = 2.0 m


Conclusion:

At BOC ULOFss Clad Failure Time of ~ 45 hrs for Peak Pin

BOC ULOFss Temperature Avg Pin, 146 W/cm and no oxide layer

537.3

487

676

699

1161

951

1079

740840

1341

300

500

700

900

1100

1300

1500


Te

mp

era

ture

s [

°C]

Cladding

Coolant

Center Fuel

Surf Fuel

Avg Fuel

Clad Failure Time ~ 19 000 hrs

BOC ULOFss Temperature Peak Pin, 201 W/cm and no oxide layer

595.5

530

763

793

1415

11171268

820943

1635

300

500

700

900

1100

1300

1500

1700

1900


Te

mp

era

ture

s [

°C]

Cladding

Coolant

Center Fuel

Surf Fuel

Avg Fuel


Proposed Spacer design:



XT-ADS ULOF-ss

at EOC :XT-ADS :

Pin = 6.55mm OD

T_in = 300 °C

Oxide Layer = 30 um


H (core-HX) = 2.0 m


Conclusion:

At EOC ULOFss Clad Failure Time of ~ 9 hrs for Peak Pin is now ok !!

EOL ULOFss Temperatures , Avg Pin 146 W/cm and 30 um Oxide Layer

558

487

676

711

1077

899

1042

721829

1270

300

500

700

900

1100

1300

1500

-30 -20 -10 0 10 20 30


Te

mp

era

ture

s [

°C]

Cladding surf

Coolant

Center Fuel

Surf Fuel

Avg Fuel


EOL ULOFss Temperatures , Peak Pin 194 W/cm and 30 um Oxide Layer

618

525

754

798

1325

1073

1249

821948

1570

300

500

700

900

1100

1300

1500

1700

-30 -20 -10 0 10 20 30


Te

mp

era

ture

s [

°C]

Cladding surf

Coolant

Center Fuel

Surf Fuel

Avg Fuel


Proposed Spacer design:



XT-ADS Transient : ULOF

Assumptions:

1. Pump Coast down charactersitics taken from Myhrra Report (Draft 2) using a pump rundown halftime = 3.8 sec

2. Assume a similiar flow transition characterisitics from pump coast down to natural convection as has been assumed for the PDS-XADS design

Source: Myhrra Report – Draft 2 June 2005

~3.8 sec



Flow transition characterisitics from pump coast down to natural convection under ULOF conditions as has been assumed for the PDS-XADS design

ULOF Transient for 80 MW LBE-cooled XADS and XT-ADS using similiar flow transition dynamics

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

0 10 20 30 40 50 60 70 80 90 100

Time [sec]

rel.

Ma

ss

Flo

w R

ate

[fr

]

XT-ADS ULOF ( SIM-ADS )

Flow_RELAP ( XADS: ANSALDO )

PDS-XADS ULOF Flow Dynamics

XT-ADS ULOF Flow using PDS-XADS transition characterics

w_nat = 25.4 % nominal for avg pin

w_nat ~ 48 % for XADS

undershoot to 28 %

undershoot to 13.5 %

I believe that this XADS transition flow characterisitcs was experimentally valided in Italy (Brasemone) and RELAP was validated using this data

TALL experimental data (LBE-loop, KTH)



Benchmarking TRAC and SIM-ADS to TALL Natural Convection Transient

TALL Natural Convection Transient Experimental data (LBE-loop, KTH)

Temperatures

200

250

300

350

400

450

500

0 200 400 600 800 1000 1200 1400 1600 1800 2000Time [sec]

Tem

per

atu

re [

°C]

Cool_out SIM-ADS

Cool_in SIM-ADS

T_in TALL exp. - 1

T_out TALL - exper

T_in HX TALL exp

T_out HX TALL -expT_in TALL exp. - 2

T_in TALL exp. -3

T_out PSI TRACE

T_in PSI TRACE

Coolant

Flow Rate

0.00.10.20.30.40.50.60.70.80.91.01.1

0 200 400 600 800 1000 1200 1400 1600 1800 2000Time [sec]

rel.

Un

its

[fr]

Flow_Cool SIM-ADS

TALL -exp. data

PSI TRACE calculation

grad ~ 1/100

Source : W. Ma (KTH),et.al., E. Bubelis, P. Coddington (PSI) „TALL Experiments …..“ NED Reference to be completed



XT-ADS ULOF Transient Cases Analysed:

1. ULOF: BOC, Peak Pin, 4 Spacer @ 0.50mm thickness

2. ULOF: EOC, Peak Pin, 4 Spacer @ 0.50mm thickness, 30 um oxide

3. ULOF: BOC, Peak Pin, 4 Spacer @ 0.25mm thickness

4. ULOF: EOC, Peak Pin, 4 Spacer @ 0.25mm thickness , 30 um oxide



Case 1 : ULOF, BOC, Peak Pin, 4 Spacer @ 0.50mm thickness, no oxide

Conclusion:

For current design XT-ADS peak pin clad will fail 32 sec into the ULOF transient already under BOC conditions because of flow undershoot < 20 % nom. flow at 36 sec into transient even though the ULOF-ss limit of 30 min is attained after 60 sec into ULOF.

ULOF FzK (SIM-ADS) : Power and Flow Rate

0.00.10.20.30.40.50.60.70.80.91.01.1

0 20 40 60 80 100Time [sec]

rel.

Un

its

[fr

]

Power_th

Flow_Cool

Power

Flow

ULOF FzK (SIM-ADS) : Temperatures

300

500

700

900

1100

1300

1500

1700

1900

2100

0 20 40 60 80 100Time [sec]

Te

mp

era

ture

[°C

] Fuel_c_peak

Clad_peak

Cool_out

Cool_in

Fuel

T_clad_max = 1100 °C

Coolant

Cladding

ULOF FzK (SIM-ADS) : Clad Failure and Fission Gas Pressure

1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1.E+12

1.E+14

1.E+16

1.E+18

0 20 40 60 80 100Time [sec]

Cla

d F

ailu

re T

ime

[s

ec

]

2.2

2.2

2.3

2.3

2.4

2.4

2.5

2.5

2.6

Fis

sio

n G

as

Pre

ss

ure

[b

ar]

Clad Failure Time [sec]

Fission Gas Pressure [bar]

30 min

Min Clad Failure Time < 1 sec



Case 2 : ULOF, EOC, Peak Pin, 4 Spacer @ 0.50mm thickness, 30 um oxide

Conclusion:

For current design XT-ADS peak pin clad will fail 32 sec into the ULOF transient under EOC conditions because of flow undershoot < 20 % nom. flow at 36 sec even though the ULOF-ss limit of ~20 min is attained after 60 sec into ULOF.


0.0

0.1

0.20.3

0.4

0.5

0.6

0.7

0.80.9

1.0

1.1

0 20 40 60 80 100Time [sec]

rel.

Un

its

[fr

]

Power_th

Flow_Cool

Power

Flow


300

500

700

900

1100

1300

1500

1700

1900

0 20 40 60 80 100Time [sec]

Te

mp

era

ture

[°C

]

Fuel_c_peak

Clad_peak

Cool_out

Cool_in

Fuel


Coolant

Cladding


1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1.E+12

1.E+14

1.E+16

0 20 40 60 80 100Time [sec]

Cla

d F

ailu

re T

ime

[se

c]

36

37

38

39

40

41

42

43

Fis

sio

n G

as

Pre

ss

ure

[b

ar]



30 min

Min Clad Failure Time < 1 sec



Case 3 : ULOF, BOC, Peak Pin, 4 Spacer @ 0.25mm thickness, no oxide

Conclusion:

For 0.25cm Spacer design XT-ADS clad will most likely survive without clad failure under BOC conditions even though clad failure time dropped down to ~ 80 sec about 36 sec into ULOF transient. Flow undershoot will recover sufficiently fast.


0.00.1

0.20.30.4

0.50.6

0.70.80.9

1.01.1

0 20 40 60 80 100Time [sec]

rel.

Un

its

[fr

]

Power_th

Flow_CoolPower

Flow


300

500

700

900

1100

1300

1500

1700

1900

0 20 40 60 80 100Time [sec]

Te

mp

era

ture

[°C

] Fuel_c_peak

Clad_peak

Cool_out

Cool_in

Fuel


Coolant

Cladding


1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1.E+12

1.E+14

1.E+16

1.E+18

0 20 40 60 80 100Time [sec]

Cla

d F

ailu

re T

ime

[s

ec

]

2.2

2.2

2.3

2.3

2.4

2.4

2.5

2.5

Fis

sio

n G

as

Pre

ss

ure

[b

ar]



30 min

Min Clad Failure Time ~ 80 sec



Case 4 : ULOF, EOC, Peak Pin, 4 Spacer @ 0.25mm thickness, 30 um oxide

Conclusion:

For 0.25cm Spacer design XT-ADS peak pin clad will however most likely fail under EOC conditions because clad failure time dropped down to ~ 0 sec about 36 sec into ULOF transient. Avg Pin clad will survive – see next figure.


0.00.10.20.30.40.50.60.70.80.91.01.1

0 20 40 60 80 100Time [sec]

rel.

Un

its

[fr

]

Power_th

Flow_Cool

Power

Flow


300

500

700

900

1100

1300

1500

1700

1900

0 20 40 60 80 100Time [sec]

Te

mp

era

ture

[°C

]

Fuel_c_peak

Clad_peak

Cool_out

Cool_in

Fuel

T_clad_max ~ 1020 °C

Coolant

Cladding


1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1.E+12

1.E+14

1.E+16

0 20 40 60 80 100Time [sec]

Cla

d F

ailu

re T

ime

[s

ec

]

37

38

39

40

41

42

43

Fis

sio

n G

as

Pre

ss

ure

[b

ar]



30 min

Min Clad Failure Time ~ 0 sec



Case 4 : ULOF, EOC, Avg Pin, 4 Spacer @ 0.25mm thickness, 30 um oxide

Conclusion:

For 0.25cm Spacer design XT-ADS avg pin clad will not fail under EOC conditions because clad failure time dropped down to only 800 sec about 36 sec into ULOF transient and thereafter recovers to several hours.


0.00.10.20.30.40.50.60.70.80.91.01.1

0 20 40 60 80 100Time [sec]

rel.

Un

its

[fr

]

Power_th

Flow_Cool

Power

Flow


1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1.E+12

1.E+14

1.E+16

1.E+18

0 20 40 60 80 100Time [sec]

Cla

d F

ailu

re T

ime

[s

ec

]

27

28

28

29

29

30

30

31

Fis

sio

n G

as

Pre

ss

ure

[b

ar]



30 min

Min Clad Failure Time ~800 sec


300

500

700

900

1100

1300

1500

0 20 40 60 80 100Time [sec]

Te

mp

era

ture

[°C

]

Fuel_c_peak

Clad_peak

Cool_out

Cool_in

Fuel

T_clad_max ~ 880 °C

Coolant

Cladding



Current Conclusions on XT-ADS ULOF Transient (1/2) :

1.) This transient is very sensitive to natural convection flow rate conditions and thus all plant and design parameters that influence this parameter. During the transient clad failure times can decrease to a few 10 seconds depending on the transitional flow dynamics (natural convection flow undershoot).

2.) The ULOF-ss (steady state) clad design limit condition of at least 30 min survival time are difficult to abide by under ULOF transient conditions for the current design even if the spacer design of 0.25mm thickness is adopted. Additional design measures are needed such as either decrease in primary system pressure drop or by increasing the elevation of the HX relative to the core above the current 2.0 m differential, or by other means (what are those ?).



Current Conclusions on XT-ADS ULOF Transient (2/2) :

3.) The XT-ADS core and primary system designs are currently still a moving target. The most recent design iteration proposal calls for a reduced secondary side pressure to 16 bar allowing for power level dependant core inlet temperature variations between 300°C and 200°C.

This calls for a revised MHX modelling (2 phase flow as saturation temperature of 16 bar is 200°C).

This implies that under norminal conditions – 300°C core inlet, the secondary side HX is mostly in the vapor state. Who has a 2 phase MHX model going and running stable at all plant conditions ???

Documents

XT-ADS Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety”