studsvik scandpower temperature modelin… · -30-20-10 0 10 20 30 40 0 10 2030 405060 7080 elapsed...

CASMO User’s GroupMay 2003Studsvik Scandpower

Kord SmithArt DiGiovineDan HagrmanScott Palmtag

CASMO User's Group 2003Studsvik Scandpower

• TFU-related data is required input for:- CASMO-4- SIMULATE-3- SIMULATE-3K and SIMULATE-3R

(implicit in XIMAGE and GARDEL)

• Fuel temperature modeling in CMS is intended to be “best estimate” and should be consistent for all CMS codes.


• Historically, many customers have used vendor-supplied fuel temperature data which has lead to inconsistencies.

• Vendor data is often driven by considerations of being “conservative” rather than accurate.

• Vendor fuel temperature correlations may be designed for safety/mechanical analysis, not for core-follow or transient analysis.

• Inaccurate data leads to poor CMS predictions of axial offset in Xenon transients, power coefficients, coastdown reactivity, etc.


• Studsvik’s INTERPIN code was originally developed to support transient fuel pin analyses at the Studsvik R2 test reactor:– rod pressurization– fission gas release– pellet/clad mechanical interaction

• Fuel temperature predictions are a natural by-product of fuel performance analysis

• In 1991, Studsvik introduced a new steady-state fuel temperature code, INTERPIN-CS, to automatically generate temperature data needed in CMS (SEG.TFU and TAB.TFU tables)


• Fuel/cladding conductivity vs. temperature and burnup

• Fuel/cladding thermal expansion• Pellet densification, cracking, swelling, relocation• Fission gas migration (radial and axial)• Fuel/cladding gap conductance (convection,

conduction, emission)• Clad stress/strain• Clad/coolant heat transfer


Fuel Pin Changes with Burnup• Attempt to separate densification, swelling and

conductance effects on fuel centerline temperature

• Fuel conductivity vs. burnup based on recent Halden measured fuel centerline temperature data:

• Pins with various gap sizes• Pins with various fission gas inventories

• See 26th CUGM presentations by Hagrman and Dean


• Fuel conductivity vs. burnup:– in INTERPIN-CS decreases ~10%– in INTERPIN-3 decreases ~ 40%

(more important now with prevalence of high burnup cores)

• Gaseous convection between fuel and cladding when gap is closed:– INTERPIN-CS decreases substantially with fission gas inventory– INTERPIN-3 nearly independent of fission gas inventory

• Net effect of changes are that fuel temperatures increase at high burnup in INTERPIN-3

(INTERPIN-CS temperatures are ~ constant at high burnup)


• Assumptions:

– All fuel pins have the same temperature

– Fuel temperature is independent of burnup

– Radial temperature distribution is spatially flat within a fuel pin


• CASMO-4 generates nuclear data as a function of instantaneous and historical fuel temperature

– TFU depletions/branches produce data for temperature coefficients and history effects (automatically included in default case matrix)

– Average and pin-to-pin temperature variations are not very important


-0.005

-0.004

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

0 10 20 30 40 50Burnup (MWd/kg)

Rea

ctiv

ity D

iffer

ence

(900

K-80

0K)

Depletion

History

• Higher temperature leads to more Pu-239 production and less U-235 depletion


• SEG.TFU and TAB.TFU data tables are used to compute the difference between average fuel temperature and coolant temperature (usually as a function of fuel pin power density and burnup)

• Node-wise coolant temperatures added to compute actual node-averaged fuel temperature

• SIMULATE-3 accounts for fuel temperature and history effects on a node-wise basis since all nodes do not have the same fuel temperature


• SIMULATE-3 needs proper Doppler feedback to model pseudo-steady-state conditions

Legend

INTERPIN-3INTERPIN-CS


-4%

-3%

-2%

-1%

0 100 200 300 400 500

Time (hours)

Axia

l Flu

x Im

bala

nce


-20%

-15%

-10%

-5%

0%

5%

10%

0 100 200 300 400 500

Time (hours)

Axia

l Flu

x Im

bala

nce

IP3 Vendor 1Vendor 2


-40

-30

-20

-10

0

10

20

30

40

0 10 20 30 40 50 60 70 80

Elapsed Time (hrs)

Axia

l Flu

x Im

bala

nce

(%�

I)

SIMULATE-3 (old tfu data)

SIMULATE-3 (INTERPIN-CS data)

Measured

• INTERPIN-3 data needed for analysis of Xenon transients

INTERPIN-CSINTERPIN-3Measured


MeasuredINTERPIN-CSINTERPIN-3


Nine Mile Point Unit 2

-0.146

-5.137

-4.991

PowerDefect

(%�k/k)

1.9%0.077-0.16059Difference

-0.3840.077-0.894836IP3

-0.377Reference-0.734777IPCS

PowerCoefficient

(%�k/k /%P)

HTFU

(%�k/k)

DopplerDefect

(%�k/k)

TFUAVE

(K)

Model


• Solve time-dependent radial heat conduction equations for each node, using slightly simpler physical model than used in INTERPIN-3

• Consistent:– Conductivity vs. burnup (Wiesenack)– Conductivity vs. temperature (MATPRO)– Radial profile of fission rate (CASMO-4)– Gas conduction properties (ideal gas)

• Different:– Gap closure model– Solid contact conductance (no contact pressure calculation)– Assume no bulk fission gas release (no high temperature historical effects)

• Net result on fuel temperatures– Steady-state temperatures are ~same in INTERPIN-3 and S3K


• “Truth” is a RACER Monte Carlo Calculation using 10 radial rings to approximate quadratic temperature profile

• Doppler reactivity:

Flat Quadratic450- 900K -108 -101450-1350K -111 -105900-1350K -114 -108

• Proper treatment of radial temperature profile lowers Doppler reactivity by ~ 6%.

• Profile effect is small relative to library uncertainties (~ 10%)

� � 52 12 1

1 2

/ 10k k T T xk k�

�


• Traditional weighted temperature model:

• Surface/center weighting model overestimates temperature profile effect (-40% vs. -6%)

0.30 0.70eff center surfT T T� �

1350 900 6.74

0.3 2250 0.7 450 0.3 1350 0.7 450 4.634.63/ 6.74 0.68

x x x x

� �

� � � �

�


• “Effective Fuel Temperature” model is not recommended in S3K(Physical average temperature is default)

• Internal gap conductance model is default in S3K

• Users can input their own conductance tables vs. temperature and exposure

– Be careful of consistency between vendor-assumed conductivity and conductance models


• ~ No change in BOL temperature• ~ 80K increase in MOL temperature• ~ 100K increase in EOL temperature

• More Doppler feedback at high burnup• 15% increase in PWR power coefficient• Xenon transients are more accurate (more

damping)


• SSP recommends INTERPIN-3 data to be used consistently throughout CMS for best results.

• Carefully check vendor-supplied fuel temperature data to make sure they are appropriate for your analysis.

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