Dynamic Response to Pulsed Beam Operation
in Accelerator Driven Subcritical Reactors
Ali Ahmad
Supervisor: Dr Geoff Parks
University Nuclear Technology Forum
April, 2011
Overview
• Introduction
• Characterisation of the dynamic response in ADSR
• The PTS-ADS code
• The thermo-mechanical stress analysis in the fuel
cladding
UNTF 2011
Ali Ahmad
Introduction
“Fukushima disaster causes fallout
for nuclear industry worldwide”
The Guardian 29 March 2011
Safety
A
g
e
n
d
a
Sustainability
“The world energy demand is expected to grow
by approx 50% from 2007 to 2035”
International Energy Outlook 2010, US EIA
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Ali Ahmad
Characterisation of the dynamic response in ADSR
FFAG works in a
pulsed mode
Agenda
FFAG accelerator seems to
be the most suitable option
for ADSR because:
- High beam intensity
- High efficiency of
power consumption
- High stability in operation
- Cheaper than Linac
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Frequent core temperature variations
Thermal cyclic fatigue in the cladding?
Ali Ahmad
The PTS-ADS code
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Ali Ahmad
Agenda
The PTS-ADS code: Fuel Pin Heat Transfer Model
Assumptions:
1- The axial power distribution has a
sinusoidal form
2- The heat generation rate is uniform
across the radial direction inside the fuel
3- Heat transfer only occurs in the radial
direction
The fuel pin heat equation can be written as:
Cp
T
1  
T 

 kr
  q' ' '
t
r r 
r 
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Ali Ahmad
The PTS-ADS code: Neutronic Model
Six-group Point Kinetics model:
6
P(t )  (t )  

P(t )   iCi (t )  S (t )
t

i 1
Ci (t ) i

P(t )  iCi (t )
t

Total reactivity can be written as:
 (t )   (0)  Doppler (Tfuel )  Coolant (TCoolant )
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Ali Ahmad
The PTS-ADS code: Validation Case Study
Benchmark study on beam interruptions in XADS
The PTS-ADS coupled model was compared to three other codes selected from
a benchmark study on beam interruption for the Experimental ADS* (80 MWt,
MOX, Lead-Bismuth coolant).
- TRAC-MOD
- SIMADS
- SAS4ADS
*) A. D’Angelo et al. Benchmark on beam interruptions in an accelerator driven
system final report on phase I calculations, Tech. Rep.
NEA/NSC/DOC(2003)17, NEA (2003).
UNTF 2011
Ali Ahmad
The PTS-ADS code: Validation Case Study
UNTF 2011
Ali Ahmad
The PTS-ADS code: Validation Case Study
UNTF 2011
Ali Ahmad
The PTS-ADS code: Validation Case Study
UNTF 2011
Ali Ahmad
The PTS-ADS code: Validation Case Study
UNTF 2011
Ali Ahmad
The thermo-mechanical stress analysis in the fuel
cladding
Fuel pin geometry and the physical
properties of the fuel, cladding and
coolant materials are taken from
the XADS data sheet.
keff  0.972
Beam characteristics:
- Frequency 1 Hz
- Beam off time 10, 50 and 100 ms
Local linear power:
- 9172 W/m (XADS ref case)
- 2500 W/m (Industrial ADSR)
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Ali Ahmad
Agenda
The thermo-mechanical stress analysis in the fuel
cladding
Life prediction of the fuel pin cladding
In a nuclear reactor, the integrity of the structural materials in general and
of the fuel cladding in particular is of high importance.
Fission products leakage to the primary
coolant circuit
Cladding failure
The thermal stress on the cladding can be calculated using:
Define the stress amplitude:  a 
 max   min

E

 T
21  
2
The stress amplitude is related to the failure limit Nf by Basquin’s Law:
 a   f (2 N f )b
'
where  f ' is the fatigue strength coefficient
and
b is the fatigue strength exponent
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Ali Ahmad
The thermo-mechanical stress analysis in the fuel
cladding
Both  f ' and b can be estimated experimentally for certain materials at
certain temperatures.
The cladding material in this study is T91 stainless steel.
Temperature
(°C)
 a
 f
(MPa)
(MPa)
300
0.24
550
0.7
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'
b
Nf
695
−0.052
Indefinite
649
−0.093
Indefinite
Ali Ahmad
Conclusions
The integrity of the fuel cladding of an ADSR can be
assumed to be unaffected by the repetitive temperature
fluctuations due to pulsed operation mode.
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Ali Ahmad
Future Work
• Use
the PTS-ADS code to measure the
temperature variations in the fuel cladding when
subjected to beam interruptions (t> 1 second) and
predict the stress-life behaviour for that case
• Study the influence of other factors such as
radiation damage and creep on the cladding
fatigue life
• Further development of the PTS-ADS code to
include the ability study all ADSR transients and for
different core configurations
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Ali Ahmad