Dynamic Response to Pulsed Beam Operation

in Accelerator Driven Subcritical Reactors

Ali Ahmad

Supervisor: Dr Geoff Parks

University Nuclear Technology Forum

April, 2011

UNTF 2011 Ali Ahmad

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

“The world energy demand is expected to grow by approx 50% from 2007 to 2035” International Energy Outlook 2010, US EIA

Safety

Sustainability

Agenda

UNTF 2011 Ali Ahmad

Characterisation of the dynamic response in ADSR

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

FFAG works in a pulsed mode

Frequent core temperature variations

Thermal cyclic fatigue in the cladding?

Agenda

UNTF 2011 Ali Ahmad

The PTS-ADS code

Agenda

UNTF 2011 Ali Ahmad

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:

'''1 qrTkr

rrtTCp

UNTF 2011 Ali Ahmad

The PTS-ADS code: Neutronic Model

Six-group Point Kinetics model:

6

1

)()()()()(i

ii tStCtPtttP

)()()( tCtPttC

iiii

)()()0()( CoolantCoolantfuelDoppler TTt

Total reactivity can be written as:

UNTF 2011 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.

972.0effk

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)

Agenda

UNTF 2011 Ali Ahmad

The thermo-mechanical stress analysis in the fuel claddingLife 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.

Cladding failure Fission products leakage to the primary coolant circuit

The thermal stress on the cladding can be calculated using:

12T

EDefine the stress amplitude:

2minmax

a

The stress amplitude is related to the failure limit Nf by Basquin’s Law:

bffa N )2('

where is the fatigue strength coefficient and b is the fatigue strength exponent

'f

UNTF 2011 Ali Ahmad

The thermo-mechanical stress analysis in the fuel cladding

Both and b can be estimated experimentally for certain materials at certain temperatures.

The cladding material in this study is T91 stainless steel.

'f

Temperature(°C) (MPa) (MPa)

b

300 0.24 695 −0.052 Indefinite

550 0.7 649 −0.093 Indefinite

a 'f

fN

UNTF 2011 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.

UNTF 2011 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