D J Coates, G T Parks Department of Engineering, University of Cambridge, UK

3rd Year PhD student

Actinide Breeding and Reactivity Variation in a Thermal Spectrum ADSR

Universities Nuclear Technology Forum

University of Huddersfield

11-13th April 2011

Motivation for the Research: Improvements in the Sustainability of Nuclear Power

Fast reactors are the subject of renewed interest due to their beneficial capability to both burn and breed transuranic actinides

Fast reactors are the subject of renewed interest due to their beneficial capability to both burn and breed transuranic actinides

However despite significant investment over many years they have never been deployed in significant numbers

However despite significant investment over many years they have never been deployed in significant numbers

The well proven thermal spectrum technology base may provide a more straightforward route to delivering improvements in sustainability

The well proven thermal spectrum technology base may provide a more straightforward route to delivering improvements in sustainability

What Role Does the Accelerator Play ?

In the fast spectrum:It provides additional re-assurance against criticality excursions beyond that provided by the delayed neutron fraction

In the fast spectrum:It provides additional re-assurance against criticality excursions beyond that provided by the delayed neutron fraction

In the thermal spectrum:It enables sub-critical operation to be established with fuel mixtures which cannot support critical reactor operation

Hence it facilitates operation with fuel cycles which would otherwise be inaccessible

In the thermal spectrum:It enables sub-critical operation to be established with fuel mixtures which cannot support critical reactor operation

Hence it facilitates operation with fuel cycles which would otherwise be inaccessible

The Carlo Rubbia Energy Amplifier

Contents:

The Thermal Model 1

• Brief description of the model used and thermal flux distribution

• Comparison of the model predictions with actual PWR operating results

Validation of the Thermal Model2

Thermal Breeder ADSR3

• Using the model to examine the constraints affecting thermal breeder reactors

Thermal Model1

The neutron reaction and decay pathways are largely the same for both fast and thermal systems, the essential difference lies in the cross-sections

The neutron reaction and decay pathways are largely the same for both fast and thermal systems, the essential difference lies in the cross-sections

Reactor Neutron Energy Distribution

Chart taken from T. Iwasaki, N.Hirakawa, 1995

Accurate representation of effective one-group cross-sections in the thermal spectrum can be challenging

Accurate representation of effective one-group cross-sections in the thermal spectrum can be challenging

Changes in reactor geometry and self-shielding effects can have significant influences on the cross-sections

Changes in reactor geometry and self-shielding effects can have significant influences on the cross-sections

The strong resonance peak which exists for 240Pu requires the capture cross-section to be continually updated as the burn-up progresses

The strong resonance peak which exists for 240Pu requires the capture cross-section to be continually updated as the burn-up progresses

Model Validation2

Comparison with Takahama-3 PWR (uranium)

Thermal Breeding 3

Thorium and UO2 Breeding Reactions

238U 239U 239Np 239Pu

232Th 233Th 233Pa 233U

Power Contribution of Selected Nuclides in a PWR

As the U235 contribution falls away the Pu239 and Pu241 increase to provide the major contributions to the total power

As the U235 contribution falls away the Pu239 and Pu241 increase to provide the major contributions to the total power

Neutron Economy in a 3.04% 235U PWR

Accelerator Contribution to extended PWR Operation

The Thermal Thorium System

An improved neutron economy can be achieved by using a Thorium fuel platform

An improved neutron economy can be achieved by using a Thorium fuel platform

A fissile “starter” will be necessary to maintain operation over the early operating period

A fissile “starter” will be necessary to maintain operation over the early operating period

Plutonium Enriched Thermal Thorium Reactor

The use of a plutonium “starter” produces an initial boost to the neutron economy but ultimately falls below that of a pure thorium fuel platform

The use of a plutonium “starter” produces an initial boost to the neutron economy but ultimately falls below that of a pure thorium fuel platform

Actinide Evolution Pathways

ThTh n 23390

),(23290

Pa23391

UUUU nnn 23692

),(23592

),(23492

),(23392

UUUU nnn 24092

),(23992

),(23892

),(23792

NpNpNpNp nnn 24093

),(23993

),(23893

),(23793

PuPuPuPuPuPu nnnnn 24394

),(24294

),(24194

),(24094

),(23994

),(23894

AmAmAm nn 24395

),(24295

),(24195

The opportunities for fission before transformation into plutonium are far greater when starting from Th232 than from U238

The opportunities for fission before transformation into plutonium are far greater when starting from Th232 than from U238

Enrichment with heavy actinides by-passes the fission opportunities and increases the proportion of heavy actinides

Enrichment with heavy actinides by-passes the fission opportunities and increases the proportion of heavy actinides

233U Enriched Thermal Thorium Reactor

Evolution of Pu, Am and Cm in a Thorium Reactor

Variation in Neutron Economy and Accelerator Power

Conclusions

• It is possible to represent the evolution of actinides within a typical PWR using a lumped model

• A 238U fuel platform produces a very poor neutron economy, the benefit of an accelerator is limited to extending the burn-up

• The 232Th fuel platform provides a significantly improved neutron economy although insufficient for critical operation

• Heavy actinide starters ultimately “choke” the reactor due to the consequential growth in the heavy actinide population

• A closed fuel cycle with a thorium fuel platform would require an accelerator in the order of 20% of the generated power

• An accelerator of this size would be challenging from both a practical and commercial perspective

• It is possible to represent the evolution of actinides within a typical PWR using a lumped model

• A 238U fuel platform produces a very poor neutron economy, the benefit of an accelerator is limited to extending the burn-up

• The 232Th fuel platform provides a significantly improved neutron economy although insufficient for critical operation

• Heavy actinide starters ultimately “choke” the reactor due to the consequential growth in the heavy actinide population

• A closed fuel cycle with a thorium fuel platform would require an accelerator in the order of 20% of the generated power

• An accelerator of this size would be challenging from both a practical and commercial perspective

The End

Neutron Absorption by Heavy Actinides

Variation Thorium Mass With Repeated Fuel Cycles

Variation in 233U Mass With Repeated Fuel Cycles

Neutron Capture Cross-sections

Magnified showing 0.5(b) vertical divisions

Cross-sections taken from T. Iwasaki, N.Hirakawa, 1995

Comparison with Takahama-3 PWR (plutonium)

Comparison with Takahama-3 PWR (americium)

Comparison with Takahama-3 PWR (curium)

Comparison with Takahama-3 PWR (curium)

Comparison with Obrigheim PWR (Am241)

Comparison with Obrigheim PWR (Cm242)

Comparison with Obrigheim PWR (Cm244)

Comparison with Obrigheim PWR (Pu238)

49 Nuclide Model

236U

230Th 231Th 232Th 233Th

231Pa 232Pa 233Pa

232U 233U 235U234U

241Pu 242Pu 243Pu

239U237U 238U

238Pu 239Pu 240Pu

237Np 238Np 239Np

A simple “lumped” homogenous reactor model using averaged neutron cross-sections and ignoring spatial effects is

adopted

A simple “lumped” homogenous reactor model using averaged neutron cross-sections and ignoring spatial effects is

adopted

241Am M242Am

243Am

242Am

244Am

242Cm 244Cm243Cm 245Cm 246Cm 248Cm247Cm 249Cm

250Bk249Bk

245Am

244Pu 245Pu

249Cf 250Cf 251Cf 252Cf 253Cf

253Es

234Pa

The Accelerator Driven Sub-critical Reactor