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Towards sustainable, secure and safe energy future: Leveraging opportunities with Thorium. Anil Kakodkar. Growing economic empowerment of a larger part of world population and little carbon space available necessitates a quick shift to non-fossil energy sources.

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towards sustainable secure and safe energy future leveraging opportunities with thorium

Towards sustainable, secure and safe energy future: Leveraging opportunities with Thorium

Anil Kakodkar


Growing economic empowerment of a larger part of world population and little carbon space available necessitates a quick shift to non-fossil energy sources.

climate change stabilization scenarios
Climate Change Stabilization Scenarios

Source: IPCC (2007), Table 5.1, p. 67

We do not know how close we are to the tipping point. However we need to act now to secure survival of our future generations.

If total primary energy consumption doubles by 2050, 85% of energy must be supplied by clean technologies in order to attain a 70% GHG cut from 2000 levels.

Source: WNA Nuclear Century Outlook

Source IEO2013

what we should do
What we should do?
  • Business as usual approach is unlikely to work
  • Apart from electricity we need energy in fluid form derived through non-fossil means
  • This would need high temperature capability
  • Since time is running out we need to explore what can be done by reconfiguration of available technologies even as we develop new technologies

Transition to Fossil Carbon Free Energy Cycle



  • (In storage or transportation)
  • Electricity
  • Fluid fuels
  • (hydro-carbons/ hydrogen)




  • CO2
  • H2O
  • Other oxides and products




Sustainable development of energy sector




Hydro carbons





Greater share for nuclear in electricity supplyreplace fossil hydro- carbon in a progressive manner recycle carbon- dioxidederive most of primary energy through solar & nuclear




Other recycle modes


Nuclear Recycle

Sustainable Waste Management Strategies

Urgent need to reduce use of fossil carbon in a progressive manner

in spite of such strong motivation what has slowed the growth of nuclear power
In spite of such strong motivation, what has slowed the growth of nuclear power?
  • Irrational fear of radiation caused by LNT logic
  • Potential for large scale displacement of people following a
  • severe accident
  • Panic potential following a terrorist action
  • Unresolved spent fuel disposal & constraints on recycle
  • Regulatory delays
evidence of threshold
Evidence of threshold
  • Colorado ,USA has a population over 5 millions residents. According to

LNT model Colorado should have an

excess of 200 cancer deaths per year

but has a rate less than the national


. Ramasar ,Iran, residents receive a

yearly dose of between 100-260 mSv.

This is several time higher than

radiation level at Chernobyl and

Fukushima exclusion zone.People

living in Ramsar have no adverse

health effect , but live longer and

healthier lives.

. We also know that China , Norway,

Sweden, Brazil and India have similar

areaswhere radiation level is many

times higher than 2.4 mSv/yr world


Crosses show the mortality of Chernobyl firefighters (curve is for rats).The numbers show the number who died/total in each dose range.

In spite of evidence for no health consequences below a threshold, mindset driven by LNT logic has caused irrational fears in public mind with regard to potential accident impact in public domain. This has led us to a situation where significant off-site impact in a severe accident is no longer acceptable.

Advanced Heavy Water Reactor (AHWR) is an innovative configuration that should nearly eliminate impact in public domain using available technologies.

Top Tie Plate



Water Tube

Fuel Pin

Bottom Tie Plate

Major design objectives

  • Several passive features
    • grace period > 3 days
    • No radiological impact
    • in public domain
  • Passive shutdown system
  • to address insider threat
  • scenarios.
  • Design life of 100 years.
  • Easily replaceable coolant
  • channels.
  • Significant fraction of Energy
  • from Thorium

The design enables use of a range of fuel types including LEU, U-Pu , Th-Pu , LEU-Th and 233U-Th in full core

AHWR Fuel assembly


AHWR 300-LEU is a simple 300 MWe system fuelled with LEU-Thorium fuel, has advanced passive safety features, high degree of operator forgiving characteristics, no adverse impact in public domain, high proliferation resistance and inherent security strength.

Peak clad temperature hardly rises even in with extreme postulate of complete station blackout and simultaneous failure of both primary and secondary systems.

Reactor Block Components

AHWR300-LEU provides a robust design against external as well as internal threats, including insider malevolent acts.

tho 2 has better physical chemical and nuclear properties to enable better safety
ThO2 has better physical, chemical and nuclear properties to enable better safety

> Higher thermal conductivity and lower co-efficient of thermal expansion compared to UO2. Melting point 3500o C as against 2800o C for UO2.

> Favourable reactivity coefficients

> Fission product release rate one order of magnitude lower than that of UO2.

> Relatively inert. Does not oxidise unlike UO2 which oxidizes easily to U3O8 and UO3. Does not react with water.

For a Typical PHWR

Ref. case







  • Lower fuel temperatures
  • Less fission gas release
  • Better dimensional stability
  • Stable reactor performance
  • Good stability under long-term storage


PSA calculations for AHWR indicate practically zero probability of a serious impact in public domain

Plant familiarization & identification of design aspects important to severe accident

Level-3 : Atmospheric Dispersion With Consequence Analysis

Release from Containment

PSA level-1 : Identification of significant events with large contribution to CDF

Level-2 : Source Term (within

Containment) Evaluation through Analysis

Level-1, 2 & 3 PSA activity block diagram






1 mSv

0.1 Sv

1.0 Sv

10 Sv

SWS: Service Water System

APWS: Active Process Water System


LLOCA: Large Break LOCA

MSLBOB: Main Steam Line Break Outside Containment





Contribution to CDF

Iso-Dose for thyroid -200% RIH + wired shutdown system unavailable (Wind condition in January on western Indian side)

Variation of dose with frequency exceedence

(Acceptable thyroid dose for a child is 500 mSv)



How can we address issues related to long term waste (legacy as well as new arising), proliferation concerns and realisation of full potential of nuclear energy?

at high burn ups considered achievable today thorium requires lower fissile content
At high burn-ups considered achievable today, Thorium requires lower fissile content

Performance potential vs fissile topping in PHWR

Performance potential vs fissile topping in BWR

Performace potential vs fissile topping in PWR

Indicative results for a set of case studies with U235 as fissile material

  • Better fertile to fissile
  • conversion
  • Smaller reactivity swing
  • with burn up
  • Greater energy from in-situ
  • generated fissile material
  • Better Uranium utilisation


provides better

utilisation of

natural uranium,

as a result of

a significant

fraction of the

Energy being extracted from fission of 233U,

converted in-situ

from the thorium

fertile host.

LEU-Thorium fuel can lead to better/comparable utilisation of mined Uranium


There is already a

  • large (~200,000
  • tons) used Uranium
  • fuel inventory.
  • Another 400,000
  • tons are likely to be
  • generated between
  • now and the year
  • 2030 (as per WNA
  • estimate).
  • Permanent disposal
  • of used
  • Uranium fuel
  • remains an
  • unresolved issue
  • with unacceptable
  • security and safety
  • risks.
  • We need to adopt
  • ways to liquidate
  • the spent fuel
  • through recycle.

Disposal of used Uranium remains an unresolved issue

  • Thorium provides an
  • effective answer to safe recycle of spent nuclear fuel.
  • Much lower Plutonium production.
  • Plutonium in spent fuel contains lower fissile fraction, much higher 238Pu content which causes heat generation & Uranium in spent fuel contains significant 232U content which leads to hard gamma emitters.
  • The composition of the fresh as well as the spent fuel of AHWR300-LEU makes the fuel cycle inherently proliferation resistant.
  • Uranium in spent fuel contains about 8% fissile isotopes, and hence is suitable for further energy production through reuse in other reactors. Further, it is also possible to reuse the Plutonium from spent fuel in fast reactors.
thorium an excellent host for disposal of excess plutonium
Options for plutonium disposition

Uranium-based fuel: Neutron absorption in 238U generates additional plutonium.

Inert matrix fuel (non-fertile metal alloys containing Pu): Degraded reactor kinetics - only a part of the core can be loaded with such a fuel, reducing the plutonium disposition rate.

Thorium: Enables more effective utilisation of Pu, added initially, while maintaining acceptable performance characteristics.

Thorium, an excellent host for disposal of excess plutonium

Plutonium destruction in thorium-plutonium fuel in PHWR

adoption of thorium fuel cycle paves the way to elimination of long lived waste problem
Adoption of Thorium fuel cycle paves the way to elimination of long lived waste problem
  • While AHWR300- LEU enables comparable utilisation of Uranium in a safe manner, issues related to spent fuel disposal can be eventually addressed through recycle of fissile and fertile materials.
  • Production of MA – lowered with Thorium
  • MAs : fissionable in fast neutron spectrum.
  • Difficult power control system of critical reactor due to:
  • - Reduced delayed neutron fraction (factor called beff) giving lower safety margin to prompt criticality.
  • - Safety parameters: (1) Doppler coefficient, (2) reactivity temperature coefficient, and (3) void fraction- all would not be benign in TRU incinerating critical fast reactor.

We thus need accelerator driven sub-critical molten salt reactor systems with P&T working in tandem to be developed rather quickly. Growth of nuclear power capacity should however pick up immediately through innovative reconfiguration of existing technologies as time is running outThorium is a logical choice for fuel cycle in both present and future systems

detectability of 233 u contaminated with 232 u for all the cases is unquestionable
Detectability of 233U (contaminated with 232U) for all the cases, is unquestionable

232U concentration in ppm

233U concentration (g/kg of HM)

232U concentration in ppm

Exposure time (hr) to acquire LD50 at 1 m for 8.4 kg 233U


Exposure time for lethal dose



Burn up GWd/te

Burn up GWd/te

Case of Pu-RG+Thoria in AHWR

Lethal dose: LD 50/30( =5 Gy) for 8.4 kg Sphere of 233U one year after reprocessing, at 1 m distance

“IAEA is not concerned with the tenth or the thousandth nuclear device of a country. IAEA is only concerned with the first.
  • And that will certainly not be based on a thorium fuel cycle”
    • ---------Bruno

-Bruno Pellaud, Former Deputy Director General,IAEA

nuclear power with greater proliferation resistance

Present deployment

Of nuclear power



Fast Reactor

Thermal reactors

Reprocess Spent Fuel

Enrichment Plant



For growth in nuclear

generation beyond thermal reactor potential


LEU Thorium fuel





Nuclear power with greater proliferation resistance

Safe &



For ex. AHWR



For ex. Acc. Driven MSR




To Conclude:Thorium is a good host for efficient and safe utilisation of fissile materials. It can support greater geographical spread of nuclear energy with lower riskThorium can facilitate resolution of waste management issue and enable realisation of full potential of available Uranium.Fast breeder reactors would however be necessary for growth in nuclear power capacity well beyond thermal reactor potential Fast reactors as well as uranium fuel enrichment and recycle needs to be kept within a more responsible domain