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

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

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

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.

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

GREATER SHARE FOR NUCLEAR IN ELECTRICITY SUPPLY

REPLACE FOSSIL HYDRO- CARBON IN A PROGRESSIVE MANNER

RECYCLE CARBON- DIOXIDE DERIVE MOST OF PRIMARY ENERGY THROUGH SOLAR & NUCLEAR

Sustainable development of energy sector Transition to Fossil Carbon Free Energy Cycle

Fossil Energy Resources

Nuclear Energy Resources

Hydrogen

ENERGY CARRIERS

(In storage or transportation)

• Electricity

• Fluid fuels

(hydro-carbons/ hydrogen)

Biomass

WASTE• CO2

• H2O

• Other oxides and products

Nuclear Recycle

Sustainable Waste Management Strategies

CO2

Sun

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

chemical reactor

CO2

CH4 FluidHydro carbons

Electricity

Electricity

Carbon/Hydrocarbons

Other recycle modes

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

• 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 average. . 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 areas where radiation level is many times higher than 2.4 mSv/yr world average.     

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.

Can we eliminate serious impact in public domain

with technology available as of now?

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

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 assemblyAHWR Fuel assembly

Bottom Tie Plate

Top Tie Plate

Water Tube

Displacer Rod

Fuel Pin

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

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

Reactor Block Components

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.

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.

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

storage

800 1200 1600

2

3

4

5

6

Therm

al C

onductivity (

W/m

K)

Temperature (K)

ThO2, BARC

ThO2, INEEL

ThO2, Bakker

UO2

Ref. case

LEULEU+Th

Pu(RG)+D.U.

Pu(RG)+ThU(WG)+ThPu(WG)+Th

For a Typical PHWR LEU

12

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

Plant familiarization & identification of design aspects important to severe accident

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

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

Level-2 : Source Term (within Containment) Evaluation through Analysis

Level-2 : Source Term (within Containment) Evaluation through Analysis

Release from Containment Release from Containment

Level-3 : Atmospheric Dispersion With Consequence Analysis

Level-3 : Atmospheric Dispersion With Consequence Analysis

Level-1, 2 & 3 PSA activity block diagramLevel-1, 2 & 3 PSA activity block diagram

Variation of dose with frequency exceedence(Acceptable thyroid dose for a child is 500 mSv)

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

western Indian side)

Contribution to CDF

SWS: Service Water System

APWS: Active Process Water System

ECCS HDRBRK: ECCS Header Break

LLOCA: Large Break LOCA

MSLBOB: Main Steam Line Break Outside Containment

SWS63%

SLOCA15%

10-3 10-2 10-1 100

10-14

10-13

10-12

10-11

10-10

Fre

qu

ency

of

Exc

eed

ence

Thyroid Dose (Sv) at 0.5 Km

1 mSv 0.1 Sv 1.0 Sv 10 Sv

10-

14

10-

13

10-

12

10-

11

10-

10

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

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 U 235 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

AHWR300-LEUprovides betterutilisation ofnatural uranium,as a result ofa significantfraction of theEnergy being extracted from fission of 233U,converted in-situfrom the thoriumfertile host. LEU-Thorium fuel can lead to

better/comparable utilisation of mined Uranium

238Pu 3.50 %

239Pu 51.87

%

240Pu 23.81

%

241Pu 12.91

%

242Pu 7.91 %

9.54 %

41.65

%

21.14

%

13.96

%

13.70

%232U 0.00 %

233U 0.00 %

234U 0.00 %

235U 0.82 %

236U 0.59 %

238U 98.59 %

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.

0.02 %

6.51 %

1.24 %

1.62 %

3.27 %

87.35

%

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, 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.

0 20 40 60 80 1000

20

40

60

80

Discharge fuel

Initial fuel

Fiss

ile p

luto

nium

con

tent

in th

e fu

el (

kg/te

)

Discharge burnup (GWd/te)

Plutonium destruction in thorium-plutonium fuel in PHWR

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 eff) 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 out

Thorium is a logical choice for fuel cycle in both present and future systems

0 20 40 60 80 100 1200

1000

2000

3000

4000

5000

6000

0

2

4

6

8

10

12

14

16

Burn up GWd/te

23

2U

con

cen

trati

on in

pp

m

23

3U

con

cen

trati

on

(g/k

g o

f H

M)

233U

232U

0 20 40 60 80 100 1200

1000

2000

3000

4000

5000

6000

1

10

100

1000

Burn up GWd/te

23

2U

con

cen

trati

on in

pp

m

Exp

osu

re t

ime (

hr)

to a

cquir

e

LD5

0 at

1 m

for

8.4

kg 23

3U

232U

Exposure time for lethal dose

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

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

Case of Pu-RG+Thoria in AHWR

21

“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

Enrichment Plant LEU

Thermal reactors

Safe &Secure

ReactorsFor ex. AHWR

LEU Thorium fuel

Reprocess Spent Fuel Fast

Reactor

Recycle

ThoriumReactorsFor ex. Acc. Driven MSR

Recycle

Thorium

Thorium

Uranium

MOX

LEU-Thorium

233UThorium

Thorium

For growth in nuclear

generation beyond thermal reactor

potential

Present deploymentOf nuclear

power

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 risk

Thorium 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

Thank you