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India’s grand thorium nuclear plan: pity it’s many decades away and not economically viable

A primer on India’s nuclear energy sector, Hans India , By Gudipati Rajendera Kumar  , 10 July 17 “………India has insufficient Uranium reserves of 1-2% of global reserves, but is endowed with one of the largest reserves of Thorium which constitute about 30 % of global reserves.

Thorium however is not fissile and can’t be used directly to trigger Nuclear Reaction. But it is ‘fertile’ and what makes it Nuclear Fuel is the fact that its isotope Thorium – 232 can be converted to Uranium -233 which is ‘fissile’. This process of conversion is called ‘Transmutation’. To exploit Thorium reserves Dr. Homi Jehangir Bhabha conceived ‘3 Stage Nuclear Program’….
 
 at present thorium is not economically viable because global uranium prices are much lower…..
 
Thorium itself is not a fissile material, and thus cannot undergo fission to produce energy.

•  Instead, it must be transmuted to uranium-233 in a reactor fueled by other fissile materials [plutonium-239 or uranium-235].

•  The first two stages, natural uranium-fueled heavy water reactors and plutonium-fueled fast breeder reactors, are intended to generate sufficient fissile material from India’s limited uranium resources, so that all its vast thorium reserves can be fully utilized in the third stage of thermal breeder reactor.

Stage I – Pressurized Heavy Water Reactor [PHWR]

•  In the first stage of the programme, natural uranium fuelled pressurized heavy water reactors (PHWR) produce electricity while generating plutonium-239 as by-product.

[U-238 ] Plutonium-239 + Heat]

[In PWHR, enrichment of Uranium to improve concentration of U-235 is not required. U-238 can be directly fed into the reactor core]

[Natural uranium contains only 0.7% of the fissile isotope uranium-235. Most of the remaining 99.3% is uranium-238 which is not fissile but can be converted in a reactor to the fissile isotope plutonium-239].

[Heavy water (deuterium oxide, D 2O) is used as moderator and coolant in PHWR].

•  PHWRs was a natural choice for implementing the first stage because it had the mostefficient reactor design [uranium enrichment not required] in terms of uranium utilisation…..

 
• In the second stage, fast breeder reactors (FBRs)[moderators not required] would use plutonium-239, recovered by reprocessing spent fuel from the first stage, and natural uranium.

•  In FBRs, plutonium-239 undergoes fission to produce energy, while the uranium-238 present in the fuel transmutes to additional plutonium-239.

transmuted to Plutonium-239?

Uranium-235 and Plutonium-239 can sustain a chain reaction. But Uranium-238 cannot sustain a chain reaction. So it is transmuted to Plutonium-239.

But Why U-238 and not U-235?

Natural uranium contains only 0.7% of the fissile isotope uranium-235. Most of the remaining 99.3% is uranium-238.

•  Thus, the Stage II FBRs are designed to “breed” more fuel than they consume.

•  Once the inventory of plutonium-239 is built up thorium can be introduced as a blanket material in the reactor and transmuted to uranium-233 for use in the third stage.

• The surplus plutonium bred in each fast reactor can be used to set up more such reactors, and might thus grow the Indian civil nuclear power capacity till the point where the third stage reactors using thorium as fuel can be brought online.

As of August 2014, India’s first Prototype Fast Breeder Reactor at Kalpakkam had been delayed – with first criticality expected in 2015, 2016..and it drags on.

Stage III – Thorium Based Reactors

•   A Stage III reactor or an Advanced nuclear power system involves a self-sustaining series of thorium-232-uranium-233 fuelled reactors.

•  This would be a thermal breeder reactor, which in principle can be refueled – after its initial fuel charge – using only naturally occurring thorium.

•  According to replies given in Q&A in the Indian Parliament on two separate occasions, 19 August 2010 and 21 March 2012, large scale thorium deployment is only to be expected 3 – 4 decades after the commercial operation of fast breeder reactors. [2040-2070]

As there is a long delay before direct thorium utilisation in the three-stage programme, the country is now looking at reactor designs that allow more direct use of thorium in parallel with the sequential three-stage programme

•  Three options under consideration are the Accelerator Driven Systems (ADS), Advanced Heavy Water Reactor (AHWR) and Compact High Temperature Reactor

Prototype Fast Breeder Reactor at Kalpakkam

•  The Prototype Fast Breeder Reactor (PFBR) is a 500 MWe fast breeder nuclear reactor presently being constructed at the Madras Atomic Power Station in Kalpakkam, India.

•  The Indira Gandhi Centre for Atomic Research (IGCAR) is responsible for the design of this reactor.

•  As of 2007 the reactor was expected to begin functioning in 2010 but now it is expected to achieve first criticality in March-April 2016.

•  Construction is over and the owner/operator, Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), is awaiting clearance from the Atomic Energy Regulatory Board (AERB).

•  Total costs, originally estimated at 3500 crore are now estimated at 5,677 crore.

•  The Kalpakkam PFBR is using uranium-238 not thorium, to breed new fissile material, in a sodium-cooled fast reactor design.

•  The surplus plutonium or uranium-233 for thorium reactors [U-238 transmutes into plutonium] from each fast reactor can be used to set up more such reactors and grow the nuclear capacity in tune with India’s needs for power.

•  The fact that PFBR will be cooled by liquid sodium creates additional safety requirements to isolate the coolant from the environment, since sodium explodes if it comes into contact with water and burns when in contact with air……

 
1. In the first stage, heavy water reactors fuelled by natural uranium would produceplutonium [U-238 will be transmuted to Plutonium 239 in PHWR];

2.  The second stage would initially be fuelled by a mix of the plutonium from the first stage and natural uranium. This uranium would transmute into more plutonium and once sufficient stocks have been built up, thorium would be introduced into the fuel cycle to convert it intouranium 233 for the third stage [thorium will be transmuted to U-233 with the help plutonium 239].

3.  In the final stage, a mix of thorium and uranium fuels the reactors. The thorium transmutes to U-233 which powers the reactor. Fresh thorium can replace the depleted thorium [can be totally done away with uranium which is very scares in India] in the reactor core, making it essentially a thorium-fuelled reactor [thorium keeps transmuting into U-233. It is U-233 that generates the energy].

 
Present State of India’s Three-Stage Nuclear Power Programme

•  After decades of operating pressurized heavy-water reactors (PHWR), India is finally ready to start the second stage.

•  A 500 MW Prototype Fast Breeder Reactor (PFBR) at Kalpakkam is set to achieve criticality any day now and four more fast breeder reactors have been sanctioned, two at the same site and two elsewhere.

•  However, experts estimate that it would take India many more FBRs and at least another four decades before it has built up a sufficient fissile material inventory to launch the third stage.

Solution to India’s Fissile

Shortage Problem – Procuring Fissile Material Plutonium

•  The obvious solution to India’s shortage of fissile material is to procure it from the international markethttp://www.thehansindia.com/posts/index/Young-Hans/2017-07-10/A-primer-on-Indias-nuclear-energy-sector/311404

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July 14, 2017 - Posted by | India, Reference, technology, thorium

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