JOIN USHasten thorium power generation
India has long been wedded to a three stage nuclear programme (TNSP) whose strategic goal is to set up large-scale thorium-based power generation capacity on a sustainable basis. In pursuit of this goal, India has demonstrated credible semi-industrial capability across the thorium fuel cycle.
While an industrial scale demonstrator is planned and an Indian molten salt breeder reactor (IMSBR) programme has been launched to provide the mainstay for a future thorium based fleet, the Department of Atomic Energy (DAE) seeks to extensively use thorium only after 2070.
This is on account of the need to build up a large enough fissile inventory that can unlock the power potential of Thorium-232 (Th-232), which is the isotopic form in which thorium occurs in nature. By itself, Th-232 is only ‘fertile’ and must be first converted to fissile Uranium-233 (U-233) by neutron irradiation for power generation purposes. However, climate change considerations and water desalination needs could drive a push for earlier deployment, though this is ultimately contingent on India’s ability to obtain fissile material internationally.
India’s thorium cycle activiti-es, though creditable, are still at a semi-industrial level. The DAE has successfully mined thousands of tonnes of monazite and extracted thorium oxide (ThO2) out of it, which in turn has been used to fabricate fuel pins for irradiation in both power genera-tion as well as research reactors.
Moreover, the U-233 obtained by reprocessing these irradiated ThO2 pins has been successfully used to fabricate fuel to drive the Kalpakkam Mini (KAMINI) research reactor in operation since 1996. Essentially a ‘closed’ thorium based fuel cycle has been demonstrated, albeit at a semi-industrial scale.
To take things to an industrial level, the DAE has validated design of a 300 MWe Advanced Heavy Water Reactor (AHWR), whose construction is supposed to begin this year or the next. This reactor is meant to demonstrate Indian capability in state of the art nuclear safety features, since the future plan is to build thorium based reactors on the site of old semi-urban coal power plants, to eschew land and water sourcing issues.
Nevertheless, the outcome of the IMSBR programme is expected to form the staple of the third stage of the nuclear programme. Early IMBSR designs rated at 850 MWe and fuelled by a lithium flouride-thorium fluoride-uranium fluoride mix have begun to take shape. Incidentally, both fast neutron and thermal neutron IMSBR designs are being considered.
The thermal breeders will have lower fissile requirements but their breeding ratios will lead to basic self-sustainment and not allow for the growth of the fleet as it were. The fast IMSBRs on the other hand have much higher fissile requirements but could exhibit breeding ratios that may lead to a growing fleet of the type over an extended period. Obviously, for a given fissile inventory, a bigger fleet of thermal IMSBRs can be set up initially.
Either way, a large U-233 inventory will have to be created, whatever the preferred IMSBR type. The TSNP envisions the use of Pu-239 fuelled FBRs for this purpose wherein Th-232 will be introduced in the blanket region of fast breeder reactors (FBR) to breed U-233. But DAE intends to do this only after a la-rge fleet of FBRs with short ‘do-ubling’ time has been built up.
Thorium deployment
The FBRs that are fuelled by plutonium and uranium in pure metallic form rather than oxide form have shorter doubling times. But metallic FBRs (MFBRs) of 1,000 MWe capacity are likely to be introduced only in the mid-2020s, with Th-232 blankets being put into them only in the third decade after the launch of the first such MFBR. This is why DAE does not envision significant thorium deployment before 2070.
The delayed introduction of Th-232 indicates that DAE intends to build up a large Pu-239 inventory first. Given that India is gradually committing itself to emission targets and its peninsula requires potable water, earlier deployment of thorium is also under consideration. The DAE also has thorium based high temperature reactor designs that are suitable for water desalination purposes.
The TNSP’s timescales are essentially based on the use of only domestic fissile resources to build an inventory of Pu-239 and U-233 to attain a large thorium based fleet. But, if Pu-239 were to become available from overseas, either from decommissioned weapons or by being allowed to reprocess the large stocks of accumulated spent fuel, thorium deployment could happen sooner.
‘Imported’ Pu-239 could be ‘burned’ in emerging new designs which though not really breeders, have high ‘conversion’ ratios and will generate a lot of U-233 in lieu of the Pu-239 which is consumed. This would suit those countries that are looking to dispose of their large Pu-239 stocks due to proliferation concerns such as Japan. However, this is subject to other countries agreeing to use of imported Pu-239 in FBRs under international ‘safeguards.’
Regardless, as V Jagannathan, a retired senior DAE scientist puts it, ‘securing plutonium from abroad will give us options’ that will run parallel to the ‘domestic only’ approach. Indeed, India may have to move faster on thorium, since China is already building a molten salt reactor demonstrator.
(The writer is a New Delhi-based commentator on security and energy issues)