heavy water reactors -india

Heavy water reactors 

Advanced  heavy water reactors

India developing the advanced heavy water reactors (AHWR) as third stage  in its plan to utilize  thorium to fuel its overall nuclear power program.  The AHWR is a 300 Mwe gross (284 MWe  net ) 920 Mwt ) reactor moderated by heavy water at low pressure . The Calandria  has about 450 vertical pressure tubes and the coolant is boiling light water circulated by convention a large heat sink “ gravity driven water pool -with 7000 cubic meters  of water is  near the top of reactor building. Each fuel assembly has 3 th - U-233 oxide pins and 24 pu-th oxide pins around  a central rod with burnable absorber . Burn up of 24 Gwd /t is envisaged.  It is designed to be self- sustaining in relation to U-233 bred  from th-232 and have a low pu  inventory and consumption, with slightly negative void coefficient of reactivity.

It is designed for 100 year plant life and is expected to utilize 65 per cent  of energy of fuel, into two -thirds of that energy coming from thorium via U-233.

Once it fully operational, each AHWR fuel assembly will have the fuel pins arranged in three concentric ring  arranged .

Inner  : 12 pins th-U-233 with 3 per cent U-233
Intermediate  : 18 pins th-U-233 with 3.75 per cent U-233
Outer        :  24 pins th -pu-239 with 3.25 per cent pu

The fissile plutonium content will decrease from the initial 75 per cent to 25 percent at equilibrium discharge burn up level.

As well as U-233, some U-232 is formed, and the highly gamma-active daughter products of this confer a substantial proliferation resistance.

In 2009 an export version of this design was announced : the AHWR-LEU . These will use  low enriched  uranium plus thorium as a fuel dispensing with Plutonium in put. About 39 per cent of power will come from thorium (via situ conversion to U-233 ) and burn up will be 64 GW/dt . Uranium enrichment level will be  19.75 per cent giving 4.21 per cent average fissile contact of U-th fuel. While designed  for closed cycle, this is not required. Plutonium  production will be less than in light water reactors, and fissile  proportion will be less and pu-238 portion three times as high giving inherent proliferation resistance. The AEC says that “ the reactor is manageable with modest industrial infrastructure with the reach of developing countries.

In the AHWR-LEU the fuel assemblies will be configured.

Inner rings : 12 pins th- U with 3.55 per cent of U-235
Intermediate : 18 pins th-U with 4.34 percent U-235
Outer ring     : 24 pins th-U with 4.444 per cent U-235

HEAVY WATER REACTORS

There are presently 44 commercial heavy water reactors (HWRs) operating or under construction in six countries. For a number of years these HWRs have been world leaders in the achievement of high annual and life time capacity factors and have proven to be viable alternative to light water reactors.

In addition to achieving high capacity factors on base load plants, HWRs have also when required given very good load following service operating performance on critical items such as fuel and steam generators has been excellent and HWRs have experienced very low fueling costs due to the use of natural uranium fuel.

HWRs represent new technology and the development potential is being actively perused by investigations of advanced designs in Argentina , Canada ,India and Japan.

Basic features of heavy water reactors

Two basic types of commercially HWRs have been developed. One type developed  by Siemens/ KWV in Germany,employs a pressure vessel containing the complete reactor core. The other type Candu reactors, was developed by Atomic energy of Canada Limited (AECL) in collaboration with Ontario Hydro and Canadian manufacturers.  It employs several hundred pressure tubes rather than a single pressure vessels- both types of commercial HWRs  use  heavy water reactors as the moderator and have several key basic features.

. An excellent neutron economy permit’s the practical use of once though natural uranium fuel cycle.
. On -power refueling  which offers several fundamental benefits : higher capacity facts by eliminating periodic refueling shut down, reduced need for core reactivity and flux distribution control  mechanism or power  replacement of defective fuel and easy assess for service inspection.

Pressurized heavy water is used as a coolant in all currently operating commercial HWRs, however experimental and prototype pressure tube HWRs have been built in several countries to evaluate use of carbon dioxide, light water and organic fluids as coolant options .

Most HWRs currently use natural uranium often, with objection of being independent of uranium enrichment facilities. The use of slightly enriched  uranium fuel results in a significant improvement in fuel cycle cost and uranium utilization. Plutonium and or uranium form spent light water reactors fuel can also be efficiently burned in existing HWR designs offering synergism between HWRs and LWRs.

Higher nuclear safety and good performance will be important to achieve enhanced confidence in the safety advanced  HWR s design since this is a world trend for all reactor types. The improved safety is based on operational experience proven technologies and conclusive research and development.

A target of which is being perused in several national programs is to reduce the radiological burden on operating and maintenance staff . This is being achieved  through such means as careful optimization of tritium management, early detection of leaks, rapid location and on power removal of failed fuel, improved shielding and coolant purification s and better control of sealing materials.

Sale of reactors by India

Nuclear power corporation of India limited (NPCIL) is ready to sell pressurized heavy water reactors of 220 Mwe  or 540 Mwe capacity to other countries according to Atomic Energy Commission (AEC) chairman Srikumar  Banerji. Dr. Banerji  who gave overview of country’s atomic energy program said work had started on ingenious pressurized heavy water reactors of 700 MWe  capacity each ( two at Kakrapur  in Gujarat  and two Rawatbhatta  in Gujarat and the first pour of concrete was planned later.

India and Canada nuclear energy

AS India  and Canada resume nuclear ties after 36 years, Indian companies discuses Mo U with their Canadian counter parts at the nuclear industry conference and trade show which ended Ottawa in Canada on Friday .

The India representative said “thrust on developing an indigenous nuclear energy program India insists on 60 percent indigenous component in nuclear power plants. So all these countries U.S.,Russia, France and others which have got contracts to build nuclear power plant will need indigenous components. We invited Canadian nuclear   companies to join our eight-company consortium to participate the India nuclear business.

This is first high level interaction by Indian nuclear companies with their Canadian counter parts after two companies signed a nuclear agreement  during prime Minister Manmohn Singh visit here for G-20 summit last year.

Since India nuclear program started with CANDU reactor donated by Canada in 1950, India was invited to the nuclear show organization of CANDU industries . CANDU stands for Canadian deuterium uranium in reference to the use of natural uranium and deuterium oxide (heavy water ) in Canadian invented reactors .

But Canada snapped ties with India after 1974 Pokran  test alleging that India used its CANDU technology to make the bomb.

It took the two countries 36 years to resume nuclear ties last year after the nuclear supplier group (NSG)allowed India access to nuclear technology and fuel in 2009.