`Total self-sufficiency in PHWR programme'

Print edition : May 04, 2007

V.V .KRISHNAN

Interview with Dr. Srikumar Banerjee, Director, BARC.

THE Bhabha Atomic Research Centre (BARC), the fountainhead of the Department of Atomic Energy's (DAE) multifaceted programme, is 50 years old. It is the largest research and development institution in the country, with activities ranging from developing futuristic nuclear power, robotics, supercomputers to radiation processing of food products, mutant varieties of pulses, groundnuts and other seeds to nano-technology.

Dr. Srikumar Banerjee, Director, BARC, calls it "a multidisciplinary and multiscale research and development organisation". The activities of scientists and engineers at BARC deal with timescales ranging from a few femtoseconds to hundreds of years and happen in temperatures ranging from milli-Kelvin to several thousand degrees Celsius. "All these extremes in any parameter you choose are there in BARC," he said. According to Banerjee, "We have done the total technology development for nuclear reactors, including the entire nuclear fuel cycle, on the basis of indigenous know-how. Besides, we have a robust strategic programme."

Excerpts from the interview he gave Frontline on March 5, on the occasion of BARC's golden jubilee:

Homi Bhabha laid down a mandate for a three-stage atomic energy programme for India. How far have you been successful in implementing it?

We have been pursuing this three-stage mandate primarily because of our resource position. We have so much of thorium but a modest reserve of uranium. So the three-stage programme is an inevitable option for India. By using thorium, we will be able to provide nuclear energy to the country for several centuries. So it is our duty to see that we reach this stage of thorium utilisation as early as possible.

Thorium utilisation depends on the accumulation of uranium-233 inventory. That is possible only when you have fast reactors, which provide not only the energy but the additional neutrons essential for converting thorium into uranium-233. With our current reasonably assured resources of uranium, we can grow our PHWR programme up to a level of 10,000 MWe of installed capacity. If we want to grow the installed capacity to about five times using indigenous resources, we must grow the programme by building Fast Breeder Reactors. After achieving such a high-installed capacity, we can sustain that power-level for a long term using thorium. This was envisaged by Bhabha, and we are committed to this plan of action.

What are BARC's contributions to the programme?

In the nuclear power area, the three-stage programme was outlined only in the late 1960s. At that time, India's capability of being totally self-sufficient in the PHWR programme was not established. A major thing that has happened from the early 1970s until today has been achieving self-sufficiency in the total technology development of the PHWR.

In the initial stage, we contributed to both the reactor technology and the fuel-cycle technology. The first PHWR fuel [natural uranium fuel] bundles were made at BARC.

The technology of fabrication of fuel, that is, uranium oxide pellets with zirconium alloy tubes as cladding material, was developed at BARC. The technology was transferred to the Nuclear Fuel Complex in Hyderabad, which has been meeting the fuel requirement of the PHWRs both in terms of stringent quality and continuously increasing quantity.

Let me give another example. BARC has contributed to the fabrication of the PHWR pressure tubes, which house fuel bundles and through which passes high temperature and high pressure heavy water coolant. We had to change the material from zircaloy to zirconium-niobium alloy, which involved a major developmental job. The zirconium - niobium tubes will have a life of about 25 years as against eight years for zircaloy. BARC participated in this development work closely, and we can today say that the NFC has been producing pressure tubes, which meet all the stringent requirements for applications in nuclear reactors, particularly the PHWRs. Then the development of fuelling machines for our PHWRs...

They look like huge robots...

Yes, you have seen how complex that system is. Today, that technology has fully matured and all our reactors have indigenously built fuelling machines.

Coming to the reactor control systems, the 540-MWe PHWRs in Tarapur have used liquid zonal control systems. The entire reactor core is divided into 14 zones, which are controlled independently. The technology for such a system was developed entirely in-house. They are now robust systems working in reactors.

BARC's responsibility lies also in the back-end of the fuel cycle. It has developed reprocessing technology. We reprocess the spent fuel arising from the nuclear reactors and recover plutonium, which is the fuel for the Fast Breeder Reactors. In this area also, BARC can claim a major achievement, namely, the development and production of mixed carbide fuel for the Fast Breeder Test Reactor at Kalpakkam. For the first time anywhere in the world, mixed carbide fuel has been used in a reactor and it has performed very well... We also have a mandate for supplying mixed oxide fuel for the 500-MWe Prototype Fast Breeder Reactor under construction at Kalpakkam.

I must mention another important thing, that is, the life management of coolant channels in the PHWRs. Pressure tubes in a reactor do not last for the entire life of a reactor.

The question that arises is how do you assess the fitness of the service of a pressure tube. This requires periodical checks on the degradation of its material by using various in-service inspection techniques.

What will be the thrust areas of BARC in the next 25 years?

We have an ambitious programme for the next 25 years. Construction of an Advanced Heavy Water Reactor [AHWR] is one of our thrust areas. This would enable us to demonstrate the technology for large-scale utilisation of thorium in a reactor, which has a number of passive safety features. Many of the technologies essential for the implementation of the third stage of our nuclear programme will be proven as we work towards the AHWR programme. Another important task is the construction of a high-flux research reactor for testing materials and producing high specific activity radioisotopes.

We have been reprocessing spent fuel on some scale and recovering plutonium, which is a fuel for the FBR. To meet the requirement of our expanding FBR programme, it is essential to augment the scale of operation. The overall growth of our indigenous nuclear power programme will depend on how fast we keep building more FBRs.

Therefore, augmenting reprocessing capacities is yet another thrust area. We are working on uranium enrichment because the Light Water Reactors that we are currently building will use enriched uranium as fuel. Our target now is to improve the capacities and efficiencies of isotope separation processes and make it at an internationally competitive cost.

Nuclear waste management is yet another important area for the growth of nuclear power. To handle high-level waste, that is, radioactive material, we are running several Waste Immobilisation Plants. Today, BARC is working on high temperature reactors and accelerator-driven systems [ADS].

At what stage is the current development of the CHTR (Compact High Temperature Reactor) and the ADS?

You may ask why we are going in for a high temperature reactor. The present generation reactors use water as coolant. So the maximum temperature will be in the region of 300o Celsius. In the FBRs, it is 550o Celsius because the coolant is liquid sodium.

We want to develop a reactor system where we get high temperature heat, that is, at about 950o Celsius, which is required to produce hydrogen from water. Our ambition in making the CHTR is to develop a reactor system, which will provide electricity and also hydrogen by decomposing water. Hydrogen is a substitute fuel for petroleum. When petroleum becomes unavailable, we will require some fluid fuel that can be stored in automobiles, and hydrogen will do that job. You must have heard of hydrogen as the new fuel of the future, for instance, hydrogen economy. Hydrogen can be stored in liquid or gaseous form and can be tapped. It may be a good fuel for internal combustion engines. For the transport sector, hydrogen will be an essential fuel.

We should have means of producing hydrogen efficiently, which requires high temperatures - 950o Celsius is the temperature required for a candidate process called sulphur-iodine process.

The CHTR requires development of a variety of materials because the reactor will be a white-hot object at 950o Celsius. The coolant has to be liquid lead or helium. But liquid lead will be easier for us. The third option is molten salt, which can extract heat at that high temperature. The entire structural material inside the reactor will be ceramic material or carbon-based material. Very few metals can withstand that kind of temperature. We are trying to develop different materials for the reactor. Besides, we have to develop the fuel for this reactor. It involves development of a totally different kind of fuel...

We are working on solid oxide fuel cells as well. If you operate the solid oxide fuel cells in the reverse direction, it can be a method of producing hydrogen. It will electrolyticaly decompose steam into hydrogen and oxygen. We can also produce hydrogen by decomposing water molecules.

What about ADS?

It is required for two reasons. One is that the ADS produces neutrons by the spallation process, which means boiling. Neutrons in a reactor are produced by fission. When high-energy protons [from an accelerator] are bombarded on heavy nuclei like lead, the nuclear particles in the target nucleus are excited to a level that some of the neutrons are liberated from the nucleus. This is known as spallation. Spallation neutrons can augment the neutron supply, which can be used again for converting thorium to uranium-233. The second reason for the development of the ADS is that they are eminently suitable for transmuting the highly radioactive waste from conventional nuclear reactors to shortlived radio-nuclides, which do not require a long-term storage under surveillance.

ADS development will take time because this involves a series of steps and each of them is technologically challenging.

What is BARC's contribution in the non-power sector? In the agricultural sector, what are the new seeds you have developed?

Ninety-five per cent of the black gram cultivated in Maharashtra is from seeds developed through radiation mutation by BARC. It is a major achievement. Now we are expanding into radiation mutation breeding of other food crops.

Food irradiation and hygienisation is another area of our contribution in the non-power sector. Once we demonstrate their commercial viability, the private industry gets attracted to invest in radiation processing plants. The Board of Radiation and Isotope Technology [BRIT] is responsible for the propagation of radiation processing applications in both food and health care sectors. Radiation processed mangoes from India have a large potential for export to the American and Japanese markets. Our radiation processing plant at Nashik called `Krushak' is getting upgraded for this purpose.

You are a metallurgist. BARC is working on advanced materials. Can you comment on this? What is a Shape Memory Alloy (SMA)?

We have to develop many advanced high temperature materials for the CHTR. We are developing several carbon-based materials. It will be carbon-carbon composites. Fuel will be carbide fuel with different coatings. Then we will develop refractory metals such as molybdenum alloy and niobium alloy. We are working on newer zirconium alloys for the fuel tubes and the pressure tubes for the water-cooled reactors. The SMA is used in our Light Combat Aircraft. We have plans to extend its use in several applications, including biomedical applications.

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