Opinion (Spotlight Weekly)

Nuclear Power And Nepal

BY Dr. AB Thapa

Nepal is one of the richest countries in the world in hydropower resources. Naturally, all of us would be considering that anybody must be having very poor understanding about our hydropower resources if he talks of nuclear power study in the context of Nepal. Unfortunately such notion cannot be true. Apart from the fact that such view is harmful to better understanding of energy related problems, it would also deprive our country of opportunities to benefit the most from the use of our vast hydropower resources. In future Nepal will have to compete on price in Indian power market if we hope to export our surplus hydroelectric power to that country. It is said that in India nuclear energy would be playing major role in fulfilling her growing demand for electricity supply considering India’s large population and limited fossil fuel base. Moreover, India has very large deposits of thorium , which can be used for the generation of nuclear energy. It is said that about 33% of the world’s thorium deposits are in India. Thus it is essential that we pay adequate attention to India’s nuclear energy program and we should equally keep abreast of current nuclear power generation technology.

India’s Nuclear Energy Generation Plans

It is reported that the importance of nuclear energy as a sustainable resource for the country was recognized at the very inception of the India’s atomic energy program five decades ago. India has only limited uranium deposits but this country is very rich in thorium deposits.

India had formulated three-stage nuclear program under the guidance of its renowned nuclear scientist late Homi J. Bhabha. The first stage comprised setting up of Pressurized Heavy Water Reactors( PHWR) and Light Water Reactors(LWR). The second stage involved setting up of Fast Breeder Reactors(FBR) backed by reprocessing plants and plutonium based fuel fabrication plants. The third stage of the Indian nuclear power program will be based on the thorium-Uranium-233 cycle.

Worldwide Use of Nuclear Energy

In 1998 a total of 437 nuclear plants operated worldwide. Another 35 reactors were under construction. Eighteen countries generate at least 20 percent of their electricity from nuclear power. The largest nuclear power industries are located in the United States (107 reactors), France (59), Japan (54), Britain (35), Russia (29), and Germany (20). In the United States, no new reactors have been ordered for more than 20 years. In many developed countries public opposition, strict building and operating regulations, and high costs for waste disposal have made nuclear power plants much more expensive to build and operate than plants that burn fossil fuels.

There were more than 100 nuclear power plants operating or being built in the United States at the beginning of 1980s. In 1996 about 22 percent of the electric power generated in the United States came from nuclear power plants. In the aftermath of the Three Mile Island accident in Pennsylvania in 1979 safety concerns and various economic factors led to suspension of additional growth of nuclear power plants in the United States. No orders for nuclear plants have been placed in the United States since 1978, and even some of those plants that had been completed have not been allowed to operate.

France occupies the topmost position in use of nuclear energy. At present France generates 80 percent of its electricity from nuclear power. However, it has recently canceled several planned reactors and may replace some of her aging nuclear plants with fossil-fuel plants for environmental reasons. As a result, the government-owned electricity utility, Electricité de France, plans to diversify the country’s electricity-generating sources.

Varieties of Nuclear Reactors

There are varieties of nuclear reactor types in operation worldwide. They are characterized by the type of fuel, moderator, and coolant used. Nuclear reactors have been built throughout the world for the production of electric power. In the United States, with few exceptions, power reactors use nuclear fuel in the form of uranium oxide enriched to about three percent Uranium-235. The moderator and coolant are highly purified ordinary water. A reactor of this type is called a light-water reactor (LWR). This type of nuclear reactors had been built from the very early period in the USA and the former USSR.

In the pressurized-water reactor (PWR), a version of the LWR system, the water coolant operates at a pressure of about 150 atmospheres. It is pumped through the reactor core, where it is heated to about 325° C. The superheated water is pumped through a steam generator, where, through heat exchangers, a secondary loop of water is heated and converted to steam. This steam drives one or more turbine generators. Afterward it is condensed, and is pumped back to the steam generator. The secondary loop is isolated from the water in the reactor core and, therefore, is not radioactive. A third stream of water from a lake, river, or cooling tower is used to condense the steam. In the USA this type of nuclear reactor was developed by Westing-house.

In the boiling-water reactor (BWR), a second type of LWR, the water coolant is permitted to boil within the core, by operating at somewhat lower pressure. The steam produced in the reactor pressure vessel is piped directly to the turbine generator for the generation of power. Thereafter it is condensed and pumped back to the reactor. Although the steam is radioactive, there is no intermediate heat exchanger between the reactor and turbine to decrease efficiency. As in the PWR, the condenser cooling water has a separate source, such as a lake or river. In the USA this type of nuclear reactor was developed by General-Electric.

In the initial period of nuclear power development in the early 1950s, enriched uranium was available only in the United States and the former Union of Soviet Socialist Republics (USSR). The nuclear power programs in Canada, France, and the United Kingdom therefore centered about natural uranium reactors, in which ordinary water cannot be used as the moderator because it absorbs too many neutrons. This limitation led Canadian engineers to develop a reactor (PHWR) cooled and moderated by deuterium oxide (D2O), or heavy water. The Canadian deuterium-uranium reactor known as CANDU has operated satisfactorily in Canada, and similar plants have been built in India, Argentina, and elsewhere.

In the United Kingdom and France the first full-scale power reactors fueled with natural uranium metal, were graphite-moderated, and were cooled with carbon dioxide gas under pressure. These initial designs have been superseded in the United Kingdom by a system that uses enriched uranium fuel. In France the initial reactor type chosen was dropped in favor of the PWR of U.S. design when enriched uranium became available from French isotope-enrichment plants. Russia and the other successor states of the former USSR had a large nuclear power program, using both graphite-moderated and PWR systems.

The power level of an operating reactor is monitored by a variety of thermal, flow, and nuclear instruments. Power output is controlled by inserting or removing from the core a group of neutron-absorbing control rods. The position of these rods determines the power level at which the chain reaction is just self-sustaining.

Nuclear Reactors in India

Currently there are 12 PHWR in India. Earlier two BWR were set up at Tarapur, Maharashtra, in 1969 to jump-start the nuclear power program. The total installed capacity of all these 14 reactors is 2,770 MW.

It is said that at present six PHWR are under construction in various parts of India. Similarly two LWR each of 1,000 MW capacity are being constructed at Kundankulam in Tamil Nadu with Russian collaboration. India is planning to have an installed capacity of 20,000 MW by 2020.

Fast Breeder Reactors

Uranium, the natural resource on which nuclear power is based, occurs in scattered deposits throughout the world. Its total supply is not fully known, and may be limited unless sources of very low concentration such as granites and shale were to be used.. The main disadvantage of the LWR nuclear power system is its very low efficiency in the use of uranium: only approximately one percent of the energy content of the uranium is made available in this system.

The key feature of a breeder reactor is that it produces more fuel than it consumes. It does this by promoting the absorption of excess neutrons in a fertile material. Several breeder reactor systems are technically feasible. The breeder system that has received the greatest worldwide attention uses Uranium-238 as the fertile material. When Uranium-238 absorbs neutrons in the reactor, it is transmuted to a new fissionable material, Plutonium.

The breeder system that has had the greatest development effort is called the liquid-metal fast breeder reactor (LMFBR). In order to maximize the production of plutonium-239, the velocity of the neutrons causing fission must remain fast—at or near their initial release energy. Any moderating materials, such as water, that might slow the neutrons must be excluded from the reactor. A molten metal, liquid sodium, is the preferred coolant liquid. Sodium has very good heat transfer properties, melts at about 100° C, and does not boil until about 900° C. Its main drawbacks are its chemical reactivity with air and water and the high level of radioactivity induced in it in the reactor.

Development of the LMFBR system began in the United States before 1950, with the construction of the first experimental breeder reactor, EBR-1. A larger U.S. program, on the Clinch River, was halted in 1983, and only experimental work was to continue. In the United Kingdom, France, and the former USSR, working breeder reactors were installed. Experimental works continued in Germany and Japan.

The first large-scale LMFBR plant for the generation of electricity, called Super-Phénix, went into operation in France in 1984. An intermediate-scale plant, the BN-600, was built on the shore of the Caspian Sea for the production of power and the desalination of water. The British have a large 250-MW prototype in Scotland.

The LMFBR produces about 20 percent more fuel than it consumes. In the LMFBR system about 75 percent of the energy content of natural uranium is made available, in contrast to the one percent in the LWR.

Fast Breeder Nuclear Reactors in India

It is reported that an indigenous 40 MW Fast Breeder Test Reactor using the unique mixed uranium-plutonium carbide fuel has been operating at the Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu since 1985. The experience with this test reactor has given India the confidence to launch a very large program based on Fast Breeder Reactor technology. In September 2003, the Government of India approved the construction of a 500 MW Prototype Fast Breeder Reactor.

It is projected that in the final stage Indian nuclear power program would be based on the thorium-Uranium 233 cycle. Thus India would be able to use its own abundant thorium deposits. This factor is said to be instrumental in encouraging to launch the fast breeder program in India.

(Dr. Thapa writes on water resources)