Moreover, the ash in Indian coal is highly abrasive and poses serious problems to power plant equipments. Coal prices over the last 15 years have been rising at a faster rate than general inflation and this trend is likely to continue in future. Coming to the environmental aspects of burning coal for power generation, it is now recognised worldwide that acid rain is a major environmental hazard.
In view of these factors, energy planners are agreed that a gradual shift from coal to other energy sources is essential from the long-term point of view. So far as hydel power is concerned, there are increasing difficulties of valuable forest areas and problems posed by rehabilitation of relatively large Populations.
It is also not clear, if the present level of production of oil and gas (on-shore and off shore) which is about two third of the present consumption, could be maintained during the next 15 to 20 years. Electricity generation based on gas which is now being considered on a limited scale due to temporary availability of gas is not a long- term solution.
Alternative sources of energy such as solar, wind, and bio-gas are diffused and can only have limited applicability.
Thus, when one looks at the energy situation on a total basis in a long-term perspective, it is evident that some new forms of energy such as nuclear which could make a large addition to the energy resources has to be developed in a big way.
The currently known uranium reserves in the country can support a pressurised Heavy Water Reactor Programme of about 10,000 MW. However, with continuing efforts being made on exploration, it is likely that additional uranium deposits may be identified as has been the experience in the case of oil and natural gas.
The long range potential of nuclear energy in India also depends on fast breeder reactors. Even with the existing proven reserved of 70,000 tonnes of uranium, it is possible to attain an ultimate capacity of about 3,50,000 MW by the latter half of 21st century using heavy water reactors followed by fast breeders.
The question of safety of nuclear reactors and consequences of their normal and off-normal operations have been receiving the most intensive attention for over 40 years, right from the time work was undertaken on the design and construction of the very early reactors.
In fact, the subject of reactor safety, which in earlier days was called “Reactor Hazards Evaluation”, has received greater attention than even the question of design itself. More people have been involved in the analysis of safety of reactor systems than in the design of the systems themselves.
Some of the Indian engineers and scientists have been trained formally in reactor safety and hazards evaluation as part of their initial orientation of reactor design work. So far as the performance of Indian reactors is concerned, their safety record has been good. There are six units in operation and from the point of view of plant personnel, general public or the environment, no serious problem has arisen in them.
Simultaneously, with the commencement of the design effort on a reactor project, a Design Safety Committee has been set up for that project consisting of people now engaged on the design of the reactor unit. The Department of Atomic Energy Safety Review Committee (DAESRC), consisting of experts in different disciplines and not involved in the actual designing, building or running of the plant carries out a second level review and audit.
There is yet another review by the Atomic Energy Regulatory Board (AERB). In the construction and operational phases also, reviews are carried out at these levels.
Thus, there is a well-organised system of reviews and this result in a fool-proof system of evaluation of designs and operating practices. The different safety committees are also empowered to call for either a reduction of power level or even closure of an operating unit if in their opinion, running of the unit constitutes danger either to the plant or plant personnel or to the general public.
There is a system of keeping track of all ‘unusual occurrence’. What is called an ‘unusual occurrence’ in the jargon of nuclear reactor technology is really not so unusual in normal life. For example, when a pump or diesel generator is started by pressing its push button and if it does not start, the event is called an ‘unusual occurrence’ even though it might not have any implications so far as the safety, of reactor is concerned.
In the case of nuclear reactors, all these unusual occurrences, no matter how insignificant, are systematically documented, reviewed and analysed to find out the cause of the incident and for taking corrective actions by way of design modification, revision of operating procedure or replacement of a component with one having much higher reliability.
A single unusual occurrence’ cannot give rise to any concern about the safety of the plant operators or the general public. The design of the reactor installation foresees that malfunctioning of components or systems can take place and this should not result in a compromise to the safety of the installation.
This approach of analysing all unusual occurrences is unique to the nuclear industry and has contributed in a great measure towards making nuclear power production, a safe activity.
In a nuclear reactor, the basic process of production of heat is by the splitting or fashioning of uranium nuclei. In this process, the heat which is liberated is carried away by a coolant. In the reactors at Rajasthan, Chennai and the ones coming up at Narora and Kakrapar, the reactor coolant is heavy water.
The heat produced in the reactors is transferred from this heavy water to ordinary water flowing in the steam generator. The steam drives the turbine generator to produce fission electricity.
When the uranium nuclei split, it produces fission products which are radioactive. Special measures are taken to ensure that this radioactivity is safely contained under all circumstances. There are many barriers which ensure that the radioactivity is contained. First, there is the cladding of the fuel which is an alloy of zirconium.
The fuel bundles are placed inside the closed heat transport system which consists of high pressure components made from special steel or zirconium alloys.
The entire reactor system is surrounded by a massive containment building. (In the case of Kalpak Kam and subsequent reactors, the containment buildings housing the nuclear reactor have a special feature the double containment).
In order to ensure that the spread of radioactivity is prevented under all circumstances, the design of these barriers, the quality control measures taken in the manufacture of the components, building and structures and the surveillance of quality in service, are all maintained at an extremely high level.
One of the most important questions concerning the safety of nuclear reactors is to ensure that adequate cooling is provided for the nuclear fuel at all time including periods when the reactor is in a shutdown condition. Normally, the cooling of the nuclear fuel is done by the heavy water of the primary heat transport system.
When the reactor has been shut down for some time, the quantum of heat decay is such that it is more appropriate to provide cooling through another system which is called “shutdown cooling” and one system is adequate for safe cooling of the reactor.
The “main cooling” through the steam generated by the process of natural convection, that is, without the intervention of any pumps, is also adequate to carry away the decay heat.
Special provisions are made in the design to ensure that adequate cooling of the fuel takes place even when there is a rupture in primary heat transport system, leading to large escape of heavy water from the reactor system. In such a condition, continued cooling of the nuclear fuel is maintained through an emergency core cooling system which provides cold water from three different resources.
As a further backup, the cold heavy water moderator in the reactor vessel, which surrounds the fuel channels, can serve as an important heat sink in some postulated severe accident sequences involving loss of normal coolant simultaneous with failure of emergency core cooling.
This practice can be called “defence in depth” concept where there are many lines of defence, one backing another. Even in the case of no external power supply to the reactor installation, on-site power through emergency diesel generators and batteries is provided to ensure effective cooling of the nuclear fuel.