''How tritium extracted from
CANDU-type power reactors
supports India's H-Bomb capability''
Nestled between the nuclear capabilities of China and the nuclear aspirations of Pakistan, India would seem to be in an unenviable strategic position. As T. S. Gopi Rethinaraj reports, however, a breakthrough by Indian scientists in the economical production of tritium may have tipped the strategic scales in New Delhi's Favour.
The importance of tritium as a strategic material in the creation of thermonuclear weaponry, given the insignificance of its other uses, cannot be overstressed. Its importance becomes even more apparent when one considers the major leap from the ability to manufacture fission weaponry to the capacity to build a thermonuclear weapon like a hydrogen bomb. It is within this context that the pioneering work in extracting highly enriched tritium conducted by scientists at India's Bhabha Atomic Research Center (BARC) assumes significance. In this area at least, Indian scientists have reason to cock a snook at the USA.
While the USA had stopped producing tritium by about 1988 due to safety reasons and ageing facilities, the Indian breakthrough underscores the fact that tritium can now be produced at a fraction of the estimated US$ 7 billion needed to produce the isotope at current costs using the accelerator process, as was done in the USA. The Indian scientists have managed to extract highly enriched tritium from heavy water used in power reactors.
The advantage of the technology developed by BARC is that it assumes heavy water as the moderator in power reactors when most of those in the West (including Russia) -- with the exception of Canada -- use light water. The other advantage is a short gestation period; the Indian tritium facility takes less than two years for completion. This is not to say that India has already secretly developed the H-Bomb, but the very fact that tritium, according to all available indications, is now being stockpiled puts India in a comfortable position in terms of nuclear deterrence, given the nuclear ambitions of Pakistan and the already-nuclear China.
On the trail of Indian Tritium
It was an innocuous paragraph at the end of a recently published paper on detritiation that let the cat out of the bag. The paper appeared in a book entitled Heavy Water- Properties, Production and Analysis, which was authored by two BARC scientists, Sharad M. Dave and Himangshu K. Sadhukhan, with a Mexican scientist, Octavio A. Novaro. On p. 461 of the work, it says the following:The Bhabha Atomic Research Center, Bombay, India, also having developed a wetproof catalyst for LPCE liquid phase catalytic exchange, has employed it for detritiation. A pilot plant based on LPCE cryogenic distillation with about 90 per cent tritium removal from heavy water has been commissioned and is under experimental evaluation. Reportedly, this facility seems to be the only operating LPCE-based detritiation facility in the world. A commercial detritiation plant based on this process is being set up at one of their nuclear power stations.According to BARC scientists, the new technology is aimed at lowering the tritium content in heavy water circulating around the moderator circuit. They argue that the project is being executed to prevent the many health hazards associated with the leakage of tritium from reactors. When asked what is exactly being done to the highly radioactive tritium so recovered, the scientists refuse to talk - even under conditions of anonymity. When pressed, some ventured to comment that a scenario in which the recovered tritium is being stockpiled for strategic purposes cannot be ruled out.
Curiously, there seems to exist some confusion regarding how classified the project is, but scientists at the Nuclear Power Corporation (NPC), the government controlled organization that constructs and runs India's commercial power reactors, remain tight-lipped on the entire issue. Both A Sanatkumar and C Surendar, group directors at NPC, said the same thing: "We are unable to understand what you are talking about. There is no such project at Kalpakkam".
When the author contacted the managing director's officers said: "Please don't ask anything about the detritiation plant. We have been asked not to talk about it". However, there was no categorical denial of such a project being at the implementation stage.
Incidentally, some time ago, the NPC management announced that one of the power reactors at Kalpakkam near Madras in southern India would be opened to research activities. According to highly placed sources, the commercial version of the pilot plant is taking shape at Kalpakkam. Recently, labour trouble hit the plant with the workers striking for nearly a month because of alleged high levels of radioactivity. Employees working in the station are still puzzled as to why their dosimeter readings have increased in recent times.
Dr. Rajagopalan Chidambaram, Chairman of the Atomic Energy Commission (AEC), evaded probing questions relating to the project. When asked persistently, he admitted: "Yes, there is a pilot plant for detritiation of heavy water in BARC" Asked whether the project is meant for stockpiling tritium, he replied: "No Comment". Also refusing to comment when asked about the project was former AEC chief P. K. lyengar, one of the pioneers of India's 1974 fission bomb experiment.
With eight operating Pressurized Heavy Water Reactors (PHWRs) at Kalpakkam, Rawatbhatta, Narora and Kakrapar plus more to come in future, India has struck a gold mine in tritium production, as the BARC pilot plant can be implemented at all of these power stations. Scientists say that the size of the commercial plant would be just two or three times the size of the pilot plant. According to technical estimates, 2400 curies of tritium could be produced for every MW of electricity produced in heavy water reactors.
Since, unlike fission bombs, fusion bombs have no critical size, bombs of various intensities could be fabricated using tritium. Fusion bombs require an ambient temperature of 100 million oC to overcome the Coulomb Repulsion Barrier (CRB) which prevents lighter atoms from coming together -- meaning that fission bombs are a prerequisite for detonating fusion bombs.
India first demonstrated its capability to explode fission bombs in 1974 in the deserts of Pokhran in Northwest India. Under the circumstances, the inference is inescapable: that the breakthrough in BARC puts India on the road of self-sufficiency in terms of strategic materials for defence purposes. It is another matter that Indian scientists are loath to call it 'production' of tritium, but instead choose to talk of 'detritiation'.
"Look, our intention is not to produce tritium," said a senior scientist directly involved with the pilot detritiation plant at BARC. "Our aim is to lower the tritium content in the heavy water, which gets contaminated after fission and neutron capture by deuterium atoms. If tritium comes out as a by-product, what can we do about it?" Asked what was to be done with the tritium so obtained, the scientist just smiled.
Tritium is a radioactive isotope of hydrogen with a half-life of 12.3 years, meaning that 5.5 per cent of tritium will decay into helium-3 every year. Deuterium, another isotope of hydrogen, along with the elementary gas itself, is stable and non-radioactive. Tritium decays and is converted into a non-radioactive form of helium.
Although tritium is present naturally in the environment, this amount is too small for practical recovery. Therefore, tritium required for strategic purposes has to be produced artificially, and there are two ways to do this, both involving nuclear reactions with neutrons: in the first method, neutrons are made to strike a target of lithium or aluminum metal, which gives tritium and other by-products; the second method involves a neutron reaction with helium-3 which gives tritium and hydrogen as by-products.
The first method is widely used and was employed for several years at the Savannah River Site (SRS) in the USA before it was shut down in 1988. The production of tritium requires the generation of energetic neutrons, the source of which can be either power reactors or accelerators. In reactors, neutrons are produced as a result of fission, while in accelerators they occur as a result of spallation, where protons strike a metallic target and 'kick off' neutrons from the metal.
Tritium finds peripheral use in medical diagnostics, but it is mainly used in the construction of hydrogen bombs and to boost the yield of both fission and thermonuclear weapons. Contained in removable and refillable reservoirs in nuclear arsenals, it boosts the efficiency of the nuclear materials. Although no official data is available on inventory amounts of tritium, each thermonuclear warhead is said to contain 4 g of the isotope. However, neutron bombs designed to release more radiation will require 10-30 g of tritium, according to a status report prepared by the US Department of Energy's Science Policy Research Division and an assessment made by the Institute for Energy and Environmental Research (IEER) in Maryland, USA.
Authoritative US reports put the USA's total tritium production since 1955 at 225 kg. After decay, it is now left with 75 kg of tritium, which is sufficient to take the country through the first quarter of the next millennium.
Even in low levels, tritium has been linked to developmental problems, reproductive problems, genetic and neurological abnormalities and other health problems. Additionally, there is evidence of adverse health effects on populations living near tritium facilities. Tritium contamination has been reported at the Savannah River site in ground water soil from operational releases and accidents. No figures are available relating to the Indian stockpile of tritium, however. The pilot plant at BARC was set up, according to well-placed sources in the department, in 1992.
India has now acquired a unique place in the annals of tritium production. Lacking the 'big money' to go in for capital-intensive methods, India's economic position - combined with the hostile attitude it faced from the West following the country's refusal to sign the Nuclear Non-Proliferation Treaty, Comprehensive Test Ban Treaty and Fissile Material cut-off Treaty - has taught Indian scientists to rely on economically viable indigenous methods. They therefore decided to extract tritium from moderator heavy water in power reactors, which is plentiful. This year India exported 100 tons of heavy water to South Korea.
India's three-stage nuclear planning has come in handy for the project:
- in the first stage Indian power reactors use natural uranium;
- the second stage employs fast breeder reactors that will use plutonium from the first stage;
- finally, the third phase aims at using thorium, since India has abundant thorium reserves in the beach sands of Kerala and Orrisa.
The first stage uses reactors moderated by heavy water, and it is in these reactors that Indian scientists have struck a gold mine in tritium production.
The tritium build-up in these reactors increases with the number of years of plant operation. The pilot plant is called the detritiation plant because the process involves lowering tritium levels in heavy water, but the fact remains that the by-product is highly enriched tritium. The reason why BARC developed new technology was to reduce radioactive levels by lowering the tritium content in heavy water. The department set up a pilot plant to achieve this and struck pay dirt: enriched tritium at low cost which needed only additional detritiation plants to be added to the country's already-available nuclear infrastructure.
The BARC technology is all the more laudable in that it is 100 per cent indigenous and the first of its kind anywhere in the world, according to experts preferring to remain anonymous. Scientists at BARC's Chemical Engineering Group recently developed a wet-proof catalyst for LPCE (the process that yields highly enriched tritium from heavy water), but they refrained from talking about the defence implications of the project. They have called the facility a detritiation plant to avoid charges of stockpiling a strategic raw material crucial in the production of thermonuclear weapons.
The presence of tritium in heavy water has been a major concern of reactor engineers in India for a long time. During the operation of a PHWR, tritium is produced as a result of fission and irradiation of reactor components with neutrons. This tritium remains in the fuel and later passes into the effluents in the fuel reprocessing plants. The BARC pilot plant produces tritium using moderator heavy water, where tritium is produced due to the capture of neutrons by deuterium atoms in the water. This reaction, as reported in scientific literature, is known to yield maximum tritium.
Although any method employed in the production and enrichment of isotopes can also be used in the case of tritium, the BARC scientists' choice of process was governed by safe handling and economic reasons. BARC scientists first worked with the water distillation and electrolytic method, which proved to be risky and inefficient. This produces tritium in its most hazardous form: liquid. They instead settled for the method of chemical exchange followed by cryogenic distillation. In this method the tritium is in a liquid phase only for a short time during the chemical exchange process, with the final product collected in gaseous form and kept in double containment to ensure safety. This method yields 90 per cent enriched tritium. It is worth noting that weapons also use tritium in its gaseous phase.
The most important hurdle in producing tritium by this method is finding a suitable catalyst for the process because heavy water from the moderator and pure deuterium gas have to pass through the column containing the catalyst. Besides, the exchange reactions of deuterium between hydrogen and water require a slow and suitable catalyst, taking into account the slow nature of these reactions. Nickel coated by chromium, platinum or other noble metals supported on silica or activated charcoal have been found effective for vapour phase exchange reactions, but BARC's exchange reactions occur in the liquid phase and require some other species of catalyst. All the catalysts mentioned above lose their activity in contact with liquid water and prevent hydrogen from reaching them.
Indian scientists have overcome this problem by imparting hydrophobicity to the catalysts. Since water in the liquid form wets and contaminates the catalyst, the suitable solution was a wet proof catalyst, which is what the BARC scientists opted for. A number of technical snags associated with the proper choice of catalyst have been eliminated, and experiments conducted to check the performance of the catalyst have shown positive results. Although the department undertook this work in the early 1970s, it was only recently that they perfected the technology.
The pilot plant's equipment is indigenously designed. Scientists, have taken into consideration various aspects of handling inflammable gases like hydrogen, deuterium and the radioactive tritium. Pipelines, fitting-valves and other equipment are made of special steel, all suitable for cryogenic conditions. The entire cryogenic part of the plants is housed inside a vacuum-insulated enclosure, which provides thermal insulation for its components. The column sections have been insulated with mylar to prevent any cold leak.
Being a multi-component distillation system, it is not simple to operate. The difficulties encountered include the decay heat of tritium (associated with the decay of tritium into helium-3), which would evaporate all the liquid. The pressure drop is minimized, however, and temperature variations are kept to a minimum.
Scientists from the group say the philosophy of the plant's operation is based on fail-safe conditions. The operation of the entire distillation column takes place at atmospheric pressure and an ambulant temperature of -268 oC . The whole plant has two sections: a low tritium activity section and a high tritium activity section (see graphic). The scientists involved say that nearly 240 stages are involved in the tritium enrichment process, and so it has to be carried out in three-stage cascade distillation units.
The deuterium-tritium gas which emerges from the second stage is 100 per cent enriched. After this the tritium is separated using an equilibrator, with the condensed product serving as the reflux for the third stage. The highly concentrated tritium is drawn off periodically from the bottom of the cryogenic column and immobilized in a matrix of metal tritride, which would be compact, safe and stable at normal temperature. The gas can be recovered at any time by heating the metal tritride. At this stage the pure tritium is ready for stockpiling.
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