Dear Panditji,

I shall be obliged if you kindly answer my following queries on nuclear reactors.

Mr L R Sharma
Via email

Dear Sharmaji,

We are receiving many queries related to nuclear reactors. The hotly debated Nuclear Liability Bill has also been passed in the Parliament. So we have decided to dedicate the letter pages of this edition of Gobar Times to your questions and our answers. Here they are in a random order.

The nuclear energy can be produced from Thorium and India has large reserves of this element. Then why India has taken great troubles of signing the Uraniumbased agreement with the USA?

Yes, indeed India is a leading country in thorium breeder reactor technology and is poised to build thorium-based reactors routinely by 2040. The deal has been the subject of intense debate and discussion among strategic experts, the scientific community and the mass public of both the countries. This is because the Agreement is crucial for operationalising the nuclear deal. India would not like to be denied its right to reprocess the fuel it gets from outside, whether it is natural uranium or enriched uranium, as India needs the uranium for its fast breeder reactors and thorium utilisation programme. Reprocessing the spent fuel that emerges from these reactors could allow India to increase the energy that it can extract from each batch of fuel, to ease its uranium shortage, and to advance on the three-stage path to the thorium fuel cycle. In addition, however, India will gain additional expertise in the separation of plutonium from spent fuel and large stocks of separated plutonium, both of which could be used in a military program if a political decision to do so is taken. It should be noted that spent fuel reprocessing is very expensive, and using reprocessed fuel in power reactors does not make economic sense at current uranium prices.

How a spent nuclear fuel is reprocessed? Won’t this reprocessing require the same amount of energy which is has emitted during its first use?

Well, all commercial reprocessing plants use the well-proven hydrometallurgical PUREX (plutonium uranium extraction) process. This involves dissolving the fuel elements in concentrated nitric acid. Chemical separation of uranium and plutonium is then undertaken by solvent extraction steps (neptunium – which may be used for producing Pu-238 for thermo-electric generators for spacecraft – can also be recovered if required). The Pu and U can be returned to the input side of the fuel cycle – the uranium to the conversion plant prior to re-enrichment and the plutonium straight to MOX fuel fabrication.

What is the different between a weapon grade nuclear fuel and an ordinary nuclear fuel as used in nuclear power generation?

A weapons-grade substance is one that is pure enough to be used to make a weapon or has properties that make it suitable for weapons use. Weapons-grade plutonium and uranium are the most common examples, but it may also be used to refer to chemical and biological weapons.  

Weapons-grade nuclear material causes the most concern, but plutonium and uranium have other categorisations based on their purity. The only difference between them is the concentration of the various isotopes used in the fuel.

How uranium is stored and transported to different locations?

Transportation and storage is an integral part of the nuclear fuel cycle. About 95 percent of the depleted uranium produced is stored as uranium hexafluoride, a crystalline solid, (D)UF, in steel cylinders in open air storage yards close to enrichment plants. The principal assurance of safety in the transport of nuclear materials is the design of the packaging, which must allow for foreseeable accidents. The consignor bears primary responsibility for this. Many different nuclear materials are transported and the degree of potential hazard from these materials varies considerably. Different packaging standards have been developed
according to the potential hazard posed by the material.

What is the difference between a nuclear reactor and a fast breeder?

A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate. Currently all commercial nuclear reactors are based on nuclear fission. Nuclear reactors generate energy through fission, the process by which an atomic nucleus splits into two or more smaller nuclei. Neutrons produced by fission have high energies and move extremely quickly. These so-called fast neutrons do not cause fission as efficiently as slower-moving ones so they are slowed down in most reactors by the process of moderation. In contrast to most normal nuclear reactors, however, a fast reactor uses a coolant that is not an efficient moderator, hence its neutrons remain high-energy. An example of coolant is liquid sodium. These reactors are called breeder reactors. In fact, a nuclear reactor can derive a significant amount of energy from such plutonium fission. But because this plutonium fissions, it reduces the amount that is left in the fuel. To maximize plutonium production, therefore, a reactor must create as much plutonium as possible while minimizing the amount that splits. This is why many breeder reactors are also called fast reactors.

What is heavy water and what is its chemical formula? How is it produced and where is it used in nuclear plants? Is it radio-active?

Heavy water is the common term for water which includes the deuterium isotope of hydrogen. The chemical formula of heavy water is 2H2O or D2O Heavy water can be referred to a quantity of water which contains any amount of deuterium, but often refers to water which has been enriched to contain at or near 100%. The deuterium in heavy water is much the same as normal hydrogen, which is also known as protium, except that it contains an extra neutron. So a deuterium atom contains one neutron, one proton, and one electron. The extra neutron adds a small amount of weight, about 10% of the total weight, to the atom,
which is what makes it heavy.

Heavy water is produced by separating heavy water directly from natural water or by first “enriching” the deuterium content in hydrogen gas. On Earth, deuterated water, HDO, occurs naturally in regular water at a proportion of about 1 molecule in 3200. The HDO may be separated from regular water by distillation or electrolysis and also by various chemical exchange processes Heavy water is used as a moderator in nuclear power plants, slowing down the fast neutrons so that they can react with the fuel in the reactor. Heavy water is also used in research as an isotopic tracer for chemical reactions and biochemical
pathways. It is important to note that heavy water is not radioactive, nor is it dangerous to humans or other life unless ingested in large amounts.

What is the market value of a kg of Uranium? Is it available in private market also?

The current value of a kg of Uranium is USD 130. Unlike other metals such as copper or nickel, uranium is not traded on an organized commodity exchange such as the London Metal Exchange.

This means that it is not available in private markets. Instead it is traded in most cases through contracts negotiated directly between a buyer and a seller. Sellers consist of suppliers as well as brokers and traders. A spot market contract usually consists of just one delivery and is typically priced at or near the published spot market price at the time of purchase.