Spent fuel from nuclear power plants is not a waste but a resource

Focus on what happens inside a nuclear reactor, the generation of spent fuel and its reprocessing

The Kudankulam unit (pictured) is known as VVER (and is not the type used at Chernobyl in Russia). The difference lies in the need to enrich the Uranium, which is not the case with the Kalpakkam reactor.

There has been a lot of noise lately about the handling of spent fuel from the Kudankulam nuclear power plant, located near Kanyakumari.

From the Speaker of the Tamil Nadu Assembly to the Chief Minister, many have spoken which unfortunately does not provide a clear understanding of the subject and requires clarification.

First, let’s understand the questions and seek answers from a scientific perspective.

What happens inside a nuclear reactor?

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All reactors have fuel in the form of tubes. The tubes contain pellets with enriched uranium oxide (U235) inside. Heat or energy is generated by fission with bombardment neutrons. Natural uranium contains a very small percentage of U235 and its proportion must be increased to five to seven percent to make it usable as fuel.

The energy of the fission products released is enormous and is intended to generate electricity using turbines. After several months of use, the fuel is no longer productive and is classified as spent fuel. The old rods are then removed and replaced with new ones for additional power generation. In a nutshell, it’s everything that happens inside a nuclear reactor.

How is nuclear waste different from spent fuel?

Spent fuel, in the form of removed rods, is stored for a long period in pools of water near the reactor, then transported to sites far from the reactor (AFR) where it is reprocessed.

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Notably, there are differences between the types of reactors used in Kalpakkam and Kudankulam power plants (both located in Tamil Nadu).

The Kudankulam unit is known as VVER (and is not the type used at Chernobyl in Russia). The difference lies in the need to enrich the Uranium, which is not the case with the Kalpakkam reactor. Also, the moderator used to control the reactions is different.

In this way, Kudankulam units are not so different from other reactors in India. Reprocessing is a method by which fissile plutonium and other radioactive substances are removed from used nuclear fuel.

After reprocessing and extraction of uranium and plutonium, besides cesium-137, strontium-90 and other useful isotopes, the remainder is a small amount which is stored in vitrified glass for long-term storage. It is at this stage that the question of underground storage arises. This is a challenge that has not yet been resolved by any country.

Several countries like Russia, China, France and India reprocess spent fuel, while the United States prohibits it by law for their own reasons. Therefore, for the United States, it is a serious problem to manage large quantities of spent fuel which is then considered as waste. The United States has also not taken up the challenge of underground storage.

Spent fuel must be protected and cooled

Spent fuel in the initial rods removed from the reactors after the fission cycle and is no longer useful for this purpose. It is kept in water basins on the reactor site, protected and cooled. The water basins are at least 20 feet deep with assemblies at the bottom. In addition, care must be taken that radioactive materials do not contaminate the surrounding area.

New spent fuel periodically replaces the old after being removed for reprocessing. Additionally, it is difficult to remove defective or leaking fuel rods, which must be done with extreme caution before placing them under the water basin to avoid contamination.

The water mainly cools the hot fuel rod and protects the environment from radiation. There are also other methods of processing spent reactor fuel, but that is beyond the scope of this article.

What happens during the reprocessing of spent fuel?

During reprocessing, plutonium and uranium (U238) are extracted for later use with other useful isotopes. Long-lived nuclides are converted to short-lived nuclides by nuclear incineration and the waste volume is thus reduced. Waste handling becomes a challenge for which underground storage will be necessary. Fortunately, the need to address this issue has not yet arisen.

Now let’s talk about the Kudankulam reactor. As mentioned earlier, its design is different from other nuclear reactors found in India. The rest of the plants are pressurized heavy water reactors (PHWR), where heavy water is used to control fission that spins out of control. Heavy water by the way has the isotope Deuterium (D2O) instead of hydrogen, which is present in normal water (H2O). The Kudankulam reactor uses enriched uranium and normal water (also known as VVER reactor – Vada Vada Energy. In Russian, Vada means Water!). The uranium for this is supplied by Russia.

Digging a little deeper into the history of the Kudankulam reactor will help us better understand how it works.

  1. The current proposal is to have 6 plants of 1,000 MW each. The first and the second resulted from the Rajiv Gandhi-Gorbachev agreement of 1988. After the collapse of the Soviet Union in 1990, the agreement was abandoned. It was revived later in 2002 although the United States opposed it. Russia, which needed huge amounts of foreign currency, cited what is euphemistically called the “grandfather clause”, namely the previous agreement, and proceeded with the supply.

2. The rest of the plants were offshoots of the 123 nuclear deal between India and the United States with the authorization of the Nuclear Suppliers Group (NSG). India got an exemption from the sanctions (imposed after the Pokhran test) to import uranium, which was a major advantage.

3. Factories that obtained uranium through imports were subject to inspection by the IAEA (International Atomic Energy Agency). Since the uranium for the Kudankulam reactor was supplied by Russia, it is under IAEA inspection.

4. The 1988 agreement included a clause providing for the transportation of spent fuel to the former Soviet Union. Practically, it would have created huge transportation problems when transitioning through the seas. The agreement was amended in 2002 and therefore the spent fuel must be stored at Kudankulam itself.

5. Coming back to spent fuel, we have to realize that only 1% of nuclear material is used in the reactor and much of the rest can still be used after reprocessing.

6. It is a misnomer to call it waste, and the correct term is only spent fuel.

7. Reprocessed extracts of uranium and plutonium also have the potential to be used in bomb making. Therefore, there are restrictions for reprocessing in many countries. Needless to say, this reprocessed material is used for various products, including fuel for the breeder reactor, known as the second stage of India’s nuclear program.

8. Plutonium is extracted from spent fuel in other reactors in India.

9. Plutonium can be used in the fast breeder reactor at Kalpakkam. A (small) test reactor (FBTR, 40 MW) was built and operated satisfactorily.

10. The design of the 700 MW Fast Breeder Reactor (FBR), known as Bhavini, is experiencing problems and has yet to be made critical (the stage when the reactor is ready to generate electricity).

The Kalpakkam FBR will use a mixed oxide of Pu-239 (obtained from reprocessed spent fuel from PHWRs) and Uranium-238 as fuel to generate power. This nuclear reaction will also produce more Pu-239 by converting both U-238 in the fuel mixture, as well as a depleted uranium blanket surrounding the core, in addition to plutonium.

Due to the presence of liquid sodium coolant in these reactors, extreme caution must be exercised. Because sodium is an extremely reactive material and reacts violently with water and air, it must be stored in an inert atmosphere at high concentration. Successfully handling liquid sodium is a serious challenge and it can take some time to overcome. But there is no doubt that it needs to be solved locally as no country has managed to master the art so far.

About the Kudankulam reactor and how it is different from others

As explained earlier, the Kudankulam reactor is of a different design from the reactors at Kalpakkam, Kaiga, Kakrapur, Rawatpur and Narora (locally designed). These plants are Pressurized Heavy Water Reactors (PHWR). The factories at Kalpakkam (Kaiga, Kakrapur, Rawatpur and later Narora) had started with Canadian assistance. However, after the Pokran I test in 1974, Canada withdrew its support and India had to supplement the Kalpakkam units with indigenous efforts.

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We now come to the storage of spent fuel away from the reactor (AFR). It should be noted that such an installation already exists on Indian reactor sites. To that extent, this is nothing new. The first two Kudankulam plants had kept spent fuel in storage pools for the past few years. They must be sufficiently cooled and can be kept in storage places inside the complex, but away from the reactor to make room for new spent fuel coming out of the reactors.

The AFR is also specific to the type of reactor and the fuel used. The AFR at Kudankulam cannot be used for spent fuel from other plants. The current status of the spent fuel reprocessing agreement is unclear as Kudankulam falls under IAEA safeguards.

The old Rajiv Gandhi-Gorbathav agreement was amended in 2002 to keep the fuel at the reactor site itself instead of transporting it to Russia. Until clarity on the spent fuel to be reprocessed for all reactors under Agreement 123 and the IAEA safeguard is achieved, they should be protected within the complex but away from the reactor. However, this is not a “waste management” problem.

They can be stored safely without any radiation risk to the environment or to people living nearby. It’s not an immediate concern.

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Instead, international agreements must be made for the safe reprocessing and subsequent peaceful use of nuclear materials.

If such a scheme works and the FBR reactor, “Bhavini” at Kalpakkam, succeeds, these questions will eventually have a natural and satisfying solution. The challenge of disposing of waste in underground repositories will also be taken up gradually.