Problem 44 - A Complete Resource Book in Chemistry for JEE Main

Question

The compound used in enrichment of the uranium in nuclear power plant is (a) \(\mathrm{UF}_{6}\) (b) \(\mathrm{U}_{3} \mathrm{O}_{8}\) (c) \(\mathrm{UCl}_{4}\) (d) \(\mathrm{UO}_{2}\left(\mathrm{NO}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

The compound used in enrichment of uranium is (a) \(\mathrm{UF}_{6}\).

Step 1: Understanding the Process

Uranium enrichment is a process used to increase the percentage of the uranium-235 isotope in uranium. This is necessary for nuclear reactors and weapons, which require a higher concentration of uranium-235 than naturally occurs.

Step 2: Identifying the Suitable Compound

For enrichment, the compound must be suitable for gas diffusion or centrifugation methods. Uranium hexafluoride, \(\mathrm{UF}_{6}\), is unique because it can be used as a gas at moderate temperatures, making it appropriate for the enrichment process.

Step 3: Reviewing Options

Let’s examine the given options: (a) \(\mathrm{UF}_{6}\) is uranium hexafluoride, commonly used in gas centrifuges for enrichment. (b) \(\mathrm{U}_{3} \mathrm{O}_{8}\) is a uranium oxide often used as fuel but not for enrichment. (c) \(\mathrm{UCl}_{4}\) is uranium chloride, which is not used in uranium enrichment. (d) \(\mathrm{UO}_{2}\left(\mathrm{NO}_{3}\right)_{2}\) is uranium nitrate, typically used for chemical purposes, not enrichment.

Step 4: Selecting the Correct Compound

Based on the information, the compound used for enriching uranium by changing it to a gaseous form is \(\mathrm{UF}_{6}\).

Key Concepts

Uranium-235

Uranium-235 is an isotope of uranium, which means it is one of the types of uranium atoms with a different number of neutrons. Uranium itself is a heavy metallic element that is mildly radioactive. It's important to note that not all uranium atoms are the same.
In nature, uranium is mostly found as Uranium-238, but a small part, about 0.7%, is Uranium-235. This particular isotope is crucial because of its ability to sustain nuclear chain reactions, making it useful in both nuclear reactors and nuclear weapons. The challenge in using uranium for these purposes lies in its natural state, where Uranium-235 is insufficient. Therefore, the enrichment process aims to raise the concentration of Uranium-235 in uranium.

• Natural uranium consists of 99.3% Uranium-238.
• Only 0.7% is Uranium-235, which needs enhancement for effective use.
• Enriched uranium has higher levels of Uranium-235, typically between 3-5% for reactors.

Enriched uranium allows for efficient reactions needed to generate energy in nuclear power plants or provide explosive power in weaponry.

Gas centrifugation

Gas centrifugation is one of the most common methods for enriching Uranium-235. This process takes advantage of the slight mass difference between Uranium-235 and Uranium-238 atoms.
The process involves converting uranium into a gaseous form, specifically uranium hexafluoride (UF6), and then spinning it at high speeds in a series of centrifuges. The centrifuge equipment spins at incredibly high speeds, creating a strong centrifugal force. This force is powerful enough to separate isotopes based on their molecular mass: 

• Heavier Uranium-238 isotopes move towards the outer edge of the centrifuge.
• Lighter Uranium-235 isotopes remain closer to the center.

This separation process increases the proportion of Uranium-235 in the gas phase, which is then collected for further processing. Gas centrifugation is preferred due to its efficiency compared to older methods like gaseous diffusion.

Uranium hexafluoride (UF6)

Uranium hexafluoride, also known as UF6, plays a central role in the uranium enrichment process. This compound is unique due to its specific chemical and physical properties.
At room temperature, UF6 appears as a white crystalline solid, but it can easily be converted to a gas when heated slightly above room temperature. This property is particularly useful because gas centrifugation processes require uranium in its gaseous form.

• Transformative Properties: It transitions from solid to gas at relatively low temperatures, facilitating the enrichment methodology.
• Reactive Nature: Its reactivity allows it to engage with other substances, making handling and storage delicate activities.

Moreover, the compound’s ability to form stable gases makes it suitable for gas diffusion and the centrifugation techniques used in enriching uranium. It is essential to note that despite its usefulness, UF6 must be managed with care due to its reactive and corrosive nature, ensuring safe and efficient enrichment operations.