Problem 56 - Chemistry An Atoms First Approach

Question

Breeder reactors are used to convert the nonfissionable nuclide \(\frac{238}{92} \mathrm{U}\) to a fissionable product. Neutron capture of the \(\frac{238}{92} \mathrm{U}\) is followed by two successive beta decays. What is the final fissionable product?

Step-by-Step Solution

Answer

The final fissionable product after Uranium-238 (\(\frac{238}{92}\text{U}\)) undergoes neutron capture followed by two successive beta decays is Plutonium-239 (\(\frac{239}{94}\text{Pu}\)).

Step 1: Neutron Capture

Neutron capture is the process where a nucleus captures a neutron and gains one neutron. This increases the mass number (A) by one but keeps the atomic number (Z) the same. For the given nuclide, Uranium-238 (\(\frac{238}{92}\text{U}\)), upon neutron capture, the mass number will increase by 1, while the atomic number remains the same. The resulting nuclide will be: \[ \frac{239}{92}\text{U} \]

Step 2: First Beta Decay

Beta decay occurs when a nucleus emits a beta particle (electron). During this process, a neutron is converted into a proton, causing the atomic number (Z) to increase by 1, while the mass number (A) remains unchanged. For the nuclide after neutron capture, \(\frac{239}{92}\text{U}\), following the first beta decay, we have: \[ \frac{239}{93}\text{Np} \] Here, Np stands for Neptunium, which has an atomic number of 93.

Step 3: Second Beta Decay

We have one more beta decay to consider. The process is the same as in Step 2. For the nuclide obtained after the first beta decay, \(\frac{239}{93}\text{Np}\), the second beta decay will lead to: \[ \frac{239}{94}\text{Pu} \] Here, Pu stands for Plutonium, which has an atomic number of 94. The final fissionable product after the non-fissionable nuclide Uranium-238 (\(\frac{238}{92}\text{U}\)) undergoes neutron capture followed by two successive beta decays is Plutonium-239 (\(\frac{239}{94}\text{Pu}\)).

Key Concepts

Breeder Reactors

Breeder reactors are a fascinating aspect of nuclear chemistry. Their primary purpose is to generate more fissionable material than they consume. This process is different from conventional nuclear reactors, which mainly consume fissionable material.

Breeder reactors work by converting non-fissionable isotopes, like Uranium-238, into fissionable ones, such as Plutonium-239. This conversion occurs through nuclear reactions involving neutron capture and subsequent transformations. By doing so, breeder reactors help to extend the fuel supply for nuclear power generation, making them a potentially sustainable and efficient option for energy production.

It's important to understand that breeder reactors don’t just generate energy; they also manufacture new fuel. This dual capability sets them apart and has significant implications for long-term nuclear fuel sustainability.

Neutron Capture

Neutron capture is a crucial nuclear reaction that plays a fundamental role in nuclear chemistry. It involves the absorption of a free neutron by a nucleus, resulting in the formation of a heavier isotope. This process does not change the atomic number of the nucleus but increases its mass number by one.

In the case of Uranium-238, when it captures a neutron, it becomes Uranium-239. The ability to transform isotopes through neutron capture is essential for breeder reactors, as it allows for the generation of new fissionable material from non-fissionable sources.

• It can happen spontaneously or can be induced during nuclear reactions.
• Neutron capture can lead to subsequent nuclear transformations, such as beta decay, which are instrumental in creating fissionable isotopes like Plutonium-239.

Beta Decay

Beta decay is a type of radioactive decay that significantly alters the composition of a nucleus. It occurs when a neutron inside a nucleus is transformed into a proton, with the emission of a beta particle, which is a high-energy electron. This process increases the atomic number by one, while the mass number stays the same.

During the transformation from Uranium-239 to Plutonium-239, two beta decays are required. First, Uranium-239 undergoes beta decay to become Neptunium-239. This increases the atomic number from 92 to 93. Then, Neptunium-239 undergoes another beta decay, resulting in Plutonium-239, with an atomic number of 94.

Beta decay is essential in converting captured neutrons into a useful form of energy-producing matter, completing the transformation started by neutron capture. This process is crucial for breeder reactors to produce fissionable material efficiently.

Fissionable Material

Fissionable materials are isotopes that can sustain a nuclear fission chain reaction upon absorbing a neutron. Fission is the process of splitting a heavy nucleus into two lighter nuclei, releasing a significant amount of energy and more neutrons in the process.

Plutonium-239, produced in breeder reactors from Uranium-238, is a prime example of a fissionable material. It can undergo fission and thereby contribute to sustaining a nuclear chain reaction, particularly in nuclear reactors or weapons.

• Fissionable materials like Plutonium-239 are crucial for both civilian nuclear power generation and military applications.
• The ability to convert non-fissionable isotopes into fissionable ones helps in efficiently utilizing the earth's natural resources for energy.

Understanding the processes that create fissionable materials is essential for appreciating both the potential and the challenges of nuclear technology.