Question

Which type or types of nuclear reactors have these characteristics? (a) Does not use a secondary coolant (b) Creates more fissionable material than it consumes (c) Uses a gas, such as \(\mathrm{He}\) or \(\mathrm{CO}_{2}\), as the primary coolant

Short answer

The nuclear reactor type that meets the characteristics given is a hypothetical Gas-Cooled Fast Breeder Reactor (GCFBR). This type of reactor would not use a secondary coolant, create more fissionable material than it consumes, and use a gas such as helium or carbon dioxide as the primary coolant.

Step-by-step solution

(Step 1: List common types of nuclear reactors)

Some of the common types of nuclear reactors are: 1. Pressurized Water Reactor (PWR) 2. Boiling Water Reactor (BWR) 3. Heavy Water Reactor (HWR) 4. Gas-Cooled Reactor (GCR) 5. Fast Breeder Reactor (FBR) 6. Liquid Metal Fast Breeder Reactor (LMFBR)

(Step 2: Identify the type or types of reactors without a secondary coolant)

Among these types of reactors, only the Gas-Cooled Reactor (GCR) does not use a secondary coolant system, as it uses a gas, such as helium or carbon dioxide, for the direct cooling of the reactor core.

(Step 3: Identify the type or types of reactors that create more fissionable material than they consume)

Fast Breeder Reactors (FBR) and Liquid Metal Fast Breeder Reactors (LMFBR) are specially designed to produce more fissionable material than they consume, by converting fertile material into fissile material through neutron capture.

(Step 4: Identify the type or types of reactors that use a gas as the primary coolant)

The Gas-Cooled Reactor (GCR) uses a gas, such as helium or carbon dioxide, as the primary coolant, which directly cools the reactor core.

(Step 5: Determine the type or types of nuclear reactors with all given characteristics)

Now, we need to find the type or types of reactors that meet all the characteristics (a, b, and c). Based on the information we gathered in steps 2, 3, and 4: - The Gas-Cooled Reactor (GCR) meets both characteristics (a) and (c). - The Fast Breeder Reactor (FBR) and the Liquid Metal Fast Breeder Reactor (LMFBR) meet characteristic (b). None of the reactors alone meet all three characteristics; however, it is possible to have a modified type of Gas-Cooled Reactor designed as a breeder reactor. This hypothetical reactor would be called a Gas-Cooled Fast Breeder Reactor (GCFBR), which could then meet all three characteristics.

Key concepts

Gas-Cooled Reactor (GCR)

A **Gas-Cooled Reactor (GCR)** is a type of nuclear reactor that uses gas as the primary coolant. Instead of relying on a liquid metal or water to cool the system, gases such as helium or carbon dioxide directly cool the reactor core. This method simplifies the cooling process.

In GCRs, the gas circulates directly through the reactor. There is no need for a secondary coolant as found in some other reactor types. This unique design allows for efficient heat transfer and can operate at higher temperatures, which could lead to improved thermodynamic efficiency.

• **Primary Coolant**: Gases such as helium or carbon dioxide
• **Advantages**: No secondary coolants, direct cooling
• **Applications**: Due to its high temperature operation, it can be used for process heat applications and potentially hydrogen production.

Overall, gas-cooled reactors offer a compact and effective way to manage nuclear reactions with swift heat removal and reduced complexity in coolant systems.

Fast Breeder Reactor (FBR)

A **Fast Breeder Reactor (FBR)** stands out because it is capable of generating more fissionable material than it consumes. Conventional reactors use neutrons to sustain the chain reaction, but Fast Breeder Reactors go a step further.

They are designed to efficiently use fast neutrons, which are not moderated, to convert non-fissionable isotopes present in the reactor into fissionable fuel. Typically, FBRs utilize a blanket of fertile material around the core, which is transmuted into the fissile material through neutron capture.

• **Key Feature**: Converts fertile material into fissile material
• **Coolant Type**: Often use liquid metal coolants like sodium for heat transfer
• **Benefit**: Extends nuclear fuel supply by making use of otherwise non-usable isotopes

Because they help maximize the usage of nuclear fuel and produce new fissile material, Fast Breeder Reactors can be vital for sustainable nuclear power development.

Nuclear Reactor Characteristics

Different nuclear reactors have distinct characteristics based on their design and intended use. These characteristics determine their efficiency, safety, and application in the energy sector.

Some key characteristics of nuclear reactors include the type of coolant used, the neutron spectrum utilized, and the fuel cycle. Each type has its own advantages and challenges:

• **Coolant**: Determines the reactor's heat transfer abilities. Can be water, gas, or liquid metal.
• **Neutron Spectrum**: Reactors can utilize either thermal or fast neutrons, affecting the efficiency of the nuclear reaction.
• **Fuel Cycle**: The method of fuel use and replenishment, with options like once-through, recycling, or breeding (as in breeder reactors).

Understanding these characteristics is essential when designing reactors that suit specific energy goals or address specific environmental or economic concerns in nuclear energy production.