Definition

Noun: A thermal reactor is a type of nuclear reactor in which the nuclear fission chain reaction is sustained primarily by neutrons that have been slowed down (moderated) to thermal energies. This slowing down increases the probability of fission in certain fissile fuels like uranium-235.

Usage

The term "thermal reactor" is used to classify and describe a fundamental type of nuclear reactor design, contrasting with "fast reactor" designs. It specifies the energy level of the neutrons responsible for sustaining the fission process.

Examples

• The most common power-generating nuclear reactors in the world, such as pressurized water reactors (PWRs) and boiling water reactors (BWRs), are thermal reactors.
• A key component of a thermal reactor is the moderator, like water or graphite, which slows neutrons without absorbing them.
• The design of a thermal reactor requires careful management of the moderator-to-fuel ratio.

Advanced Usage

• "Thermal-neutron reactor": This is a more precise technical synonym for "thermal reactor," explicitly naming the neutron type.
• The concept is central to reactor physics, often discussed in the context of the "thermal fission cross-section," which is much larger for U-235 than the fast fission cross-section.

Variants and Related Words

• Thermal neutron (n): A neutron that has been slowed by a moderator until its kinetic energy is approximately equal to that of the surrounding atoms (around 0.025 eV at room temperature).
• Moderator (n): A material (e.g., light water, heavy water, graphite) used in a thermal reactor to slow down fast neutrons produced by fission.
• Fast reactor (n): A nuclear reactor that uses fast (high-energy) neutrons to sustain the fission chain reaction, requiring no moderator.

Synonyms

• Thermal-neutron reactor

Antonyms

• Fast reactor
• Fast-neutron reactor

Noun

1. a nuclear reactor in which nuclear fissions are caused by neutrons that are slowed down by a moderator