The Role of Startup Rods in Nuclear Reactors

 Fragment of a fuel rod element of a nuclear reactor.

Put simply, a nuclear reactor generates large amounts of heat, allowing power generators to spin. This process serves a huge range of industries and applications — propelling submarines and aircraft carriers, providing electricity to homes, and even producing isotopes used in medical research and the treatment of various diseases. These reactors produce more than 11% of electricity generated at the global level.

But what drives this process, and how does it work?

How Nuclear Reactors Work

Every nuclear reactor needs fuel to carry out its various functions. Uranium-235 and plutonium-239 are the most commonly used fuel sources. These isotopes are placed at the core of the reactor in the form of rods. A core may contain hundreds of thousands of these fuel rods, also called fuel pins. Fuel is placed into a reactor vessel — such as a large tank — along with a neutron source, which is needed to initiate a chain reaction of atom splitting. Put simply, this involves the splitting of atoms by means of nuclear fission.

Startup rods, long rods of neutron-absorbing elements such as californium-252, are used to maintain the desired state of fission. Inserted inside the nuclear reactor assembly, these rods (or plates or tubes) provide the essential initial spark for a nuclear chain reaction and are necessary for ensuring optimal safety and performance. The rods are pulled up and down by technicians to achieve the desired power level.

Common applications for startup rods include:

  • Reactor startup
  • Axial offset control
  • Emergency shutdown
  • Reactor shutdown
  • Reactor and power control

Once initiated, the chain reaction releases large amounts of heat. A moderator material in the core is used to slow down the neutrons being released from fission, and a coolant substance circulates through the core to transport the heat output to the area it’s needed most: the turbines. Depending on the specific application at hand, a range of different substances can be used for coolant, including water, heavy water, helium, and liquid sodium. Any excess heat generated in this process is released via cooling towers.

All nuclear reactors are encased in a containment structure, which serves to protect the reactor from the elements while also safeguarding the environment. These structures, known as reactor vessels, are usually made of special steel-reinforced concrete material.

How Nuclear Reactors Are Employed

All nuclear reactors in operation today fulfill one of two basic purposes: power generation or research. In power generation applications, reactors may be used to supply homes and cities with electricity, help propel marine vessels, or generate electrical and space-heating energy for remote, isolated military locales.

Research reactors, on the other hand, are not primarily used as power supply sources. Often employed by research institutions or universities, research reactors may be used to produce neutrons for medical diagnostics and therapy with the help of medicinal radiocompounds. These reactors are also used for the testing of various materials.

Nuclear reactors operate on the same basic principles of previous generations’ fossil fuel plants but differ in one very important way: They do not generate pollutants as a byproduct, and therefore serve as reliable clean energy sources.

The Versatility of Nuclear Reactors

Despite the advanced technology needed for their operation, nuclear reactors actually work based on very simple physical processes, involving the conversion of atomic fission-generated heat into electricity. Powering everything from ships and submarines to military bases and homes, nuclear reactors also serve to drive important research initiatives in the medical sector and other critical industries.




Image Credit: VPales/

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