Control Rods

As the name says, Control Rod is a control device that is use to provide precise and adjustable control of reactivity in the reactor core.

When reactivity is controlled, the power output is also controlled.

Basically, control rods function by absorbing neutrons from generating another nuclear reaction.

Nuclear reaction or fission generates heat.

If the heat generated is not controlled, overheating will occur.

This will make the the reactor components such as the fuel rods melt.



Control rods also function as a safety device.

In the event of emergengy, control rods can be release completely to shut down the reactor.

Control rods materials:-

• Silver, Ag
• Indium, In
• Cadmium, Cd
• Boron, B
• Hafnium, Hf

In a more proper way of writing, the purpose of control rods includes:-

1. Coarse control and/or to remove reactivity in relatively large amounts - Shim rods.
2. Fine control and to maintain desired power or temperature - Regulating rods.
3. Provides fast shut down in the event of unsafe and emergency condition - Safety rods.



Image from Google

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Image from Google
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Image from Google
-Click for larger view-



Again, we can see that Nuclear Reactor is full of safety features!

:)







Reactor Safety Systems and Why Is A Reactor Safe?

Okay..lets talk about safety.

The most important aspect of a Nuclear Reactor.

What is Nuclear Reactor?

Nuclear Reactor is an engineering device, in which nuclear fuel and structural material are arranged such that a self-sustained fission chain reaction can occur in a controlled manner.

New and advanced reactors are designed with safety in mind, including the development and application of Passive Safety Systems as far as possible.

It requires no operator intervention in the event of major malfunction.

Passive Safety Systems depends only on physical phenomena such as pressure differentials, convection, gravity or the natural response of materials to high temperatures to slow or shut down the reaction, not on the functioning of electrical or mechanical operation on command systems.

Other safety provisions includes a series of physical barriers between the radioactive reactor core and the environment, the provisions of multiple safety systems, each with backup and designed to accommodate human error.

The barriers in a typical plant are:

1. Fuel container within the reactor, generally thousands of sealed metal tubes, rods, or plates, fabricated to the highest quality standards.
2. Closed loop of water which transport the fission energy away from the reactor. Water is converted to steam by fission.  The steam passes through a turbine-generator, is condensed and the water eventually returned to the reactor to be reheated.  Note that while this loop serves to generate steam, it also serves to cool the reactor, keeping it in thermal equilibrium.  Should one or more fuel elements fail, mechanically or due to overheating, the fission fragments would be contained in the closed cooling water loop.
3. Most reactors (except the Chernobyl type) have a third barrier, called a containment building.  It is a large steel lined, concrete structure completely enclosing the reactor and it’s cooling loops.  It is designed to completely contain all of the coolant should a major failure leak occur in the cooling loops, and all of the water flashed to steam.  So even if fission fragments were released into the cooling loop and the loop leaked, fission fragments would be held in the containment building.

So, Is a Reactor safe?

The answer is simply Yes!

P/s:- It should be emphasize that a commercial type Nuclear Reactor simply cannot under any circumstances explode like a Nuclear Bomb. :)