Chernobyl

Chernobyl accident in 1986.

This accident dated 24 years back is still a nightmare in most people's heart and is one of the contributing factor why nuclear technology is heavily opposed or go against.

It is one of the most advanced nuclear powerplant of its time, operated by a group of most brilliant scientists and engineers; however, the disaster still happened because of their pride and ego.

Basically, what happened was, they were trying to run an experiment to prove the plant's capability or performance, hence all the safety systems were bypassed, and accident occured! Without containment building, the radiation spreaded throughout Europe reaching as far as Sweden.

Another thing that makes Chernobyl as the last is that the nuclear reactor out there currently are all "negative void temp coefficient" type of reactor eversince Chernobyl occured. Chernobyl was using the "positive void temp coefficient" concept which makes it not so safe.

The below pictures will explain why.

For Chernobyl type of reactor, as the coolant heats up and vaporize, the reaction in the reactor will increase due to the absence of the coolant that acts as moderator and to capture some of the neutrons. Hence, the increase in reaction will further increase the temperature, more and more coolant will heats up and vaporize, allowing the reactor to reach a certain temperature where the core will melt down. This is called "positive void temp coefficient".

Meanwhile, for modern reactors, that mostly use water as moderator or coolant, this problem is no longer a worry. As the moderator(water) heats up and vaporize, the neutrons are not moderated and hence fission with the fuel will not present as they are still fast neutrons. As this happens, the reaction rate will slow down and the temperature of the reactor will accordingly decrease, allowing the moderator/coolant(water) to condense and fill back the void. When the void is filled, the reaction rate will rises and it keeps on repeating. In a way, such design is self-regulating and self-sustaining. This is known as the "negative void temp coefficient".

As a nutshell, Chernobyl accident is once and for all. The chances that accident of such magnitude will happen again is almost zero, as the world now is alert and cautious when dealing in nuclear. As long as we do the following, we will be on the safe side, preventing history from being repeated:

• DO NOT bypass safety systems - what is going to protect us, when safety systems are bypassed?
• DO NOT let pride take over - when pride is there, we tend to miss plenty of details.
• DO NOT neglect designed procedures - no one knows better than the designers about their systems, they experimented!
• DO NOT run dangerous experiments on any operating nuclear reactor - do it on experimental nuclear reactor!
• DO make sure containment building is there!

Once bitten, twice shy. We are in the shy state now, another accident, and nuclear will no longer be in talk. Hence, it is of utmost importance, that safety should always be the number 1 priority or concern in nuclear!