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Are Nuclear Reactors Safe?

Fukoshima reactor meltdown

Everything you don't want to know about nuclear reactors

Here we look at nuclear power, we explain how a nuclear reactor works, how they become dangerous and, in the light of the Fukushima disaster shown in the picture above, we ask the question "Are they safe?"

The Need For Electricity and Power

We all use electrical power in our homes and around the world there is increasing pressure to find 'cleaner' source of energy. Some feel that Nuclear power is the way to go and, indeed, Theresa May has just signed an agreement to purchasea new Nuclear reacor from China at a time when solar and wind power is starting to become far more viable.

But is nuclear power safe? In the past we have said no but time has passed, the pressure increases and once again people are looking towards the nuclear option.

In the 1960s people thought nuclear power was not safe

Back in the 1960's Europe was full of protests about nuclear power. Governments and commercial interests were pushing nuclear power as a solution to future energy needs tempted by the promise of clean, cheap, abundant energy. Much of the population had their doubts and mass rallies were held in many of the cities of Europe. Protests were huge and included all sections of society.

The argument at the time was simple. Nuclear power is very dangerous and you can never be 100% risk free. Concerns raised at the time were:

  • The potential for huge disasters and the scale of devastation that could result.

  • The enormous lengths of time radioactive contamination remains.

  • Nuclear facilities in areas prone to earthquakes and other natural disasters.

  • The fallibility of technology and the likelihood of unforeseen design flaws.

  • Shortcuts taken by profit driven constructors and operators.

  • The unbelievably difficult problem of safely disposing of waste that remains highly dangerous for hundreds of years.

  • The danger of bomb making materials falling into the wrong hands (Gaddafi with an atomic bomb?).

But this was all forgotten or ignored.

There are many nuclear power stations around the world

Years have passed and we now find ourselves with 442 nuclear power stations in 30 different countries around the world and another 65 under construction. America has most with 104, france is 2nd with 58 and Japan has 54 despite being in one of the most earthquake and tsunami prone areas on the planet. China has 13 in operation with 27 under construction, 50 more are planned and a further 110 are being proposed.

One of the big selling points is that nuclear power is clean. Well certainly you don't get millions of tones of carbon being pumped out into the atmosphere as you do from dirty old coal fired power stations but how does a reactor work?

How does a nuclear power station work?

Energy is produced through nuclear fission, the splitting of the atom. An atomic particle, a neutron, collides at some ridiculously fast speed with an atom of uranium, the uranium atom splits into lighter elements (such as strontium and cesium) releasing a rather humungous amount of heat energy and 2 or 3 further neutrons which then collide with further uranium atoms creating an ever increasing chain reaction. This chain reaction is, of course, the basis of the atomic bomb.

The process also releases just a bit more than a smidgeon of radiation. It can hardly be described as clean.

In a nuclear power station this chain reaction is carried out inside a nuclear “reactor” where it can be controlled, the radiation can be contained and in which the released heat can be harnessed. The fuel for the reaction is in the form of uranium rods positioned in the reactor “core” where they can react with each other. “Control rods” can be slid between the uranium rods, these are rods that absorb neutrons and so can slow down the reaction. By sliding the control rods in and out the chain reaction can be managed.

Most reactors (not all) also use water which is circulated through the reactor taking away the heat, the water also slows the neutrons down and helps to control the chain reaction but more importantly takes the heat to a heat exchanger where it is used to make steam which in turn drives turbines to generate electricity.

How does a nuclear reactor become dangerous?

If for some reason the control rods are not inserted or there is a loss of water in the reactor the reactor will start to get hotter. As it gets hotter the chain reaction speeds up and generates even more heat at an ever increasing rate. The temperature increases exponentially.

If the reactor gets too hot it goes out of control and things start to break down. The ability to control the reactor may be lost. The water level may fall exposing the fuel rods which might start to melt, the ability to insert the control rods may be lost and/or the pressure can build up in the water cooling system which may rupture. The water itself may breakdown into an explosive mixture of hydrogen and oxygen leading to a major explosion (this is what happened in the recent Japanese Fukushima disaster where the outer buildings were blown off several of the reactors and also in the far more serious case of Chernobyl in which the whole reactor was blown apart).

The meltdown of the nuclear reactor at Chernobyl

If the temperature continues to rise the fuel rods may melt down into an uncontrollable mass which can fall to the bottom of the reactor and burn its way through concrete and steel releasing huge amounts of radiation into the ground. This is known as a meltdown.

Chernobyl was the worst nuclear accident the world has known. It was an older design of reactor which used a solid block of graphite as the reactor core with uranium fuel rods and control rods slid into it and cooling water circulating through it. The disaster was not caused by failure but by stupid mistakes made by the engineers controlling the reactor who were carrying out a test, they removed most of the control rods before turning off the circulation of cooling water. The reactor overheated and melted down and, disastrously, the graphite core set on fire, the fire threw up a cloud of radiation into the atmosphere that spread radiation as far away as Scotland, Norway and North Africa and covered much of Asia.

In the case of Chernobyl there were (rather stupidly) large water storage tanks under the reactor. If the core had burned its way through to the water tanks there would have been a much larger explosion which would have made the disaster far worse. As it was 2 volunteers were found who were willing to forfeit their lives by swimming into the highly radioactive water tanks to manually release the water and avert a far more serious disaster.

Are nuclear reactors safe?

Engineering aspects are the vulnerability of nuclear reactors. Pumps, pipework, joints in the containment structures and fuel and control rod loading and unloading equipment are all expected to operate without fault. Once a nuclear reactor is live, or as they say critical, there is no going back. You can't go in there to change or repair anything later. Unfortunately total 100% reliability simply is not possible in engineering.

Mistakes made that caused the disaster at Fukushima

In the case of the Japanese reactors at Fukushima the design was totally dependant on keeping the cooling water moving. Remember the water pumps needed must be kept running with total reliability for decades. Water pumps driven by the national electric grid can hardly be considered foolproof. As we are all too aware blackouts do occur particularly in earthquake prone areas.

Backup power in Fukushima we learn, was provided by diesel powered generators which are, of course, vulnerable to any number of causes of failure particularly when built right on a coast susceptible to Tsunamis. The only further backup was a bank of batteries that gave a mere 10 hours of power.

The earthquake and tsunami cut the power to the reactors and knocked out the generators. 10 hours later the batteries died. The water pumps stopped, the reactor cores heated up and we understand fuel rods started to melt damaging the reactor cores. Hydrogen was produced which blew the buildings apart. It is amazing that they have managed to keep the reactors cool enough to avoid a full meltdown although there is obviously enough damage to cause serious radiation leakage. Remember this is in one of the most technological advanced countries in the world and a people who are fastidious in nature. It is to their credit that they have been keeping their people and the world informed regarding the details of the accident and the progress of their efforts. The disaster is still unfolding.

And a billion voices all over the world cry in unison “we told you so”.

Copyright © Phil Wilson April 2011
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