Sunday, 3 April 2011

Fukushima isn't going to go boom nuclear bomb style!

Rebuttal to “Remote Possibility of thermo nuclear at Fukushima”

http://warintel.blogspot.com/2011/04/remote-possibility-of-thermo-nuclear-at.html

This blog and comments from Robert Alvarez are so wrong I’m driven to put them straight.

“While the spent fuel rods and some rods in #2 reactor at Fukushima are  MOX fuel rods ( 6% plutonium ) And if the control rods were not fully deployed”

The control rods position makes little different to the proposed outcome. Also it is known that as soon as the quake hit the reactors were scrammed (resulting in insertion of shutdown rods). Secondly the reactors have been pumped with thousands of litres of borated water (a neutron absorber). The shut down rods would have brought the reactor subcritical at the time of the quake. Other factors contribute to keeping a reactor critical (or subcritical), shape of the core, water moderation (flow, voids, temperature). Neutron poisons (absorbers) are also present in various forms inside a reactor. One significant neutron poison Samarium-149 actually doubles in the 15-20 days following a reactor shutdown. Removing residual decay heat is the problem that has caused the main difficulty up to this point.

or if the spent MOX rods were damaged in the chemical explosions there is a possibility of a melt downand temps in the 5000 to 10000 degree range.”

Presumably the blog means 5k-10k Deg F? Either way the top end of 10k Deg F is far too hot . For comparison 10k Deg F is 60 Degrees above the average temperature at the surface of the sun.

“This could result in a uncontrolled chain reaction and another chemical explosion, similar to Chernobyl. But at the 10000 degree range is there the possibility of a thermal nuclear explosion?”

This information aside, even if the core of the reactor got this hot this could and would not result in an “uncontrolled chain reaction”. Why not? Because a critical nuclear fission chain reaction has nothing to do with the temperature of the nuclear material. This is one of the most common misconceptions surrounding all things nuclear. Although professionals use terms like “burn-up” and “burning nuclear fuel”, there is no burning in the conventional sense. Temperatures of nuclear fuels have no bearing on their state of criticality. Hypothetically even if nuclear fuel could reach one million degrees it wouldn’t cause a nuclear explosion.

Now to address Robert Alvarez comments. Video here (

“fuel core really goes into a meltdown and the fuel starts to slump, that quarter ton of plutonium can concentrate [inaudible] there'll be too much in one place at one time. And that can cause what they call a major criticality event. “

The notion that a non homogenous mixture of a totally melted reactor core, with various posions, and mixed with cladding, and many other materials will settle at the bottom of the reactor and then become super critical is absurd. Also there seems to be undue focus on the fact that 6% of the material is Plutonium. Criticallity can be acheived with any fissile material for example the fissile uranium has not been mentioned (further highlighting the confusion(?)) of the speaker.

Why is the notion of a nuclear explosion absurd? Nuclear explosions are not easy to achieve. They require highly enriched concentrations of fissile material, machined into specialist shapes, the addition of neutron reflectors (and usually neutron sources). Additionally the required concentrations of fissile material (say Pu239) are compressed into tiny masses many times their critical mass to create the super critical masses required to provide an exponential chain reaction. This all has to happen without the presence of anything to absorb neutrons that would hinder the creation of a runaway chain reaction.

In summary, a nuclear reactor core in operation provides probably the worst environment to create a nuclear explosion, a fully or partially melted one is even worse. 

Sunday, 13 March 2011

How should events in Japan effect Britain's new builds?

The recent events at Japans nuclear power facilities has once again thrust nuclear power to the forefront of world attention. If that should have been the case given the extreme natural disaster at work in Japan at the time is a different discussion.

How should the events in Japan effect Britain's new nuclear builds?

Firstly there is a big difference between how something should affect a situation and how it will.

The events in Japan shouldn't really have any great effect on British new builds. Some of the immediate lessons to be learned is that in the event of an accident communication is key. 

However I believe what will actually happen is as we are seeing in Germany, the ever-present  anti-nuclear factions will seize and exploit recent events for all they are worth.

The handling of the reactor issues in Japan, far from being a catastrophe and a 'death blow' to nuclear power actually demonstrate that in the face of the largest natural disaster the country has ever experienced problems can be overcome.

So let's do whatever we can to ensure than the events of Fukushima over the past few days will be remembered for the right reasons rather than wrong ones because the coming wave of baseless, unnecessary anti-nuclear bile will pose a direct threat to Britain's (and the worlds) future energy security.

Saturday, 12 March 2011

Fukushima 1 (Daiichi) and Fukushima 2 (Daini) Layouts

Given the various news reports on the two power stations I've been having a hard time keeping track of the layout of both. I'm putting these images here mainly for my own orientation but maybe they will help you too. You can click the images to enlarge.
 
Overhead view of Daiichi (Fukushima 1)

Fukushima 1 Daiichi (Credit: Unknown)
Plan view of Daiichi (Fukushima 1) 

Fukushima 1 Daiichi (Credit: Google)


Overhead view of Daini (Fukushima 2)


Fukushima 2 Daini (Credit: TEPCO)



 Plan view of Daini (Fukushima 2)

Fukushima 2 Daini (Credit: Google , notes by me.)

Sunday, 9 January 2011

It's not waste it's used fuel!



We all know that nuclear power often suffers with a public perception problem. The industry has done itself few favors over the years by permitting and even acknowledging certain to be regarded materials as waste.  The main material I want to focus on for the next few blog entries is uranium fuel.

Values used in my writing will relate to typical numbers for PWR type reactors but the principles apply to any thermal neutron reactor that uses Uranium fuel.

Natural uranium is mined and processed, enriched and fabricated into fuel. Reactor fuel is typically enriched to around 3.6% to 4.1%. That means the U-235 (which is needed for is fissile properties) is increased to that percentage over the more abundant U-238. In contrast natural uranium as mined contains  around 0.7% U-235.

The diagram to the right illustrates the concept of enrichment. I have left the weapons grade enrichment of uranium in place to illustrate just how much enrichment is required to obtain something that could be used in a nuclear weapon verses what is used in reactors. It is important to realise that low enriched Uranium (LEU/Reactor grade) is VERY different to high enriched uranium (HEU/Weapons Grade).

So this reactor grade uranium in the form of fuel assemblies goes into a power reactor. In current reactors it will generally remain there for at least 18 months where the reactor will use it to generate electricity. The fuel assemblies are eventually removed and replaced with new fuel. However what is not obvious is the "spent" fuel that is removed has had less than 1% of the available energy it contains used.



This "spent" fuel, which from now on I will call used fuel is as it is in no way spent is currently generally labeled as waste and treated as such.

The majority of the fuel will still be uranium except it will now have other radioactive elements present known as fission products and actinides. We want to recover most of what is found in the used fuel as it can be used for other purposes mainly producing more fuel.

Currently used fuel will be stored for a number of years often on site at the reactor as it will continue to produce radioactive decay heat. This cooling usually happens in fuel pools which are as exactly what they sound like, pools of water.

Currently the intended destination for this used fuel following several years of cooling is geological storage underground. However to date no undeground geological repository has been brought into operation.

Why are we looking to store used fuel that has 99% of it's energy remaining underground? In the past nobody was quite sure if this used fuel was an asset or a liability. This has led to the used fuel being poorly branded as waste along with all the perception problems that generates.

People rightly ask, "if this isn't waste why must we lock it underground?". Right now we need to shake of the idea that used fuel is waste. Lets not even brand it "spent fuel". Spent implies that it's of no further use and that is energy is depleted.

This is not the case. What comes out from a nuclear reactor is not and should not be viewed as waste. With a combination of reprocessing and recycling this used fuel can be used again and again to provide ultra-low/carbon free power for at least several thousand years.

So the next time somebody asks "Well what about the waste?" at least explain that the fuel isn't really waste at all and can be reused if we want to and we are not simply leaving burdensome 'waste' behind for the next generation. 

More to come on the how of recycling next time.

Thursday, 2 December 2010

Public Perception - Scary Nuclear!!

This is NOT nuclear power!


 Nuclear! Radiation! Nuclear bombs! Nuclear war! Nuclear this, nuclear that....

There is no denying or escaping the reality that the civil nuclear power has benefited enormously from the funding and research into nuclear weapons programs, however nuclear power need not be scary!

The motivations for the first nuclear reactors were to produce fissile materials such as plutonium for military weapons needs.

Although civil nuclear power has long since moved away from military involvement the association between nuclear weapons and nuclear power still looms large in many peoples perception. This seems to promote the idea that civil nuclear power is somehow inherently 'bad' or 'evil'.

It appears that many nuclear power opponents are in fact simply indiscriminately  anti 'anything nuclear'. Many current day nuclear power opponents are the very same people who were protesting against nuclear weapons at the forefront of the "Ban the bomb" movement.

Any event involving nuclear power no matter how tenuous the link to nuclear matters is pounced on and cited (always in total factual error) as 'proof' of the 'dangers' and 'madness' of nuclear technology.

A recent example of this is the media treatment of the transformer fire at Indian Point nuclear power station in New York. Those not susceptible realise that a transformer fire is and never will be a nuclear issue. Any type of power generation facillity can fall to this kind of failure.

Despite the intense focus on minor events surrounding nuclear power plants, other extremely risky and dangerous methods of power generation are given an almost free pass by the same groups. Just think how many recent incidents there have been surrounding coal mining, gas pipe explosions and need i mention Deepwater Horizon. Deaths in the mining industry often number in the thousands worldwide anually.

Deepwater Horizon fire

This said, the nuclear industry historically has not done itself any favors when it comes to communications, dispelling misinformation/misunderstanding and generally portraying itself in a positive light.

Every common argument such as safety, economic viability and 'waste' presented against nuclear power as a fatal flaw in the concept can be countered by clear communication from the industry.

The key to future and continued success from a public perception point of view is communication and support from the industry and government.

Consider that nuclear power stations in France have a number of public open days every year. In contrast it's a near impossibility to get a visit to a British nuclear facility of any kind. The French approach helps to engage the public and put hearts and minds at ease.

I have been fortunate enough to visit a number of British nuclear facilities and I know that if more of the general public were able to experience the professionalism of the industry first hand any remaining fears would evaporate.

   

Monday, 1 November 2010

50,000 Megawatts and electricity prices.

Today Britain's electricity demand reached its highest point of the year so far! At 17:00 today our electricity demand peaked at 50,685 MW.

As usual around 44% of the demand was met with combined-cycle gas power stations (or plants for our American friends), 32% by coal followed up with 16% nuclear and finally 4.6% imported from France. France of course with it's numerous nuclear reactors has abundant cheap electricity to sell to us!

The small remainder was met with a mixture of wind, pumped storage hydro and standard hydro.

During the period of peak demand electricity prices peaked at £77.90 p/MWh. This is quite a contrast to a more usual price of around £45.00 p/MWh or even earlier lows in the day of £34 p/MWh.

Why is this?

In Britain (and many other countries) electricity is traded in an open market as a commodity. Like most commodities when demand is high and supply is low prices rise. The reverse is true when supply is plentiful and demand is low.



When demand increases gas plants increase their output and generally a number of large coal plants also begin generating.

Britain's existing nuclear power stations run at (or close to) maximum output when they are online and do not alter their output in response to short term power demands. It's just not what the existing plants were designed to do.

The EPR and AP1000 reactor designs that are highly likely to constructed here are designed for load following operations. This is something that French nuclear reactors routinely do. The more demand that can be met by nuclear the more stable electricity prices will be.

Natural gas is as cheap as it's been for many years however it cannot stay that way forever and when it does start to increase due to reduced supply electricity prices will inevitably rise.

Although the new nuclear builds cannot now assist with stabilizing British electricity prices they will when they come on-line.

Friday, 15 October 2010

Oldbury visit part two

Continuing on with some more on the recent tour of Oldbury nuclear power station that I recently participated in. If you missed part one please take a look here.

The next part of the power station I want to discuss I find particularly interesting. The reactor pressure vessel. It is actually constructed of pre-stressed concrete. I believe this was the first reactor to be constructed in this way. The approach seems to have been very successful as Oldbury's sister reactor Wylfa was also constructed using this method as were the later AGR (Advanced Gas Cooled Reactor) designs.

In the image below you can see one of the areas known as a stressing gallery. What you can see here are the ends of the steel pre-stressing "tendons" as they emerge from within the concrete of the reactor pressure vessel.

Upper stressing gallery  (Photo Credit: Magnox North Ltd)


What the photograph does not show is how hot it was here! It felt to be at least 35 degrees C. A member of staff mentioned that it had been as warm as 47 degrees in recent days in this area. It's not surprising considering this is as close as somebody can get without actually being IN the reactor core.  

It may be helpful to refer to the cutaway drawing of  the similar Wylfa reactors. The cutaway and 104 others can be found at the New Mexico Digital Collection. Even if you don't take a look at the cutaways now I urge you to bookmark it for later as they really are an excellent way to get a good feel for the layout of various reactors.

Next up on the tour was the spent fuel pond. Once fuel elements have completed their stay in the reactor they require many months of cooling as the continued decay of fission products produces heat. Used fuel elements are removed from the reactor core and transferred down into the fuel storage pond. This is done via various chutes which deliver the fuel elements to the fuel pond area of the facility.

Fuel storage pond  (Photo Credit: Magnox North Ltd) 
Following a storage period in the fuel ponds the fuel elements are loaded into specialized fuel transport flasks and sent off site for disposal/storage. These flasks are rather large and are very well shielded.

Fuel transport flask  (Photo Credit: Magnox North Ltd) 

The final area of the tour was a gas recirculator hall. The Magnox type reactor (as are the newer AGRs) are cooled with Carbon Dioxide gas. Large fan like circulators are used to maintain an adequate flow of coolant gas throughout the core. Unfortunately I cannot locate any images of the circulators or the drive motors. I will attempt to locate some more information on the gas circulators. Needless to say this area was also fairly warm but was very noisy due to the circulator motors.

It's worth remembering that these reactors were operating before humankind set foot on the Moon. Thinking of the lifespan of these reactors in those terms really puts in perspective the kind of things that have already been accomplished with nuclear power.

Lookout for details of my visit to the Imperial College London CONSORT research reactor facility and a look at a very interesting future reactor concept in future posts.