How passive does passive have to be?

It's a cerebral day (easy to happen when you've been waiting two days for the production techs to change a simple needle valve on top of a well head).

Safety mechanisms are often broken down into two categories: active and passive. Active is where an operator or an automatic system must sense and take action to correct for a fault. Passive is where such action will happen without the need for anyone or anything to decide where it happens.

There are obvious examples of active and passive safety. Active safety was a pump must be activated in order to supply emergency cooling water. Passive safety is where a the natural effect of Doppler broadening will cause a pebble bed reactor to become sub-critical if the temperature rises too high, such as in the case of a loss of coolant accident.

But what about the more grey areas? In boiling water reactors, control rods are inserted from below due to the fact that attempting to control the reaction from the steam laden upper portion of the core is ineffective. To aid safety, these control rods are spring loaded. During operation, they are withdrawn against the resistance of the springs trying to push them back in.

Is this passive safety? From one perspective it is. In the event of a total loss of electrical power to the control system, the springs will force the control rods into the core without any outside assistance. However, this is still dependent on the operation of engineered components unlike the PBR system, which depends solely on the immutable Laws of Physics.

The PBR case is an example of inherent safety. The BWR case is an example of a system designed to fail safe. Can these two types of safety be described in the same manner?

Is nuclear the most independent energy source?

All energy sources rely on natural resources to make them go. Nuclear relies on actinides. Coal, oil and gas rely on their respective fossil fuels. Wind relies on wind, solar on sunlight, geothermal on subsurface heat. This means that the economics of each power source is dependent upon these inputs to a large degree. If fossil fuels are expensive in a particular area, the fossil fuel economics will be comparatively poor. If availability of wind or sunlight is poor, then ditto for those energy sources.

Nuclear is like fossil fuels in that it depends on a market commodity, whose price can vary. However, unlike fossil fuels, it is not vulnerable overall to that price because the requirement for fuel is only a small fraction of the overall cost. Like renewables, nuclear is mostly capital intensive, with most of the money going into building the power station in the first place. However, despite this, nuclear avoids the pitfalls of renewables of being dependent upon the quality of natural goods in the area.

It looks like nuclear is relatively independent of either critical factor for other energy sources. Does this mean that nuclear economics should be the least variable of all energy economics?

Time to get tactical

I said before that the nuclear vote should rally behind the Conservatives as the best hope of getting new nuclear build in Britain. The situation may have changed. Teddy Bear Brown has bounced like a ping pong ball. The Conservatives have had a row over grammar schools and have had embarassingly disappointing results in two high profile by-elections. The knives are now out for Cammy.

Whether or not Cammy holds on, the very fact that the public see the Tory desire for self-destruction reappearing once more means the next election is now lost. Given the lead they need due to the Labour bias in the electoral system, it is unlikely they will emerge from the next general election as the largest party. Therefore a Conservative government, even a minority one, is no longer on the table.

So the credible choices are Labour majority government or Lab-Lib coalition. Therefore, the nuclear vote must now rally behind Labour to ensure they hold their majority at the next election. It's our best hope.

A side note on the possible confidence motion for Cammy: what planet are these MPs living on? Do they really believe for a moment that ousting a leader mid term for the second parliament in a row would actually do anything for the party other than damage it? If the election is lost with Cammy, changing the leader will not save it. It will simply make the humiliation of defeat even worse and damage the party's chances of rebuilding in the aftermath. Not only that, but rather than allowing Cammy to be the one to fall on his sword after the election, someone else will have to do it, meaning the Conservatives are wasting a potential talent in a no-hoper election.

Whatever have to the British stiff upper lip? I thought Conservatives of all people would be the ones to appreciate that. Take your defeat like men! You can either lose with dignity, or lose in disgrace.

The search goes on

I previously posted about decorating a swimming pool with Cerenkov radiation. Cerenkov radiation is cool. My original suggestion was to use strontium-90 because it is a (almost) pure beta emitter (aka emission of a high energy electron). I had to rule out the idea, because yttrium-90, the decay product of strontium-90, emits powerful gamma emission, which cannot be realistically be shielded by the water.

But some more in depth calculation reveals a further reason to reject strontium-90.

Cerenkov radiation is caused by sub-atomic particles exceeding the speed of light in water. The speed of light in water is 0.75 times the speed of light in vacuum (the maximum speed in the universe). The question is how much energy an electron would need to achieve this speed.

In 1905, Einstein had an Annus Mirabilis. As part of that, he published his Theory of Special Relativity. Within that included an important equation on the energy of a particle.

E is the energy of the particle. m0 is the mass of the electron. c is the speed of light in vacuum. v is the speed of the electron. Putting in all these numbers, an electron travelling at 0.75 times the speed of light will have an energy of 0.775 MeV. But the electrons from the decay of strontium-90 is 0.55 MeV. This means these electrons have insufficient energy to exceed the speed of light. So in fact strontium-90 is not capable of generating Cerenkov radiation in the first place.

Oh well, back to the old drawing board.

Define "unsafe"

I sense that it may be necessary to add the Kashiwazaki-Kariwa incident to the Other accidents page, since it has been exploited by the fuddites far more than I had (naively) expected. Over at NEI Nuclear Notes, a commenter is milking it for all its worth.
Secondly, NEI can try to mitigate reality all they want...this quake has shown nuclear reactors to be unsafe, and with each passing hour, the number of SIGNIFICANT issues at the world's largest reactor site continue to grow.

This raises one important question: what does "unsafe" mean? Does it mean that the device is impervious to all forms of damage and fault? Or does it mean that the device is suitably designed so as to prevent harm to the public?

It is universally agreed that cars themselves are safer than they were decades ago. That is not just due to inventions such as seat belts and airbags. It is also due to the engineering of the vehicle itself. Such advancements are commonly made the subject of some adverts.

One such advancement is the inclusion of crumple zones. These are areas of structure in the front of the car built to collapse in the event of an impact. In collapse, they absorb the energy of collision, thereby ensuring it does not pass to the occupants, hurting or killing them. The car essentially is designed to fail, sacrificing itself, in order to save the occupants.

So safety of cars was improved by allowing them to be more heavily damaged from collisions. The importance of this is the fact that those automotive engineers had a very clear idea as to what constitutes safety. Safety is about protecting people from harm, not about protecting equipment.

If we apply this to Kashiwazaki-Kariwa, we reach one inescapable conclusion: the power station is safe. This is because no-one has been hurt as a result of it. Some equipment, especially the transformer that caught fire (not a nuclear event anyway), was damaged. Some LLW containers were knocked over (and I'm sure LLW storage methods will be reviewed), but the radioactivity released was less than the radioactivity from the hordes of feral journalists hunting down the Tepco officials for a statement.

Did the earthquake do damage to other parts of the massive facility? There's a good possibility of that and safety critical equipment should be checked as soon as possible. But equipment fault does not equate to lack of safety as long as it does not endanger the public.

We have no evidence of Kashiwazaki-Kariwa bringing credible threat to the public, certainly not on the scale of the devastating earthquake itself, which has killed 8 people and injured hundreds more. Therefore, to say the power station is unsafe, is pure FUD.

On a more general note, Japan has been waiting a long time for an overdue earthquake. Let us hope this was it.

BBC loves homeopathy

So no wonder they pounce upon this opportunity with a particularly polemical article.
Japan is the only country to have suffered a full-scale nuclear attack, and the only country to have suffered massive casualties from radioactive fallout.


It seems odd, then, that it is so addicted to nuclear energy, operating more reactors than any other country after the United States and France.


This is pathetic. If someone almost drowns in a swimming pool, it doesn't mean they stop drinking water, or if they get stabbed during a mugging, they suddenly decide to stop using cutlery (it might have a bit at first, but after a while, they'd be expected to get over it).

The Japanese are often at the forefront of technological progress. You don't reach this point by embracing CND superstitution and maintaining that because nuclear weapons brought horrible death and destruction upon your country, you cannot use a beneficial new technology that harnesses energy from the same source.

Then there's the use of the word "addicted". A more shameless use of negative connotations there is not. And only 30% of their electricity comes from nuclear power stations anyway, so their dependency is exaggerated (the Beeb exaggerating? Surely not!).

Every day in the North Sea, some platform spills a few barrels of hazardous chemicals overboard and at best gets a strongly worded letter from the DTI about it. Nobody else cares. But it seems the decades old habit of running around like a headless chicken at the mention of the words "nuclear" and "radioactive" lives on.

Homeopathic godzilla

There is word coming out from TEPCO about the scale of the leak from Kashiwazaki-Kariwa. It is may have come from LLW storage drums, which tipped over due to the quake. 1.5m³ total was discharged into the Sea of Japan with a total activity of 60 kBq. In other words, a similar activity to the human body. Of course, this is now diluted across a very large expanse of water making it negligible.

Unless of course you're one of those naive people, conned into buying distilled water in slick packaging because it is branded "homeopathic" (because technically we could argue the Sea of Japan is now radioactive in a homeopathic sense), there is nothing to worry about.

Japanese earthquake causes coolant water leak

Almost breaking news from the BBC and AFP. The Kashiwazaki-Kariwa, the world's largest nuclear power station with a combined output of over 8GWe from its 7 BWR units, was close to the epicentre of the earthquake.

No details on exactly the source of the leak nor any figures on the levels of radioactivity released (unlikely in mass media articles anyway). The leaked water is said to have been released into the sea and in both articles, TEPCO is quoted as saying the quantity was not hazardous.

There was also a large fire, again of unspecified origin, though it is likely to have been on the generator side of the process.

We'll see what more information comes out in the coming days.

Edit:
CNN confirms it was a transformer fire. It also says 315 US gallons of water was released. No indication of the total activity of that volume.

Edit edit:
It appears that 315 gal is the total amount that was spilled. The discharged volume was actually just 1½ litres, which is 0.4 gal, or less than 1% of a barrel.

Edit edit edit:
NEI Nuclear Notes is on the case. Still no mention of the origins of the water.

Thermal physics and fusion

A letter to the Scotsman published over at SONE gets it a bit wrong.

the temperature required for a deuterium-tritium reaction is about 300 million degrees, not 100. This is nearly 20 times hotter than the temperature at the centre of the Sun. A device containing plasma at such a temperature has a high potential for catastrophic failure.
This is the classic mistake of confusing heat and temperature. Heat is the energy in matter that gives it its temperature. Temperature is the behaviour of the particles of the matter due to that heat. If you have bath tub full of hot water and a lit match, the flame of the match will have a higher temperature, but because there is so little of the gases, which cause the flame, the actual amount of energy is very limited. The bath tub on the other hand, may be relatively cool, but because there is so much water, there is a lot of heat.

The torus of plasma in a fusion reactor actually has a very small mass, less than a gram in the case of ITER. So even though it is at a phenomenally high temperature, the total energy is not as much as you might expect. If confinement fails, the torus rapidly expands and cools in the process. That's adiabatic expansion at work.

Almost a good idea

One of the coolest things about nuclear reactors is Cerenkov radiation. The Theory of Special Relativity is pretty unambiguous about the speed of light in vacuum. It is unreachable. Any object attempting to approach the speed of light will have to be fed an enormous amount of energy. Since energy and mass are the same, the object will get heavier as it speeds up. This means it takes yet more energy to get it to speed up further, which means it will get heavier still and so on. In order to reach the speed of light, the object will need infinite energy, something which is of course impossible.


So even high energy beta particles spewed from decaying radionuclides, travelling as fast at 290 million metres per second, will still be below the speed of light in vacuum.


However, 200 million metres per second is faster than the speed of light in water. And when an electron travels faster than the speed of light the same thing happens as when an aircraft or a bullet travels faster than the speed of sound. There is a sonic boom, or in this case a luminal boom. This takes the form of bright blue glow known as Cerenkov radiation.


The important question that must now be asked about this phenomenon is, how can this be used for decorative purposes? The obvious answer is in lighting for a swimming pool. A swimming pool illuminated from the bottom by an eerie blue glow would be awesome.


Strontium-90 would be a rather handy isotope to use. It is a pure beta emitter, which means that the radiation will not penetrate beyond a few centimetres. Strontium can also be manufactured into the durable ceramic, strontium titanate. Small sheets of high enriched ceramic could be placed just above the bottom of the pool. A mesh barrier would be placed a few centimetres above the ceramic blocks to ensure no swimmers got within range of the radiation.

So you have a cool lighting setup and free heating to go along with it.


Unfortunately, there is a problem with this. Strontium-90 emits purely beta radiation but it decays to yttrium-90, which emits beta radiation along with some powerful gamma radiation. A few centimetres of water is not going to shield against that.


You could also raise questions about high energy ultraviolet from Cerenkov radiation, but given how many people regularly like to lie in ultraviolet grills, this particular fact wasn't considered a showstopper.


Oh well, back to the drawing board for the next million dollar idea.