All posts by Johan

Den katastrofala vattenkraften

Teton Dam failure

 

Debatten om risker inom energiproduktion är väldigt binär, antingen pratar man (media, politiker etc) om kärnkraftens risker eller så pratar man inte om risker överhuvudtaget. Klimatförändringar har lyft upp en del risker med fossil energi i rampljuset men det handlar ändå om ett en relativt avlägsen och diffus risk. När det handlar om evakueringar, plötsliga dödsfall, förstörelse av egendom och andra olyckor då är det enbart kärnkraften som diskuteras. Om man som utomstående försöker få ett grep på risker ter det nog sig väldigt lätt som att kärnkraft är det enda kraftslaget som överhuvudtaget är belastat med sådana risker.

Hur är det egentligen med andra kraftslag? Det energislag som historiskt sett har drabbats av de mest spektakulära och horribla katastroferna är utan tvekan vattenkraften (lite klumpigt infogar jag alla slags vattendammar under kategorin vattenkraft). Ingen annan industriell olycka har någonsin orsakat förintelse på en sådan skala som Banqiaokatastrofen i Kina, men enorma olyckor har även skett i Indien, Bulgarien, Italien och många fler länder. I Sverige har vi varit förskonade från olyckor med dödlig utgång men även här har dammar brustit och orsakat miljöskador.

Varför detta utlägg om vattenkraft och vattendammar? Motivet är en rapport som myndigheten för samhällsskydd och beredskap nyligen släppt som beskriver en bunt möjliga katastrofer som kan ske i Sverige, bläddrar man till sida 58 kan man läsa detta stycket.

Endast omkring 20 dammar i Sverige bedöms kunna få så stora konsekvenser  som scenariot förutsätter. Med utgångspunkt i internationell statistik blir sannolikheten för ett dammbrott i någon av dessa 20 dammar 0,002 på årsbasis, vilket motsvarar storleksordningen 1 gång 500 år.

För att ge ett perspektiv på den siffran designas nya reaktor med målet att sannolikheten för härdskador ska vara av storleksordningen en på miljonen reaktorår. Härdskador i sin tur innebär inte med automatik utsläpp och evakuation av omgivningen. Man måste förstås alltid ta sådana siffror med en stor nya salt då dom inte representerar en verklig frekvens. Det kan inte vara en verklig frekvens helt enkelt eftersom man inte kan fånga hela verkligheten i en sannolikhetsmodell och när olyckor sker är det oftast på oväntade sätt. Det är dock helt klart att det inte hade varit acceptabelt med en härdsmältefrekvens på 1/500 år i Sverige.

Greenpeace fiskar vilt efter de så kallade PSA (probabilistic safety analysis) analyserna av de svenska kärnkraftverken just för att kunna hävda att risken är si och så stor med kärnkraft och att vi omedelbart borde avveckla den. Greenpeace argumenterar alltid med utgångspunkt att ingen risk, oavsett hur liten, är acceptabel. Från den samlade miljörörelsen hörs dock inte ett knyst om risken med vattenkraft eller något annat kraftslag överhuvudtaget! Siffrorna står där svart på vitt och skriker efter uppmärksamhet men alla rycker på axlarna, det vi ser är helt enkelt en oerhörd kognitiv dissonans. Föreställningen att kärnkraften är det enda energislaget förknippat med risker är så väl etablerat att de flesta helt enkelt vägrar accepterar att exempelvis vattenkraften innebär större risker. Lyfter man frågan dröjer det inte länge innan bortförklaringarna haglar vilt och efter att diskussionen är över har förnekelsen redan trätt i kraft. Många vägrar ens ta i frågan utan byter illa kvickt ämne. Media verkar även vara helt förblindad av kärnkraftens risker och kniper nästan helt igen om alla andra energislag. Om en damm brister eller ett naturgasverk exploderar och några människor stryker med blir det en liten notis på femte sidan, sker ett obetydligt tritiumläckade från ett kärnkraftverk blir det ofantliga rubriker trots att risken från läckaget är obefintlig. På något sätt accepterar vi risker från andra energislag som något helt naturligt och rycker bara på axlarna och går vidare utan att oroa oss över att Suorva kan brista eller att Preemraff kan explodera.

Poängen med blogginlägget är förstås inte att hävda att vattenkraft är för riskabelt eller att vi ska stänga svensk vattenkraft. Vattenkraften är trots allt en ängel jämfört med vad fossila bränslen ställer till med, men det är förbannat märkligt att tystnaden är totalt runt vattenkraftens risker i en vattenkraftnation som Sverige. När riskuppfattningen är så otroligt vriden som den är idag spär vi på de riktiga riskerna. Istället för att lägga en liten summa på att sänka en medelstor risk så öser vi ofantliga resurser på att reglera och minimera redan trivialt små risker. Det är inte optimalt, det är inte vettigt och det gör oss inte säkrare.
Sluseport Harsprånget Stora Lule älv 1972 1

Why don't nuclear reactors go kaboom? A reactor kinetics primer part - 3

Water Dolphin

We have discussed the time behavior of the neutron flux and reactivity feedbacks. Now it is time for the the thermal side of things. The point kinetics model describes how much energy is produced in the fuel, but we also need a model for how the energy is transported within the fuel, through the fuel cladding and into the coolant. To figure it out we need models for heat conduction through the fuel and cladding, heat transfer to the fluid through convection, properties of the fluid at different temperatures and pressures and so on. This blog post will deal with the heat conduction in the pellet and through the cladding.

Continue reading Why don't nuclear reactors go kaboom? A reactor kinetics primer part - 3

Why don't nuclear reactors go kaboom? A reactor kinetics primer part - 2

Advanced test reactor Foto: Matt Howard, Source: Wikimedia Licens: Creative Commons Attribution-Share Alike 2.0 generic

Its time for some more fun with reactor kinetics, in the last post we ended by looking at the point kinetics equation with one group of delayed neutrons. In this post as I promised we will talk about reactivity feedbacks. To brush up your memory, reactivity is defined as:

Continue reading Why don't nuclear reactors go kaboom? A reactor kinetics primer part - 2

Why don't nuclear reactors go kaboom? A reactor kinetics primer part - 1

Nuclear reactors contain tons of fissile material and nuclear bombs contain only kilograms of fissile materials, so why does one of them explode with enough force to flatten a city but the other doesn't? I will pull out some latex skillz and geek it out with equations to describe the physics behind whats in nuclear engineering is called reactivity excursions or RIA (Reactivity Insertion Accident). The level of these blog posts will be such that an interested and fairly math savy person can understand and calculate these kind of things on their own.

Castle Romeo photo: United States Department of Energy, Source: Wikimedia

Continue reading Why don't nuclear reactors go kaboom? A reactor kinetics primer part - 1

Nuclear news

Together they are giving a picture that Russia is really beginning to go all in for nuclear. Of course Russia has always been a pioneer in the nuclear field, but despite that they "only" have 33 reactors running producing less than 18% of electricity.

 

Taken from the IAEA PRIS database

Continue reading Nuclear news

Happy birthday chain reaction!

Yesterday it was 70 years ago since Fermi and his gang of researchers pulled out the control rod in Chicago Pile one and initiated the first controlled self sustaining fission chain reaction. By all accounts a momentous moment in the history of both science and mankind. The first time we took the step from primitive chemical energy to an energy source a million times more dense and powerful. It's a day worth celebrating and remembering, and it marks the real beginning of the Atomic age (otherwise usually said to have started on July 16 in 1945 with the Trinity test). Looking back at it now it is quite amazing what the scientists then accomplished with only their brains, pen, paper and slide rulers.

Of course some nuclear opponents consider 70 years a very old age and claim that nuclear is a bit to old to party (a claim clearly disproved by the first picture in this blog post), but is 70 years a valid retirement age for an energy source? Let's consider other energy sources.

Biofuels were discovered sometime during the evolution of humanity when Grok (or was it Gruk?) started thinking about burning trees after a lightning struck. At some point he figured out that steak tastes better if tossed onto one of these burning trees, and so the biofuel powered bbq was invented. It also had a very nice side effects of making the cave more comfy in the winter and helped make it possible for humanity to spread out from warm and cozy Africa into cold(er) Europe and Asia. By all accounts we are talking about more than a hundred thousand years ago. Biofuels and fire is thus pretty damn old compared to the strapping youth of fission. So why do not anti-nuclear people seem to object to biofuels due to its immense age?

Coal can probably be crammed into roughly the same category as biofuels because it can't have taken so long for Grok to see that those weird black stones also burn when tossed into a fire, although its massive used didn't start until James Watt perfected the steam engine in the 18th century. That makes large scale use of coal a couple of hundred years older than fission.

Oil is a relative newcomer, sort of the rookie in the fossil family. It was first seen as either a health remedy or a nuisance, at first it was mostly used to rub onto all kinds of sores or warts but not much else. In 1840 James Young discovered how to distill kerosene from oil and all of a sudden a replacement for whale oil in lamps was available, leading to the use of oil really taking off. That makes oil use about 100 years older than fission, but it had been known for thousands of years.

Fossil gas came as an unwanted (and often dangerous) by-product from oil drilling and coal mining, but the commercial development of it as an energy source went i parallel with the oil extraction. The first gas well for commercial purposes was dug by hand in Fredonia, New York, by William Hart in 1821, but already the ancient Greeks used it for a more esoteric use: The Oracle of Delphi probably got her visions and divine answers from breathing the fumes of gas sipping out of the rock at the temple.

What about renewables that are seen as young upshots that can change the world? Well, wind power has been used on an industrial scale since the 19th century, among other things in order to keep the Dutch from needing to don wet-suits to get to work. Of course wind has been used for sailing for as long as humanity has known how to make a sail. That makes wind anything from 200 years older than fission to thousands of years older.

Solar power is a bit younger, at least solar cells. The process how to get electricity out of photons (the photoelectric effect) was the discovery from 1905 that gave Einstein his Nobel prize in 1921, some 40 years or so before fission. So even solar cells are younger than fission. Actually there is NO new energy source that has been discovered after fission, making fission the youngest on the block despite its 70 years. It is thus pretty moronic to nag on nuclear for being an old fart, it is hardly out of its diapers yet!

But how has this young lad done so far? Well, the first real use of fission for power (excluding things that go boom) was in 1954 with the Obninsk reactor in the Soviet Union, then followed by Calder Hall reactor in the UK in 1956 and the Shippingport reactor in the US in 1957. After that nuclear took off and within 30 years nuclear was producing close to 1250 TWh of electricity per year (over 150 GW of installed capacity). 20 years later production had more than doubled to 2800 TWh/year. The thermal energy produced is almost equivalent to the combined oil production of Saudia Arabia and Russia! Not bad, not bad at all.

The future is looking mighty bright as well, we have barely scratched the surface of the potential of nuclear energy. Right now we are only using 0.5% of the available energy in the fuel and in fairly inefficient designs as well. The next technological step has already been demonstrated in many countries, and within a short time span we can expect to see nuclear fulfill many more roles than today. Process heat for industry, nuclear reactors for space applications, small reactors for remote communities, there is no energy niche where nuclear can not play a part in the future. Furthermore, there are many niches where only nuclear is applicable (submarines and deep space exploration, for instance).

So happy birthday to fission! We wish you another 70 years of success and good health until the day comes when your cousin controlled nuclear fusion has matured enough to be a competitor.

Figure 1. World Energy Consumption by Source, Based on Vaclav Smil estimates from Energy Transitions: History, Requirements and Prospects together with BP Statistical Data for 1965 and subsequent (chart found at http://ourfiniteworld.com/2012/03/12/world-energy-consumption-since-1820-in-charts/)

 

Other blogs or web sites that honours the anniversary:


 

 

Visit to Marviken

Sometimes the NPYP bunch tires of being rough on the roughnecks and decides to leave the jungle headquarters for a walk on the streets like normal people. Such an momentous occasion happened this week, and where else could they be found other than at the only oil fired nuclear power plant in the world (don't tell us we don't know how to party!)?

The power plant in question is Marviken, located about 150 km driving distance from Stockholm. It was supposed to be the first large scale electricity producing nuclear power plant built according to "the Swedish line". The design principles behind the Swedish line was:

  • Natural uranium as fuel so that the abundant Swedish uranium resources could be utilized without any need to depend on import.
  • Heavy water as moderator because light water steals to many neutrons to be possible to use with natural uranium fuel.
  • Possibility to refuel during operation so that fuel bundles can be removed at the point where the Plutonium isotope composition is the most beneficial as weapons material.

Continue reading Visit to Marviken

A few interesting videos of reactor experiments

During the 50's and 60's a number of experiments where conducted in the US to examine criticality accidents in light water reactors. One basically inserted large amounts of criticality (by ejecting control rods from the core) to see what happens. It is quite fascinating to watch the videos of the experiments. The first two videos are from the Borax experiments and the third one from SPERT, enjoy watching them!

I will try to find some time to write more about criticality, prompt criticality and feedbacks that keep reactors stable and how one calculates transients, but until then if someone technically minded wants to read more about the experiment I recommend searching on DOE's information bride (http://www.osti.gov/bridge/basicsearch.jsp)

 

The big bad nuclear mafia

Quite often in the nuclear debate one encounters the idea that the nuclear industry is some industrial juggernaut of immense proportions, so large and rich that it can pay an army of lobbyists and crush the poor little renewable energy industry beneath its heel. Nuclear is firmly place next to oil, gas and coal in magnitude, richness and reach in the opponents mind. Renewable energy companies on the other hand are envisioned as small mom and pop buisnesses run out of the back of the yard with very small means and no political or economic clout to speak of.  But what is it really like? Continue reading The big bad nuclear mafia