#polarbearblogs

[iamapolarbear]

We're all making plans against the day we may or may not have to abandon Twitter. I'm too old to learn a new platform so I'll be on Instagram and my blog - and now, my YouTube channel! - but possibly my home for quick stuff will be here. Tumblr was created to be quick and dirty - well, unpolished anyway. Just a tumbling roll of half-baked thoughts which got out of hand.

So, a few things.

I blog twice a week (Mondays and Thursdays). In December I'm doing Blogmas because that's the best time for it. I've got four posts finished and probably about half are somewhere on the production line.

I went from "I'll make a video about my Iceland trip for badge reasons" to making a sub-ten minute daily vlog for my second trip to Iceland to "well, I've got six videos in a row up. Might as well make a video every week for ever now". Provided I can come up with three to fill December, I can keep this up until at least March or April. Then we'll see.

I'm not saying a firm hard no to TikTok... but at the moment it comes under the heading of being too old to learn a new platform.

[iamapolarbear]

Julie’s Beginner’s Guide to Nuclear Physics

With my trip to Pripyat, I realised I know nothing about nuclear physics and the internet isn’t very helpful when it comes to learning about it. It comes in two flavours: GCSE study guides written for 14-16-year-olds which look like they were written for 5-year-olds or really heavy texts that were written for people who already know everything about it.

So.

Nuclear physics involves the destruction of individual atoms of uranium or plutonium, mostly. I think they use other elements occasionally but those are the big two.

We have to go right back to atoms before we can go any further.

Atoms are the basic building block of everything. They have a core called a nucleus made of protons & neutrons. Each proton & neutron weighs about 1 (1 what I’m not sure) and then the nucleus is surrounded by orbiting electrons, which weigh pretty much nothing. Atoms have the same number of electrons as protons and generally the same number again of neutrons. The atomic number, the order they’re listed on the periodic table, is the number of protons or electrons. The atomic weight is the total number of protons and neutrons.

Of course, then there’s the small detail that the atomic weight is not always as simple as they tell you. For example, chlorine is made of 17 electrons, 17 protons and, in theory, 17 neutrons. A single molecule of chlorine, out in “the wild” is Cl2 but actually chlorine goes around in molecules made of 4 atoms, not 2. Three of those atom are an isotope known as 35Cl, which means an atomic weight of 35, which means 18 neutrons and the fourth atom is 37Cl which has an atomic weight of 37, meaning 20 neutrons. Its real atomic weight is 35.45, which is the average of those four atoms.

So what is an isotope? It’s a variant on an element. It has the same number of electrons and protons as the “real” element but it has a different number of neutrons, like you’ve just seen with the chlorine isotopes.

Let’s take hydrogen, the simplest element. Standard normal hydrogen is made of one proton and one electron. But it has an isotope called deuterium, which in any other element would be called  2H, or hydrogen-2 but in this case, it gets an entire name of its own. Water is made from two hydrogen atoms and one oxygen atom. But you can make “heavy water” from two deuterium atoms and one oxygen atom. If you read my blog about the Chernobyl disaster, you might have noticed that I mentioned that Reactor 4 was cooled using “light water” - that just means the ordinary H2O kind of water with normal standard hydrogen, the sort that comes out of your tap as opposed to the heavy water made with deuterium.

So the nuclear reactor uses uranium-235 or plutonium-239, mostly - these are pretty huge atoms. An extra neutron is fired at it and rather than just adopt this neutron and become a new isotope, it throws a tantrum and breaks into two smaller elements, a few loose neutrons and bits and pieces of random other stuff. Those new loose neutrons go on and hit other uranium or plutonium atoms and they do the same thing. Once you’ve set it going, it runs itself - neutron, unstable isotope, breakup, neutron, unstable isotope, breakup. That’s what’s called a chain reaction.

It can only happen with a slow-moving neutron and by default, electrons happen very fast so the reactor core is filled with a material, often graphite, that will slow it down enough to be able to hit other atoms. Then there are the control rods - these are rods made of graphite that fall into the reactor to stop the neutrons flying around and end the chain reactor. They’re generally held up by electromagnets or motors or something and so in the case of unexpected shutdown, whatever’s holding them up fails and they fall automatically - which means if something goes wrong, the reactor is designed to end the reaction. But as I said before, there’s a lot of heat in there and it needs continuous cooling for about a week to stop a meltdown.

A nuclear power station ultimately works exactly the same way as a coal-powered power station. Heat the water, use the steam to turn the turbines which generate electricity. It’s just that nuclear plants use nuclear reactions to heat the water instead of burning coal.

As for what the other two smaller atoms are formed in the chain reaction, the fission product - apparently that’s totally random. In the case of Chernobyl, the four elements scattered most prominently over the exclusion zone were iodine-131, caesium-134, caesium-137 & strontium-90, all highly radioactive fission product isotopes.

Now we come to half-lives. The half life is the amount of time it takes for half the material to decay - that is, how long it takes for the molecule to lose half its energy by emitting radiation. A shorter half-life means the radiation is more intense - well, not more intense but perhaps more dangerous. It’s giving off more radiation in a relatively short burst. This can be as short as microseconds or it can be thousands of years. Iodine-131 has a half-life of about 8 days and carbon-14, the one used in carbon dating, has a half-life of about 5700 years. What I don’t understand about half-lives is why if half the radiation can decay in, say, eight days, why can’t the other half? But for the radiation level to get down to nothing (well, it’ll never get down to zero but it partly depends on how accurately you can measure it - have you got a Geiger counter that can measure 0.000000000000000000001% of the radiation given off by iodine-131?) My calculation is that it takes about twenty half lives to get down to close enough zero and that makes no sense at all. After 8 days, there’s 50% left. After 16 days there’s 25% left. After 24 days there’s 12.5% left. After 32 days there’s 6.25% left. After 40 days there’s 3.125% left and so on and so on. Whatever the half-life, it takes about 20 of them to get to nothing. Why not two?

Anyway. Most of the short half-life isotopes have settled down 32 years after the accident. The mid-level ones will clear out after around 1,200 years and what’s left for the next 199,000 years are the relatively low-radiation long-lasting ones. It won’t be safe to live in until after that 200,000 years but it’ll drop off sharply after the first thousandish years and then stick at a very low rate of decay for the rest of the time.

In the event nothing goes wrong, the fuel eventually gets used up. The spent rods are still highly radioactive and very very hot so they get put in “wet storage” which is a special pool where they’re kept on racks twenty feet underwater for a couple of decades before being put into permanent “dry cask storage” which is a kind of giant barrel where the cooled and slightly less radioactive rods are stored - well, forever.

And I think that’s everything I know about nuclear physics.

[iamapolarbear]

The Chernobyl disaster

I keep trying to write a blog post about my trip to Chernobyl but every time, I get bogged down in the details - which I really want to write. So they’re going here.

It happened on the night of 25th April 1986 - well, in the early hours of the 26th, actually, about 1.15am.

Nuclear reactors get really hot - like, really hot. In the event of them being shut down, whether deliberately or in an emergency, the number one thing is to keep the cooling going. We’ve had three nuclear disasters and in all three cases, the cooling was the major issue. In the case of Chernobyl, in the event of a power failure, the reactors would automatically shut down and an emergency generator would kick in, continuing the cooling. But it took 30-90 seconds to get the emergency cooling systems online and Chernobyl bosses ruled that unsafe. So they decided to experiment with using the movement of the turbines to shorten the gap.

The experiment had already failed three times but they decided to run it again while reactor 4 was being shut down. In order to do this, they disabled a few safety systems. They had people standing by in case things went wrong.

So 1.15ish in the morning, they go for this experiment again. But something went wrong. I’m still not entirely sure what. I know that the control rods, graphite rods dropped into the reactor core to stop the nuclear reaction, jammed and shattered at some point. There was a power surge. The core began to melt and it met the light water used for cooling.

The results was a huge explosion. It blew the concrete lid of the reactor sky high and staff who ran outside to see what was going on saw rainbow flames shooting into the sky. Exposed to the night air, the white-hot graphite in the core burst into flames. Between the explosion and the fire, tons of radioactive material was flung into the air.

The power plant’s firefighters turned up, followed by the Pripyat ones and the Chernobyl ones. At this point, no one knew it was a nuclear disaster, no one even knew that the fire was in the reactor. Most of them believed it was just an ordinary fire. They were exposed to colossal doses of radiation and most of them were dead from acute radiation sickness within the month.

The next problem was that the burning reactor kept on melting and a sludge made of nuclear material, the reactor core itself and all the stuff the firefighters had thrown on it, making a highly radioactive lava called corium, began melting through the bottom of the pressure vessel, heading towards a pool of cooling water and the aquifer under that.

Had that lava hit that water, there would have been a second explosion. Minsk, 600+km away would have been levelled. Kyiv, 100km away, would have been wiped off the map. Eastern Europe would have been decimated and Western Europe would have been made uninhabitable.

There are various stories about what happened. There may have been divers who had to go underneath the reactor to drain the water away. I’m pretty sure Soviet miners were drafted in to dig a pit right underneath to install a cooling system. Helicopters dropped lead and boric acid and sand on the fire. Eventually, the fire was contained but it burned for the best part of two weeks.

This was Friday night. On Sunday afternoon authorities finally evacuated Pripyat, the city built two miles away from the power plant to house its workers and their families. On Monday, a nuclear power plant in Sweden noticed unusually high radiation levels. They checked nothing was wrong at their end and then enquired of their neighbours, there’s levels of radiation indicating a massive disaster. Have any of you done it?

That was the first pretty much anyone knew of the Chernobyl disaster. Officials in Moscow had heard rumours but hadn’t been able to get anything concrete out, or so they claimed. Soviet propaganda may well be lying there. But yes, no one knew of a massive nuclear catastrophe on Friday night until Monday.

Eventually an area 30km in diameter was evacuated. The 10km zone is still uninhabitable and although you shouldn’t be living in the 30km zone, some people are. Some of them are workers at the power plant. Reactor 1 was shut down in 1996 (after suffering a partial meltdown in 1982 that I knew nothing about until right now) , Reactor 2 in 1991 following a fire that I didn’t know about until right now and Reactor 3 in 2000. Reactor 4 was the one that exploded. Reactors 5 & 6 were being built at the time and that project was immediately stopped. Reactors 1-3 are now being decommissioned, which is the process of dismantling them and returning the area to its pre-nuclear state, including full decontamination. 

Over the course of May-December 1986, a sarcophagus was built to cover Reactor 4, to stop radioactive smoke & dust and to stop water getting in and risking another steam explosion. It was built when the radiation was at its highest, so pieces were dropped in by helicopter. It did the job, more or less, but it was gappy and it was never meant to last long. In November 2016, the New Safe Confinement was completed, a three-layer steel arch built to fit precisely over the remains, designed to keep everything out and everything in, condensation-proof and fitted with remote-operated robot arms to dismantle the wreckage. The NSC is meant to last 100 years but the current plan is to have the reactor dismantled and totally safe by 2065.

So some of the people living in the 30km zone, in the abandoned apartments in Chernobyl City, are workers decommissioning the power plant and running the solar farm. Some of them are self-settlers - people who were evacuated but chose to return to their homes. They’re not really supposed to be there but in 2004, the government decided to turn a blind eye to them and they now supply a weekly bus to take them to do their shopping and get their money etc. Their average age is 85. Some of them returned because after WWII and the Cold War, they weren’t that bothered by an enemy they couldn’t even see, like radiation. Some of them returned because the housing they were put into didn’t have heating or water or they couldn’t get jobs or get used to living in a big city after living out in the sticks - even in its heyday, the Exclusion Zone was a big empty patch of countryside. In some cases, families were separated because they couldn’t get on the same bus when the place was evacuated and in those days, finding each other again wasn’t as simple as phoning their mobile or sending them a message on Facebook. Some of those families never saw each other again.

And then there are stalkers - the people who enter the zone illegally. If they’re caught, the punishment is three days in jail in Kyiv and an 850UAH fine, which works out at $30/€26/£23 - much cheaper than an official tour and you get to decide what you want to see. It’s a stupid thing to do - on your own, you don’t know where the hotspots are, you don’t know where any places are, you’re letting yourself into crumbling radioactive buildings, you’re not following the safety rules and you’re risking being caught by Ukrainian border police, who even our guide said “are not always the nicest of people”. Stalkers are responsible for looting anything of value that survived, including the copper wires in the walls. Floors were ripped up because of an old habit of keeping anything valuable under the floor. That’s not down to time and lack of maintenance, that was ripped up deliberately in the 1980s. To be fair, today’s stalkers are mostly relatively harmless urban explorers and the kind of people who just like abandoned places. Mostly they’re not here to loot and steal and cause trouble.

More to come later but I’ve got stuff to do this morning.