Archive for the ‘energy efficiency’ Category
salt cooled nuclear reactors – part of the mix?
On a recent Skeptics’ Guide to the Universe podcast, Steven Novella presented a segment on salt-cooled nuclear reactors which really interested me. As a young person in the early 80s, I went to Roxby Downs, some six hours’ drive north of Adelaide, to protest against BHP’s Olympic Dam uranium mine, having learned something about uranium, radioactivity, fissile material and such, and having friends who had big concerns about all this stuff. There wasn’t much in the way of confrontation, but I certainly enjoyed tramping around in the semi-desert, espying desert peas, poached egg daisies and the like, and the night sky and its gadzillions of stars was definitely the highlight of the trip.
Of course I’ve learned a lot more about nuclear power since those days, and the era of the Maralinga nuclear tests, also in the South Australian outback, was then only a generation further back. The world has become a lot smarter about nuclear power, I think, since those days, and certainly I’ve noticed that nuclear power has been used in the USA (which currently has 92 operating reactors) and Europe (167, and falling) without any mishaps – uhh, excepting the Three Mile Island partial meltdown in 1979, no doubt an influence on the Roxby Downs protestors.
The only other reactor incidents of note, I think, have been Chernobyl in 1986, and Fukushima in 2011, about which there has been plenty of misinformation. I recall a fellow teacher, a few years ago, reminding us in the staff room of the Fukushima melt-down that ‘killed thousands’. She was confusing the Fukushima event with the Tōhoku earthquake and tsunami, which indeed killed over 20,000 people, a catastrophe virtually unimaginable to Australians.
I’ve written about nuclear power before, including this quite impressive piece, if I may say so myself (as nobody else will), but this is an opportunity for me to learn more about salt-cooled reactors and the input to all this of one Bill Gates, a figure who seems to raise the ire of some of my acquaintances, presumably due to what they deem as his ill-gotten wealth. Economics has never been my strong suit, which partially explains my life of relative poverty (though laziness and a kind of habitual solitude is more to blame), so I couldn’t begin to judge how ill-gotten, or not, his gains have been, but I’ve read a couple of very good books on his recommendation – Origin Story, by David Christian (a ‘Big History of Everything’) and How the world really works, by Vaclav Smil (‘A scientist’s guide to our past, present and future’) – and I’m aware of the work he’s been doing in recent years on vaccination and education in various African and Asian countries, so I’ve come to trust him on various practical issues faced by our species.
According to Steve Novella, in episode 989 of the SGU podcast series, Gates sat down with climate scientists some years ago to get the lowdown on investing in green or clean technology for the future, and the option that apparently most appealed to him, was salt-cooled nuclear reactors, or molten salt reactors. Novella himself has advocated for nuclear along with solar, wind, geothermal, hydro and any other low carbon options, in other words a multi-pronged approach, with different options obviously more or less suited to particular regions, and he believes that there are more than a few misconceptions about the dangers and downsides of nuclear energy generation.
So the nuclear industry has not been faring well of late. Existing systems are passing their use-by dates, and investment is lagging behind demand, which itself is suffering due to aforementioned misconceptions. Gates, however, has been convinced that a relatively old nuclear technology needs to be revived. A reactor is currently being built in Wyoming by a Gates-backed company, TerraPower (referenced below), which is being mooted as faster (to build), cheaper and safer than existing reactors, and with a smaller output (around 300 megawatts rather than a gigawatt). It will be salt-cooled rather than water-cooled, and this, according to Novella, is the decisive feature:
‘Water has to be under high pressure, and this high pressure is what causes much of the expense, the safety features, you have to be constantly managing the amount of pressure, and this massively complicates the design, and therefore the cost, etc’.
Another important feature of the design is that:
‘It separates out the nuclear part of the plant from the energy production part. That may sound simple, but it means that the turbine, which turns the heat from the nuclear part, the reactor, into electricity, is housed in a separate building – which means, theoretically, that you don’t need a lot of the safety features in half of the plant (the production part) that you have in the other half’.
So the ultimate idea is for a cheaper, more efficient plant. The separated design for TerraPower’s system has yet to be approved by the regulators, but it sounds quite straightforward, and is even described by TerraPower as ‘boring’ in its simplicity.
So how does ‘salt cooling’ work? The salt (fluoride or chloride) stores the energy from the reactor by heating up until molten, after which it flows to the turbine to produce electricity, but the salt retains the heat from the reactor for much longer than water does, and as such it can essentially serve as a power storage device, like a battery, which can then serve as a kind of load-following power plant for more intermittent forms of renewable energy. The more conventional nuclear power plants don’t have this compatibility with renewables.
Apparently salt-based nuclear facilities were first produced in the 1950s and were phased out in the 70s, for some reason (more research required). The Wyoming nuclear site is being built within the region of a coal plant that is due to close completely in the 2030s, so that it can use the grid connections and some of the infrastructure of that plant, with the advantage that it can ramp up and down more effectively than coal-based power plants can (natural gas is also good as a ‘peaker’ electrical source, but without the clean benefits of nuclear).
So this facility, which has yet to clear some regulatory hurdles, should serve as a proof-of-concept for further facilities as other nuclear reactors pass their use-by date. The USA currently derives about 19% of its energy from nuclear, and falling, but energy demand for that nation is expected to increase by some 50% by mid-century. As we all should know, Germany decided to decommission its nuclear reactors some time ago, with the stated aim of ‘going green’, but has instead fallen back on coal and gas.
So it seems that the salt-based technology and the architectural design of this Wyoming plant will be proof against the kind of disaster experienced at Fukushima (where ‘corporate capture’ was also a factor to be mindful of), but there is also the issue of nuclear waste, or spent nuclear fuel. Of course this is of great concern to the public, as shown when South Australians rejected plans by its government to make a bit of dosh by offering some of our vast, uninhabited land as a dumping ground for such material. But as Novella points out, there’s a linear inverse relation between the radioactivity of this spent fuel and its half-life. That’s to say, the more highly radioactive the material, the shorter the half-life. So the material, if buried well underground in a geologically stable environment, would only be dangerously radioactive for a fraction of the thousands of years of its overall radioactivity.
It all sounds relatively positive. Something to keep an eye on over the next few years.
References
giving nuclear energy a chance, please
Episode #989
https://en.wikipedia.org/wiki/Load-following_power_plant
What is a heat pump?
from How Stuff Works
Canto: So We’ve been reading, inter alia, Saul Griffith’s practical and informative little renewable energy tome, The big switch, in which he mentions, inter alia, heat pumps and their relative efficiency. He may have explained heat pumps somewhere, but I was adrift at the time. Can you inform me?
Jacinta: Well, instead of rifling through the book, which unfortunately doesn’t have an index, let’s google it. Australia’s largest electricity generator has a piece boosting heat pumps, which may sound biased, but Griffith boosts heat pumps too, so I’m presuming it can be trusted. The humble heat pump, as it’s described, isn’t a new technology, and is a proven winner in terms of energy efficiency, for example in reverse-cycle air-conditioning. Particularly so for heating. It ‘gathers heat from outside and warms it to a higher temperature, then moves it from one place to another’.
Canto: It gathers heat from outside. Easier said than done, surely. Presumably it sucks?
Jacinta: Well apparently there’s more than one type of heat pump technology, and this article mentions two – air sourced, and ground sourced (geothermal). And as they point out, it may seem counter-intuitive to think you can extract heat from outside, whether from the air or from under the ground, in the depths of winter. But heat is energy, and even in the winter there’s a lot of that energy around. Anything above absolute zero contains energy, and there’s surprisingly little difference between winter and summer heat energy.
Canto: Well I notice they highlight this statement about your standard heat pump:
It uses a compressor and liquid or gas refrigerant (the stuff that’s in your fridge) – a substance that absorbs heat from the environment – to concentrate heat and move it around to warm your house.
Now that’s something that needs explaining.
Jacinta: Well, off-hand, I understand that heat tends to disperse, when it can, from a compressed high-energy state to a low-energy one, something to do with a law of thermodynamics…
Canto: I suppose heat pumps come under the umbrella of HVAC systems – heating, ventilation and air-conditioning. But do all air-conditioning systems work with heat pumps?
Jacinta: Well I don’t think so – there’s evaporative air-conditioning, which I think’s quite different.
Canto: So a heat pump just is a reverse-cycle aircon? How, exactly, does it do the cooling? Or the heating for that matter.
Jacinta: Just off the top of my head, the cooling works just as the heating does, but in reverse. It sucks the hot air from the room and chucks it outside. And then, uhhh, brings colder air in somehow, or cools it in that big box, somehow like a refrigerator…
Canto: Brilliant. So now I’m reading How Stuff Works on heat pumps. And of course you’re on the right track, it’s all about heat transfer, so it doesn’t require energy for burning..
Jacinta: Or freezing?
Canto: Uhhh, it requires energy, of course, but it’s pretty energy-efficient. They’re particularly good in moderate climates like ours (In Adelaide), because you don’t have to transfer large amounts of heat from outside or inside to make life comfortable.
Jacinta: It’s pulling and pumping. You pull heat from the outside, or inside depending on the season, and pump it into the inside, or outside.
Canto: Yeah, I get that, but what’s the mechanism?
Jacinta; Well, sucking air in is pretty simple, our mouths do it all the time, and think of a vacuum cleaner, which does it more powerfully, but generally for shorter periods. Aircons just require a gentle, longer-term suck.
Canto: Very technical.
Jacinta: That’s probably why the emphasis is on the pumping. Now, I’m talking about air-source heat pumps in particular, because that’s what we have in our home – on the wall, with another box outside. What they call a split system. So, I’m going to quote at some length from How Stuff Works, and then we’ll try to break it down, if necessary:
One of the most common types of heat pumps is the air-source heat pump. These take heat from the air outside your home and pump it inside through refrigerant-filled coils, not too different from what’s on the back of your fridge. The air source variety is pretty basic, and you’ll find two fans, the refrigerator coils, a reversing valve and a compressor inside to make it work.
The key to allowing the air-source heat pump to also cool is the reversing valve. This versatile part changes the flow of the refrigerant so the system can operate in the opposite direction. So instead of pumping heat inside your home, the heat pump releases it, just like your air conditioner does. When the refrigerant is reversed, it absorbs heat on the indoor side of the unit and flows to the outside. It’s here that the heat is released, allowing the refrigerant to cool down again and flow back inside to pick up more heat. This process repeats itself until you’re nice and cool.
Canto: Hmmm, that sort of makes sense, the hot air inside is made to flow through these ‘refrigerant filled coils’, but what exactly is this refrigerant? Didn’t they use to use freon or something, which damaged the ozone layer? And this doesn’t exactly sound like a split system. It sounds more like an all-in-one.
Jacinta: Yeah so not all reverse cycle aircons are split systems. Apparently split systems are easy to install and work pretty efficiently. I can’t easily find how they compare with all-in-ones but I suspect they’re pretty similar, efficiency-wise. Another type of reverse cycle aircon is ducted., which can warm or cool several rooms at once through various ducts. The refrigerant most used nowadays is puron, a HFC (hydrofluorocarbon) known to be non-damaging to the ozone layer. It’s become the standard refrigerant since 2015, but our aircon is surely older than that. Freon, the culprit you mentioned, hasn’t been used in new air-conditioning systems, at least in the USA, since 2010. Freon is a HCFC (hydrochlorofluorocarbon), apparently much naughtier than HFCs. Of course, I’ve no idea what our system uses.
Canto: Okay, last question. I don’t think we’ve answered how the pump thing works.
Jacinta: Well I suppose it does so just as mysteriously and simply as it sucks. We suck air in with our mouths and noses – or we suck in oxygen, and how we separate that gas from all the others is another story – and we pump out carbon dioxide. All without the slightest effort, apparently.
Canto: So we’re actually heat pumps? And we’re pumping out CO2 at an alarming rate, eight billion of us. We’re the principal cause of global warming!
Jacinta: Haha, I think you’ll find it’s a bit more complex…