Britain's on the brink of a small-scale nuclear reactor revolution For the first time ever in April, the UK's data centres and clouds ran on electricity generated without burning coal. The National Grid celebrated the news on Twitter with the promise of more coal-free days to come. As coal-fired power plants wind down and with talk of blackouts in the air, nuclear is back on the table after …
It doesn't get around the NIMBY problem. Some folks will hate anything (ignoring the folks who automatically hate everything) and the usual fix for nuclear installations is to convince local government what a boon the installation will be, possibly via bribes such as infrastructure promises.
For SMRs, the size of the payoff can be correspondingly smaller than for something like Hinkley Point. Since SMRs are likely to be doing combined heat and power, the deal on offer will probably be based around cut-price piped hot water for domestic and industrial use.
The flip side is that SMRs still need lots of cooling water. The likes of Hinkley Point need to be on the coast with deep water close inshore or on major rivers, for SMR we could go smaller. I wonder what the Norfolk Broads would look like when lit up by Cherenkov radiation?
"The flip side is that SMRs still need lots of cooling water. "
Water-moderated ones do, because of the low temperatures they run at and their very low thermodynamic efficiency.(*)
Molten salt reactors run a LOT hotter(**), are a LOT smaller (not needing to be pressurised and not needing the associated pressure vessel and containment vessel) and as such they can dump directly to atmosphere via cooling towers (which could possibly be large enough to run a vortex and generate more power from the waste heat) and as a nice side effect they can't leak radioactive steam/water or cause radioactive hydrogen explosions.
The OTHER nice side effect is that if you use molten salt fuel (LFTR) designs you can load follow almost as quckly as gas or hydro plants without the risk of neutron poisoning as the pesky Xenon can be drawn off and stored until it breaks down or reinjected later, avoiding any prompt-critical excursions.
Alvin Weinberg should be hailed as a Hero of Humanity, after inventing the water moderated reactor for nuclear submarines he became gravely concerned by the safety issues of sizing them up to GW scale (especially the pressures!) and developed molten salt systems as a safer alternative in the 1960s - The USA ran a molten salt plant at Oak Ridge between 1962 and 1968 but Nixon killed it in 1972. Oh, what could have been.
(*) They're also intrinsically unsafe as they rely on high pressure, high temperature water being in contact with radioactive materials. Steam explosions are a fact of life and the fact that nuclear plants are 300,000 times safer than coal ones is down to careful management and paranoid design standards. It's still better not to mix water and fissionables.
(**) Water-moderated reactors top out about 450C. Most molten salt ones are just getting started at that temperature and are designed to run at 600-900C, with fission reactions self-limiting about 1100C (which is about the temperature of the inside of a conventional fuel rod) and the molten salt itself boiling at 1300-1600C depending on the exact chemistry used. The extra heat on the hot side means that conventional cooling towers can be used instead of relying on dumping heat to water, which in turn means the power station can be located away from shorelines (tsunami risk) and rivers (which tend to follow faultlines). Yes, you can dump heat to water for greater efficiency, but the greater safety margin afforded by not doing so(**) is worth considering.
AGR plants (UK's main design) can also run bloody hot and don't really need water cooling but they have their own sets of problems such as radioactive gas containment when things go pear-shaped. This isn't helped by not being designed to handle a full temperature excursion to 1100C
(***) And not having to derate your output in hot weather in order to preserve the local wildlife. This is a fundamental weakness of any plant using rivers or shallow seawater areas for cooling.
Another way you can load follow is to have another tank of just molten salt. That way you can run the nuclear island at continuous full power and sell most of that energy. Moltex Energy's 'GridReserve' may interest you: http://www.moltexenergy.com/learnmore/Moltex_Renewables.pdf
"Water-moderated ones do, because of the low temperatures they run at and their very low thermodynamic efficiency"
not entirely accurate the way you put it. total plant efficiency is generally a function of the steam temperature going into the turbines, and the rejection temperature of the condenser.
You can run PWRs at very high temperatures, but the steam plant itself limits the total capability. I would imagine that a 1200 psi steam plant (with gas-fired superheaters) is "typical". The reactor would run in the 550 degree F range for that kind of pressure. Not a problem, really. Steam itself, in many ways, determines what the max efficiency will be for a power plant. If you could drive the turbines directly with molten salt, that would be different. but you can't. You still need steam (for a practical solution, at any rate).
Water, as convenient as it is, just has physics properties that limit your overall efficiency. You can't have steam above a certain temperature (its phase is indefinite, actually, neither liquid nor gas) and you can't have heat rejection below a certain temperature (i.e. ICE formation).
https://en.wikipedia.org/wiki/File:HS-Wasserdampf_engl.png
That makes me wonder actually... there are plenty of metals that are solid way above salt's melting point (otherwise containing it would be difficult), so isn't there any way to produce a practical system for turning its energy into electricity? The stuff must still convect after all, and I bet there are pumps somewhere within the system.
"You can run PWRs at very high temperatures, but the steam plant itself limits the total capability."
You _can_ run PWRs at very high temperatures and pressures, but it's not a good idea to do so.
Water's half-jokingly known as the universal solvent. Once you get it up to 400C + 20 atmospheres and add boric acid it has a nasty habit of eating pipework AND weak welds on nuclear fuel rods. There are a number of photos on the net of such examples.
The US nuclear industry has has a number of near misses caused by corrosion. Water is simply not safe enough to be in direct contact with nuclear materials. When things do go wrong it usually escapes and carries radioactives off into the environment. (And don't get me started on molten sodium... One word: Monju)
If you have a steam explosion on the tertiary loop, it's a steam explosion. No radioactives, no big deal.
Yeah, monju (extract from Wikipedia):
An accident in December 1995, in which a sodium leak caused a major fire, forced a shutdown. A subsequent scandal involving a cover-up of the scope of the accident delayed its restart until May 6, 2010, with renewed criticality reached on May 8, 2010.[4] In August 2010 another accident, involving dropped machinery, shut down the reactor again. As of June 2011, the reactor has only generated electricity for one hour since its first testing two decades prior.[5] As of the end of 2010, total funds spent on the reactor amounted to ¥1.08 trillion. An estimated ¥160-170 billion would be needed to continue to operate the reactor for another 10 years.[6]
As of 2014, the plant had cost 1 trillion yen ($9.8 billion).[7]
A final decision on the project (e.g. to decommission or extend funding) was due by end 2016,[8] and a decision to close the facility was made in December 2016.[9][10]
... Intense vibration caused a thermowell inside a pipe carrying sodium coolant to break,...'
a
Troublesome , those vibrating pipes. Reminds one of that reactor in California...
This post has been deleted by its author
Anybody know why the plan isn't to install lots of tiny reactors at the grounds of the existing large nuclear power stations?
Grid losses, and heat. Government want the SMR build close to demand centres (cities) so that they reduce transmissions losses of around 2-3%. Overall grid losses are lower, but the existing nukes have very long distance transmission routes because they were built in the middle of nowhere. And there's a plan to use the heat from nuclear power to drive district heating systems - about two thirds of the energy potential in nuclear fuel is waste heat, and you could recover about half of that heat if you could dump it into a heat network. It's technically feasible, but even by Hinkley standards it would be hugely expensive.
The number of Towns and Cities that have declared themselves to be 'Nuclear Free Zones' (not including medical uses though) is quite large.
So it is a non starter despite making perfect sense.
Personally, I think even these SMR's are too big. I'd like to see 40ft container sized reactors. That way, they don't need to be decom'd on site or even refueled on site, just put the thing on a railway wagon and take it to Windscale/Sellafield.
Then site half a dozen or more where there used to be a coal fired plant as it has the grid connections.
People with complain about the security of the radioactive bits but if the container is made to safely shut down the terrorsts would have a hard time letting it escape before the place was bombed. Naturally, the critical bits would be hardened.
But I'll shut up and take my meds. Farr too much common sense for one day.
"I'd like to see 40ft container sized reactors."
Genuine question - what size are the reactors on subs? How are they cooled?
I really don't know that much about this area but it seems to me that if we can make a sub with a reactor we could make a sub that is JUST reactors (and propulsion) - we can connect offshore windfarms to the grid why not offshore reactors? or at the bottom of a lake?
Genuine question - what size are the reactors on subs? How are they cooled?
a) All systems included, about the volume of two or three 40 foot containers. But that's for a submarine reactor of 30 MW, which in a civil context is about 15 MW of electrical output.
b) You know all that cold seawater on the outside? Incidentally, the thermal trace of a sub is a problem when you're aiming for a stealthy, invisible vessel, and the designers want to minimise it, but unfortunately there's nowhere else to dump the surplus heat.
"Incidentally, the thermal trace of a sub is a problem when you're aiming for a stealthy, invisible vessel, and the designers want to minimise it, but unfortunately there's nowhere else to dump the surplus heat."
This is why the newer diesel-electric class boats such as Australia's Shortfin-Baracuda Collins-class replacements are making some navies nervous. They don't (quite) have the endurance of nuke boats but they're a lot harder to detect and they can stay underwater for a few weeks at a time.
"And I think they use a far higher level of enrichment un subs - around 20% instead of 3-5% 235Uranium."
that little? come now, use your imagination. The higher the enrichment, the smaller the reactor size (due to smaller critical mass/geometry being possible). there's a LOT more going on than that, of course, engineering-wise [you want to make that a "lifetime of the boat" core, by pre-loading every bit of fuel you expect to need in 30+ years, right?] but 20% enrichment is a WAY small number. Just sayin'.
what size are the reactors on subs
it depends on the sub. most reactor specs are classified. Some are published in 'Jane's Fighting Ships' etc. but they're not official. Suffice it to say, they are much larger than you think, megawatt-wise.
Back in the 1980's I was on a 688 (Los Angeles) class sub that used a core that was originally designed for a destroyer, and was adapted for a sub. They actually had to do a post-manufacturing modification to the main engines (steam turbines) for it to use 100% reactor power. And it went fast enough for 'back then', enough that they had seat belts on key watchstations for "rig for high speed".
Now, add 30 years of technological development to that timeline, and speculate. You're probably close.
Needless to say, 30MW is probably close to what the Nautilus had when it first launched in the mid 50's.
but yeah I can't truly confirm any of that. it's classified.
On carriers, the Enterprise originally had 8 reactors. I think the newest carries have only 2, and they're pretty big (more total steam than the Enterprise's 8 reactors). That gives you a perspective on how the nuclear tech has advanced over the years.
Submarine reactors are generally much smaller in output than you would need to power a town. They are built with special constraints that make them uneconomic for commercial use (which is incidentally why commercial ships don't use nuclear power). That is ok for the navy because they have a defence budget to pay for them. And as to cooling, submarines have an ample supply of seawater.
All heat engines (Coal, Nuclear) reject nearly 2/3 of their total energy. So a 300MWe plant will be rejecting nearly 600MW of heat per hour.... Laws of Thermodynamics can't be beat... This is why a Natural Gas fired plant is more efficient, but still reliant on fossil fuels... Natural Gas directly drives the turbine generator.
Natural gas generators can get close to 60% efficiency because they're a 2 step process.
1: Gas turbine engine and attached generators
2: Bog standard steam plant driven from the turbine's waste heat.
That's why they're called cogeneration systems. Standalone peaking plants are called OCGT (open cycle Gas turbines) and hideously inefficient, although cogen plants can provide some peaking capacity on the turbine side.
Super critical steam turbines can hit efficiencies of over 48%. So not much difference with CCGTs maxing at about 60%. Utterly irrelevant though, has to be considered with the fuel and the energy density of nuclear fuel can't be beaten.
https://www.xkcd.com/1162/
BTW, gas turbines are heat engines too.
(Pointless discussion but I saw an excuse to link to XKCD)
"So a 300MWe plant will be rejecting nearly 600MW of heat per hour.... Laws of Thermodynamics can't be beat..."
The trick is to find uses for the "waste" heat - hence the push for district heating (and cooling!(*)) systems driven from them.(**)
(*) https://entropyproduction.blogspot.co.uk/2005/10/solar-thermal-cooling.html - yes it says solar but any suitable heat source will do. Solarfrost.com have been working on these kinds of systems for 20 years.
(**) In some countries the district heating is used to warm greenhouses and extend the growing season as well as defrost critical roads. It's not just something for housing.
In places where it gets icy you can also put pipes under the streets and sidewalks using the waste heat tl keep them clear of snow and ice.
Holland, Michigan has been doing this in it's downtown for many years and their "Snowmelt" system has been a great success... and western Michigan winters are not to be taken lightly!
"Natural Gas directly drives the turbine generator"
Thats's why I've always wondered aloud, surely these fancy solutions for generating steam to drive turbines can't be the best way forward?
Tidal generation seems one of the most sensible to my mind, although that approach will always incur transmission losses due to the remote locations you have to build such installations.
If gas turbines can be largely powered by methane/etc produced by local organic digesters, then a lot of the 'new CO2' problem can be mitigated. It also therefore creates a recycling solution for organic waste as well as electricity.
"that approach will always incur transmission losses due to the remote locations you have to build such installations."
Frequently heard, but not all that significant.
In the UK at least, the majority of the transmission and distribution losses are in the low voltage side of things, e.g. the last mile between the end user customer and their nearest substation. That part of the loss (the "distribution" loss is unchanged whether the power to the substation comes from five miles away or five hundred miles away (the "transmission" side of things).
There are issues with the UK transmission network but they're more about capacity and connectivity than they are about losses (lots of generation in the North, lots of demand in the South), though obviously the aspects are linked somewhat.
Rooftop PV does change the "last mile" losses picture somewhat - there is no distribution loss when there is no distribution supply e.g. sunny midday, lots of people with PV - but it brings its own challenges when penetration in any given locality downstream of a substation becomes significant, e.g. curtailment of rooftop PV on sunny days. Not insurmountable by any means, but mitigation would need investment, and 'invest' isn't a word that't currently well understood by UK utilities.
Probably because there is a lot of fat on a £18 billion contract with the inevitable overruns and renegotiations that will expand the budget and keep thousands of civil servants employed for decades along with offering consultancy roles for ex-ministers and civil servants along with their families and friends.
Whereas £1.2 billion offers far less opportunity to hide cronyism and therefore is considered far less attractive by senior civil servants and ministers.
These factors are far more important than any advice from technical experts brought in to evaluate such schemes.
"No deaths, no strange glows at night and no two headed sharks."
LOL almost perfectly safely?! It was one of only two International Nuclear Events Scale level 7 events ever recorded! The other being Chernobyl.
So you must have missed the 34 that died during the evacuation, and the hundreds that will eventually die from radiation exposure? http://www2.ans.org/misc/FukushimaSpecialSession-Caracappa.pdf
Not to mention the massive leaks of radioactive material into the groundwater, sea and air!
TheVogon, no doubting nuclear on here bud, there are contracts at stake (I assume).
Besides some of that stuff will be gone in such a short time, much of it well depleted in a few thousand years and if you think us humans have a good chance at existing for long enough to see it properly cleaned up you are a more positive thinker than me.
The bags that Fukushima cleanup waste was scraped up into, and stored locally have a life of a few years and have been holding it for a few years no so they have chimneys in the stacks to take away the heat from decomposition to avoid the whole thing going up and dispersing all that lovely radio active crap into the air again.
But there I go being negative on nuclear, it just won't do.
By the way how is the Hanford Vitrification plant coming along? and where is that site going to be safe? I mean that's only about 79 tons of plutonium waste there (?), must be easy enough to drill a hole or something and drop it in see I'm getting into "this is not an issue" mindset myself right now.
I'm still sort of skeptical about the validity of that rating, as that's a logarithmic measure-of-magnitude scale, and it just doesn't seem to qualify for some of the tickboxes...
I mean, it didn't send a plume of vapourised reactor contents floating several thousand miles across a large part of the northern hemisphere for one thing. The water pollution is actually fairly slight, and although it's been measured and tracked with ease, that's because radiation detectors are very sensitive devices on the whole. No-one on the site died during the initial incident, no-one received such large doses that they died within a matter of days if not hours, and they didn't have to immediately forcibly bus the entire local population out of the area for fear of them succumbing to radiation sickness before the year was out.
We saw this drama unfolding over a matter of days after all... no actual release of solid nuclear material or fuel occurred, only irradiated cooling water and maybe a few gaseous decay products. The evacuations are mainly on a just-in-case basis. All the melted fuel is solidified somewhere in the ground underneath the plant, so it doesn't need a janky concrete cube to be hastily thrown up around it.
The plant isn't even necessarily unsalvageable, though hopefully they won't be fool enough to try... (he says, having a funny feeling he saw a news story about the second reactor having been put back into service already).
Some byproducts did escape, some people have had significant but not immediately lethal or crippling exposure - the effects of which will take time to show - and there has been significant local disruption as a civil protection measure. But it's not on a "hundreds if not thousands of deaths and immediate ruin of an area the size of Greater London which might last for millennia" scale.
"LOL almost perfectly safely?! It was one of only two International Nuclear Events Scale level 7 events ever recorded! The other being Chernobyl."
The japanese declared it as a 7 but it never came even close to that.
If you look at https://en.wikipedia.org/wiki/International_Nuclear_Event_Scale and the actual effects it was a 4 or 5 at most, but panicmongering set in.
The Register 
Biting the hand that feeds IT
Copyright. All rights reserved © 1998–2024
