back to article 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 …

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Anybody know why the plan isn't to install lots of tiny reactors at the grounds of the existing large nuclear power stations?

The staff, security and grid interconnects are already there, plus it gets around the NIMBY problem.

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"small-scale"

Did something leak again? Is that the latest name for Windscale?

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no, still NIMBYish

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?

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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.

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Re: no, still NIMBYish

I wonder what the Norfolk Broads would look like when lit up by Cherenkov radiation?

Like a typical Friday night in Wells-Next-The-Sea, but with less inbreeding taking place.

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Anonymous Coward

Sounds sendible but...

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.

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Re: Sounds sendible but...

"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?

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Re: Sounds sendible but...

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.

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Mushroom

Heat engines

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.

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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.

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Re: Heat engines

And still dumps 2/3 of their total energy... Only difference is that it dumps it to the air... along with tons of CO2.

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Opportunities

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.

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Re: Heat engines

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)

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Re: no, still NIMBYish

"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.

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Re: Heat engines

"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.

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Re: Sounds sendible but...

"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.

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Re: Heat engines

The Moltex Stable Salt Reactor runs hotter - around 600C so conversion is more efficient - around 43% I believe. This also means they can use standard turbines = cheaper than for most light water reactors.

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Re: Sounds sendible but...

Sounds expensive. And I think they use a far higher level of enrichment un subs - around 20% instead of 3-5% 235Uranium.

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Re: Sounds sendible but...

Carbon dating experts chuckle about people who declare themselves a nuclear [radiation] free zone. "They're in serious trouble. It means they've been dead at least 50,000 years."

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Re: no, still NIMBYish

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

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Boffin

Re: Sounds sendible but...

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.

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Trollface

Re: Heat engines

"along with tons of CO2."

hold your breath to reduce CO2 output. that'll help.

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Boffin

Re: no, still NIMBYish

"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

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Boffin

Re: Sounds sendible but...

"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'.

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15MW as stated above is still enough to cover the baseload of about 15,000 homes, or the typical absolute peak of about 1,500... and that's a surprisingly large area, if you're not supplying a forest of high-rises.

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Re: Heat engines

Where does propane-expanded polyethylene come on that graph?

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Re: Heat engines

Bit of a problem on a day like today, though ... if there's one thing I *don't* want right now, it's extra heat.

But I might want to use some electricity to run an air conditioner (or would if I had one)

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Re: no, still NIMBYish

"Moltex" sounds like something a James Bond villain would use...

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Re: no, still NIMBYish

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.

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Re: Heat engines

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.

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Re: no, still NIMBYish

"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.

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Re: Heat engines

"But I might want to use some electricity to run an air conditioner (or would if I had one)"

In a district heating system you might use the piped heat to run an electrolux technology cooler (solarfrost)

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Re: no, still NIMBYish

Pumping molten salts can be done without moving parts _in_ the pipes - it's an ionic liquid and moving electromagnetic fields work well. Oak Ridge have shown this already.

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Green Janet / Blue Bishop

This reminded me of a British portable reactor project in the '50s:

https://web.archive.org/web/20051109031736/http://www.skomer.u-net.com/projects/greenjanet.htm

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Re: no, still NIMBYish

gas cooled reactors could drive gas turbines then use steam as in combined cycle.

but who cares? uranium is dirt cheap and saving a bit of it is not worth the hassle.

French reactors use rivers for cooling

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Re: Heat engines

Not true. all straight steam plant heat engines yes, but combined cycle gas turbines WITH steam plants can better 60%.

But with nuclear fuel being dirt cheap, there is no economic driver to create more efficient installations.

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Anonymous Coward

Re: Heat engines

"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.

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Anonymous Coward

Re: transmission losses

"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.

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Re: no, still NIMBYish

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...

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Re: Heat engines

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!

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Anonymous Coward

Placed underground you say ?

Can anyone see a potential problem with the water table and bore hole water extraction in the UK if there was an accident ?

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Anonymous Coward

Underground

There will still be complete, multiple containment systems. https://www.youtube.com/watch?v=93PW8lcblpQ shows a US modular proposal that uses Thorium salts in a "fail safe" design.

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Happy

Placed underground you say ?

I've long believed that ALL nuclear facilities should be placed underground.

It's only a matter of time before an accident occurs involving an errant aircraft.

The roof must be designed to withstand significant impact. You might want to up that to give some protection from enemy action in war.

Bonus points if you also cover the turbine hall and essential switching. With very large stations built on the well proven "bigger is always better and cheaper" and the" lets put the eggs in as few baskets as possible" principles - where have we heard that before - loosing only one station at the wrong time could be critical.

Small district heating schemes - I'll buy that. It worked well in Pimlico with the waste heat from the coal fired Bankside station on the Thames piped under the river.

What about agriculture / market gardening? Around Sizewell in Suffolk the ground is sandy. Generally produces alternate crops of pigs and arable. Cover some of it with glasshouses, heated by the cooling water, ventilated and lit by the leccy. Alternative option - multistory hydroponics. Already being done commercially in the states. Just need the leccy.

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"Can anyone see a potential problem with the water table and bore hole water extraction in the UK if there was an accident ?"

Nope. I'm sure there is a large market for glow-in-the-dark mineral water in nightclubs, etc.

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Coat

Re: Underground

" in a "fail safe" design"

Until it doesn't of course. Wasn't Fukushima a "fail-safe" design?

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Re: Placed underground you say ?

"I've long believed that ALL nuclear facilities should be placed underground."

Iran are leading the way in nuclear facilities then.

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Boffin

Re: Placed underground you say ?

"It's only a matter of time before an accident occurs involving an errant aircraft."

All nuclear reactors in the UK have their own no-fly zone, and they're reinforced to withstand a collision from a full sized passenger aircraft on the reactor (just another reason why nuclear is expensive).

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Anonymous Coward

Re: Placed underground you say ?

>a full sized passenger aircraft on the reactor

A full-size passenger aircraft from 50 years ago - not the same thing.

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Re: Placed underground you say ?

>"The roof must be designed to withstand significant impact."

Like this? :-

https://www.youtube.com/watch?v=25vlt7swhCM

PS. Don't tell Greenpeace. They spent lots of money on fearmongering TV advert campaigns about "what if an aircraft hit?!" and they get incredibly hysterical when confronted with evidence that people actually considered these issues long before they were born.

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