Small modular nuclear reactors

[BingMan]

I read that the government is encouraging research into small nuclear reactors as part of its green agends.

But surely effective small nuclear are already in use in marine applications: submarines, aircraft carriers, ice-breakers.
Why can't these designs be repurposed to generate electricity?

 

[JamesT]

I read that the government is encouraging research into small nuclear reactors as part of its green agends.

But surely effective small nuclear are already in use in marine applications: submarines, aircraft carriers, ice-breakers.
Why can't these designs be repurposed to generate electricity?

That essentially is what they're doing. But it still has to go through the civilian approval process.
There may also need to be some adaptations. For example, I believe the submarine reactors use highly enriched uranium which may be considered a security risk so the civilian version may have to be adapted to handle normal uranium.

 

[dastocks]

There is a video here explaining Uranium enrichment for SMRs:

Enriching fuel to higher levels at Urenco

Urenco is an international supplier of enrichment services and fuel cycle products for the civil nuclear industry, serving utility customers worldwide who provide low carbon electricity through nuclear generation.

www.urenco.com

 

[jfollows]

The uranium needs to be enriched to ~3% U235 versus ~0.7% in natural uranium to allow a water moderator to be used; using graphite or heavy water as a moderator really isn’t done any more. But of course that’s not “highly enriched”.

 

[AndrewE]

I don't know where they are going to get the cooling water from for all these reactors, or where they are going to discharge it to without doing further damage to our rivers...

 

[najaB]

I don't know where they are going to get the cooling water from for all these reactors, or where they are going to discharge it to without doing further damage to our rivers...

What damage do you imagine cooling water discharge will do to our rivers?

 

[Ediswan]

What damage do you imagine cooling water discharge will do to our rivers?

Raise the temperature, potentially upsetting the ecological balance. France has had to reduce the output of some nuclear stations at times as mitigation.

 

[AndrewE]

What damage do you imagine cooling water discharge will do to our rivers?

they are too warm for adequate oxygen levels already, hot water is one of the worst pollutants for driving the last remaining dissolved oxygen off, killing the shrimps and caddis-fly things and the baby fish ...

 

[BingMan]

they are too warm for adequate oxygen levels already, hot water is one of the worst pollutants for driving the last remaining dissolved oxygen off, killing the shrimps and caddis-fly things and the baby fish ...

Could the heat be extracted from the hot water and put to some use. Such as warming nearby buildings

 

[Class 317]

It's my understanding that the designs of SMR reactor's are similar to existing ones used in the maritime environment and I believe they are closed loop as far as cooling is concerned.

 

[tomuk]

they are too warm for adequate oxygen levels already, hot water is one of the worst pollutants for driving the last remaining dissolved oxygen off, killing the shrimps and caddis-fly things and the baby fish ...

Why are they too warm already?

 

[Yew]

Raise the temperature, potentially upsetting the ecological balance. France has had to reduce the output of some nuclear stations at times as mitigation

There are lots of disused sites for old coal fired power stations. Perhaps the cooling towers might not be able to be reused, but they’d seem like good candidates.

 

[tomuk]

It's my understanding that the designs of SMR reactor's are similar to existing ones used in the maritime environment and I believe they are closed loop as far as cooling is concerned.

No. Nuclear submarines use sea water to cool the steam generated by the reactor.

 

[JamesT]

No. Nuclear submarines use sea water to cool the steam generated by the reactor.

See the diagram on https://www.navsup.navy.mil/Viper-Home/NNPO/ which also has an explanation of the various loops involved.

 

[tomuk]

See the diagram on https://www.navsup.navy.mil/Viper-Home/NNPO/ which also has an explanation of the various loops involved.

Yes and that diagram clearly shows seawater being used to condense the steam back into water in the secondary loop like I said.

 

[jfollows]

https://en.wikipedia.org/wiki/Nuclear_marine_propulsion says

Most naval nuclear reactors are of the pressurized water type, with the exception of a few[quantify] attempts[by whom?] at using liquid sodium-cooled reactors.[2] A primary water circuit transfers heat generated from nuclear fission in the fuel to a steam generator; this water is kept under pressure so it does not boil. This circuit operates at a temperature of around 250 to 300 °C (482 to 572 °F). Any radioactive contamination in the primary water is confined. Water is circulated by pumps; at lower power levels, reactors designed for submarines may rely on natural circulation of the water to reduce noise generated by the pumps.[citation needed]

The hot water from the reactor heats a separate water circuit in the steam generator. That water is converted to steam and passes through steam driers on its way to the steam turbine. Spent steam at low pressure runs through a condensercooled by seawater and returns to liquid form. The water is pumped back to the steam generator and continues the cycle. Any water lost in the process can be made up by desalinated sea water added to the steam generator feed water.[3]

which I read as saying the secondary circuit is also a closed loop but can be ‘topped up’ with desalinated sea water.

 

[michael8]

It would be great to see a proliferation of small-scale nuclear reactors, perhaps tied in with urban district heating systems, to de-centralise energy production as well as provide a more consistent source of "green" electricity nationwide.

 

[AndrewE]

Why are they too warm already?

sewage works outfalls (see https://www.aquatechtrade.com/news/wastewater/heat-from-sewage,) rain off the sun-warmed ever-bigger areas of roofs and tarmac all around the country, plain direct solar gain into streams which are now just trickles...
I would also guess the thick green turbid river Wye also mops up more warmth than a clear river with water-weed on the bed photosynthesising to turn the sunlight into plant tissues and sugars.

 

[najaB]

Raise the temperature, potentially upsetting the ecological balance. France has had to reduce the output of some nuclear stations at times as mitigation.

A non-issue. For one thing SMRs are small, meaning that the heat output is correspondingly small. And there's no reason why they can't use a mix of once through and recirculating cooling to reduce the temperature of the water being returned to the enviroment.

 

[AndrewE]

A non-issue. For one thing SMRs are small, meaning that the heat output is correspondingly small. And there's no reason why they can't use a mix of once through and recirculating cooling to reduce the temperature of the water being returned to the enviroment.

I thought all heat engines relied on a gradient, and turbines (especially) must have a condensor at the back end... if you recirculate the coolant it will rapidly stop doing that job because it is too warm.

 

[tomuk]

https://en.wikipedia.org/wiki/Nuclear_marine_propulsion says

which I read as saying the secondary circuit is also a closed loop but can be ‘topped up’ with desalinated sea water.

99.9% of nuclear submarines and aircraft carriers are PWR reactors. They use the ocean as their cooling towers. The Primary and Secondary loops are closed.

 

[najaB]

I thought all heat engines relied on a gradient, and turbines (especially) must have a condensor at the back end... if you recirculate the coolant it will rapidly stop doing that job because it is too warm.

That's why you have a cooling tower or large reservoir of water to allow it to cool naturally. As opposed to pulling in water from the river/ocean and returning it after one pass through the system.

 

[AndrewE]

That's why you have a cooling tower or large reservoir of water to allow it to cool naturally. As opposed to pulling in water from the river/ocean and returning it after one pass through the system.

and how many "large reservoirs of water" are lying round the country in populated areas waiting to receive the heat input from these reactors? We can't even build the one for desperately-needed water supply! Water isn't unlimited for feeding once-through cooling towers either.

"Global warming" is just that. I don't see how releasing loads more energy from fission can reduce the problem. (Not to mention the carbon footprint of building the things, mining and concentrating the fuel (Capenhurst had the UK grid focussed on it just to enrich uranium) and then decommissioning and managing the waste fuel.)

It's a technomaniac's delusion, but the tragedy is that the rest of us will be paying for it for generations to come, while a few fat cats and specialist engineers will do very well out of it in the short term.

 

[BingMan]

It would be great to see a proliferation of small-scale nuclear reactors, perhaps tied in with urban district heating systems, to de-centralise energy production as well as provide a more consistent source of "green" electricity nationwide.

Not in my backyard

 

[tomuk]

and how many "large reservoirs of water" are lying round the country in populated areas waiting to receive the heat input from these reactors? We can't even build the one for desperately-needed water supply! Water isn't unlimited for feeding once-through cooling towers either.

"Global warming" is just that. I don't see how releasing loads more energy from fission can reduce the problem. (Not to mention the carbon footprint of building the things, mining and concentrating the fuel (Capenhurst had the UK grid focussed on it just to enrich uranium) and then decommissioning and managing the waste fuel.)

It's a technomaniac's delusion, but the tragedy is that the rest of us will be paying for it for generations to come, while a few fat cats and specialist engineers will do very well out of it in the short term.

The water doesn't go once through a cooling tower that is the whole point, the heat is dissipated into the air not the water. For a typical 750MW power station you only need 3,600 cubic metres of water (5%) from the river per hour to replace the water evaporating in the cooling tower compared to the 70,000 odd cubic metres circulating around the cooling circuit. If it was once through you would need 100,000 cubic metres 27 times more water being extracted and then dumped back in the river.

 

[najaB]

and how many "large reservoirs of water" are lying round the country in populated areas waiting to receive the heat input from these reactors? We can't even build the one for desperately-needed water supply! Water isn't unlimited for feeding once-through cooling towers either.

The problem with building reservoirs for potable water isn't the reservoir - digging big holes in the ground is a solved problem. The issue is that it's an open system: you have to have a supply of water to go into it, and a way to get the water out of it and to the people that need it.

With a closed system like a cooling pond for a power plant you only have to fill it once and occasionally make up for evaporation (assuming that rainfall doesn't do that for you).

"Global warming" is just that. I don't see how releasing loads more energy from fission can reduce the problem.

Global warming isn't about the heat we put into the system. Global energy usage is on the order of 650EJ. Let's assume that all of that was dumped into the atmosphere as heat (it's not).

Compare that to the c 3,000,000EJ of energy that the sun puts into the system and it's clear that the issue isn't how much energy we use but the fact that we've changed the atmosphere such that an increasing percentage of that solar insolation isn't able to radiate back out into space.

Not in my backyard

Why not, specifically?

 

[AndrewE]

3,600 cubic metres of water (5%) from the river per hour

which is actually 86 Tonnes per day (for each reactor.) It will be yet more abstraction and there is no evidence that our rivers can supply it.

 

[najaB]

which is actually 86 Tonnes per day (for each reactor.) It will be yet more abstraction and there is no evidence that our rivers can supply it.

So then don't take it from rivers. This really is a non-issue.

 

[tomuk]

which is actually 86 Tonnes per day (for each reactor.) It will be yet more abstraction and there is no evidence that our rivers can supply it.

Yes there is evidence that rivers can supply it, the decades they supplied all the now closed coal\oil fired stations.
The classic 500MW based plants, preceeded by smaller and late larger units too.
01 West Burton Nottinghamshire 2,000 MW
02 Ferrybridge C West Yorkshire 2,000 MW
03 Eggborough North Yorkshire 2,000 MW
04 Kingsnorth Kent 2,000 MW Oil fired
05 Fawley Hampshire 2,000 MW Oil fired
06 Aberthaw B South Wales 1,500 MW
07 Ironbridge B Shropshire 1,000 MW
08 Fiddlers Ferry Cheshire 2,000 MW
09 Ratcliffe Nottinghamshire 2,000 MW
10 Cottam[8] Nottinghamshire 2,000 MW
11 Pembroke South West Wales 2,000 MW Oil fired
12 Rugeley B Staffordshire 1,000 MW
13 Didcot A Oxfordshire 2,000 MW
14 Ince B Cheshire 1,000 MW Oil Fired

 

[DDB]

and how many "large reservoirs of water" are lying round the country in populated areas waiting to receive the heat input from these reactors? We can't even build the one for desperately-needed water supply! Water isn't unlimited for feeding once-through cooling towers either.

There is a VERY large reservoir of water surrounding the country which can be used as well.

Also electricity is pretty easy to move around the country.