Small Modular Reactors (SMRs)

Sensors needed.
Electrical equipment housed within auxiliary buildings of nuclear power plants—such as control panels, transformers, and emergency generators—are particularly vulnerable to vibrations. Notably, during the 2016 Gyeongju earthquake, while concrete structures remained intact, power facilities had to be shut down for safety inspections. Now, a new technology allows for quick identification of equipment requiring maintenance without the need for extensive manual inspections.

Best for large facilities--but useful here too perhaps.
 
Funny how word can turn a safety undertaking into something dangerous:
''power facilities had to be shut down for safety inspections.''

Why not writing:
although there were no indications of any damage to the concrete structures, precautions were taken and the power facilities were shut down for safety inspections
 
NMaude said:
The thing with fast-reactors, Scott, is that they can be used to burnup transuranic* waste from spent fuel-rods along with pesky long-lived fission products greatly simplifying the handling and disposal of them also the refuelling intervals are longer for fast-reactors making more efficient use of their fuel.

*Except for Plutonium as that is useful as reactor-fuel.
Click to expand...
Yes, that's a very good use case for a fast reactor.

But molten lead (or even lazy lead-bismuth that melts at ~200degF) just has issues. Mostly what happens in Loss of Coolant accidents, plus what happens if you ever let that reactor freeze up.



Nicknick said:
P.S.: Nuescale is a conventional light water reactor which is built so small, that natural convection can be used instead of water pumps. Other than that, it works exactly as any other light water reactor.
Click to expand...
You can make a pretty big reactor that runs at full power on natural circulation. 1970s math got you ~160MWt in the Ohio class, though I don't think you'd get above about 50% of that. IIRC the Seawolf reactor 10 years later got more power than the Ohios before you needed to start the cooling pumps. The big A1Bs out of the Ford class are supposedly all NC, even at full power, and they're ~700MWt.
 
Intresting, didn't know that other LWR reactors have been built without cooling pumps

The freezing of a lead reactor is surly a bigger issue in a sub than in a powerplant. So bigger the reactor so larger is the decay heat to surface ratio.

Despite this, I also believe that the hughe mass of lead can store a large amount of decay heat without boiling or building up pressure. So far, it is said, that in fact all the decay heat can be adsobed until we have a equilibrium with the heat flow to the enviroment.
 
In addition to Bismuth/Lead alloy cooling there's also Potassium/Sodium liquid cooling and that has a significantly lower freezing point.
 
I didn't do the math, but I guess it would take month until a large scale lead reactor would freeze. This is are several thousand tons with a lot of decay heat inside.

Unlike water, almost all materials including lead will shrink when freezing, so even if this unlikly event would happen it would not destroy the outer structure.
 
Nicknick said:
Intresting, didn't know that other LWR reactors have been built without cooling pumps
Click to expand...
That and the 40 year cores was a very big push in the Columbia and Ford plants.

Less from a safety standpoint and more from a "less stuff that could break" standpoint.



Nicknick said:
The freezing of a lead reactor is surly a bigger issue in a sub than in a powerplant. So bigger the reactor so larger is the decay heat to surface ratio.

Despite this, I also believe that the hughe mass of lead can store a large amount of decay heat without boiling or building up pressure. So far, it is said, that in fact all the decay heat can be adsobed until we have a equilibrium with the heat flow to the enviroment.
Click to expand...
Generally a powerplant would not be offline for weeks/months like a ship would be while in refit, no.

But if you have to do anything inside the Reactor Compartment (primary containment), you're going to have to let it cool off to let workers in.




NMaude said:
In addition to Bismuth/Lead alloy cooling there's also Potassium/Sodium liquid cooling and that has a significantly lower freezing point.
Click to expand...
Oh, heck no.

Not without replacing a steam secondary with anything else. It's basically impossible to prevent the sodium or NaK from eating through the steam generator and meeting water. KABOOM. Supercritical CO2 or something might be viable.
 
I doubt, that working inside a reactor vessel has ever been concidered as normal for civil reactors. I remember, how much effort it was for India to replace a valve of a BWR with a robotic arm (in the US, a similar reactor was decomissined because of the same problem). If people could have worked from the inside, it would shurly have been easier....

Could be different in Subs (K19)...

The natrium cooled BN 600 is in operation since about 40 years, and after having some teething issues with small fires, it worked flawlessly over the past 20or 30 years. Natrium prevents corrosion by the way, because it consumes all the oxygen so that the vessel and pipes will never corrode on the inside (for Youtuber, Natrium and NaCl is the same....).

As said, Terra power uses molten salt for the second loop and heat storage, a clever approach to eliminate any danger of Natrium getting in Contact withwater.r
 
Nicknick said:
I doubt, that working inside a reactor vessel has ever been concidered as normal for civil reactors. I remember, how much effort it was for India to replace a valve of a BWR with a robotic arm (in the US, a similar reactor was decomissined because of the same problem). If people could have worked from the inside, it would shurly have been easier....
Click to expand...
I don't mean working inside the reactor vessel where the fuel is.

I mean inside the room/building that holds the reactor vessel and the steam generators, pressurizer, reactor cooling pumps, etc. The entire Primary loop.



Nicknick said:
The natrium cooled BN 600 is in operation since about 40 years, and after having some teething issues with small fires, it worked flawlessly over the past 20or 30 years. Natrium prevents corrosion by the way, because it consumes all the oxygen so that the vessel and pipes will never corrode on the inside (for Youtuber, Natrium and NaCl is the same....).

As said, Terra power uses molten salt for the second loop and heat storage, a clever approach to eliminate any danger of Natrium getting in Contact withwater.r
Click to expand...
Molten Salt secondary? So what gets boiled to spin turbines?
 
Nicknick said:
I doubt, that working inside a reactor vessel has ever been concidered as normal for civil reactors.
Click to expand...

SmarterEveryDay has just released a video of refueling operations on a civil reactor. The reactor vessel is opened up for this operation. People aren't inside the reactor, but they are right above it.

 
Scott Kenny said:
I don't mean working inside the reactor vessel where the fuel is.

I mean inside the room/building that holds the reactor vessel and the steam generators, pressurizer, reactor cooling pumps, etc. The entire Primary loop.




Molten Salt secondary? So what gets boiled to spin turbines?
Click to expand...
All natrium cooled reactors have three loops for safety reasons usually two natrium loops and the final steam loop. The middle loop is here replaced with molten salt.

There is no issue beeing in the same room like the reaktor, in case of lead, I would expect the radioactivity to be very low.

All fast reactors I know are refueled during operation.
 
Nicknick said:
All natrium cooled reactors have three loops for safety reasons usually two natrium loops and the final steam loop. The middle loop is here replaced with molten salt.
Click to expand...
Ah, that makes more sense.


Nicknick said:
There is no issue beeing in the same room like the reaktor, in case of lead, I would expect the radioactivity to be very low.
Click to expand...
There's still a 500degF/250degC reactor vessel dumping heat into the room.
 
The problem though with Lead/Bismuth cooling (It's a eutectic alloy with a significantly lower MP than Lead or Bismuth on their own) is that the Bismuth (Specifically Bi-209) is turned into Bi-210 by neutron-activation and that decays into Po-210 (Which in turn decays into Pb-26 by alpha-particle emission).
 
Also worth noting that light water reactors have built in stability due to the feedback cycle from temperature impacts on water moderator effectiveness. Hotter coolant means lower power and vice versa, so reactor power automatically follows steam demand. You can go from 100% to 10% output or vice versa in a matter of seconds with no reactor control action (just opening/closing throttles). Liquid metal or salt reactors don't do this, which means you need active control of reactor power - more things to break, more moving parts, more potential for accidents, etc.
 
Molten salt reactors do archieve the same thing by the freeze plug that mels when they get to hot. All the salt will drain out into a flat tub which stopps criticallity. This system might work for metal reactors too.

For Na cooled (I guess the same is true foe lead cooled reactors) a similar safety behavior by the Voith coefficient is not inherent, but can be archieved by design:
'

 
Last edited:
NMaude said:
The problem though with Lead/Bismuth cooling (It's a eutectic alloy with a significantly lower MP than Lead or Bismuth on their own) is that the Bismuth (Specifically Bi-209) is turned into Bi-210 by neutron-activation and that decays into Po-210 (Which in turn decays into Pb-26 by alpha-particle emission).
Click to expand...

True, I also read somewhere that Bismuth is also quite expensive and rare. This reactor type might be a better option for subs, but not for large commercial reactors. Keeping the lead molten is surly not a big issue in a large commercial reactor.

@Scott Kenny PWR reactor are operating at similar temperatures with people beeing in the room regulary.
 
Last edited:
IIRC you can't use water (Light or heavy) as a coolant for fast reactors as Hydrogen (Or Deuterium) thermalises the neutron-flux in the reactor's core.
 
NMaude said:
IIRC you can't use water (Light or heavy) as a coolant for fast reactors as Hydrogen (Or Deuterium) thermalises the neutron-flux in the reactor's core.
Click to expand...
I feel much safer with lead or salt as coolant. Both don't require pressurisation and can adsorb a lot of heat before boiling.
 
Nicknick said:
@Scott Kenny PWR reactor are operating at similar temperatures with people beeing in the room regulary.
Click to expand...
The difference is that the PWR cools a lot quicker. ~50,000lbs of water in the primary versus ~550,000lbs of lead.

We didn't let people into the Reactor Compartment until pressure was 0 and temp was below boiling.
 
In an ideal world, there are not many reasons to shut down a metal cooled fast reactor. Shure, you sometimes have to check something or replace something, but these are (to my knowledge) all designed for continous operation without having to stop for refuling. I'm quite sure, that moving components like Natriumpumps can be replaced from the outside without opening the reactor.
 
Nicknick said:
In an ideal world, there are not many reasons to shut down a metal cooled fast reactor. Shure, you sometimes have to check something or replace something, but these are (to my knowledge) all designed for continous operation without having to stop for refuling. I'm quite sure, that moving components like Natriumpumps can be replaced from the outside without opening the reactor.
Click to expand...
Pump motors might be replaceable without getting into the primary containment building, depends on how it was built.

But replacing the actual pump means getting into the reactor compartment, since the primary loop has to stay inside the primary containment building.
 
WatcherZero said:
Three RR SMR's to begin construction at Wylfa next year at a cost of £2.5bn, the site has capacity for 8.

news.sky.com

Anglesey chosen as site for UK's first small nuclear power station

Work on the site is due to start in 2026, and is expected to support 3,000 jobs in the local economy at the height of construction.
news.sky.com news.sky.com
Click to expand...
Anglesey was where the aluminum smelting facility was located and reason why it was high on the list for a nuclear power station.

I think the facility might still be there but was shut down years ago.

But this might be the signal for it's resurrection.

Edited in correction.
Just checked Wikipedia and it seems the aluminium smelter has been completely removed.
Just awful and stupid.
 
Last edited:
In regards to thermal nuclear reactors using heavy-water as a coolant and moderator is that IIRC they generate several pounds of Tritium a year due to a portion of the Deuterium atoms absorbing neutrons instead of scattering them.
 
zen said:
Anglesey was where the aluminum smelting facility was located and reason why it was high on the list for a nuclear power station.

I think the facility might still be there but was shut down years ago.

But this might be the signal for it's resurrection.

Edited in correction.
Just checked Wikipedia and it seems the aluminium smelter has been completely removed.
Just awful and stupid.
Click to expand...
Aluminum smelting takes so much electrical power that they relocate the factory to wherever the cheapest electricity is. For a long time, that was the Columbia River gorge and all the hydroelectric power there.

In the 1970s, they started to move from there to Iceland, where the geothermal was even cheaper than hydro.
Edit: and by the 1990s the last aluminum smelter in Washington state closed!
 
Last edited:
Scott Kenny said:
Pump motors might be replaceable without getting into the primary containment building, depends on how it was built.

But replacing the actual pump means getting into the reactor compartment, since the primary loop has to stay inside the primary containment building.
Click to expand...

The pumps are usually in vertical position with the electric part on the top (outside of the reactor and the shaft with it's sealing leading vertically downwards). There pumps can be pulled out vertically by a crane (there is always a crane on the roof in any commercial reactor). When this pumps are removed, only a relative small circular cross section will be temporarily opened towards the reactor. This might somehow be secured with inert gases to prevent the Na coming into contact with the air before closing it.

It might be, that there are internally some closing devices in the reactor to shut the opening before the pumps are completely pulled out (with the shaft sealing still functioning).
 
zen said:
Anglesey was where the aluminum smelting facility was located and reason why it was high on the list for a nuclear power station.

I think the facility might still be there but was shut down years ago.

But this might be the signal for it's resurrection.

Edited in correction.
Just checked Wikipedia and it seems the aluminium smelter has been completely removed.
Just awful and stupid.
Click to expand...
Why? Reusing the same facility means, the grid connection is allready there and all the geological examinations have allready been done. There might even been some remaining of nuclear industry around.
 
Nicknick said:
The pumps are usually in vertical position with the electric part on the top (outside of the reactor and the shaft with it's sealing leading vertically downwards). There pumps can be pulled out vertically by a crane (there is always a crane on the roof in any commercial reactor). When this pumps are removed, only a relative small circular cross section will be temporarily opened towards the reactor. This might somehow be secured with inert gases to prevent the Na coming into contact with the air before closing it.

It might be, that there are internally some closing devices in the reactor to shut the opening before the pumps are completely pulled out (with the shaft sealing still functioning).
Click to expand...
You'd still need to cut or unbolt the primary loop to remove the pump. And when you installed the new pump you'd need to do something to burp the air out of the pump...



Nicknick said:
Why? Reusing the same facility means, the grid connection is allready there and all the geological examinations have allready been done. There might even been some remaining of nuclear industry around.
Click to expand...
The stupid part was scrapping the smelter entirely.
 
Scott Kenny said:
You'd still need to cut or unbolt the primary loop to remove the pump. And when you installed the new pump you'd need to do something to burp the air out of the pump...
Click to expand...
No, everything can (and probably will be) done with sealings gliding into the shaft housing. You just have to unlock the flange on the very top and than you can pull the pumps out. I guess, water cooled reactors have a similar arrangement. Take a look at the water pumps from Volkswagen vehicles, you can also replace them without loosening a hose. I think, even the heat exchanger can be lifted out in the same way (pool type natrium cooled reactor)
 

Attachments

  • ____VW_wp.jpg
    ____VW_wp.jpg
    73.5 KB · Views: 8
  • _____reactor.jpg
    _____reactor.jpg
    122.9 KB · Views: 13
Last edited:
Nicknick said:
Molten salt reactors do the same thing, the reaction stops when they get to hot.

For Na cooled (I guess the same is true foe lead cooled reactors) a similar safety behavior is not inherent, but can be archieved by design:
'

Click to expand...

Appreciate the article, but you miss the point. Said article talks to the void effect during accident scenario, whereas what I am referring to is stability during operation. Emergency response is important, but operational factors are also important. This is one of those things that is generally missed by media hype and folks who get their news from popular mechanics. Light water works very very well in a number of ways, and one of the key factors in reactor safety is simplicity and reliability.
 
Yeah Wylfa is replacing the previous nuclear reactor on the same site that was decommissioned in 2015 and defueled in 2019. All the high voltage transmission connections are still there for it to supply North Wales as it was always planned to replace the power station. Plus the locals supported its replacement so you don't have the same political fight over a new site, heck its even been welcomed by The Campaign for the Protection of Rural Wales.

The three SMR's will provide the same capacity as Wylfa and Trawsfynydd nuclear power station (decommissioned 1991) combined formerly supplied.
 
sdmuleman said:
Appreciate the article, but you miss the point. Said article talks to the void effect during accident scenario, whereas what I am referring to is stability during operation. Emergency response is important, but operational factors are also important. This is one of those things that is generally missed by media hype and folks who get their news from popular mechanics. Light water works very very well in a number of ways, and one of the key factors in reactor safety is simplicity and reliability.
Click to expand...
You have any indications for that beeing a problem? The BN600 is operating for 40 years and I never heard of specific problems in respect to stability and power regulatiin.
 

Similar threads

Back
Top Bottom