Energy From Thorium Discussion Forum

It is currently Dec 14, 2017 10:18 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 12 posts ] 
Author Message
 Post subject: Hard Spectrum LWR
PostPosted: Jun 28, 2015 6:35 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1494
Attempts have been made to design light water reactors that operate with high conversion ratios.
These reactors normally require that the reactor spectrum be hardened - this normally being achieved by packing in more fuel or adopting higher density fuel like Uranium Nitride.

However, another path occurs to me - why can't we just partially replace the light water in a PWR primary circuit with heavy water?
Heavy water is a far worse moderator so partial replacement would reduce the moderation in the core, without causing any particularly nasty hydraulic problems with pressure drop across the core.

Anyone got any obvious reasons why it couldn't be made to function? It would obviously require higher enrichment fuel to overcome the reduced moderation but that should not be an intractable problem. Adding more fuel assemblies and increasing core size would counteract that without any conceptual design leaps - after all it would just be building a bigger reactor.


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jun 29, 2015 3:31 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2237
Just design with less moderator-coolant.
https://www.iaea.org/NuclearPower/Downl ... 8.RMWR.pdf
Idea could be extended to MSR too.


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jun 29, 2015 5:00 pm 
Offline

Joined: Oct 28, 2013 12:24 am
Posts: 256
There are some concepts similar to this.

There is a video of Naoyuki Takaki speaking of a PWR with primary coolant being heavy water instead of light water in the classic design.
The spectrum is fast and it achieves breeding on the thorium cycle with negative void and high burn up.
https://www.youtube.com/watch?v=I-DeS87LzPo
(The link comes from the Thorium Energy Alliance website.)

There was also the idea of spectral shift reactor at the page 6 of this doc : https://dl.dropboxusercontent.com/u/11686324/Blair_Bromley_20110204.pdf ( the links comes from Jaro, thanks to him)
They begin with D2O with a fast spectrum and then as burn up progresses they dilute it with light water in order to sustain the chain reaction, at the end they have a thermal spectrum.

There is a problem with these kind of reactors : if the coolant is mixed with light water there is an increase of reactivity if this water enters into the core. You must absolutely avoid entrance of light water in the core. And because light water is everywhere you must be very careful. Lots of precautions which drive up costs.

The current LWRs use big pools of water for safety systems ( active or passive ), and for control of chemistry of the coolant, they also use a pool of water for refuelling and there is the pool for the used fuel in the fuel building. If you don't want to use a mix of heavy water in all these pools you will maybe have to make considerable changes to current designs.

Still an interesting idea. The PWR with pure heavy water for primary coolant is very interesting also.


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 22, 2015 6:45 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1494
Well the water in the refuelling pool is only used during the refuelling process - so a multiple unit plant might be able to share a virtual lake of Heavy Water.

I will try and find out how much water is actually inside an AP1000 during normal operation.
The hard part will I imagine ensuring that the reactor will stay shut down in the worst case of a freshly shut down freshly loaded core being filled entirely with light water by emergency cooling efforts. Will need to make sure the shutdown rods are very highly rated for that, I doubt normal LWR rods would be able to restrain the core in that circumstance.
Adding more absorbers into the spent fuel pool structure should allow it to be filled with light water in an emergency, but it would probably have to be filled with heavy water during normal operation to prevent contamination of the reactor water heavy water supply.

We are going to need a lot of heavy water, even if we keep recovering the diluted (by moisture) material and running it all through tritium recovery to keep it largely non-active.

Running with 20% UOx or some such to get high conversion - or perhaps ~10% U-235 in thorium (50% of 20% enriched uranium).


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 23, 2015 5:39 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2237
There are advantages I running a reactor on 20%leu+thorium. There is a document on Indian dae website on the subject.
Adding a blanket could give a breeder like the shippingport example.


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 23, 2015 2:54 pm 
Offline

Joined: Sep 22, 2013 2:27 pm
Posts: 262
The heavy water reactor in a single pressure vessel similar to a PWR the PHWR was already designed by Prof. Bagge 1944 - 1945. It was later built with some modifications as MZFR in Karsruhe (Germany).

2 more of these reactors were built in Atucha (Argentine) and working well. http://www.na-sa.com.ar/hitos-atucha2/

Reasons that this design was not successful: The Moderation is less than in a LWR hence the power density is lower and the reactor bigger. It adds the costs of heavy water about 300 Mio. $ plus some 3 - 5 Mio. $ annual for heavy water. Since some decades fuel costs for nuclear power plants are not decisive but investment costs.

Best regards

Holger


Attachments:
schwerwassermoderierter druckkesselreaktor.docx [972.41 KiB]
Downloaded 137 times


Last edited by HolgerNarrog on Jul 23, 2015 3:13 pm, edited 1 time in total.
Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 23, 2015 3:07 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1494
But this concept is not proposing a thermal Heavy Water Reactor.
I am proposing we build a water cooled fast reactor essentially, so the lack of moderation is not a problem but a good thing.


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 23, 2015 3:19 pm 
Offline

Joined: Sep 22, 2013 2:27 pm
Posts: 262
Dear E. Ireland....if you use a water cooling you will get a strong moderation.

There were 2 concepts that might come close to your considerations...

The SCWFR Super Critical Water Fast Reactor that was studied in Japan with some German involvement

The "Dampfbrueter" Steambreeder developed in Karlsruhe in the 60ies


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 23, 2015 6:05 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1494
If you adopted a tight lattice like the RMWR and the Shippingport Reactor have done to get high breeding ratios with light water, with heavy water I imagine you would end up with surprisingly little moderation.
You might even be able to go with a looser lattice and still have a hard/fast spectrum, if not quite as hard as some of the insane metal cooled reactor proposals.


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 24, 2015 4:56 pm 
Offline

Joined: Sep 22, 2013 2:27 pm
Posts: 262
There might be two challenges of a Heavy Water Breeder:

The thermodynamic properties of water have a transition at 374°C (250 bar). That means you can design a reactor with an outlet temperature of 350°C with pressurized heavy water similar to a PWR or a "steam" reactor using the properties above 390°C. If you plan to use the temperatures 210° - 520°C as the SCWFR you will have a very complex design.

If the water inventory of this reactor concept is small a LOCA is a tough challenge as the temperature rises very quickly.

I would suggest you to study the reports on the SCWFR concept. An Advantage of heavy water is that there is a lower overall moderation.


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 24, 2015 5:38 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1494
I have finally located the information I have been looking forward in terms of the condenser offgas system from a BWR.
I now believe it might be possible to design a BWR that used a heavy water coolant in the power cycle without suffering crippling heavy water losses to the environment - and enormous tritium releases.
So some sort of Boiling Heavy Water Reactor could be a good idea.

Does an SBWR/ESBWR core filled with heavy water count as a fast reactor?


Top
 Profile  
 
 Post subject: Re: Hard Spectrum LWR
PostPosted: Jul 25, 2015 1:24 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Yes, in fact I think that much of the fast spectrum LWR work was on BWR because its easier to harden the spectrum (steam void).

An ESBWR type reactor would be a good platform for heavy water. Interestingly, while the ESBWR has quite a bit of water inventory, it is actually a good deal less on a per MWe basis, than a CANDU 6, with that ginormous calandria inventory and quite low electrical output to show up for it. The ESBWR avoids high pressure makeup inventories (IC inventory is quite small). Because of the passive safety features there is no need to operate the relief valves during the typical transients such as station blackout (only needed in much more serious events). So, you wouldn't normally lose D2O to the wetwell.

Please see this excellent SBO paper for figures (the rest of the paper is interesting as well).

http://www.kns.org/jknsfile/v44/JK0440311.pdf


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group