Energy From Thorium Discussion Forum

It is currently Jan 20, 2018 11:38 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 19 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: Feb 27, 2015 4:22 pm 
Offline
User avatar

Joined: Jul 14, 2011 9:22 pm
Posts: 33
Location: Forest Park, GA
Speaking with Dr. Boyd a while back, I stumbled upon a good topic for undergraduate level research for the summer.
I'm not filing my grant requests with Georgia Tech to try to get some money ($1500) for researching this over the summer.
I'll include the text of my grant application below. Any questions? Comments?

Study of the Transmutation Effects of Molten Salt on Corrosion Chemistry
Undergraduate Researcher: Vincent Hughes
Faculty Mentor: Dr. Preet M. Singh
Overview
Molten salts are of much interest today for their unique heat transfer properties, thermal stability, and strong solvating properties. They have very desirable properties for application in thermal storage in concentrated solar thermal, as a coolant for nuclear reactors, and even as a fuel carrying alternative to conventional nuclear fuel rods.
One of the most challenging problems facing the use of molten salts for these applications is corrosion. Fluoride salts, while having the most promise for high-temperature heat transfer applications, are highly corrosive to normal structural alloys used. Proper corrosion control depends heavily on appropriate alloy choice in design, as well as active and passive chemistry control of the salt in operation.
In nuclear applications, chemistry control can take on an entirely new dimension. With the introduction of neutron flux, elements in the salt can change into entirely different elements, causing changes in the chemical composition of the salts. Several of these transmutations have significant consequences for corrosion chemistry. Listed below are a few of these noteworthy reactions:

(Equations were removed b/c of errors with SQL when posting.)
Reaction 1: K-39 + n -> Cl-36 + alpha
Reaction 2: Na-23 + n -> Na-24 ==> (14.96 hrs) Na-24 -> Mg-24 + beta-
Reaction 3: F-19 + n -> F-20 ==> (11.07 s) F-20 -> Ne-20 + beta-

Reactions such as Na transmuting to Mg can carry much consequence if they occur too often. Changes in the chemical composition and resulting changes in the redox potential of the salt mixture can adversely affect the corrosion rates of various alloys used to contain the salts.
Current Research
I am currently assisting in research carried out to ascertain and verify corrosion behavior of various alloys in a LiF-NaF-KF eutectic at reactor temperatures (~850 °C). Length of exposure time, and salt purity are the main variables being investigated in this study. X-ray diffraction, optical microscopy, and inductively-coupled plasma mass spectroscopy will be used to determine the compositions of the salt before and after exposure to an alloy at temperature. The alloy samples will be analyzed using optical and scanning electron microscopy to ascertain extent and mode of corrosion.
Proposed Research
The research I propose would begin by calculating the expected chemical composition of FLiBe and FLiNaK after transmutation under several choice geometries, varied exposure times, and varied neutron fluxes. This calculation can be done fairly simply (depending on the geometry) using the MCNP code, developed by ORNL. There is existing data, tabulated for the FHR, citing activities of various isotopes in these salts after exposure to neutron flux. This data can be used to help verify the accuracy of the calculations. After this model has been created, various properties of the salt can be calculated, such as change in melting point, change in redox potential, and changes in Gibbs free energy. Once the salt transmutation has been adequately analyzed, properties of the transmuted salts can be used to ascertain changes in corrosion behavior relative to the pure salt. This information would be expressed as a function of exposure time, neutron flux, and geometry.
If time is available and the prediction indicates much elevated corrosion rates over that of non-irradiated salts, it may be possible to run an exposure test with a salt matching the composition of a transmuted salt to verify the predictions made.
The conclusion of the research will be a set of information detailing the predicted effect on corrosion behavior as a function of exposure time, neutron flux, and geometry.


Objectives Summary
Use MCNP to calculate transmutation of FLiBe and FLiNaK molten salt mixtures in simulated reactor conditions.
Tabulate relevant corrosion data on transmuted salt mixtures relative to pure mixtures.
Make predictions about changes in corrosion rates and mechanisms due to composition changes, using the HSC thermodynamic database and software.
Time permitting, test notable compositions of transmuted salts in order to verify predictions made.

References
Berkeley, University of California at. 2014. Mk-1 PB-FHR Technology. Accessed Feburary 26, 2015. http://fhr.nuc.berkeley.edu/pb-fhr-technology/.
Paul Kasten, et. al. 1966. Summary of Molten-Salt Breeder Reactor Design Studies. Intra-Laboratory Correspondence, Oak Ridge National Laboratory , Oak Ridge, Tennessee: Oak Ridge National Laboratory. Accessed Feburary 26, 2015. http://web.ornl.gov/info/reports/1966/3445602516436.pdf.
Singh, Dileep. 2013. "High Efficiency Thermal Energy Storage Systems for CSP." http://www.energy.gov. April 13. Accessed Feburary 26, 2015. http://energy.gov/sites/prod/files/2014 ... _singh.pdf.


Top
 Profile  
 
PostPosted: Mar 18, 2015 5:23 pm 
Offline

Joined: Mar 08, 2015 4:34 pm
Posts: 12
Awesome man!! Its great to see other students putting real work into MSRs!


Top
 Profile  
 
PostPosted: Mar 19, 2015 9:06 am 
Offline

Joined: Sep 02, 2009 10:24 am
Posts: 507
Quote:
I am currently assisting in research carried out to ascertain and verify corrosion behavior of various alloys in a LiF-NaF-KF eutectic at reactor temperatures


This sounds useful.

One of the parameters I was thinking about - but can't find much on, is the "wettingness" (http://en.wikipedia.org/wiki/Wetting) of the salt on a reactor vessel (and pumps and pipes) lining. How much does the salt stick to the reactor vessel - and also to any graphite?

It strikes me that this will be an important determinant of the ease of decommissioning or recommissioning a reactor. Once drained, if kilos of highly radioactive salt wet and freeze to the surface it will make cleaning these surfaces expensive. Will they need to be flushed with pure water (the usual way of cleaning off salt) - but then the resulting water needs purification and you end up with a lot of low level waste in all the cleaning apparatus?

I'm not sure how much of a problem this will be - but I'd expect it to be directly proportional to the wettingness, which will also impact on the corrosion behaviour.

In your current research - is it worth measuring the level of wetting?

Regarding the "Effects of Transmutation on Corrosion Chemistry" - this is the sort of contract that the UK Nuclear Regulator will subcontract for a six figure sum to a large consultancy, when they come to evaluate a Molten Salt Reactor.

For the UK ABWR, http://www.onr.org.uk/new-reactors/repo ... dec-14.pdf paragraph 30 lists last quarter's technical reports. Four out of eight are on reactor chemistry.


Top
 Profile  
 
PostPosted: Mar 19, 2015 3:10 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3069
The salt does not wet the graphite. Before washing with water typically a load of flush salt is used to "dilute" the residual salt. For example, suppose there were 14 liters of salt that remained after draining (whether due to sticking to the surface or local low spots that do not drain) in a reactor with 14 M^3 in a full salt load. Drain it, then fill with flush salt and drain the flush salt. This should reduce the residual soluble fission products by a factor of 1000. If that isn't good enough for you then do it twice.

At that point the plate out will dominate.


Top
 Profile  
 
PostPosted: Mar 21, 2015 4:27 am 
Offline

Joined: Sep 02, 2009 10:24 am
Posts: 507
But whatever you wash it through with first time needs to be cleaned / decontaminated.

Wouldn't it be easier with water - then just boil away the water (using MSR waste heat?) leaving the radioactive salt behind. (Unless tritium contamination is a problem).

My thinking is that the regulators might be more concerned about the reprocessing of the salts and decontamination of the vessels, than the actual operation of a MSR itself. That makes understanding the salt chemistry very important.


Top
 Profile  
 
PostPosted: Mar 21, 2015 8:58 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
Using a flush salt on the reactor site is a good idea. It greatly reduces equipment contamination. Yes, you get a flush salt tank and piping with some contamination in it, but that's a good compromise. You can put the tank in a shielded cell. And a tank is just a tank really. Its a simple thing, doesn't need maintenance if properly designed.

Water based solutions are attractive though, perhaps in a central recycling plant. It can dissolve stuff that salt can't, if you add soapy solutions or ammonia, it wets the graphite very well so it soaks in and leaches out any cesium and other nasty stuff. It can also dissolve many of the noble metal plateouts, with the right solution. So I expect an aqeous solution to be used for final decontamination, with flush salt for "quick and cleanish" initial work.


Top
 Profile  
 
PostPosted: Mar 21, 2015 11:40 am 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3069
One reason not to include a water wash at the NPP site is that we really need the core to be extremely dry. So after the water wash one will have to go to some extremes to be sure to remove the water and any oxygen. I think this is best left for the recycling site.


Top
 Profile  
 
PostPosted: Mar 21, 2015 11:43 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
Why would you be washing out the core in any condition other than end-of-life?
Thats the only circumstance I can think of when you would care if the tank is still hot after fuel has been pumped out?


Top
 Profile  
 
PostPosted: Mar 21, 2015 11:53 am 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3069
The noble metals will deposit on all surfaces and it is possible that we will want to clean them out periodically.

A few possible reasons:
1) If they build up at just the cold end of the heat exchanger then maybe this causes concerns about clogging. Especially, if the plate out is clumpy and might break off in chucks.
2) If we have to dispose of the heat exchanger and can remove the contamination it may be less expensive to dispose of and maybe even the metal could be recycled into a new heat exchanger (unlikely I bet). Ditto for the graphite moderator, pump impeller, plumbing, etc.
3) Inside the core then they may steal too many neutrons if they are allowed to build up. If we can periodically wash them out then they don't build up forever absorbing neutrons.


Not sure that the build up is enough to be bothered with yet. We don't really know where they will deposit. I hope they will deposit primarily on metal surfaces in the OffGasRecovery tank that are used to reduce mixing of the offgases.


Top
 Profile  
 
PostPosted: Mar 21, 2015 1:03 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
E Ireland wrote:
Why would you be washing out the core in any condition other than end-of-life?
Thats the only circumstance I can think of when you would care if the tank is still hot after fuel has been pumped out?


Yes, that is the most likely place where water washing would be used.

If you have a good washing system it is likely that all the alloy and graphite can be re-used or recycled.


Top
 Profile  
 
PostPosted: Mar 22, 2015 9:34 am 
Offline

Joined: Sep 02, 2009 10:24 am
Posts: 507
Lars wrote:
The noble metals will deposit on all surfaces and it is possible that we will want to clean them out periodically.

Not sure that the build up is enough to be bothered with yet. We don't really know where they will deposit. I hope they will deposit primarily on metal surfaces in the OffGasRecovery tank that are used to reduce mixing of the offgases.


Going a bit off-topic here, but is this the sort of thing that needs a non-nuclear test "reactor" to determine?

Add noble metals into the heated salt mix and see where they deposit - at the coldest part of the Heat Exchanger?

This information would be needed for the regulatory process - so you get into an interesting process whereby you have a non-nuclear test site being used for regulatory research.


Top
 Profile  
 
PostPosted: Mar 22, 2015 9:38 am 
Offline

Joined: Sep 02, 2009 10:24 am
Posts: 507
Lars wrote:
One reason not to include a water wash at the NPP site is that we really need the core to be extremely dry. So after the water wash one will have to go to some extremes to be sure to remove the water and any oxygen. I think this is best left for the recycling site.


How about ammonia?

http://en.wikipedia.org/wiki/Ammonia#So ... y_of_salts

Needs special handling but any remnants evaporate away. It might also be useful for getting rid of some metals.

It might be safer though to use water and just heat the reactor vessel to over 100C to make sure it's completely dry. No need to worry about steam escape.

(Sorry Vince Hughes about dragging the topic away from Effects of Transmutation on Corrosion Chemistry)


Top
 Profile  
 
PostPosted: Mar 22, 2015 3:13 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
Alex, I think you've correctly identified the right solvent. Although there is likely no benefit to using anhydrous ammonia, likely some small solution is more than sufficient. I'm looking at 1-10% solutions in water. It looks like this works very well, some researchers are thinking of using this for graphene production because it wets the graphite so well (microwave heating after wetting will then expand the graphite to delaminate graphene layers).


Top
 Profile  
 
PostPosted: Mar 22, 2015 4:56 pm 
Offline

Joined: Apr 28, 2011 10:44 am
Posts: 247
What happens if we combine the ammonia solution with ultrasonic cleaning?


Top
 Profile  
 
PostPosted: Mar 22, 2015 5:56 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3069
alexterrell wrote:
Lars wrote:
One reason not to include a water wash at the NPP site is that we really need the core to be extremely dry. So after the water wash one will have to go to some extremes to be sure to remove the water and any oxygen. I think this is best left for the recycling site.


How about ammonia?

http://en.wikipedia.org/wiki/Ammonia#So ... y_of_salts

Needs special handling but any remnants evaporate away. It might also be useful for getting rid of some metals.

It might be safer though to use water and just heat the reactor vessel to over 100C to make sure it's completely dry. No need to worry about steam escape.

(Sorry Vince Hughes about dragging the topic away from Effects of Transmutation on Corrosion Chemistry)

I think the normal procedure is to bake at 400C for many days. We REALLY don't want water and oxygen hiding out in the graphite.
The evaporated gas will have to be filtered as it may have some nasties in it.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 19 posts ]  Go to page 1, 2  Next

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