Question about Molten Salt Fast Reactors

[Tom Holtsnider]

TL;DR Summary

How are two US companies designing a MSFR going to solve disposing of the isotope Cl-35? They are planing on using NaCl as the carrier salt.

This is in regards to the Molten Salt Fast Reactor ( MSFR). Two companies in the United States are designing the MSFR using NaCl as the carrier salt along with liquid fuel salt in the reactor. There is no moderator. The chlorine used in the NaCl salt must be nearly pure Cl-37. Chlorine in nature is composed of about 1/3 Cl-37, 2/3 Cl-35. Cl-35 when bombarded with neutrons becomes a Cl-36 isotope resulting in a poison to reactor criticality along with several other problems. Separating out the Cl-35 from Cl-37 is very difficult and expensive, perhaps so much so as to render the choice of NaCl as the carrier salt economically undesirable. My question is, are they planning on absorbing this enormous cost of separation or is there a way out that’s not apparent? Also why can’t they use NaF as the carrier salt instead?

 

[Astronuc]

Summary:: How are two US companies designing a MSFR going to solve disposing of the isotope Cl-35? They are planing on using NaCl as the carrier salt.

Separating out the Cl-35 from Cl-37 is very difficult and expensive, perhaps so much so as to render the choice of NaCl as the carrier salt economically undesirable.

It's not necessarily difficult, nor very expensive (of course there is a cost, but there are trade-offs), but even so using NaCl is not the issue, but rather Cl, for which one would use a 'fast' neutron spectrum as opposed to thermal spectrum. It appears that those advocating Cl based fuel systems are considering Cl depleted in Cl-35, or conversely enriched in Cl-37.

Some discussion and considerations within these documents.
http://moltensalt.org/references/static/downloads/pdf/EIR-332.pdf
https://info.ornl.gov/sites/publications/files/Pub29596.pdf
https://www.nrc.gov/docs/ML1733/ML17331B115.pdf

 

[Tom Holtsnider]

Thanks for responding to my questions. I reviewed your links and found them very informative and beneficial. Reactors using LiF as a coolant will have the possible problem of handling actinide waste, reactors using NaCl have the Cl-35/S-35 problem although a liquid-phase thermal-diffusion based separation process might work. Links on chlorine isotope separation by this means would be greatly appreciated.

I have a particular interest in MSFR because of its design simplicity, no contents within the reactor except the molten salt, essentially no moving parts except for pumps, no graphite moderator to replace every four years, no actinide waste, a reactor which operates at atmospheric pressure, a safety feature where a meltdown is impossible, a containment structure far less massive compared to the LWR and utilization of LWR waste as nuclear fuel. I would like to promote MSFR for the sake of humanity.