Liquid Fluoride Thorium Reactor

mheslep

The question was not about the fission likelihood of elements other than U and Pu, but could lesser elements be built up to heavy through repetitive neutron capture and beta decay to arrive at U or Pu the way Thorium can be from a single neutron, i.e. breeding fissionable materials from fertile elements. Clearly this doesn't work in a fission reactor, in which case every neutron captured loses a potential ~200MeV.

I had not considered using the neutrons from a fusion reactor as ZZ suggests, but I see at least two problems with that approach: i) even in neutronic fusion, those neutrons are required to breed tritium in a net energy reactor, i.e. like fission a neutron wasted to build heavy elements wastes a potential 17MeV from making tritium. ii)I have no idea of the cross section and beta decay chain that might be required to breed, say Si into U, or if it is possible without regard to energy. I'd guess somewhere along the way there will no beta decay 'step up' available, only alpha to go down. But without researching the issue, IF the cross section decay chain was advantageous for neutron absorption all the way up to U and Th, I think we would see the production of those elements in stars like ours. We don't, short of heavy element fusion in novae.

mheslep

Quote by zapperzero

Correct me if I am wrong, but is there not a secondary cooling loop which uses water, in all MSR designs? How does this constitute "eliminating" it?

Could be water or helium gas. Most of the design design discussions focus on gas so they can go Brayton.

In any case the point is not the nature of the cooling loop, but that in an MSR the cooling loop is not needed to prevent catastrophe. The cooling loop could be turned off, lose power, be destroyed by an airplane, and there's no chance of a leak of 300atm water, then flashing to steam, expanding several orders of magnitude trying to escape containment to the outside world. Instead, a frozen plug of salt melts, draining the reactor salt by gravity into a tank where further criticality is impossible and decay heat is not a problem. Furthermore, when the cooling loop power is returned or rebuilt, there's no commercial loss, as the reactor salt is heated and pumped back into the reactor. This event happened several times with the MSR built at Oak Ridge.

zapperzero

Quote by mheslep

Could be water or helium gas. Most of the design design discussions focus on gas so they can go Brayton.

Gas sounds more reasonable. I didn't know that.

Astronuc

FYI - Antonio Cammi, Valentino Di Marcello, Lelio Luzzi, Vito Memoli, Marco Enrico Ricotti, A multi-physics modelling approach to the dynamics of Molten Salt Reactors, Annals of Nuclear Energy, Volume 38, Issue 6, June 2011, Pages 1356-1372, ISSN 0306-4549, 10.1016/j.anucene.2011.01.037.
(http://www.sciencedirect.com/science...06454911000582)
Keywords: Molten Salt Reactor; Multi-physics modelling; Thermo-hydrodynamics; Reactor dynamics

Abstract
This paper presents a multi-physics modelling (MPM) approach developed for the study of the dynamics of the Molten Salt Reactor (MSR), which has been reconsidered as one of the future nuclear power plants in the framework of the Generation IV International Forum for its several potentialities. The proposed multi-physics modelling is aimed at the description of the coupling between heat transfer, fluid dynamics and neutronics characteristics in a typical MSR core channel, taking into account the spatial effects of the most relevant physical quantities. In particular, as far as molten salt thermo-hydrodynamics is concerned, Navier–Stokes equations are used with the turbulence treatment according to the RANS (Reynolds Averaged Navier–Stokes) scheme, while the heat transfer is taken into account through the energy balance equations for the fuel salt and the graphite. As far as neutronics is concerned, the two-group diffusion theory is adopted, where the group constants (computed by means of the neutron transport code NEWT of SCALE 5.1) are included into the model in order to describe the neutron flux and the delayed neutron precursor distributions, the system time constants, and the temperature feedback effects of both graphite and fuel salt. The developed MPM approach is implemented in the unified simulation environment offered by COMSOL Multiphysics®, and is applied to study the behaviour of the system in steady-state conditions and under several transients (i.e., reactivity insertion due to control rod movements, fuel mass flow rate variations due to the change of the pump working conditions, presence of periodic perturbations), pointing out some advantages offered with respect to the conventional approaches employed in literature for the MSRs.

mheslep

Quote by Astronuc

FYI - Antonio Cammi, Valentino Di Marcello, Lelio Luzzi, Vito Memoli, Marco Enrico Ricotti, A multi-physics modelling approach to the dynamics of Molten Salt Reactors, Annals of Nuclear Energy, Volume 38, Issue 6, June 2011, Pages 1356-1372, ISSN 0306-4549, 10.1016/j.anucene.2011.01.037.
(http://www.sciencedirect.com/science...06454911000582)
Keywords: Molten Salt Reactor; Multi-physics modelling; Thermo-hydrodynamics; Reactor dynamics

Thanks! A modern model in the literature, vice on a pop web site, is overdue.

wizwom

Quote by zapperzero

Correct me if I am wrong, but is there not a secondary cooling loop which uses water, in all MSR designs? How does this constitute "eliminating" it?

I don't think using thorium is a bad idea per se, it's just that I think mixing two un-proven technologies (MSR and HEU-initiated thorium cycle) is not so safe. The Indian approach of modifying the well-known and long-proven CANDU design (for all its flaws) seems to be lower risk. Better the devil we know.

Because you are using the reaction mass itself as your primary cooling loop, and it is liquid salts, you have very low pressure, basically just the pressure required for moving the fluid.

The heat exchangers, even if they run dry on the secondary side, they will still be safe, and thus can use the much more efficient single pass heat exchangers, which were banned from PWR use after TMI. In TMi the loss of heat take-off caused the core to melt, but in a MSR, the core is already and intentionally melted.

And no, the technology is proven, just not developed. ORNL's LFTR program proved that the system was able to make thermal power, which is all you need from a NSSS.

A layman should read http://home.earthlink.net/~bhoglund/mSR_Adventure.html to get an idea of what was done, and why it stopped.

mheslep

That ORNL reactor simulated the idea starting with U233; it never used Thorium, so the Protactinium did not have to be chemically removed while it decayed to U233. There's still a bit of proving to do yet.

edpell

Even a MSR reactor core need to be cooled. If the primary cooling loop fails it needs a secondary way to cool. This can be dumping the core into a dump tank that is cool by passive means.

Stanley514

If people would be able to tap geothermal energy properly
there would be no need in nuclear reactors.There is giant ocean
of magma under our feet.But I think it would require some other
cycle than water cycle.Maybe some electron or thermoelectric cycle?
Earth crust has its own electric charge and should behaive like
thermoelectric?

etudiant

Quote by Stanley514

If people would be able to tap geothermal energy properly
there would be no need in nuclear reactors.There is giant ocean
of magma under our feet.But I think it would require some other
cycle than water cycle.Maybe some electron or thermoelectric cycle?
Earth crust has its own electric charge and should behaive like
thermoelectric?

Based on the geothermal record to date, 'unblemished by success', your reservations about a geothermally powered water cycle may be apprpriate.
However, no other approach is even at the proof of principle level afaik, so the water cycle is pretty much the only game in town for the next decade or so.
Given the scale of the energy needs, it is hard to take untested approaches seriously.

Stanley514

I do not claim it is seriously but I think insted of water could be used for example Sulfur.It`s boiling point is higher and it possible could give you higher energy density.
Also Earth is known as a good conductor.There is natural thermoelectric currents in Earth which result in magnetic field and Telluric currents which could be registered.I want to know if heat could be transfered through some kind of electric resonance?For example we have hot body which is in electric resonance with cold body.There is some electric resonance beween them.Could it work similar to thermopower?

etudiant

Quote by Stanley514

I do not claim it is seriously but I think insted of water could be used for example Sulfur.It`s boiling point is higher and it possible could give you higher energy density.
Also Earth is known as a good conductor.There is natural thermoelectric currents in Earth which result in magnetic field and Telluric currents which could be registered.I want to know if heat could be transfered through some kind of electric resonance?For example we have hot body which is in electric resonance with cold body.There is some electric resonance beween them.Could it work similar to thermopower?

You're dealing with insights I don't have.
What is a 'telluric current' or an 'electric resonance'?
Presently, I'm unaware of any demonstrated example of power generation from any Earth currents or magnetic fields. I'd be keenly interested if there is any data available.
Sulfur does indeed have a higher boiling point, but also has very little extra heat capacity in the sulfur vapor, so extracting energy from a sulfur turbine is a bear. Sulfur also has all the reactive capacity of hot oxygen, so it is a material that is not to be trifled with.
Warts and all, water is a lot easier to deal with.

Stanley514

Some inventors patented Alpha decay stimulator with help of
Van Der Graaf generator.http://www.freepatentsonline.com/5076971.html If it comes true
then aneutronic fission reactor would be possible.

mheslep

Quote by Stanley514

Some inventors patented Alpha decay stimulator with help of
Van Der Graaf generator.http://www.freepatentsonline.com/5076971.html If it comes true
then aneutronic fission reactor would be possible.

Alpha decay is unrelated to fission, and in any case has nothing to do with this thread on LFTRs.

Astronuc

Quote by Stanley514

Some inventors patented Alpha decay stimulator with help of
Van Der Graaf generator.http://www.freepatentsonline.com/5076971.html If it comes true
then aneutronic fission reactor would be possible.

As far as I can tell, the patent refers to a more rapid transmutation or decay process, not aneutronic fission. Alpha emission is a decay process; it is not fission. Many radionuclides heavier than lead undergo alpha decay. Far fewer nuclides are fissile.

Stanley514

Alpha decay is unrelated to fission, and in any case has nothing to do with this thread on LFTRs.

I think that any technology that is designed to be directly competing with LFTR and allows to undestand competitiveness of LFTR has right to be discussed here.I do not care if it is fission or decay,the most important if it is able to produce lot of net energy by decay.

Stanley514

If the proposed method with Thorium decay stimulation will
succeed and generate net power then it will have following advantages
over LFTR:

1)No neutron radiation is created during all stages of the process.Though some low energy gamma radiation may be result of decay.
2)No Uranium 235 as a kindler is requiered.
3)No long lived isotopes are created.
4)Possibly no any radioactive waste is created as a result of the process.
5)No molten salts are requiered and therefore corrosion is reduced or eliminated.

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mheslep Recognitions: Gold Member	That ORNL reactor simulated the idea starting with U233; it never used Thorium, so the Protactinium did not have to be chemically removed while it decayed to U233. There's still a bit of proving to do yet.

edpell	Even a MSR reactor core need to be cooled. If the primary cooling loop fails it needs a secondary way to cool. This can be dumping the core into a dump tank that is cool by passive means.

Stanley514	If people would be able to tap geothermal energy properly there would be no need in nuclear reactors.There is giant ocean of magma under our feet.But I think it would require some other cycle than water cycle.Maybe some electron or thermoelectric cycle? Earth crust has its own electric charge and should behaive like thermoelectric?