## Pressure at fuel salt surface

Discussion about gas-turbine and other power conversion systems for halide reactors.
Lars
Posts: 3060
Joined: Jul 28, 2008 10:44 pm

### Pressure at fuel salt surface

In a full blanket system we have one blanket thickness of blanket salt above the top of the core. If the blanket is 1 meter thick and the density is 4 grams/cm^2 this implies we have added 4 atm of pressure at the surface to the natural 1 atm of pressure.
But there is also a desire to hold the gas pressure at the surface to a mild vacuum to encourage off-gassing and a general desire to keep any gas pressure in the system low to reduce the motive force to push radioactivity into the biosphere in an accident.

The tradeoff gets worse if we increase the thickness of the fluid above the fuel salt level - such as we might do in a pool type design.

I'm wondering if we need to partition the blanket (and pool) salt into above and below the fuel salt level and have sufficient structure in place to bear the weight of the blanket (pool) salt above the fuel salt level without applying pressure on the salt below. (Rather the opposite problem that Holger was worried about).

KitemanSA
Posts: 1336
Joined: Jun 05, 2011 6:59 pm
Location: NoOPWA

### Re: Pressure at fuel salt surface

I think you slipped a decimal point. Or even more. Its more like 0.2 bar, not 4.
DRJ : Engineer - NAVSEA : (Retired)

Lars
Posts: 3060
Joined: Jul 28, 2008 10:44 pm

### Re: Pressure at fuel salt surface

Yep. 100cm = 1m (not 1000cm=1m). So the blanket salt adds 0.4 atm if it is 1 meter thick (which is a pretty thick blanket but not much for pool salt). Makes the problem less severe but still makes it hard to have a partial vacuum in the gas space above the fuel salt. But probably we could reduce the blanket to just 25 cm thick above the fuel salt level. This would allow a gas pressure at 0.1atm which is likely sufficient for the job.

The vessel outside the blanket salt could be strong enough to tolerate the extra pressure from having a significant amount of pool salt above it.

KitemanSA
Posts: 1336
Joined: Jun 05, 2011 6:59 pm
Location: NoOPWA

### Re: Pressure at fuel salt surface

Still off by 2,
10m H2O = ~1bar.
FLiBe SG = ~2.
1m FLiBe=~0.2 bar.
DRJ : Engineer - NAVSEA : (Retired)

Lars
Posts: 3060
Joined: Jul 28, 2008 10:44 pm

### Re: Pressure at fuel salt surface

But blanket salt is not pure FLiBe. It is full of thorium so it is around 4 g/cm^3.

KitemanSA
Posts: 1336
Joined: Jun 05, 2011 6:59 pm
Location: NoOPWA

### Re: Pressure at fuel salt surface

Lars wrote:But blanket salt is not pure FLiBe. It is full of thorium so it is around 4 g/cm^3.
That much? What % is that?
DRJ : Engineer - NAVSEA : (Retired)

Lars
Posts: 3060
Joined: Jul 28, 2008 10:44 pm

### Re: Pressure at fuel salt surface

Around 20% ThF4 is common. The more thorium the less neutron capture by Pa.

KitemanSA
Posts: 1336
Joined: Jun 05, 2011 6:59 pm
Location: NoOPWA

### Re: Pressure at fuel salt surface

Ok.
DRJ : Engineer - NAVSEA : (Retired)

Luke
Posts: 461
Joined: Jul 28, 2008 5:01 am
Location: Teesside, UK

### Re: Pressure at fuel salt surface

Lars wrote:Around 20% ThF4 is common....
And that is 20% mole/mole. By mass, the blanket is >50% thorium, most of the rest fluorine, and only 6-7% Li