Comments on: LFTR Article for “Machine Design”

By: Alex P.

Alex P. — Wed, 17 Mar 2010 21:28:06 +0000

” A LFTR’s gas cooling, on the other hand, rejects heat from about 100°C down to about 30°. In properly built heat exchangers, the waste heat could be used to distill seawater into fresh water ”

Have you ever considered the possibility to slightly increase that reject heat temp to, say, 100-150 °C to produce hot water for district heating/cooling or steam for the production of sustainable (cellulosic ?) ethanol or biofuels (~ half of the total energy input of the final products) ?

By: Geoff

Geoff — Wed, 17 Mar 2010 15:24:04 +0000

As a manufacturer, I’m intrigued by the possible migration from mega projects like traditional reactors to small distributed units. From a cost standpoint it’s recognised that continuous flow has it’s advantages versus batch production, (not to mention one-offs).

I’d be interested to hear more about the anticipated manufacturing challenges of building these reactors.

By: Bryan

Bryan — Wed, 17 Mar 2010 14:30:08 +0000

A simple calculation to produce a worst-case sustainability estimate*:
Mr = Estimated mass of available fuel (world)
Br = Ratio of burnable fuel to total fuel
Ee = Energy released in one energy-releasing event
Me = Total mass of one energy-releasing event originating from fuel
C = Conversion efficiency
Ec = Power consumed by one individual
Pe = Projected population of the earth
T = Time consumption could be sustained

(C * Mr * Br * Ee) / (Me * Ec * Pe) = T

Cases (50 year projection):
Worst case: high population growth with all users consuming current US levels
Ec = 91 MWh / year (10.381 kW)
Pe = 11.5 Billion
Average:
Ec = 42.5 MWh / year (4.848 kW)
Pe = 9 Billion
Best: low population growth with moderate increase in worldwide per capita consumption
Ec = 32.75 MWh / year (3.736 kW)
Pe = 7 Billion

For Thorium:
Mr = 2,230,000 metric tons
Br = 1
Ee = 200.1 MeV
Me = 234 amu (232-Th + 2n)
C = 0.5

T = 43.204 years, 118.2 years, 197.22 years

For LWR:
Mr = 3,338,300 metric tons
Br = 0.015
Ee = 202.5 MeV
Me = 236 amu (235-U + n)
C = 0.35

T = 0.39 years, 1.05 years, 1.76 years

Crude oil (as comparison, using methane as best-case combustion profile):
Mr = 1250 billion oil barrels * 0.790 g/cc
Br = 1
Ee = 799 kJ / mol
Me = 16 amu
C = 0.35

(0.35 * (1250 billion oil barrels * 0.790 g/cc) * 1 * 799 kJ amu / g) / (16 amu * 3.736 kW * 7 billion)

T = 0.72 years, 1.99 years, 3.325 years

By: Bryan

Bryan — Wed, 17 Mar 2010 14:02:26 +0000

Ooh, no sooner than I post that am I corrected! Current average *worldwide* consumption of all energy is ~23MWh/year, or about 2.7W. 1.3 kW was intended to be about double the world average, but is only electrical consumption – only half of all energy consumption, apparently.

Adjusting figures now. Will also provide T’s for stasis population estimates as well.

By: Bryan

Bryan — Wed, 17 Mar 2010 13:53:38 +0000

(Mr * Br * Ee) / (Me * Ec * Pe) = T

For Thorium:
Mr = 2,230,000 metric tons
Br = 1
Ee = 200.1 MeV
Me = 234 amu (232-Th + 2n)
C = 0.5
Ec = 12,000 kWh / year (1.3 kW)
Pe = 10 Billion

T = 226.06 years

For LWR:
Mr = 3,338,300 metric tons
Br = 0.015
Ee = 202.5 MeV
Me = 236 amu (235-U + n)
C = 0.35
Ec = 12,000 kWh / year (1.3 kW)
Pe = 10 Billion

T = 3.54 years

Crude oil (by comparison, using methane as best-case combustion profile):
Mr = 1250 billion oil barrels * 0.790 g/cc
Br = 1
Ee = 799 kJ / mol
Me = 16 amu
C = 0.35
Ec = 12,000 kWh / year (1.3 kW)
Pe = 10 Billion

T = 6.38 years

* Worst case: 10 billion people consuming at US consumption rates (apx 12MWh/y), and all world’s energy produced by cited technology alone.