Nuclear furnace for home heating

Since I was a teenager I've been interested in cheap energy sources.  In the past couple years, I've read a few articles and seen a couple Ted talks on thorium reactors.  I thought it would be simpler, cheaper, and more efficient to use the heat from a nuclear reactor directly in the home instead of converting it to electricity first.  As a result, I'm planning to test it out.

I had read about a kid who used lantern mantles as a source of thorium, but that seemed like too much work.  Then I read about thoriated tungsten welding rods.  A local welding supply shop sells a 10-pack of 2.4mm x 175mm rods for under $40.  Each rod has a volume of 0.8cm^2, and .3g of Th.  Based on the articles I've read on thorium reactors, the heat generated from the nuclear reaction of 1g of Th is 36 million BTUs.  So if I can consume all the thorium from 10 rods (3g), I'd generate 108 million BTUs of heat, at a cost of under 40 cents per million BTUs.

In my post on costs of heating in NS, I calculated that heat from electricity costs a little over $40 per million BTUs.  So the cost of heating with a thorium nuclear furnace should be about 100x cheaper than electricity!  Besides thorium, the other thing I need to make a nuclear furnace is a neutron source.  The liquid salt thorium reactor articles talk about using uranium-233, which I can't (legally) obtain.  Ka-Ngo Leung and his colleagues in Berkeley Labs have invented a cheap way to generate neutrons, but it's not commercially available yet.  The radioactive boy scout stories say he used radioactive americium-241 from smoke detectors as his neutron source.  He wrapped it in aluminum, which absorbs the alpha particles from the americium and spits out neutrons.  I'll try the same thing.

I also need a neutron moderator to slow down the neutrons so they'll be captured by the thorium atoms to start the nuclear reaction.  Hydrogen, carbon, and to some extent oxygen all make good moderators.  Candu reactors use heavy water, but that's hard to get and it's expensive.  Most nuclear ractors use regular water.  The radioactive boy scout used charcoal (carbon).  Paraffin wax is mostly carbon and hydrogen atoms, and so makes a good moderator.  I'd like to be able to easily remove the neutron source (to turn off the furnace).  Paraffin wax would melt when the furnace heats up, so my first attempt will be to wrap the neutron source with some charcoal using some aluminum foil.  I'll attach a wire, and drop the cylindrical neutron generator into a tube that is surrounded by the thoriated tungsten rods.

I'd love to hear from any physics heads on what the rate of the reaction should be.  Protactinium-233, the decay product of Th-233 has a half-life of 27 days and beta-decays into U-233.  So I'd guess it will take a couple weeks to approach full temperature.

Heat Pump Hacking

My primary heat source is a 3-ton water-to-air geothermal heat pump.  It was factory-filled with R-22 (freon).  It was designed for warmer climates, as it had a factory-installed freeze protection switch that shut the unit off when the outgoing water temperature came close to 0C.  I bypassed the freeze switch and used a water and antifreeze (windshield washer fluid) mix for the loop.

The optimal amount of refrigerant in heat pumps (and air conditioners) depends on the temperatures of the cold and hot sides. I wanted to tweak the refrigerant charge, but R-22 is bad for the atmosphere and hard to come by.  I came across some information on propane (r-290) as a refrigerant which indicated it can be used as a substitute for R-22.  I can get it cheap at my local hardware store, and even Greenpeace likes it.

I read about people using propane for DIY computer cooling, and someone that recharged an R-22 system with propane.  The first thing I needed was a manifold gauge set.  They tend to sell for $100-150, but I found what I thought was a good deal on ebay for about $50.  It has plastic handles on the valves, and one was broken on arrival.  About a minute after I hooked it up to the high and low side schrader valves I heard a loud pop.  It took several more minutes to figure out one of the hoses had burst and was leaking.  Now I would HAVE to recharge the heat pump.

I had a gauge set (with 2 of 3 hoses still good), and a couple 16oz canisters of propane.  Fuel-grade propane can have moisture in it which is supposedly bad for a heat pump.  Instead of trying to buy refrigerant-grade propane (r-290), I decided to run the propane through a drier.  I bought a drier with 3/8 copper sweat connections and a shrader valve at Wolseley (about $20 total).  I bought a propane torch and unscrewed the tip.  Here's my parts:

I cut the 1/4" copper tube off the schrader, then soldered it all together:

I hooked it up with a propane tank to my gauge set to check the pressure.  The pressure was slow coming up, probably because the pinhole orifice in the propane torch was too small.  I unsoldered the tip, drilled the pinhole out to 1/16", and then tested it to see how much more propane comes out:

I soldered my rig back together, and then hooked it up to my heat pump and started charging it from the low side.  After a few minutes I turned on the heat pump, and was reading ~30psig on low side and the suction tube temperature about an inch away from the compressor was ~5C.  That was about 20C of superheat - much higher than what it should be for optimal efficiency.  After a few more minutes I had gone through about 400g of propane and my low side pressure was 40psig, with the suction tube temperature around 0C.  The antifreeze mix coming out of the heat pump was -8C; right around the evaporation temperature of propane at 40psig.  I'll do some more performance measurements later; for now the heat pump is working OK.