Is magnifying thermal power density possible with decay heat

[Evanish]

Recently there was an interesting thread on physics forum about possible uses of spent nuclear fuel. It seems to me that one of the problems with using decay heath from spent nuclear fuel is the low power density. This got me thinking that maybe with enough insulation the low quality heat being produced could be made into high quality heat with high efficiency.

What I was picturing was a primary loop surrounded by an insulating void. Also, something to reflect photons back would probably help. Maybe even have it float using magnetic fields in order to minimize the heat transfer away from the loop except at a single point where the thermal energy is used to make steam. I drew a picture although it probably wasn't necessary. Is this at all feasible?

 

[QuantumPion]

As I stated in the other thread, there is no point in trying to harness power from spent fuel pools as the total power is not that much compared to the cost of building and maintaining such a system. The average heat load for a spent fuel pool may be around 1-2 MW thermal. If you achieved 20% thermal efficiency, you would generate 200-400 kW (250-500 HP). This comes out to around 5000 kw-hr per day, or perhaps $500 worth of energy. The cost to build and maintain the system would be in the millions, it's simply not worth it.

 

[Evanish]

As I stated in the other thread, there is no point in trying to harness power from spent fuel pools as the total power is not that much compared to the cost of building and maintaining such a system. The average heat load for a spent fuel pool may be around 1-2 MW thermal. If you achieved 20% thermal efficiency, you would generate 200-400 kW (250-500 HP). This comes out to around 5000 kw-hr per day, or perhaps $500 worth of energy. The cost to build and maintain the system would be in the millions, it's simply not worth it.

I'm a big fan of nuclear power. I'm hoping for breeder reactors someday (hopefully soon) meeting most of the worlds energy needs (unless something better comes along before then). If so then their should be somewhere in the range of thousands of tons of fission products produced each year (assuming 9 billion people with decent lifestyles). Most of that won't remain radioactive for long, but some of it will. I don't like waste. It feels like there should be some good way of make use of those fissile products. Also, portable, non fossil fuel, energy sources are likely to increase in importance as time goes on.

Probably you are right and about the economics of what I’m talking about. Still, I can't help hopping. How many millions do you think such a reactor would take? If it's only a couple million it might be worthwhile (after all a 2 MW wind turbine costs between 3 and 4 million dollars and it's capacity factor is close to 20%) , but if it's hundreds of million then probably not worth it although the PR value of using nuclear waste might trump the economic concerns. Maybe they could combine spent nuclear fuel from more than one reactor to make it more economical, or use some of the host reactors systems to save money.

 

[nikkkom]

There is a pool with some 2000 steel capsules with Sr-90 and Cs-137 fluoride salts at Hanford. Their thermal power is ~300kW. Here's a photo.