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17 comments on In Situ retorting of oil shale

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LevinK on July 5, 2006 - 10:41am

I guess the answer is Shell's electric heaters are hundreds of feet long and maintain 700 degrees

I also think this is the case... I suppose spent fuel rods are lower than 100 degrees Celsius, otherwise the water in those pools would have boiled off.

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Whitehall on July 5, 2006 - 2:30pm

The surface of the spent fuel rods in water in the spent fuel pools are less than 220 deg F or else local boiling would occur (they are under about 33 ft of water so the boiling point is higher). That doesn't happen since it takes at least 48 hours after shutdown before transfer can begin.

In full operation inside the reactor the maximum surface temperature is about 600 deg F or a bit more than the boiling point of water at 2200 psia (lower for BWRs).

There is no practical theoritical limit on nuclear spent rod temperature but spent fuel assembly loses heat emissions exponentially.

In practice, high purity water is required to prevent corrosion and/or scaling and subsequent failure of the cladding.

Real-world spent fuel pools need external cooling for a few months after fresh spent fuel is added but soon reach an approximate equilibrium with their evironment. Water continues to be circulated but more to maintain purity and clarity than for heat removal.

Using spent nuclear fuel to extract kerogen is not feasible.

But you knew that.....

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LevinK on July 5, 2006 - 3:05pm

Never mind, this is an interesting information.

The vision if fuel rods plugged in the rock riminded me of the natural fission reactors that existed back in the time when U-235 was more abundant. I wonder if something similar could be feasible for oil shale, with kerogen acting as a moderator and a coolant, but this sounds too much a pie in the sky to contemplate with.

A safer bet would be a dedicated reactor producing steam or molten metal for the heaters.

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Whitehall on July 6, 2006 - 12:56pm

Reactors making steam for direct injection has the expense of using high purity feedwater - figure $1 per gallon.

Probably electrical heaters would be the method of choice but I'm sure both methods would need detailed engineering studies for the particular site before a clear decision would be made.

As to embedment of spent nuclear fuels in rock, Yucca Mountain spaced the assemblies to keep rock temps below 300 deg C (if memory serves) but it took decades to reach that temp. The key is that rock in mass is a poor conductor of heat.

Spent fuel assemblies give off heat of maybe 1 kW-thermal after a year or so. I suspect it would liquefy the kerogen but it would take decades and that would make it non-commercial. Plus you would be expected to retrieve the assemblies and move to someplace permanent.

Better to reprocess the spent fuel and return the unreacted uranium and plutonium to the power reactor fuel cycle.

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