Waste heat at Hanford, WA

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jhochste
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Joined: Tue Jul 09, 2002 1:43 pm
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Waste heat at Hanford, WA

Post by jhochste »

As I understand the problems of storing radioactive waste, there is a
big cooling problem. Could several Stirling engines be used to
remove excess heat from the underground ponds (generating
electricity) thus lessening the problems of the stored materials.

It seems a source of heat that is hot for 10,000 years should be a
good source for running a Stirling engine.

Jim
lester_hawksby
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Response to Waste heat at Hanford, WA

Post by lester_hawksby »

Nice idea, but I think it may have a few problems:

- You have a fairly abundant heat source, but not a really good source of cooling, so the temperature difference is not that great. That means even huge Stirling engines will have a hard time removing enough heat.

- The Stirling engines can't run for 10,000+ years without maintenance. In close contact with nuclear waste they'd rapidly become contaminated, making repair pretty much impossible. Every time one broke you'd probably have to swap out a lot of it and put the old bits in at least a low-level waste store.

- Any chunk of nuclear material that gets hot enough to run a Stirling engine is emitting enough radiation to slowly damage quite a lot of materials. That would make it even harder to keep them running.

- When one of the engines breaks, the heat starts building up. To reduce the risk of disaster, enough backup cooling would be needed to take over from total Stirling engine failure, which somewhat defeats the point.

- such a system requires pretty much constant maintenance and attention. One of the reasons long-term waste storage is such a headache is that it can't be assumed that there will be someone around to look after the stuff, continuously, for 10,000 years, which is an awfully long time in terms of human history (writing, the state and urbanisation are all only 5,000 years old, after all).

This is only a cursory examination, some of these problems may be solvable, but there will almost certainly be others I haven't thought of.
tj7734.smith
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Response to Waste heat at Hanford, WA

Post by tj7734.smith »

At a former Hanford Engineer, I can give you a first-hand account.

You are correct in the sense that there is an excess of heat created when the liquid waste products are forever re-combining with the organics to create heat in the underground storage tanks.

The Solid wastes are flasked and re-flasked so many times that there is no way to absorb the internal thermal energy created.

Radiation and maintenance are also issues.

The liquid wastes are in the process of being cleaned up(www.waste2glass.com), so the best source of heat for a Stirling Engine may be on the discharge water lines at the Nuclear Reactor in south Hanford.

Regards,
Tim
jbanes
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Response to Waste heat at Hanford, WA

Post by jbanes »

Nuclear "Waste" is actually great stuff for power generation, just as long as the waste
is primarily an Alpha or Beta emitter. Gamma and Neutron emissions can cause
structural damage over time, and can result in the creation of isotopes which are
radioactive. In other words, choose your materials carefully or your machine could
become radioactive.

Traditionally, NASA has used RTGs (Radioisoptope Thermal Generators) for their
space-based power needs. These use a simple thermocouple to convert heat into
electricity. Unfortunately, these are also tremendously inefficient, converting only
about 10% of the energy into power. This means that 3.8 kilograms of Plutonium-238
(not useful for nukes, half-life of ~80 years, Alpha Emitter) only produces about 75W
of electricity. The SNAP-27s used in the Apollo missions are still providing a constant
70W of power to instruments on the moon. RTGs have also been used in pacemakers
and earthbound remote research stations. The later form tends to use the less
powerful Strontium-90 (beta emitter) as a fuel source.

NASA has recently begun looking at SRGs (Stirling Radioisotope Generators) for space
missions, because the SRGs are far more efficient and fuel conservative. The current
designs produce about 50W per 600 grams of Pu-238. None have yet flown, however,
because NASA is concerned about the vibrations interfering with the operation of
delicate instruments.

More info:

http://me.eng.sunysb.edu/~mec290/rtgs/page5.html

http://www.nasm.si.edu/exhibitions/attm ... s27.1.html

http://www.grc.nasa.gov/WWW/RT2002/5000/5490thieme.html

P.S. A lot of good power generating materials are thrown away because of the public's
fear of all things radioactive. A perfect example of this problem, was the protests
over the launch of the Casinni probe. Despite the fact that the RTGs were packed in
cases that could survive an explosion and unprotected reentry, people's primal fears
had them convinced that the RTGs were going to kill everyone. Even if the Plutonium
did escape, it wouldn't have caused as much harm as people believe. Here's a writeup
on that:

http://www.llnl.gov/csts/publications/sutcliffe/
stan.hornbaker
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Response to Waste heat at Hanford, WA

Post by stan.hornbaker »

The problems associated with the use of Stirling engines to act as a cooling agent for large quantities of hot radioactive wastes should be considered first.

The Stirling engine is a machine and as such requires periodic servicing. The mean time between servicing is 5,000 to 50,000 hours. Servicing is an activity made very difficult by the radioactive enviorment and any possible activity induced into the engine components.

Means to conduct the heat and cooling to the hot and cold sides of the engine(s) would have to be designed and provided.

Sizing of the Stirling generator units would be critical. Too small, would make for a complicated configuration. Too large and physical size makes the space required excessive for the benefits obtained.

In my opinion there are far better, simpler, more economical means to accomplish the cooling required, i.e. exactly what is being done now, water cooling.
mskroski
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Response to Waste heat at Hanford, WA

Post by mskroski »

Another possible, energy free solution may be a heat pipe. If you tune pressure, volume etc of refrigerant in a pipe and have two temperatures of enough delta, you could possibly use a heat pipe. It works this way. The cold side condenses the liquid. Hopefully the cold side is the high side of the layout. The liquid refrigerant falls to the bottom of the pipe where is changes state, evaporates and rises to the top/cold side to continue the cycle. I know little to nothing about radiation, but have seen these at work in the milk industry.
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