0. An understanding for non experts:
There’s two major categories of reactor…
The fast neutron: en.wikipedia.org...
And: Thermal Reactor: en.wikipedia.org...
In normal Thermal Reactors
low enriched fuel (about 2%) has it’s neutron slowed by a moderator. This slower speed increases the probability
of them hitting another (say uranium fellow fuel atom) and therefore produces enough collisions to keep the reactor going. The process is normally
kept stable using control rods, they absorb surplus neutrons.
The Fast Neutron Reactors
use fuel that’s so enriched that there’s enough naturally produced neutrons (of the right speed) to sustain the
reaction without a moderator. This process is still normally kept stable with control rods.
1. A Problem That Effects Both Reactors…
They both need their fuel either reprocessed or replaced. To begin with I thought this was because the fuel gets used up over time. In fact only about
1% of the fuel gets used up in about 5 years of the fuels rods operation.
The real reason for reprocessing-replacing is actually because of something called Neutron Poisons. en.wikipedia.org...
These are elements that absorb far more neutrons than they ever produce. They “get into” the fuel rods not because of any kind of leakage, but
because nuclear reactions can change one element into another (even lead into gold; though very radioactive gold!!). Therefore some of the original
fuel gets Transmuted into neutron poisons like Xe 135, and that’s what causes the fuel rods to eventually cause more harm than good.
2. My idea…
1. Build a fast neutron reactor; feed it enriched fuel. The good news is that this can be typically worthless stuff like plutonium left over from old
2. After x number of years the neutron poisons build up making the rod quite useless for a fast neutron reactor.
3. At this point it the fuel gets transferred into a Thermal Reactor 1.
The thermal reactor should be able to use this fuel because of the way it works differently. I.e. because it slows the neutrons it uses, it uses
radioactivity far more efficiently for producing energy.
4. (Again) neutron poisons continue to build up; so let’s say after bout 10 years it’s “only” got about 98% of it’s original (almost free)
plutonium fuel. So at this stage it’s transferred into Thermal Reactor Two. The difference between it and the first is that Thermal Reactor Two has
even more moderator
; thereby guaranteeing the radioactivity from the fuel (now in its third stage) would be used more efficiently still.
Thereby the effect of the neutron poisons is bypassed-ignored. In fact a name for my idea might be “The Ignore Reactor Complex” since it’s all
about ignoring-bypassing the effects of these poisons.
5. Eventually: The neutron “poisons” will have built up so much that even very powerful moderatoring reactors will be unable to use it.
A Summary of Advantages so far…
1. Cheap (essentially waste) plutonium like fuel was always used. So no need at all for expensive uranium mining (or primary enrichment).
2. No need for nuclear fuel enrichment during this first (and incredibly longer) part of the process. Nuclear Fuel Enrichment is a very messy process
since almost everything
you use to enrich the fuel becomes radioactive (robots, acid, water ect). And it’s not just a little bit radioactive
either; it’s extremely. Therefore all this stuff needs to go in more waste barrels.
Furthermore: Fuel enrichment is also the same process as you use to get weapons grade material. Fast Neutron reactors need more heavily enriched fuel;
but it needn’t ever be delivered to them at weapons grade. Therefore you could trust a country that says it just wants the stuff for peaceful
purposes (providing it doesn’t have the enrichment facilities).
3. The neutron poisoned fuel waste you end up with is about as radioactive as the neutron poisoned waste you would get from a thermal reactor. This is
quite self-evident because it’s the fact the stuff is incapable of producing much heat (due to all it’s neutron poisons) that it eventually has to
be thrown out.
6. Stage Two…
It’s a well known fact that all spent nuclear fuel is so radioactive it’s quite hot.
You can see actual figures here: www.nucleartourist.com...
Which gave me the idea of using this heat to make electricity without enrichment…
It turned out China has been thinking about this…
China to utilise spent fuel for heating and desalination.
A Chinese group has agreed to build a 200 MWt nuclear reactor run on used fuel from nuclear power stations to provide district heating and
desalination. The US$ 42 million project at Yingkou in Liaoning province will heat 5 million square metres of buildings over 4-6 months each year and
initially desalinate 3000 tonnes (3 megalitres) of seawater per day in warmer months, rising to 80,000 tonnes (80 megalitres) later. The deep-pool
reactor will operate at atmospheric pressure, which will reduce the engineering requirements for safety.
Comtex 25/6/02 (via Wilmington).
However I’ve been unable to find almost anything about how they’re planning to build. And I doubt whether it is as crude, safe, and cheap as the
(sand insulation based) idea my given ATS thread.
Meanwhile someone else has been thinking about directly using the radioactively
Basically even after the fuel becomes completely neutron poisoned (by any reactors standards) you can still make free heat out of it by placing it in
a well thermally insulated pool of water (which I would achieve by putting about a meter of sand in a cavity in it’s wall, ceiling and floor.
Who cares if you only make about 1000watts per second, rather than the 1000,000 you would get with expensive
enrichment? The only difference is
that the 1000 watt stuff would produce heat a thousand times longer than the million watt stuff (or whatever the ratio might be).
Perhaps in 500 years time the world might develop a shortage of high level nuclear waste?
So the neutron poisoned waste you’ve got (still highly radioactive) could be taken out of the decay room and: A: finally be reprocessed; B: it
perhaps even be transmuted en.wikipedia.org...
In the first Fast Neutron Reactor into less dangerous waste (though whether it would need to be unpacked to remove it’s neutron poisons is something
I don’t know) (would be worth looking into since unpacking the stuff is (like enrichment) a messy business.
C: Or if there is no shortage of radioactive material, and your decay room is getting short of space, then the waste could be dumped like normal.
So far the waste cycle has been extended to (roughly) a 500 year period
, and they’ve still had many times more heat from it than would have
been produced by a standard single use (before reprocessing) in a typical Fast Neutron Reactor, or indeed Thermal reactor.
How Not To Build My Idea…
In my original idea I would have the reactors built vertically like a block of flats. I.e. the Fast Neutron Reactor would be on top, and the
different Thermal Reactors below (with the one with the greatest moderation on the bottom).
This would save almost all contamination through transportation because the whole thing would be gravity fed making it, even more cost effective.
Because I was thinking that if (somehow) the fast neutron reactor went into meltdown (like Chernobyl) then any molten highly enriched nuclear fuel
would trickle downwards into the more moderated sections
This is a holy c*** scenario since in addition to making an unstoppable hole inside the roof of every single reactor below
; also putting highly
enriched nuclear fuel into a well moderated environment is called a nuclear bomb!!!
(Not good PR).
In all probability the stuff wouldn’t actually go super critical as the enriched stuff could lack the purity for a nuclear explosion (even when new)
or could pick up so much concrete-steel and stuff in the process of trickling down that by the time it reaches the first reactor it certainly is not
Even so: The effect of enriched fuel landing inside the well moderated reactors would cause them to overheat (which in addition to hole in the roof)
is a nuclear bonfire mess.
To avoid This:
Either build the “block of flats” layout, but don’t
1. Use (theoretically) weapons grade material anywhere
build each reactor with a clay, combed, melt proof roof so that if there is a meltdown upstairs the mess falls sideways.
3. This is ok if all the reactors are built inside a containment dome-building.
4. Maybe include additional safety measures to prevent a meltdown in the first place
Build the reactors in a straight row. The new safety problem here is what happens if some idiot puts the wrong fuel rods in the wrong
(since gravity can no longer guarantee the right order).
So I would recommend building these reactors with there own fuel transport vehicles of diminishing physical sizes, and linking the reactors with a
“corridor” that has gateways of diminishing sizes to match. This would ensure it’s not physically possible to directly transfer fuel from the
first reactor to the last (well unless a brand new delivery is taken to the wrong point; but hopefully someone would either work that out, or the last
reactors entrances could also
be designed to be too narrow-shallow to allow this to happen.
Therefore by either using the right size door ways, or using virtually melt proof materials like clay (with the containment dome) this safety problem
can be totally eliminated (even with rats rather than people running the reactor).
Hopefully clay does the trick as I quit like the gravity fed vertical design since it reduces both costs and unnecessary equipment contamination.
So ATS what are you’re thoughts?