Manual section on uranium enrichment

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Zefram 2014-08-13 02:28:25 +01:00
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manual.md
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@ -343,6 +343,162 @@ There's one more iron alloy in the game: stainless steel. It is managed
in a completely regular manner, created by alloying carbon steel with in a completely regular manner, created by alloying carbon steel with
chromium. chromium.
### uranium enrichment ###
When uranium is to be used to fuel a nuclear reactor, it is not
sufficient to merely isolate and refine uranium metal. It is necessary
to control its isotopic composition, because the different isotopes
behave differently in nuclear processes.
The main isotopes of interest are U-235 and U-238. U-235 is good at
sustaining a nuclear chain reaction, because when a U-235 nucleus is
bombarded with a neutron it will usually fission (split) into fragments.
It is therefore described as "fissile". U-238, on the other hand,
is not fissile: if bombarded with a neutron it will usually capture it,
becoming U-239, which is very unstable and quickly decays into semi-stable
(and fissile) plutonium-239.
Inconveniently, the fissile U-235 makes up only about 0.7% of natural
uranium, almost all of the other 99.3% being U-238. Natural uranium
therefore doesn't make a great nuclear fuel. (In real life there are
a small number of reactor types that can use it, but technic doesn't
have such a reactor.) Better nuclear fuel needs to contain a higher
proportion of U-235.
Achieving a higher U-235 content isn't as simple as separating the U-235
from the U-238 and just using the required amount of U-235. Because
U-235 and U-238 are both uranium, and therefore chemically identical,
they cannot be chemically separated, in the way that different elements
are separated from each other when refining metal. They do differ
in atomic mass, so they can be separated by centrifuging, but because
their atomic masses are very close, centrifuging doesn't separate them
very well. They cannot be separated completely, but it is possible to
produce uranium that has the isotopes mixed in different proportions.
Uranium with a significantly larger fissile U-235 fraction than natural
uranium is called "enriched", and that with a significantly lower fissile
fraction is called "depleted".
A single pass through a centrifuge produces two output streams, one with
a fractionally higher fissile proportion than the input, and one with a
fractionally lower fissile proportion. To alter the fissile proportion
by a significant amount, these output streams must be centrifuged again,
repeatedly. The usual arrangement is a "cascade", a linear arrangement
of many centrifuges. Each centrifuge takes as input uranium with some
specific fissile proportion, and passes its two output streams to the
two adjacent centrifuges. Natural uranium is input somewhere in the
middle of the cascade, and the two ends of the cascade produce properly
enriched and depleted uranium.
Fuel for technic's nuclear reactor consists of enriched uranium of which
3.5% is fissile. (This is a typical value for a real-life light water
reactor, a common type for power generation.) To enrich uranium in the
game, it must first be in dust form: the centrifuge will not operate
on ingots. (In real life uranium enrichment is done with the uranium
in the form of a gas.) It is best to grind uranium lumps directly to
dust, rather than cook them to ingots first, because this yields twice
as much metal dust. When uranium is in refined form (dust, ingot, or
block), the name of the inventory item indicates its fissile proportion.
Uranium of any available fissile proportion can be put through all the
usual processes for metal.
A single centrifuge operation takes two uranium dust piles, and produces
as output one dust pile with a fissile proportion 0.1% higher and one with
a fissile proportion 0.1% lower. Uranium can be enriched up to the 3.5%
required for nuclear fuel, and depleted down to 0.0%. Thus a cascade
covering the full range of fissile fractions requires 34 cascade stages.
(In real life, enriching to 3.5% uses thousands of cascade stages.
Also, centrifuging is less effective when the input isotope ratio
is more skewed, so the steps in fissile proportion are smaller for
relatively depleted uranium. Zero fissile content is only asymptotically
approachable, and natural uranium relatively cheap, so uranium is normally
only depleted to around 0.3%. On the other hand, much higher enrichment
than 3.5% isn't much more difficult than enriching that far.)
Although centrifuges can be used manually, it is not feasible to perform
uranium enrichment by hand. It is a practical necessity to set up
an automated cascade, using pneumatic tubes to transfer uranium dust
piles between centrifuges. Because both outputs from a centrifuge are
ejected into the same tube, sorting tubes are needed to send the outputs
in different directions along the cascade. It is possible to send items
into the centrifuges through the same tubes that take the outputs, so the
simplest version of the cascade structure has a line of 34 centrifuges
linked by a line of 34 sorting tube segments.
Assuming that the cascade depletes uranium all the way to 0.0%,
producing one unit of 3.5%-fissile uranium requires the input of five
units of 0.7%-fissile (natural) uranium, takes 490 centrifuge operations,
and produces four units of 0.0%-fissile (fully depleted) uranium as a
byproduct. It is possible to reduce the number of required centrifuge
operations by using more natural uranium input and outputting only
partially depleted uranium, but (unlike in real life) this isn't usually
an economical approach. The 490 operations are not spread equally over
the cascade stages: the busiest stage is the one taking 0.7%-fissile
uranium, which performs 28 of the 490 operations. The least busy is the
one taking 3.4%-fissile uranium, which performs 1 of the 490 operations.
A centrifuge cascade will consume quite a lot of energy. It is
worth putting a battery upgrade in each centrifuge. (Only one can be
accommodated, because a control logic unit upgrade is also required for
tube operation.) An MV centrifuge, the only type presently available,
draws 7 kEU/s in this state, and takes 5 s for each uranium centrifuging
operation. It thus takes 35 kEU per operation, and the cascade requires
17.15 MEU to produce each unit of enriched uranium. It takes five units
of enriched uranium to make each fuel rod, and six rods to fuel a reactor,
so the enrichment cascade requires 514.5 MEU to process a full set of
reactor fuel. This is about 0.85% of the 6.048 GEU that the reactor
will generate from that fuel.
If there is enough power available, and enough natural uranium input,
to keep the cascade running continuously, and exactly one centrifuge
at each stage, then the overall speed of the cascade is determined by
the busiest stage, the 0.7% stage. It can perform its 28 operations
towards the enrichment of a single uranium unit in 140 s, so that is
the overall cycle time of the cascade. It thus takes 70 min to enrich
a full set of reactor fuel. While the cascade is running at this full
speed, its average power consumption is 122.5 kEU/s. The instantaneous
power consumption varies from second to second over the 140 s cycle,
and the maximum possible instantaneous power consumption (with all 34
centrifuges active simultaneously) is 238 kEU/s. It is recommended to
have some battery boxes to smooth out these variations.
If the power supplied to the centrifuge cascade averages less than
122.5 kEU/s, then the cascade can't run continuously. (Also, if the
power supply is intermittent, such as solar, then continuous operation
requires more battery boxes to smooth out the supply variations, even if
the average power is high enough.) Because it's automated and doesn't
require continuous player attention, having the cascade run at less
than full speed shouldn't be a major problem. The enrichment work will
consume the same energy overall regardless of how quickly it's performed,
and the speed will vary in direct proportion to the average power supply
(minus any supply lost because battery boxes filled completely).
If there is insufficient power to run both the centrifuge cascade at
full speed and whatever other machines require power, all machines on
the same power network as the centrifuge will be forced to run at the
same fractional speed. This can be inconvenient, especially if use
of the other machines is less automated than the centrifuge cascade.
It can be avoided by putting the centrifuge cascade on a separate power
network from other machines, and limiting the proportion of the generated
power that goes to it.
If there is sufficient power and it is desired to enrich uranium faster
than a single cascade can, the process can be speeded up more economically
than by building an entire second cascade. Because the stages of the
cascade do different proportions of the work, it is possible to add a
second and subsequent centrifuges to only the busiest stages, and have
the less busy stages still keep up with only a single centrifuge each.
Another possible approach to uranium enrichment is to have no fixed
assignment of fissile proportions to centrifuges, dynamically putting
whatever uranium is available into whichever centrifuges are available.
Theoretically all of the centrifuges can be kept almost totally busy all
the time, making more efficient use of capital resources, and the number
of centrifuges used can be as little (down to one) or as large as desired.
The difficult part is that it is not sufficient to put each uranium dust
pile individually into whatever centrifuge is available: they must be
input in matched pairs. Any odd dust pile in a centrifuge will not be
processed and will prevent that centrifuge from accepting any other input.
industrial processes industrial processes
-------------------- --------------------

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@ -20,14 +20,6 @@ local recipes = {
{ "moretrees:rubber_tree_trunk", rubber_tree_planks.." 4", "technic:raw_latex" }, { "moretrees:rubber_tree_trunk", rubber_tree_planks.." 4", "technic:raw_latex" },
} }
-- Refining uranium via centrifuge is intended to make it a practical
-- necessity to set up an automated cascade of centrifuges. Once the
-- cascade has been primed, production of one 3.5%-fissile dust requires
-- input of five 0.7%-fissile dust and 490 centrifuge operations, and
-- produces four 0.0%-fissile dust as a byproduct. The busiest stage
-- of the cascade is the one taking 0.7%-fissile dust, which performs 28
-- of the 490 operations. The least busy is the one taking 3.4%-fissile
-- dust, which performs 1 of the 490 operations.
local function uranium_dust(p) local function uranium_dust(p)
return "technic:uranium"..(p == 7 and "" or p).."_dust" return "technic:uranium"..(p == 7 and "" or p).."_dust"
end end