
Ask HN: Why don't spent fuel pools have a containment strategy?  - hammock
Honest question.  We spend so much time and effort on "defense of depth" strategy for the nuclear reactor itself, with multiple containments, etc. But for the spent fuel rods, why are we content to basically drop them in the bottom of a giant rooftop swimming pool and call it a day? Is that really it?<p>As I understand it, the final consequences of a loss of cooling event for the spend fuel rods is the same as for a reactor - the rods melt down, you reach a criticality, they start burning and releasing radioactive smoke and ash into the atmosphere. Then why don't spent fuel pools have a containment strategy?
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cperciva
_As I understand it, the final consequences of a loss of cooling event for the
spend fuel rods is the same as for a reactor - the rods melt down, you reach a
criticality, they start burning and releasing radioactive smoke and ash into
the atmosphere. Then why don't spent fuel pools have a containment strategy?_

First, a correction: The fuel rods heat up, and can potentially burn, but do
not become critical -- you need either more U235 or a moderator in order to
produce criticality.

But to answer the original question: The vast majority of heat released is
from fission products rather than the uranium; when the reactor is stopped,
these short-lived fission products are releasing about 7% of the original
reactor power, but they decay rapidly. Spent fuel in the storage ponds is
normally very "cold".

Unfortunately, reactor 4 was defueled a very short time before the earthquake,
so its fuel was still quite hot.

This is why the storage pond for reactor 4 is a problem while the storage
ponds for reactors 1, 2, 3, 5, and 6 aren't -- the fuel in all the other ponds
isn't producing anywhere near as much heat and is thus not boiling off the
other ponds.

I expect that the #1 recommendation to come out of nuclear regulatory bodies
in the post-mortem reports will be to require that fuel be left inside stopped
reactors for longer prior to being moved into the cooling ponds.

~~~
kstenerud
There is also boron in the spent fuel pools to further retard neutron
production. As well, the steel structures for the spent fuel pools are often
made of borated steel.

It's not like they just toss the spent fuel into a kiddie pool and call it a
day.

