Thorium Accelerator Driven Nuclear Power - Why not ?

[Morbius]

The reactor plants I worked on were on an aircraft carrier,

Dewey,

Just to add; all naval reactors are PWRs - even the ones designed by General Electric
[KAPL]. GE's commercial power reactors are BWRs. However, one doesn't want a
"free-surface" i.e. an interface between water and steam; in a reactor that is moving,
where the water and the free-surface can "slosh" around.

Unfortunately (or fortunately), my ship was relatively new so we didn't really have a huge issue with decay heat. Even without RCPs we could establish enough flow to keep the reactor cooled by thermal flow if necessary.

The fission products that give you a shutdown decay heat that is 7% of nominal power
are all short lived fission products. So they equilibrate VERY quickly to an equilibrium
value. If the aircraft carrier reactor has been operating for a few days, or even less;
you essential have reached the equilibrium level of fission products that give the
decay heat that is of concern from a meltdown point of view.

Dr. Gregory Greenman
Physicist

 

[Morbius]

Well yes, naval reactors are quite different animals than commercial power reactors. Enrichments are higher and that certainly leads to differences in reactivity management/control.

Astronuc,

Yes - naval reactors use HEU - Highly Enriched Uranium for fuel. In fact, the HEU that
is used in naval reactors has a higher enrichment than "weapons-grade" uranium.

Ther primary reason was so that one could override a "Xenon transient". In a normal
power reactor; if the reactor is shutdown, one has to wait a day or so for the Xenon
to decay in order to restart the reactor. That would be unacceptable as the power plant
of a naval vessel. A warship has to be able to move anytime the captain orders it to
move. They can't sit around and wait for Xenon to decay. So naval reactors are fueled
with HEU. Naval reactors are also not refueled on an annual basis. The current
generation of reactors used in Trident subs and Nimitz-class carriers will go for about
20 years between refuelings. In fact, in the subs; there's no hatch over the reactor to
facilitate refueling. When a Trident is refueled, they cut a hole in the hull; and repair
it after refueling. A Trident will probably be refueled only once in its operating lifetime.

From the late '50s to the '80s; the Ford Nuclear Reactor at the University of Michigan
used naval reactor fuel. If you toured the FNR, they would show you a mock fuel
assembly. That mock assembly had "Property of U.S. Navy" embossed on the side.

There were many other university reactors that used highly enriched uranium as fuel.
There was concern in the late '70s that the use of HEU in university research reactors
was a proliferation risk - someone could hijack HEU meant for a university research
reactor.

Starting in the '80s there was a program run out of Argonne National Lab called RERTR -
Reduced Enrichment Research and Test Reactors. The goal was to redesign the fuel
for research reactors so that they were no more than 20% in enrichment. The FNR at
the University of Michigan was the test-bed for that effort. The FNR operated for many
years on the reduced enrichment, and was shutdown a few years ago.

At present, practically all university research reactors use fuel that is about 20%
enriched. I know of one university reactor, my alma mater's; that still uses HEU.
That's because the core is very small; and one needs the high enrichment to operate.
However, that also means that when it is refueled; the incoming charge of fresh fuel
is less than that needed to make a bomb. So the bad guys can't get their hands on
enough HEU in a single hijack.

If that reactor is redesigned, [ it's in its second incarnation having been designed with
this very compact core in the early '70s ], the redesign would also entail being able
to operate at lower enrichment.

Dr. Gregory Greenman
Physicist

 

[Dewey2k]

All,
Thanks for the feedback. I kind of feel like I trespassed into hallowed ground, at it were.