Building Nuclear Power Plants Underground: Pros & Cons

[Arctic Fox]

Is there any reason not to build nuclear power plants underground?

All of the ones I know of (http://pravda.ru/main/2002/02/05/36613.html) are all above ground - if there’s a problem like meltdown, it gets scattered all around. My thinking is that if we build these things underground this would provide better protection of the environment in the case of a major problem...

Comments?

 

[chroot]

In the case of a meltdown, the released radioactive material would end up directly in the groundwater, which is the worst possible situation. You might be able to build them in highlands or in deserts where the water table is very deep, but doing so would present very large logistical problems.

- Warren

 

[hitssquad]

The Rubbia fast reactor (energy amplifier)

nuclear power plants underground?

My thinking is that if we build these things underground this would provide better protection of the environment in the case of a major problem...

That seemed to be Carlo Rubbia's thinking. He invented the underground accelerator-linked lead-cooled fast reactor. The accelerator provides some of the neutrons necessary to achieve criticality. That makes it easy to stop the reaction - you just turn off the accelerator and the reaction has to stop because there are no longer enough neutrons to sustain it (the accelerator, of course, cannnot accelerate neutrons since they have neutral charge - it generates neutrons indirectly by firing protons at the lead which then, in turn, undergoes spalatial fission, releasing neutrons).

Here are http://lpsc.in2p3.fr/gpr/images/rubbia.gif of the Rubbia Energy Amplifier.

Rubbia's idea was that the reactor had almost no way of melting down (a common scenario for a meltdown involves coolant pump failure and in Rubbia's design there are no pumps - the lead coolant relies instead on natural heat-driven circulation), so his reactor actually might not be a good example of one that is built underground to protect against the hazards of a meltown. But his reactor might still be a good example of building underground to avoid a meltdown. Being underground, it is difficult for the coolant to escape. It would also seem to present a more challenging target for human-guided missile-airplanes.

On a side note, Richard Garwin thought of a variation on the Rubbia reactor where the accelerator is left out and the resulting neutron deficit is made up with either decommissioned weapons plutonium or uranium-233 bred from thorium-232. See Megawatts and Megatons for details (Amazon let's you read about fifty scanned pages for free with their Search Inside this Book feature - search for the keyword rubbia. Also, http://groups.yahoo.com/group/Know_Nukes/ is a good place to ask nuke questions.

 

[Morbius]

That seemed to be Carlo Rubbia's thinking. He invented the underground accelerator-linked lead-cooled fast reactor. The accelerator provides some of the neutrons necessary to achieve criticality. That makes it easy to stop the reaction - you just turn off the accelerator and the reaction has to stop because there are no longer enough neutrons to sustain it (the accelerator, of course, cannnot accelerate neutrons since they have neutral charge - it generates neutrons indirectly by firing protons at the lead which then, in turn, undergoes spalatial fission, releasing neutrons)...

Rubbia's idea was that the reactor had almost no way of melting down (a common scenario for a meltdown involves coolant pump failure and in Rubbia's design there are no pumps - the lead coolant relies instead on natural heat-driven circulation), so his reactor actually might not be a good example of one that is built underground to protect against the hazards of a meltown.

However, terminating the fission process and its energy production
has never been THE problem.

The main problem is what to do about decay heat.

The Three Mile Island reactor successfully shutdown at the start of
the accident. The heat energy to melt the core did not come from
fission - but was decay energy - the heat released by the radioactive
decay of fission products.

An accelerator driven sub-critical reactor has exactly the same
problem - one can shutdown the accelerator in order to stop the
fissions [ just like scramming the control rods ] - but what does one do
about the decay heat?

The Rubbia design is very similar to the "pool-type" LMFBR [ Liquid Metal
Fast Breeder Reactor ] designs. The "pool-type" design addresses the
decay heat problem mentioned above - because of the thermal inertia
of the pool. The following link shows the IFR concept - the reactor is
colored orange, and the liquid sodium "pool" is blue:

http://www.anlw.anl.gov/htdocs/anlw_history/images/image_large/ifr_concept.html

The Integral Fast Reactor [ IFR ] design from Argonne National Lab is
a pool design - as is it's predecessor and testbed - Experimental Breeder
Reactor II [ EBR-II ] at Argonne-West in Idaho - built in 1964.

http://www.anlw.anl.gov/divisions/facilities/EBR_II_Page/EBRII_Frameset.htm

So the saving grace for Rubbia's design is not that it is driven by an
accelerator - but that it uses the "pool" concept; just as LMFBR designs
have done for decades.

Dr. Gregory Greenman
Physicist LLNL