Can Very High Burnup Reactors Lower the Cost of Nuclear Energy?

[shaegelin]

I am interested in lowering the cost of nuclear reactors through the use of novel reactor designs, particularly fast reactor designs.

The Integral Fast Reactor (“IFR”) is a good starting point for a discussion since it was a real reactor with a long operating history. A few features of the IFR seem to have the potential for greatly reduced cost:

1) Core power density of the IFR was about 10x as great as a conventional light water reactor (“LWR”)
2) The coolant, liquid sodium, was kept at atmospheric pressure and did not go through a phase change
3) The IFR was capable of a much higher breeding ratio and higher fuel burnup than LFR’s

High power density means a small reactor core and atmospheric pressure/ no phase change greatly reduces the size of the containment structure. Ideally this would allow for a reactor small enough to be factory built and transported by barge. Although they are still only concepts, the Toshiba 4s Reactor and the “Traveling Wave Reactor” share these ideas.

Higher fuel burnup allows for more efficient use of uranium and potentially for simpler design. The IFR was designed to allow for fuel reprocessing which greatly complicated its overall design. (Moving fuel in and out, keeping spent fuel in the sodium bath while it cooled, transport and handling of highly radioactive spent fuel, etc.) A very high burnup reactor would eliminate much of this complexity (lifetime fuelling).

One of the Physics Forum posters, Vanesch, wrote the following:
“To me the most logical design of a breeder is a rather homogeneous mix of "initial fuel" and of fertile material, such that the breeding ratio is close to 1: the consumed initial fuel is then replaced by newly bred fuel. The problem is of course the build-up of fission products and the diminuation of U-238 concentration. For the neutron balance, the fission products will eat some neutrons, on the other hand the U-238 will eat less of it, so the neutron balance must remain close to the same. Of course you can't burn up everything, as you need a certain amount of U-238 for passive safety (Doppler effect) and in any case your fuel elements will be damaged after a while (first barrier).”

This raises two important problems with the Very High Burnup Reactor (“VHBR”) – safety and the need for new materials to handle extended periods of high flux.

In terms of safety – reactivity control is a concern. The reactor would be running on Pu 239, which has relatively few delayed neutrons.

Material evaluation of certain forms of steel and of the fuel itself had begun at the IFR. U-Pu-Zr alloys and different forms of steel tested. At least some of this work has been completed.

Any thoughts?

 

[mgb_phys]

1) Core power density of the IFR was about 10x as great as a conventional light water reactor (“LWR”)

and that's a good thing?

2) The coolant, liquid sodium, was kept at atmospheric pressure and did not go through a phase change

You hope! The trouble is that when it does have a phase change things get rather bad.

3) The IFR was capable of a much higher breeding ratio and higher fuel burnup than LFR’s

If you re-process fuel as MOX is this a big deal?

High power density means a small reactor core and atmospheric pressure/ no phase change greatly reduces the size of the containment structure. Ideally this would allow for a reactor small enough to be factory built and transported by barge.

The secondary cooling circuit/steam plant + generators still dominate the size of the overall system.
You can build small PWRs that fit inside a submarine already. Is there a need for a portable 600MW system?

 

[shaegelin]

1) I am mainly interested in keeping reactor construction cost down. Economy of volume production generally means factory production and so keeping size down is important.

2) Ha.

3) Reprocessing is politically difficult in the US. I am trying to conceptualize a solution to some of the problems nuclear energy faces in the US, not all of which are due to the underlying science.

You can generate a gigawatt with 1,000 1MWe modules or with one 1GWe module. The golden mean is somewhere in between. I think the submarine cores that are being built today are a good guide as to what could be done, but I would rather rely more on breeding and less on highly enriched initial fuel loading.

 

[Astronuc]

One needs to look at the Clinch River Breeder reactor design. It was designed for about 1000 MWt (380 MWe gross, 350 MWe net). The fuel was about 18-24% Pu-239 in MOX. That's more highly enriched than commercial LWR fuel.

MOX fuel cost quite a bit more than commercial UO₂ fuel, and much of the cost is because it require remote handling in the fabrication (and inspection) process.

The IFR was not completed and operated. The two largest operating fast reactors EBR-II and FFTF had limited lifetimes, and were not large commerical operations, but largely research/experimental reactors. FFTF did not generate electricity, and unfortunately only operated 10 years. As part of the shutdown, they trashed a lot of good experimental work, which is irretrievably lost.

The earliest fast reactors EBR-I and Fermi-I were very small and of limited operation on a research scale.

The cover gas was about 1 atm, but the core inlet pressure is somewhat greater due to the depth of sodium above and in the core.

The structural and cladding steels were designed in conjunction with FFTF and EBR-II. SS316L is an old reference design for the cladding material. There are certainly more advanced materials with low swelling and growth.

Material evaluation of certain forms of steel and of the fuel itself had begun at the IFR. U-Pu-Zr alloys and different forms of steel tested.

Material testing begun under the IFR program, but there was no IFR in which to test them. They would have been tested in FFTF and/or EBR-II, and possibly ATR.

Mixed carbide or nitride, tri-carbide and carbonitride fuels have some benefits over MOX.

 

[shaegelin]

When I described the IFR in my first post I was referring to the EBR-II, sorry for the confusion. Although EBR-II was small, 20MWe, it did operate for 30 years and was a reliable base load power station in addition to being a research reactor.

There is a very detailed book on the EBR-II written by Leonard J. Koch, I think he has done the nuclear community a service by taking the time to preserve a lot of valuable information.

Does anyone have knowledge of a book written on the design and operation of the Fast Flux Test Faciliity? A good textbook on Fast Reactors?

Any thoughts on how difficult it would be to control a plutonium fueled reactor given the low proportion of delayed neutrons?

Astronuc - what about metallic fuels? I believe that Toshiba mentions U-Pu-Zr metal fuel for its 4s reactor.

 

[Morbius]

The IFR was not completed and operated. The two largest operating fast reactors EBR-II ...

Material testing begun under the IFR program, but there was no IFR in which to test them. They would have been tested in FFTF and/or EBR-II,..

Astronuc,

Argonne converted EBR-II into an IFR prototype! It was not as powerful as a full scale IFR - only
because it was not as large. However, it did have most, if not all the properties of a full-scale IFR
including the passive safety characteristics which then Argonne Associate Director, Dr. Charles Till
describes in this interview with PBS's Frontline from about 10 years ago:

http://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/till.html


Q: And you in fact ran an experiment that was comparable to what happened at Chernobyl?

A: Yes, yes. Let me go on a little bit about that, because it is a rather dramatic characteristic. The
Chernobyl accident happened in April 26 of 1986. Earlier that month, the first week in April, with our test
reactor in Idaho, in fact the same reactor control room where we're now sitting, we performed a
demonstration of that characteristic, where if you cut off the coolant from the reactor, what would happen?
And there are two ways to cut off the coolant. One is that simply the pumps that are pumping the reactor
stop. The reactor just shut itself down. And in the afternoon, we brought the reactor back up to full power
again and did an accident situation where the reactor's unable to get rid of the heat it produces, because
the heat normally is taken away by the electrical system, and so we isolated the electrical system from
the plant, and the reactor then has to deal with the heat it produces itself. Again, another real accident
situation. Again, the reactor just quietly shut itself down.


Dr. Gregory Greenman
Physicist

 

[Astronuc]

Granted that IFR concepts were tested at EBR-II. I was thinking more in terms of a scaled up commercial plant. EBR-II was designed to produce about 62.5 megawatts of heat and 20 megawatts of electricity.

There are papers on FFTF. I have a few somewhere. One of my colleagues worked there briefly, so I'll ask him if anything more is available. I've seen papers on EBR-II, but I'd have to try and find them again.

Here's some useful background material courtest of UWisc NE - http://fti.neep.wisc.edu/neep423/FALL99/lecture5.pdf