Proposal of a Deuterium-Deuterium fusion / PWR fission hybrid reactor

[Patrick Lindecker]

Hello,

As power plants working thanks to D-T fusion will not probably be available before the end of this century, an intermediate solution easier to realize would be a fusion / fission hybrid reactor (as the famous Carlos Rubbia "energy amplifier"). However the Rubbia reactor has its own problems.
Hybrid reactors could supply energy for thousands of years (but not millions of years as for fusion), as they use all the U238 and Th232 energy containt, i.e. 90 more than PWR or Candu reactors.

So, for information, I propose a hybrid reactor based on a Stellarator D-D fusion reactor, breeding in neutrons a PWR reactor, at this WEB address
https://zenodo.org/records/14108287.
You will find the main paper (39 pages) but also a summarized paper (only 6 pages) for just the principle.

Here is the abstract:

This article proposes to associate a Deuterium-Deuterium (D-D) fusion reactor with a PWR (fission Pressurized Water Reactor) in a hybrid reactor. Even if the mechanical gain (Q factor) of the D-D fusion reactor is below the unity and consequently consumes more energy than it supplies, due to the high energy amplification factor of the PWR fission reactor, the global yield is widely superior to 1. As the energy supplied by the fusion reactor is relatively low and as the neutrons supplied are mainly issued from D-D fusions (at 2.45 MeV), the problems of heat flux and neutrons damage connected with materials, as with D-T fusion reactors, are reduced. Of course, there is no need to produce Tritium with this D-D fusion reactor.
This type of reactor is able to incinerate any mixture of natural Uranium, natural Thorium and depleted Uranium (waste issued from enrichment plants), with natural Thorium being the best choice. No enriched fuel is needed. So this type of reactor could constitute a source of energy for several thousands of years, because it is about 90 more efficient that a standard fission reactor, such as a PWR or a Candu one, by extracting almost completely the energy from the fertile materials U238 and Th232.
For about the fission part, the PWR technology is mature. For about the fusion part, it is based on reasonable hypotheses done on present Stellarators projects.
The working of this reactor is continuous, 24 hours a day. In this paper, it will be targeted a reactor able to provide a net electric power of about 1400 MWe, as a big fission power plant.

Patrick Lindecker

[Richard Hull]

Sounds interesting provided someone moves on it. Deuterium is relatively easy to obtain in quantity if needed. Tritium is not so easy to obtain at power producing quantities in any proposed D-T fusion reactor if one is ever successfully built.

Richard Hull

[Frank Sanns]

Fusion is such a lossy process that even a hybrid fusion/fission is not even a great winner.

The idea of using fast neutrons to fission U-238 is done in some reactor designs.

It seems that having some rods that are allowed to build up Pu that would produce Curium to be produced in significant quantizes would be another route. As the curium builds up, Cf-242 would then be building up. These special pellets would not be refueled but rather reused without separating out the elements. New clad would be used for each use.

A continuous source of Cf-242 would be a prolific source of neutrons for fast fission. No excess energy would be needed to breed such materials but it would take a while to build up unless it was seeded with curium to start.

[Patrick Lindecker]

Hello,

Yes Tritium is one of the big difficulty for D-T reactors. As far as I know, it seems no so evident that Lithium blanket will be able to supply a sufficient TBR (Tritium Breeding ratio) to breed the reactor in Tritium. It will depend of the real loss of Tritium of these D-T reactors.

Fast fissions reactors are still "in the running" as three different models are still selected for the "Generation IV" program.

Californium is used in PWR (at least here) as a source of neutrons, to have a minimum of counting when the reactor is stopped (as far as I remember).

Patrick Lindecker

[Dennis P Brown]

This idea was proposed for ITER some years ago. I learned of it at a conference. ITER would produce enough fissionable fuel to power 20 conventual fission reactors per year. I agree the stellarator is a better likely source but ITER is being built and has enough neutrons (of course, how long before cataclysmic failure is the issue - so a stellarator would be a vastly safer bet.) While such a fusion device is wildly expensive as a neutron source, such a device could supply 20 conventual reactors which is vastly cheaper than all the required breeder reactors. That is, it takes 10 breeders to supply one conventual reactor IMS.

[Patrick Lindecker]

Hello Dennis,

Yes this idea to use a D-T reactor to breed a fission reactor is common and old, at least since the last years of the 70's. I read several (see many) articles about this way to do. Even a Stellarator was proposed. However, I noted that, in all cases, if the fusion is well described, the fission is rapidly described, without details.

In fact, I don't think that such D-T hybrid reactor be possible, because a neutron generated by a D-T fusion must:
* either induces a fission, after thermalization,
* or induces a reaction with Li6 to breed Tritium.

It's not sure that a real future D-T reactor will be able to breed sufficiently Tritium to compensate for the loss of Tritium by fusions, on the wall and in the Divertor, as the present TBR are sllghtly above 1. So adding a certain neutrons rate for the fissions seems not very realistic. If the TBR was close to 2, it would be OK...

Not speaking of the other problems for a D-T hybrid reactor:
* Lithium and water (to moderate neutrons and carry the heat) cause an exothermic reaction, when in contact,
* the life of fission reactors is limited (for a part) by degradation of metal by neutrons, the fission neutrons having a mean value of about 2 MeV. With 100% of 14.1 MeV fusion neutrons, the life will be reduced (even if the rate of neutrons will be much lower than for a standard D-T reactor).

A hybrid D-T reactor would necessarily be very complex (if feasible), contrary to a D-D hybrid reactor. The sole issue with the D-D hybrid reactor is that it would be necessarily much bigger than a D-T hybrid reactor. But it would be relatively simple. However, I'm not absolutly sure that it can work, this because the physics calculations made in this paper are relatively rough, even if in general conservative. Let's hope that this paper gives ideas to others (having powerful simulation programs).

Patrick Lindecker