Energy From Thorium Discussion Forum

Small Mobile Reactor for Underdeveloped Countries and Remote Locations

The objective of this project is to design a small reactor that can be transported by truck to a remote location. In addition to its small size, it will not be refueled on site but rather will be removed by truck and replaced with a reactor with a fresh core. Although the capacity remains to be chosen, 100 MW electric is a reasonable goal.

This project has considerable latitude it its design. Weight and size will probably make a pressure vessel impractical. However, a CANDU type design might be used with water as a coolant. Selection of the coolant will be a major design task left wide open. Liquid metals, gas, molten salt, or water will all be considered. The secondary plant must also be considered. However, the entire plant need not be delivered on a single truck; it might take several truck loads with a single load for the reactor at the time of refueling.

The reactor need not be thermal. We will also consider the advantages of a fast spectrum reactor using a liquid metal coolant.

Elements of Design

1. Power Coefficient and Void Coefficient

Both of these coefficients are of utmost importance for operation and safety. Since most of our experience is with water reactors, consideration of other coolants will introduce us to a new regime. Fast reactors will also bring us into a new area. In all cases, we must have a negative void coefficient and a negative power coefficient.

2. Neutron transport

This area will be important in evaluating the longevity of the fuel cycle, the power and void coefficients, and the flux profile. The small size is expected to aid in reactor control. The core geometry may be adjusted to optimize power coefficient and flux shape.

3. Heat Transfer

Thermal hydraulics will be considered not only for steady state heat removal but for decay heat removal upon shutdown or accident conditions. Many designs are available that enable natural circulation cooling under accident conditions. This will also be a consideration in our reactor.

4. Materials Selection

High temperature and high efficiency are not prime considerations. However, the more efficient, the smaller the reactor can be made. We must select materials that will withstand operating temperatures and the long fuel cycle. However, this is not a research project, only a conceptual design. We will identify areas for future research on materials or other requirements.

5. Secondary System

The secondary system will not be an area on which we will focus. However, we must identify the type of system and have an estimate of its size. Steam generators are very large. Perhaps another system will be more favorable.

6. Safety

Safety is always a consideration in a design project. For a remote reactor, it is a goal for it to operate with a minimum of intervention. Convection cooling in case of pump failure is a major advantage. Containment is essential. However, this will not be a major part of the design effort. Concepts that are already established can be used.

If the high radiation flux in the graphite is the limiting factor, is there no hope on progress in this front? Carbon materials science has done amazing things. Fullerenes were found in the eighties...

On the other hand, if you had a core moderated by D2O, with fuel flowing through insulated graphite tubes, then the heat would tend to flow from the graphite to the D2O, and the graphite would assume a temperature LESS than the salt. Temperature improvements have a huge effect on graphite performance.

And if a uranium fuel cycle can be made to look this good, what would be the advantages of modifying this design to use thorium as a fuel other than the relative ease of mineral extraction and processing?

Why did you not design this as a fast MSR if you are going to use natural or enriched uranium as a fuel source? I think the best hope of getting anyone to invest in MSR technology is to get a fast version running that can be used as a burner for any long term wastes, or excess weapons material. Eventually as the technology improved you could probably make a U233 breeder burning Pu and other transuranics, and eventually minimal investment would be required to get a thorium economy underway.

What am I missing?

The fact that the proven flouride technology has gotten little attention over the last 50 years, it doesn't seem like to much of a stretch to push for the Cloride LCR instead. When I think of congress's ability to grasp technological concepts, I think of the statement by Ted Stephens after making a critical decision on the future of the internet, he stated that the internet is not a like a truck you can just dump stuff on, its a series of tubes.

Seeing as you have to address congress in the most basic terminology, imagine pitching them a reactor designed like a vat that you could dump High level nuclear waste into and generate heat. A reactor that could dump plutonium from nuclear weapons into and burn it up. There is no need for any fuel fabrication of radioactive materials, you just dump it in. You can also take those piles of Depleted uranium that I assume are accumulating all around the enrichment facilities and burn them up to. These fast reactors could also be used to create start charges of U233 for thorium fueled thermal breeder reactors. Given that Yucca mountain will cost an estimated $43.6 billion before its finished, I would think you could leverage that cost against ~$2 billion for funding this burner that would destroy most of the long lived waste.

Also it doesn't seem logical to use D2O as a moderator for a LFR. You are introducing water to the reactor which if I am not mistaken is highly incompatible with the salt? The D2O would also need to be under high pressure creating an explosion hazard inside the core, removing one of the nice safety features of having the core operate at atmospheric pressure.

congratulations to your nice study, it was some enjoyable reading. There is just one thing I didnt find an answer for - if some problem occurs and the freeze valve will open and dump the fuel to the emergency tank, is there a way to recover from such accident?