LFTR Power for a Stable Grid

I have suggested on several occasions that several unique features of the Liquid Fluoride Thorium Reactor (and other molten salt reactors) makes it suitable for several important roles in supplying electricity to the electrical grid as demand shifts over time. Daily and seasonable shifts in electrical demand require part time generating capacity, that can be brought on line as demand increases, and withdrawn as it declines. In addition to the predictable variations in customer demand, a quick response reserve generating capacity is required as protection against a sudden loss of generating capacity. Power plants may go off line at short notice due to equipment problems. In order to keep the grid stable, grid managers must be able to quickly bring reserve generating capacity on line.

There are predictable cycles of electrical daily demand. Overnight power demand is filled by base load generating capacity. Most base load power in the United States is produced by nuclear and coal fired generating plants. Good base load generating capacity is both reliable and low cost. As people get up in the morning, start heating water for coffee, frying eggs, and running hot water to wash their faces, electrical demand increases. This increase requires that more power be brought on line. This power is called mid load power. Mid load power supports human activity in advanced societies during the 16 hours a day when most people are awake. Mid load power is highly predictable. Power companies keep track of power demand over time, and can usually predict in advance with high reliability what day time power demand will be. However equipment reliability is less predictable, thus reserve power plants must be kept on tap in case a mid load plant needs to be replaced quickly. Electrical utilities like to bring their lowest cost electrical producers on first, and as day time demand increases bring on higher cost producers later.

Power demand over time is not constant. It goes up and down with human activity. These shifts in power demand can destabilize an electrical grid, and if not corrected can create grid blackouts. In order to prevent rapid shifts in power demand, some generating has to be devoted to following electrical demand. A good load following generator can quickly increase or decrease its electrical output. Not every electrical generating system performs equally well in load following. Some do it more efficiently than others. Nuclear plants are reputed to be poor load followers, but this is exaggerated by nuclear critics. Increases in electrical demand are feed back to generators. As demand increases, greater force or torque is required to turn the generator. In a steam power system torque is supplied by increasing steam pressure to the steam turbines. In a nuclear plant this could be done by increasing power output in the reactor. But it also can be done by dumping excess steam from the steam system. Thus as electrical demand increases, more steam is directed through the turbine, and as demand is reduced more steam is dumped. This is slightly more expensive than varying the chain reaction inside the reactor, but it causes less system stress.

Much load following in the United States is performed by gas turbine generators. Hydroelectric systems including pumped storage have good load following characteristics. The United States has virtually exhausted its good hydroelectric potential, and it is not clear how much economical pumped storage potential remains. Gas turbine generators are inexpensive to purchase, but the fuel cost is expensive, and in the long run we will run out of natural gas. In addition CO2 is emitted when natural gas is burned, and from the view point of global warming prevention, the replacement of natural gas powered generators by a post carbon technology is desirable.

Finally power demands may at times exceed the capacity of mid load and load following generators. Perhaps the most extreme example of this is power demand in Texas on hot summer afternoons. As air conditioners struggle to keep indoor temperatures at comfortable levels more and more electricity is drawn from the grid. At that time electrical companies draw on their peak generating reserves, which often include old and inefficient coal fired power plants and inefficient and expensive to operate natural gas fired plants. In some cases peak reserve plants may be operated for only a few dozen hours a year.

Some people who live in more temperate climates imagine that this heavy demand on air conditioning is simply a luxury, that less self indulgent people could well do without. But when Texas-like climate conditions prevailed over much of un-air conditioned Western Europe during the summer of 2003, over 50,000 Europeans died as the result of the heat. The availability of air conditioning during the summer is a question of public health, not a luxury. Inexpensive peak power is a matter of valid concern in any future electrical system.

Conventional nuclear plants, despite their high capital costs are well suited to the base load generating role. Over time as debt is paid off the cost of electricity generated by conventional reactors drops. It is a myth that the cost of conventional nuclear power is more expensive than renewables. In fact if the cost of making solar or wind generated power reliable enough to generate base load, or mid load generating roles is factored in, nuclear power is less rather than more expensive than renewables. However, conventional nuclear is far too expensive for load following and peak generation roles. The high expense of delivering power on demand with renewables would strongly argue against using renewables for load following and peak reserve power roles.

Thus none of the candidate post-carbon power systems appear to be capable of providing low cost load following and peak load generating capacity. I have recently pointed out some of the features that makes the LFTR the best candidate for the load following and peak generation roles on a post-carbon grid. These include relatively low capital cost compared to the other candidate systems, low operating costs compared to current peak load operating costs, and the potential for rapid deployment of factory built LFTRs. LFTRs hold reserve heat in their core salts, and heat can be rapidly drawn from the heat exchange into a turbine generator system. The limits of the system would come from the limits of the turbines to cope with changes in torque demands and input.

The LFTR is can rapidly increase its power output, because it slows its power output by increasing heat, while increasing power demands lowers core salt heat, while increasing reactor core power output. The LFTR is very well suited for the peak load standby role. It is possible to lower LFTR manufacturing costs by making compromises that lower thermal and fuel conversion efficiency. Such compromises are acceptable in part time generating systems where low capital costs and low fuel costs would make a very attractive combination for electrical utilities.

It would appear that the LFTR would cost less than other post carbon electrical generating systems, and is uniquely suited for certain generation applications including load following and peak power generation. A lack of competition among current post carbon technologies would suggest that building LFTRs for to fulfil these applications might present a positive business opportunity. Several considerations might apply here:

1. Natural gas may become increasingly expensive, and a carbon tax would add to that expense.

2. The load following ability of the LFTR could be seen as complimentary to renewables, making the adoption of a load following LFTR a priority for a high renewables penetration grid. Thus the load following LFTR could be sold alongside renewables.

3. The load following and peak load LFTRs would present relatively fewer technological challenges than mid load and base load LFTRs.

4. The load following LFTR could be built using primarily ORNL tested technology lowering developmental costs, and enabling developers to treat the MSRE as their proof-of-concept prototype and proceed directly to a commercial prototype.

5. Since efficiency compromises can be made to reduce costs, the LFTR can be truly a low cost reactor.

The load following and peak load LFTRs would seem to have good potential to make money for their manufacturer. Because of their potential to stabilize the post-carbon grid, the development of the load following and peak load LFTRs might receive favorable treatment by the US Department of Energy. The relatively low developmental risk, and potentially low developmental costs, might attract the interests of private investors, VC investors, energy related businesses, and others interested in establishing a manufacturing stake in the post-carbon energy world.