Thursday, June 18, 2009

Large and Small Reactors: David Walters

David Walters posted an essay about reactor size yesterday on Left Atomic, My view has been that large reactors carry cost penalties, and that clustering small, factory built modular reactors will produce nuclear power at a far lower cost than building large reactors. A small reactor would be a reactor that is transportable by truck or rail. At the very least the core of a small reactor must be rail transportable as a single unit. The upward size of a small reactor would be is often defined as being around 350 MWe output, but David LeBlanc has designed a 400 MWe LFTR core that is easily truck transportable. My view is that optimal size is very much a matter to be identified by engineers. Middle size reactors would be too big to be easily transported in a few modules, but small substantially smaller than the standard Generation II, III and III + reactor. Generation III + reactors generally run from 1100 MWe on up, but the Chinese are still building a generation II reactor that is less than 1000 MWe in generating capacity. The transition between middle and large reactor size runs somewhere between 750 and 800 MWe. A medium reactor should produce half of the power of a large reactor, and not be transportable. The Indians are building a 500 MWe LMFBR that is quite obviously too big to be a small reactor, but only about half the generating capacity of a large reactor.

Indian accounts describe the PFBR reactor vessels:
The main vessel made of stainless steel measures 13 metres in diameter, 13 metres in height, weighs 200 tonnes and will go inside the safety vessel to hold the coolant liquid sodium, reactor fuel, grid plates and others.

The third and smaller of the three vessels is the inner vessel - 11 metres tall - and supports equipments like pumps, heat exchangers and others.
We are clearly dealing with a reactor that is far to large, heavy and complet to be truck or train transportable in a few modular units. The Indian PFBR is clearly a medium size reactor, but the 300 MWe Indian AHWR is a small reactor, that is probably suitable for factory manufacture. Current Indian PHWR designs run about 700 MWs, and it is not clear if the Indians intend to build the 300 MWe AHWR in serial production, or use it as a prototype for a larger commercial power generator.

The usual economic advantage mentioned for large reactors is economies of scale, although the empirical evidence for the economies of scale does not seem especially convincing. However, the skill set required for large reactor construction project managers is extremely demanding. Given the same project to project learning curve, constructing a 1600 MWe will yield the same advance on the learning curve as constructing a 200 MW reactor. Thus if it is possible to build 8 small 200 MWe reactors in the same amount of time as one 1600 MWe reactor, The project manager of the small reactors will be 8 times further advanced on the learning curve as the large reactor project manager. Indeed it will take the large reactor project manager another 21 years to catch up to the point where the small reactor project manager arrived after 3 years.

I have elsewhere argued that large scale construction projects are inherently less efficient in their use of labor in factories. The skill set of factory workers is typically smaller for factory workers than for nuclear construction workers. Wages for factory workers will be lower. Factory workers have assigned work areas allowing for convenient storage of work tools. Factories are more amenable for labor saving devices, and those devices can be employed to typically greater effect in factory settings, Work patterns in factories are likely to be better organized and production lines laid out in a rational fashion to begin with.

David W. recognizes the usefulness of small reactors and indeed he argues in effect for the use of mini reactors (reactors of less than 100 MWe output):

The LFTR is unique from all of the above because it is amazingly scalable...there is no real downward or upward limit to the size or use a LFTR can be employed in. Say, from a small LFTR 'battery' of 20 MWs to a large, base load plant offering 1800 MWs gross base-load power to the grid.

It is my contention that there will be a 'market' for all these sizes. We should first review what these markets are.

On the smaller end, the LFTR, as a high temperature reactor, can provide process heat. A small chemical plant, requiring thousands of tons of steam an hour, can use a LFTR to provide this heat and, to electrically power the plant. A slightly larger version may be able to provide power and vast qualities of heat to an oil refinery or a tar-sands operation thus providing carbon-free process heat to what otherwise would be a huge carbon-spewing operation.

These smaller LFTRs, from 20 to 200 MWs could provide, also, site specific load balancing for a grid that has a lot of load in place but generation many hundreds of miles away. Using a 200 MW LFTR to 'anchor' the grid would be very helpful to any utility. Additionally these smaller LFTRs could be plopped down in various transmission substations to provide quick, peaking power or variable load changing that responds to frequency changes throughout the day.
Arguably here David has conceded that the bulk of reactor output will be from small reactors. The argument between us then boils down to the relative economies of clusters of small reactors verses a single big reactor as base power sources. David wants to phase
out gas and coal plants with big 1000+ MW units.
I have employed a variety of arguments for the economy of the small reactor cluster in the past. We are simply mapping potential parameters. It will be up to those assigned to turn those parameters into tangible realities to decide what size to build, and assign to specific tasks. What we offer the future is some possibilities and the potential for flexibility. David correctly notes:
One thing that is important for this discussion to note, however, is that LFTRs, from the get go, are cheaper to produce, having a much higher power density than any currently running or under-construction Generation II or III Light Water Reactors. From the reactor core itself to the turbine, size is about 1/2 to 2/3 smaller, thus allowing for a cheaper, and therefore far more efficient, product based on size/cost per MW output. We are looking at, generally a similar ratio in cost reduction.
My argument for the factory production of of small LFTR cluster however, is based on a rapid deployment expectation. We simply have to convert our entire energy system from a carbon base to a post carbon base. Factory production works best for rapid deployment, and small reactors work better for factory production than large reactors.

David correctly points to the price per Watt as the critical issue, and this will not be determined before we know a great deal more about the economics of factory produces reactors in general and LFTRs in particular. I have tried to provide some ideas about factory produced LFTR costs, but my hat does not say expert, and indeed if I were an expert, I would probably say, "We don't know enough yet."

Clearly what we have is potential that should be investigated. I have offered a vision of the future which suggests that low cost, abundant and sustainable is a possibility if we want it. i believe that this would be a better future be far for the bulk of humanity than the future offered by the advocates of so called renewable energy, and the cult of limited future resources, It is not in my power, however, to choose this future. Rather it is my role, as well as David's, Kirk Sorensen's, Robert Hargraves, and numerous others to provide the information that this choice is possible, and to suggest that the investment required to make the suggestion that sufficient research and development money be provided so to assure that the choice be available if it is considered desirable.


steve_c said...

There are quite a lot of spelling or typing errors in this, which detracts from the message. Was it scanned, or something? The content is worth it to take the time to get it right.

Charles Barton said...

I do check my spelling, but i have very poor eye sight.


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