Saturday, January 19, 2008

Controlling Reactor Reactor Construction Costs

There are a large number of more important and expensive inputs to the
construction design decision than the amount of concrete and steel

Some of the most important include labor, capital, machine tools,
specialized materials, and legal/regulatory overhead. For "through
life costing" (as my friend Gulian Crommelin says) you need to think
about criteria like availability, cost of maintenance actions, and
cost of spare parts. - Rod Adams

Reactor construction costs are related to a number of factors. Among them are the
cost of materials, the amount of materials needed, the cost of labor for assembly.
There are other costs. These include the cost of manufactured parts, the length of time manufacturing takes, the cost of capitol, and the cost of siting.

During the early daysa of automobile production auto manufacturers opperated on two manufacturing models. One involved the assembly of parts kits. Business was conducted primarily through the mail. Potential customers would read avertisements for the auto manufacturer, and contact it by mail. Once a deal was struck, a parts kit and an assembly team would be dispatched to the customer. The auto would be assembled locally, and then the assembly team would move on to another customer. This model worked best when autos were expensive and rare. Labor and parts manufacturer were very expensive under this model. Labor productivity was also limited by the need to travel between assembly sites.

Reactor manufacturers continue to follow this manufacturing model.

A second manufacturing model soon followed. Manufacturers found that labor costs could be lowered by situating assembly at a central location rather than manufacturing each car at the customers home. Once cars were manufactured, they could be shipped by rail to customers. By adopting the factory manufacturing model, manufacturers lowered their labor costs. This in tern allowed manufacturers to lower prices to customers. Lower prices brought greater market penetration, since more people could afford to own cars. As demand for autos increased, manufacturers found other ways to lower the price of production. Because they were ordering large number of parts, manufacturers began to demand a volume discount from parts suppliers. Since more laborers were involved in the manufacturing process, they could be individually assigned fewer tasks. This meant that laborers needed fewer skills, hence wage levels could be dropped.

Henry Ford took auto production to the next level by instituting mass assembly line production of autos. Mass production opened up the possibility of controling some or all of the parts manufacturing process. Because parts were needed in large numbers, they could also be mass produced on sub assembly lines. The mass production of parts opened a new business, because worn out parts could now be replaced by manufacturers, and the sale of replacement parts became a profitable sideline.

Manufacturers generally control manufacturing costs by centralizing production, and undertaking the continuous production of large numbers of products on assembly lines. Reactor builders gave not adopted the centralized production model for several reasons. First , the prevailing power reactor design, the Light Water Reactors, is a very large object. The economies of locally assembled reactors favor the large size. Thus while assembly line production of reactor components is possible.

Some now obsolete cost estimates from Westinghouse are instructive. Westinghouse estimated that by serial production, AP-1000 kits could be produced for about 1.2 billion each. They further estimated that the cost of local assembly and housing construction would add another billion to the cost. Costs were lowered by careful attention to all phases of the design. Capitol costs were contained by developing final assembly techniques that would shorten assembly time. Still at the end of the day, the AP-1000 is still extremely expensive.

Much of the expense of building light water reactors has to do with reactor seftey. There are several safety problems in the light water design, and dedicated safety and containment systems add to LWR manufacturing expenses.

One way to lower reactor manufacturing costs is to adopt an inherently safer reactor design. Among proposed reactors two concepts stand out for safety. They are the Pebble Bed Reactor (PBR) and the Molten Salt Reactor (MSR). While they represent very different reactor design concepts, they posses a very important design feature. The possibility of a destructive core melt down is made impossible by the design of the reactor. In the case of the MSR the core is already molten, thus handling a molten core is built into the reactor design.

LWRs use water as their moderators and coolants. Water is heated under pressure. Even in the simple Boiling Water Reactor (BWR) the water inside the reactor is under 75 times atmospheric pressure. This means that the containment of high pressure water and steam creates considerable safety problems for LWRs. The loss of coolant does not, in itself, end the nuclear reaction within a LWR reactor. Even worse a flaw in pressure containment system can lead to an explosion of high pressure steam. Core melt down can lead down can lead to the release of highly radioactive ands toxic fission byproducts, which in the event of a breach of the containment system can be released from the reactor, Thus a massive secondary containment system is needed. Reactor overheating as the result of coolant loss, must be controlled by a secondary emergency cooling system.

The PBR reactor is cooled by gas. The reactor is cleverly designed so that if the cooling gas stops flowing, the chain reaction ceases. Heat from continuing radiation inside the reactor is dissipated by thermal radiation from the reactor. Experiments conducted in Germany demonstrated that a PBR remained safe when its cooling system shut off. The nuclear reaction immediately halted, and the fuel did not melt. Fission products remained inside undamaged fuel spheres. Because PBRs do not release fission products under the worst accident conditions they do not require massive amounts of steel and concrete for containment structures. Nore do they require heavy and expensive pressure containment structures. Thus material requirements for Pebble Bed Reactors are modest compared to LWRs.

Similar considerations apply to MSRs. MSRs operate at higher heat levels than LWRs, without generating steam. Hence they operate under normal atmospheric pressures. Since the core is molten, core melt down does not constitute a problem. Safety is passive, If the reactor becomes over heated, a plug in the bottom of the reactor melts, and the reactor fuel fluid drains into holding containers whose shape prohibits further chain reaction. Volatile fission products are continuously removed from the reactor. Other fission products are chemically bonded to the reactor fluid. Thus even in the unlikely event of a containment breech, virtually no fission products would be released into the outer containment structure. After an emergency shutdown it is highly desirable that the reactor fuel remain molten after it drains into emergency containment vessels. Thus some heat from radiation is desirable. Surplus heat can be controlled by passive heat radiators.

Since the design of the MSR and the PBR basically precludes the sort of accident that can occur to a LWR, many safety features that are required in traditional reactors, are not needed with these advanced reactor designs. This means that these reactors are simpler, and thus less expensive to build.

There are other advantages to the PBR and the MSR. The can operate at at far higher heats than traditional reactors. During the early 1950's Captain Hyman Rickover, General James Doolittle, and Admiral Lewis Strauss, witnessed a new type of reactor in operation at in Oak Ridge. They were astonished to see the reactor glowing bright red with heat. The bright red glow caused the reactor to be called "the fireball reactor." It was, in fact, the world's first Molten Salt Reactor. The fuel formula for the react0r was invented by my father, C.J. Barton, Sr., who was issued a patent for it.

The Fireball reactor was originally designed to provide power to jet engines. Scientists like my father had little confidence that the "fireball reactor" could fly, but the believed that with the Molten Salt Reactor concept, they were on to something.

Because the molten salt reactor operated at a high temperature, it could be used to drive gas turbines instead of driving steam turbines. The higher heat allowed electricity to be generated with thermal efficiency. Using the Brayton gas turbine thermal efficiencies of over 50% are possible. Thus the MSR does not need to be efficient.

Here we can begin to see the beginning of a method of lowering reactor construction costs. Small reactors can be built in factories, just like cars. Mass production on assembly lines can lower assembly costs. Not only that, but just as building cars on assembly lines was much faster and made better use of labor, as well as reducing prices for parts, the mass production of reactors on assembly lines will lead to a dramatic decrease in reactor prices.

Furthermore, small safe MSR do not require massive containment structures, thus greatly lowering siting costs. Since MSR rely on air cooling, they need not be located close to water.


Sovietologist said...

I do have a question regarding the potential material costs of the MSR. Doesn't the carrier salt contain a considerable amount of beryllium? I'm not sure whether this is an indispensable part of the MSR. Could shortages of this element be a serious problem? That would be too bad, as I believe that the MSR is probably the most attractive of all reactor designs- breeding, efficiency, and passive safety in one convenient package.

Charles Barton said...

Soviet, this is a good question, but I am not the right person to answer it. Kirk Sorensen's blog would be my first choice for answers. You might look at ORNL 2548 in his document repository. Also look in the discussion form for "Why bother with Lithium and Beryllium Salts?"

My father's original Molten Salt fuel patent called for the use of a NaF, ZrF4, UF4 mixture. This was the actual fuel used in the "Fireball reactor." The reactor chemists knew that better mixtures were possible, but since the "fireball reactor" was not intended to be a breeded, and the properties of the NaF, ZrF4, UF4 mixture were well researched, it was chosen.


Blog Archive

Some neat videos

Nuclear Advocacy Webring
Get Your Free Web Ring