Monday, May 11, 2009
Confusion About Reactors
It has long been know among reactor researchers that the prevailing reactor design, the Light Water Reactor, is far from the best possible reactor design. Alvin Weinberg, who held the patent on the Light Water Reactor, believed that the fluid core Molten Salt Reactor was a far superior design. Weinberg's mentor Eugene Wigner who played a major role in the early development of reactor theory and design, also believed that fluid core reactors would open the door to low cost electrical production with nuclear power. Oak Ridge reactor experts pointed to evidence that the molten salt reactor could be built at low costs, were very safe, largely solved the problem of nuclear waste, could be used to dispose of the nuclear waste from other reactors, were proliferation resistant in their simple implementation, and could be modified to further lower the risk of nuclear proliferation.
Despite these notable advantages, development of the Molten Salt Reactor was terminated by the the Nixon/Ford Administration, primarily for budgetary reasons, and never renominated. Thus the Light Water Reactor remains the standard reactor world wide. The Light Water reactor has a number of defects. The first is that it is a uranium fuel cycle thermal spectrum reactor that is dependent on enriched uranium to maintain criticality. Uranium-cycle reactors convert some U-238 into Pu-239, but in the thermal-spectrum not enough to burn the U-238 deeply. Pu-239 is a relatively poor nuclear fuel in the thermal spectrum, and fissions twice for every three neutron captures. The solid uranium dioxide fuel used in Light Water Reactors, retains fission product Xenon-135--a neutron poison that inhibits chain reactions and further mitigates against breeding in Light Water Reactors. Unlike Molten Salt Reactors, the solid fuel of the Light water reactor prevents the removal of Xenon-135 fro the core, and this leads to problems maintaining stable reactivity patterns in the reactor core. The Light Water Reactor requires complex monitoring and frequent operator intervention through a complex system of fission controls in order to maintain a stable fission pattern through the core. Without such interventions problems such as xenon transients can develop.
Interrupted coolant flow, and coolant loss can lead to significant problems in LWRs and can lead to core meltdown if not properly managed. Passive safety features can manage most LWR safety problems and systems of multiple barriers to radiation release make the LWR extremely safe, and indeed the operations of LWRs create far fewer human health and safety problems than the operation of fossil fuel power plants, or the manufacture of photovoltaic cells. Yet the safety of LWR is obtained at a high capital cost.
The high capital cost for constructing LWRs have become a major obstacle to their construction. Reactor manufacturers and purchasers believe that large reactors lead to economies of scale. There are reasons to doubt this, however. The very size of large reactor construction project seems to impose a certain amount of chaos on the flow of materials and labor, with over 25% of worker-on-the-job hours lost from productive use due to a variety of inefficiencies. The accrual of interest over multilayer construction projects adds another economic penalty on LWR construction. An large number of highly skilled workers who can command high wages , especially under conditions of labor skill scarcity further adds to construction costs. Finally the prolonged nature of large-scale projection project leads to leisurely advances on the cost lowering learning curve. Thus the LWR construction process leads to a perfect storm of capital costs.
There are unfortunately few remedies for these problems. Asian counties have had some success with the management of LWR construction projects, but it is not clear that transference of those management skills to the United States and Western Europe is possible. Chinese and Indian labor costs are far lower that Western labor costs, and this appears to give Asian economies a significant advantage in capital costs associated with new reactor construction.
A shift to small generation IV reactors may not automatically bring nuclear cost lowering. For example the cost of Factory-Kit-manufactured PBMRs in China are comparable to the cost of Generation 2 and Generation 3+ LWRs there. However, because the core of the LFTR is much smaller than a PBMR core. it appears to build the whole LFTR in factories, possibly in the form of several transportable and easily assembled supermodules. A variety of innovations could lower LFTR costs in comparison to LWRs, and capital costs approaching $1 per watt, seem possible although by no means certain.
Thus the solution to LWR capital costs, is a shift to MSR technology coupled with a number of nuclear cost lowering approaches made possible by the technology switch. There is an up front investment involved in this switch, and that investment might run from as low as $2.5 billion to $10 billion. Considering the potential cost savings which might result from this investment, even a $10 billion investment would be a trivial sum.
Until investments in cost lowering generation IV technology will lead to low cost nuclear technology, we have little choice other than to invest in LWRs. The rational for doing so is very powerful:
1. LWRs provide reliable electricity at a lower cost than reliable electricity from renewable.
2. LWRs do not require CO2 emitting natural gas generators for backup.
3. LWRs use far less land for electrical production than renewables.
4. LWRs are not effected by time of day, or season of the year.
5. LWRs are subject to far fewer geographic limitations than renewables.
6. In many cases, LWR construction need not require expensive grid expansions.
Although renewables supporters often point to the high capital costs of nuclear, they are actually comparing apples to oranges. In fact the capital costs for nuclear plants brings with it a facility that generates at its rated electrical capacity 90% of the time. At best wind facilities produce 40% of their rated capacity over time, while solar facilities produce electricity at half of that rate. While renewable facilities are not producing electricity 60% to 80% of the time, the electricity that cannot produce is typically generated by fossil fuel power plants. The Nuclear plant produces a far greater lowering of fuel costs, and incidentally a far greater reduction of CO2 emissions than wind and solar generating facilities.
Electrical utilities know this. The first year TVA had its rebuilt Browns Ferry Unit 1 reactor in service it saved over $800 million in costs. It had been buying electricity from sources outside the system, and the $800 million plus was what the outside electricity cost TVA, Of course the cost of fuel varies a lot. We need to talk about the cos of last year's coal and natural gas, this year, and next years. Last year coal was up $100 per ton, this year maybe $65. Next year, well that depends on how well the national and international economies do. We could be back in the $100 per ton range for coal.
At $100 a ton, a Brows Ferry size plant might save TVA $250 million a year on coal. That fuel saving is going to go a long way toward paying the interest on the nuke. Research has shown that heath care spending is high in areas that are close to coal fired power plants. Now it is not going to a utilities bottom line, but the nuke will save a community on health care expenses. So suppose we have a decline of 10% in health care expenses due to the switch from coal to nuclear. So we are looking at indirect benefits. Wind saves some on the fuel cost of coal, but we still end up paying 60% of what we were paying for coal after we install the wind mills. We still have kids hitting the ERs with asthma attacks. Probably not as often, true.
So the story is that Light Water Reactors are expensive, but then so are windmills and solar technology if you are going to do carbon replacement. Light Water Reactors are far from perfect, but they are safe and they produce lots of electricity. They produce nuclear waste, but nuclear waste will power generation 4 reactors and that is good not bad. Light Water Reactors may be expensive, but are cheaper than wind or sun for coal replacement. The fuel cost saved by switching to reactors will help to pay for them.
Light Water reactors will not replace coal and other fossil fuels in powering America, but neither will sun and wind. Light Water reactors are at least a start, until lower cost Generation 4 LFTRs are moving off the assembly lines.
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