F O R U M O N P H Y S I C S & S O C I E T Y
of The American Physical Society
January 2002

Current Situation

The California electricity "crisis" gave national prominence, once again, to the issue of energy supply. The "crisis" apparently came and went and will likely soon be forgotten. What it did accomplish however was a more lively discussion of the importance of supply, recognizing the ever increasing demand as we electrify. In this discussion of demand came the realization that approximately 20% of the nationUs electricity was being generated by nuclear energy which was not subject to the escalating cost of natural gas that drove electricity prices far above what the public would tolerate. The net consequence of a number of factors, such as a faulty deregulation scheme that drove one of the major electric companies in California into bankruptcy, were rolling blackouts due to lack of generation at any price. Given that, in California, the construction of new plants of any type was frowned upon and the regulatory climate somewhat hostile, no company was interested in making generation investments. So, a "crisis" was created that has for the time being abated at a cost to the economy of at least $ 5 Billion.

In the rest of the world, serious people are debating the existence and implications of increasing greenhouse gases in our environment due to the burning of these same fossil fuels. While the environmental ministers of nations from around the world seek to find ways to meet the 1992 Kyoto accords which call for reductions in CO2 and other greenhouse gases to 10% below 1990 levels, the reality almost 10 years later is that CO2 emissions have not decreased at all but increased by 10%. As most know, one of the key advantages of nuclear energy is that it is essentially a greenhouse-gas-emission-free technology. Yet, at its most recent meeting of the Conference of the Parties in Bonn in July, these same environmental ministers voted to specifically exclude nuclear energy fom helping address the global warming problem. Clearly, there is something wrong here since, in the United States, nuclear energy provided over 69% of the emission-free generation, far exceeding the 30% hydroelectric power. Solar and other renewables provide the rest (~1%).

For many years, nuclear energy, while arguably a -CO2 emitting energy source, has been judged to be unacceptable for reasons of safety, unstable regulatory climate, a lack of a waste disposal solution and, more recently, economics. In recent years, however, the nuclear industry has made a remarkable turnaround. While a number of older plants have been shutdown for largely economic reasons, the 104 operating nuclear plantsU performance has increased to the point, that as an overall fleet, its capacity factor was 89% in 2000. This means that these plants were operating full power for over 89% of the year. This improvement in the last 10 years is essentially the same as building 23 new 1,000 Mwe plants in that time period, based on historical performance averages. In addition, all safety statistics, as measured by the Nuclear Regulatory Commission, have shown dramatic improvements as well. The Three Mile Island accident occurred over 22 years ago. The image of nuclear energy as an unsafe technology still persists. Yet the record is quite the opposite.

There has not been a new order for a nuclear plant since the mid 1970Us. The reason for the lack of new orders was the high capital cost. When operating in a difficult regulatory environment, utility executives simply avoided new nuclear construction and went to the cheapest and fastest way to make on-line generation available, which was natural gas. Combined cycle gas plants were the generation source of choice for many years for those companies that needed to build plants. Hence the beginning of the "crisis."

Today, utility executives still do not have new nuclear plant construction in their future plans even though the regulatory regime has stabilized. Nuclear plants are performing extremely well. Safety issues have been addressed with no new issues emerging and slow progress is being made to finally dispose of spent fuel at Yucca Mountain. What has happened is a consolidation of the utility and nuclear industry with some larger utilities purchasing existing nuclear plants from companies that do not want to be in the business. To address the inevitable problem of replacing existing generation, utilities have chosen to re-license existing plants from the current 40 years to 60 years. Several nuclear plants have applied and received Nuclear Regulatory Commission approval to do so. These extensions will allow utilities to continue to use these plants as long as they are economic and continue to be safely operated. Unfortunately, we still donUt see anybody ready to build a new nuclear plant. The reason is there is no new nuclear plant on the market that can compete with natural gas or mine mouth coal plants.

However, there are developments in two parts of the world that are aimed at changing that situation. The objective of these related efforts is to design, license, and build a nuclear power plant that can compete with natural gas. The two projects started independently but reached the same conclusions P that small modular high temperature gas reactors, that are naturally safe, can be built in two to three years and can compete in the electricity market. While the basic technology is over 20 years old, the application and concepts are quite new. The leader in this effort is ESKOM, the 5th largest utility in the world, located in South Africa. The other effort is being lead by the Massachusetts Institute of Technology with support from the Idaho Nuclear Engineering and Environmental Laboratory.

The nuclear energy plant that both groups are developing is a modular 110 Mwe high temperature, pebble bed reactor, using helium gas as a coolant and conversion fluid and gas turbine technology. The fundamental concept of the reactor is that it takes advantage of the high temperature properties of helium which permit thermal efficiencies upwards of 50%. It utilizes an online refueling system that can yield capacity factors in the range of 95%. Its modularity design concepts, in which the balance of plant can fit on a flat bed truck be shipped from the factory, allows for a 2 to 3 year construction period, with expansion capabilities to meet merchant plant or large utility demand projections.

Economic projections for the plant in South Africa indicate capital costs of between $ 800 to $ 1,000 per kilowatt. Staffing levels for an 1100 Mwe, 10 unit module are about 85, and fuel costs about 0.5 cents/kwhr. When all is combined, the total busbar cost of power ranges from 1.6 to 2 cents/kwhr. Very preliminary estimates in the US for the MIT project show higher costs but, on a relative, scale the numbers are well within the range of competitive prices with new combined cycle plants, at 3.3 cents per kilowatt hour.

What is a Pebble Bed Reactor?

Pebble bed reactors were developed in Germany over 20 years ago. At the Juelich Research Center, the AVR pebble bed research reactor rated at 40 Mwth and 15 Mwe, operated for 22 years, demonstrating that this technology works. The reactor produced heat by passing helium gas through a reactor core consisting of uranium fueled pebbles. A steam generator was used to generate electricity through a conventional steam electric plant. Germany also built a 300 Mwe version of the pebble bed reactor but it suffered some early mechanical and political problems that eventually lead to its shutdown. In December of 2000, the Institute of Nuclear Energy Technolog, of Tsinghua University in Beijing China, achieved first criticality of their 10 Mwth Mwe pebble bed research reactor. In the Netherlands, the Petten Research Institute is developing pebble bed reactors for industrial applications in the range of 15 Mwth. The attraction to this technology is its safety, simplicity in operation, modularity and economics.

Advances in basic reactor and helium gas turbine technology have produced a new version of the pebble bed reactor concept. Instead of wasting heat by using steam to produce electricity, new designs are going to direct or indirect cycle helium gas turbines to produce electricity. By avoiding the use of high temperature water all the difficulties associated with maintaining high temperature water systems is eliminated. The optimum size for a pebble bed was concluded to be about 250 Mwth thermal to allow for rapid and modular construction as well as maintaining its inherent safety features. These designs do not require expensive and complicated emergency core cooling systems since the core can not melt. These advances have lead ESKOM and the MIT team to independently conclude that the modular pebble bed reactor can meet the safety and economic requirements for a new generation. Each group is working cooperatively to develop and demonstrate the technology for commercial application. The time line for demonstration in South Africa is to have the first reference plant in startup testing in 2005 and commercial operation in 2006. Presently, a detailed design feasibility study is underway that will lead to a decision in November of 2001 as to whether the South African project will continue to build the demonstration plant. Licensing submittals are being prepared for submission to the South African nuclear regulator. In short, within the next 5 years, should this project be successful, there will be a credible nuclear alternative to fossil fuels that is projected to be competitive with natural gas even under the old, uninflated prices.

A pebble bed reactor is graphically illustrated in Figure 1. The reactor core contains approximately 360,000 uranium fueled pebbles about the size of tennis balls. Each pebble contains 9 grams of low enriched uranium in 10,000 tiny grains of sand-like microsphere coated particles, each with its own hard silicon carbide shell. These microspheres are embedded in a graphite matrix material as shown in Figure 2. The unique feature of pebble bed reactors is the online refueling capability in which the pebbles are recirculated with checks on integrity and consumption of uranium. This system allows new fuel to be inserted during operation and used fuel to be discharged and stored on site for the life of the plant. It is projected that each pebble will pass through the reactor 10 times before discharge in a three year period, on average. Due to the on-line refueling capability, plant maintenance outages are now required every 6 years.

The key reactor specifications for the modular pebble bed reactor are shown in Table 1.

Table 1
Nuclear Specifications for the MIT Pebble Bed Reactor

Thermal Power			250 MW
Core Height			10.0 m
Core Diameter			3.5 m
Pressure Vessel Height		16 m
Pressure Vessel Diameter	5.6 m
Number of Fuel Pebbles		360,000
Microspheres/Fuel Pebble	11,000
Fuel				UO2
Fuel Pebble Diameter		60 mm
Fuel Pebble Enrichment		8%
Uranium Mass/Fuel Pebble	7 g
Coolant				Helium
Helium Mass Flow Rate		120 kg/s (100% power)
Helium entry/exit temperatures  450 C/850 C
Helium Pressure			80 bar
Mean Power Density		3.54 MW/cubic meter
Number of Control Rods		6
Number of Absorber Ball Systems 18