April 15, 2008

Developing the next generation of reactors

By James M. Hylko

In any technology-based business, after its scientists unlock nature’s secrets, its engineers use that knowledge to design new products that we eventually can’t live without. Without scientists, there are no technical advances. Without engineers, there are no products. One of the greatest challenges for a technology-based company is to focus its R&D investments in areas with the greatest potential payoff. Such is the case for the U.S. nuclear power industry.

This article summarizes the relative merits of several nuclear power systems that are under development and competing for attention and investment. To get a sense of how stiff the competition is, consider this comparison: Last year, Microsoft spent over $7 billion in R&D to stay competitive in the burgeoning market for online services, with the expectation of earning many times that sum in the future; the DOE’s total budget for “science & technology” for this fiscal year is $3.9 billion.

Generation next

Three generations of nuclear power systems, derived from designs originally developed for naval use beginning in the late 1940s, are operating worldwide today (Figure 1). The first generation consisted of early prototype reactors from the 1950s and ’60s, such as Shippingport (1957–1982), Dresden-1 (1960–1978), and Calder Hall-1 (1956–2003) in the UK. There are only two commercial Generation I (Gen I) plants still operating: Oldbury nuclear power station, owned by the British Nuclear Group and scheduled for closure this year, and Wylfa nuclear power station in Wales, scheduled for closure in 2010.

1. The evolution of nuclear power reactors. More than two dozen Generation III+ reactors based on five different technologies are planned for the U.S. Generation IV reactors are expected to be available around 2030. Source: DOE

The Gen II systems began operation in the 1970s and comprise the bulk of the world’s 400+ commercial pressurized water reactors (PWRs) and boiling water reactors (BWRs). These reactors, typically referred to as light-water reactors (LWRs), use traditional “active” safety features involving electrical or mechanical operations available on command. Some engineered systems still operate passively (for example, using pressure relief valves) and function without operator control or loss of auxiliary power.

Time is money

A few Gen III plants have already been built. The most visible is an advanced BWR that entered service in Japan in 1996. None are in service today in the U.S., although the Nuclear Regulatory Commission (NRC) lists more than two dozen in its certification queue. All of the proposed reactor designs being scrutinized by the NRC are considered Generation III+ designs: Areva’s evolutionary pressurized water reactor or EPR, GE’s enhanced simplified BWR or ESBWR, Westinghouse’s APR1000 as amended, and Mitsubishi Heavy Industries’ advanced PWR or ABWR.

The only examples of a Gen III reactor design in operation are six ABWRs, including four in Japan. Hitachi carefully honed its construction processes during the building of the Japanese units. For example, Kashiwazaki Kariwa Unit 7 broke ground on July 1, 1993, went critical on November 1, 1996, and began commercial operation on July 2, 1997—four years and a day after the first shovel of dirt was turned. If the U.S. nuclear power industry were to adopt Hitachi’s construction techniques (for details, see POWER, May 2007, p. 43) in coming years, many billions of dollars and years of time could be saved.

There’s no denying that the first three generations of nuclear reactors have been economically successful, after enduring the usual reliability growing pains early in their lives. According to the Nuclear Energy Institute, U.S. nuclear power plants in 2006 supplied the second-highest amount of electricity in the industry’s history while achieving a record-low average production cost of 1.66 cents/kWh. In fact, average production costs have been below 2 cents/kWh for the past eight years while capacity factors have remained higher than 90%. What’s more, efficiency improvements to operations over the past decade have yielded the equivalent of some 20 new nuclear plants.

The Gen III and Gen III+ systems began development in the 1990s by building on the operating experience of the American, Japanese, and Western European LWR fleets. Perhaps their most significant improvement over second-generation designs is the incorporation of “passive” safety features that do not require active controls or operator intervention; instead, they rely on gravity or natural convection to mitigate the impact of abnormal events. This feature, among others, will help expedite the reactor certification review process and thus shorten construction schedules. Once plants using the Gen III and Gen III+ reactors come on-line, they are expected to achieve higher fuel burn-up (reducing fuel consumption and waste production (see sidebar, "Now you're cooking with thorium") and operate for up to 60 years.