Nuclear, O&M, Reactors

Nuclear Performance: A Shifting Target

Issue 9 and Volume 114.

By Brian Schimmoller, Contributing Editor

We hear a lot about the commendable “performance” of the nuclear power industry. But a discussion about its performance cannot be done in a vacuum. Performance is not a static metric. It changes over time, hopefully for the better, in response to multiple factors, including technological advances, ongoing learning, the introduction of new participants and regulatory and market forces. So although the nuclear industry is performing well today, standing still will never sustain high performance, particularly as plants age and as new designs and new players come on-stage.

The World Association of Nuclear Operators (WANO) released its 2009 performance indicators report earlier this year and, while there aren’t any big surprises in the numbers, the data provide some useful insights into fleet performance. Further, as much of the world contemplates nuclear power birth, expansion or re-birth, such data also can provide insights into future expectations.

Let’s look first at safety. The WANO data reports the industrial safety accident rate, which tracks the number of accidents that result in lost work time, restricted work or fatalities per 200,000 man-hours. From 1990 to 2009, the accident rate fell from 5.2 to 0.78, a commendable 85 percent decline. The Occupational Safety and Health Administration doesn’t track accident rates in quite the same way, but injury and illness statistics reinforce the positive safety record. Nuclear is lumped into the broad “utility” category, which reports an illness and injury rate of 1.9 per 200,000 man-hours. This is better than comparable heavy industries such as manufacturing (2.7) and construction (2.5) and on par with industries such as real estate (1.8) and education and health services (2.3).

Looking forward, one might question whether similar accident rates are plausible as the global nuclear fleet grows to 500 or more reactors. Notably, over the 1990 to 2009 period covered by WANO, the number of units reporting data rose from 169 to 216. In other words, the decline in accident rate occurred even as the “population” of units expanded.

Let’s turn now to operational performance. In the nuclear industry, the scram rate provides a useful indication of effective plant operations. Unplanned scrams can lead to thermal and hydraulic transients that stress the plant, potentially shortening component life or requiring some manner of mitigation. The scram rate per 7,000 hours of critical operation declined from 1.8 in 1990 to 0.4 in 2009 according to WANO, a 78 percent drop, reflecting the industry’s attention to reliable plant operations.

Scrams challenge nuclear plant operations because their occurrence means something unexpected has happened. As the nuclear power industry expands, keeping the scram rate this low will be difficult. But it’s precisely the kind of challenge organizations like WANO were created to address through sharing of plant experiences, regular benchmarking and best-practice documentation.

Another metric, the unit capacity factor, or unit capability factor, is often used to gauge the cost-effective reliability of a given power plant, indicating how close the plant has come to generating its maximum amount of electricity possible based on nameplate capacity. Nuclear power plants typically score high on this metric and the WANO data back this up. Average unit capability factor across the world nuclear fleet climbed from 77.2 percent in 1990 to 87.3 percent in 2009. The metric has been fairly steady at 86 to 87 percent for the last five years.

One question is whether introducing new nuclear plant designs will lead to reduced reliability in the future. With little to no operational experience with the advanced Generation III/III+ designs, it’s difficult to know. A bump in the scram rate or dip in the capacity factor could almost be expected as the new designs work out the kinks. Lessons learned from the 40-plus years of commercial nuclear power, however, might eliminate or moderate this degradation.

South Korean data is revealing. The Korean nuclear fleet, which numbers 20 operational reactors with eight more in active construction or development, has progressed through several non-native designs and is now building fully Korean-designed nuclear power plants. The OPR-1000 design, first deployed at Yonggwang Unit 3 in 1995, achieved a first-year availability factor of 99.6 percent. Korea’s latest nuclear plant design, the APR-1400, could provide additional validation that new designs don’t necessarily equate to lower reliability.

It will be interesting to observe how various forces impact performance indicators. For example, will national decisions to invest heavily in nuclear power – such as in South Korea – eventually lead to nuclear cycling and loan-following more regularly? Will the introduction of renewable portfolio standards or feed-in tariffs push nuclear plants down the dispatch curve? Some Canadian, European and U.S. plants reportedly have had to dial back operations because of requirements to run renewable energy assets.

The very perception of capacity factor may need to change to account for differences in how nuclear plants are used in the future. Consider how the introduction of small modular reactors would affect nuclear fleet performance. In serving smaller, local would these plants invariably assume a cycling posture?

Although performance is not a static parameter, some performance indicators are rigid and nonnegotiable. Safety falls in this category. Other indicators, however, may take on a more amorphous character. The trick in assessing nuclear power industry performance will be in winnowing wheat from chaff.

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