Nuclear Power Debate - Reliability

Reliability

See also: Intermittent power sources and Energy security and renewable technology

In 2010, the worldwide average capacity factor was 80.1%. In 2005, the global average capacity factor was 86.8%, the number of SCRAMs per 7,000 hours critical was 0.6, and the unplanned capacity loss factor was 1.6%. Capacity factor is the net power produced divided by the maximum amount possible running at 100% all the time, thus this includes all scheduled maintenance/refueling outages as well as unplanned losses. The 7,000 hours is roughly representative of how long any given reactor will remain critical in a year, meaning that the scram rates translates into a sudden and unplanned shutdown about 0.6 times per year for any given reactor in the world. The unplanned capacity loss factor represents amount of power not produced due to unplanned scrams and postponed restarts.

The World Nuclear Association argues that: "Obviously sun, wind, tides and waves cannot be controlled to provide directly either continuous base-load power, or peak-load power when it is needed,..." "In practical terms non-hydro renewables are therefore able to supply up to some 15–20% of the capacity of an electricity grid, though they cannot directly be applied as economic substitutes for most coal or nuclear power, however significant they become in particular areas with favourable conditions." "If the fundamental opportunity of these renewables is their abundance and relatively widespread occurrence, the fundamental challenge, especially for electricity supply, is applying them to meet demand given their variable and diffuse nature. This means either that there must be reliable duplicate sources of electricity beyond the normal system reserve, or some means of electricity storage." "Relatively few places have scope for pumped storage dams close to where the power is needed, and overall efficiency is less than 80%. Means of storing large amounts of electricity as such in giant batteries or by other means have not been developed."

According to Benjamin K. Sovacool, most studies critiquing solar and wind energy look only at individual generators and not at the system wide effects of solar and wind farms. Correlations between power swings drop substantially as more solar and wind farms are integrated (a process known as geographical smoothing) and a wider geographic area also enables a larger pool of energy efficiency efforts to abate intermittency.

Sovacool says that previously intermittent sources such as wind and solar can displace nuclear resources. "Nine recent studies have concluded that the variability and intermittency of wind and solar resources becomes easier to manage the more they are deployed and interconnected, not the other way around, as some utilities suggest. This is because wind and solar plants help grid operators handle major outages and contingencies elsewhere in the system, since they generate power in smaller increments that are less damaging than unexpected outages from large plants".

According to a 2011 projection by the International Energy Agency, solar power generators may produce most of the world’s electricity within 50 years, with wind power, hydroelectricity and biomass plants supplying much of the remaining generation. "Photovoltaic and concentrated solar power together can become the major source of electricity". Renewable technologies can enhance energy security in electricity generation, heat supply, and transportation.

Amory Lovins explains that even large nuclear plants cannot supply continuous baseload electricity:

"All sources of electricity sometimes fail, differing only in how predictably, how often, how much, for how long, and why. Even the most reliable giant power plants are intermittent: "they fail unexpectedly in billion-watt chunks, often for long periods. In the United States, 132 nuclear plants were built, and 21% were permanently and prematurely closed due to reliability or cost problems, while another 27% have at least once completely failed for a year or more. The remaining U.S. nuclear plants produce approximately 90% of their full-time full-load potential, but even they are not fully dependable. Reliably operating nuclear plants must shut down, on average, for 39 days every 17 months for refueling and maintenance.

"To cope with such intermittence by both nuclear and centralized fossil-fuelled power plants, utilities must install a "reserve margin" of roughly 15% extra capacity, some of which must be continuously fuelled, spinning ready for instant use. Regions which depend heavily on nuclear power "are particularly at risk because drought, a serious safety problem, or a terrorist incident could close many plants simultaneously".

Lovins says that nuclear plants have an additional disadvantage: for safety, they must instantly shut down in a power failure, but for nuclear-physics reasons, they can’t be quickly restarted. For example, during the Northeast Blackout of 2003, nine perfectly operating U.S. nuclear units had to shut down. For the first three days after restart, when they were most needed, their output was below 3% of normal.

Since nuclear power plants are fundamentally heat engines, waste heat disposal becomes an issue at high ambient temperature. Droughts and extended periods of high temperature can "cripple nuclear power generation, and it is often during these times when electricity demand is highest because of air-conditioning and refrigeration loads and diminished hydroelectric capacity". In such very hot weather a power reactor may have to operate at a reduced power level or even shut down. In the 2006 European heat wave, a number of nuclear plants had to secure exemptions from regulations in order to discharge overheated water into the environment; several European nations were forced to reduce operations at some plants and take others offline and France, normally an electricity exporter, had to buy electricity on European spot market to meet demand. In 2009 in Germany, eight nuclear reactors had to be shut down simultaneously on hot summer days for reasons relating to the overheating of equipment or of rivers. Overheated discharge water has resulted in significant fish kills in the past, impacting livelihood and raising public concern.