Power plant performance
TMI versus Fukushima1 June 2012
Although famous for its effect in reforming the US nuclear industry, the Three Mile Island accident of March 1979 was not known for its impact on operating units. A new analysis of performance data from 1979 and 1980 has revealed some intriguing parallels between the effects of the two accidents. By Caroline Peachey
February 1979, the month before the TMI accident, was a record-breaking month for nuclear power generation in the USA. Nuclear power generated 26 TWh of electricity that month; up 19% on the previous year according to old figures from the US Department of Energy.
As shown in the graph below, the decline in US reactor performance begins in the second quarter of 1979, and by the end of that year the average annual load factor for US reactors had fallen from 65% to 54.6%.
Furthermore, NEI load factor league tables for 1979 (NEI March 1980 pp. 58-50) report that five US units were among the top ten performers in terms of average annual load factor. The following year just one unit, Nine Mile Point 1, remained in this list with a load factor of 84.8% (ranked ninth). NEI also noted a sharp decline in pressurised water reactor (PWR) annual performance figures (at the time 41 of the world’s 67 PWRs were in the USA.)
In 1979, immediately after the TMI accident, the US nuclear regulator ordered other B&W pressurized water reactors to shut down. The units affected were TMI 1 (which was about to start up following a refuelling outage), Rancho Seco in California, Davis Besse in Ohio, Oconee (three units) in South Carolina, and Crystal River in Florida.
The main issue for the commission at that time was whether or not the licensed operators of the B&W units understood exactly what had happened at TMI and what lessons they needed to learn from the accident. There is an uncorroborated report that operators at the B&W plants had to take a locally-administered lessons-learned examination and receive a score of 90% or higher before the units would be allowed to restart.
In addition, all US nuclear power plants had to meet the regulator’s short-term procedural- and equipment-related requirements. Five units also remained offline for seismic upgrades.
By the mid-1980s, performance started to pick up; NEI reported that over half of the operating reactors in the States had met the NRC’s short-term requirements by end of 1979.
Following on from these near-term (and little-known) impacts of TMI, it is important to note the wider impact, which was much more far-reaching and long-term. The president’s commission on the accident at Three Mile Island (the Kemeny Commission) made numerous recommendations to the industry as well as to the regulator. The industry addressed most, if not all, of the recommendations by creating the Institute of Nuclear Power Operations (INPO).
There were several physical reactor modifications that resulted from TMI, most notably a reliable physical position indication for the power-operated relief valve. Other changes included a meter that measured subcooling in the primary system and human factors upgrades in the control room.
More than 30 years on, parallels can be drawn between Fukushima and TMI.
First, there is the operational impact of Fukushima in Japan, which is much more marked than that following TMI. By the end of 1980 the average annual load factor for US reactors was 10 percent lower than it had been in 1979. In Japan, the average load factor in 2011 was 39.5%, nearly half the figure for 2010 (69.5%). Furthermore, since February 2011 the average monthly load factor for Japan’s nuclear power plants has declined by more than 90% from 70.6% for Feb. 2011 to just 6.1% for Feb. 2012.
Both the TMI accident and Fukushima raised concerns about the security of electricity supply. The impacts were again more significant in Japan, where nuclear supplies more than a third of the country’s electricity. In 1979, nuclear energy accounted for 11% of electricity generation in the United States (around 20% today). Nevertheless, at the time there were still concerns about power shortages, with the NRC being urged for example to permit some of the Oconee units to stagger the shutdowns to avoid power shortages in the winter of 1980. In Japan, old thermal power stations were started up to compensate for the lack of nuclear electricity and utilities asked customers to reduce their electricity use.
In terms of the industry response, Japan has set up its own lessons-learned task force and plants are implementing additional measures to protect against earthquakes and tsunami, including installing seawalls, waterproofing equipment and adding hardened vents.
As with TMI, the focus is on learning the lessons from the Fukushima accident, which, like TMI, is likely to focus at least partly on instrumentation & control factors. For example, the US NRC has ordered US plants to install spent fuel pool water level indicators.
Japan is in the process of setting up its own INPO-like organization with the aim of improving nuclear reactor training and operation. Led by the Federation of Electric Power Companies, this organization should be up and running by the end of 2012.
In terms of international response, it appears that Germany’s knee-jerk reaction to immediately shut down its older units had parallels with what happened in 1979.
In the immediate aftermath of the TMI accident, the Tihange pressurized water reactor in Belgium was shut for three days out of concern for safety problems. NEI reported that police arrived at the Tihange site at night on Friday 30 March with an order from the mayor of Huy to close the reactor. However, in that case, the decision was quashed by ministerial order and the reactor was back online by the following Monday.
This article was first published in the May 2012 issue of Nuclear Engineering International