Japanese people are discussing about the resumption of nuclear plants after the result of last week's Tokyo gubernatorial election and the Chubu Electric Company's application for a state safety assessment of the No. 4 unit at its Hamaoka nuclear power plant.
Fears of electricity supply shortage encourage people who support the resume of nuclear units.
Kansai Electric Power Company has been spending the first high electricity demand season without nuclear units. Although the company had expected a very severe situation, its spare supply capacity has been secured enough. KEPCO's spare capacity slipped below the 8% of stable level only once since the beginning of this winter. Meanwhile, Tokyo Electric Power Company's spare capacity has dropped below 8% four times in this season. However, both two major power companies have not recorded less than 5% of spare capacity.
One of the major reasons why Japanese utility firms have avoided the critical situation is declining electricity demand in the country. Efforts of saving power and changes of industrial and social structures have cut Japan's power consumption. Electricity demand in the nation basically has shown year-on-year decrease after the severe earthquake in March 2011. The tendency is likely to continue.
On the other hand, people who request the resume of nuclear units often mention about the overuse of aging thermal power units.
Utilization rates of thermal power units by Japanese electricity companies have increased from around 40% to about 60%. It rises toward 70% during the high demand season.
Generally speaking, the 60% utilization rate is not much high. But thermal power units in Japan had been used to make up the demand gap between day time and midnight. Therefore, power companies do not have enough system to maintain high utilization rates at thermal power units for long hours.
Moreover, thermal power units that account for about half of entire thermal power generation capacity in Japan have more than 30-years age. Units that account for 20% of the total capacity have more than 40-years age. Those units seem to have exceeded their useful life.
The serious power supply shortage caused by accidents at thermal power units might be seen in Japan in the near future. Power companies need to replace their aged thermal power units urgently or to resume nuclear units.