The impact of the magnitude-6.8 earthquake July 16 off Niigata Prefecture on Tokyo Electric Power Co.'s Kashiwazaki-Kariwa nuclear power plant was clearly felt Aug. 22 when TEPCO, on short notice, requested that 23 large-lot industrial customers cut back on their use of electricity that afternoon.

The closure of the 8.21-million-kW nuclear power plant and a surge in air conditioner use during the current heat wave necessitated taking the emergency adjustment measure for the first time since August 1990. Depending on weather conditions, TEPCO may be forced to take a similar measure again.

With the help of other power companies and the cooperation of large-lot industrial customers, the Tokyo utility perhaps will be spared having to suspend delivery of electricity. But the shaky power-supply situation offers an opportunity to rethink the nation's power supply for the mid- and long range. The government and power industry have pushed the policy of using nuclear power plants as a base portion of supply and thermal power plants as a means of meeting changes in demand. For TEPCO, as of March 31, nuclear power accounted for 28 percent and thermal power 57 percent of its total output capacity of 61.83 million kW.