Japan’s efforts to cool reactors at the crippled Fukushima Dai-Ichi plant had some success, with reports two of the six reactors are under control and a second electric cable has been connected to the station.

Tokyo Electric Power Co., the operator, declared Units 5 and 6 safe after cooling water pumped into them reduced temperatures, The Associated Press reported. An electric cable was hooked up to the No. 5 reactor, Kyodo News said, also citing Tepco.

U.S. Energy Secretary Stephen Chu said the Obama administration believes the worst of the crisis is over. Unit 2 — where Tepco connected a mile-long power cable on Friday as it tried to revive cooling systems knocked out by the magnitude-9 temblor and tsunami — is the main source of concern, Chu said on CNN’s “State of the Union” program.

“Because of the higher levels of radiation there, we take that as evidence that there might be a breach in that containment vessel,” he said. “But they’re not extraordinarily high, so it appears if there is a breach, it would be a limited breach. But, again, we don’t really know.”