TOKYO—Cooling water levels have fallen in two reactors at the wrecked Fukushima nuclear plant since a powerful earthquake hit the area last weekend, indicating possible additional damage, its operator said Friday. New damage could further complicate the plant’s already difficult decommissioning process, which is expected to take decades. Tokyo Electric Power Co. spokesman Keisuke Matsuo said the drop in water levels in the Unit 1 and 3 reactors indicates that the existing damage to their primary containment chambers was worsened by Saturday’s magnitude 7.3 quake, allowing more water to leak. The leaked water is believed to have remained inside the reactor buildings and there is no sign of any outside impact, he said. In 2011, a powerful magnitude 9.1 earthquake and tsunami damaged the Fukushima plant’s cooling systems, causing three reactor cores to melt and nuclear fuel to fall to the bottom of their primary containment vessels. TEPCO will monitor …