(CNN) -- Japan's government and the owner of the damaged Fukushima Daiichi nuclear power plant are reviewing efforts to wind down a two-month crisis that has prompted the country to re-evaluate its plans for nuclear energy.
Plant workers are making step-by-step progress toward restoring normal cooling, the Tokyo Electric Power Co. said. But nearly 80,000 people have now spent two months away from their homes in the 20-kilometer (12.5-mile) zone around the plant, while tens of thousands more are awaiting orders to evacuate more distant towns where radiation levels are likely to raise the long-term cancer risk.
Residents of several cities and towns outside the 20-kilometer zone have been told to be ready to move by mid-May. They were put on notice in April that evacuation orders would be coming in about a month, and about a third have already left, government spokesman Noriyuki Shikata said Wednesday.
"It depends on the circumstances of individuals," Shikata said. "It's a bit difficult to get the most updated figure, but I understand that over half the original residents are still residing in the zone."
In the city of Fukushima, displaced residents berated Tokyo Electric President Masataka Shimizu and other top utility executives, who asked for forgiveness on their hands and knees Tuesday.
About 100 residents from the village of Kawauchi were allowed to return home for a short visit the same day. They were issued protective gear, allowed to pack one small bag and spend two hours in their homes. Some returned to find pets -- left behind in the initial confusion -- dead of starvation, Japan's Environment Ministry reported Wednesday.
Private animal-rescue groups had mounted expeditions into the evacuation zone to rescue pets before the government began enforcing the restricted area in late April.
The two-month mark falls a day after Japanese Prime Minister Naoto Kan announced that his government will rethink its plans for nuclear energy "from scratch" as a result of the disaster. Alternative sources of energy like biomass, wind and solar "should be regarded as one of the major pillars" in a new plan, and conservation efforts will be ramped up, Kan said.
"Under the basic plan for energy in 2030, the proportion of nuclear energy and total electricity supply would be 50% for nuclear energy and 20% renewable energy," Kan told reporters Tuesday. "But with the occurrence of a major nuclear disaster, the basic plan for energy is going to have to be reviewed thoroughly from scratch."
In addition, after years of complaints from anti-nuclear activists, the Japanese government has called on Japanese utility Chubu Electric to shut down the Hamaoka nuclear power plant southwest of Tokyo. The facility sits on a fault line that Japan's science ministry says has an 87% chance of producing a massive earthquake within the next three decades.
Chubu Electric said it would suspend operations at Hamaoka "until further measures" are completed to protect the plant from a tsunami like the one that crippled Fukushima Daiichi.
Japan marked two months since the March 11 earthquake and tsunami with a moment of silence Wednesday. While no deaths have been attributed to the Fukushima Daiichi accident, the earthquake and tsunami have killed nearly 15,000 and left 10,000 more missing, Japan's National Police Agency reported.
In April, the Tokyo Electric power company laid out a 6- to 9-month plan to bring an end to the world's worst nuclear accident since Chernobyl by restoring normal cooling systems and fully shutting down the reactors. That plan is being reviewed by the utility and the government, and its results are expected to be announced in mid-May, Tokyo Electric spokesman Hiro Hasegawa said Wednesday.
The tsunami knocked out cooling systems at Fukushima Daiichi, causing the three operating reactors to overheat. That compounded a natural disaster of already-historic proportions by spewing vast quantities of radioactive material into the atmosphere.
Workers have been able to install air filters inside the No. 1 reactor building to contain radioactive particles and have begun filling the primary containment shell around the reactor core with water in an attempt to draw heat off the core. The plan is to recirculate that water through a heat exchanger to cool it, then send it back into the reactor core in hopes of covering the now-exposed fuel rods, said Yoshikazu Nagai, another spokesman for Tokyo Electric.
Similar plans are being considered for unit 2, which is believed to be leaking radioactive water, and 3, where engineers noted a disturbing rise in the reactor's temperature readings last week, Nagai told CNN.
"First we have to tackle unit No. 1, and we need to see if we can succeed," he said.
Meanwhile, equipment that will be used to decontaminate water pooling in the plant's basements is expected to arrive by mid-May. Tens of thousands of tons of radioactive water have flooded the basements where the cooling systems were housed, making it impossible for workers get into the facilities, and the company has so far managed to pump 5,600 tons of the fluid into a waste treatment reservoir at the plant.
Tokyo Electric reported a new problem Wednesday, as radioactive water was found leaking into the adjacent Pacific Ocean from a utility shaft behind the No. 3 reactor plant. Workers plugged the conduit that was pouring water into the shaft and filled it with concrete to plug the leak Wednesday evening, the company said.
Radiation levels at the water's surface were reported at 1.5 millisieverts per hour. By comparison, the average resident of an industrialized country receives about 3 millisieverts per year.
And the spent but still-energetic fuel assemblies housed in pools of water at the reactor sites remain a concern. Water samples taken Sunday from the No. 3 spent fuel pool showed a sharp spike in levels of radioactivity after finding negligible concentrations of reactor byproducts such as radioactive iodine and cesium the previous week, the company reported.
A previous increase in radiation levels in the unit 4 spent fuel pool was blamed on radioactive debris falling into that pool, which was exposed by damage to the reactor building. But the cause of Sunday's reading was unknown, Nagai said.
Tokyo Electric has "a number of balls in the air," as it tries to wind down the crisis, said Margaret Harding, a nuclear engineer and former executive at General Electric, which designed the reactors.
"We want them going in with a well thought-out plan that will succeed, because failure here is really not something any of us want them to have happen," Harding said.
CNN's Kyung Lah, Noriaki Kawai and Yoko Wakatsuki in Tokyo contributed to this report.