Tepco has been walking a tightrope at the Fukushima No. 1 nuclear plant for the last three years, and many of its missteps have been glaring.

Having to clean up the worst nuclear disaster since Chernobyl was never going to be simple or easy, but senior officials of Tokyo Electric Power Co. have been forced time and again to apologize for serious problems.

Most recently, just weeks before the three-year anniversary of the start of the catastrophe, they had to admit that 100 tons of highly toxic water had leaked from one of the huge tanks set up at the site.

Tackling the buildup of highly radioactive water is proving to be a major challenge in the decommissioning process.

The direct cause of the incident was the mishandling of a valve operation, which caused contaminated water to flow into a tank that was already nearly full.

But what was more disturbing was how workers had overlooked the signs that something was wrong. The incident triggered renewed concerns over Tepco’s ability to oversee the ongoing cleanup.

“If we had acted with more care after hearing an alarm warning of a rise in the tank’s water level, we would have been able to minimize the consequences,” Tepco spokesman Masayuki Ono told a news conference after the company announced the leak Feb. 20, referring to an alarm that went off more than nine hours before workers found water spilling from the tank’s lid.

Because the water-level readings showed irregular movements following the alarm and because people on patrol were not able to find any trace of a leak near the tank in the two hours or so after the warning sounded, the utility judged that the water-level gauge had malfunctioned.

But Ono admitted that workers could have noticed the leak sooner had they gone up on the 10-meter-tall tank to check how much water it contained or if workers in a control room had paid attention to data showing that the water level in tanks designated to receive the water was not rising.

Officials at the Nuclear Regulation Authority have pointed to the need for Tepco to become more vigilant and criticized its tendency to blame abnormal data readings on mechanical failures.

“I think it is extremely important that workers assume the worst when instruments show abnormal movements, considering that the crippled plant is barely being managed,” one NRA official said.

Further efforts to eliminate human error are extremely important until the water stored in the sprawling tank farms can be decontaminated more quickly and bolted-joint tanks are replaced with more reliable containers.

Currently, a large portion of the radioactive water stored in tanks has been sent through a facility that can reduce cesium. But it still contains high concentrations of radioactive substances such as strontium, which is believed by medical authorities to cause leukemia and other kinds of bone cancer.

Tepco has said it wants to drastically reduce the radiation level of all the highly toxic water kept in tanks by the end of March 2015. The problematic water totaled some 340,000 tons as of Feb. 11.

Yet Tepco has not even finished testing a trouble-plagued system that is reportedly capable of removing 62 different types of radioactive material from the contaminated water, with the exception of tritium.

While Tepco plans to boost the processing capacity of the facility, called ALPS, an acronym standing for advanced liquid processing system, another official admitted that scrubbing the water by the end of fiscal 2014 is “an extremely lofty goal” that won’t be met unless the system can achieve a high operating rate.

Trying to address another festering wound, the next 12 months or so will be a crucial period in the unprecedented attempt to create a barrier of frozen soil around the basement areas of the buildings housing reactors 1 through 4.

The barrier of ice, which Tepco aims to start operating by the end of March 2015, is intended to block groundwater from seeping into the reactor buildings’ basement areas and mixing with highly toxic water used to cool the plant’s three crippled reactors.

Should the project be successful, it will represent major progress in fundamentally addressing the buildup of toxic water, which is increasing at a rate of 400 tons a day.

But whether it will work remains to be seen as impermeable walls of this nature, used in civil engineering works such as subway construction, have never before been created on such a large scale and have not been operated for more than around two years.

Last year, as concerns grew over leaving the huge workload of cleaning up and decommissioning Fukushima No. 1 to Tepco alone, the Abe administration decided to directly fund technically challenging projects that will help contain the toxic water buildup, including the frozen barrier, and the government is moving ahead to strengthen its monitoring of the plant’s decommissioning process.

Akira Watanabe, a professor at Fukushima University, said local people are encouraged by the central government’s increased financial support as they fear the nuclear complex might not be scrapped should Tepco’s business conditions worsen.

But Watanabe, who serves as a member of the NRA’s panel monitoring safety measures at Fukushima No. 1, is skeptical that government support alone will bring a change to the overall situation.

“I believe one of the major reasons behind the poor safety management is that Tepco has no option but to rely on massive numbers of subcontractor workers, six or seven layers in some cases,” Watanabe said. “I wonder whether safety can be managed by a company out of touch with workers involved in various operations at the plant.”