A new report says Japan's tsunami-ravaged nuclear plant was so unprepared for the disaster that workers had to bring protective gear and an emergency manual from distant buildings and borrow equipment from a contractor.

The report by plant operator Tokyo Electric Power Co. was released over the weekend and is based on interviews of workers and plant data.

It portrays chaos amid the desperate and ultimately unsuccessful battle to protect the Fukushima Dai-ichi nuclear plant from meltdown in March in the wake of damage caused by an earthquake and subsequent tsunami.

The report shows that workers struggled with unfamiliar equipment and fear of radiation exposure.

The March 11 earthquake and tsunami destroyed the plant's power and crucial cooling systems, causing three reactor cores to melt and causing several explosions.

TEPCO has been criticized for dragging its feet on venting and sea water cooling — the two crucial steps that experts say could have mitigated the damage. Company officials have said the tsunami created obstacles that were impossible to anticipate. An investigation by an independent panel is pending.

The report revealed insufficient preparations at the plant that TEPCO hadn't previously acknowledged. It said plant workers had a disaster drill just a week before the tsunami and "everyone was familiar with emergency exits," but it apparently did not help them cope with the crisis.

When the Unit 1 reactor lost cooling functions two hours after the quake, workers tried to pump in fresh water through a fire pump, but it was broken.

A fire engine at the plant couldn't reach the unit because the tsunami left a huge tank blocking the driveway. Workers destroyed a power-operated gate to bring in the engine that arrived at the unit hours later. It was early morning when they finally started pumping water into the reactor — but the core had already melted by then.

They eventually ran out of fresh water and had to switch to sea water, which meant scrapping the reactor.

Manual not in control room

Other workers were tasked with releasing pressure from Unit 1's containment vessel to avoid an explosion. But first they had to get the manual, which was not in the control room but in a separate office building at the plant. Aftershocks struck as they retrieved it.

To activate an air-operated part of the vent, workers had to borrow a compressor from a contractor. And the workers who had to get close to the unit for the venting had to get protective gear from the offsite crisis management centre, five kilometres away from the plant.

It took an hour just to put on air tanks, coveralls and face masks before the first two workers headed for the reactor building. The operation was a relay of three two-member teams to minimize exposures.

Rising radiation also disrupted the work, the report said. The second team had to abort their mission as radioactivity almost exceeded the limit at midway. Workers had to switch to a remote control, which was less effective than having humans do the work directly.

After repeated failures, workers managed to vent the containment vessel. But an hour later, the Unit 1 building exploded, damaging similar preparations at two other units, forcing workers to start all over and causing further delays.

Eight of the workers who fought the initial crisis were found to have been exposed to high levels of radiation and were removed from plant work.

The report also said workers borrowed batteries and cables from a subcontractor on the compound to set up a backup system to gauge water levels and other key readings.