Three former executives of the Tokyo Electric Power Company, known as TEPCO, will face trial today over their roles in the disaster at the Fukushima nuclear power plant in March 2011.

Key points: TEPCO Chairman Tsunehisa Katsumata will face court today

TEPCO Chairman Tsunehisa Katsumata will face court today His two co-accused were in charge of the utility's nuclear division

His two co-accused were in charge of the utility's nuclear division It is alleged the executives had seen reports warning of a potential disaster

The men have been charged with professional negligence leading to injury or death.

While there were not any deaths directly attributable to the triple reactor-core meltdown, 44 very sick patients died after being hastily evacuated from a hospital in the evacuation zone.

TEPCO employees and members of Japan's military were also injured in the aftermath.

TEPCO Chairman Tsunehisa Katsumata will face court today — his two co-accused, Sakae Muto and Ichiro Takekuro, were in charge of the giant utility's nuclear division at the time of the disaster.

None of these men were in Fukushima on the day of the accident. Mr Katsumata was on a business trip to China when he heard the news.

It will be argued that in the years before the nuclear disaster, these executives had seen internal reports and simulations warning of the risk of a major earthquake in the region triggering a massive tsunami.

The plant was built to withstand a wave of 5.7 metres in height; the tsunami that struck was 15 metres high.

"I hope the truth of the nuclear accident comes out as it's still not clear why it happened and who was responsible," said Ruiko Muto, head of the Fukushima Nuclear Disaster Plaintiffs group.

"The people who were in charge should take proper responsibility."

Ms Muto's group has long been campaigning for charges to be laid. Prosecutors in Tokyo had decided against charges against any executives because of a lack of evidence.

The remains of the town of Rikuzentakata, where 80 per cent of homes were swept away. ( ABC News: Mark Willacy )

But in a quirk in Japan's law, a citizen's panel — which has the power to review judicial decisions — overturned the decision and charges were laid against the men early last year.

"They neglected the safety measures which they could have taken. As a result, hundreds of thousands of people's lives were turned upside down and caused huge damage," Ms Muto said.

'They're not our employees'

Kyle Cleveland, an associate professor of sociology at Japan's Temple University, said the trial is focused on how the nuclear disaster could have been prevented, rather than how it was managed.

"The charge here is that they [TEPCO] basically didn't comply with their own corporate recommendations about the protective measures along the coast and that made the plant vulnerable to the tsunami," Mr Cleveland said.

Prosecutors say they will table more than 4000 pieces of evidence in the trial. ( Reuters: Toru Hanai )

He said these three men might be taking the fall for a much larger system of regulation that was at fault in Fukushima.

"The point here is that with a disaster of this magnitude, you're dealing with an interlocking matrix of corporate entities, all of whom are partially responsible for this," Mr Cleveland said.

"To be able to focus blame on a particular individual is something that is rather difficult to do."

The trial will run for many months and prosecutors have indicated they will table more than 4000 pieces of evidence.

For its part, TEPCO is washing its hands of these three men.

"This trial is about the individuals, not the company," a spokesman told the ABC.

"As a company, we are not in a position to make any comment, they're not our employees."

The Fukushima disaster triggered an overhaul of safety at Japan's nuclear power facilities.

At the time of the disaster there were 48 nuclear reactors in operation, six years on, five reactors are currently operating.