Political activist Srisuwan Janya has urged locals in Nakhon Nayok to rally against the 20-megawatt nuclear reactor to be built on the bank of Nakhon Nayok River at the project's third public hearing on Sunday.
According to Mr Srisuwan, the government first pushed for the 10-megawatt nuclear reactor project in Ongkharak district of Nakhon Nayok in 1990.
However, the project ground to a halt in 2010 due to corruption allegations and resistance from residents.
In 2017, attempts to rebuild the nuclear reactor were revived, only for the project to go into limbo again.
Most recently, public hearings have been organised as its proponents try to get it off the ground again.
The third and last hearing is scheduled to be held on Sunday.
Mr Srisuwan said the main obstacle has been residents' concern over radioactive contamination of water sources including Bang Pakong River in nearby Chachoengsao and Rangsit Canal in Pathum Thani, which is connected to the Chao Phraya River in Bangkok.
He also said a study on the feasibility of the project, conducted in 1990, contained outdated information and now contradicts design principles prescribed by the International Atomic Energy Agency (IAEA) as most parts of the Nakhon Nayok blueprint cover land intended for agriculture or residential areas.
Mr Srisuwan also alleged some residents may have been bankrolled to vote in support of the project.
He cited the case of water recently discharged from the ruined Fukushima Daiichi nuclear power plant which he said has hurt Japan's reputation on a global scale.
The Thai government has never fully briefed the public about what will be the country's biggest nuclear reactor, he claimed.
In light of this, he said he was calling on residents in Nakhon Nayok to attend en masse the public hearing on Sunday.