Three staff at the Lucas Heights nuclear facility have been decontaminated after being exposed to a chemical spill.

Key points: Australia's only nuclear reactor is located at Lucas Heights, about 40km south of Sydney's CBD

Australia's only nuclear reactor is located at Lucas Heights, about 40km south of Sydney's CBD Two men and a women were decontaminated and taken to Sutherland Hospital

Two men and a women were decontaminated and taken to Sutherland Hospital The facility has had several contamination scares in recent years

A spokesman for Australia's Nuclear Science and Technology Organisation (ANSTO) said the workers were exposed to sodium hydroxide when a cap came off a pipe in the nuclear medicine manufacturing building.

NSW Ambulance said the chemical splashed onto the arms and faces of the two men and a woman who have all been taken to Sutherland Hospital for further assessment.

Sodium hydroxide is corrosive and can cause severe burns.

The ANSTO spokesman said the building where the incident occurred was not associated with the nuclear reactor.

"Before 8am this morning, a cap came off a pipe resulting in a spill of around 250ml of sodium hydroxide," he said in a statement.

"Three staff members were involved. Emergency services attended ANSTO and the three staff members involved have been taken to hospital for observation.

"The incident occurred in a nuclear medicine manufacturing building that is not associated with the OPAL nuclear reactor.

"More information will be provided later today."

ANSTO apologised to a worker exposed to radioactive material in 2017. ( AAP: Tracey Nearmy )

Australian Manufacturers Workers secretary Steve Murphy said ANSTO should be the safest workplace in the country.

"ANSTO workers make vital nuclear medicine for the rest of the country, they shouldn't have to risk their health to make it," he said.

"We've had substantial complaints about the safety culture at ANSTO (and) we've expressed those complaints publicly in order to prevent this sort of situation."

Contamination scares

The Lucas Heights facility, about 40 kilometres south of the Sydney CBD, has had several contamination scares in recent years.

In August 2017 a worker suffered blisters on his hands after he dropped a vial of radioactive material and was contaminated through two pairs of gloves.

The event was deemed the most serious in the world in 2017, according to the International Nuclear Event Scale — the global grading system for nuclear incidents.

ANSTO apologised to the worker who was exposed to the radioactive material and produced an "action plan", in response.

An independent review of the facility was conducted in October 2018 and found that it failed modern nuclear safety standards and should be replaced.

In the same week ANSTO confirmed five workers had received a dose of radiation at the facility, but that the amount of radiation was "less than a chest X-ray".