On Monday, the BBC's Panorama programme uncovered several safety concerns, from staffing levels to waste storage.
The Mannin Branch of the Celtic League has called on the Manx government to campaign for a full, independent inspection of the plant in Cumbria.
Sellafield says the site is safe and has been improved with significant investment in recent years.
A spokesman added: "Safety is our priority and we are managing a very complex site which has got a great deal of hazardous radioactive materials on it."
The Isle of Man is located about 34 miles (55km) from the nuclear fuel reprocessing plant.
Due to its potential impact on the Manx fishing industry, the Manx government began monitoring radioactivity levels in the Irish Sea in 1989.
A government spokesman said: "Seafood fished in Manx waters can contain traces of radio-nuclides associated with effluent discharges from Sellafield to the Irish Sea, therefore these are monitored regularly to confirm that they remain well below maximum safe limits."
The BBC investigation was prompted by a whistle-blower - a former senior manager who was worried by conditions at the plant.
He said his biggest fear was a fire in one of the nuclear waste silos or in one of the processing plants.
The Manx government said it was particularly concerned about "the structural integrity of ageing waste storage ponds and silos".
A spokesman added: "However we are content that Sellafield Ltd and the nuclear regulators are trying to improve the safety situation.
"The government has asked questions about the technical solutions being developed to decommission these redundant structures and representatives have visited the site to look at the work under way".
The Manx government is "concerned" about the safety of the Sellafield nuclear site, a spokesman said.