By Steve Kingstone
BBC Sao Paulo correspondent
Inspectors from the United Nations nuclear watchdog are due to begin a visit to Brazil on Monday to examine the country's plans to enrich uranium.
Brazil insists some of the plant is off-limits to inspection
The Brazilian government says its plant at Resende, near Rio de Janeiro, is designed solely to generate energy.
But the International Energy Agency (IAEA) team will need to be satisfied that none of the nuclear material is being diverted into weapons production.
This is not the first time Brazil has ventured into nuclear territory.
The country's interest in nuclear technology stretches back more than half a century.
The defining decade was the 1970s, when Brazil's then military rulers set up the first nuclear power plant.
They tried to move in secret beyond energy and into weapons production, with little practical success, according to independent experts.
Today the government's energy programme is more open to scrutiny by the academic community.
And things are very different from the secretive past, according to Alejandro de Toledo of Sao Paulo University.
"The nuclear energy programme in Brazil was closed to the very small circle in the government and the academic world had no access to it," he said.
"Nowadays the Brazil government wants the real collaboration of the academic world, of the university, with the atomic energy commission. This ensures that the programme will be more transparent."
But despite the new openness, the IAEA will find that some of today's technology is off-limits.
The Brazilian government says the centrifuge responsible for enrichment is too commercially sensitive to be shown in full.
The agency is used to access negotiations of this kind but it has strict criteria for what the inspectors must see to give Brazil the green light to move forward.