Weapons-grade uranium is quietly being transported within Canada, and into the United States, in shipments the country's nuclear watchdog wants to keep cloaked in secrecy.

A confidential federal memo obtained through the Access to Information Act says at least one payload of spent, U.S.-origin highly enriched uranium fuel has already been moved stateside under a new Canada-U.S. deal.

The shipments stem from the highly publicized agreement signed last year by Prime Minister Stephen Harper and U.S. President Barack Obama, amid fears that nuclear-bomb-making material could fall into the hands of terrorists.

The Canadian stash gradually being shipped from Chalk River, Ont., contains hundreds of kilograms of highly enriched uranium — large enough to make several Hiroshima-sized nuclear bombs.

But even as the radioactive freight travels toward the U.S. border, the Canadian Nuclear Safety Commission has no plans to hold public hearings or disclose which communities lie along the delivery route.

The shipments themselves are protected by intense security protocol, which means specifics like routes, transportation method, quantities and schedules remain top secret.

The federal nuclear body, a co-regulator of the uranium transfers, says rules restrict it from disclosing such information to the public.

A ministerial memorandum, classified as "Secret," says the nuclear watchdog considers it unnecessary to hold public sessions that would allow citizens to ask questions and comment on the shipments.

'Intense' interest in similar case

That same memorandum, dated Feb. 25, 2011, points out that recent hearings for another nuclear-shipment case generated intense public and media interest. The controversy has stalled the project to ship 16 generators from a Bruce Power nuclear plant through the Great Lakes, up the St. Lawrence River and on to Europe.

"Given the public and media interest surrounding Bruce Power's plan ... there may be an expectation that similar information be made public on the shipments of spent HEU (highly enriched uranium) fuel to the U.S., and that the CNSC (Canadian Nuclear Safety Commission) hold public hearings," said the document, addressed to then natural resources minister Christian Paradis.

The government added that there has never been a significant transport accident involving nuclear materials, anywhere in the world, and that such shipments occur regularly in Canada.

It said only authorized people or agencies, like police forces along the shipment route, are made aware of the details.

One nuclear expert said theft is the primary concern when shipping highly enriched uranium fuel — because there is virtually no danger of leaks or explosions.

"If I were the people doing the shipping and so on, I'd want to keep as low a profile as possible … you don't want to give terrorists or criminals any advantage," said Bill Garland, a professor emeritus from McMaster University in nuclear engineering.

Containers resistant to collisions

As for non-theft incidents, like possible road accidents, he described the containers carrying the substance as highly resistant to collisions, chemicals, fire and explosions.

Garland added that drivers share Canadian highways every day with trucks carrying loads of liquid chemicals, like gasoline and chlorine, that would pose a much bigger danger in a smash-up than nuclear waste.

While the risks are small, he said, that doesn't mean they don't exist. He warned that radiation could be released if someone deliberately opened a container, for instance.

Garland said moving uranium poses far more danger than shipping Bruce Power's old generators up the St. Lawrence.

Canada has been importing highly enriched bomb-grade uranium from the U.S. to make medical isotopes at Chalk River for the past two decades. While Canada has been pushing for all nations to move to low-enriched uranium, it maintains a large inventory of the substance at Chalk River.

The Canada-U.S. agreement is part of a broader international project by the Obama administration to consolidate highly enriched uranium at fewer, more secure sites around the world.

The U.S. government says it wants to convert the uranium into a form that cannot be used to build nuclear weapons.