A Temporary solution

When people think about the storage of used nuclear fuel, their minds often wander to episodes of the Simpsons, with images of green, glowing fuel leaking out of barrels.

These images couldn't be further from the reality of how used nuclear fuel is stored.

On the grounds of Ontario Power Generation's (OPG's) Darlington Nuclear Generating Station stands a cavernous warehouse filled with hundreds of large, white concrete containers.

These 73-tonne reinforced concrete containers, known as dry storage casks, contain cylindrical bundles of used nuclear fuel.

There's currently 224 dry storage casks at the Darlington waste management facility, although the building will hold up to 500.

OPG also has five similar warehouses at the Pickering nuclear plant and the Bruce nuclear plant, which currently store 1,370 dry storage casks.
At capacity, the buildings in Pickering and Kincardine will hold more than 2,000 of these casks.

In total, the 1,594 dry storage casks currently stored by OPG contain 612,096 bundles of used nuclear fuel.

For now, this is how the province stores its used nuclear fuel.
Ted Gruetzner, a spokesperson for OPG, said storing the material in this manner is extremely safe.

“They've been storing this material on site for a number of years, and we've never had any issues,” he said.

Quebec and New Brunswick use minor variations on their storage process — Quebec's fuel is stored in concrete vaults, and New Brunswick's in concrete vaults. In the United States, the fuel is stored in water-filled pools.

But the country's used nuclear fuel can only be managed this way for so long, explains Mike Krizanc, a spokesperson for the Nuclear Waste Management Organization (NWMO).

The NWMO has been tasked with finding a solution for storing the country's nuclear fuel.

Through public consultations, the organization determined that the best option would be to bury the waste 500 metres underground in a facility known as a deep geological repository.

“Leaving the used fuel at reactor sites was one of the many options that was considered,” Krizanc said.

“But when people looked at the options, and determined that safety and security was the most (significant) requirement of the long-term management approach, they said that yes, it's safe and secure where it is now, but over the very long term it has to be carefully managed, a deep geological repository is safer.

“In addition to the safety and security aspect, there's the ethical consideration. Canadians said we should not leave this used nuclear fuel as a legacy for future generations to look after. This generation has to take responsibility for it now.”

If the used nuclear fuel were left on the surface indefinitely, it would have to be “repackaged” in new dry storage casks roughly every 100 years, Krizanc said.

Once the material is in a sealed deep geological repository, it doesn't require any more human intervention, he said.

When used fuel bundles are removed from the nuclear reactors, they're placed in a water-filled bay for at least 10 years, during which they cool and become less radioactive.

Gruetzner said the fuel bay area is safe for employees to work in.
“Water acts as a very effective shield,” he said.

“Workers in this area generally do not require any special protective clothing. Depending on the work - and as a conservative measure - additional protection such as tyveck coveralls maybe be worn depending on the work.”

As part of the country's adherence to the nuclear non-proliferation treaty, OPG must account for each and every bundle of nuclear fuel when asked by inspectors from the International Atomic Energy Agency (IAEA).

“IAEA inspectors regularly visit our site - often unannounced - to verify compliance and high standards in meeting the international safeguard requirements,” Gruetzner said.

There's also a constant live feed in all of the fuel bays, which is monitored and recorded by the IAEA.

Once the fuel has cooled in the fuel bays, the dry storage cask is loaded by submersing the base into one of the bays, where fuel bundles are loaded into the container under water.

The lid of the container is then installed and secured to the base with a clamp.

The container, now holding 384 used fuel bundles, is removed from the bay, drained, decontaminated and vacuum dried. It's then moved to the storage facility with a large transport vehicle.

Once there, the lid is welded to the container's base with 10 passes.
After the inside of the container has been vacuum dried, it is filled with helium gas, which provides a means of leak detection for the sealed container, and creates an inert atmosphere for the stored used fuel.

Before the container is placed into storage, safeguard seals are applied by an inspector from the IAEA.

“These tamper-proof seals are checked and validated by IAEA representatives,” Gruetzner said.

The casks themselves are made of reinforced, high-density concrete roughly 20 inches thick, and is lined inside and outside with half-inch-thick steel plates.

They've been tested to ensure they'd survive disasters such as fires and storms, he said.

“They're also in an area that has very heavy security, in terms of fencing and armed security staff,” Gruetzner said.

The radiation levels given off by the casks are “very low” because of the thickness of the containers.

“There is no risk to the public, and the risk to staff is very low,” he said.

For more information about OPG's waste management facilities, visit www.opg.com.

Footnote:

Low-level waste is minimally radioactive materials that have become contaimnated during routine cleanup and maintenance, such as mop heads, cloths, paper towels and protective clothing.

Intermediate-level waste consists primarily of used reactor core components and filters used to keep water systems clean.

OPG stores low-level waste in concrete warehouse structures and the intermediate-level waste in steel-lined concrete structures partially buried in the ground. Both types of waste are stored at the Bruce nuclear site.

However, OPG has contracted the NWMO to seek regulatory approval to build a deep geological repository for this material on the Bruce nuclear site.

Posted by Arron Pickard