Geological dating radioactive isotope

02-Apr-2020 13:17 by 4 Comments

Geological dating radioactive isotope

Used fuel from each reactor is stored on-site in deep water pools used for cooling and shielding.There are about two million used fuel bundles (0.5 m long, weighing 20 kg each) in Canada, which would fill a soccer field to the height of a player.

The vaults, tunnels, and shafts of this disposal site would be backfilled and sealed during its closure stage.

The cooling, by either water or air flow, is required because used fuel contains a small inventory of fission products (created by the fission of less than 2% of the original uranium inventory) that continue to emit energy as they radioactively decay.

In fact, immediately upon removal from the reactor core, a used CANDU fuel bundle generates about 10% of the heat that it produced in the core, but this figure drops to about 1% only a day after removal, and less than 0.1% after a year has passed.

The average heat generation of a fuel bundle at this point (one year) is about 100 W -- comparable to a household lightbulb.

The radiation accounting for this heating creates a simultaneous need for shielding.

Arthur Porter and known as the "Porter Commission") [9, 10].

In response to the Hare Report, the governments of Canada and Ontario jointly established in 1978 the Canadian Nuclear Fuel Waste Management Program (CNFWMP).Used nuclear fuel is highly radioactive, particularly within a few years of its discharge from the reactor core.The radiation is emitted by both the fission fragments (what the uranium atoms become after they split roughly in half) built up over the duration of the fuel's residence in the reactor core, and the higher actinides (what the uranium atoms become after they absorb a neutron and fail to split).The radiation level drops to about 1 Sv/h after 50 years, 0.3 Sv/h after 100 years, and less than 0.001 Sv/h (100 mrem/h) after 500 years.At this time the major hazard from the used fuel is no longer one of external exposure; for example, by these estimates, spending an hour about a foot away from a 500-year-old CANDU fuel bundle would result in radiation dose about 1/4 of the average annual background exposure, and thousands of times less than what is known to lead to physical harm.Through natural decay of the radioactive isotopes in the used fuel, a comparable toxicity with high-grade uranium ore (such as that found in Canada, although the current average ore grade is Canada is actually closer to 20% — see related FAQ) is reached after several centuries, and with lower-grade uranium ore after about 10,000 years (unless the used fuel is chemically processed to remove and recycle long-lived actinides like plutonium, in which case the time to comparable toxicity with uranium ore is again measured in centuries).

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