Low- and intermediate-level waste

Amara takes Hana to see where the station's low- and intermediate-level waste goes. At the waste processing building, bags of protective clothing are sorted, compacted into drums and loaded onto trucks for the Western Waste Management Facility at the Bruce site. "Most of what we handle is like this," Amara says. "Very little activity, a lot of volume. The craft is in reducing the volume, packaging it properly and knowing exactly what is in each package."

Where the waste comes from

Nuclear power plants produce low- and intermediate-level waste during normal operation and maintenance, and in much larger amounts during refurbishment and decommissioning. Operational wastes include protective clothing, rags, tools and plastic sheeting; filters and ion-exchange resins that clean the reactor coolant, moderator and pool water; and contaminated equipment. Refurbishment and decommissioning add activated components such as pressure tubes, calandria tubes, reactor vessel internals and steam generators, as well as large volumes of slightly contaminated concrete and metal. Hospitals, universities, research laboratories and industry produce smaller amounts.

Activation and contamination are the two ways material becomes radioactive. Activation happens when neutrons are absorbed by stable nuclei in reactor components, turning, for example, cobalt-59 in steel into cobalt-60. Contamination happens when radioactive material from the coolant or fuel is deposited on a surface. Contamination can often be removed by cleaning; activation is in the material itself and cannot.

Treatment and conditioning

Treatment reduces the volume of waste or changes it into a more suitable form; conditioning puts it into a stable form inside a container suitable for storage and disposal. Common treatment methods include compaction, in which dry waste is pressed into drums or the drums themselves are crushed by a supercompactor; incineration, which can reduce the volume of combustible waste by a factor of 50 or more, leaving ash to be conditioned; and decontamination of metals, which can allow them to be melted and recycled. Conditioning methods include cementation, in which resins, sludges or ash are mixed with cement, and drying or polymer encapsulation of resins.

# Low-level waste: decay of short-lived nuclides during storage and the effect of compaction.
import math
nuclides = [("Co-60", 5.27, 2.0e5), ("Cs-137", 30.1, 5.0e4), ("C-14", 5700.0, 1.0e3)]   # half-life y, Bq/g
for years in (0, 10, 50, 100):
    tot = 0.0; parts = []
    for n, hl, a0 in nuclides:
        a = a0 * math.exp(-math.log(2) * years / hl); tot += a; parts.append(f"{n} {a:9.2e}")
    print(f"after {years:3d} y: " + "  ".join(parts) + f"   total {tot:9.2e} Bq/g")
drums, factor = 1000, 5.0
print(f"compacting {drums} drums at a volume reduction factor of {factor:.0f} leaves the volume of {drums/factor:.0f} drums")

after   0 y: Co-60  2.00e+05  Cs-137  5.00e+04  C-14  1.00e+03   total  2.51e+05 Bq/g
after  10 y: Co-60  5.37e+04  Cs-137  3.97e+04  C-14  9.99e+02   total  9.44e+04 Bq/g
after  50 y: Co-60  2.79e+02  Cs-137  1.58e+04  C-14  9.94e+02   total  1.71e+04 Bq/g
after 100 y: Co-60  3.88e-01  Cs-137  5.00e+03  C-14  9.88e+02   total  5.99e+03 Bq/g
compacting 1000 drums at a volume reduction factor of 5 leaves the volume of 200 drums

The output shows that cobalt-60, with a half-life of 5.3 years, decays by more than a factor of 700 in 50 years and essentially disappears in a century, while caesium-137 falls only by a factor of three in 50 years and carbon-14 hardly changes. This is the logic of near-surface disposal: the short-lived nuclides that dominate the early activity decay within the few hundred years of institutional control the site is designed for, but long-lived nuclides such as carbon-14 must be limited in the waste accepted. The compaction line shows how volume reduction lowers storage and disposal costs.

Storage and disposal

In Canada, OPG stores the low- and intermediate-level waste from all of its stations at the Western Waste Management Facility at the Bruce site, which includes incineration and compaction facilities, low-level storage buildings and in-ground containers for intermediate-level waste. OPG proposed a deep geological repository for this waste at the Bruce site, about 680 m below ground in limestone, but withdrew the proposal in 2020 after the Saugeen Ojibway Nation voted against it. Canadian Nuclear Laboratories has proposed a Near Surface Disposal Facility at Chalk River for low-level waste; the CNSC authorised its construction in 2024, and the decision was then challenged in the Federal Court by the Kebaowek First Nation over the adequacy of consultation. The Port Hope Area Initiative has moved historic low-level waste from the town into two engineered mounds at Port Hope and Port Granby.

In 2023, after a national engagement process, the NWMO published its Integrated Strategy for Radioactive Waste, which recommended a deep geological repository for intermediate-level waste and non-fuel high-level waste and several near-surface disposal facilities for low-level waste. The NWMO has been given responsibility for planning the intermediate-level repository, which would be separate from the used fuel repository described in the next two lessons.

Decommissioning waste

Decommissioning a power reactor produces large volumes of waste, most of it very low-level or low-level. Activated components near the core, such as reactor vessel internals or, in a CANDU, pressure tubes and calandria tubes, are the main intermediate-level wastes. Careful characterisation, segmentation and sorting are essential, because the cost of disposing of slightly radioactive concrete as low-level waste is far higher than recycling or disposing of it as cleared material if it meets clearance levels.

The shutdown of two of the units at OPG's Pickering station in 2024, the planned refurbishment of its other units, and the refurbishments at Darlington and Bruce have given Canadian industry extensive experience in handling and packaging activated components.

Packaging and storage of intermediate-level waste

Intermediate-level waste needs shielding, so it is stored in thick concrete or steel containers, in in-ground structures or in shielded buildings. Activated components removed during refurbishment, such as CANDU pressure tubes and calandria tubes, are cut into sections, placed in shielded containers and transferred by remote handling. Ion-exchange resins with high activity are stored in tanks or dewatered into high-integrity containers. Because these wastes contain long-lived nuclides such as carbon-14, chlorine-36 and nickel-59, they must eventually go to a facility deeper than a near-surface trench.

At the Western Waste Management Facility, OPG stores intermediate-level waste in in-ground containers, trenches and tile holes, which are lined concrete holes in the ground, as well as in above-ground structures. Refurbishment waste from Darlington, Bruce and Pickering is packaged in purpose-built containers. The volume of intermediate-level waste is much smaller than that of low-level waste, but its management will last much longer, since it will await the NWMO's intermediate-level repository.

Design of near-surface facilities

A modern near-surface disposal facility is far more than a trench in the ground. It is an engineered structure with several barriers: a durable waste package, cement or grout filling the spaces between packages, a concrete vault or a carefully designed cell with a low-permeability liner, a drainage system to collect any water that enters during operation, and a multi-layer cover that sheds rainwater, resists erosion and deters intrusion by plants, animals or people. Monitoring wells around the site check that nothing leaks into groundwater. After closure, the site is kept under institutional control, typically for 100 to 300 years, during which access is restricted and monitoring continues.

The safety assessment of a near-surface facility considers both expected evolution, such as slow degradation of the cover and concrete, and less likely events, such as a person drilling a well or building a house on the site after institutional control ends. Inventory limits for long-lived nuclides are set so that even such an intrusion would not cause unacceptable doses. Examples of well-regarded facilities include El Cabril in Spain, the Centre de l'Aube in France and the Vaalputs facility in South Africa.

Repositories for intermediate-level waste

Several countries already operate repositories for low- and intermediate-level waste at depth. Sweden's SFR facility at Forsmark, operating since 1988, lies about 60 m under the Baltic Sea floor in crystalline rock and is being extended. Finland has operated similar repositories at Olkiluoto and Loviisa since the 1990s. Hungary operates the Bátaapáti repository in granite. Germany is converting the former Konrad iron mine into a repository for low- and intermediate-level waste. These facilities demonstrate the technology for disposing of intermediate-level waste at depths from tens to hundreds of metres.

Records and knowledge management

Waste management lasts for generations, so records are essential. For each package, the generator records its origin, contents, nuclide inventory, dose rate, treatment, container type and storage location. These records support acceptance at disposal facilities, safety assessments and inspections, and must be kept long after the people who created them have retired. Modern waste tracking systems use bar codes or radio-frequency tags on each package and databases that link to measurement data. For historic waste with poor records, characterisation campaigns may be needed to rebuild the inventory before the waste can be disposed of, which is one of the main costs of legacy cleanup programs.

Knowledge management goes beyond records. Waste organisations must keep the skills and understanding needed to manage waste over decades, through training, documentation of the reasons for decisions and links with universities and research centres. International bodies such as the IAEA and the OECD Nuclear Energy Agency run programs on preserving records and knowledge across generations, including for the very long periods after a repository is closed.

Costs of low- and intermediate-level waste management

The cost of managing low-level waste depends strongly on its volume, which is why volume reduction pays. Disposal charges at commercial sites are quoted per cubic metre or per cubic foot, with surcharges for higher activity, so compaction, incineration and segregation of clean material can save large sums. Intermediate-level waste is far more expensive per unit volume, because of the shielding, remote handling and deeper disposal it needs, but its volume is much smaller. Over the life of a power station, including decommissioning, these costs are a small but important part of the total cost of electricity, and they are included in the decommissioning and waste funds that operators must maintain.