Shielding waste
11 July 2005At Ontario Power Generation’s Bruce site, a waste incineration plant vital to waste volume reduction efforts has been given a clean bill of environmental health. There are also tentative plans for a deep repository. By Stephen Salaff and Mazin Saba
The Canadian Nuclear Safety Commission (CNSC) recently endorsed in a regulatory document the environmental performance of a radioactive waste incinerator at the Bruce nuclear park of Ontario Power Generation (OPG) in Bruce County on the Lake Huron shoreline, 250km (155 miles) northwest of Toronto. Since the initial licensing of an incinerator at the Bruce nuclear park by the CNSC in 1977, the incinerator has been one of OPG’s volume-reduction options for utility system low- and intermediate level radioactive waste (LILW).
The Bruce nuclear park, formerly known as the Bruce Nuclear Power Development of Ontario Hydro, is the historic birthplace of nuclear power in Ontario and Canada. Best known for its four-unit Bruce A and Bruce B nuclear generation stations, the park also contains other Candu fuel chain installations, including an OPG heavy water plant now being decommissioned on a licence awarded by CNSC in 2004, and OPG’s Western Waste Management Facility (WWMF), so termed because it is more westerly than OPG’s Darlington and Pickering nuclear generating stations.
In May 2001 OPG leased Bruce A and Bruce B to Bruce Power until 2018, with lessee options to renew for up to 25 years.
Although Bruce Power’s responsibilities nominally apply to the pair of 4-unit stations, regulatory proceedings reveal that the CNSC currently expects Bruce Power to exercise certain overall site security and radiation protection responsibilities at the park and its vicinity.
Radioactive waste is transported from the 20 power reactors in Ontario to the park. OPG’s Towards Sustainable Development 2002: Progress Report declares that the annual quantity of LILW is influenced by stations’ operational plans, and utility initiatives for waste minimisation at source. OPG seeks to reduce the volume of these wastes by careful waste separation at the stations.
The Darlington and Pickering nuclear stations produced a combined 4817m3 of LILW in 2002, compared to 5298m3 in 2001 and 4774m3 in 2000.
OPG is significantly concerned about potential shortfalls in its ongoing capacity for managing the LILW volumes which it centralises at the WWMF.
OPG’s March 2004 Environmental Assessment Study Report (EASR) prepared for the CNSC review of the utility’s proposed amendment to its operating licence for the WWMF reports that total LILW received at the facility averages 6150m3 annually. The amendment, received in May 2004, permits OPG to construct three new low-level storage buildings, numbered 9, 10, and 11 at the facility.
Waste that can be compacted, such as polyvinyl chloride (an essential plastic); fluoroethylene plastics; fibreglass and metal pieces will be stored in containers in buildings 9,10, and 11. The packages or containers are generally stackable and placed to maximise the use of storage space to a height of 6m inside the LLW storage buildings. Solid waste containers approved for use include baled waste racks, drums, compactor boxes, non-processible waste containers, low-level resin containers, radioactive incinerator ash containers, polyethylene pallet tanks, monolithic containers and B-25 compactor boxes.
According to OPG’s EASR document, the utility’s radiation protection group classifies low- and intermediate level radioactive waste received at the facility by its contact dose rate, measured in Sv/h.
OPG considers ‘cellulosic’ low-level waste, such as paper and cotton, as incinerable. OPG’s acceptance criterion for incinerable waste is 0.6mSv/h.
The Ontario Ministry of the Environment awarded to OPG a Certificate of Approval dated January 2004 for a new incinerator at the WWMF with a design capacity of 2270kg in varying radioactive waste types per day.
According to the ministry’s senior communicator, John Steele, the responsibility for monitoring and regulating radionuclide emissions from the Bruce incinerator resides at the federal level in Canada with the CNSC.
Conventional emissions, Steele explains, are regulated provincially. “Ontario Ministry of the Environment is assuredly authorised and empowered to regulate the mercury, dioxin and furan discharges from the Bruce incinerator, and we are vigorously performing that role,” Steele affirmed.
Responding to a written stakeholder question on the health and environmental risks of the Bruce incinerator presented in CNSC’s review of the buildings 9, 10 and 11 licence amendment, the CNSC’s director of waste and geosciences in May 2004 claimed that operations at the Bruce incinerator “do not result in significant effects on the atmospheric environment.”
CNSC media and community relations advisor, Aurele Gervais, reported to NEI the CNSC staff justification for this assertion. Staff claim that radionuclides released to air and water from the Bruce incinerator would cause an effective dose to the critical member of the public below natural background in Ontario.
CNSC staff named Bruce Power’s report, Annual Summary and Assessment of Environmental Radiological Data, published April 2003, as its source of data on radionuclide emissions from the Bruce incinerator. According to CNSC staff, this assessment of doses to the public from operation of the Bruce site reveals that “all the radionuclides released to the air and water from the Bruce site (Bruce A, Bruce B and the WWMF that includes the incinerator, and other installations) could result in an effective dose to the most critical member of the public of 2.1µSv. which is a small fraction of the public dose limit of 1000µSv.”
Environmentalists object that the most critical person is usually a man who works outside, a farmer or a lineman for example. It is not the most vulnerable, a foetus or a pregnant woman. They claim that this is because radiation protection standards are calibrated to the most exposed person, not the most vulnerable person. If the dose comes from plutonium or americium, the radiation may deliver a lethal dose to lung tissue, and still be within the dose requirement.
Despite its programmes for the incineration and compaction of radioactive waste, OPG appears saddled with mounting volumes of LILW not readily incinerated or managed above ground. These refractory wastes include metal components such as pipes, valves, the hardware components from reactor maintenance, and spent ion exchange resins originating from radioactive process systems and from radioactive decontamination of systems and equipment. Some of this waste is contaminated with long-lived radionuclides such as C-14.
OPG commissioned an above ground dry storage facility for spent nuclear fuel at the WWMF in 2002. A spent nuclear fuel dry storage facility has been in operation at Pickering since 1994, and a similar facility for Darlington is scheduled for service in 2007. OPG reports that as of December 2002 the number of used fuel bundles in storage in Ontario totalled approximately 1.36 million.
OPG is also now examining long-term geological disposal options at the Bruce nuclear park for LILW (see Panel).
A conceptual stratigraphic cross-section of the rock underlying the proposed LILW storage buildings at the WWMF was prepared for OPG by Golder Associates, a Toronto based geological consulting firm in January 2003.
OPG submitted this geological conceptualisation of the earth environment beneath the Bruce nuclear park to support its March 2004 application for an amendment to its WWMF licence to permit construction of storage buildings 9, 10 and 11.
At a depth of 800m below the site, Cambrian and pre-Cambrian materials, which generally characterise the Canadian Shield rock formation underlying about one half of the country, can be found. Geologists technically define a shield as a large area in which pre-Cambrian rocks outcrop.
Owing perhaps to the doubtlessly controversial implications of a deep-rock shield solution to Canada’s vast spent nuclear fuel management problems,
CNSC has not yet formally reported on the OPG deep repository proposal. In January 2005, Gervais declined NEI’s request for an interview with staff on CNSC potential consideration of OPG’s proposed deep rock repository for disposal of LILW. At the time, OPG and the municipality of Kincardine were in the midst of a public poll of community support and no application had been made.
| A repository at Bruce? |
| Ontario Power Generation (OPG) has proposed the construction of a deep geological repository (DGR) for low- and intermediate-level radioactive waste (LILW) at its nuclear park in Bruce County, Ontario. The DGR would hold waste generated at Ontario’s Pickering, Darlington, and Bruce nuclear stations. Regulatory approval for the DGR must be obtained from agencies including Canadian Nuclear Safety Commission (CNSC). According to OPG, LILW received at the site is defined by its contact dose rate measured in Sv/h. OPG intends to exclude from the DGR used Candu reactor fuel, which is classified as high-level waste. Also beyond the published scope of the DGR are provisions for monitoring and retrieving the radioactive waste. In the December 2004 Canadian Nuclear Society Bulletin, OPG radwaste manager Frank King explained that the geology of the Bruce site is “ideally suited” to isolation and containment of nuclear waste. The underground repository would initially comprise a number of caverns or vaults arrayed in parallel rooms on either side of central access tunnels. King said the DGR would provide “for all low- and intermediate-level waste OPG’s site characterisation efforts could begin with mining near Douglas Point on the eastern shore of Lake Huron where geoscientists say that about 300m of limestone and shale overlie Canadian Shield basement rocks. The Douglas Point area encroaches on the Grenville Front Tectonic Zone, a prominent structural feature in pre-Cambrian basement rock traversing Lake Huron from north to south into Michigan. The presently assumed reference location for the DGR, however, is near the WWMF. At depth of about 600m, the DGR would be within a low-permeability deep limestone layer overlain by 200m of shale. A 220MWe prototype Candu reactor was built by OPG’s predecessor, Ontario Hydro, at Douglas Point in 1961. It was closed in 1984. Geoscientists have recommended detailed geophysical measurements of this feature and other geological anomalies in the surrounding area in order to calculate the potential for impact of water percolating along the pressure gradient though fractured rock. The considerable hydraulic head of Lake Huron to the west causes an appreciable from in near-surface rocks, but at the propsed DGR depth groundwater is thought to be practically stagnant. OPG expects to receive DGR environmental assessment guidelines from CNSC and potentially other federal regulatory authorities in 2007. Given detailed site characterisation, engineering design, safety and environmental assessments, construction approval should be forthcoming. Construction of the C$800 million facility could begin in 2013. Excavated to its final depth of 660m, the DGR would penetrate the rocks below the park to a distance in excess of that to which the CN Tower (including its mast) pierces the Toronto skyline. |
