Ontario Hydro

Pickering Waste Management Facility Safety Report

A Report to the Atomic Energy Control Board
June 1988.

EXCERPTS Storage Area

Concrete peripheral walls of 0.2 m (8 in) thickness limits the radiation dose at the exterior surface of the wall to less than 25 mSv/hr (0.25 mrem/hr). Building Services

The building services provided for the storage facility include the following: domestic water, sewage, instrument and service air, heating for the shop and office area, air conditioning for the office area, electrical power, ventilation, normal and active drainage, PA system, fire prevention and control, radiation monitoring equipment, telephones, provisions for surveillance cameras, alarm system and a local control panel for instrumentation in the welding area. Ventilation

The workshop is provided with active ventilation consisting of exhaust fans, radioactive filter assemblies and a discharge stack....

In the storage area, openings through breeze vents in the ceiling and walls, provided at the commissioning stage, have been covered to prevent the ingress of snow and rain. These openings can be uncovered if the ambient temperature inside the facility becomes unacceptably high. Fire Prevention and Control

Fire protection at the storage facility is provided by three hydrants, each located within 15 m (50 ft) of each vehicle access door (on north, west and south side of the building). Drainage

Drainage from the UFDSF welding and decontamination area is treated as active liquid waste. Under normal conditions no liquid wastes are expected to arise in the UFDSF container storage area. For contingencies, however, floor drains are provided in the storage area. All drainage is directed to two underground active-liquid stainless-steel lined sumps and transferred via sump pumps to stainless steel holding tanks, each of a working volume of 4 m3 (141 ft3), located above ground in the workshop area.

After monitoring, the contents of the holding tanks are periodically transferred for routine treatment by pumping their contents, via underground nuclear class stainless steel piping, to the existing active liquid waste treatment system at Pickering NGS.... DSC Handling in the UFDSF

After the loaded DSC is received at the storage facility operations area, it is inspected and prepared for the welding operation and transfer to storage. Receiving the DSC

The DSC lifting beam is picked up by the overhead crane. The transporter unloads the DSC and places it on the floor, from where the DSC is lifted off by the overhead crane and placed in the welding station. The transfer clamp is then removed and the pre-weld vacuum system is connected to the drain port [of the container] to maintain a vacuum in the DSC cavity. Heaters are installed around the DSC flange to pre-heat the flange for the welding process. Seal-Welding the DSC

The welding equipment is installed on the container and the lid of the Dry Storage Container is joined to the base by a full penetration groove weld.... The weld is deposited in 7 layers with up to 11 weld passes.... The system is remotely operated from a control room adjacent to the welding station.

Leading and trailing CCTV cameras provide views of the weld puddle to the operator during the welding process. Additionally, warning systems are provided to inform the operator if the welding torch approaches the side walls too closely....

Next, the welding equipment is removed, gases in the DSC cavity are evacuated and the container is backfilled with helium. Vent and drain shield plugs are installed and welded to seal the vent and drain openings....

Following the leakage test, weld affected areas are cleaned and painted and the DSC is checked for surface contamination. If any contamination is found then further decontamination is carried out. Permanent safeguards seals are then installed and the DSC is transferred to its final storage location using the transporter.

3.2.1 Dose Assessment Methodology

As discussed in section only krypton-85 and tritium can contribute to airborne emissions. These are the only potential releases from the UFDSF since liquid effluents are routed to the PNGS active liquid waste management system.... Airborne Emissions

... The only possible source of airborne radioactive emissions resulting from normal UFDSF operations is residual contamination on the DSC's outside surface.

This DSC surface contamination could become airborne during welding, therefore, to minimize potential emissions, the welding area is provided with an active ventilation system. The exhaust air is passed through active filter assemblies consisting of demisters, prefilters and particulate (HEPA) filters before being discharged to the atmosphere via the exhaust stack. The design exhaust flow is approximately 10 percent higher than that of the supply system in order to maintain a negative pressure differential in the welding area.

Since it is very imprecise to evaluate potential emissions from the resuspension of surface contamination, and these values are expected to be insignificant, a set of conservative assumptions are made in this assessment to obtain an upper bound for airborne emissions.... Liquid Emissions

... Any liquids used in the operations area of the dry storage facility are collected in the active liquid waste collection system and then transferred to the station's active liquid waste management system.... Emissions Monitoring

The active ventilation exhaust from the workshop is monitored for radioactive particulates ... as a precautionary measure since the closure operations might cause resuspension in air of surface contamination on the DSCs.... Contamination Control

... A designated decontamination area with appropriate ventilation is provided in the shop area of [the] dry storage facility.... Contamination survey equipment and interzonal monitors are available in the storage facility to prevent the spread of contamination. Airborne Contamination Monitoring

Airborne contamination is monitored by a Continuous Air Monitor (CAM) in the welding shop. A portable monitor is also used for weekly monitoring of the air inside the storage area of the facility. Surface Contamination Monitoring

Portable contamination and smear counters are used to monitor surface contamination on DSC's in the shop and the storage area. Head and foot monitors and friskers are provided at inter-zonal boundaries to monitor personnel, equipment and material movement to avoid transfer of contamination.

[ end of excerpts ]

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