Annex G Venting of containment during nuclear emergencies
(Reference: Section 7.11)
1.0 General
1.1 The considerations herein are applicable to the venting of radioactive material from the containment systems at the Pickering, Bruce and Darlington nuclear stations, following an On-site Emergency or General Emergency notification.
1.2 The Pickering, Bruce and Darlington Nuclear Generating Stations are equipped with sub-atmospheric containment systems designed to hold up, for some time, radioactive material released from failed nuclear fuel in an accident.
1.3 In some reactor accident scenarios, released radioactive materials may be drawn into the vacuum building. The nominal venting strategy approved by the CNSC and followed by these nuclear stations, is to commence venting through the filtered air discharge system shortly before the vacuum building repressurizes to atmospheric pressure, and to continue venting at a rate just sufficient to keep containment sub-atmospheric.
1.4 In other accident scenarios, the vacuum building may not necessarily be activated. Any released radioactivity will be confined to other parts of the containment system, and vented through other exhaust systems, such as the contaminated exhaust stack, which contains equipment capable of removing most of the radioactive materials from the exhaust.
2.0 Aim of Venting Strategy
2.1 The ability to control (within certain limits) the venting of radioactivity from containment systems within a venting window could be useful to allow prior implementation of protective actions before the release takes place.
2.2 Any decision to use an alternate venting strategy (i.e., other than the nominal venting strategy outlined in Paragraph 1.3 above) should be taken only after consultation among the province, CNSC, Health Canada, the reactor facility and affected municipalities.
3.0 Containment Venting Responsibilities
3.1 Reactor facility emergency response plans shall specify that:
- A designated person with the authority for venting is on-site at all times.
- The PEOC Commander is consulted before undertaking any venting activity, unless venting must be performed in an urgent manner to protect the structural integrity of containment.
- Time estimates of when venting will be required are reported to the province.
- If venting must be performed in an urgent manner to protect the structural integrity of containment, the reactor facility shall inform the PEOC Commander, as early as possible.
3.2 The PEOC Commander, as operational lead for the off-site response (Section 5.6) should initiate the following ancillary measures as appropriate:
- Institute the appropriate protective measures in any populated area before venting is carried out which could affect that area. The population in this area, as well as the community/municipal Emergency Response Organization, must also be notified in advance of such venting.
- Notify and restrict air traffic, marine traffic and boaters on the adjacent Great Lake before venting initiated.
- Confirm through the federal liaison officers in the PEOC that the Federal Government has consulted with the affected jurisdictions in the United States of America (USA) before venting is initiated.
3.3 The Federal Government (i.e., Health Canada) shall consult with the affected jurisdictions in the USA before venting is initiated, as appropriate.
3.4 Nuclear emergency response plans of stakeholders in Paragraph 2.2 above should identify how venting decisions are established, documented, approved, and communicated.