[en] In 1970, the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) was established. Canada was one of the first countries to ratify the treaty and to accept International Atomic Energy Agency (IAEA) inspection at its nuclear facilities. In support of the NPT, Canada provides support to the IAEA for the development of safeguards schemes, equipment and techniques relevant to Canadian designed and built nuclear facilities. A safeguard scheme is a set of measures designed for the timely detection of diversion of nuclear materials from a nuclear facility, and includes a combination of safeguards equipment installed in the plant, together with a program of periodic inspections by IAEA safeguards inspectors. The instrumentation scheme used in CANDU reactors was developed in the 1970s and 80s by the IAEA, with technical support from the Canadian Nuclear Safety Commission (CNSC), Atomic Energy of Canada Limited (AECL) and other organizations. The approach taken to safeguarding CANDU nuclear facilities is based on a combination of containment surveillance, monitoring measures, and accounting for fuel bundle movements through the facility. Instruments are used to detect any unusual fuel-handling activity, which could be significant from a fuel-diversion point of view. The safeguards instrumentation includes television surveillance systems, bundle counters for spent fuel, security seals and covers for large number of spent fuel bundles in the storage bays, yes/no radiation monitors and core discharge monitors. There are four main inventories of nuclear material in CANDU reactors. These are in the fresh-fuel storage room, the reactor core, the irradiated (spent) fuel storage bays and the dry-fuel storage. The instrumentation must, among other things, detect (i) the unreported removal of irradiated fuel from the reactor core and (ii) the unreported removal of irradiated fuel from the storage bays or the dry-storage facility. In addition, the instrumentation should detect substitution of spent fuel by dummy or unirradiated fuel. This paper describes the shielding and dose-rate analysis carried out for bundle counters, which perform accounting of spent fuel discharged from the reactor core to the spent-fuel bays for CANDU 6 reactors. The mode of operation, the bundle-detection threshold determination, and the collimator shielding design for proper functioning of the bundle counters are described. The ORIGEN code was used to obtain the fission-product decay-gamma source in spent-fuel bundles, and the QAD-5K code was used for the collimator shielding design and detector-response calculations. These calculations provided the basis for similar collimator shielding arrangements for AECL-designed bundle counters used in Pickering A and B, Bruce A and B, and Darlington reactors. (author)