Preliminary hazard identification for the Mark II conceptual design

Operational safety is an important aspect of concept development. This report describes the methodology used and results obtained from a preliminary hazard identification assessment performed for Adaptive Phased Management (APM)'s Mark II conceptual design. Failure Modes and Effects Analysis has been used to identify potentially hazardous events and accident scenarios that could result in an increase in radiological consequence during the operating period. Internal and external initiating events were considered. The identified failure modes were grouped into the following categories based on the anticipated initiating event frequencies: Anticipated Operational Occurrences (AOOs): Events with frequencies > 10^-2 a^-1; Design Basis Accidents (DBAs): Events with frequencies > 10^-5 a^-1 but < 10 -² a^-1; Beyond Design Basis Accidents (BDBAs): Events with frequencies < 10^-5 a^-1 but > 10^-7 a^-1; and Non-credible Events: Event with frequencies < 10^-7 a^-1. The estimation of initiating event frequencies is preliminary at this early design stage. Based on this preliminary work, twenty-three AOOs, six DBAs, and four BDBAs have been identified, with most of these events resulting in extended outage periods at the Used Fuel Packaging Plant. Due to the high frequency of operations, the dropping of a module by the overhead transfer crane/gantry and the potential damage of fuel bundles during fuel transfer operations are identified in the AOO category. The DBA category includes the failure and fall of an elevator during a used fuel transport package (UFTP) operation, the failure of the scissor lift resulting in the fall of a module/fuel bundles, a UFTP transport vehicle fire, a used fuel container (UFC) placement vehicle fire, the dropping of a UFTP containing an undetected flaw, and the dropping of an UFC containing an undetected flaw. Shaft cage fall with an UFC, flooding of the repository facility, a major earthquake leading to repository cave-in, and repository collapse on the UFCs are all placed in the BDBA category. The presence or absence of ventilation system filters is also considered in combination with specific accident scenarios. (author)