DID is a philosophy that ensures the facility is operated in a safe manner through multiple means. DID
features include the entire suite of safety controls, encompassing Safety Class and Safety Significant
SSCs, Administrative Controls (ACs), safety management programs, and other engineered controls. Only
the significant contributors to DID should warrant TSR designation. Those passive features that provide
significant safety benefit are covered by the TSR Design Features section. Compensatory measures
should be provided for those existing TSR Design Features that do not meet functional requirements.
DOE G 423.1-1 provides additional guidance for consideration.
Many important aspects of the defense in depth strategy are implemented through the safety management
programs. The holistic approach embedded in the SMPs and their effective implementation as part of the
ISMS must continue to optimize the intended safety benefits. The discipline imposed by the SMPs
extends beyond simply supporting the assumptions made in the hazard analysis and is an essential part of
defense in depth safety posture.
The radiation protection of the workers during normal operations is governed by 10 CFR 835,
Occupational Radiation Protection and is discussed in the Radiation Protection chapter of the DSA.