Nuclear Safety, Licensing and Regulatory Framework
This domain tests the safety case, defence in depth, licensing stages and the regulator's role in permitting and oversight.
Core rules
- IAEA safety standards provide the international framework: fundamental safety principles, requirements for facilities, and guidance on safety assessment.
- Defence in depth uses successive levels: preventing abnormal operation, detecting and controlling deviations, controlling accidents, managing severe accidents, and mitigating radiological consequences.
- The safety case includes deterministic analysis, probabilistic safety assessment, operating limits and conditions, and a demonstration that risks are ALARP.
- Licensing typically covers siting, design, construction, commissioning, operation, modification and decommissioning. A periodic safety review re-examines the safety case against current standards and plant ageing.
- The regulatory body must be independent, competent and empowered to inspect, enforce and, if necessary, shut down a facility. Safety-related modifications require assessment and approval before implementation.
Worked example
An operator proposes changing an emergency core cooling system setpoint. The correct reasoning is: classify the change, update the safety analysis and safety case, assess the effect on accident sequences and PSA, update operating limits and conditions, and obtain regulatory approval before implementation. The change is not merely a maintenance adjustment. If the new setpoint delays ECCS injection, the safety analysis must show that peak cladding temperature and other acceptance criteria still hold. Configuration records and operator procedures must be updated, and the change must be tested and verified.
Traps
Do not assume a modification that seems small is outside the licensing basis. Do not treat PSA as a substitute for deterministic compliance. Do not confuse ALARA with ALARP; they are related but not identical. Do not overlook the need to update the safety case after plant ageing or new standards. Do not assume regulatory approval can be retrofitted after implementation.
Key points
- Defence in depth has multiple independent levels.
- The safety case combines deterministic and probabilistic evidence.
- Operational limits and conditions are part of the licence.
- Periodic safety review challenges ageing and current standards.
- Safety-related modifications need prior assessment and approval.
- Regulators must be independent and empowered to enforce.