Development of a Methodology for Aggregation of Various Risk Contributors for Nuclear Facilities

In determining whether any nuclear facility or activity is sufficiently safe, it is necessary to compare the apparent safety level with what is desired or required. Risk-related safety goals are established in many countries; the goals are also included in some IAEA publications (e.g. INSAG-12). Regulatory bodies in many Member States require submitting and utility organizations pursue performing Probabilistic Safety Assessment (PSA) studies to evaluate risk and demonstrate compliance with the specified risk metrics (core damage frequency, large release frequency, etc.).

The IAEA is supporting the development and use of PSA by publishing relevant safety standards (e.g. SSG-3 and SSG-4) and other documents. Lessons learned from the Fukushima Daiichi accident are also being addressed. Specifically, SAS/NSNI is finalizing a TECDOC on Development and Application of a Framework of Safety Goals for Nuclear Installations. However, this publication does not address practical aspects of aggregating all risk contributors associated with operation of a single reactors and site-wide radiological  inventory, such as reactor units, spent fuel pools, fuel dry storage, etc.

Objective

To develop a publication (Technical Report) that would provide a methodology for aggregation of external and internal risk contributors into an overall safety goal including:

• Risk metrics covering all sources of radioactivity for nuclear facilities on the site (e.g.  reactor units, spent fuel pools, fuel dry storage)
• All operational states of the facilities
• All possible hazards, namely: internal initiating events caused by random component  failures or human errors, internal hazards (e.g. internal fires and floods), and external hazards (both natural and human-induced)

In addition, a practical implementation exercise is suggested to be conducted as part of the project to test the methodology developed and back fit the findings from the exercise into the final publication.