Basis for the Derivation of Safety Goals and New Challenges
An abstract of the technical presentation presented at:
19th Pacific Basin Nuclear Conference
Vancouver, British Columbia, Canada
August 24–28, 2014
Canadian Nuclear Safety Commission
Ottawa, Ontario, Canada.
“Safety goals” for nuclear power plants have often been referred to at public hearings in Canada over the last few years. Extensive work in this area is also being done internationally, as this topic attracts the interest of the International Atomic Energy Agency and most regulators.
This presentation will shed some light on the definition of safety goals and show how these support the fundamental safety objectives that aim to protect people and the environment from harmful effects of ionizing radiation. The basis for the derivation of the safety goals for core damage frequency (CDF) and large early release frequency (LERF) (referred to as surrogate safety goals) will be included.
This presentation will also highlight challenges related to the scope as well as the implementation of safety goals in the regulatory framework, which currently has no international consensus. Safety goals have been published in different ways spanning from legal documents to internal guides, and can be applied as legal limits down to “orientation values”.
Finally, this presentation will address the new challenge presented by the Fukushima Daichi accident, for the development of acceptable representative risk metrics (goals) that include integrated risks from multi-unit sites. In the current state-of-the-art Probabilistic Safety Assessment (PSA), it has been common practice in the application of safety goals to consider risk assessment and to evaluate the acceptability of risk levels on an individual reactor basis. Such comparisons are now questionable for multi-unit sites, as the total risks from all the reactors on the site have not been taken into account. It is worth noting that the total risk of a multi-unit CANDU reactor cannot be obtained simply by multiplying the CDF and LRF by the number of units, as the contribution of some events will be double-counted and the total risk overestimated.
The presentation will conclude with a high-level discussion about the technical challenges in order to move from the current practice “PSA developed on an individual plant” to a “site-integrated risk evaluation”.
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