PNNL

Abstract

The mission of the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) includes the mid-to-long-term decommissioning planning of the reactors at the Fukushima Daiichi Nuclear Power Station. To carry out its mission, NDF needs to be able to assess worker safety and public health risks that currently exist at the Fukushima Daiichi Nuclear Power Station and the implications of various actions that may be taken to reduce such risks. Pacific Northwest National Laboratory (PNNL) entered into a contract with NDF to support NDF’s mission by developing a risk assessment methodology that will support NDF’s evaluation of options for transitioning molten and solidified fuels within each unit into safer, more stable, configurations given the ever-changing state of knowledge and large uncertainties. The underpinning of this approach, which incorporates both expert elicitation and adapts probabilistic risk assessment and hazard analysis techniques, is its organization of potential release mechanisms and accident scenarios into a more manageable set of safety issues, which are systematically characterized to allow for useful comparison between fuel debris retrieval options as well as the identification of risk drivers and discriminators. The approach also lends itself to be easily updated as the general state of knowledge improves and will serve as a vital input to prioritizing future investigations associated with human health and safety at the Fukushima site. This paper describes the overall approach developed by PNNL to risk-inform the comparison between fuel debris retrieval strategies and discusses lessons learned from implementing the approach.