United States Nuclear Regulatory Commission - Protecting People and the Environment

A Pilot Probabilistic Risk Assessment of a Dry Cask Storage System at a Nuclear Power Plant (NUREG-1864)

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Publication Information

Manuscript Completed: June 2006
Date Published: March 2007

Prepared by:
Gordon Bjorkman, Tze-Jer Chuang, Robert Einziger, Shah Malik, Asimios Malliakos,
Jocelyn Mitchell, Carlos Navarro, Christopher Ryder, Syed Shaukat, Anthony Ulses, Ghani Zigh

Asimios Malliakos, NRC Project Manager

Division of Risk Assessment and Special Projects
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
Spent Fuel Project Office
Office of Nuclear Material Safety and Safeguards
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice


In response to a request from the U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Material Safety and Safeguards (NMSS), the Office of Nuclear Regulatory Research (RES) and the NMSS Spent Fuel Project Office (SFPO) have jointly developed and applied a methodology for performing a pilot probabilistic risk assessment (PRA) of a dry cask storage system at a nuclear power plant site (i.e., an independent spent fuel storage installation). This RES/NMSS report documents the pilot PRA for a specific dry cask system (Holtec International HI-STORM 100) at a specific boiling-water reactor (BWR) site. The methodology developed can serve as a guide for performing similar PRAs in the future. The pilot study can provide guidance for assessing the risk to the public and identifying the dominant contributors to that risk. The cask system consists of a multipurpose canister (MPC) that confines the fuel, a transfer overpack that shields workers from radiation while the cask is being prepared for storage, and a storage overpack that shields people from radiation and mechanically protects the MPC during storage. The study covers various phases of the dry cask storage process, from loading fuel from the spent fuel pool, preparing the cask for storage and transferring it outside the reactor building, moving the cask from the reactor building to the storage pad, and storing the cask for 20 years on the storage pad.

The study develops and assesses a comprehensive list of initiating events, including dropping the cask during handling and external events during onsite storage (such as earthquakes, floods, high winds, lightning strikes, accidental aircraft crashes, and pipeline explosions). Potential cask failures from mechanical and thermal loads are modeled. The study estimates the annual risk for one cask in terms of the individual probability of a prompt fatality within 1.6 km (1 mile) and a latent cancer fatality within 16 km (10 miles) of the site.

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