Burnup Credit Approach Used in the Yucca Mountain License Application

Conference · Mon Oct 26 04:00:00 EDT 2009

OSTI ID:982724

Scaglione, John M. ^[1]; Wagner, John C. ^[1]

---

1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

The United States Department of Energy has submitted a license application (LA) for construction authorization of a deep geologic repository at Yucca Mountain, Nevada. The license application is currently under review by the United States Nuclear Regulatory Commission (NRC). This paper will describe the methodology and approach used in the LA to address the issue of criticality and the role of burnup credit during the postclosure period. The most significant and effective measures for prevention of criticality in the repository include multiple redundant barriers that act to isolate fissionable material from water (which can act as a moderator, corrosive agent, and transporter of fissile material); inherent geometry of waste package internals and waste forms; presence of fixed neutron absorbers in waste package internals; and fuel burnup for commercial spent nuclear fuel. A probabilistic approach has been used to screen criticality from the total system performance assessment. Within the probabilistic approach, criticality is considered an event, and the total probability of a criticality event occurring within 10,000 years of disposal is calculated and compared against the regulatory criterion. The total probability of criticality includes contributions associated with both internal (within waste packages) and external (external to waste packages) criticality for each of the initiating events that could lead to waste package breach. The occurrence of and conditions necessary for criticality in the repository have been thoroughly evaluated using a comprehensive range of parameter distributions. A simplified design-basis modeling approach has been used to evaluate the probability of criticality by using numerous significant and conservative assumptions. Burnup credit is used only for evaluations of in-package configurations and uses a combination of conservative and bounding modeling approximations to ensure conservatism. This paper will review the NRC regulatory criteria relevant to postclosure criticality, explain the role of criticality within the overall repository performance assessment, describe the strategy for preventing criticality via design features and waste form properties, and discuss the numerous considerations relevant to criticality and burnup credit for spent nuclear fuel disposed of in a geologic repository, with emphasis on the burnup credit approach and analyses.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 982724
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
96 KNOWLEDGE MANAGEMENT AND PRESERVATION
APPROXIMATIONS
BURNUP
Burn Up Credit Analyses
Burnup Credit in Postclosure Period
CONSTRUCTION
CRITICALITY
Criticality Considerations
Criticality Issues
DESIGN
Deep Geologic Repository
FISSIONABLE MATERIALS
GEOMETRY
LICENSE APPLICATIONS
License Application (LA)
Methodology and Approach
NEUTRON ABSORBERS
NUCLEAR FUELS
Nuclear Criticality Safety Program (NCSP)
PERFORMANCE
PROBABILITY
Prevention of Criticality
SCREENS
WASTE FORMS
WASTES
WATER
YUCCA MOUNTAIN