Human Intrusion in Deep Geologic Repositories in the U.S. Christopher Markley, PhD US Nuclear Regulatory Commission

National Academy of Sciences: Recommendations for Human Intrusion Standards Not possible to make scientifically supportable predictions of the probability of human intrusion. The key to the intrusion consequence analysis is whether the repository performance would be substantially degraded. The stylized, single borehole intrusion scenario is recommended because it removes a number of "imponderables."

Regulations for HLW Disposal (a) The applicant must determine the earliest time after disposal that the waste package would degrade sufficiently that a human intrusion could occur without recognition by the drillers. (b) The applicant must demonstrate that there is a reasonable expectation that the reasonably maximally exposed individual receives, as a result of human intrusion, no more than the following [mean (1) or median (2)] annual dose: (1) 0.15 mSv (15 mrem) for 10,000 years following disposal; and (2) 1.0 mSv (100 mrem) after 10,000 years, but within the period of geologic stability. (c) The applicant’s analysis must include all potential environmental pathways of radionuclide transport and exposure.

DOE’s Performance Assessment Results for Human Intrusion

NRC’s Technical Evaluation of DOE’s Human Intrusion Analysis The TSPA for the human intrusion calculation is performed separately from the TSPA for individual protection and is consistent with the guidance criteria. The TSPA model for the human intrusion calculation assumes the specified characteristics. The estimate of the mean dose is statistically stable. The dose estimate is consistent with the overall repository performance and the assumed characteristics of the human intrusion scenario.

DOE’s Human Intrusion Scenario for the Waste Isolation Pilot Plant (WIPP)

Passive Institutional Controls at WIPP Any compliance application shall include detailed descriptions of the measures that will be employed to preserve knowledge about the location, design, and contents of the disposal system. Any compliance application shall include the period of time passive institutional controls are expected to endure and be understood. The Administrator may allow the Department to assume passive institutional control credit, in the form of reduced likelihood of human intrusion.