Assessment of Potential Flood Events and Impacts at INL's Proposed Remote-Handled Low-Level Waste Disposal Facility Sites

A. Jeff Sondrup ; Annette L. Schafter

关键词: AQUIFERS;    CAPACITY;    DRAINAGE;    FLOODS;    INEEL;    LOW-LEVEL RADIOACTIVE WASTES;    POSITIONING;    PRECIPITATION;    PROBABILITY;    RADIOACTIVE WASTE MANAGEMENT;    RADIOISOTOPES;    RIVERS;    SEISMIC EVENTS;    TRANSPORT;    US NATIONAL ENVIRONMENTAL POL;   

DOI  :  10.2172/989873
RP-ID  :  INL/EXT-10-18191
PID  :  OSTI ID: 989873
Others  :  TRN: US1007238

学科分类：社会科学、人文和艺术（综合）

美国|英语

来源: SciTech Connect

【 摘 要 】

Rates, depths, erosion potential, increased subsurface transport rates, and annual exceedance probability for potential flooding scenarios have been evaluated for the on-site alternatives of Idaho National Laboratory???s proposed remote handled low-level waste disposal facility. The on-site disposal facility is being evaluated in anticipation of the closure of the Radioactive Waste Management Complex at the INL. An assessment of flood impacts are required to meet the Department of Energy???s Low-Level Waste requirements (DOE-O 435.1), its natural phenomena hazards assessment criteria (DOE-STD-1023-95), and the Radioactive Waste Management Manual (DOE M 435.1-1) guidance in addition to being required by the National Environmental Policy Act (NEPA) environmental assessment (EA). Potential sources of water evaluated include those arising from (1) local precipitation events, (2) precipitation events occurring off of the INL (off-site precipitation), and (3) increased flows in the Big Lost River in the event of a Mackay Dam failure. On-site precipitation events include potential snow-melt and rainfall. Extreme rainfall events were evaluated for the potential to create local erosion, particularly of the barrier placed over the disposal facility. Off-site precipitation carried onto the INL by the Big Lost River channel was evaluated for overland migration of water away from the river channel. Off-site precipitation sources evaluated were those occurring in the drainage basin above Mackay Reservoir. In the worst-case scenarios, precipitation occurring above Mackay Dam could exceed the dam???s capacity, leading to overtopping, and eventually complete dam failure. Mackay Dam could also fail during a seismic event or as a result of mechanical piping. Some of the water released during dam failure, and contributing precipitation, has the potential of being carried onto the INL in the Big Lost River channel. Resulting overland flows from these flood sources were evaluated for their erosion potential, ability to overflow the proposed disposal facility, and for their ability to increase migration of contaminants from the facility. The assessment of available literature suggests that the likelihood of detrimental flood water impacting the proposed RH-LLW facility is extremely low. The annual exceedance probability associated with uncontrolled flows in the Big Lost River impacting either of the proposed sites is 1x10-5, with return interval (RI) of 10,000yrs. The most probable dam failure scenario has an annual exceedance probability of 6.3x10-6 (1.6x105 yr RI). In any of the scenarios generating possible on-site water, the duration is expected to be quite short, water depths are not expected to exceed 0.5 m, and the erosion potential can easily be mitigated by emplacement of a berm (operational period), and an engineered cover (post closure period). Subsurface mobilization of radionuclides was evaluated for a very conservative flooding scenario resulting in 50 cm deep, 30.5 day on-site water. The annual exceedance probability for which is much smaller than 3.6x10-7 (2.8x106 yr RI). For the purposes of illustration, the facility was assumed to flood every 500 years. The periodically recurring flood waters were predicted to marginally increase peak radionuclide fluxes into the aquifer by at most by a factor of three for non-sorbing radionuclides, and to have limited impact on peak radionuclide fluxes into the aquifer for contaminants that do sorb.