Background on a representative unsaturated

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1 Unsaturated Zone Repositories and Alternative Fuel Cycle Choices Peter Swift Sandia National Laboratories Advanced Summer School of Radioactive Waste Disposal with Social-Scientific Literacy University it of California, i Berkeley August 4, 2009 Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy s National Nuclear Security Administration i i under contract DE-AC04-94AL The content of this presentation reflects the views of the author and does not necessarily reflect the views or policies of the United States Department of Energy or Sandia National Laboratories 1 SAND C Outline Background on a representative unsaturated zone repository Topics related to long-term dose Topics related to thermal performance 2

2 July 2009 Status of Yucca Mountain License Application for Construction Authorization submitted to US Nuclear Regulatory Commission June NRC docketing decision September , initiated 3-4 year review and hearing process Earliest possible decision on licensing September 2011 Christopher Kouts (OCRWM Acting Director) testimony to U.S. House of Representatives Committee on the Budget July 16, 2009 The Department s FY 2010 budget request announces the Administration s intended termination of the Yucca Mountain repository project and includes the funding needed to explore alternatives for nuclear waste disposal and to continue participation in the Nuclear Regulatory Commission license application process. The Department t remains committed to meeting its obligations for managing and ultimately disposing of spent nuclear fuel and high-level radioactive waste. To that end, the Secretary is convening a Blue-Ribbon Panel of experts to evaluate alternative approaches for meeting the Federal Government s responsibility. 3 Yucca Mountain Repository License Application DOE/RW-0573 Rev 0 June DOE/RW-0573 Rev 1 February General Information (GI) General Description Proposed Schedules for Construction, Receipt and Emplacement of Waste Physical Protection Plan Material Control and Accounting Program Site Characterization Safety Analysis Report (SAR) Repository Safety Before Permanent Closure Repository Safety After Permanent Closure Research and Development Program to Resolve Safety Questions Performance Confirmation Program Administrative and Programmatic Requirements Available from the NRC 4

3 Spent Nuclear Fuel and High-Level Radioactive Waste in the United States t Current locations of spent nuclear fuel (SNF) and highlevel radioactive waste (HLW) destined for geologic disposal: 121 sites in 39 states Proposed Yucca Mountain Repository United States Department of Energy (DOE) Office of Civilian Radioactive Waste Management (OCRWM) Mission: to manage and dispose of high-level radioactive waste and spent nuclear fuel in a manner that protects health, safety, and the environment; enhances national and energy security; and merits public confidence. 5 Waste Proposed for Yucca Mountain Commercial Spent Nuclear Fuel: 63,000 MTHM (~7500 waste packages) DOE & Naval Spent Nuclear Fuel: 2,333 MTHM (65 MTHM naval spent fuel in ~400 waste packages) (DSNF packaged with HLW) DOE & Commercial High-Level Waste: 4,667 MTHM (~3000 waste packages of co-disposed DSNF and HLW) Yucca Mountain Total 70,000 MTHM 6 DSNF: Defense Spent Nuclear Fuel HLW: High Level Radioactive Waste MTHM: Metric Tons Heavy Metal

4 Historical and Projected Commercial Spent Nuclear Fuel Discharges (as of 05/21/07) 7 Proposed Repository for High-Level Waste and Spent Fuel at Yucca Mountain 8

5 Yucca Mountain Exploratory Studies Facility 9 Yucca Mountain Subsurface Design Emplacement drifts 5.5 m diameter approx. 100 drifts, m long Waste packages ~11,000 packages ~ 5 m long, 2 m diameter outer layer 2.5 cm Alloy 22 (Ni-Cr-Mo-V) inner layer 5 cm stainless steel Internal TAD (transportation, aging, and disposal) canisters for commercial spent fuel, ~ 2.5 cm stainless steel Drip shields free-standing 1.5 cm Ti shell 10

6 Estimating Dose to Hypothetical ti Future Humans Modeled groundwater flow paths and hypothetical exposure pathways 11 Scenarios for the Total System Performance Assessment License Application (TSPA-LA) Four scenario classes divided into seven modeling cases Nominal Scenario Class Nominal Modeling Case (included with Seismic Ground Motion for 1,000,000-yr analyses) Igneous Scenario Class Intrusion Modeling Case Eruption Modeling Case Early Failure Scenario Class Waste Package Modeling Case Drip Shield Modeling Case Seismic Scenario Class Ground Motion Modeling Case Fault Displacement Modeling Case 12

7 TSPA Architecture 13 TtlM Total Mean Annual ld Dose TSPA-LA Results DOE/RW-0573 Rev 0 Figure ,000 years 1,000,000 years 10,000-year Standard: Mean annual dose no more than 0.15 msv (15 mrem) TSPA-LA estimated 10,000 yr maximum mean annual dose: msv (0.24 mrem) 1,000,000-year Standard: Mean annual dose no more than 1 msv (100 mrem) TSPA-LA estimated 1,000,000- yr maximum mean annual dose: 0.02 msv (2.0 mrem) 14

8 Modeling Cases Contributing to Total Mean Annual Dose 10,000 years 1,000,000 years DOE/RW-0573 Rev 0 Figure TSPA-LA Radionuclides Important to Mean Dose 10,000 Years 2 (TSPA AMR AD01 Fig 8.1-1[a]) DOE/RW-0573 Rev 0 Figure a

9 TSPA-LA Radionuclides Important to Mean Dose 1 Million Years E L L L E L 17 DOE/RW-0573 Rev 0 Figure b E indicates early and refers to the time period before ~ 200,000 yr. L indicates late and refers to the time period after ~ 200,000 yr Topics related to Long-Term Dose 18

10 Commercial Spent Nuclear Fuel Decay History Cs-137 Sr-90 Am-241 Np-237 Pu-239 Th-230 Tc-99 Pu-242 I-129 Pu-240 Pu-238 DOE/RW-0573 Rev 0, Figure , inventory shown for an single representative Yucca Mountain waste package 19 Observations on the Impact of Reprocessing on Long-Term Performance Yucca Mountain License Application shows compliance with long-term standards disposing of current waste forms Pu-242 is the largest contributor t to dose at 1 Myr, followed by Np-237, Ra- 226, and I-129 Tc-99 (half-life 213,000 yr) and I-129 (half-life 15,700,000 yr) will dominate peak dose if actinides are removed Iodine-129 tracks with Tc-99, less important than Tc-99 until after 300,000 yr when decay lowers dose from Tc-99. Possible reprocessing impact (assuming Yucca Mountain design and models) Total estimated peak mean dose might be reduced by less than an order of magnitude if actinides were removed, and would still occur at 1 Myr, dominated by I-129 Additional separation of Tc-99 would could significantly reduce dose at 10,000 years, but would not impact overall peak Increases in total spent fuel equivalent inventory would increase Tc-99 and I- 129 dose proportionally 20

11 Topics Related to Thermal Performance 21 Thermal Decay of Spent Fuel 22 Wigeland, R.A., T.H. Fanning, and E.E. Morris, Separations and Transmutation Criteria to Improve Utilization of a Geologic Repository, Nuclear Technology v. 154, Figure 1

12 Yucca Mountain Design Aspects Related to Thermal Performance Drift spacing of 81 meters Mid-pillar peak temperature of 96 C Waste package spacing of 0.1 meters Average emplacement drift line load of 1.45 kw/m Maximum waste package thermal output of 18.0 kw Ventilation flow rate of 15 m 3 /s 23 years of waste emplacement followed by 50 years of forced ventilation following emplacement of the last waste package 23 Thermal Impacts of Reprocessing Design of the process and the waste form determines thermal load DOE/RW-0573 Rev 0 Table Forty-year old Andra HLW will produce ~0.7 kw/canister, which is ~4.0 kw/m 3 Hanford HLW in 2017 will produce ~0.626 kw/m 3 At a system-level, average Andra HLW contains 7.1 metric tons of heavy metal equivalent (MTHM) per cubic meter. ANDRA (Agence nationale pour la gestion des déchets radioactifs) (2005b), Dossier 2005: Argile. Tome: Safety Evaluation of a Geological Repository High level waste in the Yucca Mountain inventory averages 0.66 MTHM per cubic meter 24

13 Conclusions Geologic disposal is robust, and long-term performance should not require reprocessing and separation Repository efficiency i (e.g., waste loading, cost of engineered barriers) may be enhanced by reprocessing 25 Backup 26

14 Uncertainty in YM TSPA Aleatory Uncertainty Inherent randomness in events that could occur in the future Alternative ti descriptors: irreducible, ibl stochastic, ti intrinsic, i i type A Examples: Time and size of an igneous event Time and size of a seismic event Epistemic uncertainty Lack of knowledge about appropriate value to use for a quantity assumed to have a fixed value Alternative descriptors: reducible, subjective, state of knowledge, type B Examples: Spatially averaged permeabilities, porosities, sorption coefficients, Rates defining Poisson processes 27 Uncertainty in YM TSPA (cont.) Epistemic uncertainty incorporated through Latin hypercube sampling of cumulative distribution functions and Monte Carlo simulation with multiple realizations (approx. 400 uncertain epistemic parameters in TSPA-LA) Aleatory uncertainty incorporated through the design of the analysis 28

15 Example: Calculation of Expected Seismic Dose SAR Figure Example: Eruptive Dose ve1.004_gs_ _20kyr_et100.gsm; 10 4 LA_vE1.004_20Kyr_Dose_Total_event_times_REV00.JNB ve1.004_gs_ _20kyr_et[event time].gsm; LA_vE1.004_20Kyr_Total_Dose_interpolation_REV00.JNB Dose to RM MEI (mrem/yr) Dose to RM MEI (mrem/yr) Time (years) Eruptive dose: 40 realizations of aleatory uncertainty conditional on a single eruption of 1 WP at time zero Τime (yrs) Eruptive dose averaged over aleatory uncertainty associated with a single eruption of 1 WP, eruptions at multiple times 10-2 ve1.004_gs_ _20kyr_[event times].gsm; LA_vE1.004_20Kyr_exdose_horsetails_stats_CCDF_REV00.JNB Ex xpected Dose to RMEI (mrem m/yr) th Percentile Mean Median 5th Percentile Expected eruptive dose; 300 realizations, each showing expected dose from a single sampling of epistemic uncertainty with events at all times (d) Time (yrs) Summary curves showing overall mean dose from eruption MDL-WIS-PA Rev 00, Figures J7.3-1, 2,&4 30