ML052350164
| ML052350164 | |
| Person / Time | |
|---|---|
| Site: | WM-00011 |
| Issue date: | 08/24/2005 |
| From: | Tae Ahn Office of Nuclear Material Safety and Safeguards |
| To: | Nuclear Energy Institute |
| Shared Package | |
| ML052350081 | List: |
| References | |
| -nr | |
| Download: ML052350164 (29) | |
Text
Long-Term Materials Behavior at the Potential Yucca Mountain Repository Tae M. Ahn U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001, U.S.A.
Presented to Workshop on Design and Assessment of Radioactive Waste Packages in European Commission, Joint Research Center, Institute for Energy, Petten, The Netherlands October 5 - 7, 2005
Disclaimer:
The NRC staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of a license application for a geological repository at Yucca Mountain.
Schematic Illustration of the Emplacement Drift with Cutaway Views of Different Waste Packages (DOE, 2002)
Schematic Illustration of the Ten General Processes Considered and Modeled for Total System Performance Assessment (DOE, 2002)
Proposed Monitored Geologic Repository Facilities at Yucca Mountain (DOE, 2002)
View Looking Down Exploratory Studies Facility (DOE, 2002)
Risk-Informed Performance-Based Licensing
- Pre-Closure Period
- Post-Closure Period
- Performance Objectives: 10 CFR Part 63
Tools for Risk Assessments
- Pre-Closure Safety Analysis (PCSA)
- Total-system Performance Assessment (TPA)
- Screening of Event Sequences and Scenarios
- Models
- Bases for Model Supports
Waste Package (Alloy 22, Ni-22Cr-13.5Mo-3W-4Fe)
- Long-Term Passivity in Uniform Corrosion
- Localized Corrosion
- Long-Term Phase Stability
- Mechanical Failure
- Fabrication and Reliability
Drip Shields (Ti-7 and Ti-24, Pd addition)
- Long-Term Passivity in Uniform Corrosion
- Fluoride Uniform Corrosion
- Hydride Embrittlement
- Creep
Pressurized Water Reactor Absorber Plate Waste Package Design (DOE, 2002)
Spent Nuclear Fuel
- Matrix Dissolution- Tc and I
- Secondary Phase Formation and Solubility- Np
- Matrix Oxidation - Pu and Am
- Colloid Formation - Pu
- Hydride Reorientation High-Level Waste Glass
- Leaching
- Colloid Formation - Pu
Environmental Conditions Aqueous 1.2 Dry air oxidation corrosion Relative Humidity 1
o Aqueous Dry air Aqueous 0.8 corrosion oxidn. corrosion Temperature ( C) 0.6 DH=50 0.4 %
DH=30 0.2 %
0 1 10 100 1000 10000 Time (year)
Deliquescence Humidity and Aqueous or Dry Air Corrosion (Yang, 2001)
Localized Corrosion Effect of temperature on the repassivation potential crevice corrosion of Alloy 22 in Cl-(Dunn et al., 2003) solutions (Brossia et al., 2001)
(100 °C = 212 °F)
Uniform Corrosion
- Data from DOE, CNWRA, industries and international community (e.g., long-term German tests in rocksalts) point out similarities of uniform corrosion rates. A container lifetime of greater than 10,000 years can be estimated.
- A long-term integrity of passive film is suggested by various models for point defects, chemistry segregation, and passive film growth.
- Analogue studies suggests that modern electrochemical theories for corrosion may explain the analogue observation:
void formation, stoichiometric dissolution of meteorites and josephinite, possible passivity of Indian Pillar, and long-term passivity of carbon and stainless steel over half a century (Sridhar and Cragnolino, 2002).
Stress Corrosion Cracking (SCC)
Conversion: 32.7 MPa m1/2 (29.7 ksi in1/2), 3x10-13m/s (9.84x10-13 ft/s)
(Cragnolino, 2003)
Time-Temperature-Transformation Diagram for Alloy 22 Base Metal (DOE, 2000)
Ti-7 Corrosion
- DOE uses weight loss measurements of titanium in fluoride concentrations
- No fluoride, [F-] = 7.37 x 10-4 M, and [F-] = 7.37 x 10-2 M
- General corrosion rate determined to be 3.25 x 10-4 mm/yr
- No enhanced corrosion by fluoride observed by DOE tests.
Effects of groundwater anions on fluoride- (1 A/cm2 = 1.55x10-1 A/in2, induced corrosion of T-7 (Brossia et al., 2001) 1 mm/yr = 3.94x10-2 in/yr)
Ti-7 Corrosion 101
- Most common products of 100 Titanium Remaining (%)
99 titanium-fluoride reaction 98 are TiF62- and TiF4 97 96 95 94 93
- Is there sufficient water for 92 0 2000 4000 6000 8000 10000 complete corrosion of drip Time (years) shield?
Cumulative reduction of drip shield titanium from corrosion by fluoride at average influx (Lin et al., 2003)
Low-Temperature Drip Shield Creep (Neuberger et al., 2002)
- Expected drip shield creep after rockfall loadings near material yield stress while drift operating temperatures are approximately 100 - 150° C
Conceptual Model of Commercial Spent Nuclear Fuel Cladding Degradation (DOE, 2002)
Environmental In-Package Chemistry Cation Effects Uranium Concentration Measured in a Flow-Through Tests with UO2 where Water Chemistry and Temperature were Periodically Adjusted
[ng/mL: 3.6x10 -11 lb/in3]
(Wilson and Gray, 1990)
- Ca and Si (Ca2+ and SiO44-) tend to decrease SNF dissolution rates by as much as or more than two orders of magnitude at 25 °C (77 °F) compared with those in carbonate solutions of (2x10 2x10-2 M).
- Carbonates and low pH ease the inhibition effects of these cations. However, repository relevant solutions did not show the effects (Table).
- These ions may be depleted in drip tests. However, Schoepite formed instead could impede the oxygen transport to the bare SNF resulting in the decrease of the dissolution rates.
Np Solubility (DOE, 2004)
Transmission Electron Microscopy (TEM) Micrographs of Particulate Material Isolated on a Holey Carbon TEM Grid:
(a) Colloids Formed from Solution and (b) Material in Liquid Spalled from the Glass Surface (Bates et al., 1992)
Dry Oxidation of Spent Fuel Matrix
- Weight Changes of Oxidized Bare Fragments of Turkey Point Fuel at Temperatures from 250° to 360° C (Einziger et al., 1992)
- At temperatures above 280° C, the plateau at O/M = 2.4 is very short and the oxidation proceeds rapidly to U3O8.
Hydride Reorientation - Creep Tests Tsai, 2003 (1 MPa = 0.145 ksi)
Metal Fabrication Reliability (Jain et al., 2003)
Metal Fabrication Reliability (Jain et al., 2003)