Sedimentary Geology and

its Potential Role in Storing Nuclear Waste

By J.C. Routhier and Gabrielle PangCatering to future

generations of the nuclear family...

►Long-term disposal of high-level Long-term disposal of high-level radioactive wasteradioactive waste

►Wastes dangerous ~ 10 000 yearsWastes dangerous ~ 10 000 years►Need safe, stable storage of materials Need safe, stable storage of materials

for unprecedented time periodsfor unprecedented time periods

Problem:Problem:

►Remote area far from major Remote area far from major population centerspopulation centers

►Arid areaArid area Above water tableAbove water table Far from major water/well sourcesFar from major water/well sources Long residence time of waterLong residence time of water

Requirements for Safe Requirements for Safe RepositoriesRepositories

►High geological stabilityHigh geological stability

Low earthquake activityLow earthquake activity Low volcanic activityLow volcanic activity Few fracturesFew fractures Predictable long-term homeostasis of Predictable long-term homeostasis of

environmentenvironment

Requirements (Continued)Requirements (Continued)

►Suitable host rocks: Clays, Suitable host rocks: Clays, mudstones, shalesmudstones, shales Fine grainedFine grained Low porosityLow porosity Laterally extensiveLaterally extensive HomogeneousHomogeneous

Why Sedimentary Rocks?Why Sedimentary Rocks?

Why Sedimentary Rocks?Why Sedimentary Rocks?

►Clay rich sediments are Clay rich sediments are bestbest

Low hydraulic conductivity Low hydraulic conductivity Long residence timeLong residence time Uncemented deposits Uncemented deposits

retain plasticityretain plasticity Self-sealing discontinuitiesSelf-sealing discontinuities

Not this clay...

More like this

Problems with ClayProblems with Clay

►Clays can lose plasticityClays can lose plasticity

►Radionuclides may travel faster Radionuclides may travel faster through clay than previously predictedthrough clay than previously predicted

►Possibility of sharp grain size changes Possibility of sharp grain size changes vertically and horizontally (paths of vertically and horizontally (paths of lesser resistance)lesser resistance)

Evaporite DepositsEvaporite Deposits► Both bedded and salt Both bedded and salt

domes are suitabledomes are suitable

► Transport of Transport of radionuclides in salt radionuclides in salt very slowvery slow

► Plastic behaviorPlastic behavior self- self-sealingsealing

► Higher thermal Higher thermal diffusivity than clay diffusivity than clay

Problems with EvaporitesProblems with Evaporites

►Beds of K and Mg-rich salts dissolve Beds of K and Mg-rich salts dissolve more easily than rock saltmore easily than rock salt

►Can lead to pathways for easier Can lead to pathways for easier transport of radionuclidestransport of radionuclides

►Salt domes produced by density Salt domes produced by density instability (possibility of later recurrence)instability (possibility of later recurrence)

Waste Disposal around the Waste Disposal around the GlobeGlobe

►German repositories planned in salt German repositories planned in salt domesdomes

►Belgium, France, Spain, Switzerland, Belgium, France, Spain, Switzerland, Japan use Argillaceous repositoriesJapan use Argillaceous repositories

►Canada is planning a deposit in Canada is planning a deposit in crystalline basement rock of the crystalline basement rock of the Canadian shieldCanadian shield

►U.S. planning a major repository in U.S. planning a major repository in Yucca mountain, Nevada.Yucca mountain, Nevada.

Why Yucca Mountain?Why Yucca Mountain?(the “Screw Nevada Bill”)(the “Screw Nevada Bill”)

“What you are watching is an exercise in pure politics…I am participating in a nonscientific process-sticking it to Nevada” – Rep. Al Swift, Washington

Why Yucca?Why Yucca?

►Located within a thick sequence of Located within a thick sequence of welded rhyolitic tuffwelded rhyolitic tuff

►Welded tuff Welded tuff layers of hot ash layers of hot ash accumulate and are welded together accumulate and are welded together by the surrounding heatby the surrounding heat

►Very remote area (no residents)Very remote area (no residents)

Why Yucca?Why Yucca?► 350m underground350m underground

► Arid desert climate (>20cm Arid desert climate (>20cm annual precip.)annual precip.)

► Water mobility very low in host Water mobility very low in host rocksrocks

► Surrounding area already Surrounding area already contaminated (Weapons tests)contaminated (Weapons tests)

Why Yucca?Why Yucca?►350m above average 350m above average

water tablewater table

►Closed water basin Closed water basin (land slopes up in all (land slopes up in all directions)directions)

►Underlying aquifer Underlying aquifer does not supply water does not supply water to population centersto population centers

Follow the light...

Problems with YuccaProblems with Yucca

►Syzmanski Theory:Syzmanski Theory: Possibility of upwelling of warm water due Possibility of upwelling of warm water due

to deep fault movementto deep fault movement Upwelling dates to ~10 000 years agoUpwelling dates to ~10 000 years ago Left behind calcium carbonate depositsLeft behind calcium carbonate deposits Warm upwelling very dangerous to Warm upwelling very dangerous to

repositoryrepository

Problems with YuccaProblems with Yucca

►Sundance fault passes through proposed Sundance fault passes through proposed repository siterepository site

►32 other nearby faults present and 32 other nearby faults present and recently activerecently active

►Heat production of waste could turn Heat production of waste could turn water into steam, produce fractures and water into steam, produce fractures and vent radioactive gas.vent radioactive gas.

Problems with YuccaProblems with Yucca

► Seismicity concernsSeismicity concerns Yucca relatively close to plate boundaryYucca relatively close to plate boundary Recent magnitude 5.6 earthquake in 1992Recent magnitude 5.6 earthquake in 1992

► Volcanic concernsVolcanic concerns Lathrop Wells Volcano (18km from proposed Lathrop Wells Volcano (18km from proposed

repository) may have been active 5k-20k years repository) may have been active 5k-20k years agoago

Shh… I didn’t say nuthin’