Science I Radiation Effects in Nuclear Waste Forms and their Consequences for Storage and Disposal Waste Classification Exempt waste EW Waste that meets the criteria for clearance exemption or exclusion from regulatory control for radiation protection purposes ID: 542321
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Slide1
Wasteform Science I
Radiation Effects in Nuclear Waste Forms and their Consequences for Storage and DisposalSlide2
Waste Classification
Exempt waste (EW):
Waste that meets the criteria for clearance, exemption or exclusion from regulatory control for radiation protection purposes. Very short lived waste (VSLW): Waste that can be stored for decay over a limited period of up to a few years. This class includes waste containing primarily radionuclides with very short half-lives often used for research and medical purposes. Very low level waste (VLLW): Does not need high level of containment and isolation, suitable for disposal in near surface landfill type facilities with limited regulatory control. Typical waste includes soil and rubble with low levels of activity concentration. Low level waste (LLW): Limited amounts of long lived radionuclides. Requires robust isolation and containment for periods of up to a few hundred years. Suitable for disposal in engineered near surface facilities. This class covers a very broad range of waste. Intermediate level waste (ILW): Requires a greater degree of containment and isolation. Heat dissipation usually not an issue. ILW may contain long lived radionuclides, in particular, alpha emitting radionuclides. ILW requires disposal at 10’s–100’s m. High level waste (HLW): Levels of activity concentration high enough to generate significant quantities of heat by radioactive decay, or waste with large amounts of long lived radionuclides. Disposal in deep, stable geological formations usually several hundred metres deep.
Other common acronyms frequently seen:
SNF:
Spent Nuclear Fuel (in HLW)
NORM:
Naturally-Occurring Radioactive Material:
materials enriched
with radioactive elements found in the environment,
e.g. U,
Th
, K, Ra, Rn. Present
in very low concentrations in earth's crust and are brought to the surface
via e.g. oil
and gas exploration
and natural leakage
of radon
gasSlide3
SOURCES of RADIATION in wasteSlide4
By
Table_isotopes.svg
: Napy1kenobiderivative work:
Sjlegg (talk) - Table_isotopes.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6703703Most fission products are slightly n-heavymid-mass elements: 137Cs (Z=55), 90Sr (Z=38).Predominant decay: b− (n→p)Actinides are heavy Z>89.Predominant decay a
-emission
Since both emissions usually leave a nucleus in an excited state, one or more
g
-rays may be emitted Slide5
Fission Products: b
−
-
decayBimodal: 90Sr and 137Cs, both ca. 30 y., near peaks Dominates first 500 yearsJWB at en.wikipedia [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia CommonsBimodal thermal fission products for 235U, 233U and 239Pu.Due to shape of nucleus before fissionSlide6
Major, Minor Actinides: a
-decay
Responsible for the majority of the long-lived radioactivity.
Typical a-decay energies 4-5 MeVBy Sandbh - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45579529U,Pu = Major Actinides. All others = Minor ActinidesSlide7
Activation
Products
Structural Steel
; e.g.59Co (n,g) 60Co t1/2=5.27yCement/Concrete; e.g.151Eu (n,g) 152Eu t1/2=8.5 y 153Eu(n,g) 154Eu t1/2 = 13.4 yZircalloy/stainless steel fuel cladding (long-term) etc;e.g.13C(n,g)14C (e.g. graphite); 14N(n,p)14C (e.g. interstitial) 5730 y58Ni(n,
g) 59Ni t1/2 = 76,000 y
Principally
via neutron
captureSlide8
Performance criteria for waste formsSlide9
Cements and Bituminous Waste(
usually
LLW, ILW)
Cementitious/geopolymersBased on OPC / other formulationshigh pH of pore fluidsVery fine pores (~nm) in CSH gel. Permeability controlled by macropores and cracksComplex mineralogy and possibilities for RN incorporation; e.g. 14CNatural analogues: e.g. JordanBituminousHigh molecular weight hydrocarbonsCan achieve high loadings of specific kinds of wastesNatural analogues: Italy, Athabasca etc.
By Jpvandijk (Own work) [Attribution], via Wikimedia CommonsSlide10
Spent Nuclear Fuel (once through)
Courtesy: Atomic Energy of Canada Limited
US NRC
US NRCModular Dry Storage (10’s years)Reactor3-7 yearsCooling Bay9
mths ->5 years
Deep Geological Storage
100,000-400,000 years
By DOE Photo - http://www.doedigitalarchive.doe.gov/ImageDetailView.cfm?ImageID=2014923&page=search, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2509646Slide11
National decisions on majority of HLW
Direct disposal SNF
Reprocessed HLW
Typical CANDU (PHWR) fuel bundle
Courtesy: Atomic Energy of Canada Limited
Typical PWR (B&W) fuel bundle
Vitrified WasteSlide12
Reprocessing
Commercially via PUREX [
P
lutonium Uranium Redox Extraction] and related solvent-extraction methodsConcentrated HNO3 is used to oxidize UO2 to UO2(NO3)2Tributylphsophate and kerosene are added and mixedTBP forms complexes with nitrates of Pu and U which preferentially dissolve in keroseneWaste must be solidified/vitrified and then packaged for long term storage or disposalAn alternative method, pyroprocessing, using molten salts has not been exploited on a commercial scalePu MOX fuel; (all actinides fast reactor)European Nuclear Society
http://www.materials.cea.fr/en/PDF/MonographiesDEN/Nuclear%20waste%20conditioning_CEA-en.pdf
Vitrified Waste
Vitrified Waste ContainerSlide13
Medical Isotopes: fission 99Mo
Dissolve U-foils after typically 6 days in reactor
99
Mo near the left hand fission peak Majority of supply produced by fission of 235U, dissolution of target, and chemical separation of 99Mo. http://cra.iaea.org/cra/stories/2014-09-15--F23031-Radioisotope-emissions.htmlInitial residue is highly radioactive, liquid waste, containing a suite of fission products and actinitides.This liquid waste can be either acidic or alkalineSlide14
How Long Must Fission Waste be Contained?
A) Lifetime Activity of SNF
b
--dominated90Sr,137Cst1/2~30 yrs
a-dominatedhttp://blogs.egu.eu/network/geosphere/2015/02/
Long-lived
b
-emitters
Typical lifetime:
≳
100,000. NWMO goal: 400,000 yearsSlide15
….Or
B) the
l
ifetime activity of any residual minor actinides in reprocessed wastehttp://blogs.egu.eu/network/geosphere/2015/02/
Remove Pu, U by PUREX (or similar)
Remove
all incl. MA (burner)Slide16
GLASSES
SNF is one form, but for reprocessed waste there are choices…Slide17
Vitrification
Liquids may come from SNF,
99
Mo fission waste, and Pu warheadsLiquid waste is usually calcined to dry it and then glass-forming “frit” is added.A variety of methods are used. A two-step calcining and vitrification method is shown.Neutron absorbers may be added to prevent criticality for high-loadings of U/PuSlide18
Glasses: e.g. silica based
“Continuous random network”
By Silica.jpg:
en:User:Jdrewitt - Silica.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4104670SiO4 tetrahedron concatenates to form 3-d bonded glassPure silica is very viscous, difficult to form etc.Add network modifiers that open up the fully bonded networkand require cations for charge balance.e.g. SiO2⇔ Na
(+)AlO2(-) (charge balance)Alkali
aluminosilicate
glasses.
More formable, more variable local environments, wide chemistrySlide19
Borosilicate
Borosilicate = alkali
aluminosilcate
+ B2O3 Still lower melting and forming temperatures (1150 °C – further limits volatile radionuclides)Low thermal expansion, good shock resistance!Wide variety of coordination environmentsPlatinoids (Pt, Ru, Rh) form metal (oxide) particlesHandbook of Advanced Radioactive Waste Conditioning Technologies. OjanovNeed to avoid 2-phase glass separation:controlled by compositionSlide20
Phosphate glasses
Advantages
Can accept very high %
Al, MoLess corrosion (solubility) than borosilicate while glass.1-step formation: no calcininglow melting point (1000°C for Na-Al-P)DisadvantagesNa-Al-Pcorrosive meltdevitrifies at relatively low temperatures (early stages of storage)high solubility after devitrifiedPublic Domain, https://commons.wikimedia.org/w/index.php?curid=950616Russia uses Na-Al-P glasses for HLW
Fe-P shows better properties: solubility of chemical species/cations;less corrosive melts; loadings 25-50 wt%.
Lab scale only.Slide21
Crystalline forms
…can be formed by solid state reaction of calcined products or via melt processingSlide22
Natural Analogs
Rock
: multiphase (usu.) mixture of minerals
Mineral: individual crystalline phase, with distinct compositions and structures; e.g.By Khruner (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia CommonsAlkali feldspar granite Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
orthoclase
By Didier
Descouens
- Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=7899984
muscovite
quartz
amphibole
By
user:Lamiot
- Photos personnelles prises dans le cadre du GLAM au Museum d'Histoire Naturelle de Lille., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=50303558
=
+
+
+
We can design artificial phase with high loadings of radionuclides that are resistant to radiation
etc
and if necessary mix phases with different properties into a synthetic rockSlide23
Synroc and relatives
Waste form
Main phases
Application/waste loadingSynroc-Czirconolite, perovskite, hollandite, rutileHLW from reprocessing ≤20 wt%Synroc-Dzirconolite, perovskite,spinel nephelineUS defence wastes, 60-70 wt%Synroc-F
pyrochlore, perovskite, uraniniteConversion of SNF, ~50wt%
Tailored ceramics
magnetoplumbite, zirconolite, spinel, uraninite, nepheline
US defence wastes, ≥60 wt%
Pyrochlore
pyrochlore
, zirconolite-4
M
,
brannerite
, rutile
Separated
actinides / Pu≤35
wt
%
Zirconolite
zirconolite, rutile
Separated actinides ≤25 wt%
Monazite
monazite
Act-Ln
wastes, ≤25
wt
%
Zircon
zircon
Pu-rich waste from warheads
Glass-ceramics
titanite, zirconolite, pyrochlore, perovskite, nepheline, sodalite, alumino-silicate glass
Cdn waste (low actinide), complex legacy waste, ILW
Others
britholite, kosnarite, murataite, crichonite
Proposed hosts for
Ln
and
Act
Lumpkin, Ceramic Waste Forms for Actinides. EL
E M E N T S
, V O L . 2 , P P.
365–372, 2006
Synroc began to be developed in the 1970s, and a variety of different
polyphase
synthetic rocks with “minerals” that had favourable properties for waste were developed.
Glass is technically advanced and cheap, so later “Synroc”-style forms have been targeted recently to “boutique” wastes: e.g. complex, heterogeneous formsSlide24
Summary of Crystalline Phase Stability Criteria for Single-Phase Actinide
Storage
Aqueous Durability
Chemical FlexibilityWaste LoadingRadiation ToleranceVolume Swelling
Natural Analogs
Perovskite
(
Ca,Sr
)TiO
3
Low
Medium
Low
Medium
High
Yes
Pyrochlore
Gd
2
(
Ti,Hf
)
2
O
7
High
High
High
Low-High
Medium
Yes
Zirconolite
CaZrTi
2
O
7
High
High
Medium
Low-Medium
Medium
Yes
Zircon
ZrSiO
4
High
Medium
Low(?)
Low
High
Yes
Monazite
Ln
PO
4
High
Medium
High
High
Low
Yes
Zirconates
Gd
2
(Zr,Hf)
2
O
7
High
Medium
Medium
High
Low
No
Zirconia
(Zr,
Ln
,
Act
)O
2-
x
High
Medium
Medium
High
Low
No
Brannerite
UTi
2
O
6
Medium
Medium
High
Low
?
Yes
Crichtonite
Ca(Ti,Fe,Cr,Mg)
21
O
38
?
High
Medium
Low (?)
?
Yes
Murataite
Zr(Ca,Mn)
2
(Fe,Al)
4
Ti
3
O
16
High
High
Medium
Medium
?
Rare
Garnet
Ca
3
Zr
2
(Al,Si,Fe)
3
O
12
?
High
Medium
Low
?
Yes*
Titanite
CaTiSiO
5
Medium
Medium
Low
Low
Medium
Yes
Apatite group
e.g.
(
Ln,Act
,Nd
)
5
(SiO
4
,PO
4
)
3
(OH,F
)
Medium
Medium
Low
Low
Medium
Yes
Kosnarite
NaZr
2
(PO
4
)
3
Medium
Medium
Medium
Low
?
Yes
Lumpkin, Ceramic Waste Forms for Actinides. EL
E M E N T S
, V O L . 2 , P P.
365–372, 2006Slide25
Glass-ceramic composite forms
The best of both worlds?Slide26
Glass-ceramic compositesSlide27
long-term processes in nuclear wasteSlide28
Principal Damage Causing Events
a
-decay:
a-particleassociated recoilchange in chemistry of nucleib--decay: e- emission Change in chemistry of nuclei. Design waste to accommodate different chemistries, oxidation statesSpontaneous fission: recoil fragments + fast n’s. Cannot be prevented, but can prevent criticality: add B (glasses), Hf, Gd (crystalline) Radiolysis: production of free radicalsSlide29
a-decay
particle:
4
He
2+High energy, electronic E transfer + nuclear near endLow volumes. Few hundred atoms displaced, over an extended range (~10,000 nm)
Recoil nucleus:
Lower energy, more nuclear collisions, large damage (~1000 atoms displaced), short range (~10nm)
c.f.
a
-particle 4.5-5.5MeV typical; recoil nucleus
≲
100
keV
(typical)
b
-
decay: 0.5 MeV (typical) Slide30
b
−
-decay
Energy partitioned with neutrino and nucleusElectron moves near speed of lightRecoil negligible: me = 1/1840 amu cf. 137CsBy Inductiveload - self-madeThis vector image was created with Inkscape., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2859203By HPaul - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=39687813
If all k.e. in electron
That part of the energy not retained as long-term stored energy (displacement) is given out as heatSlide31
Cascade creation
Animation of high-energy ion interaction with a crystalline lattice producing a collision cascade
By
Knordlun - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5601607Slide32
DV and other physical changes
SNF:
Radiation hardening and other
physical effects such as delayed hydride cracking could lead to cladding failure Volume swelling can be caused by coalescence of vacancies, or of gas bubbles (chiefly He from a-decay, but possibly H2, O2 from radiolysis) Large swelling changes undesirable: potential to breech containers in extreme casesGlasses can expand, contract or DV ~ 0 dependent on compositionCrystalline forms usually swellVolume swelling increases with dose as the fraction of amorphous material increases but usually eventually saturates.Slide33
Amorphization
Natural
analog
: metamictization; e.g. zircon [ZrSiO4], thorite [ (Th,U)SiO4]The periodic crystal lattice is gradually destroyed by a-decay (a emission and especially recoil) usually retaining external form but destroying internal orderThis does not necessarily mean that RNs are not retainedInhomogeneous damage and swelling can lead to inhomogeneous stress fields and possibly accelerate corrosion in some waste formsRob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia CommonsSlide34
Devitrification
Glass is…already amorphous
But there is no one structure of “glass”
Natural analog: obsidian (volcanic glass) However, sometimes “spherulites” (crystallites) form within the glass=>Therefore, obsidian rarely older than 20 MaRisk for glass waste forms (esp. Na-Al-phosphate)Dependent on glass compositionHigh heat loads may promote nucleationInsoluble (encapsulated) phases may act as nucleation sites and change leachability etc.CCBY 2.0. Simon St JamesSlide35
Radiation Effects in Glass
Changes in polymerization of
tetrahedrally
coordinated glass (less non-bonded oxygen)Alkali segregation and migration(RIS associated with defect migration to sinks)BO4 tetrahedron ⇔ BO3 planar trigonal
⇔Transmutation: changes in radius, valence ⇒ coordination changesSlide36
Glass-ceramic composites
Factors in design: Slide37
Radiolysis
H
2
O→ e− ,HO● ,H● ,HO2● ,H3O+ ,OH−,H2O2, H2In moist air, can form nitrogen radicals and end up as HNO3Radiolysis of hydrous/hydrogenous phases in waste phases/mineralsProduction of H2 gas within cements & bitumen Ojovan, WednesdaySlide38
Summary
Waste classifications
Types of nuclear waste
Waste formsChanges in waste forms due to damage