Preparations for Hydrothermal Corrosion of
Uranium Nitride Composite Fuels
1,2
Braine ,
Thomas
1Boise
A DVA N C E D
M AT E R I A L S L A B
I. Background
•
•
Uranium mononitride (UN) has
been identified as a possible
ATF, because of its…3,4
•
•
•
•
•
Lower enrichment requirements
(3.4% U-235 vs. 4.2% in UO2)
Higher fuel burn efficiency
Larger power uprates
Low fission-gas release
Increased fuel cycle time from
Fig. 1: Diagram of a PWR, a type of advanced LWR with
extra accident safeguards and better efficiency.5
18 to 25 months
These advantages are due to UN’s properties
Lower operating and fuel
centerline temperatures
compared to standard UO2 fuel:6
Low temperature gradients
Property
Desired UN
UO2
Compatibility with cladding
Value
materials
Uranium density (g/cm3 )
High
13.55 9.66
Good irradiation stability
Heat capacity (J/kg·K) at 500 °C Low
230
300
Low swelling
W
Thermal conductivity ( /m·K) at High
500 °C
20.5
2 to 4
Melting Point (°C)
2650
2700
High
Autoclave Technical Specs
Max heating rate
150
Max temperature
Chamber sealing temperature
Max pressure
800 °F (427 °C)
200 °C (392 °F)
5500 psig (38 Mpa)
Pure UN corrodes in water and
super-heated steam to form
uranium dioxide (UO2). 8-11
2𝑈𝑁 + 4𝐻2 O ↔ 2𝑈𝑂2 + 𝐻2 + 2𝑁𝐻3
3𝑈𝑁 + 2𝐻2 𝑂 ↔ 𝑈𝑂2 + 𝑈2 𝑁3 + 2𝐻2
Fig. 2: Proposed oxidation model with and
• Corrosion resistance of nuclear fuel
without UO2 phase adapted from Rao et al.10
is crucial for the safety and
longevity of current reactors, in case
of cladding breach, exposing the
fuel to the water coolant (Fig. 3).
• Limited studies have been done on
hydrothermal corrosion of uranium
nitride in the public sector.7-10
Fig. 3: Cutaway of an advanced nuclear fuel rod.11
Proposed Solution for Advanced Fuel Fabrication
•
•
UN composite fuels are proposed to be resistant to hydrothermal corrosion and
be used in LWRs (UO2 alone is mostly resistant).
Rao et al has shown that 8 wt% UO2 composite fuel increases the activation
energy of the hydrolysis reaction from 59 kJ/mol to 136 kJ/mol at p(H2O)=28.2
Torr.10
Acknowledgements
This project was supported by the
National Science Foundation’s
Research Experiences for
Undergraduates (NSF-REU) grant
#1359344 as well as the
Department of Energy Nuclear
Energy University Program (DOENEUP) grant #00120690.
°C/
•
•
•
Fig. 4: Cross section of enclosure design from 3D
rendering.
•
hour
UN was prepared from elemental
atomized uranium using a hydridedehydride-nitride thermal
synthesis (Fig. 8, 9).12
X-ray diffraction (XRD) suggests
that the powder is phase-pure UN
(Fig. 11).
Process reduces residual carbon
and oxygen impurities found in a
large-scale carbothermic reduction
synthesis.13
300 μm
Carbon impurities can form
Fig. 8: (a) Vial of atomized elemental uranium (U)
obtained from the Idaho National Laboratory, and
uranium carbide (UC) that is
(b) its corresponding scanning electron microscope
detrimental to the UN’s corrosion
12
(SEM)
image.
resistance.11, 13
Fig. 9: (a) A
high
temperature
alumina tube
furnace (right)
was used for (b)
the thermal
synthesis
process (left).12
Aluminum base plate:
•
•
•
Fig. 6: Removal of sealing
bolt for testing chamber
access.
Readily oxidizes in air
exothermically (Fig. 2).7-10
2𝑈𝑁 𝑠 + 2 + 𝑥 𝑂2 𝑔 → 2𝑈𝑂2+𝑥 𝑠 + 𝑁2 (𝑔)
•
III. Fabrication of UN Composites
Design
Disadvantages of UN
Fuel
•
and Darryl P.
1
Butt
State University Department of Materials Science and Engineering
2Colorado College Department of Physics
An autoclave is a high temperature, high pressure,
steam chamber for testing corrosion resistance of
materials under extreme conditions.
An enclosure was designed using 3D software
(Fig. 4) and fabricated from aluminum and PVC to
contain any release of radioactive material during
testing (Fig. 5).
Valves were moved and tubing reworked to make
room for the enclosure and allow safe access for
an operator (Fig. 7b).
•
Advantages of UN Fuel
•
•
•
•
Jennifer
1
Watkins ,
II. Autoclave Safety Preparations
The nuclear energy branch of the United States Department of Energy has been
emphasizing the development of accident tolerant nuclear fuels (ATFs) that will
increase the safety of present and future generations of light water nuclear
reactors (LWRs).1,2 LWRs are the most common nuclear reactors worldwide, and
use water as a coolant and neutron moderator (Fig. 1).
•
Brian J.
1
Jaques ,
Bolted with a silicone
O-ring to provide a
water-tight seal
(Fig. 4, 5).
Square perimeter
holds up to 60 mL of
water of the 100 mL
testing chamber
capacity (Fig. 6).
Allows access for
removal of sealing
bolt (Fig. 6).
Fig. 5: Disassembled enclosure parts.
Thermocouple
Gas inlet
Sealing bolt
PVC Tube
Containment:
•
•
•
•
•
Steam and
projectile water
containment
Removable for
sample exchange
and maintenance
(Fig. 6, 7a).
Transparent tube
to observe
leakages.
Silicone gasket
creates secondary
water-tight seal
(Fig. 4).
Two PVC caps
create a
depressurized top
cover (Fig. 7).
Vent valve
50 μm
Fig. 10: (a) As synthesized UN in tungstenlined alumina crucible with (b) its
corresponding SEM image.12
•
Fig. 11: X-ray diffraction patterns of atomized U
and synthesized UN.12
•
High pressure
and temperature
environmental
testing chamber
Pressure
gauge
Process resulted in a powder with
reduced particle size and irregular
morphology (Fig. 10b) compared to
the spherical uranium (Fig. 8b).
UN was milled with UO2 (Fig. 12) to
create the composite fuel (Fig. 13).
Controller
Vent water beaker
Fig. 7: (a) The autoclave ready for testing with radioactive materials (right) with (b) the
assembled enclosure around the sealing bolt (left).
5 μm
Fig. 13: SEM of UN- UO2 composite powder
after milling for 1 hour at 400 RPM in
planetary ball mill.12
References
[1] L.J. Ott, K.R. Robb D. Wang, Journal of Nuclear Fuels, 448 (2014) 520-533.
[2] F. Goldner, Development Strategy of Advanced LWR Fuels with Enhanced Accident Tolerance, in: Enhanced Accident Tolerant LWR Fuels National Metrics Workshop, Germantown, MD,
2012.
[3] G.J. Youinou, R.S. Sen, Nuclear Technology, 188 (2014) 123-138.
[4] H. Zhao, D.H. Zhu, K.S. Chaudri, S.Z. Qiu, W.X. Tian, G.H. Su, Prog. Nucl. Energy, 71 (2014) 152-159.
[5] "The Pressurized Water Reactor (PWR)." NRC. Nuclear Regulatory Committee, 29 Mar. 2012. Web. 15 July 2015. <http://www.nrc.gov/reading-rm/basic-ref/students/animatedpwr.html>.
[6] S.L. Hayes, J.K. Thomas, K.L. Peddicord, Journal of Nuclear Materials, 171 (1990) 289-318.
[7] Josef Bugl, A.A. Bauer, 13, Nuclear Metallurgy, 10, (1964) Battelle Memorial Institute, Columbus, OH.
[8] S. Sugihara, S. Imoto, J. Nucl. Sci. Tech.-T, 6 (1969) 237.
[9] S. Sunder, N.H. Miller, Journal of Alloys and Compounds, 271-73 (1998) 568-562.
[10] G.A.R. Rao, S.K. Mukerjee, V.N. Vaidya, V. Venugopal, D.D. Sood, Journal of Nuclear Materials, 185 (1991) 231-241.
[11] O'Donnell, Casey. "Advancing Nuclear Fuel | INL." INL. Idaho National Laboratory, 9 Dec. 2014. Web. 19 July 2015. <https://www.inl.gov/article/advancing-nuclear-fuel/>.
[12] B.J. Jaques, J. Watkins, J. Croteau, G.A. Alanko, D.P. Butt, Journal of Nuclear Materials, 465 (2015).
[13] R.B. Matthews, K.M. Chidester, C.W. Hoth, R.E. Mason, R.L. Petty, Journal of Nuclear Materials, 151 (1988) 334.
300 μm
Fig. 12: SEM image of UO2 as received from
Bioanalytical Industries.12
IV. Future Testing
•
•
•
•
UN composites (Fig. 13) will be pressed and sintered, then tested by placing
samples in the water-filled autoclave at 320 C and approximately 9 MPa.
Fuel pellets will be characterized for mass change, surface hydration, and grain
boundary deterioration using a digital balance, optical microscope, and SEM.
Corrosion products will be identified using energy dispersive X-ray spectroscopy
(EDS) and XRD.
Leached uranium will be measured using inductive coupled plasma mass
spectroscopy (ICPMS).