Preparation of uranium carbide throughcarbothermic reduction of uranium dioxide

Emil Lundgrenemlundg@kth.se

SA104X Degree Project in Engineering Physics, First Level

Supervisor: Dr. Mikael Jolkkonen

Department of PhysicsSchool of Engineering Sciences

Royal Institute of Technology (KTH)

Stockholm, Sweden

May 21, 2014

Abstract

The project started with a preparatory literature study and thermodynamic consid-erations. The main purpose was to synthesise uranium carbide through carbothermicreduction. The synthesis method was developed through a serie of experiments. Ele-mental analysis for carbon, oxygen and nitrogen was performed on the product andmodifications were made to the method based on the results in the analysis. Inaddition, XRD was performed to complement the elemental analysis and obtain in-formation about the structure and phases present in the product. The purest productcontained 1.9 wt. % oxygen, 1.3 wt. % nitrogen and 5.2 wt. % carbon. The stoi-chiometric composition of the product was UC1.1O0.3N0.2. The conclusion is that inorder to obtain a pure carbide it is important to ensure good mixing of reactants andminimise potential contamination.

Contents

1 Introduction 31.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.1 Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2.2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Method 72.1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.1 Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.1.2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 Results 113.1 Elemental analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.2 XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4 Discussion 18

1

List of Tables

1.1 Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3 Mass of pellet, temperature and atmosphere in the experiment . . . . 82.4 Furnace program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1 Reaction completion based on elemental analysis data. . . . . . . . . 133.2 Results oxygen and nitrogen analysis of carbide . . . . . . . . . . . . 133.3 Results carbon analysis of carbide . . . . . . . . . . . . . . . . . . . . 133.4 Results oxygen and nitrogen analysis of graphite and uranium dioxide 143.5 XRD results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2

Chapter 1

Introduction

In this chapter the project is put in a wider context and the aim is stated. Inaddition, theory about the reaction and working principle of the equipment used willbe provided.

1.1 Background

In the effective and safe nuclear reactors of the future, new fuel types are required.Uranium nitride is a promising option that offers excellent thermal conductivity, ahigh melting point and compatibility with existing reprocessing methods. However,in nitride fuel, carbon as well as uranium carbide can be present. Too high carbideconcentration makes it impossible to reprocess the fuel with traditional liquid-liquidphase extraction. One such method is plutonium uranium redox extraction (PUREX),which will not be discussed further here. If carbide is present in the extraction,hydrocarbons and carboxylic acids can be formed when carbon reacts with nitric acid[1]. These compounds interfere with the extraction processes, and can in additionbe flammable and explosive. Therefore it is interesting to investigate if the expectedlevels of carbide in nitride fuel will be a problem in reprocessing.

The aim of this project is to produce a smaller amount of uranium monocarbidewith known levels of carbon, nitrogen and oxygen. Stoichiometric uranium monocar-bide contains 4.8 wt. % carbon. It is desirable that the nitrogen content is close tozero and oxygen content below 0.5 wt. % since these elements have to be consideredcontaminations in context of this experiment. Uranium carbide can be synthesisedby at least five different methods [2]. The primary method chosen for this studyis carbothermic reduction of uranium dioxide with graphite. The product of thisproject will later be used in another experiment where the carbide will be mixed witha nitride and dissolved in nitric acid.

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1.2 Theory

The overall reaction is

UO2(s) + 3C(s) −→ UC(s) + 2CO(g)

Temperature (K) ∆G (kJ mol-1) ∆H (kJ mol-1)1400 -264.229 -750.1831500 -229.611 -747.5351600 -195.173 -744.8511700 -160.897 -742.1391800 -126.790 -739.4071900 -92.819 -736.6572000 -59.011 -733.903

Table 1.1: Thermodynamics

1.2.1 Reaction

The reaction is exothermic and the Gibbs potential [3] is negative for all temperaturesof interest (table 1.1). The reaction is thus spontaneous at all of these temperatures.

The reaction rate between solid reactants are, among other factors, determined byparticle size and how well the reactants are mixed. Thorough mixing can be achievedby ball milling the reactants together for a long period of time. Ball milling alsopresses the reactants together, ensuring good contact, hence higher reaction rate andmore complete reaction. However, ball milling will not be used in this experiment,because the lab has a finite number of milling cups and none of them are designated forcarbon containing substances. Furthermore, the partial pressures of gaseous productsalso affect the rate [4]. As reported by Lindemer et al the rate determining step inthe reaction between uranium dioxide and graphite is removal of oxygen, a processwhich is diffusion controlled.

It is assumed that the reaction will start on the surface of the pellet and graduallycontinue towards the center. As the reaction proceed a carbide layer of increasingthickness will form. Consequently, gaseous by products, in this case carbon monoxidehave to diffuse through the carbide layer. It is likely that this process is the ratedetermining step in the removal of oxygen process. In addition, the flow of gas fromwithin the pellet will lead to increased porosity of the final pellet.

As pointed out by Becvar, the pellet can be expected to sinter and become denserand more uniform at high temperatures. This is likely to hinder removal of carbonmonoxide due to healing of defects. It has also been reported by above mentioned

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authors that depending on the rate of heating during the reaction, different mecha-nisms and different reaction rates can be expected. Becvar argues that slow heatingrate ensures more effective removal of carbon monoxide, higher rate of reaction, loweroxygen content and thus more effective reduction. On the other hand, Lindemer etal suggest that the rate will be up to five times higher [4] with fast compared to slowheating rate. However, with a fast heating rate the product will not be uniform, bothmono and dicarbide can be expected.

It is likely that the highest reaction rate is achieved if the reaction is done invacuum, since the ventilation of carbon monoxide will be more effective due to thelower pressure outside the pellet. However it is also possible to run the reaction inargon.

Carbides of uranium are pyrophoric [5]. In pellet form surface oxidation is rapidand in powder form the oxidation can be so fast that the powder starts to smoulder.Therefore carbides cannot be handled in open atmosphere. Unfortunately transferfrom the reaction furnace to protected atmosphere will expose the product to atmo-spheric oxygen for a short period of time.

1.2.2 Analysis

The oxygen and nitrogen content in the product will be analysed using a LecoTC436DR analyser. In the analyser, a small sample (approximatley 30 mg) is heatedin a carbon crucible to a very high temperature (up to 2800 °C). At those temper-atures oxygen and nitrogen are released from the sample and reacts with carbonfrom the crucible. After catalytic treatment and purification of the combustion gasesthe oxygen content is measured through the IR-absorption of carbon monoxide andcarbon dioxide from the combustion gases. Nitrogen content is measured by thermo-conductivity of nitrogen (N2) in the combustion gases.

Carbon content will be measured using a Leco CS-444 analyser. In the analyser thesample is heated together with gaseous oxygen in a ceramic crucible. Carbon fromthe sample will be released and reacts with the oxygen. After catalytic treatmentand purification the gases are analysed for carbon content through IR-absorption ofcarbon monoxide and carbon dioxide in the combustion gases.

The TC436DR and CS-444 analysers can be customised to deliver accurate andprecise results for a wide array of inorganic compounds. The process of doing sois not trivial and will be outlined in section 2.1.2. Depending on properties of thesubstance being analysed the light atoms (oxygen, nitrogen and carbon) are releasedat different temperatures and this need to be taken into account when setting up theequipment.

The structure and phase composition of the product was analysed with X-raydiffraction (XRD). The samples were in powder form. A Siemens D5000 diffractome-ter working at 40 mA current and 35 kV voltage was used in combination with a

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Bruker A100B33 air tight specimen holder. The computer program MAUD[6] wasused for XRD analysis. From MAUD it is possible to obtain the value of the latticeparameter a0 and to approximate the relative abundance of each phase.

The crystal structure of uranium dioxide is face-centered cubic (fcc) with latticeconstant a0 = 5.4663 A. Uranium monocarbide is also fcc with a0 = 4.9605 A.Uranium dicarbide is tetragonal in the most common phase, α−UC2] that has thecomposition UC1.9 [7]. The lattice constants are a0 = 3.5241 A and c0 = 5.9962 A.

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Chapter 2

Method

In this chapter the experimental procedure for synthesis and analysis will be described.

2.1 Procedure

The aforementioned method of carbothermic reduction has previously been used tosynthesise uranium monocarbide [8, 9, 10]. It has been proved that carbide of knownphase, stoichiometric composition and high purity can be produced [7, 8]. Here themethod was chosen mainly due to its relative simplicity.

2.1.1 Synthesis

The starting materials were graphite powder and uranium dioxide powder (table 2.1).The powders were mixed manually in an agate pestle for approximately five minutes.The molar ratio of uranium to carbon was 1 : 3. Uranium dioxide and graphite weremixed in glove box to avoid handling uranium powders in open atmosphere. In totaltwo batches of reactant mixture were prepared (table 2.2). Finally the powder waspressed into a pellet with 4 ton cm-2 pressure. The pellet was put in an yttrium oxidecrucible with another crucible made of the same material as lid. Those two crucibleswere in turn put in a third crucible and a fourth was used as lid. This arrangementwas chosen to protect the pellet from oxygen during the transfer from the furnace toinert atmosphere.

The reaction took place in a sintering furnace under different atmospheric con-ditions (table 2.3). The furnace was a Thermal Technology Inc, Labmaster furnace,model 1000-3560-FP20. The furnace was loaded, sealed and flushed with argon sothat vacuum could established. At full vacuum the pressure was 0.1 mbar. Duringreactive sintering a low flow rate of argon was maintained, yet keeping the furnace atvacuum. Then the furnace was heated from room temperature to 900°C with a rateof 30°C min-1. Then the heating rate was lowered to 10°C min-1 and the temperature

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Figure 2.1: A pellet before sintering

was taken to reaction temperature and held constant for a specified time (table 2.3).Finally the furnace was backfilled with argon and cooled down to room temperaturebefore the product was taken out.

Substance Source SpecificationUranium dioxide Manne Siegbahn laboratory

Stockholm universityMedium coarse powder

Graphite BDH chemicals ltd Poole Eng-land: graphite powder synthetic

Fine powder

Table 2.1: Raw materials

Batch # Total mass (g) Uranium dioxide mass (g) Graphite mass (g)1 10.197 8.997 1.2002 8.472 7.495 0.997

Table 2.2: Preparation

Synthesis # Mass (g) Temperature (°C) Time (hour at Treaction) Atmosphere1 3.055 1500 2.5 vacuum2 From syn # 1 1500 4 vacuum3 5.560 1600 8 argon4 3.267 1500 8 vacuum5 7.204 1500 10 vacuum

Table 2.3: Mass of pellet, temperature and atmosphere in the experiment

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2.1.2 Analysis

All light atoms had to be be released during the analysis. For that to happen afour step furnace program was developed (table 2.4) to control the analyser furnace.The program ensured that neither the TC cell nor the IR cell were saturated duringthe analysis and that all light atoms were released. During the ramp sections of theprogram the power was gradually increased during a certain period of time. It ensuredthat all the light atoms were released during a longer time, to avoid the TC/IR cellfrom being saturated.

Step # Time (s) Type Power (W)1 10 Ramp 10002 20 Constant 20003 20 Ramp 49504 50 Constant 4950

Table 2.4: Furnace program

Use of the air tight specimen holder for XRD added background noise to theresults. The noise was more prominent at small and large angles. Measurement wasdone between 40° and 150° with 0.02° increment. Each increment was held for 0.5seconds. The analyser was set to ‘locked couple’ where the angle between the sourceof x-rays and the sensor is constant. A blank XRD was also performed, with theair tight specimen holder only. It was used to subtract background noise from othermeasurements.

Figure 2.2: Left: Carbon analyser. Right: Oxygen & nitrogen analyser

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Figure 2.3: The sintering furnace & vacuum pump

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Chapter 3

Results

In this chapter the raw data from elemental analysis and XRD is presented. Further,the data is also presented in processed form.

3.1 Elemental analysis

The oxygen sensor was calibrated against a standard containing 3.03 wt. % oxygenand the nitrogen sensor was calibrated against a standard containing 1.89 wt. %nitrogen. After calibration the analyser was tested by analysing the standard again.All analyses were performed on the same occasion. Finally the standard was analysedonce more to make sure the values were consistent. The result was satisfactory.

The oxygen content of stoichiometric uranium dioxide is 11.85 wt. %. Elementalanalysis showed that the uranium dioxide sample contained 13.37 wt. % oxygen,sufficiently close to the stoichiometric value. Reason for discrepancy is measurementerror and probably oxidation to triuranium octoxide (U3O8).

The carbon analyser was calibrated against a standard containing 9.03 wt. %carbon .

The empirical formula of the product can be deduced from the elemental anal-ysis. From synthesis # 4 the carbon, oxygen and nitrogen levels correspond toUC1.1O0.3N0.2. For the product in synthesis # 5 it was UC1.1O0.3N0.6. In the cal-culation, the unweighted mean value of the two elemental analysis values has beenused to obtain the empirical formula. (First the relative amount of uranium wasdetermined by subtracting the aggregate weight percentage of light atoms from 100.Secondly weight percentages was converted into moles by assuming a fixed mass anddividing by the molar mass of each substance. Thirdly and finally the values wasnormalised with the number of moles of uranium to get the desired coefficients in theempirical formula. UuCxOyNz where u = 100−mx−my−mz

238and i = mi

Miui = x, y, z; mi

= wt. %; Mi = molar mass).

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As seen in table 3.2 all oxygen and nitrogen analyses was performed twice. Theobtained values was close to each other for all measurement pairs except the oxygenanalyse of synthesis # 4 and # 5. Hence the uncertainty is higher in these measure-ments. It should be noted that the uncertainty of the empirical formula is large dueto large variation between the oxygen measurement values.

Figure 3.1: Pellet after reactive sintering

3.2 XRD

In MAUD, the obtained spectra was compared to reference values. The results fromthe XRD suggest that that the uranium oxide powder was indeed uranium dioxide.However, it is likely that traces of other oxides, notably triuranium octoxide werepresent too. It was not determined what phases were present, further analysis would

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have been required. In the carbide samples, peaks matching uranium monocarbideand uranium dioxide were found. Analysis did not reveal in what form nitrogen waspresent.

Synthesis # With respect to oxygen (%) With respect to carbon (%)1 54 572 88 783 24 214 94 825 95 86

Table 3.1: Reaction completion based on elemental analysis data.

From synthesis # Mass (g) Oxygen (wt. %) Nitrogen (wt. %)1 0.03594 4.562 0.41281 0.03241 4.411 0.46232 0.02157 1.285 1.4722 0.02386 1.181 1.4803 0.02458 7.866 -0.074673 0.02543 8.083 -0.011324 0.02337 2.555 1.2064 0.03147 1.253 1.3195 0.02556 1.834 3.3895 0.02191 1.196 3.353

Table 3.2: Results oxygen and nitrogen analysis of carbide

From synthesis # Mass (g) Carbon (wt. %)1 0.209 7.9992 0.203 2.6083 0.208 9.2894 0.207 5.2465 0.207 5.104

Table 3.3: Results carbon analysis of carbide

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Substance Mass (g) Oxygen (wt. %) Nitrogen (wt. %)Uranium dioxide 0.02775 13.37 0.06688

Graphite 0.03967 0.610 0.017Graphite 0.04067 0.602 0.043

Table 3.4: Results oxygen and nitrogen analysis of graphite and uranium dioxide

Sample a0 UC a0 UO2 Relative abundance Mass (g)Synthesis # 4 4.9470 5.4758 83 % UC & 17 % UO2 81 0.215Synthesis # 5 4.9146 5.4489 71 % UC & 29 % UO2 67 0.200

Uranium dioxide - 5.4439 100 % UO2 - 0.445

Table 3.5: XRD results

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UC synthesis #4

00-009-0214 (N) - Uranium Carbide - UC - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Cubic - a 4.95500 - b 4.95500 - c 4.95500 - alpha 90.000 - beta 90.000 - gamma 90.000 - Face-centered - Fm-3m (225) - 4 - 100-041-1422 (*) - Uraninite-C - UO2 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Cubic - a 5.46700 - b 5.46700 - c 5.46700 - alpha 90.000 - beta 90.000 - gamma 90.000 - Face-centered - Fm-3m (225) - 4 - 163.39Operations: Background 1.000,1.000 | ImportUC synthesis #4 - File: UC.raw - Type: 2Th/Th locked - Start: 40.000 ° - End: 150.000 ° - Step: 0.020 ° - Step time: 0.5 s - Temp.: 25 °C (Room) - Time S tarted: 20 s - 2-Theta: 40.000 ° - Theta: 20.000 ° - Chi: 0

Lin

(Cou

nts)

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

2-Theta - Scale

41 50 60 70 80 90 100 110 120

Figure 3.2: Diffraction spectra from XRD of the product in synthesis # 4

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UC synthesis #5

00-041-1422 (*) - Uraninite-C - UO2 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Cubic - a 5.46700 - b 5.46700 - c 5.46700 - alpha 90.000 - beta 90.000 - gamma 90.000 - Face-centered - Fm-3m (225) - 4 - 163.3900-009-0214 (N) - Uranium Carbide - UC - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Cubic - a 4.95500 - b 4.95500 - c 4.95500 - alpha 90.000 - beta 90.000 - gamma 90.000 - Face-centered - Fm-3m (225) - 4 - 1Operations: Enh. Background 1.000,1.000 | ImportUC synthesis #5 - File: UC 10h.raw - Type: 2Th/Th locked - Start: 40.000 ° - End: 120.000 ° - Step: 0. 020 ° - Step time: 0.5 s - Temp.: 25 °C (Room) - Ti me Started: 21 s - 2-Theta: 40.000 ° - Theta: 20.00 0 ° - C

Lin

(Cou

nts)

0

100

200

300

2-Theta - Scale

40 50 60 70 80 90 100 110 120

Figure 3.3: Diffraction spectra from XRD of the product in synthesis # 5

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UO2

00-041-1422 (*) - Uraninite-C - UO2 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Cubic - a 5.46700 - b 5.46700 - c 5.46700 - alpha 90.000 - beta 90.000 - gamma 90.000 - Face-centered - Fm-3m (225) - 4 - 163.39Operations: ImportUO2 - File: UO2.raw - Type: 2Th/Th locked - Start: 40.000 ° - End: 150.000 ° - Step: 0.020 ° - Step ti me: 0.5 s - Temp.: 25 °C (Room) - Time Started: 10 s - 2-Theta: 40.000 ° - Theta: 20.000 ° - Chi: 0.00 ° - Phi:

Lin

(Cou

nts)

0

100

200

300

400

500

600

700

2-Theta - Scale

40 50 60 70 80 90 100 110 120

Figure 3.4: Diffraction spectra from XRD of the uranium dioxide

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Chapter 4

Discussion

It has been shown in the present work that uranium carbide can be synthesised withvery small means indeed. The purest carbide produced contained 5.2 wt.% carbon,1.3 wt.% nitrogen and 1.9 wt.% oxygen (table 3.2 and 3.3). In previous work Becvarreported carbon and oxygen levels of 4.78 wt.% and 0.003 wt.% respectively. Analyseof XRD data in MAUD suggest a relatively large proportion of the uranium dioxideremained in the pellet after 8 as well as 10 hours of reactive sintering (table 3.5). Itcan be concluded that the experimental set up and procedure can be improved inorder to obtain a purer product. In addition, to provide basis for sound statisticalanalysis more data points (elemental analysis) would be required.

Analyse of XRD data with MAUD suggested a certain phase composition of theproduct (table 3.5). Taken the assumption that the two major phases were uraniummonocarbide and uranium dioxide the result does not agree well with the results fromthe elemental analysis. If the phase composition suggested by XRD was to be correct,the reaction in synthesis # 4 & 5 respectively would be 81 and 67 % (table 3.5),compared to 94 & 95 % suggested by elemental analysis (table 3.1). The reason forthe discrepancy is probably that the product contained nitrogen in addition to carbonand oxygen, and probably different phases mixed with each other. Furthermore, allpeaks in the XRD spectra were not explained and connected to a certain phase. Itcan be concluded that the two major phases were uranium monocarbide and dioxide,however since the combined stoichiometry of the product was approximately 1 : 2uranium versus light atoms, other phases were bound to be present too.

As improvement of the method, the importance of good mixing as suggested byLindemer et al can probably not be exaggerated. Further discussion of the importanceof mixing was done by Johnson where comparison between ball milling and manualmixing was done [11]. It is suggested that diffusion during the reactive sinteringprocess is insufficient with manual mixing. In the context of this study it is likelythat insufficient diffusion leads to significantly lower rate of reaction and non completereaction.

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The oxygen and nitrogen content of the product was higher than expected fromearlier work. Since no nitrogen is deliberately introduced a possible explanation is aleak in the reaction furnace. This hypothesis is supported by the fact that when thereaction was done in argon atmosphere, the nitrogen levels were very low (table 3.2).Furthermore, an air leak would also lead to higher oxygen levels. In summary, thepotential for improvement by ball milling the reactants and sealing the furnace leakare estimated to be quite large.

The uncertainty of the empirical formula and the oxygen levels are high. Sincethe variation between the values was large and the number of measurements was onlytwo, the mean value of the oxygen level is perhaps not close to the real value. Withadditional measurements statistical analysis could have been used to narrow down theuncertainty and also provide an estimate of how large it was. The aggregate of oxygen,nitrogen and carbon is used to calculate the amount of uranium in the derivation ofthe empirical formula. Consequently, the uncertainty in the oxygen term affects allthe figures in the empirical formula. One can speculate about the reason for the largedifference between the measurement values. As seen in table 3.2, it seems that thevalues are close to each other for all measurements but synthesis # 4 and # 5. Itis strange, since the final analyse of the calibration standard, done after all carbideswas analysed, was consistent with the initial calibration. The reason might not bedirectly linked to the analyser, but a random error such as weighing error.

During different conditions the completion of reaction varied (table 3.1). Synthesis# 1 was roughly 55 % completed after 2.5 hours and synthesis # 5 was 95 % completeafter 10 hours. However, in synthesis # 5, as suggested by XRD some uranium dioxideremained unreacted even though 95 % of the carbon had reacted. It is interestingthat # 3, done in argon atmosphere at a higher temperature for 8 hours was only25 % complete. This was not expected beforehand, argon atmosphere was tested tosee if it would bring down oxygen and nitrogen levels. It did, but the drawback wasvery low rate of reaction. According to previous experiments [2] it is possible to dothe reaction in vacuum or inert gas. However this work suggests that the reaction ismuch faster in vacuum.

The rate determining factor of the reaction is likely diffusion of carbon monoxidethrough the pellet. If diffusion is too slow the partial pressure of carbon monoxideinside the pellet will become too high, so the reaction in practice take place in carbonmonoxide atmosphere. Ventilation of carbon monoxide is presumed to be faster atvacuum, and this is consistent with the aforementioned results. However since this hasnot been reported as a problem from previous authors, another possible explanationis that insufficient mixing limit reaction rate.

It is also worth to comment on the reactants that were used. Since propertiessuch as purity, surface area and particle size was not specified it is recommendedto investigate these factors beforehand. The purity was assessed to some degree byelemental analysis, surface area can be calculated, for instance with BET theory, and

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particle size can be estimated by SEM.The quality of this study was negatively affected by technical difficulties with,

primarily the elemental analysers. In addition, during the course of the project sev-eral factors with adverse impact on the results was discovered, for instance that theanalytical balance was subjected to vibrations and the balance was not configured tocompensate for this.

Other methods must also be considered. Depending on the nature of the investiga-tion different methods might be suitable. Carbothermic reduction has the advantageof simplicity and is also possible to scale up to synthesise large quantities. For ana-lytical purposes however, other techniques might prove more efficient, especially if avery pure product is desired. For further suggestions see Akhachinskii et al [2].

Finally, beyond the scope of this project, previous authors have investigated thekinetics of the carbothermic reduction of uranium oxide. Aided by sophisticatedequipment and elaborate methods the mechanisms of this reduction have been de-duced, to a great degree of detail. The aim here, was not to reproduce the resultsof others, merely produce a reasonably pure product as simply as possible. In thefuture, uranium carbide or uranium nitride might replace today’s nuclear fuels dueto their superior properties. In the meantime it is of great importance to learn moreabout these substances in order to be able to provide clean and safe nuclear energyin the future.

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Bibliography

[1] L. M. Ferris and M. J. Bradley. Reactions of uranium carbides with nitric acid.Journal of the American chemical society, 87, 1965.

[2] V. V. Akhachinskii and S. N. Bashlykov. Systems of uranium and plutoniumwith carbon, oxygen and nitrogen: phase diagrams and methods of production.Atomnaya Energiya (translated), 27, 1969.

[3] I. Barin, O. Knacke, and O. Kubaschewski. Thermodynamical properties of in-organic substances. Springer-Verlag, 1991.

[4] T. B. Lindemer, M. D. Allen, and J. M. Leitnaker. Kinetics of the graphite-uranium dioxide reaction from 1400°to 1756°. Journal of the American ceramicsociety, 52, 1969.

[5] C. Berthinier, S. Coullomb, C. Rado, E. Blanquet, R. Boichot, and C. Chatillon.Experimental study of uranium carbide pyrophoricity. Powder technology, 208,2011.

[6] L. Lutterotti. Materials Analysis Using Diffraction (MAUD). http://www.ing.unitn.it/~maud/.

[7] J. F. A. Hennecke and H. L. Scherff. Carbon monoxide equilibrium pressures andphase relations during the carbothermic reduction of uranium dioxide. Journalof nuclear materials, 38, 1971.

[8] J. Becvar. The preparation of uranium monocarbide. Journal of nuclear mate-rials, 32, 1969.

[9] T. M. Besmann and T. B. Lindemer. High-temperature equilibrium betweenuranium dicarbide, uranium dioxide, carbon and carbon monoxide. Journal ofchemical thermodynamics, 14, 1982.

[10] J. R. Piazza and M. J. Sinnott. High temperature phase equilibria in the sytemcarbon-oxygen-uranium. Journal of chemical and engineering, 7, 1962.

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[11] K. Johnson. Formation of solid-solution in mixed nitride fuel. Master’s thesis,Royal institute of technology, 2012.

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