A method for producing uranium nitrides from solid stock
Patent Information
- Application Number
- CA3321881
- Authority / Receiving Office
- CA · CA
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-02-28
- Filing Date
- 2025-02-28
- Publication Date
- 2025-09-04
AI Technical Summary
Existing methods for producing uranium nitride from uranium tetrafluoride and tetravalent uranium fluorides are complex and costly, and the use of ammonia as a reactant is hindered by catalysts like UN2 and metal surfaces that reduce yield and require expensive reactor linings to prevent ammonia dissociation.
A method involving a steel reactor with controlled ammonia atmosphere (200-800°C, 100-600 bar pressure) suppresses ammonia dissociation by maintaining a high mole fraction of ammonia (≥5%), allowing the production of uranium dinitride and lower nitrides without expensive reactor linings, using tantalum alloy or boron nitride coatings for protection.
Enhances the yield of uranium dinitride and lower nitrides production while reducing costs by preventing ammonia dissociation and avoiding the need for expensive reactor materials, enabling efficient production in a standard steel reactor.
Abstract
Description
[0001] A METHOD FOR PRODUCING URANIUM NITRIDES FROM SOLID STOCK
[0002] TECHNICAL FIELD
[0003] The invention relates to a method for making uranium nitride powders from uranium tetrafluoride and / or tetravalent uranium ammonium fluorides.
[0004] BACKGROUND
[0005] The present invention relates to a process for conversion of solid uranium tetrafluoride and / or tetravalent uranium fluorides to uranium nitride powders, which can be used to produce nuclear fuels.
[0006] UN is a promising candidate for new nuclear fuel. It has high density, high thermal conductivity, high melting point, and irradiation resistance are further properties that make UN fuel pellets an interesting option as a nuclear fuel.
[0007] Use of the isotope15N is preferable because the predominant isotope,14N, has a significant neutron absorption cross section which affects neutron economy and, in particular, it undergoes an (n,p) reaction which produces significant amounts of radioactive14C which would need to be carefully contained and sequestered during reprocessing or permanent storage.
[0008] Known UN manufacturing process are however complex and costly.
[0009] A method for generating UN is carbothermic reduction of uranium oxide (UO2). Another method suggested is hydriding of metallic uranium to form UH3 followed by nitriding to form U2N3 which can be heated to be decomposed to UN.
[0010] US 2022 / 0333254 Al discloses an electrochemical method for UN production comprising two steps: 1) exposing UH gas to a nitrogen bearing salt at or near a cathode to produce UxNy, where x is an integer of 1 or 2 and y is an integer of 1 to 3; and 2) converting UxNyto UN and nitrogen gas.
[0011] US 7 582232 Bl discloses a method for producing UN by converting uranium oxide to a uranium fluoride salt and heating in ammonia gas to produce uranium nitride.
[0012] Other methods for producing uranium nitride, including exposing uranium tetrafluoride or uranium hexafluoride to ammonia gas, are discussed in the following articles: Ekberg, C., Costa, D , Hedberg, M. et al (2018). Nitride fuel for Gen IV nuclear power systems. Journal of Radioanalytical and Nuclear Chemistry, 318(3): 1713-1725. http: / / dx.doi.org / 10.1007 / slQ967-018-6316-0
[0013] Zagoraios, G. (2022). Synthesis of uranium nitride fuel from UF4 stock. Master Thesis at Reactor Physic Division, KTH. https: / / kth.di vaportai . org / smash / record.j sf?pid=diva2%3 A 1705317&dswid=-4248
[0014] Uranium tetrafluoride (UF4) is a green crystalline solid that melts at 960°C.
[0015] The present invention relates to improvement of ammonia synthesis of uranium nitride fuel from uranium tetrafluoride and / or tetravalent uranium ammonium fluorides.
[0016] DESCRIPTION OF THE INVENTION
[0017] It is an object of the present invention to provide an improved process for conversion of uranium tetrafluoride and / or tetravalent uranium fluorides to a uranium nitride powder comprising of UN2 and / or U2N3 and / or UN.
[0018] UN2 acts as a catalyst and dissociates ammonia in a parasitic process, strongly reducing the yield of the synthesis and therefore constituting a big problem for upscaling. Also, any metal in contact with the ammonia, such as the steel walls of the reactor, can acts as catalysts and dissociate the ammonia. For the latter, a solution could be to line any metal part in contact with the ammonia with a material that have low catalytic activity for ammonia dissociation at the relevant temperature, such as tantalum. This would however be very expensive and would not solve the problem with the UN2 as a catalyst.
[0019] The inventor therefore suggests a solution to suppress NH3 dissociation by moving the equilibrium of the reaction 2NH3 ±TN2 + 3 H2 to favour NH3. Increasing temperatures favours N2 and H2. However, increasing temperatures also favours a higher reaction rate of the ammonia synthesis of the uranium nitride(s). Increasing the pressure favours NH3. Hence, for a given temperature, the pressure can be raised sufficiently high to favour a large portion of NH3 in the reaction. Preferably, the mole fraction of ammonia is at least 5 %. The lower limit may be set to 10%, 15%, 20%, 25 %, or 30 %. By suppressing the NH3 dissociation the catalytic dissociation becomes acceptable since a sufficient degree of NH3 activity is still maintained in the equilibrium state. The same applies for other catalysts. This means that the reactor can be made of steel without the need of expensive lining of the reactor. Moreover, an improved yield of uranium dinitride and lower nitrides can therefore be reached.
[0020] Optionally, the reactor can be provided with a lining or coating to protect the steel from direct exposure to the ammonia atmosphere. This can further supress ammonia dissociation and protect against hydrogen embrittlement. This could be a metallic or ceramic coating / lining. A preferred metallic lining or coating comprises or consist of a tantalum alloy. A preferred ceramic coating or lining comprises or consists of boron nitride, more preferably hexagonal boron nitride.
[0021] According to the present invention, there is therefore provided a method for producing uranium dinitride or lower nitrides, in particular UN2 and / or U2N3 and / or UN, the method comprising the steps of: a) providing a reactor made of steel; b) providing to the reactor an NH3 atmosphere heated to 200-800 °C at a pressure of 100-600 bar;
[0022] The temperature range may be restricted to 300 -700 °C or 400 - 600 °C.
[0023] The pressure may be restricted to 150 - 400 bar or 200 - 300 bar.
[0024] For a given temperature the pressure can be adapted to suppress the NH3 dissociation. c) providing a powder comprising uranium tetrafluoride and / or tetraval ent ammonium uranium fluorides to the reactor for a time period sufficient to react the uranium tetrafluoride and / or tetravalent ammonium uranium fluorides to uranium dinitride or lower nitrides.
[0025] The tetravalent ammonium uranium fluorides can be of the type (NH4)x-4UFxnNHa, which formula can be rewritten as (UF4) (NH4F)XnNFF as described in “Ekberg, C., Costa, D., Hedberg, M. et al (2018). Nitride fuel for Gen IV nuclear power systems. Journal of Radioanalytical and Nuclear Chemistry, 318(3): 1713-1725. http : / / dx, doi . org / 10.1007 / s l 0967-018-63 16-0 “
[0026] The reactor may be of type fluidised bed or including rotary means, or oscillatory means, or other mechanical means to improve contact between the ammonia and the powder. d) Optionally heating the powder in step c) in vacuum or an inert atmosphere, preferably vacuum, at temperatures between 1000 - 1300 °C up to 10 hours for conversion of the powder to uranium mononitride.
[0027] Step c) can be done in the same reactor after evacuation of the NHa atmosphere or in a separate reactor to which the powder from c) is transferred.
Claims
CLAIMS1. Method for producing a powder of uranium dinitride or lower nitrides, in particular UN2 and / or U2N3 and / or UN, the method comprising the steps of: a) providing a reactor made of steel; b) providing to the reactor an NH3 atmosphere heated to 200-800 °C at a pressure of 100-600 bar; c) providing a powder comprising uranium tetrafluoride and / or tetravalent ammonium uranium fluorides to the reactor for a time period sufficient to react the uranium tetrafluoride and / or the tetravalent ammonium uranium fluorides to uranium dinitride or lower nitrides; and d) optionally heating the powder in step c) in a vacuum or inert atmosphere at temperatures between 1000 - 1300 °C up to 10 hours for conversion of the powder to uranium mononitride.
2. Method according to anyone of the preceding claims, wherein the temperature and pressure in step b) is 300 -700 °C respectively 150 - 400 bar.
3. Method according to anyone of the preceding claims, wherein the temperature and pressure in step b) is 400 -600 °C respectively 200 - 300 bar.
4. Method according to anyone of the preceding claims, wherein the pressure is controlled such that the mole fraction of NH3 is at least 10%.
5. Method according to anyone of the preceding claims, wherein the pressure is controlled such that the mole fraction of NH3 is at least 30%.
6. Method according to anyone of the preceding claims, wherein the reactor is of type fluidised bed.
7. Method according to anyone of the preceding claims, wherein the reactor including rotary means, or oscillatory means, or other mechanical means to improve contact between the ammonia and the powder.
8. Method according to anyone of the preceding claims, wherein the reactor comprises a metallic and / or a ceramic coating or lining.
9. Method according to claim 8, wherein the lining or coating comprises boron nitride, preferably hexagonal boron nitride.
10. Method according to claim 8 or 9, wherein the lining or coating comprises a tantalum alloy.