Uranium corrosion. Dr N.Harker NRC-UK PONI Nuclear futures conference

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1 Uranium corrosion Dr N.Harker NRC-UK PONI Nuclear futures conference

2 Corrosion in air Oxide Uranium Uranium U + ( 2+x ) O 2 UO 2+x 2

3 Corrosion in air Oxygen diffuses to reach the metal UO 2 O 2 O 2- New oxide Uranium Old oxide U

4 Corrosion in air Old oxide New oxide Uranium Fracturing of oldest oxide

5 Spallation The oxide created is non-protective. ρ U metal = 19.1 g.cm -3 ρ U oxide = 11.0 g.cm -3 Fracturing of oldest oxide ~ x 2 volume expansion

6 Spallation Surface Surface at 45 o UO 2 Metal FIB SE images

7 Corrosion in air Rate at 30 O C = 5.4 x 10-5 mgu.cm -2.h years for complete consumption of a 1cm 3 uranium sample.

8 Corrosion in water vapour Rate at 30 O C = 1.3 x 10-3 mgu.cm -2.h years for complete consumption of a 1 cm 3 uranium sample. Uranium UO 2

9 Corrosion in water vapour In a sealed container Sealed uranium storage container

10 Corrosion in water vapour H 2 O H 2 Uranium UO 2 Uranium U + H 2 O 2UO 2 + H 2

11 Corrosion in hydrogen H 2 Uranium UH 3 2U + 3H 2 2UH 3

12 Hydriding basics nucleation sites Scratches Inclusions Grain boundaries Crystal twins FIB SE images

13 Corrosion in hydrogen H 2 Uranium 2U + 3H 2 2UH 3

14 Exposure of UH 3 to air UH 3 UO 2 2UH 3 + 2O 2 2UO 2 + 3H 2

15 Exposure of UH 3 to air UO 2 X 244

16 Exposure of UH 3 to air UO 2 X 1,200

17 Exposure of UH 3 to air UO 2 X 20,000

18 Corrosion in moist air U + H 2 O + O 2 Which species reactions with the metal?

19 Introduction This has been investigated in numerous ways, but never the whole system holistically. H 2 O UO 2 O 2 U

20 The gas control system Pressure controller Gas reservoir RGA Leak valve Transducer Thermocouple Vacuum system

21 The gas control system 1. Pressure controller Gas reservoir RGA Leak valve Transducer Thermocouple Vacuum system

22 The gas control system Pressure controller Gas reservoir Leak valve 2. Transducer i.e. U + O 2 = UO 2 RGA Thermocouple Vacuum system

23 The gas control system Pressure controller Gas reservoir 3. RGA Leak valve Transducer Thermocouple i.e. U + H 2 O + O 2 = UO 2 Vacuum system

24 The gas control system Pressure controller Gas reservoir RGA Leak valve Transducer Thermocouple Vacuum system 4.

25 Experiment Two uranium samples were prepared, one a fine powder, the other a polished coupon. Using the pressure controller, a 1:1 gas mix of H 2 18 O ( *O in figures) vapour and 16 O 2 ( O in figures) was made and scanned with the RGA. This is then opened to the reaction cells (final reaction gas pressure 9.3 mbar H 2 O & 10.9 mbar O 2 ) The leak valve set to open to 1 x 10-7 mbar every 5 minutes for the duration of the experiment. When all the reactive gas has been consumed the uranium coupon is then transferred into the SIMS for depth profiling. The surface area of the powder is measured using BET Both powder and coupon are then imaged using the focused ion beam.

26 RGA data H 2 H 16 2 O H 18 2 O O 2 Cell pressure

27 RGA data H 2 O 2 H 2 16 O H 2 O H 2 18 O Cell pressure

28 RGA data

29 RGA data H 2 O 2 H 2 16 O H 2 O H 2 18 O Cell pressure

30 Oxygen minimum

31 Oxygen minimum Oxygen reaches a minimum at ~0.05 mbar.

32 Rate

33 Rate P O 2 > 0.05 mbar U + H 2 O + O 2

34 Rate P O 2 < 0.05 mbar U + H 2 O

35 Surface oxide - SIMS Uranium Oxide

Total ion count x10 6 (O & H) SIMS 16 18 O O Total H

36 % Isotopic % Isotopic composition composition of oxygen of oxygen ion ion count count ( 16 O & 18 O) Total ion count x10 6 (O & H) SIMS O O Total H Total O Negative - ion UO (2+x) Thickness ~ 350 nm U metal

37 Last formed (youngest) First formed (oldest) SIMS O from H 2 O O from O 2 Uranium

38 Time zero

39 Oxygen and water vapour Oxygen is removed. Water is created from the oxygen. Oxide is preferentially created from the water vapour..

40 Oxygen minimum Oxygen disappears. Rate increases.

41 Oxygen minimum H 2 H 2 H 2 O O 2 Oxygen reaches a minimum at ~0.05 mbar. Rate increases.

42 Water vapour reaction

43 Oxidation complete Uranium left in an H 2 only environment.

44 Last formed (youngest) First formed (oldest) Conclusions Oxide preferentially forms from water vapour.. O from H 2 O O from O 2 Uranium

45 Conclusions Oxide preferentially forms from water vapour. Reaction is manifested by a observed drop in O 2 pressure.

46 Conclusions Oxide preferentially forms from water vapour. Reaction is manifested by a observed drop in O 2 pressure Corrodes at the slowest rate when P O2 > 0.05 mbar..

47 Conclusions Oxide preferentially forms from water vapour. Reaction is manifested by a observed drop in O 2 pressure Corrodes at the slowest rate when P O2 > 0.05 mbar. After which H 2 gas is evolved rapidly..

48 Thank you Any questions?

Differentially pumped quadrupole SIMS probe on FIBbased and two-beam microscopes

Differentially pumped quadrupole SIMS probe on FIBbased and two-beam microscopes Richard J Chater (1), Barbara Shollock (1), David McPhail (1), Alan J Smith (2) and Graham Cooke (2) (1) Department of Materials,