Isotope Hydrology: Tritium

1. Isotope Hydrology: Tritium Peter Schlosser, February 14, 2008

2. Syllabus

3. Syllabus

4. Transient Tracers • Tracers: trace substances of natural or anthropogenic origin (stable and radioactive isotopes; chemical compounds. Sometimes toxic or otherwise harmful (contaminants) • Transient tracers: ‘Dyes’with known delivery rates to the environment (e.g.,3H, 3He, CFCs, 129I, SF6, 85Kr) • Radioactive clocks (e.g., 14C,39Ar) • Special sources (e.g., 18O, Ba, nutrients, Ra isotopes, Rn isotopes) • Deliberately released tracers (e.g., SF6, 3He)

5. Tritium Tritium: 3H: radioactive isotope of hydrogen; mass: 3.016 amu 1935/36: Rutherford electrolyzed 13000 tons of water and found a T/H ratio <10-5 Discovery in nature ca. 1950/51 by von Faltings and Harteck Grosse, Johnston, Wolfgang, Libby Discovery was made in atmosphere Kulp and Broecker (Lamont) were involved in early tritium work

6. Tritium production Tritium is produced in the upper atmosphere by interaction of cosmic radiation with nitrogen and, to a small extent, oxygen. The production rate is 0.5 ± 0.3 atoms cm-2 sec-1

7. Tritium decay Tritium decays via β – decay to the noble gas isotope 3He Half life: 12.32 years (formerly: 12.26, 12.43) Qmax: 18.6 keV http://library.lanl.gov/cgi-bin/getfile?00326911.pdf

8. Notation Tritium typically is measured in TU A TU or tritium unit is not a physical unit. It is a convenient notation. One TU is equivalent to 3.2 pCi per kg of water This radioactive activity equals 0.12 Bq per kg of water One gram of water contains only ca. 57,000 tritium atoms

9. Natural 3H background The natural background of tritium in precipitation is ca. 5 TU It has been determined from measurements of tritium in old, pre – bomb wine and in groundwater

10. Early 3H studies

11. Early 3H studies

12. Early 3H studies

13. ‘Bomb’ tritium Most of the tritium found in the environment today has been produced during the surface tests of nuclear devices (‘bomb’ tritium). Weiss and Roether, 1980 http://pubs.usgs.gov/circ/circ1213/major_findings2.htm

14. ‘Bomb’ tritium In 1973 tritium in the environment came from the following sources: Natural: 2.5 % Bomb tritium: 97.5 % Nuclear power plants: 0.02 % Today, ca. 4 half lives after The release of the major portion of the bomb tritium, more than 90 percent has decayed. Thus, modern tritium levels are approaching the natural background. Weiss and Roether, 1980 http://pubs.usgs.gov/circ/circ1213/major_findings2.htm

15. Tritium Release from Nuclear Power Plants Sometimes, there are measurable tritium releases from nuclear power plants Weiss et al., 1976

16. Continental effect Tritium concentrations in precipitation is higher over continents Weiss et al., 1979

17. Continental effect Tritium concentrations in precipitation is higher over continents Weiss et al., 1979

18. Continental effect Tritium concentrations in precipitation is higher over continents Weiss et al., 1979

19. N/S asymmetry Broecker Tritium has been released primarily in the northern hemisphere leading to an asymmetry in the N/S tritium distribution. This asymmetry is compounded by the asymmetry in the land distribution which results in a stronger sink for tritium in the southern hemisohere.

20. N/S asymmetry Tritium has been released primarily in the northern hemisphere leading to an asymmetry in the N/S tritium distribution. This asymmetry is compounded by the asymmetry in the land distribution which results in a stronger sink for tritium in the southern hemisohere. Weiss et al., 1979

21. 3H transfer to the ocean Measurements provide: Time series of cp Spatial patterns of cp Factorization into temporal and spatial components possible because the ratio of tritium at any two monitoring stations is nearly constant in time W. Weiss, thesis

22. 3H transfer to the ocean Tritium concentration in water vapor Moisture content ρ: saturation water content H: relative humidity Tritium Inventory C: tritium concentration

23. 3H transfer to the ocean Water and tritium fluxes (E and T, respectively) between atmosphere and ocean k: atmosphere/ocean transfer coefficient

24. 3H transfer to the ocean Water and tritium fluxes between atmosphere and ocean

25. 3H transfer to the ocean Water and tritium fluxes between atmosphere and ocean Weiss et al., 1979

26. 3H transfer to the ocean d: tritium deposition Weiss et al., 1979

27. 3H transfer to the ocean 0 Weiss et al., 1979

28. 3H transfer to the ocean

29. 3H transfer to the ocean D: total tritium deposition S: time integrated tritium supply

30. 3H inventories in the ocean Oceanic tritium inventory can be estimated via integrated flux or by integrating measured concentrations at stations in the ocean

31. 3H inventories in the ocean Flux calculation compared to measurement of ocean inventory

32. 3H inventories in the ocean Flux calculation compared to measurement of ocean inventory

33. 3H inventories in the ocean Flux calculation compared to measurement of ocean inventory

34. 3H inventories in the ocean Tritium inventories by ocean in 1972

35. 3H surface conc in the ocean Surface concentrations in the ocean can be estimated as a function of time

36. 3H surface conc in the ocean

37. 3H surface conc in the ocean

38. 3H surface conc in the ocean

39. 3H surface conc in the ocean

40. Summary • Tritium is the radioactive isotope of hydrogen and has a natural component of ca. 5 TU • ‘Bomb’ Tritium is a transient tracer released mainly during the surface nuclear weapons tests in the 1950’s and early 1960’s and masks the natural background more or less completely. • Most of the tritium can be found in the northern hemisphere due to its release pattern • The ocean is the main sink for tritium in the environment (it de facto acts as a ‘black surface’ for tritium) • There is a strong continental effect with high concentrations over continents due to the strong sink over the ocean • The tritium concentrations in the environment are approaching natural levels since ca. 4 decades have been passed since the major releases during the surface nuclear weapons tests