Tritium: tracing the hydrological cycle

Tritium – the radioactive hydrogen isotope: A multi-porpose environmental tracer for thehydrological cycle

helishelium isotopes studiesBremen

Jürgen Sültenfuß suelten@uni-bremen.de

Institut für UmweltphysikAbt. Ozeanographie

Tritium: tracing the hydrological cycle

• fundamentals of tritium– properties of tritium– origin and distribution of tritium

• studies & applications– atmospheric circulation– water vapor transport– ocean circulation– groundwater dating– river discharge– lake ventilation– …

helishelium isotopes studiesBremen

Jürgen Sültenfuß suelten@uni-bremen.de

Institut für UmweltphysikAbt. Ozeanographie

Tritium decay:

33H → H → 33He + He + ββββ- + νννν + E Emax = 18.6 KeV (very low)

half-life t1/2 = 12.32 yrλλλλ = 0.0563 yr-1 = 1.79 10-9 s-1

NICE:

t1/2 just right to study environmentalanual & decadal variations

decay product 3He - a stable noble gas (no chemical reactions)

if trapped in compartment: mother-daughter pair

OriginOrigin and and abundanceabundance of of tritiumtritium

NaturalNatural tritiumtritium::CosmicCosmic raysrays in in atmosphereatmosphere: : 1414N(n,N(n,33H)H)1212CC

Rapid Rapid reactionreaction to HTO to HTO →→ waterwater cyclecycle →→ precipitaionprecipitaion

SubsurfaceSubsurface productionproduction 66Li(n, Li(n, αααα))33H H

specificspecific activityactivity: Bq/kg : Bq/kg oror forfor tritiumtritium in form of HTO:in form of HTO:

1 TU (1 TU (tritiumtritium unitunit) = 3H/1H = 10) = 3H/1H = 10--1818

= 0.118 Bq/kg =1.11 10= 0.118 Bq/kg =1.11 10--1616 mol/kg = 6.68 10mol/kg = 6.68 1077 atomsatoms/kg /kg

Natural global tritum inventory

Steady state: production = decay PA = λN

Mean production rate: P = 0.28 atoms/cm2 s-1

Area of the Earth: A = 5.1 1018 cm2

Decay constant: λ = 0.0563 yr-1

→ amount of natural tritium = 1.3 kmol = 4kg

compare to global water mass: 1.4 1021 kg H2O = 1.6 1020 kg H

VeryVery lowlow productionproduction → → veryvery lowlow concentrationconcentration::ActivityActivity in in surfacesurface waterwater ~ 10TU ~ 10~ 10TU ~ 10--1515 mol/kgmol/kg

Cosmogenic production – latidute dependence

Charged particles in cosmic radiationare deflected by the geomagnetic field:

Fluxes and production largest near poles

0-10°: 0.12 60-90°: 0.6

other radio isotopes produced byspallation in the atmosphere

Anthropogenic Tritiumextreme large tritium production by hydrogen bomb testsend 50ies and early 60ies

mainly released to stratosphere in northern hemisphere

Bomb tests

Precipitation data: IAEA GNIP North America and Europeform Fritz & Clarke 1997

Bomb tests conduced in Northern Hemisphere

Tritium deposited in stratosphere: Time scale for inter hemispheric air mass exchange in stratosphere: ~ 2 yr

precipitation concentrationIAEA, GNIP

form Fritz & Clarke 1997

Stratospheric tritium concentration:

Mean life time for water vapour: 5.4 yr

from Ehhalt et al. 2002

Ottawa, 45°N, 75°W, 116m asl, CanadaValentia, 52°N, 10°W, 0m asl, IrelandHarare 18°S 31°E, 1500m asl SimbabweKaitoke 42°S, 175°E, 0m asl New Zealand

Tritium in the troposphere:

Mean life time for water ~ 4 weeks

Decline displays general structure

Ocean acts as global sink: max T <<< precipitation

Continental effect

1:1

Weiss et al. 1979

Marine water vapour

Continental water vapour

mean ridge of the alps

Minimum <3.4TU

Minimum >4.5TU

Minimum >4TU

Austria

Atlantic vs. Mediterranian

Umweltbundesamt Österreich 2005

Water vapour in polar regions: Greenland

black: Summit 72°Nred: Eureka 80°Nblue: Mould Bay 76°N

Fourre et al. 2006

partly reconstructed from ice cores

Fourre et al. 2006

Water vapour in polar regions: Antarctica

partly reconstructed from ice cores

Concentrations decline towards coast

substantial tropospheric-stratospheric water vapour ex change

marine or continental precipitation?

tritium in snow cover in the Weddell Sea

tritium records from river run-off:

comparing to precipitation concentration⇒ age spectrum

Esser 1980

0 1000 2000 3000 4000 5000

distance [km]

WOCE A9 19°S Tritium [TU]

-6000

-5000

-4000

-3000

-2000

-1000

0

dept

h [m

]

0

0.01

0.02

0.03

0.04

0.05

0.06

0.08

0.1

0.2

0.4

0.6

0.8

1North Atlantic Deep WaterTmax ~0.04TU

SouthAmerica

Africa

tracing water masses in the oceantritium in the South Atlantic

1TU = 13H/1018 H = 0.12 Bq/kg

Tmax ~1TU

Combining tritium with its decay product:33H → H → 33He + He + ββββ-if 3He is trapped ⇒ dating tool

τ = / ln 2t1/2 . ln (1 + / T

3He* )

Application:- oceanography- limnology- hydrogeology

3He - tritium - age in the Mediterranian:

exploring change of ocean circulation

0 500 1000 1500 2000

Distance [km]

M5 Helium/Tritium age [years]

-4000

-3000

-2000

-1000

0

Pre

s [d

bar]

780

779

778

777

773

761

760

759

758

756

751

723

725

730

734

739

740

741

743

1987

0 500 1000 1500 2000

Distance [km]

M31 Helium/Tritium age [years]

-4000

-3000

-2000

-1000

0

Pre

s [d

bar]

7 8 9 10 26 32 46 53 56 57 72 75 74

10.00 15.00 20.00 25.00 30.00 35.0030.00

35.00

40.00

1995

0 500 1000 1500

Distance [km]

M44 Helium/Tritium age [years]

-4000

-3000

-2000

-1000

0

Dep

th [m

]

306

305

303

300

295

294

292

291

290

289

251

265

247

239

238

237

236

219

217

10.00 15.00 20.00 25.00 30.00 35.0030.00

32.00

34.00

36.00

38.00

40.00

42.00

1999

stagnant: water just gets olderno steady state

3He - tritium - age in a groundwater system:exploring transit times

verify modells, date contaminations, study chemical reaction rates (O2, pharmaceuticals,…)

ditch

Industrial tritium:<1013 Bq per nuclear power plant/yr<1015 Bq nuclear reprocesing plant (Sellafield, La Hague)

heavy water reactorcommerial use: gaseous tritium light sourceused for military equipment, exit signs, watches, keyring pendant,…worldwide total production <1 kg

Summary:

tritium reservoirs: natural 4kgH-bombs 700kgcommercial use 1kg

converted to HTO ⇒ part of hydrological cycle ⇒ ocean acts as sink

precipitation: latitude dependent (increase towards poles)

continental effect: re-evaporation of tritium-rich water from continents ⇔ ocean as sink

seasonal variation: seasonality of stratosphere - troposphere exchange

atmosphere: water vapour residence time:

5yr stratosphere ⇔ ~4 weeks tropospherepathways & exchange between reservoirs:

N⇔S stratosphere ⇔ troposphere

Applications of tritium

marker of younger water in ocean, lakes and groundwaterstudy dynamics

combining with decay product:quantitative dating in ocean, lakes and groundwater

precipitation distribution: atmosphere dynamics

(much more in chemistry, biology, medicine)

Attention needed in the future for

locally elevated tritium concentrations

tritium release from nuclear power plants, reprocessing plants and industry

large amount of tritium will be needed for fusion reactor (10kg/unit)

helishelium isotopes studiesBremen

Jürgen Sültenfuß suelten@uni-bremen.de

thank you for your attention

BfG, 2006

BfG, 2006