Revis&ng radionuclide sources at the Marshall Islands Ken - - PowerPoint PPT Presentation

Revis&ng radionuclide sources at the Marshall Islands

Ken Buesseler, Ma- Chare-e, John Breier, Steve Pike, Paul Henderson, Lauren Kipp, Kaitlyn Tradd Woods Hole Oceanographic Inst.

Baker 1946 Marshall Islands- ground zero for US nuclear tes&ng

Bravo First H bomb Bikini 1954 Bravo site 2015

Bikini- Bravo Crater

Enewetak- Runit dome

137Cs (Bq kg-1)

0 1 2 3 4 50 100 150 200 250

Depth (cm)

10 20 30 40 50 60 70 80

Runit Shore 1 Runit Shore 2 Mike Crater

Enewetak Cesium-137

Mike crater Runit Dome up to 4.5

Water ac&vi&es Bq m-3 Sediment ac&vi&es Bq kg-1

Enewetak Americium-241

(from decay of plutonum-241 t ½ = 14 yr)

Mike crater Runit Dome

Water ac&vi&es (est.) mBq m-3 Sediment ac&vi&es Bq kg-1

241Am (Bq/kg)

Depth (cm)

20 40 60 80 0 50 100 200 400 600 800 1000

Runit Shore 1 Runit Shore 2 Mike Crater

Up to 480 In lagoon

Cesium -137

Bravo Mike Runit Lagoon global Fukushima

water (Bq m-3)

2 4 6 8 200 400

sediment (Bq kg-1)

3 6 9 250 500 750 1000 1250 1500

inventory (kBq m-2)

20 40 60 80 100

H20 Sed

Inventory

Marshall Islands- how does it compare?

Marshall Islands

Plutonium-239+240

Bravo Mike Runit Lagoon global Fukushima

water (Bq m-3)

0.0 0.1 0.2 0.3

sediment (Bq kg-1)

• r inventory (kBq m-2)

5 10 15 250 500 750 1000 1250

H20 Sed

Inventory

Marshall Islands- how does it compare?

Hydrogeology of Enewetak Atoll

Lagoon Flushing Times (TW)

Loca%on Flushing Time (d) Method Reference Bikini Atoll 37 (Jan. 2015) Ra isotopes This study 39 (winter) 80 (summer) Field measurements- scale lab model Von Arx (1948) 17 (Jul. 1946) Radioisotopes Ford (1949) Enewetak Atoll 16 (Jan. 2015) Ra isotopes This study 28 (n/a) Circula&on box model Atkinson et al. (1981) Majuro Atoll 15 Tidal Current Model

At steady-state, lagoon export fluxes for 137-Cs and 241-Am can be calculated as:

Flux (Bq/d) = (Alagoon– APacific)*Vlagoon/TW

Loca%on

224Ra 223Ra 226Ra

Average Bikini Atoll 5.6 3.1 1.2 3.3 Enewetak Atoll 1.1 2.7 2.1 2.0

Credit: Burneg and Dulaiova (2003)

Submarine Groundwater Discharge using radium isotopes (m3/m2/d)

Lagoon groundwater 137-Cs and 241-Am inputs can be calculated as:

SGD Flux (Bq/d) = SGD*AreaSGD*AGW

Lagoon 137-Cs and 241-Am Sources and Sinks

(Bq/d)

1.E+00& 1.E+02& 1.E+04& 1.E+06& 1.E+08& 1.E+10&

Lagoon& Export& GW&Input& Sediment& Input& Bq/d&

137-Cs& 241-Am&

1.E+00& 1.E+02& 1.E+04& 1.E+06& 1.E+08& 1.E+10&

Lagoon& Export& GW&Input& Sediment& Input& Bq/d&

Bikini Atoll Enewetak Atoll

• Groundwater inputs too small to be main source of both

137Cs and 241Am

• Lagoon & crater sediments are likely source of water

column Cs and Am (calculated here assuming Ra isotopes apply to en&re lagoon)

Cs Am

Marshall Islands today

Ongoing source of radionuclides to the N. Pacific lagoon waters show elevated ac&vi&es bigger source for Pu than Cs to N. Pacific Pu isotopes show ongoing long range transport from MI Lagoon and crater sediments are likely source highest water column levels just above seafloor in craters Seafloor sediments are largest radionuclide inventory well mixed to >80 cm (most prior inventories to 20-30 cm) Groundwater inputs can be quan&fied with radium isotopes need more than single snap shot and limited loca&ons GW levels of Cs, Am (and likely Pu) elevated Plutonium isotopes will separate Runit Pu from other sources

Marshall Islands Future? Jet-Yak Autonomous cesium sampler

Success!

20 Bq/m3 = more than 100 &mes less than US drinking water limit = 10 &mes seawater in Woods Hole in 2015 Bikini - Cesium 137 in early 1970’s

20 Bq/m3