Radionuclide Release at Fukushima Peter F. Caracappa, Ph.D., CHP American Nuclear Society Connecticut Section November 16, 2011
Overview Accident Review Radioactive Material Releases Transport and Deposition Dose Impacts On-site impacts Comparisons with Chernobyl are problematic, but inevitable 2
Accident Review 6/14/2012 3
Reactor Status at time of Earthquake Units 1, 2, and 3 were operating normally Unit 4 was shut down and empty, core fully offloaded in spent fuel pool Units 5 and 6 were shut down, but remained fully loaded 4
Progression of the Accident 14:46, 11 March 2011 (Day 1) Magnitude 9.0 Earthquake Units 1 to 3 shutdown automatically (SCRAM), per design Power generators tripped, per design Movement of plant foundation exceeded design basis earthquake ground motion (DBEGM) Disabled offsite power systems No serious damage to onsite safety systems 5
Progression of the Accident Earthquake resulted in Loss of Offsite Power Tsunami disabled diesel generator backup power Battery power operable for only a limited time (<6 hr to ~3 days)
Progression of the Accident Fission product release from damaged fuel Some discharge through valves to wet well Some stay in wet well water Some enter dry well Some deposit on dry well surfaces Build up of hydrogen, nitrogen and water vapor pressure
Progression of the Accident Gas is released into the reactor service floor Pressure reduced (~ 4 bar) Hydrogen and some fission products (iodine, cesium and noble gases)
Progression of the Accident 12 March 2011 (Day 2) H2 explosion in Unit 1 service area Steel frame roof destroyed Concrete building intact Seawater injected j
Expected Radioactive Material Releases WASH 1400 identified four stages of core material release Gap Release Meltdown Release Vaporization Release Oxidation Release Time since shutdown has significant effect Spent fuel pools will not contain short-lived products 10
Expected Radioactive Material Release Noble Gasses (Xe-Kr) I Cs, Rb Te, Sb Ba, Sr Ru, Mo, Rh, Tc, Co Nd, Y, Ce, Pr, La, Nb, Am, Cm, Pu, Np, Zr Decreasing Likelihood of Release Radiation and Fukushima 11
Observed Radioactive Material Releases I-131 130-160 PBq (3.5-4.3 MCi) Cs-137 6.1-15 PBq (165-405 kci) Chernobyl: 1760 PBq I-131 & 81 PBq Cs-137 Reports indicate small quantities of Sr and Pu detected outside of plant (3.4-4400 Bq/kg combined Sr-89 & Sr-90 on site) Isotopes detected in stagnant water in plant: Cl-38, As-74, Y-91, I-131, Cs-134, Cs-136, Cs-137, La-140 12
Radioactive Material Transportation and Deposition 6/14/2012 13
Transport and Deposition of Radioactive Releases Iodine-131 detected worldwide Cesium-137 & -134 detected over relatively broad areas, including western US 14
Early Radionuclide Analysis Kyoto University personnel performed gamma spec on soil samples in Iiate prefecture (25-45 km NW of plant) ~17-18 days after the accident 15
Early Radionuclide Analysis 16
Transport and Deposition of Radioactive Releases I-131 Transport 17
Transport and Deposition of Radioactive Releases Cs-137 Deposition Nuclear weapons testing responsible for ~2000 Bq/m 2 of Cs-137 (in undisturbed soil @ 40 N) 63095 10000 1585 251 40 6.3 1.16 18
Transport and Deposition of Radioactive Releases Cs-137 Deposition 398k 63095 10000 1585 251 40 6.3 1.16 19
Transport and Deposition of Radioactive Releases Deposition of Cs-134 and Cs-137 in the area immediately surrounding the plant 20
Radiation Monitoring Results in CA Air monitoring 21 Radiation and Fukushima UC Berkeley, Nuclear Engineering Dept.
Radiation Monitoring Results in CA Rainwater monitoring Radiation and Fukushima 22 UC Berkeley, Nuclear Engineering Dept. UC Berkeley, Nuclear Engineering Dep
Radiation Monitoring Results in CA Milk samples 23 Radiation and Fukushima UC Berkeley, Nuclear Engineering Dept.
Dose Impacts 6/14/2012 24
Dose Due to Radioactive Releases Air Submersion Instantaneous/transient Inhalation Dose commitment Ground Irradiation Persistent Ingestion Dose commitment 25
Radioactive Material in Air Early dose measurements dominated by atmospheric submersion Radiation monitoring posts registered spikes that quickly quc returned eu edto oeevaed elevated steady state 26
Radioactive Material in Air 27
Radioactive Material in Air 28
Radioactive Material in Air Dose commitment from breathing contaminated air: Dose commitment per hour is up to 240 times external exposure rate 1.2 m 3 /hr breathing rate Cs-137:Cs-134:I-131 at 1:1:16 Absent I-131, dose commitment is ~74x (time dependent value) 29
Radioactive Material on Ground After plume passes, radiation dose will be dominated by material deposited on ground Estimated dose rate is 16.6 msv / MBq/m 2 Accounts for time spent inside/outside 30
Radioactive Material on Ground 31
Radioactive Material on Ground Inhalation hazard may be generated by resuspension of deposited material Assuming resuspension factor ~ 10-6 m -1, inhalation dose commitment rate ~0.4% of external dose rate (combined Cesium) 32
Radioactive Material on Ground Material deposited on the ground may enter the food chain and be ingested 33
Radioactive Material on Ground Some radioactive material, primarily I-131, detected in water supplies and foodstuffs Most measurements returned to background by early April 34
Radioactive Material on Ground I-131 contamination of varying levels was detected in milk, spinach, and other produce following the accident Export and consumption restrictions remain in effect for much of the area 35
Impacts of Radioactive Releases Measured external integrated dose (MEXT monitoring stations most begun ~1 week after accident) 36
Impacts of Radioactive Releases Projected external dose for year following accident (not including potential consumption or inhalation) 37
Impacts of Radioactive Releases Population (outside 20 km zone) affected by radioactive deposition (pre-earthquake census information) Government has set 20 msv/a limit for occupation 38
Impacts of Radioactive Releases All cumulative dose estimates outside 80 km (50 miles), and much of the area inside that distance, are less than 1 msv/a Collective dose estimates can vary widely based upon assumptions and future evacuation plans, but reasonable current estimates are in the range of 800-1800 person-sv to the most affected population, and perhaps several times that to the greater surrounding population Chernobyl ~255,000 person-sv TMI ~20 person-sv (total) At this level, projected increase in cancer mortality would be ~0.001% above the natural rate 39
Reported Doses to Plant Workers As of 9/15 Dose Category (msv) External Internal Total >250 0 5 6 200-250 0 1 2 150-200 9 1 14 100-150 28 5 77 50-100 165 78 309 20-50 515 259 985 10-20 1451 684 1652 <10 12673 12552 11340 Total 14841 13585 14385 40
Conclusions Deaths due to earthquake/tsunami: ~25,000 Deaths or serious injuries due to direct radiation exposures: 0 Cancer deaths due to accumulated radiation exposures: can t be ruled out conservative risk estimates ~100s cases, against an expected ~10 million cases Remediation efforts or further evacuation may be necessary to avoid a sub-population with a significantly higher risk 41