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Pathway Monitoring

Pathway Monitoring. Radiochemistry and Internal Dosimetry Robert L. Metzger, Ph.D. Pathway Monitoring. The Daiichi Incident produced airborne concentrations of radioactive materials (primarily 131 I, 137 Cs, and 134 Cs.

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Pathway Monitoring

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  1. Pathway Monitoring Radiochemistry and Internal Dosimetry Robert L. Metzger, Ph.D.

  2. Pathway Monitoring • The Daiichi Incident produced airborne concentrations of radioactive materials (primarily 131I, 137Cs, and 134Cs. • Air monitoring using Hi-Vol and Medium Vol air samplers with particulate and TEDA impregnated charcoal filters was started shortly after the initial releases from the plant. • TEDA impregnated charcoal or silver zeolite filters are required to capture the 131I which is primarily a vapor. • ARRA and RSE were operating air samplers.

  3. Air Results

  4. Air Monitoring • Results (see handout), show low but detectable quantities of I-131 as both particulate and vapor in the air. Little to no Cs-137 present. ARRA and RSE results are comparable. Las Vegas results are also similar. • The radiation dose from inhalation of these quantities of I-131 are small (<0.1 mrem). Background is ~630 mrem per year including medical. • On March 21, a large rainstorm washed out the air column and produced wet deposition. Rainwater was analyzed for I-131, Cs-137, Cs-134, Sr-90, and H-3.

  5. Daiichi Plume Dispersion

  6. Rainwater Analysis

  7. Rainwater • The March 21 rainstorm had 200 to 600 pCi/L of I-131 in the rain. • This concentration is not an issue for surface water as the dilution factor is very large. • The rain deposited on the ground and initiated the grass to cow to milk pathway. • Shortly after this rainout ARRA started monitoring milk and leafy vegetables. • ARRA results can be found at www.azein.gov.

  8. Timeliness of Analysis • Pathway monitoring is only effective if the samples can be analyzed and reported in a timeframe that allows public health officials to act, should the radioactive concentration in the food or water warrant it. • For I-131, a thyroid seeker, this time is very short. • For effective treatment KI or Lugol’s solution must be taken within 12 hours of exposure. • For food and water the results must be returned before the food is consumed (and before it spoils).

  9. Timeliness of Analysis • For drinking water, the water utilities must know in time to shift from surface water to ground water. Practically, they must monitor the air data and make a decision on estimated rainout when a storm appears. • EPA and the other government labs (all located on the East Coast) insist they are protecting you. Yet all of the results they posted were 4 or more days old. Their labs are too distant and too slow for I-131 in clinical or public health settings.

  10. Limits • The Food and Drug Administration has published Protective Action Guides (PAGs) for food, milk, and water. See www.radsafe.com for a link to the guides. • Small concentrations of I-131 have been observed in Arizona milk, but at levels far below the PAGs. • No restrictions on milk or leafy vegetables have been made. • Air and Rainwater concentrations have declined to background levels (see handout).

  11. Rainwater Analysis 4/9/11

  12. Internal Dosimetry • Rescue teams sent to Japan to provide aid in the aftermath of the earthquake and tsunami were provided with training, protective clothing, and monitors. • Upon return, bioassays for thyroid uptake of I-131 and internal dose assessment were performed. • One team of physicians from Window of Hope have returned, and bioassay results indicate that the protective measures taken to protect the staff working in and near the exclusion zone were effective. Doses were small (<1 mrem).

  13. Imported Foods from Japan • The plume from the early releases of the accident largely precipitated out in Fukushima and the surrounding prefectures. Fallout patterns are quite erratic (looks like spots on a Dalmation). • The airborne releases have largely terminated, but releases to the ocean continue. • Shortly after the start of the accident, importers of fresh fish from Japan began voluntarily testing their fish for radionuclides. • FDA began testing about a week later.

  14. FDA Methods • The FDA tests imported foods at the border using hand-held meters and portal monitors (where they are available). Positive samples are sent to their WEAC radiochem lab for analysis by gamma spectroscopy. • The FDA method of using hand-held probes is not robust. While they have been able to detect some products contaminated at the PAG, the mass of the contaminated product must be large, and in close proximity to the detector. The LLD for the probe is in Bq, while the PAG is in Bq/kg. Many kg of contaminated product are necessary to exceed the detection threshold of the hand-held probe. • Nonetheless, the food supply is safe.

  15. FDA Food Monitoring

  16. Portal Monitors

  17. Import Alert 99-33 • On April 12, 2011, the FDA issued an alert that requires food imports from six prefectures in Japan be tested for radioactive contamination prior to being released from impound. • The importers must now show radiochemistry lab results using high resolution gamma spectroscopy for samples of the imported products. • The link for this new alert can be found at www.radsafe.com.

  18. Gamma Spectroscopy

  19. Daiichi Water Releases • While airborne releases of radioactive materials have been reduced to very small levels, discharges to the sea are large and continuing. • The effect on the fishing industry is not expected to be significant as the dilution factor for the ocean is very high. • The current at the Daiichi plant is strongly Northward so fishermen have been staying well away from the area of releases. • Contaminated fish products have been rare.

  20. The Future • While the situation at the Daiichi plant has been stabilized, the accident is not over. Units 1 –3 are not in cold shutdown. • Intensely radioactive water is still being produced and some of it is leaking from the assumed breach in the unit 2 torus. • The spent fuel pool in unit 4 contains the active core from the plant. This core is damaged, and it is outside of containment. • Mitigation efforts are being hampered by numerous aftershocks, some as high as Richter 7.

  21. Roadmap to Restoration • In mid-April TEPCO published their roadmap to restoration, a guide for how they are going to stabilize the Daiichi reactors over the next 6 to 9 months. • They are going to fill the reactor vessels of unit 1 & 3 with water and use heat exchangers to bring the temperature below boiling. • They are going to study how to deal with the breach in the torus in unit2. • The damaged outer buildings will be covered. • A waste processing plant will be installed to clean up and reuse the cooling water.

  22. The Future • Pathway monitoring for food imports will need to be continued for most of this time,or at least until the water discharges to the ocean are curtailed. Airborne emissions are now very low. • Overall doses to the populations in the US will be negligible. • Doses in Japan are observable, but small due to effective evacuation and good pathway monitoring.

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