Recovery Act, and CERCLA. NRC : licenses the possession and use of radioactive materials. DOE : responsible for conducting or overseeing ongoing operations, and for managing some inactive sites with its jurisdiction. DOT : issued regulations on packaging, labeling, record keeping, and reporting requirements for transport of radioactive materials. Others: DOD, states, NCRP, ICRP. Regulations of Contaminated Sites 20 Note: Many laws and regulations have a dedicated chapter for radionuclides.
Develop a conceptual model during scoping. Field measurement of radiation: beta-gamma monitors, alpha surface monitors, tritium monitors, and air monitors ( Exhibit 10-2 ). Lab measurement of radiation : gas proportional counters, liquid scintillation counters, ionization chambers, and solid state detectors ( Exhibit 10-3 ). Always follow the standard procedures . Collect other site information ( e.g., background, modeling parameters, and etc. ). Data Collection 21
Similar to that for regular CoPCs. Evaluating analytical methods. Evaluating quantitation limits. Evaluating background and blank samples. Sort by class. Reduce # of radionuclides to be assessed ( if possible ). Data summary. Data Evaluation 22 QA/QC
A combination of internal ( e.g., ingestion, inhalation, dermal contact ) and external exposure ( e.g., immersion in contaminated air and water ). Chemical transformation of radionuclides should be considered. Radioactive decay during transport may produce hazardous materials. Radioactive decay and ingrowth of radioactive decay products need to be included in the fate and transport models. Exposure Pathway 23
Direct measurement is always preferred. Modeling would be necessary when: It’s impossible to collect representative samples for all radionuclides of concern; The contaminants have not yet arrived at the exposure point; The contaminants are below the detection limit but still represent a significant risk. Models, codes and methodologies are available from EPA and NRC. Exposure Level 24
Note: “Exposure” means differently for chemicals than for radionuclides. For chemicals, exposure refers to the intake of the mass of chemicals via ingestion, inhalation and dermal contact. The intake (e.g., CDI) is often presented in unit of mg/kg-day ( so that cancer and non-cancer risks can be easily calculated ). For radionuclides, intake is typically expressed in units of radiological activity (e.g., Bq or Ci ) instead of mass. Exposure Quantification 25 Why? Reasons: (1) In addition to internal exposure, we also have external exposure. Concentration measures do not apply to external exposure. (2) Absorbed dose (D) is proportional to decay rate while decay is measured by activity not mass.
Different Approaches 26 Intake calculation Chemicals Risk Characterization Toxicity information (e.g., RfD, SF) Nuclides Intake calculation Dose Equivalent Toxicity information (e.g., risk factor) C (e.g., Bq/kg, Bq/L)
You've reached the end of your free preview.
Want to read all 33 pages?
- Spring '19
- Xufei Yang
- Radioactive Decay, Ionizing radiation, Gamma ray, Address