Radiological Dose Assessment for the Public

Overview

Radiation Dose Overview

Radiation can damage living cells because of its ability to deposit energy as it passes through living matter. Energy deposited in the cell can result in cell damage, cell death, and, rarely, cell mutations that survive and can cause cancer. Because energy deposition is how radiation causes cell damage, radiation doses are measured in the quantity of radiation energy deposited per unit mass in the body. Different types of radiation carry different amounts of energy and are multiplied by adjustment factors for the type of radiation absorbed. Radiation affects different parts of the body with different degrees of effectiveness, but we need to report the "effective" dose the whole body has received. The term "effective dose equivalent" (EDE), also referred to as dose, is the "effective" dose calculated to have been received by the whole body, generally from an external radiation source. To calculate this dose we sum the doses to individual organs or tissues.

Long-lived radionuclides that a body inhales or ingests continue to deposit energy in the body and give doses for a long time after their intake. To account for this extended dose period, we also calculated a "committed effective dose equivalent" (CEDE), also referred to in this report as "dose." The CEDE gives the total dose, integrated over 50 years, that would result from radionuclides taken into the body from short-term exposures. Calculated doses generally include the contributions from internally deposited radionuclides (CEDE) and from radiation exposures received from sources outside the body (EDE) all under the general term "dose."

Regulations

Regulations & Requirements

Federal government standards limit the dose that the public may receive from Laboratory operations. The Department of Energy (DOE Order 5400.5 1990) public dose limit from DOE operations to any individual is 100 mrem per year received from all pathways (i.e., all ways in which people can be exposed to radiation, such as inhalation, ingestion, and direct exposure). The dose received from airborne emissions of radionuclides is further restricted by the dose standard of the Environmental Protection Agency (EPA) of 10 mrem per year, which is codified in the Code of Federal Regulations (40 CFR 61); see Appendix A. These doses are in addition to exposures from normal background, consumer products, and medical sources.

Pathways

Pathways and Scenarios

The objective of our dose calculations is to calculate and report incremental (above background) doses caused by LANL operation. Therefore, we don't include dose contributions from radionuclides present in our natural environment or from radioactive fallout unless we identify LANL as a source for some of these radionuclides. Our assessments are intended to be realistic but conservative enough to demonstrate with a high degree of certainty that larger doses did not occur. Annual radiation doses to the public are evaluated for three principal exposure pathways: inhalation, ingestion, and external (also referred to as direct) exposure. We calculate doses that the population as a whole within 80 km may have received and also doses to specific hypothetical individuals within that population as shown below.

• The entire population within 80 km of the Laboratory. We base this modeled dose on all significant sources of radioactive air emissions at LANL. The modeling includes direct exposure to the radioactive material as it passes, inhalation of radioactive material, and ingestion of material that is deposited on or incorporated into vegetation and animal products such as poultry, eggs, and beef.
• The Rad-NESHAP maximally exposed individual (MEI). For this calculation, we use the definition of location in 40 CFR 61, which defines the receptor as someone who lives or works at the off-site location. Any school, residence, or non-LANL workplace would be considered a potential location for the off-site MEI.
• The All-pathway MEI. The calculated dose to the off-site MEI we present here is an "all-pathway" assessment, which includes contributions from air emissions from stack and diffuse sources at LANL, ingestion of food gathered locally, drinking water from local supply wells, exposure to soils in the Los Alamos/White Rock area, and any other significant exposure route.
• An "average" resident of Los Alamos and White Rock. We used average air concentrations from LANL's Air Monitoring Network (AIRNET) in Los Alamos and White Rock to calculate these doses. To these calculated doses, we add the contributions from other potentially significant sources, which may include the Los Alamos Neutron Science Center or LANSCE (LANSCE emissions are not measurable by AIRNET), from ingestion of local food products and water, and from exposure to radionuclides in local soils.
• Ingestion doses for various population locations in northern New Mexico from ingestion of food (fruits and vegetables) harvested (deer, elk, beef, and fish) or grown locally. Because not all food products are available everywhere within the 80-km radius, we do not have a uniform set of ingestion data on which to calculate doses. We report doses for all locations from which food was gathered.

Methodology

General Methodology

Additional information is available regarding the methodologies we follow in our radiological dose calculations.

• General Methodology