use of the RESRAD-BUILD code to calculate building surface contamination limits

Surface contamination limits in buildings were calculated for {sup 226}Ra, {sup 230}Th, {sup 232}Th, and natural uranium on the basis of 1 mSv y{sup -1} (100 mrem y{sup -1}) dose limit. The RESRAD-BUILD computer code was used to calculate these limits for two scenarios: building occupancy and building renovation. RESRAD-BUILD is a pathway analysis model designed to evaluate the potential radiological dose incurred by individuals working or living inside a building contaminated with radioactive material. Six exposure pathways are considered in the RESRAD-BUILD code: (1) external exposure directly from the source; (2) external exposure from materials deposited on the floor; (3) external exposure due to air submersion; (4) inhalation of airborne radioactive particles; (5) inhalation of aerosol indoor radon progeny; and (6) inadvertent ingestion of radioactive material, either directly from the sources or from materials deposited on the surfaces. The code models point, line, area, and volume sources and calculates the effects of radiation shielding, building ventilation, and ingrowth of radioactive decay products. A sensitivity analysis was performed to determine how variations in input parameters would affect the surface contamination limits. In most cases considered, inhalation of airborne radioactive particles was the primary exposure pathway. However, the direct external exposuremore » contribution from surfaces contaminated with {sup 226}Ra was in some cases the dominant pathway for building occupancy depending on the room size, ventilation rates, and surface release fractions. The surface contamination limits are most restrictive for {sup 232}Th, followed by {sup 230}Th, natural uranium, and {sup 226}Ra. The results are compared with the surface contamination limits in the Nuclear Regulatory Commission`s Regulatory Guide 1.86, which are most restrictive for {sup 226}Ra and {sup 230}Th, followed by {sup 232}Th, and are least restrictive for natural uranium.« less