Pete Shanahan discusses modeling fundamentals with U.S. NRC staff at the 2015 training course.

RAC presents training course to NRC staff

IMG_0597cropRAC presented a 5-day training course on environmental risk assessment to Nuclear Regulatory Commission (NRC) staff from  April 27 through May 1, 2015, at the NRC Professional Development Center in Rockville, Maryland. John Till, Helen Grogan, Peter Shanahan, Art Rood, and Justin Mohler presented lectures during the week, and the course was very well received. IMG_0601cropThe course was designed to allow participants to use the acquired knowledge for performance evaluations of licensee environmental assessments, performing environmental impact reviews, inspecting licensee programs, and managing environmental projects. RAC is contracted to present up to four more training courses for the NRC through 2019.

Helen Grogan tours Hudson and East Rivers on Fire Boat 343 with NCRP committee

Helen Grogan and other members of the National Council on Radiation Protection and Measurements (NCRP) Scientific Committee 3-1 on Emergency Response Dosimetry were very fortunate to be given a tour of the Hudson River and the East River on Fire Boat 343. This is a rescue boat complete with an air-purification system that went into operation in 2010 and can operate in areas tainted by chemical, biological, or nuclear agents. Its four pumps can spray a combined 50,000 gallons of water per minute at 150 psi—twice the capacity of older ships.

John Till honored at 2015 NCRP Annual Meeting

John Till received a medal at the 51st Annual Meeting of the National Council on Radiation Protection and Measurements (NCRP), held March 16 and 17, 2015, that commemorated his presentation of the 37th Lauriston S. Taylor Lecture at the 2013 Annual Meeting of the NCRP. The lecture series honors the late Dr. Lauriston S. Taylor, the NCRP founding President. John is pictured with NCRP President Dr. John Boice and Eleanor A. Blakeley who were also previous recipients of the award.

NCRP committee report co-authored by Helen Grogan published

Helen Grogan attended the 51st Annual Meeting of the National Council on Radiation Protection and Measurements (NCRP), held March 16 and 17, 2015. Helen and her fellow NCRP committee members celebrated the publication of the report they co-authored, NCRP Report No. 175, “Decision Making for Late-Phase Recovery from Major Nuclear or Radiological Incidents”. The report is available for purchase at

NAS committee report co-authored by Helen Grogan published

NAS committee report co-authored by Helen Grogan published

Helen Grogan, Ph.D. co-authored a recently published report prepared by the National Academy of Sciences (NAS) Committee on Research Directions in Human Biological Effects of Low-Level Ionizing Radiation that was chaired by Hedvik Hricak, M.D., Ph.D. The report, “Research on Health Effects of Low-Level Ionizing Radiation Exposure: Opportunities for the Armed Forces Radiobiology Research Institute”, examines recent scientific knowledge about the human effects of exposure to low-dose radiation from medical, occupational, and environmental ionizing-radiation sources, focusing on the work of and opportunities for the Institute.

The report is available from The National Academies Press at

Art Rood selected to be a member of ICRP Task Group 98

Art Rood selected to be a member of ICRP Task Group 98

Mr. Art Rood was invited to be a full member of ICRP Task Group 98, Application of the Commission’s Recommendations to exposures resulting from contaminated sites from past industrial, military, and nuclear activities. The mandate of the task group is to develop a report that describes and clarifies the application of the Commission’s Recommendations on radiological protection of workers, the public, and environment to exposures resulting from sites contaminated due to past industrial, military and nuclear activities.

RAC awarded NRC contract to present training courses to agency personnel

RAC has been awarded a contract with the Nuclear Regulatory Commission to present up to five training courses from 2015 through 2019 to agency personnel on the topic of “Environmental Risk Assessment Analysis.” RAC’s lectures, discussions, and demonstrations for these courses will be designed to allow participants to use the acquired knowledge for performance evaluations of licensee environmental assessments and to perform environmental impact reviews, inspect licensee programs, and manage environmental projects. RAC presented a similar course for NRC personnel in 2009.

MACCS2 comparison paper published

RAC published a paper on a comparison of the MACCS2 Gaussian Plume atmospheric dispersion model with Lagrangian Puff models as applied to deterministic and probabilistic safety assessment. RAC found that at distances greater than 5 km, the Gaussian Plume model implemented in MACCs calculates higher 1-hour average concentrations compared to Lagrangian puff models.

ABSTRACT: The suitability of a new facility in terms of potential impacts from routine and accidental releases is typically evaluated using conservative models and assumptions to assure dose standards are not exceeded. However, overly conservative dose estimates that exceed target doses can result in unnecessary and costly facility design changes. This paper examines one such case involving the U.S. Department of Energy’s pretreatment facility of the Waste Treatment and Immobilization Plant (WTP). The MELCOR Accident Consequence Code System Version 2 (MACCS2) was run using conservative parameter values in prescribed guidance to demonstrate that the dose from a postulated airborne release would not exceed the guideline dose of 0.25 Sv. External review of default model parameters identified the deposition velocity of 1.0 cm s−1 as being nonconservative. The deposition velocity calculated using resistance models was in the range of 0.1 to 0.3 cm s−1. Avalue of 0.1 cm s−1 would result in the dose guideline being exceeded. To test the overall conservatism of the MACCS2 transport model, the 95th percentile hourly average dispersion factor based on one year of meteorological data was compared to dispersion factors generated from two state-of-the-art Lagrangian puff models. The 95th percentile dispersion factor from MACCS2 was a factor of 3 to 6 higher compared to those of the Lagrangian puff models at a distance of 9.3 km and a deposition velocity of 0.1 cm s−1. Thus, the inherent conservatism in MACCS2 more than compensated for the high deposition velocity used in the assessment. Applications of models like MACCS2 with a conservative set of parameters are essentially screening calculations, and failure to meet dose criteria should not trigger facility design changes but prompt a more in-depth analysis using probabilistic methods with a defined margin of safety in the target dose. A sample application of the probabilistic approach is provided.

J.E. Till, A.S. Rood, C.D. Garzon, and R.H. Lagdon. 2014. “Comparison of the MACCS2 Atmospheric Transport Model with Lagrangian Puff Models as Applied to Deterministic and Probabilistic Safety Analysis.” Health Physics, 107, 213-230.

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