RADTRAD-NAI

The RADionuclide Transport, Removal, And Dose (RADTRAD-NAI) code is designed to estimate radiological doses at offsite locations and in the control room of a nuclear power plant as consequences of certain postulated accidents. The potential radiological consequences of a postulated nuclear power reactor accident depend on the timing, quantity, physical form (i.e., vapor or aerosol) and chemical species of the radioactive material released into the environment. Another important application of RADTRAD-NAI is the estimation of radiation exposure as part of Environmental Qualification of equipment. In addition, RADTRAD-NAI may be used to estimate the effect of facility modifications and alternative accident management strategies on release of predicted source terms to the environment. These estimates may be used to support probabilistic safety assessment (PSA) and licensing studies.

RADTRAD-NAI is designed to model two types of releases from the reactor coolant system into the containment. Instantaneous releases are specified in Calculation of Distance Factors for Power and Test Reactor Sites, TID-14844 and in Regulatory Guides 1.3 and 1.4. More protracted and realistic source terms are specified for boiling water reactors (BWRs) and pressurized water reactors (PWRs) in Accident Source Terms for Light-Water Nuclear Power Plants, NUREG-1465. These instantaneous and protracted releases are represented through default input files that are included for convenience with RADTRAD-NAI. In practice, plant-specific source term data is required. Such data can be implemented by making consistent modifications to a set of the source term files.

RADTRAD-NAI includes models for a variety of processes that can attenuate and/or transport radionuclides. It can model sprays, filtered flow and natural deposition that reduce the quantity of radionuclides suspended in the containment or other compartments. It can model the flow of radionuclides between compartments within a building, from compartments within buildings into the environment compartment and from the environment compartment into a control room compartment. Flows between compartments can be through piping, filters, a suppression pool or convection pathways. For piping, filters and suppression pool pathways, models in RADTRAD-NAI can be used to account for the removal of radionuclides from the flow between compartments. The convection pathway provides the ability to model flow between compartments without removal of radionuclides.

Other features in RADTRAD-NAI are available to model various influences on the distribution of radionuclides. Among these are radioactive decay and in-growth of daughters, and moderation of the source term by radionuclide removal in an overlying pool during the ex-vessel phase of an event.

Given an input description of the power plant under consideration, a description of the source term and a description of the removal mechanisms, RADTRAD-NAI calculates the transient distribution of radionuclides throughout the model. RADTRAD-NAI can then use the radionuclide concentrations in conjunction with user-defined /Q dispersion factor data, breathing rates, and occupancy factors to calculate estimated dose at user-selected locations. All dose is due to either inhalation or submersion in a contaminated cloud; there is no direct shine or streaming. Also, RADTRAD-NAI does not perform shielding calculations.

Added features of RADTRAD-NAI include the ability to track the pH level in a suppression pool and the ability to model variable volumes. The pH tracking calculation is performed in parallel with the calculations for the transient distribution of radionuclides in the model. The variable volume capability is a general feature applicable any compartment in which a changing liquid level results in a change in the vapor volume over the pool.

Historically, the RADTRAD-NAI solver is derived from version 3.01 of the RADTRAD solver, which was prepared at Sandia National Laboratory. Changes were implemented to make the RADTRAD-NAI solver conform to version 3.02 of the RADTRAD solver. Several significant contributions have been made by NAI. First, the source code was brought into a code control system under NAI's QA program to assure that future development and maintenance would be performed according to the requirements of 10CFR50, Appendix B. Second, the code package was subjected to a design review to document the status of the code, as received. The design review evaluated the accuracy and completeness of the code and documentation. This included verification of the consistency of the code with respect to referenced information and verification of the consistency of the code with respect to code documentation. The design review also involved validation, with particular emphasis on evaluation of models that allowed specific code features to be isolated, thereby facilitating comparison of results to known solutions. As a result of the design review and subsequent analyses, several errors were identified in the solver. These errors have been corrected and were presented to the distributors of the RADTRAD code package. Third, clear, complete and orderly line-by-line input instructions were written to facilitate preparation of input. Finally, as noted above, NAI has added the ability to track the pH level in a suppression pool and to model variable volume compartments.

RADTRAD-NAI Web Interface

The web interface for RADTRAD-NAI allows you to create new input files, edit existing input files, run cases, view output files, and upload and download files from your PC, UNIX, or Macintosh web browser.

The basic scenario for a new user would be to use the menu commands to:

• upload an existing input file
• upload other files used by the input file
• make any changes desired to the plant or scenario input
• save the changes to disk
• run the case
• view or download the output

The editing capability is provided by stepping through a sequence of forms that are arranged by categories of input.

RADTRAD 3.02 File Compatibility

The web preprocessor can read old input files generated by RADTRAD version 3.02. It automatically converts the information to what is needed by RADTRAD-NAI.

For more information please contact Jim Harrell by e-mail at Jim.Harrell@numerical.com or by phone at (919)465-7230 x227.