CCC-0783 RASCAL 4.3.

RASCAL 4.3

RASCAL Version 4.3 is the latest in the series of the Radiological Assessment System for Consequence AnaLysis codes. It evaluates releases from nuclear power plants, spent fuel storage pools and casks, fuel cycle facilities, and radioactive material handling facilities. Developed for the U.S. Nuclear Regulatory Commission, RASCAL is designed to be used in the independent assessment of dose projections during response to radiological emergencies. The system supplements assessments based on plant conditions. RASCAL will be used by response personnel to conduct an independent evaluation of dose and consequence projections and for training and drills. The model was developed to allow consideration of the dominant aspects of source term, transport, dose, and consequences. Source term calculations in RASCAL estimate the amount of radioactive (or hazardous) material released based on a wide variety of potential radiological accident scenarios. The source term calculations performed that pertain to fuel-cycle facility and materials accidents can generally be categorized as (1) fuel-cycle facility/UF accidents, (2) uranium fires and explosions, (3) criticality accidents, and (4) isotopic releases (e.g., transportation, materials).

Major changes and improvements in RASCAL 4.3 are listed below.

• Create Inventory Base File option which allows users to enter information about how a reactor has been operated to develop a more realistic and accurate reactor core inventory for use in the STDose model calculations.

• Source Term Merge/Export option which allows users to combine source terms for two or more reactors on a single site into a common source term to allow the user to assess the consequences from a multi-reactor event.

• Configure Met Download option allows users to setup an automated meteorological data acquisition module to gather and retrieve of meteorological data from the National Weather Service.

• Changes to the Source Term to Dose (STDose) to include:

        - Long Term Station Blackout (SOARCA) option for accident progression as described in NUREG-1935,

          State-of-the-Art Reactor Consequence Analyses (SOARCA)

        - The (LOCA) (NUREG-1465) option (previously named Time Core Is Uncovered in RASCAL 4.2) which

          incorporates a change in the containment pressure/hole-size method of estimating release rates

        - Coolant Release Accidents option (previously named Specified Core Damage Endpoint in RASCAL 4.2)

          which is now associated with a specific accident that result in core damage (LTSBO and LOCA)

          and updated coolant source terms consistent with the Gale codes (NUREG-0016 and NUREG-0017)

        - Use of Custom Reactor Inventory option which allows the user to model realistic source terms based

          upon fuel management practices of the site using the Create Inventory Base File option

• Spent Fuel Source Term calculations have not changed significantly in RASCAL 4.3; however, the calculation details require a more complete description of the fuel pools contents and the determination of the nuclide inventory at risk.

• The changes to the transport, dispersion and dose calculation adds a fourth Cartesian computational grid which increases the RASCAL 4.3 domain from a 50 mile radius to a 100 mile radius with the associated surface roughness data files for all grids. The calculation of the child thyroid dose has been added to allow for administration of potassium iodide (KI) and ingestion DCFs from Federal Guidance Reports 11 and 13 are included in the radionuclide database.

• Creation of activity balance file which allows the user to track the activity for selected nuclides and nuclide groups from the reactor core and coolant systems through various pathways to the environment.

• Addition of an importance model utility, which allows the user to process the total nuclide activity released to the environment in the course of an event by evaluating the relative importance of the nuclides to four dose measures and ranking the nuclides in order of importance.

• The ability to export and import a time dependent source term file describing the release of radionuclides to the atmosphere and surface concentration in the STDose model in either a XML or CSV format.

RASCAL is a set of tools for emergency response applications. There are four primary tools and three support tools. Two of the primary tools make dose calculations, and the other two display information related to radionuclides and their decay.

The most used tool is STDose. It has modules that calculate the release of material to the atmosphere from several types of nuclear facilities, including nuclear power plants, fuel cycle facilities, and industrial facilities that use radioactive material. Material released to the atmosphere is transported, dispersed, and deposited using Gaussian models. A straight-line Gaussian model is used for near-field calculations, and a Lagrangian Gaussian puff model is used for far-field calculations. Deposition is calculated using a deposition velocity approach in which spatially and temporally varying deposition velocities are estimated using a resistance analogy. Iodine is treated as consisting of three species, iodine associated with particles, reactive iodine gas (e.g. I2), and non-reactive gas (e.g.CH3I). Doses may be calculated using either ICRP-26/30 or ICRP 60/72 dose conversion factors. Submersion doses are calculated using both finite plume and semi-infinite plume models. Calculated doses are compared with various protective action criteria as appropriate.

The other dose calculation tool is Field Measurement to Dose (FMDose). It calculates dose for the first year after the event, the second year after the event, and 50 years after an event from field measurements of deposited radionuclides. The tool calculates groundshine, submersion, and inhalation doses at the measurement point. All dose calculations include decay and ingrowth of daughters. Groundshine doses include the effects of weathering, and submersion and inhalation doses include both weathering and re-suspension.

The support tools are used in conjunction with STDose. The first of these tools is used to create a file that describes the recent operational history of a power reactor. The file is used if an option to create custom core and spent fuel inventories is selected in STDose. The second tool is used to merge source term files from two or more reactors in the event of a multiple reactor event. The tool may also be used to create a source term file for use with other codes. The third support tool is used to set up a utility program that can download meteorological data (observations and forecasts) from the internet.

RASCAL is a set of tools for emergency response applications. As a result, it bases its estimates of material released on limited information that should be available at the time of the event. The atmospheric transport, dispersion, and deposition of the released material are calculated using available meteorological information, which may be limited. The consequence assessments are based on simple models. Each of these components has inherent uncertainties. RASCAL does not model the uncertainties or estimate confidence intervals for its consequence estimates. It is the responsibility of the consequence assessor to understand the limitations of the models implemented in RASCAL and determine whether or not RASCAL output is reasonable.

RASCAL is designed to permit a complete consequence assessment and evaluation of results within 15 minutes.

Data entry times for RASCAL depend on the complexity of the problem being addressed. Data for simple problems can be entered in less than a minute. Data entry for more complex problems can generally be accomplished in less than five minutes. Run times depend on the computer and duration of the period being modeled. The run time for a 24-hour release takes less than 30 seconds on a computer with an Intel i7 CPU with Windows 8. Running the same problem on a computer with an Intel i5 CPU and Windows 7 takes about 35 seconds.

Background Documentation:

• J. V. Ramsdell, Jr., G. F. Athey, S. A. McGuire, and L. K. Brandon: RASCAL 4: Description of Models and Methods, NUREG-1940 (December 2012).

• G. F. Athey, L. K Brandon, and J. V. Ramsdell, Jr.: Draft RASCAL 4.3 Workbook, (September 2013).

RASCAL runs on computers using the Windows operating system (XP, 7, or 8).

Source files are not included in this release.

RASCAL 4.3 is a Windows-based application. Executables included in the package were created using Microsoft Visual Basic 6, Microsoft VB.NET, and Intel Visual Fortran compilers. No source files are distributed. The software was tested under Windows 8, Windows 7, and XP service pack 3. Some modules require Microsoft.NET Framework 4.

Contributed by: Radiation Safety Information Computational Center

                Oak Ridge National Laboratory

                Oak Ridge, Tennessee, USA

Developed by:   Athey Consulting, Charles Town, West Virginia, USA

                Ramsdell Environmental Consulting, Redmond, Washington, USA

                Pacific Northwest National Laboratory, Richland, Washington, USA

                Nuclear Regulatory Commission, Washington, D.C., USA