Source terms

In order to account for the heat loss through the metallic body of the cone, a heat conduction equation, obtained by the elimination of the convection and source terms in Equation (5.25), should also be incorporated in the governing equations. 

Table 5. Source Terms Used in the Dispersion Calculations.

The effects of the surface stresses are accounted for explicitly, and source terms Sj y, and include contributions due to the body process only. For example, the body force due to gravity would be modeled by S x = 0, S y = 0, and S z = -pg-... 

The materials leaving containment are source terms for offsite convective-diffusion transport calculations. Codes. such as CRAC-2 calculate atmospheric diffusion with different probabilities of meteorological conditions to estimate the radiological health effects and costs. 

The amounts of material released from a damaged plant are usually expressed in fractions of the isotopic quantities in the core. These source terms (meaning source for the ex plant transport) depend on accident physics, amount of core damage, time at elevated temperatures, retention mechanisms, and plate-out deposition of material as it transports from the damaged core to release from containment. This section gives an outline of early source term assessments, computer codes used in calculations, and some comparisons of result.s. 

An accident sequence source term requires calculating temperatures, pressures, and fluid flow rates in the reactor coolant system and the containment to determine the chemical environment to which fission products are exposed to determine the rates of fission product release and deposition and to assess the performance of the containment. All of these features are addressed in the... 

Release of fission products to the environment Source Term... 

Fig, 8.2- BMI-2104 suite of codes used in the source term assessment... 

Refinements have been made on the source term calculational methods since WASH-1400. The general trend has been toward source term reduction (e.g., the iodine release for the large LOCA) as compared with the RSS results. In cases such as Station Blackout, the RSS underestimated the tellurium and barium compared with results from the BMI-2104 suite. 

Some codes just calculate source terms (release quantities) and others just calculate the dispersion after release, and some codes do both. Each heading in the following identifies th... 

The Air Force Dispersion Assessment Model (ADAM -1980s) calculates the source term and dispersion of accidental releases of eight specific chemicals chlorine, fluorine, nitrogen tetroji ogen sulfide, hydrogen fluoride, sulfur dioxide, phosgene, and ammonia. It Ut a ... 

Output mass rate and vapor temperature of release, mass rate of air entrained, density of mixtu >1 mass fraction in cloud. Limitations single chemical source terms, limited chemical... 

ALOHA has a comprehensive chemical source term library (>700 pure chemicals). The code can address many types of pipe and tank releases, including two-phased flows from pressurized/ cryogenic chemicals. The user may enter a constant or variable vapor source rate and duration of... 

EMGRESP is a source-term and dispersion emergency response screening tool for calculating downwind contours with a minimum of user input and computational expense in the event of a release of a hazardous chemical. The program provides hazardous contaminant information, calculates toxic concentrations at various distances downwind of a release, and c" the... 

The source-term models consist of gas release from a reservoir, a liquid release from a... 

FIRAC is a computer code designed to estimate radioactive and chemical source-terms as.sociaied with a fire and predict fire-induced flows and thermal and material transport within facilities, especially transport through a ventilation system. It includes a fire compartment module based on the FIRIN computer code, which calculates fuel mass loss rates and energy generation rates within the fire compartment. A second fire module, FIRAC2, based on the CFAST computer code, is in the code to model fire growth and smoke transport in multicompartment stmetures. 

It is user friendly and possesses a graphical user interface for developing the flow paths, ventilation system, and initial conditions. The FIRIN and CFAST modules can be bypassed and temperature, pressure, gas, release energy, mass functions of time specified. FIRAC i.s applicable to any facility (i.e., buildings, tanks, multiple rooms, etc,) with and without ventilation systems. It is applicable to multi species gas mixing or transport problems, as well as aerosol transport problems, FIRAC includes source term models for fires and limitless flow paths, except the FlRlN fire compartment limit of to no more than three... 

HGSystem offers the most rigorous treatments of HF source-term and dispersion analysis a ailable for a public domain code. It provides modeling capabilities to other chemical species with complex thermodynamic behavior. It treats aerosols and multi-component mixtures, spillage of a liquid non-reactive compound from a pressurized vessel, efficient simulations of time-dependent... 

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