Fig. (4) 30-minute plume (Scenario 1), This graphic, which was created using HotSpot at a release height of 1.5 m, depicts the radiological plume dispersion pattern 30 min- utes after the discharge. The concentration contours show how radioactive material (Bq•s/m³) spreads with down- wind distance (Homann and Aluzzi, 2020). The “hotspot” area, where exposure danger is highest, is indicated by the red zone, which represents the highest concentration region close to the release point. As the plume disperses and dilutes with distance, the concentrations in the green and blue zones decrease. The elliptical shape of the plume, which spreads mostly down the wind direction with little crosswind diffusion and where radionuclide concentration rapidly drops with distance due to atmospheric mixing and dilution, illustrates how wind and atmospheric stability ef- fect the dispersion (Gaudio et al., 2010).

Figure (5): Variation of TEDE (in Sv) from the Release Point (Height = 1.5 m), The Total Effective Dose Equiva- lent (TEDE) is plotted against the distance downwind from the discharge location in this graph. The TEDE curve grad- ually decreases after rising significantly close to the source and reaching a maximum value at about 0.3–0.5 km. Be- fore dilution takes over, this peak indicates the place where airborne concentration is high enough to result in the most inhalation and external exposure. The TEDE quickly decreases when the plume disperses after one kilometer. This curve’s form is typical of short-term releases: a sharp rise brought on by high near-field concentrations, then a gradual decrease as the dose decreases with distance due to dilution and deposition (Junxiao et al., 2016).

Figure (6): Deposition on the Ground (kBq/m2) Varia- tion from the Release Point (Ground Level) displays the radioactive deposition pattern on the ground surface as a function of distance. Near the release site, deposition rises significantly and peaks between 0.1 and 0.3 km before pro- gressively declining downwind. This tendency illustrates how tiny particles stay in the air longer and deposit farther away, whereas bigger particles and aerosols settle quickly close to the source. The findings show that the primary fallout or contaminated zone is a small area of high ground contamination close to the origin (ICRP Publication 72, 1995).

Table (3) show how the maximum exposure and contami- nation happen near the source (within the first kilome- ter) during a brief near-ground distance from the release source (0.03–80 km). TEDE (Sv) is the total effective dose equivalent received from inhalation and external expo- sure. TEDE confirms the greatest exposure zone around the source, peaking between 0.3 and 0.5 km (0.19 and 0.09 Sv). TEDE drastically decreases after about 2 km because of plume dilution. Similar trends are seen in air concentra- tion (Bq•s/m³), which is very high close to the source (~10o Bq•s/m³) and decreases with distance. This illustrates how, as the plume travels, radionuclide density decreases (ICRP, 1995). Ground surface deposition (kBq/m²) illustrates the accumulation of deposited activity on the ground. Where the contamination is most severe, the readings are high- est between 0.1 and 0.5 kilometers. The radiation dose rate from deposited materials is called the ground shine dose rate (Sv/hr). The external exposure risk is highest close to the source (up to ~8.6×10o¹ Sv/hr) and declines with dis- tance and arrival time (hour:min), which shows how long it takes the plume to reach each location. It mirrors ground deposition values. The plume exhibits a rapid release under windy or neutral stability circumstances, reaching a dis- tance of around two kilometers in less than a minute. Ar- rival time is more than an hour over 20 km (ICRP 60,1991; IAEA, 2010; Anvari and Safarzadeh, 2012; Malek et al., 2012 and Muswema et al., 2016)

Table 3. (Scenario 1) Output value from HOT SPOT

Results of Accident (Scenario 2); the Accident Scenario 2 presents a variation in meteorological conditions (the sta- bility class D has been uploaded in this case). It has been selected to analyze variation between two stability classes very different. In the figure 7, Plume at 30 minutes (Sce- nario 2), HotSpot software was used to create this figure, which depicts the radioactive plume’s dispersion 30 min- utes after emission. The radionuclide concentration (in Bq•s/m³) varies with distance from the source, as indicated by the colorful contour lines. The hotspot, or maximum concentration area, where radiation exposure is highest, is indicated by the red area close to the source. As the plume disperses and dilutes downwind, the blue and black con- tours indicate decreasing concentrations. The elongated and thin plume shape indicates that, under Scenario 2, the wind speed is moderate and air stability is relatively strong, which limits vertical mixing but extends the plume farther horizontally. In contrast to unstable situations, this indicates that the expelled material moves farther down- wind with less lateral dispersion (ICRP 60,1991). Figure (8): shows that, how the downwind distance from the discharge point affects the Total Effective Dose Equiva- lent (TEDE). Near the source, the TEDE rises quickly and peaks between 0.5 and 0.7 km before progressively declin- ing. The maximum human exposure point, when inhala- tion and external exposure to the plume are most intense, is represented by the peak of the curve. As the plume dis- perses, dilution and radioactive decay cause the TEDE to drop quickly beyond 1 km. This curve, which exhibits a strong dependence on atmospheric dispersion character- istics and distance, is typical for a near-surface short-dura- tion release (Muswema et al., 2016).

Figure (9): shows the rate of radioactive deposition on the ground as a function of distance from the release site. The majority of deposited activity takes place near the source, as indicated by the ground deposition curve, which peaks between 0.2 and 0.5 km. Beyond this point, the deposition gradually diminishes, indicating that tiny particles stay in the air longer and disperse farther, while larger particles settle earlier. This curve has a TEDE-like form, except it shows surface contamination instead of human dose. As a result, the area one kilometer downwind is the most con- taminated, thus increasing exposure to ground shine (Bel- lecci et al., 2010 and Dahia et al., 2018).

Table (4): displays the simulated plume’s numerical results at different distances from the release source (0.03–50 km). The TEDE, air concentration, ground surface deposition, ground shine dosage rate, and plume front arrival time are all included. TEDE (Sv) stands for total effective dose equivalent, which combines exterior exposure and inhala- tion. Near 0.6 km, the TEDE reaches its maximum (~0.22 Sv), after which it diminishes as the plume spreads. Near the peak exposure position, the air concentration (Bq•s/m³) is at its highest (~1.7×10¹ Bq•s/m³); it drastically de- creases after one kilometer. reflects the air’s radionuclide density. Deposition on the ground surface (kBq/m2), Peaks at 0.6 km (3.8×10² kBq/m2), in keeping with Fig- ure 9’s plume centerline and deposition pattern. shows the highest level of surface pollution close to the plume axis. The ground shine dosage rate (Sv/hr) exhibits a similar pattern to deposition, peaking near the source and sharply declining beyond one kilometer. represents the exposure to gamma rays from deposited material. Arrival timing (hour:min) shows the arrival of the plume at each dis- tance. The plume disperses quickly, reaching the first kilo- meter in less than a minute. The arrival time increases to several minutes or hours beyond 20 km, indicating slower plume transport (Cenciarelli et al., 2013a and Cenciarelli et al., 2013b). Scenario 2 is described in Figs. (9) and Table 4, which illustrate the regional variations in radio- nuclide concentration, dosage, and deposition following a near-surface release. Within the first kilometer (particu- larly between 0.5 and 0.7 km) from the source, both the maximum TEDE and deposition take place. Rapid dilu- tion lowers exposure and contamination outside of this area. According to the findings, inhalation continues to be the primary exposure route in this situation, with ground shine making a smaller contribution at longer distances. These results emphasize how important it is to take pre- cautions and act quickly in the immediate downwind area following a nuclear leak (Pazienza et al., 2013 and Pazienza et al., 2014).

Table 4. (Scenario 2) Output value from HotSpot

Conclusions

The study’s results explain that modeling radioactive ma- terial dispersion with HotSpot software is a useful tool for helping in nuclear emergency decision-making. The simulation showed a strong ability to describe the radio- active cloud’s behavior and precisely locate hazard zones with the necessary temporal and spatial accuracy, and its demonstrated that the first kilometer from the emission site is where the highest levels of radiation exposure and ground deposition are concentrated, with wind speed and air stability having a significant impact, this confirm how important climatic factors are in influencing the level and dispersion of radioactive contamination. Additionally, the analysis of the dispersion pattern and intensity of radio- active accumulation varies significantly depending on the atmospheric stability classes, this shows the importance of meteorological data incorporate for emergency response strategies. and from this work the two scenarios are com- pared, it is evident that Scenario 1’s plume area is wider than Scenario 2’s, and the plume is spread across a larger surface and according to the simulation results, the highest value of contamination is 3.10E+04 (kBq/m2) at a distance of 210 meters from the release point for Scenario 1 and 3.80E+04 (kBq/m2) at a distance of 1 km for Scenario 2, and its notice for Scenarios 1 and 2, the plume maps dis- play the geographical dispersion of radioactive elements after 30 minutes ,the hot spot, or greatest concentration, forms an elongated shape along the wind direction and emerges near the release site before progressively decreas- ing with distance, the plume in Scenario 2 is longer and thinner, suggesting more stable atmospheric conditions that promote horizontal transport while limiting verti- cal mixing, due to dilution and decay , the Total Effective Dose Equivalent (TEDE) rises quickly close to the source, peaking between 0.5 and 0.7 km before declining with dis- tance, this peak zone represents the maximum area where humans could be exposed to radiation by inhalation and external exposure, the majority of radionuclides land on the surface near the source (around 0.5–1 km), where the ground deposition rate (kBq/m2) likewise peaks. As light- er particles stay in the air longer beyond this range, deposi- tion drastically decreases, indicating that surface contami- nation is mostly contained close to the release location, displays arrival time, TEDE, air concentration, and ground deposition at various distances, Near 0.6–0.7 km from the release point, the greatest TEDE (≈0.19 Sv) and ground deposition (≈1.3×10² kBq/m²) take place, the plume con- firms early-stage rapid dispersion by reaching the first ki- lometer in less than a minute, shows a similar pattern, but the concentration and dosage values are somewhat greater, suggesting that Scenario 2 conditions—a more stable at- mosphere—cause a stronger local accumulation of radio- active particles and Once more, the highest TEDE (≈0.22 Sv) and ground deposition (≈3.8×10² kBq/m²) occur close to 0.6 km before decreasing with distance. Thus, the work explains that employing advanced computer models as a prediction tool can greatly enhance prevention strategies and lessen the hazards to human health and the environ- ment risk by nuclear accidents.