Dispersion and deposition of fallout from nuclear testing @ B. E. Moroz Er AL. 263 Salt Lake City —__ Denver e “42 St. George HYSPLIT fallout pattern Cederwall arrival time Fig. 3. HYSPLIT fallout pattern resulting from simulations of the Upshot-Knothole Harry test. The solid black line indicates the estimated centerline of the radioactive cloud as simulated by Cederwall and Peterson (1990). Dashedlines delineate the HYSPLIT predictions of the geographic boundary ofthe fallout pattern at the time noted. were strong northeasterly winds estimated at 47-60 km h' with almost no wind shear (Shoikhet et al. 1998; Imanaka et al. 2005). given in Table 1. The release heights in the simulation ranged from 450 m AGLto the reported maximum cloud HYSPLIT simulations were performed to compare height, ~9 km, and are shown in Table 8. The cloud bottom, estimated at 2.7 km, was based on the reported published estimates of the fallout pattern and the spatial particle sizes varied from 5 wm up to 300 wm, in 5 wm predicted estimates of '’Cs deposition density with distribution of '*’Cs and ****°Pu near the village of Dolon, Kazakhstan. Fallout was reported to have reached Dolon, approximately 118 km northeast of ground zero, at roughly H+2 h (Yamamotoet al. 2008; Gordeevetal. 2002). Soil samples were collected in 2005 by Yamamoto et al. (2008) at 21 locations along a line approximately perpendicular to the supposed centerline of the plume. Their analyses of '’Cs and *?”*°Pu suggested that (1) the spatial distribution of '*’Cs and Py is roughly Gaussian in shape and perpendicular to the axis of the fallout trajectory with maximums located near the supposedaxis-center, and (2) the width of the fallout pattern near Dolon was approximately 8-10 km (Yamamotoetal. 2008). To calculate the fallout deposition at locations downwind, particle releases at varying altitudes were simulated using HYSPLIT. The total numberofparticles in the simulated debris cloud was apportioned using the estimated total '°’Cs activity, particle size, and spatial distribution model described previously for the Marshall Islands simulations as well as the alternate distributions cloud dimensions of the Trinity test. The assumed increments, depending on the activity distribution, and the simulation wascarried out to 5 h post-detonation. The total numberof particles tracked in different simulations varied from 1 X 10’ to 2.5 x 10’. Results. The calculated '°’Cs deposition pattern for the first Soviet nuclear detonation, using the MI '’’Cs activity-size distribution from Table 1, is shownin Fig.4. The simulation data were griddedat a resolution of ~4.3 km*. Sites A, B, and C in Fig. 4 correspond to the Table8. Particle release heights andfraction of total '*’Cs activity corresponding to each release height for the first test at the Semipalatinsk Nuclear Test Site. Release height (m AGL) 450 2,875 3,925 5,150 7,075 8,125 to to to to to to 2,700 3,750 4,800 6,900 7,950 9,000 Height increment (m AGL) Fraction of total BICs activity 450 175 175 350 175 175 0.12 0.10 0.16 0.36 0.16 0.10