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and the forward compartment of the control system. One assembly with a freshly loaded core was 

 blown out of the reactor. The fueling shack was also partially destroyed, and its roof was blown 

 off to a distance of 70-80 meters, landing in the water 30 meters from shore. The NS sustained 

 damage to its pressure hull in the aft portion of the reactor compartment. 



Immediately after the explosion in the reactor compartment, a fire broke out, which was 

 brought under control after four hours. The combustion products, along with fission and activa- 

 tion products and particles of unreacted fuel compound in the form of fine particles and slurry, fell 

 out within a radius of 50-100 meters around the damaged NS. 



A radioactive plume was deposited with an axis intersecting Dunay peninsula in a northwest- 

 erly direction and extending seaward toward the coast of Ussuri Inlet. The plume was 5.5 km 

 across on the peninsula (later fallout of aerosol particles occurred on the water surface up to 30 

 km from the release site). 



The release of radioactive substances into the atmosphere was calculated (neglecting radio- 

 active noble gases) at about 185,000 TBq (5 MCi). The release of radioactive noble gases was 

 estimated at approximately 81,000 TBq (2 MCi). The heaviest contamination was noted at the 

 epicenter of the release and along the axis of the radioactive plume. Seven and one-half hours af- 

 ter the accident the exposure dose rate (EDR) of radiation in the area of the accident reached 

 250-500 mr/hr, and contamination of surfaces by beta-emitting nuclides was 0.5-4.0x10* de- 

 cays/cm^-min. 



Significant radioactive contamination affected submarines and special vessels near the acci- 

 dent site, piers, and the shipyard's land and manufacturing structures. 



Also radioactively contaminated was a large part of the water area of Chazhma Bay, especial- 

 ly near the damaged NS. Contamination of the bay occurred at the time of the explosion and for- 

 mation of the plume, and also when radioactive water from the damaged compartment entered the 

 water through the hole formed in the pressure hull. One hour after the explosion, the activity of 

 short-lived radionuclides in the seawater reached 74 kBq/1 (2 \iC\A). Two months after the acci- 

 dent, radionuclide levels in the seawater had declined to original background values, where they 

 remain today. 



The accident created a focus of radioactive contamination on the bottom of the water area of 

 Chazhma Bay. The area of intense radioactive contamination is concentrated at the accident site 

 and within the limits of EDR>240 nr/hr occupies an area of about 100,000 m^. In the central part 

 of the focus, the EDR is 20-40 mr/hr, with a maximum of 117 mr/hr as of 1992. Currents are 

 gradually moving the radioactive contamination toward the entrance to Chazhma Bay. The radio- 

 activity of bottom sediments is due mainly to ^Co (96-99%) and partly to '"Cs. 



The maximum ^^Co unit activity in bottom sediments at the accident site is 78 kBq/kg (2.1 

 nCi/kg), and in marine water life 670 Bq/kg (18 nCi/kg). The total ^OCo activity in the bottom 

 sediments of Chazhma Bay as of 1992 was approximately 185 GBq (5 Ci). 



Contamination of bottom sediments by '^^Cs is seen in local areas and in concenuations 

 comparable to or slightly above background values. 



Radioactive contamination of the water area affects the southeastern part of Chazhma Bay. 

 The area of maximum contamination of the bay bottom is 0.08-0.1 km^ (within limits of gamma 

 ray EDR>240 jir/hr). Contamination of bottom sediments can be observed moving from the acci- 

 dent area toward the western entrance to Streiki Inlet. Contamination of the water area of eastern 

 Ussuri Inlet within a radius of 3-5 km from the explosion site of the shore radioactive plume cre- 

 ates an elevated gamma ray EDR over background of between 1 and 8 jir/hr. 



Radioactive contamination in the water area of Chazhma Bay, the western passage of Streiki 



42 



