Large quantities of radioactive wastes are produced during the operation and repair of nuclear-powered ships. The wastes, including spent nuclear fuel, are handled using specialized atomic-technological service ships, which perform a chain of operations on reloading of reactor cores and receiving, reprocessing, and transporting radioactive wastes to the locations of constant or temporary storage. An example of such vessels are the floating technological base and transport for transporting and reprocessing radioactive wastes. When such vessels are scuttled, they can be sources of stronger radioactive contamination of the environment than ships with nuclear power plants, since three or more spent cores can be present at the same time onboard such a ship.When atomic-technological service ships with radioactive wastes or elements of nuclear power plants onboard are scuttled, the radiation effect on the environment is determined mainly by the scale of the damage to or disruption of the seal of the structural safety barriers preventing the spreading of radionuclides to outside the systems and equipment in the scuttled object. The final criteria for estimating the radiation consequences of accidents are the scales of the water areas involved in the postaccident contamination, the concentration of the most important radionuclides, from the standpoint of radiation hazard, in the sea water and bottom deposits, possible levels of accumulation of radionuclides in organs and tissues of commercial marine organisms and their food base and, in consequence of this, uptake of the radionuclides by humans consuming the marine organisms.For the criteria indicated, working limits satisfying the NRB-69 hygenic requirements were proposed in [ 1] for the concentrations of radionuclides in sea water during prolonged contamination of regions with different commercial use [2]. A dose load quota for the population from contamination of the sea, equal to 10% of the maximum irradiation dose of a limited portion of the population, was introduced.The introduction of new radiation safety standards (NRB-96) [3], which establish more stringent limits of irradiation for personnel and the public, as well as the publication of the IAEA recommendations [4], which refine the limits for the accumulation of radionuclides by marine organisms, make it necessary to choose new control levels of concentrations of radionuclides in sea water. In this connection, the control concentrations of radionuclides in sea water for different industrial objects, calculated on the basis of the approach of [1] using the dose limits for individuals from the population [3] and data on the consumption of marine products and accumulation factors of radionuclides in them [4], are presented in Table 1.The scale of radiation consequences can be estimated by comparing the data presented in [1] and Table 1 with the data on radionuclide concentrations in sea water as a result of accidental sinking of atomic-technological service ships.The radiation hazardous systems and equipment in...
The planning and implementation of various projects involving possible radioactive contamination of seawater require a prediction of the effect of radiation on the public. The main pathway for a radiation effect is the consumption of seafood from contaminated fisheries. A method is proposed for assessing the radiation effect due to the consumption of seafood. A special feature of the method proposed is that it uses dose coefficients to convert the volume activity of seawater in the area of a fishery into the effective irradiation dose to an individual from the general public. The computed dose coefficients for 57 radionuclides and seven types of seafood are presented.As a result of the redistribution of contamination between objects in a marine environment, technogenic radionuclides which have entered seawater can affect humans by various pathways. The pathway for the irradiation of the public as a result of the contamination of the marine environment is peroral entry of radionuclides with the consumption of seafood [1]. Consequently, when developing methods for predicting the irradiation of the public as a result of the contamination of the marine environment, the contamination of fisheries should be examined.An important criterion for assessing the ecological consequences of the radioactive contamination of fisheries is the volume activity of biologically significant radionuclides in water and bottom deposits and, in consequence of such contamination, the accumulation of the indicated radionuclides in the organs, tissues, and food base of commericially valuable marine organisms, desalinated seawater, and edible salt obtained from seawater.The method of normalization of the radioactive contamination of seawater in marine fisheries [2] and the reference concentration of radionuclides calculated on its basis [1] can be used to determine the boundaries of the zone of dangerous contamination of a water area as a result of radioactive discharges into the sea. However, this method does not permit assessment of the effect of radioactivity on the public as a result of the consumption of seafood obtained at the boundaries of the indicated zone.It is proposed that the dose coefficients which convert the volume activity of seawater in a fishery into an effective dose due to the consumption of seafood obtained in this region be used to estimate the possible effect of radiation on the public. The dose coefficients e ij are the expected effective dose from the consumption of 1 kg of the jth seafood product obtained in seawater with volume activity of the ith radionuclide 1 Bq/m 3 . In this case, the expression for calculating the expected effective irradiation dose to one person from the general public due to the ith radionuclide accompanying the consumption of the jth seafood product can be written as
There are a number of possible characteristics to consider in determining the radiation consequences of an accidental sinking of a ship containing a nuclear power plant and radioactive wastes. These include the dimensions of the zone of pollution of the body of water; the field of concentration of the most significant radionuclides in the liquid mass caused by their escape outside the sunken vessel; and the dynamic nature of the variation of these indicators over time.The rate of escape of radionuclides from the fuel core of the nuclear power plant of a sunken nuclear-powered vessel is determined by the scouring velocity of the fuel composition by the sea water and by the rate of their subsequent transport into the space outside the ship, a result of natural circulation when there is residual heat release into the fuel core as well as diffusion through the solid protective shielding and the puncture in the hull structures, fluctuations in the hydrostatic pressure in these shieldings caused by tides, and ejection processes as a consequence of washing of the hull by the bottom currents. To arrive at an evaluation of the degree of pollution of a body of water, it is essential to take account of the state of the reactor's fuel core at the time of the sinking and, subsequently, the extent to which the nuclear power plant's systems and circuits have become depressurized and lost their hermetic sealing; the degree and nature of the destruction of the bulkheads and hull of the vessel; and the hydrodynamic characteristics of the marine environment at the spot where the ship sank. A conservative estimate of the radiation consequences of a sinking presupposes taking account of the state of all systems whose destruction may lead to the most serious radioactive pollution of the water. One such system is the nuclear power plant. Therefore, in estimating the aftereffects of a sinking, it is essential to consider the state of the reactor compartment and the equipment in the primary tuned circuit of the nuclear power plant once the ship is resting on the bottom soil. Evaluations of the consequences of external damage and samples of the significant events leading up to the sinking of a vessel which have been constructed on the basis of these evaluations demonstrate that the length of time from the onset of an accident to the point when the ship has become unstable may be in the range of several hours to several days, a period of time sufficient to halt the reactor and switch it to the shut-down cooling regime. Table 1 presents the approximate content of radionuclides with half-life greater than 30 days in the fuel core of a transportable reactor following energy production (3" 106 MW.h) in a typical operating regime. It is assumed that for 24 h immediately preceding the accident, the reactor functioned at its rated power, and that 5 h elapsed from the time the reactor halted to the time the ship reached the bottom of the sea.When it sinks, a nuclear-powered ship is affected by both static and dynamic loads that result in damage to...
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