Dose commitment

The dose of radiation delivered by an internally deposited radionuclide depends on the quantity of radioactive material residing in situ. This quantity decreases as a function of the physical half-life of the radionuclide and the rate at which the element is redistributed or excreted (i.e., its biological half-life). Because the physical half-life is known precisely and the biological half-life can be characterized within limits for most radionuclides, the dose to a tissue that will ultimately be delivered by a given concentration of a radionuclide deposited therein can be predicted to a first approximation. The collective dose to a population that will be delivered by the radionuclide—the so-called collective dose commitment—serves as the basis for assessing the relevant long-term health effects of the nuclide. 

TABLE 2. Individual dose commitment, radiation risks and environmental implications under hypothaical emergencies during NS complex... 

Hadditional dose commitment by a risk coefficient and a value of individual (collective) dose. The life-long risk coefficient characterizes reduction of the duration offull-valuelifeby 15 years (on average) per one stochastic effect (due to fatal cancers, serious hereditary effects and non-fatal cancers with similar-to-fatal-cancer consequences). 

To reduce dose commitment for personnel, the Environmental Foundation Bellona (Norway) supplied the MSC with module building constructions to arrange therein - at 50-m distance from Tepxe board - workplaces for the FSV watch service and specialists performing radiation-hazardous operations. 

F. Radiation Dose (committed dose equivalent, committed effective dose)... 

The collective effective dose committed by an event, a decision or a finite portion of a practice k, 5, is given by ... 

Absorbed dose, organ dose, equivalent dose, effective dose, committed equivalent dose, or committed effective dose, depending on the context. The modifying terms are often omitted when they are not necessary for defining the quantity of interest. 

The upper bound for annual release can then be derived from the dose upper bound by using the overall transfer factors (. ., ) where j represents population group, k represents release mode and / represents the radionuclide. If the dose commitment to the critical group / per unit release of a radionuclide is given by fj,, then the release upper bound, Ri i, is given by... 

The concept is best described by Figure 18.11, where each rectangle represents the dose delivered in one year from an annual release. A is the dose from the first year s release the next year contains a smaller dose B because of radioactive decay (or other removal processes) the third year yields an even smaller dose C. We assume that the fourth year is the last year that the dose contribution (D) is significant. In this same fourth year, we have a "first year release". A, equal in amount to A, plus what is left from the previous years, B and C. Thus, the annual dose at release equilibrium is equal to the dose commitment for one year. 

The collective dose concept allows for extrapolation of the consequences from large scale introduction of nuclear power, which, in turn, establishes the need to ensure that the total annual dose stays within agreed safe limits. If it is assumed that fission power will be used for only about 1(X) y, the dose commitment integral may be limited to 100 y (sometimes called "incomplete collective dose"). 

Kr, Tc and are of major concern. The liquid effluents firom nuclear power plants and from reprocessing plants are about equally responsible for the global collective dose commitment of nuclear power generation (i.e., 0.8 man Sv per GW y of the total 2.5 man Sv). 

The estimated 50-year dose commitment from plutonium for people in the north temperate zone due to atmospheric tests conducted before 1973 is 0.2 mrad (0.002 mGy) to the bone lining cells (Eisenbud 1987). [The gray is an SI unit of absorbed dose and is equal to 0.01 ram.] The average annual dose equivalent from all background radiation to an individual residing in the United States is estimated to be 360 mrem (3.6 mSv) (NCRP 1987). [The sievert is an SI unit of dose equivalent and is equal to 0.01 rem.]... 

Besides, increased requirements of safety are imposed on a repository, as it is a subject of danger for the present and future generations of mankind. So, the International Commission on Radiologic Protection (ICRP) recommends a possible dose commitment from a repository within the limits of 1-3 % from the regulated annual dose limit of 1 mSv, corresponding to a risk 10" year" (the number of fatal diseases of cancer per one year). 

Strict controls are exercised to limit the dose commitment of any personnel in the emergency teams from exceeding the specified maximum. 

Conditions in the damaged reactor building may be so hazardous that progress will be slow and backup teams will be required so as to limit radiation dose commitments to the individual teams. Teams returning to base may be heavily contaminated and will require substantial clean-change facilities near the ICC. 

In V-392 reactor the measurements of coolant temperature and core power are combined and brought through the common nozzles of in-core instrumentation (ICI), while in V-320 reactor there are separate nozzles for temperature monitoring and nozzles for core power monitoring. With this, all ICI nozzles are arranged on the periphery of the reactor upper head that facilitates the access to them when reactor assembling or removing the upper head unit, and reduces the repair personnel dose commitment. 

The physical and chemical nature of the material being vented, e.g. gaseous (halogen, inert gas, etc.), particulate, soluble/insoluble and Other dose commitments incurred by operators and the pnblic. 

Committed doses are defined in cases of intakes of radioactive materials, mainly by ingestion, inhalation, or absorption through the skin, in terms of internal radiation impact. In most cases, the quantities of committed absorbed dose, committed equivalent dose, and committed effective... 

The SI unit of committed effective dose is Sv, the same as for effective dose. Similarly, one can derive a committed equivalent dose. The quantity of dose commitment differs from the committed dose only by the upper integration limit. It is defined as the infinite time integral (t = oo) of the per caput dose rate Hi or E) ofthe population due to a specified event. The unit of the dose commitment is the same as for committed dose. Both individual dose commitment and collective dose commitment can be defined. 

Radionuclides Effective dose commitment/ jiSv External Ingestion Inhalation Total exposure... 

Globally dispersed activities and corresponding world average effective dose commitments for the period of 1970-1997. The energy produced was 3,860 GWy, the reprocessed fuel was equivalent to 420 GWy... 

Release radioactivity/PBq Radionuclides Reactor Reprocessing Total Average annual effective dose commitment/nSv... 

Although the concepts of justification of practices, optimization of protection, dose commitment, and collective dose were all already treated and considered in the ICRP Publication 9 (1965), they were explicitly expressed not until in the ICRP Publication 26 (1977). The implementation of the new approach after 50 years of stepwise development meant adaptation of a modem protection concept which in a refined and addended form is continuously iqiplicable. 

The general principles for exen tion are reformulated by requiring that radiation risks to individuals and the collective radiological impact are both "sufficiently low as not to warrant regulatory control". In addition, it is stated that practices and sources may be exempted "without further consideration" provided that individual doses do not exceed 10 ftv/y and the collective effective dose committed by one year of the practice is no more than about 1 man.Sv. Compliance with these conditions allows for "automatic exemption". 

The projected absorbed doses or dose commitments to organs and tissues (whole body, bone marrow, lung, skin, thyroid gland, lens of the eye and gonads) for a period of two days in the event of a severe accident ... 

Carbon-14 is produced in LWRs and HWRs by (n, a) reactions with the present in the oxide fuel and moderator, by (n, p) reactions with the present in impurities in the fuel and by ternary fission. Because of the large moderator mass, C is produced mainly from reactions in the moderator in HWRs. This may be the main source term for this nuclide and a contributor to the global long term collective dose commitment. However, in some HWR systems the contribution of C to the total collective dose is relatively small because C is effectively removed from the moderator by the purification system. 

Table 12.6. Estimated Whole-Body Dose Commitments for Various Stages of the Fuel Cycle (Units of Man-mSv/MWe yr)...

Exemption may be granted if the regulatory body is satisfied that the justified practices or sources within practices meet the exemption principles and criteria specified in Schedule I of the BSS, the exemption levels specified in Schedule I of the BSS or other exemption levels as specified by the regulatory body on the basis of the exemption criteria specified in Schedule I of the BSS. The criteria for exemption are that (a) the effective dose expected to be incurred by any member of the pubUc due to the exempted practice or source is of the order of 10 gSv or less in a year, and (b) either the collective effective dose committed by one year of performance of the practice is no more than about 1 man Sv or an assessment for the optimization of protection shows that exemption is the optimum option (Ret [1], para. 1-3). 

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