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Salient features of the forthcoming ICRP recommendations-2007. Dr. Pushparaja Ex. Head, Radiation Hazards Control Section, RSSD, BARC (Based on the ICRP approved draft recommendations -2007 (13/2/2007) www.radsafetyinfo.com. Since 1990 Recommendations.
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Ex. Head, Radiation Hazards Control Section, RSSD, BARC
(Based on the ICRP approved draft recommendations -2007 (13/2/2007)
Radiological protection deals with two types of harmful effects:
Dose to individuals
To contribute to an appropriate level of protection for people and the environment against the detrimental effects of radiation exposure without unduly limiting desirable human endeavours and actions that may be associated with such exposures. The recommendations are based on the scientific knowledge and expert judgements.
The system of protection of humans is based on the use of:
The two principles which are source-related and applicable to all situations are:
Individual-related, and applies to planned exposure situations. Total dose should not exceed the limits. Not applicable to medial exposures, public exposures in emergency situations and to existing exposure situations.
The limits are same as those given in ICRP-60, 1991.
Applies to all radiation sources, both natural and man-made, and controllable exposures from any source or sources regardless of its size and origin. Also applies to all radiation exposure situations.
Commission moves from the earlier process based approach to the following three types to address all conceivable types of exposure situations:
Radiological protection can be planned in advance, before exposure occurs-magnitude and extent of the exposure can be reasonably predicted, cover medical exposure of patients, comforters and carers, all categories of exposure can occur, also covers potential exposures, which may result from deviations from the normal operating conditions, safety and security of sources is the issue of concern
Type of existing exposure situations where exposures can be high enough to warrant radiological protective actions are:
Appropriate level of protection is achieved by optimization using dose constraints and reference levels
Operating management and Licensee responsible for the safety
All exposures other than occupational and medical exposures incurred as a result of a range of radiation sources, natural and man-made
Has recognized rights and duties in relation to occupational radiological protection.
Pregnant workers not to avoid work, can work in designated areas; should not be involved in emergency actions involving high radiation doses; treated like members of the public.
Additional equivalent dose to the fetus would not exceed 1 mSv during the reminder of the pregnancy.
A large number of different natural and man-made sources is contributing; Dose restrictions are applied to the mean dose in the appropriate critical group.
Critical group concept is replaced by “The representative person” (Pub: 101, 2006); Typical habits of individuals in a representative group in the most exposed, are used.
Individuals, who receives an exposure from diagnostic, therapeutic and screening procedures, which are justified and optimized. Dose limits/constraints not applicable. To use diagnostic reference levels. (ICRP-73, 1996)
Dose constraints (in planned exposure situations) and Reference levels (in emergency and existing situations) are used for protection of members of the public or workers from a single source in all exposure situations (Source-related restriction). These are used in conjunction with optimization of protection to assure ALARA
Due to multiplicity of the sources, sole reliance on source-related restrictions may not provide the required level of protection. Restriction on the sum of the doses from the sources is required; this individual-related restriction is called – Dose Limit
To keep likelihood of incurring exposures, the number of people exposed and the magnitude of individual doses ALARA below the dose constraints or reference levels, taking into account economic and societal factors.
Optimized protection is the result of an evaluation, which balances the detriment (economic, human, societal, political) and the resources available for protection of individuals. Best option need not necessarily the one with the lowest dose.
It is useful to determine a single value of effective dose for both sexes. The tissue weighting factors are sex averaged values and are valid for the male and female breast, testes and ovaries taken together in the value for the gonads, and other organs and tissues with assigned explicit Wt values. The effective dose is computed from the weighting factor multiplied by the arithmetic mean of the equivalent dose assessed for organ or tissue T of the male, and female including the remainder tissues.
ICRP’s risk estimates are called nominal because they relate to the exposure of a nominal population of females and males with a typical age distribution and are computed by averaging over age groups and both sexes. Effective dose is the dosimetric quantity recommended for radiological protection. Use absorbed dose in known exposure scenarios.
Risk of hereditary effects continues to be included in the Commission’s system of radiological protection. Post 1990 human and animal data on the quantitative aspects of radiation-induced germ cell mutation and the fundamental understanding of the human genetic diseases indicated that the risk of heritable disease was overestimated in the past.
The newly estimated hereditary risks employing human and mouse studies and in view of the lack of clear evidence in human of germ line mutations caused by radiation (in demonstrable genetic effects in offspring), works out to be 0.2% per Sv.
This value relates to continuous low dose-rate exposure over these two generations (UNSCEAR-2001: NAS/NRC-2006)
The judged value for tissue weighting factor for gonads is considerably reduced.
The ICRP detriment was based on fatal cancer risk weighted for non-fatal cancer, relative life lost for fatal cancers and life impairment for non-fatal cancers.
Each exposure situation must be carefully analyzed to identify the individual characteristics and exposure parameters that best describe the exposure distribution among concerned population. In the decision taking process, less weight should be given to very low doses and to doses received in the distant future since the doses and sizes of exposed population becomes increasingly uncertain as time increases.
Benefit to society; Planned operation of practices with marginal increase in exposures above natural background; Provides rigorous level of protection by direct action on the source; periodic checks. Ex: Constraints set for public exposure.
Individuals get direct benefit from an exposure situation not necessarily from the exposure; Individual monitoring, training; constraints set for occupational exposure in planned situations, exposure involving high levels of natural background radiation; Exposure control by action at the source or at the exposure pathways. Ex: Constraints set for Occupational exposure in planned situations; Reference levels for radon in dwellings
Projected dose over a time period; Total dose from all the sources; Source can not be controlled; extreme situations where actions taken to reduce exposures are disruptive such as in radiological emergency; acute exposures not expected to be repeated. Important: Selection of an appropriate value for the reference level is the necessary and important for protection, whatever the situation.
Medical exposure covers:
Need is felt for internationally acceptable policy, advice and guidance to assess the impact of radiation exposures on the environment and the radiological protection aspects. A comprehensive and systematic approach is being developed (ICRP-91, 2003). The Commission is setting out data for some reference animals and plants (hypothetical entities with certain assumed basic biological characteristics), and intends to offer more practical advice in the future.