ISO 14152 pdf download – Neutron radiation protection shielding一 Design principles and considerations for the choice of appropriate materials

ISO 14152 pdf download - Neutron radiation protection shielding一 Design principles and considerations for the choice of appropriate materials

ISO 14152 pdf download – Neutron radiation protection shielding一 Design principles and considerations for the choice of appropriate materials.
The fwst critenon, consists of deternining the maxinial ambient dose equivalent and ambient dose equivalent rate at the different working areas and on the factory boundary, with respect to the radiation protection regulation concerning the exposure of workers and general public to Ionizing radiation. In accordance with ICRP recommendations and according to the ALARA principle, these values should be kept as far below the regulatory limits as is reasonably achievable (see 5.4). Additional considerations for the selection of these radiological objectives are given in 5.2 to 5.4.
The second senes of critena concerns all the additional safety requirements with which the shielding shall comply with respect to the general purpose of the plant or the installation (e.g. participation to the containment wall, playing a role of gamma radiation shielding, participation to the fwe compartment, need for decontamination, necessity of removable parts). In order to achieve complete Implementation, all kinds of hazards or constraints such as mechanical constraints, chemical constraints, fire constraints, thermal constraints, architectural constraints, general salety constraints, shall, in addition, be considered.
Consequently, persons Involved in shielding design should review the locally applicable radiation protection regulations and requirements as well as regulations concerning building. fre protection, factory sale(y or other regulations applicable at the facility or for the operation. Examples of items to be considered are discussed in 5.2.
5.2 Classification of work areas (based upon general occupancy, limited occupancy, etc. and on specific protection requirements)
5.2.1 General
The control of radiation sources is helped by requiring that the workplaces containing exposure flsk be formally designated. The ICRP recommendations use two such official designations: controlled areas and supervised areas. For practical reasons, some local regulations, have Introduced a third category of designation, which Is called unrestncted areas.
5.2.2 Controlled areas and supervised areas A controlled area is one in which normal working conditions, including the possible occurrence of minor mishaps, require the workers to follow well-established procedures and practices aimed specifically at controlNng radiation exposure. A supervised area is one in which the working conditions are kept under review but special procedures are normally not required.
5.2.3 UnrestrIcted aras
An unrestricted area Is a working area where it Is not necessary to take any special health precautions. An unrestncted area may be inside or outside a building or in part of a building, and shall be characterized by unlimited access and ogress by the general public.
5.2.4 Dos. limits within these workplaces
NOTE I Th. viding line between controlled areas and supervised areas, if the latter are ed, has commonly been set with the awn of ensuring that the doses to workers in the supervised areas can confidently be predicted to be less than 3/10 of the occupational dose limits. ICRP now regards this definition as being too arbitrary and recommends, in its publication 60 (1991). that the designation of controlled and supervised areas be decided either at the desigu stage or locally by the operating management on the basis of operational eeflence and udgement This judgement has to take into account the expected level on the hkely vanations 01 the doses and intakes, and the potential for accidents
NOTE 2 As a consequence of the previous desigeations. an unrestflcted area could be considered as an area where doses do not exceed 1 mSv per year or a dose correspondwig to 1110 of the annual occupational dose lamts ñxed for workers exposed to radiation and for whom iIi not necessy to foresee any particular measures to afford protection from radiation.
National competent authorities shall elaborate criteria or orientation for the classification of areas takmg into account specific circumstances. The requirements stated in these national regulations shall be selected prior to receiving the ICRP recommendations.
5.3 DetermInation of the occupancy and frequency of work
The total effective dose in a controlled or supervised area is the summation of the effective doses received as a result or tasks conducted within the area. The effective dose for each single task is the product of the effective dose rate and the exposure time It is important for the shielding system designer to separate:
— persons for whom the shielded area Is a permanent work place and for which the shielding Is being designed
persons who have to work for a short duration with some frequency of occurrence (recurrence, cumulative total duration, etc.);
and establish exposure times and exposure frequency for each.
5.4 Choice of design criteria in terms of radiological objectives
5.4.1 SpecIfication for dose and dose rate limitation
For the purposes of this International Standard, the definitions of ICRU Report 51 and ICRP 60 shall be applied to dosimetry terminology. The system for dose regulation recommended in this International Standard is based on recommendations of the International Commission on Radiological Protection (ICRP 60). Users of this International Standard should familiarize themselves with the applicable national or international systems for dose limitation in use at the facllty or in effect for the operation prior to selecting shielding materials and designing the protection shield.
The recommended dose limits are staled in terms of the effective dose and the equivalent doses to the lenses of the eyes, the skin and the extremities,
The radiological objectives are usually expressed as a percentage of the applicable occupational dose limit or the dose limit for members of the general public.

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