IEC 60544-4-2003 pdf – Electrical insulating materials – Determination of the effects of ionizing radiation – Part 4: Classification system for service in radiation environments.
1 Scope and object This part of IEC 60544 provides a classification system that serves as a guide for the selection and indexing of insulating materials intended to serve in the radiation environment of nuclear reactor facilities, reactor fuel-processing facilities, irradiation facilities, particle accelerators, and X-ray apparatus. The classification system provides a set of parameters defining the utility of the three types of polymeric materials (rigid plastics, flexible plastics, elastomers) for use in devices which are exposed to ionizing radiation. This part of IEC 60544 forms the basis for a quantitative statement of the suitability of such materials for radiation environments and therefore provides a guide for material specifications and for procurement agreements between suppliers and users. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60212:1971, Standard conditions for use prior to and during the testing of solid electrical insulating materials IEC 60544-1:1994, Electrical insulating materials – Determination of the effects of ionizing radiation – Part 1: Radiation interaction and dosimetry IEC 60544-2:1991, Guide for determining the effects of ionizing radiation on insulating materials – Part 2: Procedures for irradiation and test IEC 61244-1:1993, Determination of long-term radiation ageing in polymers – Part 1: Techniques for monitoring diffusion-limited oxidation IEC 61244-2:1996, Determination of long-term radiation ageing in polymers – Part 2: Procedures for predicting ageing at low dose rates
3 Classification system The classification of a particular material for a specific application is established by the results of testing for changes in the appropriate mechanical and/or electrical properties by measuring them before and after irradiation to the indicated absorbed dose under selected conditions described in IEC 60544-2. On the basis of these tests, the material is assigned a “radiation index”. To qualify for a particular radiation index, a material shall satisfy an end- point criterion after being irradiated to the classification dose under specified conditions. The end-point criterion may be expressed as an absolute property value or a percentage of the initial value. Either method may be used to classify materials for radiation resistance. Table 1 provides recommendations for properties and percentages of initial values. All measurements shall be made after removal from the radiation exposure unless otherwise stated in the “qualifiers of the radiation index”. Post-irradiation treatment of test specimens shall be conducted as specified in 3.5 of IEC 60544-2. 3.1 Definition of radiation index The radiation index shall be determined by the logarithm (log 10 rounded off to two significant figures) of the absorbed dose in grays above which the appropriate critical property value has reached the end-point criterion under specified conditions. For example, a material which satisfies a particular end-point criterion to a dose of 2 × 10 4 Gy has a radiation index of 4,3 (i.e. log 10 (2 × 10 4 ) = 4,301). The values shall be taken from the series given in Table 2.
The radiation index shall include the dose rate (see 3.2.1), or the notation “vac” (see 3.2.2), and include special qualifiers, when applicable, such as the critical property (see 3.3), temperature (see 3.4), and the medium (see 4.2.3). For further qualification see Clause 4. As recommended in IEC 60544-2, it is preferable to use gamma-rays, X-rays or electrons for the test irradiation. The type of radiation to which the material was exposed shall be specified. 3.2 Dose rate 3.2.1 Depending on the material and the irradiation conditions, different values of radiation index may be obtained when the test is carried out at different dose rates in atmospheres containing oxygen. Also, dose rate effects caused by diffusion-limited oxidation (see IEC 61244-1) can depend on sample thickness. Therefore, under long-term exposure conditions (see 3.6 of IEC 60544-2), the radiation index shall be given with qualifiers indicating the dose rate and the sample thickness at which the radiation index was obtained. For example: radiation index 4,3 (50 Gy/s, 1 mm). 3.2.2 In the absence of a reactive medium (e.g. in a vacuum or an inert gas), no dose-rate effect needs be considered. In this case the dose rate qualifier may be replaced by the notation (vac). For example: radiation index 4,3 (vac).