Fixed contamination

Fixed contamination. A term used in the context of radiation for nonremovable contamination. 

Scenario 1 Formulation for fixed outlet concentration and fixed contaminant mass load... 

Macroencapsulation is used for large objects such as concrete debris that is contaminated, or structural steel that has fixed contamination. The chemical stabilization and microencapsulation work together to immobilize chemical constituents, while the macroencapsulation is used to physically encapsulate large objects. For this reason, we will discuss chemical stabilization and microencapsulation together and address macroencapsulation in a separate section in this chapter. 

Contamination in the laboratory must be avoided. This is controlled by smear tests i.e., a filter psqier is wiped over the surface and the paper is checked with a suitable instrument. In a so-called "clean area, the fixed contamination should not exceed 2 Bq for a, and 4 Bq for 8-7 on a surface of 100 cm. For an "active area" the rules are a maximum of 20 Bq for a per 100 cm, and 0.01 mGy h from j5-y at a distance of 2 cm from the surface. Radioactive aerosols ate monitored by air samplers in which a certain amount of air is drawn through a ftne filter paper after which the paper activity is measured. 

Contamination. The presence of a radioactive substance on a surface in quantities in excess of 0.4 Bq/cm (0.01 nCi/cm ) for beta and gamma emitters and low toxicity alpha emitters, or 0.04 Bq/cm (0.001 nCi/cm ) for all other alpha emitters. This is either Fixed contamination -contamination other than non-fixed contamination or Non-fixed contamination — contamination that can be removed from a surface during normal handling. ICAO 2-7.2, lATA App. A... 

Fixed contamination shall mean contamination other than non-fixed contamination. IAEA para. 216... 

Non-fixed contamination means contamination that can be removed from a surface during normal handling. IMO Class 7,2.8.2... 

SCO-II A solid object on which either the fixed or non-fixed contamination on the surface exceeds the applicable limited specified for SCO-I in 10.3.6.1.1 and on which (a) the non-fixed contamination on the accessible surface averaged over 300 cm (or the area of the surface if less than 300 cm ) does not exceed 400 Bq/cm (10 nCi/cm ) for beta and gamma emitters and low toxicity alpha emitters, or 40 Bq/cm (1 nCi/cm ) for all other alpha emitters (b) the fixed contamination on the accessible surface averaged over 300 cm (or the area of the surface if less than 300 cm ) does not exceed 800 kBq/cm (20 pCi/cm ) for beta and gamma emitters and low toxicity alpha emitters, or 80 kBq/cm (2 pCi/cm ) for all other alpha emitters and (c) the non-fixed contamination plus the fixed contamination on the accessible surface averaged over 300 cm (or the area of the surface if less than 300 cm ) does not exceed 800 kBq/cm (20 pCi/cm )... 

Yang etal. (2014) optimized a water network for total cost, which consists of annualized investment and operating costs here, shortcut models for treatment units are developed instead of using a fixed contaminant removal model. 

For a restricted area, a level of fixed contamination well below the occupational level of... 

Intrusive work in soil contamination areas or fixed contamination areas. 

Contamination includes two types of radioactive material on surfaces or embedded in surfaces, namely fixed contamination and non-fixed contamination. There is no definitive distinction between fixed and non-fixed contamination, and various terms have been used to describe the distinction. For practical purposes a distinction is made between contamination which, during routine conditions of transport, remains in situ (i.e. fixed contamination) and, therefore, cannot give rise to hazards from ingestion, inhalation or spreading, and non-fixed contamination which may contribute to these hazards. The only hazard from fixed contamination is that due to external radiation exposure, whereas the hazards from non-fixed contamination include the potential for internal exposure from inhalation and ingestion as well as external exposure due to contamination of the skin should it be released from the surface. Under accident conditions, and under certain use conditions such as weathering, fixed contamination may, however, become non-fixed contamination. 

Industrial package (Type IP-1). The higher level of non-fixed contamination permitted on objects classified as SCO-II requires the higher standard of containment afforded by Industrial package lype IP-2. 

Measurement techniques for fixed and non-fixed contamination of packages and conveyances are given in paras 508.2 and 508.7-508.12. These techniques are applicable to SCOs. However, to apply these techniques properly, a consignor needs to know the composition of the contamination. 

Examples of derived limits in the Regulations include the maximum activity limits Aj and Aj, maximum levels for non-fixed contamination, radiation levels at the surfaces of packages and in their proximity, and segregation distances associated with the transport index. The Regulations reqnire assessment and measurement to ensure that standards are being complied with. 

The Regulations set no specific limits for the levels of fixed contamination on packages, since the external radiation resulting therefrom will combine with the penetrating radiation from the contents, and the net radiation levels for packages are controlled by other specific lequiranents. However, limits on fixed contamination are set for conveyances (see para. 513) to minimize the risk that it may become non-fixed as a result of abrasion, weathering, etc. 

In a few cases, a measurement of contamination may be made by directly reading contamination monitors. Such a measurement will include both fixed and non-fixed contamination. This will only be practicable where the level of background radiation from the installation in which the measurement is made or the radiation level from the contents does not interfere. In most cases the level of non-fixed contamination will have to be measured indirectly by wiping a known area for a smear and measuring the resultant activity of the smear in an area not affected by radiation background from other sources. 

Operators should be adequately trained to ensure that samples are obtained in a consistent manner. Comparison between operators may be valuable in this respect. Attention is drawn to the difficulties which will occur if different organizations use techniques which are not fully compatible — especially in circumstances where it is not practical to maintain the levels of non-fixed contamination at near zero values. 

Conveyances may become contaminated during the carriage of radioactive material by the non-fixed contamination on the packages. If the conveyance has become contaminated above this level, it should be decontaminated to at least the appropriate limit. This provision does not apply to the internal surfaces of a conveyance provided that the conveyance remains dedicated to the transport of radioactive material or surface contaminated objects under exclusive use (see para. 514.1). 

Limits are also set on fixed contamination to minimize the risk that it may become non-fixed as a result of abrasion, weathering, etc. 

If the non-fixed contamination on a conveyance exceeds the limits laid down in para. 508 of the Regulations, the conveyance should be decontaminated and, following the decontamination, a measurement should be made of the fixed contamination. The radiation level resulting from the fixed contamination on the surfaces may be measured using a portable instrument of an appropriate range held near to the surface of the conveyance. Such measurements should only be made before the conveyance is loaded. 

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