Radiation and thermal cycling

Figure 23. Effect of radiation and thermal cycling between —115 C and 80 C on microcrack density. (Reproduced from reference 8.)...

The research and development efforts on polymer materials for fusion reactors have been intensified in recent years. Some polymers and composites are able to withstand the radiation doses in excess of 108 Gy even at cryogenic temperatures. Furthermore, international research projects on organic insulators used for fusion magnets are currently in progress. As one of the important subjects, the combined effects of intense radiation and thermal cycling are being tested. 

The effects of thermal cycling and radiation plus thermal cycling on the modulus and strength of these laminates are shown in Figures 17 and 18. 

The VKR-MT nuclear steam supply system uses a direct cycle vessel-type boiling water reactor, which includes (see Fig. X-10 and X-11) (a) The reactor vessel (b) The reactor vessel cover (c) An internal metallic shaft (d) The core (e) Two stages of the centrifugal separators (f) The block of protective tubes (g) Radiation and thermal shielding of the reactor vessel (h) The supporting structure (i) Jet pumps (j) Control rod drives (k) The reloading system for micro fuel elements. 

Because the PCR exponentially copies the target molecule or molecules, amplicon contamination in the laboratory is a serious concern. It is recommended that the mastermix is prepared in an isolated area, such as a PCR station equipped with a UV light. This work area should be exposed to UV radiation after use to destroy any DNA contaminants. The use of dedicated pipets and Altered pipet tips is also recommended. The template DNA should be prepared and added to the reaction in an area that is isolated from the mastermix preparation hood. The thermal cycling and gel electrophoresis should be conducted in a third work area and care should be taken not to introduce amplified PCR products into the mastermix or template preparation work areas. 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

The effect of radiation on the thermal expansion of this toughened composite (T300/CE 339) is shown (191 in Figure 24. The thermal strains measured during the cool-down portion of the first thermal cycle (cooling from RT to -150°C) are shown for the baseline composite (no radiation exposure) and for samples exposed to total doses as high as 10 0 rads. Radiation levels, as low as 10 rads... 

Figure 25. Effect of radiation fluence on microcrack formation in composite specimens subjected to 100 thermal cycles between 80 C and -150 C (Reproduced from reference 19.)...

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