Ceramic Needs in Nuclear Measurement Applications

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1 Ceramic Needs in Nuclear Measurement Applications 4/26/2017 Jim Lustig Senior Engineer

2 GE Reuter Stokes GE offers an expansive line of detectors for use in radiation detection and for sensing applications in harsh environments. Environmental Monitoring Neutron Scattering Ex-Core Nuclear Detectors Nuclear Reactor Instrumentation Homeland Security and International Safeguards

3 Cable Material Selection: Alumina vs. Magnesia vs. Silica Silica: Used in applications where it is important to have low cable capacitance, such as the reactor startup detectors used in pulse mode. Inferior insulation resistance at higher temperatures which makes it unsuitable for most full power applications. Alumina: Good insulation resistance for most applications. Used for almost all sealing applications due to hardness, low porosity and brazability of material, moderately hydrophilic. Used for in-core fission chamber cables and seals. Susceptible to material property changes from impurities, especially sodium and iron oxides. Magnesia: Used for applications where very high insulation resistance is needed, especially at high temperatures. Superior performance for small signals at high temperatures. More hygroscopic than alumina, and softness can mean higher compaction density, which can mean longer, more difficult cable processing.

4 Radiation Concerns for Ceramics in Sensor Applications Swelling- Radiation damage causes many ceramic materials to swell which can compromise the brazed seal interfaces, resulting in leaks. Parameters influencing degree of swelling are not well documented, though grain size is believed to be more influential than impurities in alumina. <3% swelling from radiation damage acceptable. Radiation Induced Conduction (RIC)- Ionizing radiation can reduce the insulation resistance of ceramics by several decades. This must be accounted for in design. There is little data available specific to ceramic formulations regarding susceptibility to RIC. Neutron activation/absorption- Generally of lower relative concern, though there are some impurities which can be of concern such as boron and hafnium which may accompany zirconia additions.

5 Best Practices: Contamination Glazes rarely used on seals for nuclear due to often lower insulation resistance at temperature, unknown effects of radiation damage and proprietary formulations that make design specification difficult. Cleaning by wet blasting is preferred over dry blasting as it is less aggressive and less likely to alter dimensions. Wet blasting is typically followed up immediately with solvent cleaning and air firing for pure ceramics or hotbox drying for metallized ceramics. Storage is ideally individual to prevent chipping or transfer of metal from metallized surfaces to insulating surfaces. Soft plastics and halogenated (PVC) plastics are avoided for nuclear parts. Moisture is the enemy of good insulation resistance in mineral insulated cables.

6 Best Practice: Materials Selection High purity is often desirable because of fewer unknowns with regard to behavior under radiation and high temperature exposure. Very high purity may cause metallization adhesion difficulties though. Some deliberate additives may also improve characteristics such as reduced swelling or electrical resistance properties. Higher purities often carry higher costs and may not provide impactful benefits to the product. Fine grain size- (<30µm) seems to provide better resistance to neutron damage High density- typically specify near full theoretical density for seal ceramics as low porosity is desirable for hermeticity and superior mechanical ruggedness. Low porosity is also a benefit for drying out ceramics-reduced moisture issues.

7 Ceramics for Sensors Wish List Standardized techniques for metallizing high purity ceramics More data on swelling in ceramics from radiation damage (fast neutron in particular) Easier access to electrical resistivity vs temperature for specific ceramic formulations Data on glazes regarding the chemical makeup and electrical performance

8 Acknowledgements and References Jack Doyle Gregg Nallo W. Kesternich, F. Scheuermann, S. Zinkle. J. of Nucl. Mater (1995) 219. F.W. Clinard, Jr., G. F. Hurley. J. of Nucl. Mater (1981) 103 & 104. S.J. Zinkle, G.P. Pells. J. of Nucl. Mater (1998) 253. G.P. Pells, D.C. Phillips. J. of Nucl. Mater (1979) 80.