Reentry thermal testing of light-weight radioisotope heater units

Peterson, D.E.; Starzynski, J.S.

doi:10.2172/5253353

Cited by 2 publications

(2 citation statements)

References 3 publications

(8 reference statements)

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“…lower than was experimentally measured for LWRHU capsules containing fuel pellets >8 yr old. 3 This difference is supported by the current study, which verified that the age and microstructure of the older fuel led to significantly higher release rates at high temperatures than do the age and microstructure of the currently used heat source fuel.…”

Section: Discussionsupporting

confidence: 66%

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Helium release from radioisotope heat sources

Peterson¹,

Early²,

Starzynski³

et al. 1984

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Diffusion of helium in 238 PuO 2 fuel was characterized s?. s a function of the heating rate and the fuel microstructure. The samples were thennally ramped in an induction furnace and the helium release rates measured with an automated mass spectro neter. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metaJlographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release ss controlled by move nent of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles piong grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranislar bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel. Activation energies and diffusion constants were correlated with previous measurements conducted on inert gases diffusing in ceramics. The helium release measured from a LightWeight Radioisotopic Heater Unit in an earlier study was verified, and the release behavior was predicted for a heat source containing the current fuel form.

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Section: Discussionsupporting

confidence: 66%

“…Linear least squares analysis of each plot of log D' vs 1/T yields an E a value from the slope and a log DQ value from the intercept. We used the following equation, based on the decay rate and pellet weight, to calculate the helium level generated by alpha decay in each plutonia sample: V He [cm 3…”

Section: Theoretical Analysismentioning

confidence: 99%