The Fracture and Aerosol Release of Impacted HLW Glasses and HLW Canisters

Abstract

The fracture and release mechanism of radioactive aerosols of HLW glass and HLW canisters are studied experimentally by laboratory scale and full scale drop tests. The experimental conditions model the conditions of accidental drops in a deep salt repository. The laboratory scale drop tests have a scaling factor of 1:10. Accelerated probes of simulated HLW glass impact on a ground plate and the size distributions of broken fines and released aerosols are measured by sieving and scanning electron microscopy (SEM) of aerosol samples.The impact velocity is determined as the dominating impact parameter. Further parameters tested, such as waste glass composition, cooling time (residual thermal stresses), probe temperature at impact, and ground characteristics, show no measurable influence. Source terms of released respirable aerosols are evaluated for two reference cases, borehole drop (impact velocity v = 80 m/s) and reloading hall drop (v = 14 m/s), the values being 0.1 % and to 2.10-4 % respectively of the glass probe mass. The full scale drop tests are performed with European Standard HLW canisters. The canisters keep their integrity in all tests up to drop heights of 14 m. On opening the canisters, the broken fines are analyzed by sieving. The results are in good agreement with the small scale tests and confirm their acceptability for use in a safety analysis.

Mechanical properties of nuclear waste glasses

“…Fracture of vitrified wasteforms has two likely causes, either thermal shock in the container during cooling [6][7][8][9] or impact damage due to accidents during handling [10,11]. Fracture on cooling is inevitable in large-scale glass blocks (typically 0.3-0.6 m in diameter, 1-3 m in length).…”

“…The possibility of impact damage to canisters during handling must be carefully considered as failure of the canister and significant fracture of the glass can result in the generation of respirable fines [16]. The result of a canister impact can be tested by dropping the canister or smaller scale model glass samples [10] from a significant height and observing the result. However, the drop test technique is expensive and not realistic for all glass compositions.…”