No abstract

The Department of Energy (DOE) is currently managing nearly 13 metric tons of aluminum-clad spent nuclear fuel (ASNF), and some of this ASNF will be placed in helium-backfilled canisters for extended (> 50 years) dry storage. Due to in-reactor and cooling pond conditions, oxyhydroxide corrosion layers have formed on the surface of the ASNF elements. These corrosion layers are susceptible to radiolysis and the formation of molecular hydrogen gas (H 2 ) due to the fuel's inherent radiation field. Consequently, a rigorous evaluation of the effect of helium gas on radiolytic H 2 production is necessary to support the "Technical Considerations and Challenges for Extended (> 50 years) Dry Storage of ASNF" program, especially as previous "Task 2 -Oxyhydroxide Layer Radiolytic Gas Generation Resolution" work demonstrated a significant effect of gas composition on the radiolytic yield (G-value) of H 2 . Here, we report preliminary G-values for the radiolytic formation of H 2 from the gamma irradiation of pre-corroded aluminum alloy 1100 coupons flame sealed in helium environments. Irradiations yielded G(H 2 ) values of (5.1 ± 0.5) 10 -4 and (9.4 ± 0.9) 10 -4 µmol J -1 for pristine coupons, and (10.1 ± 0.4) 10 -4 and (15.1 ± 1.2) 10 -4 µmol J -1 for pre-corroded coupons for 0% and 50% relative humidity, respectively. These helium environment G(H 2 ) values are between 28% and 58% higher than previously reported values for argon environments. This enhancement is attributed to the significant difference in first ionization energy between helium (24.59 eV) and argon (15.76) facilitating additional processes (e.g., Penning ionization). These new preliminary helium environment G(H 2 ) values will be employed by Task 3 -Sealed and Vented System Episodic Breathing and Gas Generation Prediction to model the effect of radiolytic H 2 accumulation in helium environments to evaluate the practicality of extended storage in the DOE Standard Canister. v

Corrosion of aluminium alloy clad nuclear fuel, during reactor operation and under subsequent wet storage conditions, promotes the formation of aluminium hydroxide and oxyhydroxide layers. These hydrated mineral phases and the chemisorbed and physisorbed waters on their surfaces are susceptible to radiation-induced processes that yield molecular hydrogen gas (H2), which has the potential to complicate the long-term storage and disposal of aluminium clad nuclear fuel through flammable and explosive gas mixture formation, alloy embrittlement, and pressurization. Here, we present a systematic study of the radiolytic formation of H2 from aluminium alloy 1100 (AA1100) and 6061 (AA6061) coupons in “dry” (~0% relative humidity) and “wet” (50% relative humidity) helium environments. Cobalt-60 gamma irradiation of both aluminium alloy types promoted the formation of H2, which increased linearly up to ~2 MGy, and afforded G-values of 1.1 ± 0.1 and 2.9 ± 0.1 for “dry” and “wet” AA1100, and 2.7 ± 0.1 and 1.7 ± 0.1 for “dry” and “wet” AA6061. The negative correlation of H2 production with relative humidity for AA6061 is in stark contrast to AA1100 and is attributed to differences in the extent of corrosion and varying amounts of adsorbed water in the two alloys, as characterized using optical profilometry, scanning electron microscopy, Raman spectroscopy, and X-ray diffraction techniques.

No abstract

The Department of Energy (DOE) is currently evaluating strategies for the extended dry storage of aluminum-clad spent nuclear fuel (ASNF). Part of this assessment concerns the extent of radiolytic molecular hydrogen (H 2 ) generation from the aluminum cladding's oxyhydroxide corrosion layers. Understanding this radiation-induced process and the factors affecting it (e.g., system conditions such as temperature and gaseous environment) are essential for the development of predictive computer models to support the Technical Considerations and Challenges for Extended (> 50 yrs) Dry Storage of ASNF program. To achieve this goal and ensure that the experimental data gathered by Task 2 (Oxyhydroxide Layer Radiolytic Gas Generation Resolution) research groups (Idaho National Laboratory and Savannah River National Laboratory) are consistent, a round-robin H 2 analysis capability comparison was initiated.Here we present the results from said round robin and conclude that despite differences in sample preparation, irradiation parameters, and analytical procedures, the measured data are sufficiently consistent between the two laboratories (≤ 15%).