Generation of the TSL for Zirconium Hydrides from Ab Initio Methods
- Naval Nuclear Lab., Schenectady, NY (United States)
- Naval Nuclear Lab., West Mifflin, PA (United States)
Zirconium hydride (ZrH$$\mathcal{x}$$) is a moderator material used in TRIGA and other reactors as well as a corrosion product in Zircaloy. ZrH$$\mathcal{x}$$ may exist in multiple phases with varying stoichiometry, the most significant of which are the $$\mathcal{δ}$$ phase and the ϵ phase. At room temperature the $$\mathcal{δ}$$ phase is dominant for 1.56 < $$\mathcal{x}$$ < 1.64 and the ϵ phase for $$\mathcal{x}$$ > 1.74. Current ENDF/B-VIII.0 ZrH$$\mathcal{x}$$ thermal scattering law (TSL) evaluations do not distinguish between phases. These sub-libraries were generated with the LEAPR module of NJOY using historic phonon spectra derived from a central force model and assume incoherent elastic scattering for both bound hydrogen and zirconium. While the use of incoherent elastic scattering is appropriate for hydrogen, it neglects the effects of crystal structure important for scattering from zirconium bound in ZrH$$\mathcal{x}$$. In this work the TSLs for hydrogen and zirconium bound in $$\mathcal{δ}$$-ZrH$$\mathcal{x}$$ (H-ZrH$$\mathcal{x}$$ and Zr-ZrH$$\mathcal{x}$$) and ϵ-ZrH2 (H-ZrH2 and Zr-ZrH2) were generated from phonon spectra derived from modern ab initio lattice dynamics methods and ab initio molecular dynamics. Density functional theory calculations were performed using the VASP code for supercells of cubic ZrH$$\mathcal{x}$$ and of tetragonal ZrH2 to generate partial phonon spectra for hydrogen and zirconium for each phase with the PHONON code and velocity autocorrelation function. TSLs for hydrogen and zirconium in ZrH$$\mathcal{x}$$ and ZrH2 were generated from these spectra using the FLASSH (Full Law Analysis Scattering System Hub) code. The generalized coherent elastic routine in FLASSH was used to generate the elastic contribution to Zr(ZrH$$\mathcal{x}$$) and Zr(ZrH2), thereby capturing the previously neglected effects of crystal structure. The present TSLs provide both a re-evaluation of the current ZrH sub-libraries, and expansion of the set of TSLs available for the examination of neutrons in systems with zirconium hydride, permitting explicit treatment of $$\mathcal{δ}$$ and ϵ phases.
- Research Organization:
- Naval Nuclear Lab., Schenectady, NY (United States); Naval Nuclear Lab., West Mifflin, PA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
- DOE Contract Number:
- 89233018CNR000004
- OSTI ID:
- 1909592
- Country of Publication:
- United States
- Language:
- English
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