### Abstract

The diffusivity of hydrogen is an important property of light water nuclear reactor (LWR) fuel cladding. LWR cladding absorbs hydrogen during normal operation, a contributing factor to embrittlement that decreases the lifetime of the fuel. Mass transport of hydrogen is dictated by an Arrhenius behavior typical of solid state diffusion and the associated activation energy is therefore a property relevant to LWR fuel performance. We have used incoherent quasi-elastic neutron scattering (QENS) to directly measure the diffusivity of hydrogen in recrystallized Zircaloy 2 with a hydrogen concentration of 170 μg/g. We rely upon the low-Q expansion for long-range diffusion to determine diffusivity as a function of temperature between 572 and 780 K. We find the diffusivity is given by D(T) = 0.0067 exp (-0.461 eV/kT) [cm ^{2} /s] below 670 K and by D(T) = 0.0012 exp (-0.36 eV/kT) [cm ^{2} /s] above 670 K. Our activation energy below 670 K agrees with the value typically used to assess hydrogen diffusivity in LWR cladding [Kearns, Journal of Nuclear Materials 43 (1972) 330], but is approximately 20% lower above 670 K. The two different activation barriers are attributed to impurity trapping of hydrogen solutes at lower temperature that ceases to influence diffusivity at higher temperature. The application of the Oriani model for diffusion with impurity trapping to our system demonstrates the plausibility of this hypothesis. We believe this mechanism may be responsible for historical discrepancies of measured hydrogen diffusivity in Zr-based alloys. The elastic intensity versus temperature in fixed window scans exhibit inflection points that are in good agreement with the published terminal solid solution solubility limits for hydrogen in Zircaloy 2.

Original language | English (US) |
---|---|

Pages (from-to) | 177-189 |

Number of pages | 13 |

Journal | Journal of Nuclear Materials |

Volume | 518 |

DOIs | |

State | Published - May 2019 |

### Fingerprint

### Keywords

- Activation energy
- Hydrogen diffusion
- Neutron scattering
- Solubility limit
- Zircaloy

### ASJC Scopus subject areas

- Nuclear and High Energy Physics
- Materials Science(all)
- Nuclear Energy and Engineering

### Cite this

_{0.0155}) using incoherent quasi-elastic neutron scattering

*Journal of Nuclear Materials*,

*518*, 177-189. https://doi.org/10.1016/j.jnucmat.2019.02.045

** Direct measurement of hydrogen diffusivity and solubility limits in Zircaloy 2 (formula unit of ZrH _{0.0155} ) using incoherent quasi-elastic neutron scattering .** / Heuser, Brent J; Prisk, Timothy R.; Lin, Jun li; Dax, Tanya J.; Zhang, Yongfeng.

Research output: Contribution to journal › Article

_{0.0155}) using incoherent quasi-elastic neutron scattering ',

*Journal of Nuclear Materials*, vol. 518, pp. 177-189. https://doi.org/10.1016/j.jnucmat.2019.02.045

_{0.0155}) using incoherent quasi-elastic neutron scattering Journal of Nuclear Materials. 2019 May;518:177-189. https://doi.org/10.1016/j.jnucmat.2019.02.045

}

TY - JOUR

T1 - Direct measurement of hydrogen diffusivity and solubility limits in Zircaloy 2 (formula unit of ZrH 0.0155 ) using incoherent quasi-elastic neutron scattering

AU - Heuser, Brent J

AU - Prisk, Timothy R.

AU - Lin, Jun li

AU - Dax, Tanya J.

AU - Zhang, Yongfeng

PY - 2019/5

Y1 - 2019/5

N2 - The diffusivity of hydrogen is an important property of light water nuclear reactor (LWR) fuel cladding. LWR cladding absorbs hydrogen during normal operation, a contributing factor to embrittlement that decreases the lifetime of the fuel. Mass transport of hydrogen is dictated by an Arrhenius behavior typical of solid state diffusion and the associated activation energy is therefore a property relevant to LWR fuel performance. We have used incoherent quasi-elastic neutron scattering (QENS) to directly measure the diffusivity of hydrogen in recrystallized Zircaloy 2 with a hydrogen concentration of 170 μg/g. We rely upon the low-Q expansion for long-range diffusion to determine diffusivity as a function of temperature between 572 and 780 K. We find the diffusivity is given by D(T) = 0.0067 exp (-0.461 eV/kT) [cm 2 /s] below 670 K and by D(T) = 0.0012 exp (-0.36 eV/kT) [cm 2 /s] above 670 K. Our activation energy below 670 K agrees with the value typically used to assess hydrogen diffusivity in LWR cladding [Kearns, Journal of Nuclear Materials 43 (1972) 330], but is approximately 20% lower above 670 K. The two different activation barriers are attributed to impurity trapping of hydrogen solutes at lower temperature that ceases to influence diffusivity at higher temperature. The application of the Oriani model for diffusion with impurity trapping to our system demonstrates the plausibility of this hypothesis. We believe this mechanism may be responsible for historical discrepancies of measured hydrogen diffusivity in Zr-based alloys. The elastic intensity versus temperature in fixed window scans exhibit inflection points that are in good agreement with the published terminal solid solution solubility limits for hydrogen in Zircaloy 2.

AB - The diffusivity of hydrogen is an important property of light water nuclear reactor (LWR) fuel cladding. LWR cladding absorbs hydrogen during normal operation, a contributing factor to embrittlement that decreases the lifetime of the fuel. Mass transport of hydrogen is dictated by an Arrhenius behavior typical of solid state diffusion and the associated activation energy is therefore a property relevant to LWR fuel performance. We have used incoherent quasi-elastic neutron scattering (QENS) to directly measure the diffusivity of hydrogen in recrystallized Zircaloy 2 with a hydrogen concentration of 170 μg/g. We rely upon the low-Q expansion for long-range diffusion to determine diffusivity as a function of temperature between 572 and 780 K. We find the diffusivity is given by D(T) = 0.0067 exp (-0.461 eV/kT) [cm 2 /s] below 670 K and by D(T) = 0.0012 exp (-0.36 eV/kT) [cm 2 /s] above 670 K. Our activation energy below 670 K agrees with the value typically used to assess hydrogen diffusivity in LWR cladding [Kearns, Journal of Nuclear Materials 43 (1972) 330], but is approximately 20% lower above 670 K. The two different activation barriers are attributed to impurity trapping of hydrogen solutes at lower temperature that ceases to influence diffusivity at higher temperature. The application of the Oriani model for diffusion with impurity trapping to our system demonstrates the plausibility of this hypothesis. We believe this mechanism may be responsible for historical discrepancies of measured hydrogen diffusivity in Zr-based alloys. The elastic intensity versus temperature in fixed window scans exhibit inflection points that are in good agreement with the published terminal solid solution solubility limits for hydrogen in Zircaloy 2.

KW - Activation energy

KW - Hydrogen diffusion

KW - Neutron scattering

KW - Solubility limit

KW - Zircaloy

UR - http://www.scopus.com/inward/record.url?scp=85062838405&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85062838405&partnerID=8YFLogxK

U2 - 10.1016/j.jnucmat.2019.02.045

DO - 10.1016/j.jnucmat.2019.02.045

M3 - Article

AN - SCOPUS:85062838405

VL - 518

SP - 177

EP - 189

JO - Journal of Nuclear Materials

JF - Journal of Nuclear Materials

SN - 0022-3115

ER -