Review of Uranium Hydriding and Dehydriding Rate Models in GOTH_SNF for Spent Fuel MCO Calculations

Kirkpatrick, John R. ; Dahl, Chris A.

Idaho National Laboratory

关键词: Uranium Hydriding;    Storage;    Dissociation;    Hydrides;    Spent Fuels;   

DOI  :  10.2172/911530
RP-ID  :  DOE/SNF/REP-089
RP-ID  :  DE-AC07-99ID-13727
RP-ID  :  911530

美国|英语

来源: UNT Digital Library

【 摘 要 】

The present report is one of a series of three. The series provides an independent technical review of certain aspects of the GOTH_SNF code that is used for accident analysis of the multicanister overpack (MCO) that is proposed for permanent storage of spent nuclear fuel in the planned repository at Yucca Mountain, Nevada. The work documented in the present report and its two companions was done under the auspices of the National Spent Nuclear Fuel Program. The other reports in the series are DOE/SNF/REP-087 and DOE/SNF/REP-088. This report analyzes the model for uranium hydriding and dissociation of the hydride that was documented in the SNF report titled MCO Work Book GOTH_SNF Input Data.1 Reference 1 used a single expression from a model by Bloch and Mintz for both the uranium hydriding and dehydriding reactions. This report compares the results of the GOTH_SNF expression for both phenomena with those from the models proposed by J. B. Condon and further developed by Condon and J. R. Kirkpatrick. The expression for the uranium hydriding rate used in GOTH_SNF (from the model of Bloch and Mintz) gives consistently lower values than those from the models of Condon and Kirkpatrick. This is true for all hydrogen pressures and for all temperatures. For a hydrogen pressure of 1 atm, the hydriding rates given by the models of Condon and Kirkpatrick are zero by the time the temperature reaches 400°C. That is, the term representing the dehydriding reaction has become large enough to overwhelm the term representing the hydriding reaction. The same is true for the expression used in GOTH_SNF. For lower hydrogen pressures, the hydriding rates reach zero at even lower temperatures for the Bloch and Mintz model and also for the Condon and Kirkpatrick models. Uranium dehydriding rates can be calculated for temperatures as high as 2,000°C. The dehydriding rates from GOTH_SNF contain an assumption that there is a 0.22 psia hydrogen pressure in the atmosphere surrounding the hydride. For temperatures >~700°C, the expression from GOTH_SNF (the model of Bloch and Mintz) gives higher dehydriding rates than that from Condon. However, in calculations of MCOs using GOTH_SNF, the dehydriding is complete by ~400°C so that rates for temperatures higher than that are not relevant. In the temperature range 275–400°C, the dehydriding rate from the Condon model is much higher than that from GOTH_SNF. The practical consequences of the differences in hydriding and dehydriding rates are not obvious. A way to evaluate the consequences is to repeat an important MCO calculation on GOTH_SNF using hydriding and dehydriding rates that have been artificially modified to be closer to those given by the expressions of Condon and Kirkpatrick and see if the conclusions about the safety of the MCO are changed.