WM 2011 Conference , February 27 – March 3 , 2011 , Phoenix , AZ Evaluation of Hydrogen Generation and Maximum Normal Operating Pressure for Waste Transportation Packages

The U.S. Nuclear Regulatory Commission certifies several types of radioactive waste packages and verifies that the package designers have shown that there will be no significant chemical, galvanic, or other reactions among the package components and contents, in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 71.43(d). For a transportation package containing substances that could generate hydrogen gas, the package designer should calculate the gas generation rate and ensure that it is limited to a molar quantity of no more than 5 percent by volume in the package over a 60-day shipping period under standard temperature and pressure conditions. In addition, the maximum normal operating pressure (MNOP) of the containment vessel should be designed below the design pressure. Therefore, the MNOP calculations should include the hydrogen gas generated in the payload and released into the inner cavity. Package designers have used various approaches to estimate hydrogen gas generation and demonstrate compliance with the regulatory limits. Because it may be difficult to directly measure the hydrogen gas concentrations during transportation operations, it is important that designers use consistent and reliable methods to evaluate hydrogen gas generation. This paper presents a generic evaluation approach for estimating hydrogen generation from radiolysis and thermal decomposition in generic transportation packages. It also presents the calculation of associated MNOP induced by the potential combined effects of radiolysis, thermal decomposition, thermal expansion, and water vapor. In addition, this paper discusses a generic inerting process commonly used to control combustible gases during the normal conditions of transport. A fictitious data set is used to illustrate the evaluation approach.