Guidance for Evaluating Combustible Gas Generation to Demonstrate Compliance with 10 CFR 71.43(d) 

This guidance applies only to DOE elements or persons working under contract to DOE elements

DOE elements means ​programs, operations offices, field/site offices, and other organizational units of the Department of Energy, excluding those of the National Nuclear Security Administration.  The list of DOE elements is hereexternal (link to DOE Directives website).

This guidance is based on 10 CFR Part 71 and the references cited below, and only applies to DOE elements and persons under contract to DOE elements for preparing applications in accordance with 10 CFR 71, Subpart D, Application for Package Approval  for Type B or fissile radioactive materials packages to demonstrate compliance with 10 CFR 71.43(d).

The applicant should evaluate combustible gas-generation with their Maximum Normal Operating Pressure (MNOP) calculation [Note – Ref. Regulatory Guide 7.9: the applicant should also address gas-generation in Sections 1.2.2 (Contents), 2.2.2 (Chemical, Galvanic, or Other Reactions), etc. of the application].  This evaluation of MNOP assumes the package is closed and under the Normal Conditions of Transport heat condition for 1-year.  No credit should be taken for getters, catalysts, or other recombination devices, that is, a combustible gas suppression system (e.g., vapor pressure catalytic recombiner, getters, etc.) is not allowed; however, credit may be taken for diffusion and leakage to evaluate the combustible gas release rate vs. the generation rate.

The application [i.e., Safety Analysis Report for Packaging (SARP) or supplement] must demonstrate that hydrogen and other flammable gases comprise less than 5% by volume of the total gas inventory within any confined volume.  For contents other than Transuranic (TRU) waste, inerting is typically not allowed to limit the concentration of flammable gases; however, if inerting is proposed, at a minimum the applicant must:

  1. Demonstrate the inerting process will prevent the development of flammable gas mixtures in any confined area of the package throughout the entire shipment period, 
  2. Provide a detailed evaluation or analysis to demonstrate that there are no flammable gas mixtures (considering the worst case concentrations of hydrogen or any other flammable gases, and oxygen) during shipment,
  3. Provide a detailed configuration of all passages to ensure that the inert gas could be introduced effectively (e.g., injection path, port orientation, to the innermost packaging or other confined areas within the containment system of the package),
  4. Demonstrate that the inert gas either effectively occupies the containment cavity or is in uniform concentration through the cavity,
  5. Discuss how the concentrations of combustible gases would be quantitatively analyzed, and
  6. Provide detailed information on the different steps of the inerting process in the Package Operations section of the application.

For TRU waste, compliance with the 5% by volume hydrogen concentration limit is determined by the methods discussed in NUREG/CR-6673.

If the total combustible gas inventory within any confined volume exceeds 5% by volume, then the applicant may use a factor of two as a conservatism when providing the expected shipment period limit.  For example, if the contents show that 5% by volume combustible gas is generated in 8 months, the shipping period limit in the Certificate of Compliance (CoC) condition would be 4 months (see NRC Information Notice 84-72).  

Based on IN 84-72, and for consistency with NRC CoCs, at this time DOE CoCs will only include a specific condition-of-use to limit the shipping period if flammable gases reach 5% in less than 2 years.

Chapter 3 of the SARP should include a calculation that shows the time it takes to reach 5% by volume combustible gas in any confined volume for each of the contents listed in Chapter 1, or by another method of demonstration acceptable to DOE PCP (e.g., see 49 CFR 173.461).  Chapter 7 should include the shipment period limit if the total combustible gas inventory within any confined volume exceeds 5% by volume in less than 2-years.

For contents with shipping period limits, the SARP should be clear WHEN the shipping period begins, which is typically when the package containment boundary is sealed, and not when the package is offered for shipment.  Consequently, the shipping period includes storage of the package pending shipment.   

Non-transportation use (e.g., indefinite storage or disposal) of a Type B or fissile material package is outside the scope of Part 71 and the DOE Certifying Official's package certification authority under Order 460.1D, Hazardous Materials Packaging and Transportation Safety; therefore, it is responsibility of package users (i.e., shipper/consignor and receiver/consignee) to understand and comply with the applicable safety requirements for non-transportation uses of a Type B or fissile material package.  DOE PCP strongly advises package users to consult with the Certificate Holder and their subject matter expert for safe use of packages outside the scope of transportation.


  2. NUREG-1609, Standard Review Plan for Transportation Packages for Radioactive Material (
  3. NRC Information Notice 84-72, Clarification of Conditions for Waste Shipments Subject to
    Hydrogen Gas Generation (
  4. NUREG/CR-6673, Hydrogen Generation in TRU Waste Transportation Packages ( )
  5. Radwaste Radiolytic Gas Generation Literature Review, EPRI NP-5977, Research Project 2724-1, Final Report, September 1988 external (link to NRC website at​

​Questions or comments? Contact the DOE Packaging Certification Program Manager, Dr. Shuler, (301) 903-5513,

Added July 10, 2020

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