{"operation":"document","citation":"25-0135","title":"Atkins Réalis Nuclear Secured — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2026-06-16","effective_on":null,"summary":"25-0135 response to Atkins Réalis Nuclear Secured concerning 173.403.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0135.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0135.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0135","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2026-06/250135.pdf","body":"<<<PAGE 1>>>\n\n1200 New Jersey Avenue, SE\nWashington, DC 20590\nU.S. Department\nof Transportation\nPipeline and Hazardous\nMaterials Safety\nAdministration\nJune 16, 2026\nMr. Bradley Scott\nAtkins Réalis Nuclear Secured\n2801 George Washington Way\nRichland, WA 99354\nReference No. 25-0135\nDear Mr. Scott:\nThis letter is in response to your October 7, 2025 email requesting clarification of the Hazardous\nMaterials Regulations (HMR; 49 CFR Parts 171-180) as they apply to the definition of “fissile\nmaterial.” Specifically, you request clarification on the scope of exclusions for irradiated natural\nor depleted uranium as specified in § 173.403.\nWe have paraphrased and answered your questions as follows:\nQ1. In the definition of fissile material under § 173.403, is the exclusion of “natural uranium\nor depleted uranium that has been irradiated in thermal reactors only” intended to exclude\nonly the U-235 component that may have become slightly enriched during irradiation?\nA1. Yes. The definition of fissile material means plutonium-239, plutonium-241, uranium-\n233, uranium-235, or any combination of these radionuclides. The exclusion of natural or\ndepleted uranium that has been irradiated in a thermal reactor is limited solely to the U-\n235 component.\nQ2. Does this exclusion also apply to fissile isotopes, such as plutonium-239 or plutonium-\n241, that are created because of the irradiation of natural or depleted uranium in a thermal\nreactor?\nA2. No. See answer A1.\n\n<<<PAGE 2>>>\n\nQ3. Does the Department of Transportation (DOT) consider U-233, produced from the\nirradiation of natural thorium within a thermal reactor, to be excluded from the definition\nof fissile material?\nA3. No. See answer A1\nI hope this information is helpful. Please contact us if we can be of further assistance.\nSincerely,\nDirk Der Kinderen\nChief, Standards Development Branch\nStandards and Rulemaking Division\n\n<<<PAGE 3>>>\n\nCardez, E.\n25-0135\nFrom: INFOCNTR (PHMSA)\nTo: Baker, Yul (PHMSA)\nCc: Hazmat Interps\nSubject: FW: Request for Letter of Interpretation\nDate: Tuesday, October 7, 2025 15:00:44\nAttachments: image001.png\nGood afternoon,\nPlease see the following interpretation request. Let us know if you need anything else.\nBest,\nAminah\nFrom: Brad Scott <brad.scott@atkinsrealisusn.com>\nSent: Tuesday, October 7, 2025 11:44 AM\nTo: INFOCNTR (PHMSA) <INFOCNTR.INFOCNTR@dot.gov>\nSubject: Request for Letter of Interpretation\nYou don't often get email from brad.scott@atkinsrealisusn.com. Learn why this is important\nCAUTION: This email originated from outside of the Department of Transportation (DOT). Do\nnot click on links or open attachments unless you recognize the sender and know the content\nis safe.\nMr. Shane Kelley\nDirector, Standards and Rulemaking Division\nU.S. DOT/PHMSA (PHH-10)\n1200 New Jersey Avenue, SE East Building, 2nd Floor\nWashington, DC 20590\nRegarding the definition of Fissile Material in 173.403:\nIs the DOT’s exclusion of “any natural or depleted uranium that has only been irradiated\nin a thermal reactor” from the definition of fissile material in 49 CFR 173.403 intended to\nexclude only the U-235 component of that natural or depleted uranium that could\nbecome slightly enriched due to the conversion of U-238 to some other isotope, thereby\nincreasing the U-235 enrichment? Or is the intent of DOT to also exclude from that\ndefinition of fissile material any fissile plutonium-239 or plutonium-241 that could be\ncreated because of the irradiation of natural or depleted uranium in a thermal reactor?\nFollow up question, if DOT did intend to also exclude from that fissile material definition\n\n<<<PAGE 4>>>\n\nany fissile plutonium-239 or plutonium-241 that could be created because of the\nirradiation of natural or depleted uranium in a thermal reactor, does DOT have an\nopinion on whether U-233 that could be produced from the irradiation of natural thorium\nwithin a thermal reactor would also be excluded from the definition of fissile material?\nThank you,\nBradley Scott\nTransportation Training Manager\nT&FS Business Unit\nAtkinsRéalis Nuclear Secured\n2801 George Washington Way, Richland WA 99354\nbrad.scott@atkinsrealisusn.com\nOffice: 509-940-2071\nMobile: 509-539-8657\nSee our website at www.atkinsrealisusntraining.com\nNew name. New era.\nDISCOVER MORE","truncated":false,"body_characters":4265}