How much fuel is in the core: 76 elements on paper, 24 cleared to ship, and 'very lightly loaded' in Valar's words
unresolvedtechnical
What was said
- Valar Atomics (safety agreement, Table 6) (2025-10): Describes a core of 76 fuel elements with about 250 kg of heavy metal at 4.95% U-235, which is about 12.4 kg of U-235.
- Cory Gardner, speaking for Valar at the Trust Lands board (auto-generated transcript) (2026-09-17): Said Ward 250's fuel would fit in about a five-inch cube and: "It's very lightly loaded. It's not a fully loaded core."09.17.2026 TLA Board of Trustees Meeting Audio Transcript (auto-generated) (Utah Trust Lands Administration (Utah Public Notice Website), 2026-09-17)
What the record shows
- DOE's shipping review says 'only 24 packages (24 fuel elements) would be authorized for shipment', each block holding 170 TRISO compacts and at most 234.94 g of U-235: at most about 5.64 kg of U-235 in all, in fuel up to 19.9% enriched. Per element, the NSDA's own figures imply 162.83 g of U-235 in 3.29 kg of heavy metal; DOE's block holds at most 234.94 g of U-235 (about 1.18 kg of uranium if at the 19.9% maximum). The per-element figures differ (76 such blocks holding 250 kg would need 7.14% fuel, not Table 6's 4.95%), so Table 6's equal per-element loading does not match the block DOE cleared, unless some of the 76 elements are unfueled or loaded differently, which the paper does not say.Safety Evaluation Report, Letter Amendment of Certificate of Compliance No. 9979 for the Model 9979 Package, Docket 26-35-9979 (U.S. Department of Energy, Packaging Certification Program, 2026-05-20)
- DOE's criticality release reports a 'zero-power fueled criticality demonstration' and gives no core loading. No public record read gives the number of fuel blocks loaded, the startup physics results, or how the safety analyses were adjusted for a partly loaded core of richer fuel; the approved DSA, which would, was not found in public records.Department of Energy Celebrates Second Advanced Reactor Achieving Criticality (U.S. Department of Energy, 2026-06-18)
- DOE's shipping review limits the count to 24 fuel elements 'under this letter amendment', that is, under this one approval; it does not say the core can never hold more, and no other shipment approval was found.Safety Evaluation Report, Letter Amendment of Certificate of Compliance No. 9979 for the Model 9979 Package, Docket 26-35-9979 (U.S. Department of Energy, Packaging Certification Program, 2026-05-20)
The gap: The public safety paper describes its design core: 76 elements of 4.95% fuel. DOE's shipping approval covers 24 elements of fuel up to 19.9% enriched under one letter amendment, and a Valar speaker says the core is 'very lightly loaded'; those two statements agree with each other. What is actually in the reactor, and how the safety analysis was adjusted for that core, were not found in public records read to late September 2026.
In plain termsThink of the core as a honeycomb of 76 fuel elements. The paper the public can read describes all 76 filled with ordinary-grade fuel; that was the design on paper. DOE's shipping review cleared 24 fuel blocks (its term for the elements) of richer fuel, and a Valar speaker told the state board the reactor is 'very lightly loaded.' Those two fit together, and a test reactor starting with a partly filled core is not by itself a warning sign. A statement of what is actually inside the reactor, and of the safety numbers for that core, was not found in public records.
Why it matters: How much fuel is in the core, and how rich it is, sets how the reactor behaves and what radioactivity builds up; the published safety analysis describes a different core.
What would settle it: FOIA to DOE Idaho Operations Office for Ward 250's core-loading records, startup physics test results and the approved DSA core description; FOIA to DOE and NNSA for nuclear material transaction reports (NMMSS) recording fuel received at the San Rafael Energy Lab.