The accident analysis assumed 3 megawatt-days of fuel use; the same document's limit allows 30, ten times more

recordconfirmed

2025-10 · safe-009 · Valar Atomics, U.S. Department of Energy

In the NSDA's Maximum Hypothetical Accident analysis (pages 34-36), the radioactive inventory is based on 'OpenMC neutronic analysis with 3 MWd total burnup' and 'Conservative 30 EFPD operation assumed for inventory buildup' (30 effective full-power days at 100 kW is 3 megawatt-days). Earlier (page 10) the NSDA says the analysis assumes operation at maximum licensed power long enough to reach equilibrium inventories. Its operating limits (page 25) set 'Fuel burnup limit: 30 megawatt-days', and its objectives call for 12 months of operation with availability above 80% and steady operation up to 250 kWth (page 8). The limit is ten times the burnup the accident inventory was built on. Valar's July 2025 county presentation (orig-045) and its June 2026 draft post both describe 30 effective full-power days, which matches the accident analysis rather than the 30 MWd limit. The lifecycle also differs: the NSDA gives about 18 months 'from authorization through decommissioning', DOE's categorical exclusion a 24-month program (12 months of operation, 6 of cooldown, 6 of decommissioning). No public copy of the approved DSA, which would fix the inventory and limits, was found as of late September 2026 (safe-007). Our check using standard half-lives: going from 3 to 30 MWd at the same power would raise iodine-131 by about 8% and the iodine and noble-gas dose by about 4%; cesium-137 and strontium-90 would grow about tenfold but stay about 4% of the iodine-131 activity. The NSDA's 18 months is also shorter than its own schedule: Table 7's dates plus 12 months of operation already exceed 18 months before any decommissioning, unless counted from startup.

In plain termsThe longer and harder a reactor runs, the more radioactive by-products build up in its fuel, and an accident analysis has to assume the worst amount. Valar's worst-case analysis assumed about 30 days at full power. The same document's own limit would allow roughly ten times as much fuel use, and its goals speak of a year of operation. The company's later statements point to 30 days, which would fit the analysis. No public record found as of late September 2026 shows which limit DOE approved.

Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft; issued for Public Release) (Valar Atomics, 2025-10) primary company “Conservative 30 EFPD operation assumed for inventory buildup”
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft; issued for Public Release) (Valar Atomics, 2025-10) primary company “Fuel burnup limit: 30 megawatt-days”
NEPA Determination DOE-ID-26-005: Valar Ward250 Research Reactor (categorical exclusion B5.26) (U.S. Department of Energy, Office of Nuclear Energy (Idaho), 2026-04-22) primary government “approximately 12 months of reactor operation followed by 6 months of in-vessel cooldown”
Ward 250 By the Numbers (unlisted company page with placeholders, signed Isaiah Taylor) (Valar Atomics (Isaiah Taylor), 2026-06-28) primary company

verified 2026-10-02: Re-read NSDA pp. 8-10, 25 and 34-37 and CX in late September 2026. Holds: '3 MWd total burnup' and '30 EFPD' (p. 34) against a 30 MWd limit (p. 25); I-131 named 'primary dose contributor'. Arithmetic checked (30 days x 0.1 MW = 3 MWd). Corrected in late September 2026: last sentence replaced with our half-life check (I-131 +8%, iodine and noble-gas dose +4%); added the 18-month schedule point.

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