Valar Watch · Claims vs Record disc-011

Claims vs Record disc-011

unresolvedsafety 'Walk-away' cooling: Valar's design target is 72 hours hands-off; DOE's review says 'indefinitely'; neither analysis is public

disc-011

What was said

U.S. Department of Energy (categorical exclusion for Ward 250) (2026-04-22): The passive system "maintains fuel temperatures below safety limits indefinitely without operator action or external power".
NEPA Determination DOE-ID-26-005: Valar Ward250 Research Reactor (categorical exclusion B5.26) (U.S. Department of Energy, Office of Nuclear Energy, 2026-04-22)
Valar Atomics (Castle Country page): Says that on 26 June 2026 it shut Ward 250 down, switched off active cooling, simulated a total power loss: "Then we watched the reactor cool itself safely, exactly as designed."
Castle Country (Carbon & Emery County, Utah) (Valar Atomics)

What the record shows

Valar's own safety design target: 'No operator action required for 72 hours', with natural circulation within 30 minutes.
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), page 23 (Valar Atomics, 2025-10)
No DOE or independent record of the 26 June test, and no power log before it, has been published; the only power figures before it are Valar's own announcements (10 kW on 22 June, as ANS reported).
Valar's Ward 250 reaches criticality in Utah (American Nuclear Society, Nuclear Newswire, 2026-06-22)
The 72 hours sits in a list of 'target performance' ('No operator action required for 72 hours'): a minimum the design must meet. It does not say cooling stops after 72 hours; the same paper credits heat loss by conduction and radiation to surrounding structures as an 'ultimate heat sink that cannot be disabled'. So DOE's 'indefinitely' goes further than the target but does not contradict it.
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), pages 15 and 23 (Valar Atomics, 2025-10)

The gap: Valar's safety paper sets a minimum target of 72 hours with no operator action; DOE's categorical-exclusion review, under which no full environmental study was required, states that the passive system keeps fuel within limits indefinitely. A design can exceed its minimum target, so the two are not in conflict. The stronger 'indefinitely' is not backed by any public analysis, and the 26 June demonstration rests on Valar's account.

In plain terms'Walk-away safe' means that after shutdown the reactor can shed its leftover heat with no pumps, no power and no people. Valar's safety paper sets a minimum target: nobody needs to act for at least 72 hours. DOE's environmental review goes further and says the cooling works 'indefinitely.' Both can be true, because a design can beat its minimum. What is missing is proof the public can see: the heat analysis behind 'indefinitely' is not published, and Valar's 26 June public test of passive cooling has no DOE or outside record.

Why it matters: DOE relied on attributes like this to find the risk of an offsite release low enough for a categorical exclusion.

What would settle it: FOIA to DOE Idaho Operations Office for the approved DSA's decay-heat analysis, the 26 June 2026 test plan and results, the Joint Test Group records and the power history before the test.

facts safe-020, csite-009, csite-020, plan-006 · checked 2026-09-29: Defence pass 2026-09-29: Defended: re-read NSDA pp. 15 and 23 (72 hours is 'target performance'; conduction path 'cannot be disabled') and CX p. 5. A minimum target and an analysed indefinite capability are compatible, so the earlier 'conflict' does not survive; what remains is that neither the decay-heat analysis nor the 26 June test is public. Moved to unresolved; summary line rewritten to state only what the records show. | Earlier verify pass: Re-read on 2026-09-29: CX p. 5, NSDA p. 23, Castle Country, ANS (quotes exact). | Correction 2026-09-29 (wording review): verification wording updated ('summary line'). Correction 2026-10-01 (precision review): wording made more exact against the cited records.