Outlet temperature: 650°C is the limit, and Valar's public summary says 650°C; the same draft lists 750°C 'under normal operations' as a goal

unresolvedsafety

What was said

Valar Atomics (safety agreement, performance objectives, page 8) (2025-10): Goals include "steady-state operation at power levels up to 250 kWth" and core outlet temperatures of "750°C under normal operations".
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), page 8 (Valar Atomics, 2025-10)
Valar Atomics (safety agreement, reactor vessel code section, page 49) (2025-10): Evaluates vessel creep "at maximum operating temperature (750°C)".
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), page 49 (Valar Atomics, 2025-10)
Valar Atomics (web summary of the same agreement) (2025-10-13): Calls Ward 250 "a 250 kWth High Temperature Gas-cooled Research Reactor" and says it will test at temperatures up to 650°C.
Ward250 Nuclear Safety Design Agreement (web summary; not listed in Valar's library) (Valar Atomics, 2025-10-13)
Valar Atomics (Isaiah Taylor, August 2025 selection post) (2025-08-12): Pitches the design's "Operating temperatures above 750°C" for process heat and hydrogen (a general claim, not a stated Ward 250 limit).
Valar Atomics Selected for the President's Accelerated Nuclear Program (Isaiah Taylor) (Valar Atomics, 2025-08-12)

What the record shows

Safety limits (page 25): 'Maximum continuous power: 100 kWth'; 'Maximum short duration power (1hr): 250 kWth'; 'Maximum outlet temperature: 650°C'.
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), page 25 (Valar Atomics, 2025-10)
Key design parameters (Table 6, page 52): thermal power 100 kWth continuous, basis 'License limit', with up to 250 kWth for limited tests; core outlet 650°C nominal, basis 'Material limits'.
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), Table 6, page 52 (Valar Atomics, 2025-10)
Fuel performance target (page 23): 'Maximum normal operating temperature: 650°C'.
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), page 23 (Valar Atomics, 2025-10)
Valar's own public summary of the safety agreement says Ward 250 supports testing 'at temperatures up to 650°C', matching the limit.
Ward250 Nuclear Safety Design Agreement (web summary; not listed in Valar's library) (Valar Atomics, 2025-10-13)
The draft calls Ward 250 a '≤250 kWth' reactor and lists up to 250 kWth for 'Limited tests'. The goal of 'steady-state operation at power levels up to 250 kWth' fits the one-hour 250 kWth limit if 'steady-state' means holding power level during those limited tests, so the power goal is not a conflict.
Ward250 Nuclear Safety Design Agreement, No. 100403, Rev 02 (status: Draft), pages 2, 8, 25 and 52 (Valar Atomics, 2025-10)
Valar says the reactor system was tested without fuel in California at 'temps above 750c' before shipping, and its August 2025 post pitches operating temperatures above 750°C for the design in general. The 750°C in the draft matches the hardware's tested range and the design's ambition, not an authorized nuclear limit.
Ward 250 By the Numbers (Isaiah Taylor; unlisted page that still carries placeholders) (Valar Atomics, 2026-06-28)
Valar's August 2025 post: 'Operating temperatures above 750°C' for process heat and hydrogen (the design in general).
Valar Atomics Selected for the President's Accelerated Nuclear Program (Isaiah Taylor) (Valar Atomics, 2025-08-12)

The gap: In the draft, 650°C is the maximum outlet temperature (a safety limit tied to material limits) and the fuel's normal maximum; 750°C appears as a performance goal 'under normal operations' and as the temperature for a cautious vessel creep check. Valar's public summary sides with 650°C, and 750°C matches the hardware's non-nuclear test range, so the likeliest reading is an out-of-date goal line in a draft. The power goal fits the one-hour 250 kWth limit. Which numbers bind is set by the Technical Safety Requirements, which were not found in public records.

In plain termsA reactor's safety paperwork sets hard limits. Ward 250's draft safety paper says the gas leaving the core may not go above 650°C, a limit set by what the materials can take, and Valar's own public summary repeats 650°C. The same draft also lists, among its goals, reaching 750°C 'under normal operations.' The likeliest explanation is an out-of-date goal: the hardware was run hotter than 750°C in tests before it had fuel, and checking the steel vessel at 750°C is the cautious direction. The approved operating limits that would settle which figure applies were not found in public records.

Why it matters: In the draft, the 650°C outlet temperature is a safety limit tied to material limits, while 750°C is listed as a goal; the approved operating limits that say which applies were not found in public records.

What would settle it: FOIA to DOE Idaho Operations Office for the Technical Safety Requirements (operating limits) in the approved DSA and any DOE approval of power ascension above 100 kWth or outlet temperatures above 650°C.

facts orig-006 · checked 2026-10-02: Checked for fairness to Valar, late September 2026: re-read NSDA pp. 2, 8, 23, 25, 49, 52, the NSDA web summary ('up to 650°C'), By the Numbers ('temps above 750c' in non-nuclear testing) and the August 2025 post. The power half of the old gap dissolves ('steady-state' up to 250 kWth fits the one-hour limit); the temperature half is an internal inconsistency with a plausible stale-goal reading and Valar's own public summary on the 650°C side. Moved to unresolved. Summary line literally true (p. 8 and p. 25). | Earlier check: Re-read in late September 2026: NSDA pp. 8, 23, 25, 49 and 52 (all quotes exact), the web summary and the August 2025 post. New in this check: page 49 calls 750°C the 'maximum operating temperature' for the vessel creep check, and page 23 sets 650°C as the maximum normal fuel operating temperature. Added: using the higher temperature for the creep check is conservative for the vessel. | Revised before publication (late September 2026): source title parenthetical now 'not listed in Valar's library'; verification wording updated ('summary line').