# Specifications & Drawings

> HELIX design-of-record specification and dimensioned engineering drawings, module elevation and core cross-section. All figures are design targets; pre-application.

Design of record · targets held to an honest ceiling

# Specification & engineering drawings.
The HELIX module and core at design-of-record fidelity. Every value is computed, not measured in the field. Dimensions on the drawings are representative of the current design basis and will be superseded by qualified design documents.

Figure 1 · Module elevation, not to scale · design targets

Figure 2 · Core cross-section, control drums, fuel channels, diverse rod

## Specification sheet
Module output | 4.40 MWe at the cycle (11.0 MWth, 40% net dry sCO₂). Delivered at the meter is lower and site-specific once dry-cooler fans, house load and ambient derate are taken off; the configurator computes it per site
Site output | Number-up, 1 to 20+ identical modules; roughly 4–100 MWe (design target)
Configuration | Identical factory-sealed modules with N+1 reserve per site
Package | 1.80 m core; 2.70 m pressure-boundary OD (casing stack not yet fixed)
Heat transport | 421 sealed sodium heat pipes; no pumps (EM-pumped pool evaluated, not selected)
Fuel | UCO-TRISO, 19.75 wt% HALEU, graphite-moderated; inside the NRC-accepted EPRI-AR-1(NP)-A particle envelope
Heat-pipe wick | Composite: 14.7 µm surface pore, 48 arteries; 1.52× margin on peak duty (entrainment-limited)
Reflector | BeO, 0.40 m radial
Control | 16 B4C control drums + 1 diverse shutdown rod
Reactivity feedback | −6 to −8 pcm/K (screening)
Core life | 6.67 full-power yr at the current design point; bounded 6.67–6.91 pending the energy-per-fission normalisation (screening; unqualified)
Cooling | Fully dry, forced-draft dry coolers; zero cooling water
Power conversion | Dry sCO₂ Brayton, air-cooled, on skids outside the sealed module
Thermal storage | Molten-nitrate-salt buffer (peak-shave + trip bridge)
Safety I&C | FPGA deterministic (NRC-approved platform lineage)
Attestation | Non-safety, observe-only, behind a hardware one-way path
Transport | Factory-sealed. Outbound at 2.70 m OD is oversize and permittable. Road-legal is 2.60 m and costs core life. Whether a unit travels on ordinary roads or needs superload permitting is an open question, and the shield architecture inside the envelope is not yet fixed
Core return | Ship the irradiated core, not the module, in a Type B cask. Estimated 72 t, a superload. No certified cask is presently dimensioned for a 1.80 m core

All values are pre-QAPD screening resulargets. Heat transport is sealed sodium heat pipes; an EM-pumped sodium pool was evaluated and not selected. Physics figures are unqualified screening, pre-QAPD.