Design Summary of the Mark-I Pebble-Bed, Fluoride Salt–Cooled, High-Temperature Reactor Commercial Power Plant

TLDR

The Mk1 pebble‑bed fluoride‑salt reactor is a 236‑MW thermal plant that uses a nuclear air‑Brayton cycle with a GE 7FB gas turbine to deliver 100 MW(e) base‑load power, can boost to 242 MW(e) with natural‑gas co‑firing, and employs direct salt‑to‑air heating, coated‑particle pebble fuel, active and passive safety systems, and validated neutronics, thermal‑hydraulic, and pebble‑dynamic models to define its annular core and key functional features. UCB’s preconceptual design of a commercial pebble‑bed fluoride‑salt high‑temperature reactor is illustrated by detailed three‑dimensional CAD models based on the Mk1 design criteria.

Abstract

The University of California, Berkeley (UCB), has developed a preconceptual design for a commercial pebble-bed (PB), fluoride salt–cooled, high-temperature reactor (FHR) (PB-FHR). The baseline design for this Mark-I PB-FHR (Mk1) plant is a 236-MW(thermal) reactor. The Mk1 uses a fluoride salt coolant with solid, coated-particle pebble fuel. The Mk1 design differs from earlier FHR designs because it uses a nuclear air-Brayton combined cycle designed to produce 100 MW(electric) of base-load electricity using a modified General Electric 7FB gas turbine. For peak electricity generation, the Mk1 has the ability to boost power output up to 242 MW(electric) using natural gas co-firing. The Mk1 uses direct heating of the power conversion fluid (air) with the primary coolant salt rather than using an intermediate coolant loop. By combining results from computational neutronics, thermal hydraulics, and pebble dynamics, UCB has developed a detailed design of the annular core and other key functional features. Both an active normal shutdown cooling system and a passive, natural-circulation-driven emergency decay heat removal system are included. Computational models of the FHR—validated using experimental data from the literature and from scaled thermal-hydraulic facilities—have led to a set of design criteria and system requirements for the Mk1 to operate safely and reliably. Three-dimensional, computer-aided-design models derived from the Mk1 design criteria are presented.