Pebble-Bed Fluoride-Salt-Cooled High-Temperature Reactor

University of California at Berkeley researchers provide a Technical Description of the “Mark 1” Pebble-Bed Fluoride-Salt-Cooled High-Temperature Reactor (PB-FHR) Power Plant.

MIT leads (with partners at the University of California at Berkeley, the University of Wisconsin, and Westinghouse) a 3-year research program to investigate a new high-temperature reactor that may enable economic variable electricity production and can’t have accidents with on-site releases of radioactivity. The potential for such a breakthrough is a consequence of improvement in technologies developed for other purposes over the last 50 years. The reactor is called the Fluoride-salt-cooled High-temperature Reactor (FHR).

Goals
* Superior economics (30% less expensive than LWR)
* Limit severe accidents
* 700°C for higher thermal eciency and process heat
* Better non-proliferation and waste characteristics

A report describes the results of work at the University of California, Berkeley (UCB) to develop an initial pre-conceptual design for a small, modular 236-MWth pebble-bed fluoridesalt-cooled, high-temperature reactor (PB-FHR). This design study contributes to a larger U.S. Department of Energy Integrated Research Project (IRP) collaboration with the Massachusetts Institute of Technology and the University of Wisconsin, Madison to establish the technical basis to design, license, and commercially deploy FHRs.

The Mark-1 (Mk1) PB-FHR design described here differs from previous FHR designs developed and published by UCB and others. It uses a nuclear air-Brayton combined cycle (NACC) based upon a modified General Electric 7FB gas turbine, designed to produce 100 MWe of base-load electricity when operated with only nuclear heat, and to increase this power output to 242 MWe using gas co-firing for peak electricity generation. Due to the high thermal efficiency of the NACC system, the steam-bottoming condenser of the Mk1 PB-FHR requires only 40% of the cooling water supply that is required for a conventional light water rector (LWR), for each MWh of base-load generation. As with conventional natural-gas combined cycle (NGCC) plants, this makes the efficiency penalty of using dry cooling with air-cooled condensers much smaller, enabling economic operation in regions where water is scarce.

The primary purpose of the Mk1 design, with its co-firing capability, is to provide a new value proposition for nuclear power. The new value proposition for NACC arises from additional revenues earned by providing flexible grid support services to handle the everincreasing demand for dispatchable peak power, in addition to traditional base-load electrical power generation. Because under base-load operation NACC power conversion has lower fuel costs than NGCC, and under peaking operation has higher efficiency in converting natural gas to electricity than NGCC, NACC plants will always dispatch before conventional NGCC plants.

The reference configuration for the Mk1 site uses 12 Mk1 units capable of producing 1200 MWe of base load electricity, and ramping to a peak power output of 2900 MWe. The Mk1 design uses the same steel-plate composite wall modular construction methods as the Westinghouse AP1000, and its modular components can be manufactured in the same factories. A Mk1 reactor uses 10 structural modules, so the total number of structural modules needed to build a 12-unit station is quite similar to the ~120 structural modules used to build an AP1000 reactor. Estimated quantities of steel and concrete needed to construct a Mk1 station compare favorably, per MWe, with requirements for LWRs. The major difference between construction of a Mk1 station and an AP1000 is the highly repetitive construction tasks for the Mk1 station, arising from the construction of 12 identical units.

PB-FHR fuel pebbles are 3.0 cm in diameter, smaller than golf balls (4.3 cm). Four Mk1 pebbles can provide electricity for a full year for an average U.S. household, which in 2011 consumed 11.3 MWe-hr. These four small pebbles are far less than the 8.1 tons of anthracite coal, or 17 tons of lignite coal, needed to produce the same amount of electricity using a coal power plant.

Each Mk1 pebble contains 1.5 g of uranium encapsulated inside 4730 coated particles.

There was a Jan, 2014 Current Status of the UCB PB-FHR Mark-1 Commercial Prototype Design Effort presentation

Current FHR Development Efforts

• DOE Integrated Research Project (IRP) – Collaborative university effort with MIT, UCB, and UW – Includes commercialization strategy, commercial prototype and test reactor pre-conceptual design effort, and assorted technology development efforts
• Oak Ridge National Laboratory – Ongoing FHR development work on technology roadmap and reactor design (plate fuel)
• ANS Standards Committee 20.1 – Currently developing FHR-specific GDCs and design standards
• Shanghai Institute of Applied Physics (SINAP) – Currently developing FHR and MSR technology – 10 MW FHR test reactor deployment planned for 2017

SOURCES – IAEA, MIT, Berkeley, UCB

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