United States: Power Reactor Inherently Safe Module (PRISM) design

The US Advanced Liquid-Metal Reactor (ALMR) program in the 1980s resulted in the design of the 160 MWe Power Reactor Inherently Safe Module (PRISM) sodium — cooled reactor. The PRISM design was one of the first advanced reactor designs to employ significant use of passive safety features and was designed as a power module to be used in multiple three-unit packs to form a large electrical-capacity power plant. The PRISM design was originally intended to be a breeder reactor for improved uranium resource management, but more recently has become focused on recouping the unused energy content in discharged LWR fuel and also to consume the very long-lived higher actinide elements that dominate the long-term hazard in a geologic repository.

General Electric, now teamed with Hitachi, has resumed development of the 311 MWe PRISM design, although the name has been changed to Power Reactor Innovative and Small Module. The design has similarities to LWR-based integral

Key parameters

Electrical capacity:

311 MWe

Thermal capacity:

500 MWt



Primary coolant:


Primary circulation:


Outlet temperature:

500 °C

RV diameter/height:

9.2 m/19.4 m

Steam generator:


Power conversion:




U-Pu-Zr metal

Reactivity control:


Refueling cycle:

16 months

Design life:

60 years


Detailed design

Control rod drive mechanisms

EM pump


Figure 2.22 PRISM (United States) — General Electric-Hitachi (GEH) © GE Hitachi Nuclear Energy.

designs except that the internal steam generators are replaced with intermediate heat exchanges that transfer heat to two secondary sodium loops. External secondary heat exchangers are coupled to a supercritical Rankine power-conversion unit. The design uses U-Pu-Zr metal fuel and can accommodate actinide waste products from LWR spent fuel. Four electromagnetic pumps circulate the sodium coolant in the pool-type primary system, which operates at nearly atmospheric pressure.

The current deployment strategy is to couple two PRISM modules into a single ‘power block’ with a shared turbine-generator. One or more power blocks would be co-located with a small electro-refining fuel recycle facility. Although there was significant regulator review of the PRISM design earlier, there are no immediate plans to license PRISM for commercial power production. Key parameters and a representative graphic for the PRISM design are given in Figure 2.22. [21]

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