Economic Simplified Boiling Water Reactor
The Economic Simplified Boiling Water Reactor (ESBWR) is a Generation III+ light-water nuclear reactor design developed by GE-Hitachi Nuclear Energy (now GE Vernova Hitachi Nuclear Energy), characterized by its use of natural circulation for core cooling, passive safety systems that operate without external power or operator intervention for 72 hours following an accident, and a simplified single-cycle boiling water configuration that generates steam directly within the reactor pressure vessel for turbine use.[1][2][3] Evolving from the earlier Simplified Boiling Water Reactor (SBWR) concept of the 1990s, the ESBWR incorporates advanced features from the Advanced Boiling Water Reactor (ABWR) while emphasizing economic viability through design simplifications, such as the elimination of recirculation pumps, a 25% reduction in pumps and mechanical drives compared to active-safety plants, and modular construction to lower operational costs by approximately 20% and capital costs relative to predecessors like the ABWR.[4][3] With a thermal power output of 4,500 megawatts (MWt) and a net electrical output of approximately 1,535 megawatts electric (MWe)—varying by site and turbine configuration—the reactor employs a gravity-driven cooling system (GDCS), passive containment cooling system (PCCS), and isolation condensers to ensure core cooling, containment integrity, and spent fuel pool management during emergencies, all integrated into a low-leakage, steel-lined concrete containment vessel designed to withstand severe events like aircraft impacts and earthquakes.[1][2] The ESBWR received design certification from the U.S. Nuclear Regulatory Commission (NRC) on October 6, 2014, following an application submitted in 2005 and detailed review under 10 CFR Part 52, Appendix E, with the certification valid for 40 years following a 2025 NRC revision extending the duration of design certifications and incorporating provisions for post-Fukushima enhancements like diverse mitigation strategies and spent fuel pool instrumentation.[1][2][5] Although certified, no ESBWR units have been constructed as of November 2025, positioning it as a foundational design influencing smaller successors like the BWRX-300 small modular reactor, with its passive safety and economic focus aimed at supporting global carbon-free energy goals through reliable, low-maintenance operation.[3][4]Overview and Specifications
Design Concept
The Economic Simplified Boiling Water Reactor (ESBWR) is a Generation III+ boiling water reactor (BWR) design developed by GE Hitachi Nuclear Energy, operating as a single-cycle, direct-cycle BWR where steam generated in the reactor core directly drives the turbine without intermediate heat exchangers. It evolved from predecessor designs including the Simplified Boiling Water Reactor (SBWR) and the Advanced Boiling Water Reactor (ABWR), integrating passive safety elements from the SBWR with the operational maturity of the ABWR to achieve greater simplicity and reliability.[6][4] Central to the ESBWR's core design principles is the reliance on natural circulation for coolant flow, which eliminates the need for recirculation pumps and their associated systems. This is facilitated by a taller reactor pressure vessel, measuring approximately 28 meters in height with an inside diameter of 7.1 meters, paired with a shorter core height to generate sufficient driving head for passive upward flow through the core and downward return via gravity-driven paths. These geometric optimizations enhance heat removal during normal operation and transients, supporting stable power output without active mechanical intervention.[7][8] The ESBWR incorporates economic simplifications to reduce construction and operational burdens, including the elimination of 11 major systems from prior BWR designs and a 25% reduction in pumps, valves, and motors, which minimizes maintenance requirements and potential failure points. Modular construction methods further streamline assembly, enabling factory prefabrication of components and shorter on-site build times while lowering overall capital costs compared to earlier BWR generations.[3][9][4] As a Generation III+ reactor, the ESBWR builds on evolutionary enhancements to BWR technology, prioritizing inherent safety through passive mechanisms, improved fuel efficiency, and standardized components to deliver higher reliability and cost-effectiveness for utility-scale deployment.[3]Key Parameters
The Economic Simplified Boiling Water Reactor (ESBWR) is designed with specific technical parameters that enable its simplified operation and passive safety features, including reliance on natural circulation for coolant flow. These parameters define its power generation capacity, core configuration, physical structure, and operational conditions, supporting a 60-year design life.[10] Key specifications are summarized in the following table:| Parameter | Value | Description/Source |
|---|---|---|
| Thermal power rating | 4,500 MWth | Rated core thermal output.[1][10] |
| Electrical output (gross) | 1,594 MWe | Turbine-generator output at rated conditions.[1][11] |
| Electrical output (net) | 1,535 MWe | After house loads and auxiliaries.[1][11] |
| Thermal-to-electric efficiency | Approximately 34% | Net electrical efficiency based on rated thermal power.[1][11] |
| Number of fuel assemblies | 1,132 | Standard GE14 configuration in the core.[10][12] |
| Fuel type | Uranium dioxide (UO₂) | With gadolinium oxide ((U, Gd)O₂) as burnable absorber in select assemblies.[10] |
| Fuel enrichment | Up to 5 wt% U-235 | Average reload enrichment around 4.2 wt%; initial core 1.7–3.2 wt%.[10] |
| Refueling cycle | 24 months | Standard cycle length for equilibrium core.[10] |
| Reactor vessel diameter | 7.1 m | Inside diameter for the pressure vessel.[10] |
| Containment volume | Drywell free volume: 7,206 m³; Wetwell free volume: 5,467 m³ (total free volume approximately 12,700 m³) | Optimized free volumes for passive heat removal and flooding.[10] |
| Operating pressure | 7.2 MPa | Core operating pressure (1,045 psia).[10] |
| Steam temperature | 286°C | Saturated steam at core outlet.[10] |
| Natural circulation flow rate | 34.5 million kg/h (core coolant) | Mass flow rate during normal operation, driven by buoyancy in the chimney section.[10] |