PWR-20 by Last Energy: status and timeline

Milestones

Next · First criticality (DOE pilot program)

Last Energy founded2019Complete.
Series A fundingDec 2021Complete.
Series B fundingAug 2024Complete.
PWR-20 preliminary design review cleared by UK regulators2025Complete.
First criticality (DOE pilot program)Target 2026Current milestone.
First plant commissioned in PolandTarget Q4 2026Not yet reached.
First UK plant commissionedTarget 2027Not yet reached.

Most important updates

Last Energy raises $100 million Series C to commercialize PWR-20 productionDec 2025
Last Energy PWR-20 design clears preliminary design review by UK regulators2025
Last Energy closes $40 million Series B to advance PWR-20 small modular reactorAug 2024

Upcoming

2026First criticality (DOE pilot program) (next)
2026First criticality demonstration
Q4 2026First plant commissioned in Poland
2027First UK plant commissioned
Dec 2027UK site licence decision

Current obstacles

First-of-a-kind regulatory riskNew design. UK and Poland must complete reviews and issue site licences, potentially delaying deployment.
Factory scale and supply chain maturityNo existing factory. Building capacity and establishing suppliers for specialized components is needed.
Cost competitiveness with larger reactorsSMRs have higher per-MW costs. Must achieve efficiency and scale to compete with industrial customers.

Physics limits

Pressurized water reactors require a trained workforcePWRs require operators trained in water chemistry and pressure. Expertise exists but not abundantly.
Small size raises per-MW costFixed regulatory and engineering costs spread over 20 MW cost more per MW than a 1,000 MW plant. Requires fleets sharing infrastructure.

How it works

4 parts

Modular design

Factory-made components assemble on site

Dozens of rectangular modules transport to site and assemble mechanically in months, not years.

Pressurized water cooling

Proven reactor physics scaled down

Standard PWR: pressurized water flows through the core, absorbs heat, and transfers it for power or industrial use.

Air-cooled condensers

No cooling towers or cooling ponds

Closed-cycle air cooling eliminates cooling towers. Works in water-scarce regions and industrial areas.

Rapid factory production

Economies of fleet production

One factory produces modules for many reactors, spreading fixed costs and enabling incremental growth.

Spec sheet

Spec	PWR-20
Electrical output	20 MWe^R (reported)
Thermal output	60 MWth^R (reported)
Operating temperature	300°C^R (reported)
Fuel enrichment	4.95%^R (reported)
Cooling system	Closed-cycle air cooling^R (reported)
Target deployment time	Approximately 2 years^R (reported)

^R reported by the company

Update log

3 updates

About Last Energy

The team behind PWR-20

Last Energy

PWR-20 SMR, micro-modular reactor, factory-built

Last Energy develops the PWR-20, a 20 MWe small modular reactor made of factory-built modules. It has signed power purchase agreements for 34 units in Poland and the UK.

PWR-20 is 20 MWe with factory-built modules that assemble on site in roughly 24 months instead of a decade.
Raised $164M total; Series C of $100M closed December 2025. 10 PWR-20s for Poland, 24 for UK.
DOE Reactor Pilot Program: targeting first criticality and plant commissioning in Poland by end-2026.

lastenergy.com (opens lastenergy.com)Company profile →

Founded: 20197 yrs
Headquarters: United States
Status: Private
Valuation: $400Mest. privateDec 2025estimate
Raised: $160M4 rounds
Last round: Series C · $100MDec 2025
Works in: EnergyFission
Coverage: 1 program · 4 updateslatest 2d 14h agochecked 10 Oct
Lead investors: Astera InstituteGalaxy InteractiveGigafundAutodesk FoundationFirst Round Capital
Customers: Katowice Special Economic Zone (opens ans.org)UK Industrial Partners (opens powermag.com)
Partners: US Department of Energy (opens lastenergy.com)Export-Import Bank of the United States (opens wnn.world-nuclear.org)
People: Bret Kugelmass (opens linkedin.com)Founder and CEO

Spec

PWR-20

Electrical output

20 MWe^R (reported)

Thermal output

60 MWth^R (reported)

Operating temperature

300°C^R (reported)

Fuel enrichment

4.95%^R (reported)

Cooling system

Closed-cycle air cooling^R (reported)

Target deployment time

Approximately 2 years^R (reported)

PWR-20

Milestones

Most important updates

Upcoming

Current obstacles

Physics limits

How it works

Factory-made components assemble on site

Proven reactor physics scaled down

No cooling towers or cooling ponds

Economies of fleet production

Spec sheet

Update log

Dec 2025

2025

Aug 2024

About Last Energy

Current obstacles

Physics limits

How it works

Factory-made components assemble on site

Proven reactor physics scaled down

No cooling towers or cooling ponds

Economies of fleet production

Spec sheet

Update log

Dec 2025

2025

Aug 2024

About Last Energy