# Next Generation Nuclear Facilities

How small modular and advanced reactors compare with older nuclear plants: size, fuel, operation, efficiency, safety and waste

By Laura Hales

Topic: Energy

[Open the interactive Jig](https://ask.jig.com/j/wYRo2agDbUHk)

## Transcript

### 1. Next generation nuclear

On the left stands a large nuclear plant of the kind built for decades\. On the right is a small modular plant: six reactor modules sitting in one pool of water\. In front of them are the fuel, one module opened up, and a comparison of efficiency\. Drag empty space to turn the table\.

Scroll or pinch to move closer\.

### 2. How big are they?

One AP1000 reactor makes about 1,117 megawatts inside a steel containment 40 metres wide\. A NuScale module makes 77 megawatts and is 4\.6 metres wide and 23 metres tall, so it can travel by truck or rail\. Six modules together make 462 megawatts\.

Both plants are modelled at 1:500\. The land used per megawatt is of a similar order\. The bigger change is building reactors in a factory\.

### 3. What fuel do they use?

Most reactors, including NuScale modules, burn uranium oxide pellets with less than 5 percent uranium\-235, sealed in metal rods\. Many Generation IV designs use HALEU fuel with 5 to 20 percent uranium\-235\. The Xe\-100 packs it into 60 millimetre graphite pebbles\. Open the pebble, or click it\.

Each pebble holds about 18,000 TRISO particles, each about 1 millimetre wide\. Layers of carbon and silicon carbide around the uranium kernel trap the radioactive products\.

### 4. How a module runs

The core heats the water around it\. Hot water is lighter, so it rises up the central riser without pumps\. At the top it turns and flows down past the coiled steam generator tubes, gives up its heat and sinks back to the core\. The steam drives a turbine\.

Other designs use other coolants\. The Xe\-100 blows helium through its pebbles at 750 degrees Celsius\. Natrium uses liquid sodium and stores heat in molten salt\.

### 5. Are they more efficient?

Efficiency is the share of reactor heat that becomes electricity\. Older water reactors reach about 33 percent\. A NuScale module reaches about 31 percent, because its water runs cooler\. The hotter Xe\-100 and Natrium designs reach about 40 percent\.

Ratios of the vendors' electric and thermal ratings: 1,117 of 3,400, 77 of 250, 80 of 200 and 345 of 840 megawatts\.

### 6. Are they safer?

Older plants need pumps and backup diesel generators to keep the core cool\. At Fukushima, the power was lost and cooling failed\. Newer designs are designed to be passively safe\. Cut all power to watch the module shut down and keep cooling itself\.

The control rods drop by gravity\. Natural circulation keeps moving the decay heat into the steel wall and the surrounding pool, with no power or operator action needed\.

### 7. What about the waste?

Every reactor makes spent fuel\. After a few years cooling in a pool, it is sealed in steel and concrete casks on a guarded pad\. Xe\-100 pebble waste weighs 40 to 50 percent less, but takes 25 to 30 times more space\. Natrium fuel needs extra treatment to remove sodium\.

The United States still has no permanent deep geological repository, so spent fuel stays stored at the plants\.

### 8. The road ahead

The NRC approved the NuScale VOYGR\-6 design on 29 May 2025\. Construction of the first Natrium plant began in Wyoming on 23 April 2026, with completion planned for about 2031\. None of these designs is yet operating commercially at scale\.

Smaller and safer is the design goal, but cost and construction time will decide how many get built\.