What about the “First-Wall” problem?

Summary

The challenge of protecting the device materials from neutron damage is one of the big unsolved problems in fusion. Our solution is to construct our target chamber from conventional, low-cost steel and to replace it every ~5 years. We are focused on making chamber replacement a quick and low-cost endeavor, substituting a major materials science breakthrough for a simple economic solution.

D-T fuel is the most common design for fusion power, due to the lower ignition temperatures and higher energy yields, but it does release a large number of neutrons in the process.

The target chamber, where the fusion occurs, is fully surrounded by concrete protecting all the gear and people outside while the plant is operating. But the target chamber itself is within the walls, so it is bombarded with these energetic neutrons which, over time, degrade most materials. The so-called “First-Wall” problem is the question of how to deal with this damage and ensure longevity for a fusion power plant.

Some have proposed the need for materials science to engineer new materials that are more resilient to neutron damage, thus extending the life of a fusion power facility’s structures.

Inertia’s strategy is to take the most direct, lowest risk path from what is working today at the National Ignition Facility (NIF) to commercial energy. While we would be very pleased to see materials advancements, our design does not require any such advancements to be commercially viable. Instead, we are just going to ensure the chamber is low cost enough to replace as needed. Here’s how:

Our patented Laser Inertial Fusion Energy plant design decouples the driver, the laser, from the target chamber. The complicated laser components sit outside the target chamber, far away from any potential neutron damage. The laser light travels through periscope-like holes in the concrete walls which allow laser beams through but stop neutrons from escaping.

What is the chamber?

It’s a large, multi-meter diameter shell made of metal (like an enormous boiler). It has holes in the top and the bottom to let laser light through into the center of the chamber, where the lasers heat up the fuel targets. The walls of the chamber are actually pipes that contain flowing liquid lithium (for heat exchanging, see “How do you produce electricity”) and tritium breeding (see “Why D-T Fuel”). We plan to produce the target chamber inexpensively from conventional steel materials, and replace it 3-5 years, which eliminates the need to invent a new material that achieves unprecedented levels of neutron resilience.

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