# Why don't we coat the pressure vessels of nuclear reactors in boron to reduce neutron embrittlement?

Neutron embrittlement is a big problem in reactor design, as high energy neutrons cause lattice defects in materials like steel by slamming into iron nuclei. This limits the lifetime of the reactor, because nobody likes a pressure vessel failure.

In order to combat this, why don't we coat the inside of a pressure vessel in boron? The boron would absorb the neutrons and thus the steel would avoid embrittlement.

• How thick does the boron need to be? Is it going to mix into the water? What happens as it absorbs neutrons over time? How many other engineering problems can you come up with? – Jon Custer Jun 9 at 22:51

But embrittlement in pressure vessel is not a major concern during reactor design. Neutron economy is the most important as it has direct impact on nuclear reactor economy. Every neutron = $(you can ether trade it for fuel regeneration or lower fuel enrichment = lower costs). In the nuclear reactor design it is preferred to use as much neutrons as possible, and hence try to reflect neutrons back to the core rather than dump them into the pressure vessel. Without reflector you will have very high non-uniformity of neutron flux in the volume of the core and it will be hard to operate. In VVER PWR reactors reflector is made from water-steel sandwich. In graphite-based reactors reflector is also made from graphite. You can see reactor composition example here: https://www.researchgate.net/figure/Horizontal-Top-and-vertical-Bottom-cross-section-of-3D-60-0-symmetric-two-energy_fig8_309576283 • If neutrons =$, then what is preventing us from using stupidly high neutron fluxes (I read somewhere that the typical neutron flux is around 1E13 n/cm^2, why can't we do 1E16 and therefore minimize core size) - is it thermal problems? – Nikhil Murali Jun 10 at 16:35