Doppler Broadening in Gen 4 Nuclear Power

[snatchingthepi]

I was reading about the new pebble bed gas-cooled reactor China is building and was looking into how the fuel design reduces the risk of meltdown. Apparently this is largely due to something called "Doppler Broadening" and this somehow affects neutron absorption. I don't see how this works and would really appreciate someone clearing this up for me.

 

[mfb]

Moderated neutrons get a thermal energy spectrum. A hotter reactor has hotter neutrons. Typically low-energetic neutrons have a higher fission cross-section, so heating the reactor reduces the reaction rate. That is an important safety feature: an increased reactor activity raises the temperature of the fuel, which reduces the reactor activity.

 

[snatchingthepi]

Moderated neutrons get a thermal energy spectrum. A hotter reactor has hotter neutrons. Typically low-energetic neutrons have a higher fission cross-section, so heating the reactor reduces the reaction rate. That is an important safety feature: an increased reactor activity raises the temperature of the fuel, which reduces the reactor activity.

Thank you very much.