Finding Reactance from System Fault Level

[Physicist3]

Hi, apologies if this is very simple but I am still learning the basics of power system analysis and would like it if someone would be able to clarify what I have been told regarding system fault levels and subsequent system reactance values (X) from this. Basically, I have been told that system reactance is simply the reciprocal of the system fault level. We were given the following info;

System Voltage = 400kV, System Fault Level = 10000MVA

I was then told that in per unit, the system reactance would be 1/10000 = 0.0001 (on 10000MVA Base)

I would just like some clarification as this seems a little too simple to be honest, shouldn't the voltage come into it?

Sorry if this is very simple.

Thanks :)

 

[Baluncore]

Maybe this will help;
http://myelectrical.com/notes/entryid/214/fault-calculation-per-unit-system