 In modern machines like NIF, the initial frozen hydrogen fuel load has a density less than water which is increased to about 100 times the density of lead.In these conditions, the rate of fusion is so high that the entire fuel load undergoes fusion in the microseconds it takes for the heat generated by the reactions to blow the fuel apart.Although modern ICF machines like NIF are also extremely large, this is a function of their "driver" design, not an inherent design criterion of the fusion process itself.