No, the debt is not manageable because interest payments equals $96 million per year.
Annual interest payments on the debt are:
0.08 x $1,200,000,000 = $96,000,000
While it is possible to cover interest on the debt with $100 million in tax revenues, that would leave just 4% ($4,000,000/$100,000,000 x 100) of tax revenues to pay the principal on maturing loans and all other government expenditures (assuming no additional debt is incurred). This is not a manageable level of debt.