If the amount causes a crossover in the of their debt :GDP ratio beyond 60% then the $3 billion will payable to Russia as it will put in default the $3 billion Russia bought in bonds last December.
See :
As CNBC has reported, some aid money is bound to go into Russia as a result of energy trade and other economic factors. But the situation is actually much more acute than just that: An existing agreement between the two countries makes an immediate, direct transfer from Ukraine to Russia legally enforceable.
As Western leaders prepare a bailout package for embattled Ukraine, they face a startling irony: Thanks to the almost bizarre structure of a bond deal between Ukraine and Russia , billions of those dollars are almost certain to go directly into the coffers of the Putin government.
In December, Russian President Vladimir Putin agreed to lend Ukraine $15 billion. Few details were released at the time, except that Ukraine would issue bonds and Russia would buy them in installments through 2014.
>
-Paragraph 3 (b) under Covenants:
(b) Debt Ratio
So long as the Notes remain outstanding the Issuer shall ensure that the volume of the total state debt and state guaranteed debt should not at any time exceed an amount equal to 60 percent of the annual nominal gross domestic product of Ukraine.
The implications of that clause are that the minute the West or the International Monetary Fund extend a large loan to Ukraine, that country will almost certainly have a debt-to-GDP that exceeds 60 percent, immediately putting the Russian loan into default. That gives Russia the right to demand immediate repayment. And because the bonds are governed by British courts-which, presumably, neither Ukraine nor Russian can manipulate-it would be extremely difficult for Ukraine to avoid making the payment, using its new bailout money.
http://finance.yahoo.com/news/3-billion-ukraine-straight-russia-172652361.html