Ukraine’s latest drone strike has forced the shutdown of a major processing unit at the Kirishi refinery near St. Petersburg, in what industry sources describe as the most damaging attack yet on Russia’s northwest energy hub. Reuters reported today that operations at the 355,000-barrel-per-day facility, which handles roughly six percent of Russia’s refining capacity, have been curtailed after fires broke out over the weekend. The Kirishi outage comes on the heels of a separate Ukrainian strike on the Primorsk oil terminal, where…