Question:
Answer:
If someone who is Russian Orthodox had no access to a church of their own, they could receive in a Catholic church. However, the Catholic Church does not encourage this out of respect to the Eastern Orthodox Churches, which do not normally permit their members to receive communion in non-Orthodox Churches.
Code of Canon Law:
Catholic ministers administer the sacraments of penance, Eucharist, and anointing of the sick licitly to members of Eastern Churches which do not have full communion with the Catholic Church if they seek such on their own accord and are properly disposed. This is also valid for members of other Churches which in the judgment of the Apostolic See are in the same condition in regard to the sacraments as these Eastern Churches (can. 844 §3).
Catechism of the Catholic Church:
The Eastern churches that are not in full communion with the Catholic Church celebrate the Eucharist with great love. “These Churches, although separated from us, yet possess true sacraments, above all—by apostolic succession—the priesthood and the Eucharist, whereby they are still joined to us in closest intimacy.” A certain communion in sacris, and so in the Eucharist, “given suitable circumstances and the approval of Church authority, is not merely possible but is encouraged” (1399).