Name the nuclear weapons test with the lowest explosive energy equivalent whose country of origin is soviet union?
select ?ent where { ?ent wdt:P31 wd:Q210112 . ?ent wdt:P2145 ?obj . ?ent wdt:P495 wd:Q15180} ORDER BY ASC(?obj)LIMIT 5 
nuclear weapons test: Q210112 soviet union: Q15180