Japan\'s nuclear safety agency cannot say how long it will take to assess stress tests ordered for nuclear plants to examine reactor safety and bolster public confidence, although it does not want them dragging on for a year or two, Reuters quoted an agency official as saying. The official also said the Nuclear and Industrial Safety Agency (NISA) was aiming for nuclear power plant operators to submit reports for the second round of the two-tier stress tests before the end of this year. \"We cannot assume how comprehensive the reports from the utilities will be,\" the official told a news briefing on Friday.