running rake db:seed without duplicating data

Use find _ or _ create_by method

nomination_titles = [
                      'Репортаж',
                      'Новость',
                      'Статья',
                      'Интервью',
                      'Обзор'
                    ]

nomination_titles.each do |title|
  Nomination.find_or_create_by_title title
end