It’s been six months since three reactors at the Fukushima nuclear plant over-heated following a tsunami, forcing 100,000 people living within a 12 mile radius of the site to evacuate. Today, the reactors are still not fully stabilized, but radiation levels in one area of what has come to be known as the “exclusion zone” have dropped. The BBC’s David Shukman  is one of the few journalists to venture inside the exclusion zone.