This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
If there is a lobby group involved, I think that the nuclear industry can be ruled out. One of the myths of the Green movement is that there exists a powerful 'nuclear lobby' always pushing for nuclear expansion, almost on a par with 'Big Oil', but this assertion does not stand up to examination. If the nuclear industry has the influence in the present day to get an arbitrary factor of safety of more than a hundred removed from radioactive safety limits, then I think it would have had the influence decades ago to ensure that the factor of safety had not been imposed in the first place. In the heyday of the Western nuclear industry, in the 1960s and 1970s, it might have had a bit of influence, but I'd say the influence is almost nil in the present day.
I can give an example to show that the UK nuclear industry has little or no influence - consider a tax in the UK called the "Climate Change Levy", details of which are given in this Wikipedia article:
The tax is basically a 'polluter pays' tax introduced by the Blair government in 2001 that is slapped on UK businesses to penalise them for using electricity which supposedly contributes to climate change. The tax is applied to fossil fuel generated electricity as might be expected, but is also applied to nuclear generated electricity, with only renewable energy being allowed an exemption from the tax. I'm pretty sure that the UK nuclear industry would have made some attempt to arrange that CO2-free nuclear generated electricity was exempt from the tax, but they obviously had no influence on Brtish politicians.
The reasons given in the news story for substantially raising the radioactive safety limits actually sound quite plausible to me. Terrorism can be regarded as being 'asymmetric warfare', and one of the main features of the asymmetry is that terrorists tend to operate on a shoestring budget, whereas their opponents are likely to be spending orders of magnitude more money to engage in the same conflict. Islamic terrorism, under the guidance of Bin Laden, has been particularly keen on the idea of squandering the money of its opponents, as this news article from 2004 describes:
In this news story Bin Laden announced that his plan was to defeat the USA by effectively bankrupting it, and he believed that his group had defeated the Soviets in the 1980s by making the war too expensive for them to continue with it. One way of economically damaging the USA would be to explode radioactive dirty bombs, taking advantage of unduly pessimistic radioactive safety limits.
I think I may have identified the potential class action lawsuit that the US Government might be nervous about. There was a news story several months ago which announced that the death toll of 1656 for people currently living in evacuation camps in the ƒukushima prefecture now exceeds the death toll of 1607 that occurred in the original tsunami event in 2011. The 1656 evacuee deaths are apparently due to stress and other illnesses related to the disaster. I assume there have been no radiation-induced deaths amongst the evacuees, otherwise the BBC and the Guardian would have been rather enthusiastically reporting such deaths and I'm sure I would have heard about it.
The problem with the super-conservative radiation limits for evacuation is that they don't appear to recognise the potential mental health problems that might be associated with evacuating more people than is necessary. A radioactive contamination hazard will be different from other hazards requiring evacuation in that it is likely to require a much lengthier evacuation, which might even be permanent, and it also has a unique feature where a powerful lobby group (Big Green), assisted by the mainstream news media, has a vested interest in making the evacuees think they are 'doomed' or have been subject to the most terrible of injustices, which won't help anybody with mental health issues.
There has also been a news story in the last day or two that the ƒukushima nuclear power plant operator, TEPCO, has been successfully sued by the family of a Japanese woman who committed suicide and has been ordered to pay nearly $500K in compensation.
I would deduce from this recent story that TEPCO must be responsible for setting the evacuation criteria in Japan rather than the Japanese government, and I would guess TEPCO have adopted something like USEPA criteria for the evacuation.
I'm not sure what we do about evacuation criteria for nuclear accidents and other radioactive contamination incidents in the UK. The only nuclear accident we have had in the UK was the 1957 Windscale fire. No evacuation was carried out for that incident even though it did involve a reasonably big release of radioactive material, probably because Big Green didn't exist back in those days.