Sorry, but the burden of proof is on he who is fracking things up. And a lack of data does not indicate safety, either.
Before fracking as we know it today was commercially viable, under the "Plowshares" program, nuclear bombs were detonated to stimulate the release of natural gas. They included Project Rio Blanco and Project Rusilon in Colorado, and Project Gasbuggy in New Mexico.
For the most part, this was not a successful venture. Rio Blanco, a test which used three bombs in close proximity, failed entirely. Rusilon and Gasbuggy succeeded -- Rusilon especially -- but as you probably correctly guessed already, the gas was radioactive and unmarketable.
But, all the plans required careful designs for preventing the release of contamination to a degree no one has to live up to with modern fracking.
Now, pull up Google Earth and look at 39.405278, -107.948528 . This is the where the Rusilon device was detonated in Colorado. Now start zooming out and panning around. You will note a great deal of little patches of concrete and dirt in the area. These are natural gas wells. The DOE is still accountable for making sure no radioactive contamination from Rusilon ever gets out.
So what you see here is someone taking advantage of mysterious, conveniently rich and abundant quantities of natural gas suddenly found in this region in the last 40 years. But none of it's directly contaminated by the Rusilon test. Either the isotopes have decayed or secondary effects from the blast unrelated to contamination resulted in long-term changes to the region. The water quality in the Rusilon area has been extensively monitored, so at least that was not affected here.
But the point is, I can state things definitely here because the DOE has spent millions watching these sites like a hawk. And even the most minute traces of radioactive contamination can be detected, because it is its own radioactive tracer.
Can anyone say the same about modern fracking? Who's going to be watching modern fracking sites in 40 years? Who's making sure the secondary long-term effects upon region geology don't negatively impact others?
I'm not arguing for detonating nukes for natural gas production, I think it's a dumb idea, but these tests have shown long-term effects upon area geology caused by the blast effects alone, which while not negative in these three cases, certainly have the potential to be, no matter what force of nature you're relying on to frack things up for you.
And then there's the contamination. And you have to use a lot more fracking stuff to stimulate the same amount of natural gas production as a couple kilograms of plutonium. That equates to injecting a lot of fracking crap in the ground. No monitoring, no testing, changes to area geology, no half-life that it will decay in... do you think every fracking site out there is going to sequester things away forever?