The idea is to carry an atomic bomb in an orbiter and throw it towards the surface, would it be plausible?
You may not send a nuclear bomb into space if you're one of the 105 countries that have signed the Outer Space Treaty that, among other things, forbids
deploying nuclear weapons or any other kinds of weapons of mass destruction in outer space.
Even disregarding that...
By measuring the craters of bombs we exploded in the 1950's, we found that a crater with diameter D km requires a bomb of D3 megatons. Skimming wikipedia, these craters' depths were 3% to 4% of their widths.
So a crater 11 km deep would be 11 / 0.035 = 314 km wide, about a tenth of Europa's diameter. So the bomb's yield would need to be at least 30 million megatons. So the bomb would mass at least 30 million tonnes.
Even if these numbers are off by four orders of magnitude, they're still deep into fantasy. A much more efficient way to penetrate the ice would be to direct energy straight down, to make a thin hole instead of blasting open an entire lake. For example, NASA's ARCHIMEDES project proposes using a laser.
Addressing @uhoh's concern about melting rather than mechanical removal, here are the numbers. The energy corresponding to 1 megaton TNT equivalent is 4.2E+15 Joules. Tsar Bomba had a theoretical yield of 100 Mt if it had been fully optimized, or 4.2E+17 J.
Water's enthalpy of fusion is 80 Joules/gram and ice's specific heat capacity is 2 J/g/K and water's is 4.2 J/g/K, so warming the ice up by 100 K then melting it then warming it up another 5 K is about 300 J/g or 3E+08 J/m^3.
So one optimized Tsar Bomba might have the power to melt 1.4E+09 m^3 of ice, which is a hemisphere with a 900 meter radius. Of course most of the energy would vaporize and dissociate material close to the surface and almost no energy would reach several kilometers deep, but even if perfectly efficient you'd need 1000 Tsar Bombas to melt a hemisphere 10 km deep.
Perhaps a hundred thousand of them would be required to do it in practice.
You'd have to bring a pretty large bomb to do this. We've detonated lots of bombs on Earth, and none of them came close to making a hole 11 km deep. We even did tests specifically aimed at making large holes (Project Plowshare):
The 104 kiloton, 1962 Sedan nuclear test formed a crater 100 m (330 ft) deep with a diameter of about 390 m (1,300 ft)
These tests were done by lowering the bomb into a hole in the ground. Detonating a bomb on the surface would be less effective than this. To deliver a bomb to Europa without a manned mission to drill a deep hole, you'd have to build a bomb along the lines of a bunker buster - but even those are only designed to penetrate a few dozen meters.
Consider this: if we were to use such a device on Earth, we'd be able to break up the Earth's crust and expose the mantle.
The very largest detonations on Earth were all airbursts. I haven't found a way to estimate the effect of such bombs when buried before detonation.
If we ignore the legal aspects, we can at least get a bomb there. The Cassini spacecraft weighed 2500 kg (counting Huygens), while Wikipedia mentions a thermonuclear weapon that weighs only 1100 kg, so there would be weight left over for communications, etc. I don't know if the yield of 1.2 million tons of TNT would be enough to get through that much ice - I suspect not if it was detonated on the surface, but mabye if we can get it below the surface first.