The Chernobyl disaster was not over when the sarcophagus took shape above the ruins of reactor number four in the summer and autumn of 1986.
By Stephen Mulvey
BBC News website
Nor will it be over when a new giant arch - as tall as St Paul's cathedral or the Statue of Liberty - slides over the top of the sarcophagus three or four years from now.
The Chernobyl ghost will not be laid to rest until the plant has been transformed into an "ecologically safe system", as Ukrainian officials put it, and that will not be for a very long time.
There are currently three main obstacles on the path towards this goal:
- the lava-like remains of the melted-down reactor
the spent fuel from the other three reactors
- hundreds of
leaking nuclear waste dumps
For the last decade, the main concern has been that the hastily built sarcophagus might collapse, blowing tonnes of highly radioactive dust into the surrounding forests and waterways.
But work is now under way to shore up badly leaning walls, secure unsteady beams, and strengthen tilting supports under the plant's giant red and white chimney.
The sarcophagus is being shored up - before being dismantled
By the end of 2006 it will be much stronger, though fingers may still need crossing in case of tornadoes or earthquakes.
It's a measure of the urgency of these stabilisation tasks, that they are being carried out despite plans to un-do them again - and dismantle most of the sarcophagus - once the new arch is in place, some time after 2008.
THE MELTED CORE
The arch is a vast project - "the largest movable structure to be built in the history of mankind", as one of those involved has called it.
But critics argue it is a little more than a carpet to sweep the main problem under, because the fuel within the wrecked reactor will simply be left as it is.
"The new, stable and environmentally safe structure will contain the remains of the reactor for at least 100 years," says a press release from the European Bank of Reconstruction and Development, which will disburse the 840 million euros ($1bn) the arch is expected to cost.
"During (this) time an even longer-lasting solution to the Chernobyl problem must be found."
To Mykhailo Khodorivsky, a member of a consortium which in the 1990s investigated ways of removing the fuel, this seems like storing up problems for the future.
The arch will last for 100 to 300 years, while the fuel will remain deadly for thousands.
"A new confinement is necessary, but it does not tackle the root of the problem," Mr Khodorivsky says. "Our conclusion was that in 100 years the problem will not get simpler."
For one thing, some of the plutonium will be decaying into americium, which is even more hazardous for health.
"If nothing is done with the fuel, and the arch is contaminated from the inside, what do you do when it gets old?" he asks. "Build an even bigger one on top?"
If this is a problem for future generations to grapple with, the decommissioning of the other three reactors at Chernobyl is one for today.
The job was put on hold after the last Chernobyl reactor stopped generating in December 2000, because there was nowhere to take the spent fuel.
Work began on a dry fuel storage facility in 1999 but it was later found to be unsuitable for some of the Chernobyl fuel assemblies, which have cracked, soaked up water and changed shape.
Work on the dry waste facility was suspended in 2003
Construction has been at a standstill for three years, while arguments rage over who is to blame, and what to do next.
To get the spent fuel out of the reactors, a decision was finally taken to make space in a Soviet-era wet fuel storage facility, by packing its contents more tightly.
But this alarms some observers, such as Mykola Karpan, a former safety official at the plant.
He points out that the Soviet-era facility comes to the end of its life in 2016 - and that the question of what to do then with the wet and cracked fuel assemblies has not yet been answered.
He also argues that it could be risky to pack the damaged fuel assemblies more tightly, and claims an identical facility in St Petersburg has sprung alarming leaks.
The graveyards are described as a "radiation emergency" by one of the men responsible for them, Valery Antropov, because no-one knows where they all are, or what is in them.
The unlined, leaky trenches were quickly dug and filled with low and medium-level radioactive waste in 1986.
They were intended to be temporary, but 20 years on, only half of them have even been mapped and inventorised.
An estimated 500 trenches in seven areas around the plant have yet to be studied at all.
"We know the graveyards are in these areas, but exactly where - so as not to step on them - we cannot be sure," says Mr Antropov, a senior member of a waste and decontamination unit known as "Complex".
Some of the trenches closest to the Pripyat river have been partly washed away by spring floods, others are slowly seeping radionuclides into ground water.
Mr Antropov is also worried by two repositories built hastily in 1986 for severely contaminated waste, for example graphite blocks thrown out of the reactor in the explosion.
Valery Antropov: No-one wants to see this problem
Neither was properly built, he says, one is too close the river, and the contents of both should really be somewhere deep underground.
"Where to store highly radioactive and long-lived waste is a huge problem," he says.
"We have containers queuing up. We need to build a deep geological deposit, but Greens object. It's a problem that people don't want to see."