By Rob Broomby
BBC Radio 4
"It's just like checking books in a library" remarks Ivo Herrez Perrera, as he walks around one of the huge steel flasks containing nuclear material.
Iran has made a steady drip of concessions to the IAEA
He is one of scores of nuclear inspectors employed by the UN's nuclear watchdog the International Atomic Energy Agency (IAEA).
His current mission is to the Ulba uranium fuel plant in Kazakhstan.
This huge facility was once known simply as "Mailbox 10" and it was a top secret part of the Soviet nuclear weapons programme.
Ivo's words are something of an under statement, the Safeguards Inspectors are on the frontline, the eyes and ears of an agency which is in effect the custodian of the Nuclear Non Proliferation Treaty.
It is these inspectors who have to verify that a nuclear programme like this one, is indeed peaceful.
While recording these two programmes, I was given a rare opportunity to accompany the nuclear inspectors in Kazakhstan .
Their work involves a painstaking process which includes taking readings, checking batch numbers and applying tamper proof seals to sensitive materials.
The inspectors have to assure themselves the nuclear material here is safe and is not being diverted to make bombs.
The Kazakhs have built up trust with the IAEA over time, and they have now agreed to even more intrusive inspections under an agreement called the Additional Protocol.
This atmosphere of trust contrasts with Iran - its own uranium enrichment programme at Natanz was begun secretly and in breach of the rules.
When it was revealed they indeed had a secret enrichment plant, Iran initially agreed to the Additional Protocol, but it has since backed out and this has put the country on collision course with the international community.
Iran and the West are in conflict over its nuclear programme
Tension has mounted because the West fears the plant could eventually give them access to material for a nuclear weapon, though Tehran denies this, saying it will simply give them fuel for nuclear power stations.
Throughout the year I spent with the IAEA there has been a steady drip of tiny concessions from Iran but not enough for the Inspectors to rule out a secret parallel weapons programme.
Since the matter of Iran's refusal to stop enrichment was sent to the UN Security Council, individual inspectors have been blocked (though Iran says it is acting within its rights) and co-operation has been reduced to the minimum.
Sanctions have not made Iran comply - they are still enriching uranium in defiance of the UN Security Council - and now, the agency says their understanding of what Iran is up to is "deteriorating".
And then there is that document which the inspectors turned up in Iran showing how to manufacture uranium into hemispheres for use in a nuclear warhead.
That can only have come from one of the dealers in black market nuclear technology such as A Q Khan, the disgraced father of the Pakistani nuclear bomb, now under house arrest.
The document is not a smoking gun in itself, says the Head of the Inspectors, Olli Heinonen, but it is a document which has to be fully "explained".
The inspectors have been refused permission to take the paper away for analysis but it is now under agency seal within the country.
As the Agency's Director General, Mohamed ElBaradei put it, more colourfully, "they owe us a confession".
The United States administration is convinced that Iran is set on a nuclear weapons programme.
Its Ambassador to the IAEA Greg Schulte says that if Iran has 3000 centrifuges for enriching uranium running by later this year it would take them just 12 months to produce enough material for a bomb, though a weapon itself would take longer.
Dr Mohamed ElBaradei says Iran owes the IAEA a 'confession'
But at this late hour, even Dr ElBaradei can not say whether he thinks Iran wants a nuclear bomb. The agency does not like to judge intentions, "The jury is out" he says.
The contrast with Kazakhstan could not be greater. The country inherited over 1000 nuclear war heads with the collapse of the Soviet Union but it rejected the weapons and shipped them back to Russia, inviting in the IAEA inspectors.
They are now shipping Uranium for fuel to the four corners of the earth.
But under a welter of challenges from Iran, and North Korea and the reluctance, as Dr ElBaradei sees it, of the existing weapons states to take meaningful steps towards disarmament, the whole non proliferation regime is "faltering".
He has questioned Britain's decision to go ahead with renewing the Trident missile system which he says sends the "wrong signal".
It is clear he feels he has a diplomatic role to play and that there can be no military solution to the Iran crisis.
Intervention in Iraq had shown the limits of military power and on the uranium enrichment programme he says, "you can't bomb knowledge".
The Iran dossier is still open.