Cooling system must be brought under control to prevent meltdown

Nuclear expert Walt Patterson tells Michael McCarthy of the extraordinary complexity of the challenge engineers face

Several "alarming scenarios" face the engineers who were last night struggling to prevent meltdowns of two atomic reactors damaged in Japan's tsunami disaster, one of Britain's leading nuclear experts said yesterday.

Disturbing possibilities range from another explosion of hydrogen gas, like that which destroyed one reactor's outer shell on Saturday, to an accidental restart of the nuclear chain reaction inside the damaged plants, to a rupture of the steel pressure vessels holding the reactors' highly-radioactive cores, according to Walt Patterson, a veteran authority on nuclear policy.

"Even if this were happening under normal conditions it would be a huge challenge, but it's happening in circumstances of extreme complication because of the earthquake and the tsunami," said Dr Patterson, an associate fellow of the foreign policy think-tank Chatham House. "There are clearly a number of alarming scenarios that they're trying to cope with."

The nightmare facing Japan is of nuclear meltdown in the middle of its greatest catastrophe since the Second World War, with two of the six atomic reactors at the Fukushima power plant in dire trouble – as their water-cooling systems, essential to carry away the immense heat the reactors produce, have been knocked out by the earthquake and subsequent tidal wave. The danger is that the uranium fuel assemblies in the reactor core will overheat, melt and eventually release large amounts of radioactivity.

Engineers at Fukushima have been flooding the threatened reactors with seawater treated with boron, which inhibits nuclear reactions, but they could not prevent a build-up in the more severely damaged No 1 reactor of hydrogen gas, produced when the zirconium coating of the fuel rods began to melt and react with the water. The hydrogen was "vented" from the pressure vessel, the solid steel casing housing the reactor core, but on Saturday the gas exploded, blowing the outer containment walls of the No 1 reactor to bits. Now there are fears the same could happen with the No 3 reactor, which is also in trouble.

"They have certainly indicated that they're afraid that something similar might happen at unit 3, if they try to vent, that is, try and reduce the pressure inside the reactor vessel by opening valves, because that will let what will be very concentrated hydrogen up into the air," Dr Patterson said.

He went on: "The other consideration that caught my eye is that they have made a point of stating that they're using boric acid, that they're using borated water. This suggests to me that they're afraid the fuel damage is sufficiently bad that the stuff might collapse back into a critical configuration and start up the chain reaction again – which would really put the cat among the pigeons."

This would mean dealing with much more heat that is being dealt with at the moment, which comes from the "fissions products", the radioactive substances such as caesium, strontium and iodine produced inside the fuel by the reaction itself. "They're now obviously wanting to make sure that they don't have the additional compound problem of suddenly having a chain reaction start again," Dr Patterson said.

The worst case, he said, would be if one of the steel pressure vessels broke apart. "They're old," he said. "The No 1 vessel has been there since 1971 and was actually due to be decommissioned later this month.

"These pressure vessels are almost a foot thick, they're cast steel because they have to be, because of the high pressure they're containing.

"But they're also under bombardment from neutrons for, in this case, about 40 years, and you really do not know what condition of that metal is – and particularly if you then have violent shocks both of pressure and temperature, if the reactor is moving outside its normal operating conditions."

In the Chernobyl disaster in 1986, the reactor – of a completely different design to those at Fukushima – overheated so violently that it blew off its pressure vessel's 2,000-tonne lid, allowing the escape of vast amounts of radioactivity.

If a pressure vessel ruptures at Fukushima, Dr Patterson said, "all bets are off".

Voices
On the last day of campaigning before the polling booths open, the SNP leader has written to voters in a final attempt to convince them to vote for independence
voicesIs a huge gamble on oil keeping the First Minister up at night?
Arts and Entertainment
Rosalind Buckland, the inspiration for Cider with Rosie died this week
booksBut what is it like to be the person who inspires a classic work of art?
Life and Style
techApple has just launched its latest mobile operating software – so what should you do first?
News
A male driver reverses his Vauxhall Astra from a tow truck
newsThe 'extremely dangerous' attempt to avoid being impounded has been heavily criticised
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
News
ebooksAn unforgettable anthology of contemporary reportage
Arts and Entertainment
Lionel Messi in action for Barcelona
filmWhat makes the little man tick?
Arts and Entertainment
tvReview: An undercooked end (spoiler alert)
News
i100
Arts and Entertainment
Pharrell dismissed the controversy surrounding
musicThe singer said 'the last thing I want to do is degrade'
Sport
Cesc Fabregas celebrates his first Chelsea goal
footballChelsea vs Schalke match report
Arts and Entertainment
Toby Jones (left) and Mackenzie Crook in BBC4’s new comedy The Detectorists
tvMackenzie Crook's 'Detectorists' makes hobby look 'dysfunctional'
Life and Style
fashion

Olympic diver has made his modelling debut for Adidas

News
i100
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Science Teacher

£100 - £125 per day: Randstad Education Cardiff: Science Teacher - NewportKey ...

Year 6 Teacher required - Cardiff

£100 - £110 per day + Travel Scheme and Free Professional Training: Randstad E...

HR Advisor - Camden / Kentish Town, North London

£30000 - £35000 per annum + Benefits: Ashdown Group: HR Advisor - Camden / Ken...

Year 5 Teacher

£100 - £150 per day: Randstad Education Birmingham: Year 5 class teacher vacan...

Day In a Page

Mystery of the Ground Zero wedding photo

A shot in the dark

Mystery of the wedding photo from Ground Zero
His life, the universe and everything

His life, the universe and everything

New biography sheds light on comic genius of Douglas Adams
Save us from small screen superheroes

Save us from small screen superheroes

Shows like Agents of S.H.I.E.L.D are little more than marketing tools
Reach for the skies

Reach for the skies

From pools to football pitches, rooftop living is looking up
These are the 12 best hotel spas in the UK

12 best hotel spas in the UK

Some hotels go all out on facilities; others stand out for the sheer quality of treatments
These Iranian-controlled Shia militias used to specialise in killing American soldiers. Now they are fighting Isis, backed up by US airstrikes

Widespread fear of Isis is producing strange bedfellows

Iranian-controlled Shia militias that used to kill American soldiers are now fighting Isis, helped by US airstrikes
Topshop goes part Athena poster, part last spring Prada

Topshop goes part Athena poster, part last spring Prada

Shoppers don't come to Topshop for the unique
How to make a Lego masterpiece

How to make a Lego masterpiece

Toy breaks out of the nursery and heads for the gallery
Meet the ‘Endies’ – city dwellers who are too poor to have fun

Meet the ‘Endies’ – city dwellers who are too poor to have fun

Urbanites are cursed with an acronym pointing to Employed but No Disposable Income or Savings
Paisley’s decision to make peace with IRA enemies might remind the Arabs of Sadat

Ian Paisley’s decision to make peace with his IRA enemies

His Save Ulster from Sodomy campaign would surely have been supported by many a Sunni imam
'She was a singer, a superstar, an addict, but to me, her mother, she is simply Amy'

'She was a singer, a superstar, an addict, but to me, her mother, she is simply Amy'

Exclusive extract from Janis Winehouse's poignant new memoir
Is this the role to win Cumberbatch an Oscar?

Is this the role to win Cumberbatch an Oscar?

The Imitation Game, film review
England and Roy Hodgson take a joint step towards redemption in Basel

England and Hodgson take a joint step towards redemption

Welbeck double puts England on the road to Euro 2016
Relatives fight over Vivian Maier’s rare photos

Relatives fight over Vivian Maier’s rare photos

Pictures removed from public view as courts decide ownership
‘Fashion has to be fun. It’s a big business, not a cure for cancer’

‘Fashion has to be fun. It’s a big business, not a cure for cancer’

Donatella Versace at New York Fashion Week