The findings of the MoD's Board of Inquiry will be announced later to MPs by Defence Secretary Des Browne.
"My department has taken a number of steps to ensure that a similar accident cannot occur again," Mr Browne told the Commons.
The aircraft, call sign XV230, exploded while on an intelligence-gathering mission.
"We are learning the lessons from the accident and have already implemented many of the recommendations of the BOI report."
The pilot had reported a fire in the bomb bay.
These include reviews of the Nimrod's fuel and hot air systems and air-to-air refuelling procedures.
It is thought the blaze was started when a fuel leak caught fire.
Hot air pipes
There are... a host of unanswered questions about the safety of the ageing Nimrod fleet as a whole which the Ministry of Defence must answer Angus Robertson MP
The MoD Board of Inquiry (BOI) report concluded that fuel probably escaped into a bay on the starboard side of flight XV230 either because of a leaking coupling in the fuel system or an overflowing fuel tank.
The father of one of the men who died in the explosion says he believes his son's death could have been averted if safety warnings had been acted upon.
The fuel probably caught fire when it made contact with hot air pipes which could have been as hot as 400C.
Graham Knight, the father of Ben Knight, told BBC Radio 4's Today programme: "Something good has to come out of something so awful, and I hope it leads to the aircraft being safer to fly."
[The crew] acted throughout with calm professionalism, and did everything possible to save their aircraft Air Chief Marshall Sir Glenn Torpy The report also highlighted a number of factors which could have contributed to the explosion.
He also said he wanted to know what caused the leak which led to the fire.
These included the age of some of the Nimrod's components, the maintenance of the fleet's fuel and hot air systems and the lack of fire detectors and extinguishers within the area where the fire started.
Westminster SNP leader Angus Robertson MP, who represents the Nimrods' home base at RAF Kinloss in Moray, wrote to Mr Browne ahead of the report's publication with a number of questions.
Mr Browne said: "On behalf of the MoD and the Royal Air Force, I would like to apologise to the House of Commons, and most of all to those who lost their lives, and to their families.
"Everybody hopes that the inquiry will answer all of the relevant questions about the Nimrod which crashed in Afghanistan and help avoid a repeat of the tragedy," he said.
"I am sorry."
"There are, however, a host of unanswered questions about the safety of the ageing Nimrod fleet as a whole which the Ministry of Defence must answer."
The Chief of the Air Staff, Air Chief Marshall Sir Glenn Torpy, said the Nimrod's crew "behaved in an exemplary manner during the tragic events".
NIMROD CRASH VICTIMS Flt Lt Allan Squires, 39, from Clatterbridge, MerseysideFlt Lt Steven Johnson, 38, from Collingham, NottinghamshireFlt Lt Gareth Nicholas, 40, from Redruth, CornwallFlt Lt Steven Swarbrick, 28, from LiverpoolFlt Lt Leigh Mitchelmore, 28, from Bournemouth, DorsetFlt Sgt Adrian Davies, 49, from Amersham, BuckinghamshireFlt Sgt Gary Wayne Andrews, 48, from Tankerton, KentFlt Sgt Gerard Bell, 48, from Newport, ShropshireFlt Sgt Stephen Beattie, 42, from DundeeSgt Gary Paul Quilliam, 42, from ManchesterSgt Ben Knight, 25, from BridgewaterSgt John Langton, 29, from LiverpoolMarine Joseph Windall, 22 from Hazlemere L/Cpl Oliver Dicketts, from Wadhurst class="" href="/1/hi/uk/5121552.stm">UK fatalities in Afghanistan
He said the BOI stated that the crew "were faced with a series of complex and demanding emergencies and acted throughout with calm professionalism, and did everything possible to save their aircraft".
Six Nimrods were sent out to Afghanistan and Iraq, flying lengthy missions, often using air-to-air refuelling to keep them in the air for longer.
"Their families, friends and colleagues should be very proud of them all."
The MR2 aircraft that came down was almost 40 years old, and should have left service years ago, but its replacement, the MRA4, will not be ready until at least 2011.
Critics have blamed cost-cutting by the Treasury and the MoD for the delays to its introduction.
Defence analyst Robert Fox said he felt "there has been neglect in looking after these aircraft".
"The bottom line is we are still trying to run two war-like operations on a peacetime budget," he said.
However, the MoD said the safety of servicemen and women remained its "highest priority".
"In line with this we have continued to adapt our Nimrod force maintenance and operating practices," a spokesman said.
He continued: "We are confident that the aircraft remains fit to fly and all necessary safety measures have been implemented.
"If we did not have confidence in aircraft we would not allow them to be flown."
The Nimrod was originally designed as a sea patrol and anti-submarine aircraft, but is now considered vital to British troops on the ground, especially in Afghanistan, acting as their eyes in the sky gathering intelligence over enemy positions.
