some could be in mountains and hard terrain. they could be 50 ft underground covered in hard granite.
US "Mass Ordnance Penetrators" fail initial testing, doubtful if they can take out underground, reinforced facilities, according to 'Wall Street Journal' report; Pentagon asks congress to fund upgrade program.
The US' 30,000-pound (13,600 kilo) "Mass Ordnance Penetrator" (MOP) was specifically designed to be able to take out Iranian and North Korean nuclear facilities. According to the report, initial tests indicated that the bomb would be incapable of performing these tasks, either because of the depth of the facilities or their recent reinforcement.
In an interview with the Wall Street Journal on Thursday, US Defense Secretary Leon Panetta admitted to the bomb's shortcomings.....
Panetta also said that the MOP was not specifically designed for Iran. "It's not just aimed at Iran. Frankly, it's aimed at any enemy that decides to locate in some kind of impenetrable location.
Regarding potential alternatives to the MOP, the Journal quoted a US official as saying that "The Massive Ordnance Penetrators are by no means the only capability at our disposal to deal with potential nuclear threats in Iran." Iranian nuclear facilities have been attacked through sophisticated computer viruses as well as bombs, and a number of Iranian nuclear scientists have been killed.
Another senior official said that the Pentagon could make up for the MOPs' shortcomings by dropping them along with other guided bombs on bunkers' entry and exit points. "There is a virtue to deepness but you still need to get in and out," he said.

One unnamed officials said Pentagon analysts estimated that currently held conventional bombs would not be effective against Iran's enrichment plant in Fordo, adding that a tactical nuclear would be the only option if Washington sought to destroy the facility.
"Once things go into the mountain, then really you have to have something that takes the mountain off," the official told the Wall Street Journal.
Image of a B-61 thermonuclear weapon. In the back it is assembled, in the middle it is divided into its major subcomponents, in the front it is almost completely disassembled. The warhead is contained in the bullet-shaped silver canister (see Image:W80_nuclear_warhead.jpg for a different, but similarly shaped, warhead casing).
The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.
The B61 is a variable yield bomb (0.3 to 340 kiloton yield in various versions and settings) designed for carriage by high-speed aircraft. It has a streamlined casing capable of withstanding supersonic flight speeds. The weapon is 11 ft 8 in (3.58 m) long, with a diameter of about 13 in (33 cm). Basic weight is about 700 lb (320 kg), although the weights of individual weapons may vary depending on version and fuze/retardation configuration.
Total production of all versions was approximately 3,155, of which approximately 1,925 remain in service as of 2002, and some 1,265 are considered to be operational. The warhead has changed little over the years, although early versions have been upgraded to improve the safety features.
Nine versions of the B61 have been produced. Each shares the same "physics package", with different yield options.
The newest variant is the B61 Mod 11, deployed in 1997, which is a ground-penetrating bunker buster.
The B61 unguided bomb should not be confused with the MGM-1 Matador cruise missile, which originally was developed under the bomber designation B-61.
When the B61 was still classified, aircrew were not allowed to use the term "B61". Instead, it was referred to as a "shape", "silver bullet", or even "external delivery".
Bunker-busting nuclear weapons, also known as earth-penetrating weapons (EPW), are a type of nuclear weapon designed to penetrate into soil, rock, or concrete to deliver a nuclear warhead to a target. These weapons would be used to destroy hardened, underground military bunkers buried deep in the ground. In theory, the amount of radioactive nuclear fallout would be reduced from that of a standard, air-burst nuclear detonation because they would have relatively low explosive yield. However because such weapons necessarily come into contact with large amounts of earth-based debris, they may, under certain circumstances, still generate significant fallout. Warhead yield and weapon design have changed periodically throughout the history of the design of such weapons. An underground explosion releases a larger fraction of its energy into the ground, compared to an explosion at or above the surface which releases most of its energy into the atmosphere.
In World War II the British designer Barnes Wallis, already famous for inventing the bouncing-bomb, designed two bombs that would become the conceptual predecessors of modern bunker busters: the five tonne Tallboy and the ten tonne Grand Slam "Earthquake" bombs. The designs were very aerodynamic with a tail which caused them to spin. This allowed them to exceed the speed of sound as they fell from 22,000 ft (6,700 m). They had casings of high grade steel, much stronger than the typical WWII bomb so that they would survive hitting a hardened surface, or penetrate deep into the ground.
Though these bombs might be thought of as 'bunker busters' today, in fact the original 'earthquake' theory was more complex and subtle than simply penetrating a hardened surface. The Earthquake bombs were designed not to strike a target directly, but to impact beside it, penetrate under it, and create a 'camouflet' or large buried cavern at the same time as delivering a shock wave through the target's foundations. The target then collapses into the hole, no matter how hardened it may be. The bombs had strong casings because they needed to travel through rock rather than reinforced concrete, though they could perform equally well against hardened surfaces. In an attack on the U-boat pens at Farge two Grand Slams went through the 15 ft (4.5 m) reinforced concrete hardening — equalling or exceeding the best current penetration specifications.

Natanz (33°43′24.43″N 51°43′37.55″E / 33.7234528°N 51.7270972°E / 33.7234528; 51.7270972) Natanz is a hardened Fuel Enrichment Plant (FEP) covering 100,000 square meters that is built 8 meters underground and protected by a concrete wall 2.5 meters thick, itself protected by another concrete wall. In 2004, the roof was hardened with reinforced concrete and covered with 22 meters of earth. The complex consists of two 25,000 square meter halls and a number of administrative buildings. This once secret site was one of the two exposed by Alireza Jafarzadeh in August, 2002. IAEA Director General Mohamed ElBaradei visited the site on 21 February 2003 and reported that 160 centrifuges were complete and ready for operation, with 1000 more under construction at the site.[19] Under the terms of Iran's safeguards agreement, Iran was under no obligation to report the existence of the site while it was still under construction. There are currently approximately 7,000 centrifuges installed at Natanz, of which 5,000 are producing low enriched uranium.
The case of a nuclear electromagnetic pulse differs from other kinds of electromagnetic pulse (EMP) in being a complex electromagnetic multi-pulse. The complex multi-pulse is usually described in terms of three components, and these three components have been defined as such by the international standards commission called the International Electrotechnical Commission (IEC).[16]
The three components of nuclear EMP, as defined by the IEC, are called E1, E2 and E3.
For a normal low air burst or ground burst detonation, the EMP effects reach no further than the flash burn and blast effects, IE roughly 30 miles for the typical "city buster" bomb. In other words, if it cooks your radio, it'll cook you too.
High-altitude nuclear detonations and electromagnetic bombs can generate EMP that has the potential to damage or destroy electronic devices over widespread areas. Electric power systems would also be at risk from surges produced by such weapons. However, the EMP from a kiloton-range surface nuclear explosion would not be expected to produce serious damage outside the radius of severe destruction from blast.