aftermath of the explosions, forensic examination was undertaken on two of the casualties recovered from the stern section, these being identified as the reactor control room operators. These casualties had sustained skeletal damage indicative of body shock loading of just over 50g. This provided a degree of reassurance that the reactor resilient mounts, being below or about the design limit, had not been damaged and that the reactors could have closed down automatically as intended after power supplies had been lost.
Other factors relating to the condition of the reactor systems included:
i) The shock level (~50g) would have also temporarily disoriented the reactor control personnel who would not have been expected to recover for several minutes by which time most, if not all, of the power required for operator intervention would have been lost;
ii) the shock would have caused opening of electrical circuit breakers leading to loss of power, e.g. to the main coolant pumps;
iii) automatic reactor shutdown sequences would have been initiated probably by the above power loss — this sequence causes the insertion under gravity, with spring and pneumatic assistance, of two diverse means of neutron absorption which then lock into place, and the initiation of decay heat removal which makes use of the large thermal capacity of the water in the shield tank — this sequence cannot easily be interrupted by the operator and it was unlikely that its essentially passive role was impeded by the shock loading;
iv) the reactor shutdown and decay heat removal equipment had a design basis for an inclination of the submarine in excess of 45° for forced cooling during pump spin down, and thereafter a lesser angle of inclination for heat dissipation by natural circulation — the depth of water (108m) in conjunction with the submarine’s length (155m) precluded a larger inclination — in view of the perceived accident sequence it is probable that the maximum trim angle was much less than 45?, although this may have been exceeded for a few seconds or more when the hull responded to the expansion of the explosive gas products; and
v) the design provides four barriers to the escape of fission products (or particulates) from the nuclear fuel. These comprise the fuel assembly cladding, the reactor primary circuits, and the reactor shield boundaries.
To confirm the state of the reactor the RF deployed gamma spectroscopy in the range 4 to 8 MeV (characteristic of reactor operation) in the lower regions outside the pressure hull and the thermal gradient in the flood hull space was profiled to detect any thermal input. Negative results suggested that:
i) the reactors remained shutdown;
ii) there was effectively no contamination (e.g. fuel particulate) in the shield tank, suggesting that the reactor primary circuit containment is complete;
iii) there is no contamination between the shield tank and the pressure hull, suggesting that the shield tank containment is complete; and
iv) the lack of any thermal gradient indicated that no significant heat was being generated in either of the reactor compartments.
On this basis, the NCG’s criterion that at least two of the reactor containments be in place was satisfied.
ESTABLISHING DATUM CONDITIONS FOR THE MUNITIONS
Torpedoes: At the time of sailing the
These missing rounds could have been hidden within the hull, particularly in the mangled wreckage of what remained of the bow compartment and some could have been thrown into the wreckage of the second compartment (which was subsequently shown to be the case when the internals of the wreck was dried out and inspected at Rosljakovo). Some or all of the rounds could have burnt during the explosions, some might have fragmented, and others might remain intact and hidden under the submarine hull.
Such was the uncertainty surrounding the presence, state and stability of these missing torpedo rounds that an explosion from this source had to be considered a credible fault condition at any time during the lift operations. Factors in mitigation were:
i) the dispersion of the remaining torpedoes and fragments of torpedoes, made a sympathetic detonation less likely;
ii) detonation would be unconfined and not directed through the hull towards the reactor compartment (compared to the original explosion that was initially confined by the pressure hull);
iii) the design basis capability of the reactor plant to withstand shock remained available (to an undeclared amount); and
iv) any fragment revealed during silt clearance etc., be removed by the RF, using remotely operated equipment to at least 70m from the submarine — torpedoes and fragments within the cut zone would also be removed.
v) the silt clearing equipment was unlikely to cause detonation of a torpedo or explosive fragment.
The NCG nominated a fault condition whereby the equivalent of two torpedo rounds (~450kg TNT in total) simultaneously detonated during the bow separation operation or the lifting operation. The NCG sought assurance, with explanations, from the RF of each reactor’s capability to withstand such an explosion. In addition, an analysis of the effect of the explosion gave the strength requirements of the hull plating of the attending barges and the length limitation for smaller vessels attending the barges, a requirement that these be larger that the sea surface bulk cavitation and gas bubble diameters that would put smaller vessels at risk of sinking. Also, the analysis provided the minimum lashing requirements for the heavy equipment operating on the barge decks, particularly the two 60t crawler cranes working on the
Missiles: At the time of loss, the
Relevant features of the SS-N-19 missiles are:
i) the propellant fuel is kerosene, with a small (7kg TNT equivalent) powder charge for ejection from the silo to the turbojet firing altitude above the sea surface;
ii) the launching ‘trigger’ or arming and firing system (AFS) comprised five independent degrees of protection or latches;
iii) each missile was held within shock mountings within the silo, which itself had the same material characteristics and strength as the submarine pressure hull; and
iv) the missile could be launched only after the silo cap had been opened, which required hydraulic actuation that was no longer available.
Unlike a torpedo round explosion, which was considered to be credible and tolerable, full detonation of a single 760kg missile warhead could not be tolerated at any stage of the lift, conveyance from the wreck site and transfer to the floating dock because this would have imperiled all of those personnel manning the salvage vessels and had the potential to result in a release of radioactivity to the marine environment and hence to the M-S personnel. Thus, it was absolutely essential to determine the most unstable condition for the missile systems and the main fill and ejection charges and if any of the five AFS latches had been enabled by the foundering explosions and the subsequent M-S recovery operations.
This was determined by a series of trials in which fully assembled missiles were subject to a range of
