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Il Tireless riaccese il reattore durante l'avaria

Francesco Iannuzzelli22 dicembre 2000

Solo alcuni giorni fa si e' venuti a conoscenza di un fatto che ha dell'incredibile e mostra ancora il comportamento gravemente irresponsabile dell'equipaggio del Tireless durante l'avaria che lo ha colpito a maggio al largo della Sicilia

La Marina militare inglese ha ammesso che, una volta scoperta l'avaria nel circuito primario del reattore che stava provocando una pericolosa perdita di liquido di raffreddamento, ha prima spento il reattore, poi in seguito lo ha riacceso e tenuto funzionante per 36 ore (!) per poi spegnerlo definitivamente.

Questo comportamento e' particolarmente grave perche', con un incidente di questo genere in corso, il reattore va spento e basta (il sottomarino ha comunque un motore diesel di scorta), per essere poi analizzato in una sede opportuna. Rendere operativo un reattore con una perdita in corso e' pericoloso, perche' la situazione puo' sfuggire di mano da un momento all'altro (provocando anche la fusione del nocciolo o l'esplosione del reattore) e certamente l'equipaggio del sottomarino non era a conoscenza delle dimensioni reali della crepa dalla quale usciva il liquido di raffreddamento e non poteva quindi pensare di tenere sotto controllo l'avaria.

E' l'ennesima conferma di come in ambito militare non vengono applicate intenzionalmente le misure di sicurezza obbligatorie per la gestione di reattori nucleari.

La rivelazione e' stata fatta da un ufficiale durante un'intervista a un programma della BBC. Ecco la trascrizione della prima parte della trasmissione:

BBC Radio 4 File on 4 12/12/00 8 pm
(Lt Cmd Cordoroy) "we are now in the manouvering room which effectively is the control room for the nuclear reactor and the propulsion systems onboard .. (we were) at sea when the incident occurred, it was a Friday afternoon around dinner time we were on a surface passage going across the Mediterranean sea and simply one of our instruments which would normally give us a steady reading on a level actually indicated a minor drop in that level"

(Julian OHaloran) Lt Commander John Cordoroy the deputy marine engineer was one of the first to be alerted. He realised that a small change on one dial could signal a major fault in the cooling system of the nuclear pressurised water reactor which propels the vessel. Without remedial action it could cause the reactor to overheat leading to a severe nuclear accident. To see where the fault was crew members had to enter the reactor compartment itself where there might be a radiation hazard.

(Cordoroy) "We did a controlled shutdown what is called a reactor SCRAM that allowed us to then go down into this compartment into the reactor and try and investigate the source of our small leak we actually discovered that we actually had a very minor crack on a pipe down there which in physical terms most people would accept would be a very small crack however to us in terms of maintaining our levels of safety. We were able to come out and again within our normal operating rules restart the reactor and carry on propelling the submarine."

(OHaloran) The escape of water was at a critical junction in the cooling system on the wrong side of safety valves which can isolate and stop leaks from other parts of the pipework. The worst place says the Navy for a leak to occur. But if the cracking suddenly got bigger or became a rupture there would be no way of stopping the escape of cooling water and the reactor could potentially overheat leading to every nuclear engineers nightmare - an uncontrollable meltdown. The man in charge of nuclear safety in the Navy, its nuclear regulator is Captain Hurford. He strongly denies a newspaper report that the reactor came within minutes of meltdown. He conforms that despite the risks the reactor was restarted and for a lengthy period after it was first shut down

(Capt Hurford) "The crew then started the reactor back up and monitored the leak rate extremely carefully then having assertained exactly where it was. At that time the leak rate was very low."

(OHaloran) Was that not possibly a questionable thing to do to restart the reactor once having discovered that there is a problem and that there is indeed a leak in the primary coolant circuit.

(Hurford) "There is always a balance to make between operating the reactor which is the submarine's main form of propulsion and submarine safety. Is it safe enough to operate the reactor to maintain safe propulsion for the submarine, to keep out of the way of shipping, to return to port, to keep safe on the high seas. Clearly there are very close limits such that if the reactor goes outside of those limits it must be shut down and the submarine use other means of propulsion which are much less powerful and are not its principle mode of propulsion."

(OHaloran) How long did Tireless continue until the second shut down took place ?

(Hurford) "I think it was about 36 hours."

(OHaloran) Was there a risk at that time, during those 36 hours that the small crack could become either a larger crack or a total rupture ?

(Hurford) "The materials of construction are designed to operate so that they dont fail in a brittle manner. So although there is a very slight chance the engineering says that this will not happen."

(OHaloran) But while the reactor was kept running for those extra 36 hours the rate of leakage was growing. When the risk became too great it was shut down for good. Tireless then motored slowly back to Gibraltar on its deisel auxiliary.

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