Scram

The reactor scram (short RESA or SCRAM - Safety Cut Rope Axe Man, su, and reactor trip, ugs trippen ) is a process in nuclear power plants. The RESA can be triggered manually by the operator or in accidents but also by a reactor protection system when crossing certain thresholds automatically. The reactor protection system determines readings with multiple redundancy to avoid false alarms as possible.

The RESA makes the reactor strongly subcritical, thus ends the fission chain reaction. It does not serve the usual reactor control, since in a RESA, the reactor is shut down immediately.

In general, a reactor is shut down by the collapse or complete insertion of the control rods between or directly into the fuel (depending on the type of reactor ) fast. As an additional redundant Abschaltmaßnahme is the feeding of boric acid over a Hochdruckeinspeisesystem in the reactor coolant system available. Through these measures, the nuclear chain reaction is stopped and the power of the reactor is reduced to decay heat. It corresponds initially about five percent of the thermal power of the reactor in normal operation and sounds in a period of a few days with good approximation exponentially. During this time, this power must be removed by cooling the reactor to prevent a meltdown and damage to the shield, which did not work, for example in the nuclear power plant Fukushima Daiichi in March 2011 after failure of the emergency power supply and led to a catastrophic accident series.

The Chernobyl disaster occurred due to the reactor design after initiating the RESA to a short-term power increase, which made ​​the arrangement prompt critical and thus triggered the explosion of the reactor.

Already Enrico Fermi in 1942 provided for commissioning of the first nuclear reactor, Chicago Pile of a Schnellabschaltmöglichkeit. A specially trained person, the Safety Cut Rope Axe Man (literally about " security man who cuts the rope with an ax " ) or short scram should, in an emergency, initiate an emergency shutdown by the penetration of a cord with an ax (to the English word scram means something like " run away fast," " cut off ," " beat it "). Pull the cord hung a control rod, which would have stopped the nuclear fission when entering the reactor immediately. The term SCRAM for the reactor scram is also today still common in English usage.

As ATWS ( Anticipated Transient without scram ) an event is indicated, in which the fast cut-off is unsuccessful.

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