Core cooling

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

Pipe Break PB) Stii critfeat (RS) Qarvtainmerrt ov -pressure (coi Core cooling (ECl) Containment ove pressu e (C02) Ccxe cooling (ECR)... 

LOCA, is presented in Table 3.4.5-1. In preparing the event tree, reference to the reactor s design determines the effect of the failure of the various systems. Following the pipe break, the system should scram (Figure 3.4.5-2, node 1). If scram is successful, the line following the node goes up. Successful initial steam condensation (node 2 up) protects the containment from initial overpressure. Continuing success in these events traverses the upper line of the event tree to state 1 core cooled. Any failures cause a traversal of other paths in the evL-nl tree. 

If scram fails, the core melts regardless of other successes. Scram can succeed but the core melts by failure of the core cooling. Slow melt occurs if the long-term core cooling fails. Sequences 5, 9, and 10 have missing nodes to indicate inapplicability of ECl, C02, and ECR for the cases shown. 

The pressure vessel is 79 ft high with an upper diameter of 23 ft and lower diameter of 20 ft. This height is key to establishing natural circulation core flow by providing a chimney in the space between the top of the core and the steam separator assembly. This large top diameter increases the water inventory above the core (no accumulators needed), and the smaller lower diameter reduces the volume of water needed to be replaced to provide core cooling. 

At 0100, the two idle recirculation pumps were turned on causing a greater than normal circulation flow with the pumps verging on cavitation. The four pumps powered by the grid were on to run the test a second time if it failed the first time and to continue core cooling when the others stop. 

Chapter 6 was concerned, with determining the probability of various failures leading to insufficient core cooling of a nuclear reactor. This chapter describes how the accident effects are calculated as the accident progresses from radionuclide release, radionuclide migration within the plant, escape from retaining structures, atmospheric radionuclide transport and the public health effects. 

Improved emergency core cooling (ECC) reliability by reduction in number of valves, auto change-over to recirculation phase, sustained low pressure conditioning, four heat exchangers and four pumps... 

The Secondary LOCA sequences are related to large breaks (23/24) with small breaks and expansion joint (< 1%). Response to Secondary LOCA involves shutdown, leak control and/or isolation, water removal from the building to avoid flooding of pumps, and direct core cooling in the event of pump flooding. 

A fire in either of two critical areas would disable all front line and emergency core cooling systems, but not affect confinement isolation and effluent filtration. 

Piantado.si, C. A., Thalmann, E. D., and Spauq W. H. (1981). Metabolic response to tesoira-tory heat loss—induced core cooling. /. Appl. Physiol. 50, 829-8,34. 

Systems covered include primary, secondary and emergency core cooling systems, control rod, refueling, scram, electrical power, and lube oil, airsupply, battery supplies. 

Fans, cooling blankets, and tepid water baths ° Consider core cooling in acute severe hyperthermia ° Antipyretic pharmacotherapy is not effective... 

Heat Transfer in Emergency Core Cooling Systems 287... 

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