Decay heat

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. 

LQCAs with failure of fang-term decay heat removal (LTDHR) Inc. event V 59%... 

Functional and hardware relationships between systems are considered in selecting the order of event tree headings. Systems that depend on the operation of other systems in order to perform their function should be listed after the other systems. For example, the decay-heat removal system... 

Issue Resolution, JCOs, Plant Modifications EOOS performs sensitivity analyses to determine the significance of e. Ihe removal of offsite power or decay heat removal equipment. 

The only human actions important in more than 50% of the BWR IPEs are manual depressurization, containment venting, initiation of standby liquid control (SLC), and system alignment for decay heat removal. In PWRs, only switch over to recirculation, feed-and-blecd, and the actions associated with depressurization and cooldown are important in more than 50% of the... 

Remove core decay heat High pressure injection system Low pressure injection system High pressure recirculation system Core flood tanks Auxiliary feedwater system Power conversion system Remove core decay heat Auxiliary feedwal stem Power conversion m High pressure inj( i system pow. peiuicd relief valves... 

Removing decay heat has been the "Achilles Heel" of nuclear power. The designs shown in this section use active methods to remove the heat, (a) Sketch and discuss a design that removes the heat passively, (b) It would seem that the energy in the decay heat could be used for its own removal. Sketch and discuss a design that uses this property to remove the decay heat. 

Early BWRs used an isolation condenser, although such is not specific to the direct cycle. This device removes decay heat by steam flow through a heat exchanger the other side of which is water vented to the atmosphere. Discuss the relative merits of such a boiler. 

Relocation of the decay heat source as fission products are released from the fuel and transported to the containment. 

The high risk POSs R6, RIO, and D6 have different decay heats and plant configurations ... 

R6, for eddy current testing of the steam generator tubes, is performed in a refueling ouiagL by quickly draining the RCS loops, hence, the decay heat rate is high. 

D6 is MLO with the highest rate of decay heat among the three mid-loop POSs. 

Av.iil.ihility of an isol.ilion condenser in older BWRs for sequences with loss of decay heat removal (DHRl... 

Pressure-tubes allow the separate, low-pressure, heavy-water moderator to act as a backup hesit sink even if there is no water in the fuel channels. Should this fail, the calandria shell ilsdf can contain the debris, with the decay heat being transferred to the water-filled shield tank around the core. Should the severe core damage sequence progress further, the shield tank and the concrete reactor vault significantly delay the challenge to containment. Furthermore, should core melt lead to containment overpressure, the concrete containment wall will leak and reduce the possibility of catastrophic structural failure (Snell, 1990). 

The two primary pumps with AC and DC pony motors flow 18,000 gpm of heavy water through the core for cooling. Following 60 MW operation, for 3 minutes, forced flow is needed to remove the decay heat. Upon loss of pony motors and primary pumps, forced flow is established through the shutdown cooling water system consisting of two pumps in parallel - one pump running and the other on standby. 

Effective half-life Average neutron energy Neutron emission rate Decay heat... 

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