Lesson 18 - Decay Heat DEFINE the term decay heat. Given the operating conditions of a reactor core and the necessary formulas, CALCULATE the core decay heat generation. DESCRIBE two categories of methods for removing decay heat from a reactor core.

Decay Heat The release of energy by the decay of fission products Caused when highly radioactive fission products radioactively decay at a rate determined by the amount and type of radioactive nuclides present Radioactive materials that remain in the reactor at the time it is shut down and the fission process halted will continue to decay and release energy. Amount of decay heat is very significant – amount present in reactor immediately following shutdown will be roughly 7% of the power level that the reactor operated at prior to shutdown. Reactor design must provide some means of removal of this decay heat from the core.

Calculation of Decay Heat Exact solution – Detailed process takes into account the fact that there are hundreds of different radionuclides present in the core, each with its own concentration and decay half- life – Dependent upon power history. – Must calculate the amount of fission products present at the time of shutdown. Approximate solution - Uses single half-life that represents the overall decay of the core over a certain period of time.

Calculation of Decay Heat

Decay Heat Limits Major concern - can cause melting of and/or damage to the reactor core (Three Mile Island) Concern will vary according to reactor type and design. Low power, pool-type reactors. – Low concern Limits during shutdown – Based upon decay heat considerations. – Vary because of Steam generator pressure, Core temperature, Any other parameter that may be related to decay heat generation. For each limit developed, there is usually some safety device or protective feature established.

Decay Heat Removal Two general categories – Methods which circulate fluid through the reactor core in a closed loop – Methods which operate in an open system Normally removed by the same methods used to remove heat generated by fission during reactor operation Emergency cooling system of some sort will be included in the reactor design

HVAC Principles Purpose Basic Equipment Principles of Operation Main Structural Components Failure Mechanisms and Symptoms

Purpose of HVAC Systems

HVAC – Basic Equipment Chiller units Heating units Fans Blowers Filters Ductwork Blowout ducts

HVAC Principles of Operation Basic Refrigeration Cycle

HVAC Components Chiller Units Circulation Pumps, both condenser and evaporator Air Handling Units Cooling Towers Expansion Tank/Air Release Systems Chemical Treatment Systems

HVAC Failure Mechanisms and Symptoms Loss of environmental control Loss of coolant charge High- and low-pressure cutoffs Gas binding of cooling system