Types of Nuclear Reactor: Boiling & Pressurized Water Reactors - Essay Sample

Introduction

The Boiling water reactors and the Pressurized water reactors are the most commonly used types of reactors in nuclear power plants that use water as a working fluid. These two reactors use light water (H2O). The Boiling water reactor design: This type of reactor uses nuclear energy directly to boil water in the reactor to create steam. The reactor itself has the reactor core, the pressure vessels, and the containment system (Francis, Vanek, Louis, Albright, Largus, Angenent, 2012).

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The reactor core houses the ever continuous nuclear reactions and has the following components.

Fuel rods: with a diameter of 1.2 centimeters and a length of 4meters, these can number up to several thousand in a single reactor. They contain enriched uranium oxide fuel and are encased in Zirconium alloy.

Moderating Medium; the most commonly used medium for this purpose is the water that circulates in the system, but additional graphite can also be used to lower the temperature in the reactors to a few hundred degrees Celsius. Moderation of the nuclear reaction is required because of the high amount of energy produced from the fission of the atoms which can lead to the splitting of other uranium atoms whereas only one atom fission is required drive the chain reaction.

Control Rods: usually about 200 in number and made from materials that absorb the neutrons in the reactors without causing further fission, these rods can be inserted or removed from the core during operation to control the rate of fission. In emergency cases, the control rods can be used to stop the chain reaction in the center when fully inserted.

The core is housed in a pressure vessel made up of high strength metal. The bottom part of the pressure vessel contains the water used in the reaction while the top section includes the steam resulting from the reaction.

The containment system of the reactor is made up of reinforced concrete that surrounds the pressure vessel. The function of the containment system is to cool the contents of the pressure vessel as well as prevent the escape of radioactive material into the environment. A containment spray injection system is usually included to absorb the neutrons and cool the contents. These concrete containment systems are what give nuclear power plants their distinctive landmark (Francis et al. 2012).

Thermal and Mechanical Function Of Nuclear Reactor

At full operational power, the largest existing nuclear reactor produces power at the rate of 4 Gigawatts which corresponds to approximately 12*1020 atomic fissions per second. The energy produced is transferred to the fission fragments as well as gamma photons and neutrons in the reactor.

The kinetic energy that is transformed into the heat energy used to heat the working fluid is generated when the fission fragments collide with other particles in the fission site.

The heat hence generates the steam that is transported out of the containment chamber of the reactor and into the turbine.

For safety purposes measures have been put in place such as regulating the operating steam pressures set at 22.4 Pascal which is below the critical pressure. The water released from the plants is also highly regulated to avoid contamination of the environment with radioactive substances (Francis et al. 2012).

Exchange of Fuel Rods

The output from fuel rods can be affected by the low amount of fissile material in the rods as a result of the rods being spent over time. At this point the rods require to be replaced; this is done after a period of about three to six years. Every twelve to twenty for months, there is a refueling cycle in which a third of the rods are replaced until eventually all the rods are replaced.

Costing of Power Plant Operations

The total cost of operations put into consideration factors such as; fuel costs, nonfuel operating costs as well as the capital costs. These components determine overall the cost of electricity produced by the plant. The fuel costs do not, however, play a significant role in the change in the price of generated electricity. Capital investment, yet, has a substantial impact on the electricity price. This is what has driven some countries especially those with vast deposits of fossil fuel to be reluctant in investing in nuclear power plants.

Cost of Decommissioning of Power Plants

Once past its useful lifetime, a nuclear power plant has to be decommissioned. This process comes with a cost attached to it as several steps need to be taken including; removal of the spent fuel rods, removal of the core and the cooling water to waste storage facilities. The decommissioned plant has to be sealed off afterward for safety purposes.

For operating power plants, the cost of decommissioning is supposed to be accumulated during its lifetime by a charge per kilowatt per hour of electricity produced. Currently, it is estimated that a decommissioning process would cost about 300 to 500 million dollars for one plant in the USA. Up to date, however, no plant has yet been decommissioned, and the actual cost will be determined in the future when the first plant is decommissioned.

References

Francis M. Vanek, Louis D. Albright, Largus T. Angenent, (2012). Energy Systems Engineering: Evaluation and Implementation, Second Edition. Retrieved from: https://epdf.tips/energy-systems-engineering-evaluation-and-implementation.html