PWR FUEL BUNDLE

The pressurized water reactor (PWR) is a type of nuclear reactor used to the generate electricity and propel nuclear submarines and naval vessels. They make use of light water (ordinary water, as opposed to heavy water) as their coolant and neutron moderator. The bundles are arranged vertically in fuel tubes within the core. As the fuel is "burned" in the reactor, its density gradually increases, resulting in small voids to develop inside the fuel tube. These void spaces can cause a problem because high pressures could cause stress to the tubes, increasing the likelihood of a rupture. To avoid this problem, the tubes are pressurized with helium at about 3.4 MPa. As fission gas products accumulate over the fuel's lifetime, the pressure gradually balances with the high pressure of the core.

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