{"id":27147,"date":"2020-05-01T07:42:36","date_gmt":"2020-05-01T07:42:36","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=27147"},"modified":"2023-07-28T10:13:16","modified_gmt":"2023-07-28T10:13:16","slug":"spent-fuel-pool","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power-plant\/spent-fuel-pool\/","title":{"rendered":"Spent Fuel Pool"},"content":{"rendered":"
Spent fuel pool<\/strong> (SFP) is a storage pool for spent nuclear fuel<\/a> from nuclear reactors<\/a>. A spent fuel pool may be located inside the containment building<\/a> or the fuel building<\/strong> (outside the containment building).<\/div><\/div>\n
\"Spent<\/a>
Spent fuel pool. Source: wikipedia.org License: Public Domain<\/figcaption><\/figure>\n

When located outside the containment building, the two areas are connected by a fuel transfer system<\/strong> which carries the fuel through a normally closed opening in the reactor containment. In this case, spent fuel is removed from the reactor vessel by a manipulator crane and placed in the fuel transfer system. In the spent fuel pool, the fuel is removed from the transfer system and placed into storage racks<\/strong>. After a suitable decay period, the fuel can be removed from storage and loaded into a shipping cask for removal from the site. Spent fuel pools<\/strong> are typically 12m or deeper, with the bottom equipped with storage racks designed to hold fuel assemblies removed from the reactor. A reactor\u2019s pool is specially designed for the reactor where the fuel was used and situated at the reactor site.<\/p>\n

Spent fuel pools<\/strong> are fitted with stainless steel and aluminum racks that hold the fuel assemblies and are lined with stainless steel to prevent leaking. No drains would allow the water level to drop or the pool to become empty. The plants have a variety of extra water sources and equipment to replenish the water that evaporates over time or in case of a leak. Plant personnel is also trained and prepared to respond to a problem quickly. The water serves two purposes: it cools the fuel and shields workers at the plant from radioactivity. Although water is neither<\/strong> high density<\/strong> nor<\/strong> high Z material<\/strong>, it is commonly used as a gamma shield. Water provides a radiation shielding of fuel assemblies in a spent fuel pool during storage or transport from and into the reactor core<\/strong><\/a>. Although water is a low-density material and low Z material, it is commonly used in nuclear power plants because these disadvantages can be compensated with increased thickness.<\/p>\n

To conserve space, in all plants, open storage racks were replaced with so-called high-density racks<\/strong> that incorporate (boron-10<\/a>) or other neutron-absorbing material to ensure subcriticality<\/a>. Fuel assemblies can be stored in about one-half the volume required for storage in standard racks using such racks.<\/p>\n

<\/span>Spent Nuclear Fuel<\/div>
\n
\"Spent<\/a>
Typical fuel assembly<\/figcaption><\/figure>\n

Spent nuclear fuel<\/strong>, also called the used nuclear fuel<\/strong>, is a nuclear fuel that has been irradiated in a nuclear reactor<\/a> (usually at a nuclear power plant or an experimental reactor), and a fresh fuel<\/strong> must replace that\u00a0due to its insufficient reactivity<\/a>. Spent nuclear fuel<\/strong> is characterized by fuel burnup<\/a>, a measure of how much energy is extracted from nuclear fuel<\/a>, and a measure of fuel depletion<\/a>. Due to fuel depletion and fission fragments<\/a> buildup, spent nuclear fuel is no longer useful in sustaining a nuclear reaction<\/a> in an ordinary thermal reactor and must be replaced by fresh fuel. It may have considerably different isotopic constituents depending on its point along the nuclear fuel cycle.<\/p>\n

It must be noted that irradiated fuel is due to the presence of a high amount of radioactive fission fragments and transuranic elements that are very hot and very radioactive<\/strong>. Reactor operators have to manage the heat and radioactivity<\/a> that remains in the \u201cspent fuel\u201d after it\u2019s taken out of the reactor. In nuclear power plants, spent nuclear fuel<\/strong> is stored underwater in the spent fuel pool<\/strong> on the plant, and plant personnel moves the spent fuel underwater from the reactor to the pool. Over time, as the spent fuel is stored in the pool, it becomes cooler as the radioactivity decays away. After several years (> 5 years<\/strong>), decay heat<\/a> decreases under specified limits so that spent fuel may be reprocessed or interim storage.<\/p>\n

At first glance, it isn\u2019t easy to recognize fresh fuel from used fuel. From a mechanical point of view, the used fuel (irradiated) is identical to the fresh fuel. In most PWRs, used fuel assemblies<\/strong> stand between four and five meters high, are about 20 cm across, and weigh about half a tonne. A PWR fuel assembly<\/strong> comprises a bottom nozzle into which rods are fixed through the lattice, and it is ended by a top nozzle to finish the whole assembly. There are spacing grids<\/strong> between these nozzles. These grids ensure an exact guiding of the fuel rods. The bottom and top nozzles are heavily constructed as they provide much mechanical support for the fuel assembly structure. Western PWRs use a square lattice arrangement, and assemblies are characterized by the number of rods they contain, typically 17\u00d717 in current designs. In contrast to the fresh fuel, which is simply shiny, the oxide layer<\/strong> forming on the surface of used fuel assemblies during the four-year fuel cycle makes them dark. Moreover, \u00a0Cherenkov radiation<\/a> is typical only for spent nuclear fuel. The glow is also visible after the chain reaction stops (in the reactor). The Cherenkov radiation can characterize the remaining radioactivity of spent nuclear fuel, therefore it can be used for measuring fuel burnup.<\/p>\n<\/div><\/div>\n

\n

Safety of Spent Fuel Pool<\/h2>\n

The safety of spent fuel pools stands on various criteria. These criteria may be grouped according to the following aspects:<\/p>\n