Spent Fuel Storage at Diablo Canyon Power Plant

it takes a lot of energy to make enough safe clean electricity for three million northern and central California homes day after day year after year but that's what Pacific Gas and Electric companies Diablo Canyon powerplant does making a significant contribution to the production of carbon free energy this is new nuclear fuel which will power the plant once it is placed in the reactors while it is clean and efficient nuclear fuel must periodically be replaced and the used fuel stored on the plant site for now the new fuel is being inspected and stored upon arrival at this point it can be handled safely because it has not been placed in the reactor and irradiated yet nuclear fuel is made into small pellets and placed inside long tubes called fuel rods the rods are put together in what are called fuel assemblies later when the fuel assemblies are placed in the reactor each one can power a small city after three to five years of producing heat inside the reactor to create steam turn a turbine and then generate electricity the fuel assemblies are replaced with fresh assembly like the ones being temporarily stored here until 2009 all of the used fuel assemblies produced by the power plants two units were stored under water and one of two used fuel pools which are inside the fuel handling building behind the reactor containment domes inside most of the grid squares is a used fuel assembly while the used fuel is not strong enough to efficiently create electricity it still produces some heat and is still radioactive water is an excellent barrier to radiation so employees can work safely around the pools which are made of up to six feet of reinforced concrete with a stainless steel liner all built on bedrock with the pools filling up with fuel assemblies it became necessary to create a system to safely store the used fuel outside of the pool storage of used fuel at nuclear power plants and tested concrete and steel containers is a proven technology approved by the Nuclear Regulatory Commission and used at many nuclear power plants in the United States planning engineering approving and constructing the used fuel storage project at Diablo Canyon took several years to assure the highest levels of safety and security the process of removing the older used fuel from the pools starts with an empty 15 foot tall stainless steel used fuel storage canister it is placed inside a separate transportation canister which helps block radiation and is later used to move the fuel to the storage pad both canisters are then moved to a specially designed corner within the used fuel pool under a minimum of 23 feet of water this is where they are filled with used fuel assemblies the stainless steel alloy of the inner canister is designed to absorb impacts so that it would bend or dent before breaking the transportation canister is made of lead and steel after the canisters are placed in the pool fuel assemblies are identified lifted from their storage locations in the pool and moved to the used fuel canister and lowered in a honeycombed internal framework adds strength evenly distributes the heat and provides radiation shielding each canister holds up to 32 fuel assemblies when it is filled a heavy steel lid is lowered into the pool and secured to the top of the canister with the water still inside for now next with lead and steel providing radiation shielding it is lifted from the pool while workers make sure that any radioactive material is cleaned from the outside from there an overhead crane system moves the canisters to another work area at the used fuel storage pool for the opposite unit every step is designed with safety in mind including seismic safety for example here a special seismic restraint band is placed around the canister to hold it in place in the event of an earthquake next a permanent lid is welded on to the top of the used fuel canister then all moisture is removed from the inside of the canister and it is filled with helium an inert gas that removes heat and prevents oxidation of the used fuel next the canisters are lifted and placed on a low rolling platform then winched out from the used fuel handling building by the transporter this transporter was specifically designed to safely move the used fuel from the plant to the unique storage pad an approximate one wild trip as it is with safety every step of the transfer has a comprehensive security component special modifications were made for climbing the hill to the pad in the unlikely event that the transporter engine failed the unit locks its tracks in place so that it cannot roll backwards even though the lead and steel of the transport and fuel canisters block most radiation every effort is made to minimize all exposure it is kept well below safe federal limits for workers just outside of the storage pad the transporter and used fuel canisters stop and are prepared for the final stage of transportation but before moving the used fuel from the plant the transporter is used to place the heavier longer-term concrete and steel outer storage container called the over value in this below ground facility a mating device is attached to the top of the overpack container to aid in the lowering of the used fuel canister from the transport canister now carrying the used fuel the transporter places the canisters on the mating device over the overpass container with the aid of positioning pins part of the seismic safety process involves attaching struts to the transporter to make sure it remains secure should an earthquake occur while the transfer process is being carried out with the transporter secured it is then hooked up directly to the used fuel canister so that it can then be lowered into the below ground facility and nested inside the heavier over packed container this is made possible by a lid at the bottom of the transport canister the lid is removed with the help of the mating device which slides the lid out from under the transport canister then the used fuel canister can be lowered inside the open packed container so below ground transfer facility is also a seismic safety measure because it allows the transfer to be done below the ground as opposed to higher in the air after the transfer is complete the transportation canister is removed the mating device and lower lid are removed and then the overpacked lid is installed at this point the transporter moves back over the transfer facility to lift out the outer container with the used fuel canister now nested inside the transporter then backs away from the transfer facility the lifting sling is removed and the container is directly attached to the transporter now begins the final leg of the journey to a designated position on the pack from a security perspective the used fuel storage facility is much like the plant itself it is protected with high technology security systems fencing and armed officers 24/7 and access to the area is strictly controlled the concrete pad was designed as another seismic safety feature as it is with much nuclear safety and security it's what you don't see that makes a big difference what can't be seen about this pad is that it is seven and a half feet thick of the strongest concrete available laced with steel rebar through out another seismic safety feature is the location of the pad itself one of the reasons it was chosen is that beneath it is the same bedrock on which the plant was built further adding to the seismic stability of the pad the containers are transported to a location on the pad and then carefully set down on pre-positioned guides and then securely bolted into place the used fuel is now protected by more than two hundred seventy eight thousand pounds of concrete and steel twice the weight of a modern US military tank and about half its size they are among the strongest containers ever made by man the protection includes the 1/2 inch of stainless steel alloy of the used fuel canister and the overpack consisting of 28 inches of shielding and protection concrete sandwiched between two 1-inch steel plates the containers are designed to withstand the strongest credible earthquake for the plant and they meet all nuclear regulatory commission security the used fuel storage pad is designed to be built in stages and is capable of safely and securely storing all of the used fuel generated by the plant through the year 2025 the used fuel storage project provides safe secure storage in a small space allowing Diablo Canyon power plant to continue operating as one of our most important sources of carbon free electricity for millions of Californians you

Channel: pgevideo

Views: 240,158

Rating: 4.5032492 out of 5

Keywords: nuclear, power, safety, nrc, diablo canyon, calfifornia, pg&e, pacific gas and electric, energy, clean, environment

Id: mILvWNgggfU

Length: 11min 12sec (672 seconds)

Published: Fri Sep 30 2011