ClabFOR SPENT NUCLEAR FUEL CENTRAL INTERIM STORAGE FACILITY FOR SPENT NUCLEAR FUEL

CENTRAL INTERIM STORAGE FACILITY FOR SPENT NUCLEAR FUEL CENTRAL INTERIM STORAGE

FUEL CENTRAL INTERIM STORAGE FACILITY FOR SPENT NUCLEAR CENTRAL INTERIM STORAGE FOR

SPENT NUCLEAR FUEL CENTRAL INTERIM STORAGE FACILITY FOR SPENT NUCLEAR FUEL CENTRAL

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Sweden has been producing electric-ity by means of nuclear power sincethe early 1970s. The spent nuclearfuel from the Swedish reactors iskept in Clab, which is located northof Oskarshamn, near the Oskars-hamn nuclear power plant. Here thefuel is interim-stored in large waterpools more than 30 metres belowthe ground surface.

Transport to ClabSpent nuclear fuel contains manyradioactive substances, or radionu-clides, which emit both radiation andheat. The fuel is toxic and extremelyhazardous if it is handled improperly.When the fuel is taken out of thereactor, it is stored in water-filledpools at the nuclear power plant forat least nine months. During thistime its radioactivity declines consid-erably (by about 90 per cent), but the

fuel is still so radioactive that peoplecannot come near it without radia-tion protection.

The spent fuel is then transportedto Clab in transport casks by a spe-cially-built ship, m/s Sigyn. InsideClab, it is lifted over to special stor-age canisters. The storage canistersare taken down into the under-ground facility and are placed in oneof the water pools. In Clab the fuelis kept under constant surveillance,and all handling takes place understrict control.

The fuel is kept in interim stor-age for about 30 years. During thistime its radioactivity and heat outputdecline further. After interim storageabout one percent of the radioactivitythat was in the fuel when it was takenout of the reactor remains. But thefuel still needs to be radiation-shielded.

Long-term solution:geological disposalThe radioactivity of the fuel declineswith time. The fuel therefore be-comes less hazardous as time passes.After 1,000 years most of theradioactivity has disappeared but thefuel is still dangerous.

It takes a very long time, about100,000 years, before the radio-activity has declined to the same levelas that of the quantity of uraniumore from which the fuel was origi-nally fabricated. In order to protectman and the environment in the

This is where Sweden’sspent nuclear fuel is storedIn Sweden we have a system – including both transportation andfacilities – for managing and disposing of waste from the Swedishnuclear power plants. An important part of this system is Clab –Central interim storage facility for spent nuclear fuel.

The spent nuclear fuel is interim-stored in Clab on the Simpevarp Peninsula, where the Oskarshamn nuclear power plant isalso located (to the right at the photo).

Forsmark

Oskarshamn

ClabRinghals

Barsebäck

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long term, the fuel will be encapsu-lated and isolated 500 metres downin the bedrock in a final repository.

Water protects and coolsThe most important thing in allhandling and storage of spent nuclearfuel is to protect man and the envi-ronment from radiation. In Clab,water is used as a radiation shield.All handling and storage take placeunder water, protecting plant person-nel as well as people and the envi-ronment outside the facility. The fuelis always covered by 3– 8 metres ofwater, which is enough to enable thepersonnel to work inside the facilitywithout any special protectiveequipment.

The water in the pools also acts asa coolant. It circulates in a closedsystem, which is cooled by sea water.

The temperature in the pools isaround 35°C during normal opera-tion. If the primary fuel coolingsystem should cease to function, thereis a backup system. Otherwise, lossof cooling could lead to a gradual risein temperature, causing the water toevaporate faster. There is so muchwater in the pools that it would takeabout a month before the fuel beganto be exposed. This allows ampletime to arrange backup cooling ifneeded.

The rock caverns themselves are alsoa part of the safety system. They pro-tect against intrusion and sabotage.The pools are specially designed towithstand earthquakes. Sliding bear-ings between the pools and the rockprevent the fuel and the pools frombeing damaged in the event of move-ments in the bedrock.

All safety equipment in Clab isredundant. For example, the facilitycan be supplied with electricity fromseveral independent systems. Clabalso has its own diesel generator.Furthermore, important parts of themonitoring and control systems canbe battery-powered.

Inspection and reportingComprehensive regulations applyto inspection and reporting for allhandling of spent nuclear fuel. Themost important laws governing activ-ities at Clab are the Nuclear ActivitiesAct and the Radiation Protection Act.

The activities are supervised bythe authority Swedish RadiationSafety Authority (SSM). The CountyAdministrative Board also supervisesactivities at Clab. International over-sight is exercised by among othersEuroatom and the UN’s Interna-tional Atomic Energy Agency, IAEA,which makes sure that no uraniumfalls into the wrong hands.

Receiving hall.

All transport casks are inspected when they arrive at Clab.

A terminal vehicle drives the fuel between m/s Sigyn and Clab.

Oskarshamn

32 m

(granite)

Facts about Clab

Next to the Oskarshamn nuclear power plant

1980

1985, second cavern finished in 2005

8,000 tonnes of spent nuclear fuel

About 220 tonnes of uranium plus six storage canisters of corecomponents per year

Reception, offices, ventilation, electricity

Two rock caverns with eight storage pools,40 metres beneath the surface

About 80 Full-Time Equivalents

Location

Start of construction

Start ofoperation

Capacity

Reception

Surface facility

Underground facility

Personnel

The rock is prepared for a third rock cavern.

The underground part of Clab consists of two rock caverns. Each rock cavern contains four water pools for storage plus a reserve pool. All handling under ground is performed by a handling machine. When a storage canister comes down, the machine is used to lift it out of the elevator cage. The machine then places the storage canister in a predetermined location in one of the pools.

Handling under ground

The facilityClab consists of two parts: one above ground and one under ground. The buildings onthe surface contain offices, workshops and control room. This is also where the spentnuclear fuel enters the facility and is transloaded prior to transport under ground.The fuel comes to Clab in a transport cask on a terminal vehicle that resembles a truck.

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The storage canister is brought down by awater-filled elevator cage to the storage pools.

Power supply

Offices

Reception

The storage canister is moved underwater by means of a handling machine.

The cask is lowered into a pool, where the fuel assemblies are transferred to a storage canister.

A terminal vehicle arriveswith a transport cask.

Storage canisters

The fuel will remain in the storage canisters throughout the storage period in Clab. They therefore have to meet stringent requirements on quality and design. The storage canisters are made of steel and specially designed to prevent spontaneous nuclear fission during storage.In recent years, SKB has developed a new type of storage canister that holds more fuel.

Graphic: MENTAFORM

5 m Boron-alloyedsteel

Handling above ground

The transport cask is lifted into the reception building and placed in a cell where the cask and the fuel are cooled.

The storage canister is placedin a predetermined location.

To transload the fuel, the entire cask is loweredinto a water pool. Beneath the water surface,the cask lid is removed, after which the fuelassemblies can be lifted out, one by one. Theyare placed in storage canisters before beingtaken down to the rock caverns in a water-filledelevator cage.

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Radioactive materials that emit radi-ation exist in nature. They can befound in our bodies, in the soil andin the bedrock. Similar radiationcomes from outer space. Man hasalways been exposed to radiationfrom radioactive materials.

Radiation from radioactive mate-rials can affect, harm or kill biologi-cal cells. Very high radiation dosescan be directly lethal or cause severeinjuries in living beings. Lower dos-es can cause cancer or damageresulting in genetic mutations. Radi-ation doses to humans are measured

in Sieverts. There are several typesof radiation with differing proper-ties, see page 7.

Radiation from spentnuclear fuelNuclear fuel consists of uraniumdioxide, a ceramic material that ishighly insoluble in water. The fueltakes the form of small cylinderscalled pellets. They are stacked ontop of each other in slender metaltubes. The fuel rods, as the tubes arecalled, are assembled into bundlescalled fuel assemblies. When the

Fuel pellets before they have been usedin nuclear power plants. Each pellet hasa diametre of one centimetre.

Nuclear fuel and radiation Radiation can be harmful, and larger doses can be downright lethal.It is relatively easy to protect against radiation. Water is a goodradiation shield that is often used for handling of radioactive materials,for example spent nuclear fuel.

Every day we are exposed to radiation from the world around us. Background radiation comes from radioactive substancesin the bedrock, in outer space and in our own bodies.

fuel is spent, the whole assembly ishandled as waste.

Before the fuel pellets have beenused in the nuclear power plants,they are handled with only gloves asprotection. (Gloves are needed sothat the new fuel will not be con-taminated by handling.) In the reac-tor, the uranium is split (fission),forming new substances (nuclides).Many of the new nuclides are radio-active and emit radiation. Most ofthe radionuclides that are formedhave a short, or very short, half-life.This means that the spent fuel emitsvery powerful radiation at first, butthat the radiation declines consider-ably with time.

Radiation and timeWhen the fuel is removed from thereactor it emits so much radiationthat it is life-threatening to get closeto it without a thick radiation shield.

The fuel is stored for at least ninemonths in water-filled pools at thenuclear power plant. During thattime its radioactivity declines by90 per cent. The fuel is still veryradioactive and hot. It must there-fore continue to be radiation-shieldedand cooled.

The spent fuel is hazardous intwo ways: Direct radiation, mainlyin the form of gamma rays, can pen-etrate the body from the outside,while alpha radiation can causeharm if radionuclides from the fuelenter the body.

After about 30 years of storage inClab, the fuel’s radioactivity hasdeclined by an additional 90 per cent.Now only a few per cent of theradioactivity remains in the fuel.

Most of the radionuclides leftafter 30 years of storage decay with-in the course of a few hundred years.After that only a few nuclides, mainlyalpha-emitting ones, make the fuelhazardous. They must be kept iso-lated so that humans and other livingcreatures don’t ingest them. Some ofthese nuclides will remain for a verylong time, up to 100,000 years.

Nuclear waste in the futureIn Sweden we have a well-function-ing system in operation for dealingwith the radioactive waste from thenuclear power plants. The system

consists of facilities for managementand disposal of the waste as well astransportation between them.

We have a transportation systemfor shipping radioactive waste bysea. The low- and intermediate-levelwaste is taken to SFR (Final reposi-tory for radioactive operationalwaste) at Forsmark, while the high-level waste is transported to Clab inOskarshamn.

In order for the system to becomplete, we also need an encapsu-lation plant and a final repositoryfor spent nuclear fuel and otherlong-lived waste. The fuel will thenbe taken from Clab to the encapsu-

lation plant, where it is dried andplaced in copper canisters. A lid iswelded onto the canister, which ischecked carefully to make sure it iscompletely tight.

Final solution in a finalrepositoryThe copper canisters with fuel arethen transported to the final reposi-tory. There will be an industrialplant on the surface where canistersand backfill material are handled.A tunnel and a shaft lead down tothe repository, which will be locatedat a depth of about 500 metres.There the canisters will be embeddedin bentonite clay. Both the coppercanister and the clay and rock actas barriers, preventing radioactiveparticles from reaching the surface.

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Alpha radiation consists of posi-tively charged helium nuclei.They travel only a few centime-tres in air and are stopped by apiece of paper or clothing.

Beta radiation consists of elec-trons that travel up to 20 metresin air but are stopped by heavyclothes or a glass window.

Particles that emit alpha or betaradiation can harm us if we inhalethem or ingest them via food.

Gamma radiation consists ofelectromagnetic waves of veryhigh energy content. They havea very long range and great pen-etrating power. In air, a dou-bling of the distance to a pointradiation source causes theradiation dose to decrease toone fourth. In our facilities,gamma radiation is attenuatedto a sufficiently low level by ametre of concrete or a coupleof metres of water.

Neutron radiation consists ofneutrons emitted during nuclearfission in nuclear reactors. It isstopped by several metres ofwater or concrete and virtuallyceases when nuclear fission isinterrupted.

DIFFERENT TYPESOF RADIATION

alpha

beta

gamma

Swedish Nuclear Fuel and Waste Management CoBox 250, SE-101 24 Stockholm, Sweden

Phone +46 8 459 84 00 www.skb.se

Svensk Kärnbränslehantering AB(Swedish Nuclear Fuel and Waste Management Co, SKB)

has been assigned the task of managing and disposingof the radioactive waste from the Swedish nuclear power

plants, including spent nuclear fuel.The waste must be disposed of to protect human healthand the environment, in both the short and long term.

SKB’s mission is an important environmental undertakingand a part of the national environmental objective.

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