brochure cement at ion juni 2007

8/3/2019 Brochure Cement at Ion Juni 2007

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Cementation ofRadioactive Waste


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NUKEM Technologies GmbH2007

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CEMENTATIONOF RADIOACTIVE WASTEIntroduction

Cementation is one of the mostcommonly used methods for condi-tioning radioactive wastes. Itprovides a cost-effective solution forencapsulation of various kinds ofradioactive waste into a solid, safeform suitable for long term storage.The main advantages of cementation

are: Simple, low-temperature process.

Well proven technology.

The cemented product is not com-bustible and has good thermalstability.

The cemented product is chemi-cally and biochemically stable.

All forms of waste can be eitherincorporated in a cement matrix orencapsulated by grout.

NUKEM offers five different mixingtechniques: High PerformanceIn-Drum Mixer, Lost Stirrer In-Drum

Mixer, Slant Batch Mixer, High ShearMixer and High ThroughputContinuous Mixer.

Overview on Characteristics of Mixing Techniques

High Per-formance

In-DrumMixer

Lost Stir-rer In-

DrumMixer

SlantBatchMixer

HighShearMixer

HighThroughput

ContinuousMixer

ThroughputRate

Suitable forPortableUnit

VariableBatch Size

N/A

Product

Quality

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Suitable forGroutPreparation

Easy De-con-tamination

low, high, very high, excellent

1Compressive Strength, Leach Rate


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High Performance In-Drum Mixer

The High Performance In-DrumMixer is a combination of planetary

mixer with double helical mixer. Themixing elements are in the form oftwo counter-rotating cylindrical heli-ces. This design ensures high sheardispersion and compensates alltorque forces that might be transmit-ted to the drum. Intimate mixing isaccomplished by having the mixingunit assembly revolving in a plane-tary motion so that the rotating heli-

cal blades sweep the entire circum-ference of the drum. The mixing

elements are raised from the drumby a vertical lift. After separation, themixing elements drain into the drum.If maintenance is required theblades can be cleaned with a handheld vibrator after curing of the resi-due. As an alternative, it is possibleto decontaminate them in place byrotating them in decontaminationsolution.

Process Description

Fig. 1 Simplified Flow Sheet of the In-Drum Mixer


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A waste storage drum, prefilled withcement or a mixture of cement anddry additives appropriate to the ce-mentation recipe is placed onto the

roller conveyor. The roller conveyortransfers the drum beneath thedocking hole of the mixer box/cell.Here, the docking device lifts thedrum and seals the rim to the mixerbox/cell. After the liquid waste fillingtube is directed into the drum thefirst portion of waste is metered intothe drum. This portion constitutes athird of the total waste quantity forone drum for a given cementation

recipe.

The mass flow is measured by aCoriolis flow meter, integrated andcounted electronically. When thepoint is reached, the waste flow isshut off automatically. Usually, thedrum is filled up to 95% of its heightafter the first portion of waste isadded. The first mixing cycle nowtakes place. The mixer-unit assem-bly is lowered into the drum, down toapproximately one third of its depth.

The mixing elements revolve for afew minutes and bring the level ofwaste/cement down. The drum isthen ready to receive the secondportion of waste. This portion, aswell as the third portion, is treated inthe same way as the first.

While mixing the third portion ofwaste, the mixing elements are sub-mersed down within of a few centi-meters of the bottom and rotated ata higher speed than before. Thisensures the highest achievablehomogeneity of the grout. This highdegree of homogeneity ensures theproduct quality is very high. Com-pressive strength and leach rate will

achieve be at their optimum values.

ApplicationNUKEM's High Performance In-Drum Mixer has been used success-

fully in a series of permanent andmobile applications. The flow sheet,shown in Figure 1, is applicable toboth applications.For permanent installation the HighPerformance In-Drum Mixer isarranged in-side a hot/warm cell.Depending on the radiation level,the machinery will be operated byremote manipulators or hands-onthrough gloves fitted on the cell. An

example of such arrangement isgiven in figure 2 and 3. These fig-ures show a facility, that is ownedand operated by the Research Cen-ter Karlsruhe, Germany. Auxiliaryequipment is arranged in the build-ing around the cell to suite the spe-cific requirements of the client.

The mobile unit as described below,is called DEWA. It represents amovable hot/warm cell containingthe High Performance In-DrumMixer.


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Fig. 2 In-Drum Mixer arrangedinside a Hot-Cell

Fig. 3 Operator Filling the Drum

with Liquid Waste


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Mobile Solidification Unit DEWAThe DEWA is an assembly of simple,robust and reliable components. Themethod of operation is simple. The

cementation process takes place inthe waste container itself; the cementis filled in beforehand. There is norequirement for the transportation ofthe binding agent or for its meteringin the area where the radioactivematerial is handled.

Tests have shown that the physicalproperties - such as compressivestrength and leach rates - of the

products obtained are excellent. Theproducts meet the regulations forfinal disposal. The dose rates arewithin the required limits. The finalproducts contain no free water.The DEWA solidification unit doesnot make high demands regardingthe wastes to be solidified. Thewastes must merely be pumpable.They may contain up to 25% boricacid, and up to 35% dry matter. As to

cementation, it is unimportantwhether the wastes to be solidifiedare high or low activity. However, thelevel of radioactivity requires a suit-able container for shielding.

The DEWA cementation unit isshipped to the point of use on a flat-bed trailer. The unit unloads by self-action using its telescopic legs,which are swung in position and thanrun out. For setting up, a 6 m by 3.3m foot print with a loading capacity of0.09 N/mm and total height of4.53 m is required.

The unit consists of a cube-shapedframe in which the steel-shieldedhot/warm cell is arranged. There isan operating platform with a controlpanel and a roller conveyor for the

transportation of the drums to be

filled. The drum docking device joinsthe drum to the cell where the wasteis metered in and the content ofdrum is mixed. The cell accommo-

dates the High Performance In-DrumMixer, an ultrasonic level sensor, thehand held vibrator for cleaning, a linefor ash supply, if required, and theexhauster with HEPA filter system. Aswivelling lid covers the docking holein the bottom of cell. The container,pre-filled with cement, is carried tothe roller conveyor by a forklift and isclamped to the docking hole. Theliquid waste is then transferred in

portions by a Coriolis quantity meterand homogeneously mixed with thecement. The mixing process can beobserved through lead glass win-dows. The closing of the containertakes places on the roller conveyor.If the wastes are low activity it isdone manually. If the activity ishigher, lid closure is performed byremote control.

The plant can also deal with solidwastes. In this case the drum, whichis about half filled with waste material(e.g. powder, granules etc.), is trans-ported to the cells opening as be-fore. Cement is now added dry ormixed with water. In all other re-spects, the procedure is similar tothat described above. Contaminatedparts that cannot be compacted (filtercandles, small parts) can also beplaced in drums and treated likewise.The DEWA can handle all types ofdrums licensed by the authorities.The type of drum chosen dependson the level of activity and the par-ticular qualities of the waste to bedisposed of.The dimensions of the DEWA unit inworking position are shown inFigure 4.


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Operating experienceSince the start of operations with theDEWA unit, several campaigns ofsolidification of radioactive wasteshave been carried out at the BWR at

Gundremmingen, Germany and atthe PWRs at Biblis, Germany andNeckarwestheim, Germany. Includ-ing the foreman, a team of three tofour operators was needed. Depend-ing on the local conditions, the set-ting-up times ranged from 1 to 2days. The availability reached 95%not considering the delays caused bythe plant. Filter aid sludge, precipi-tated slurries, decontamination efflu-

ents and evaporator concentrateswith activities between 3.7 E +09Bq/m and 1.85 E +11 Bq/m havebeen solidified. The performance ofthe unit depends on the specific ac-tivity of the wastes, the resulting

shielding requirements and on thedry substance content. A volume to1.8 - 2.2 m per day can be solidifiedin externally shielded 200 l drumsand a volume of 3.6 - 4.6 m per day

can be solidified if using internallyshielded 400 l drums. The massivesteel and lead shielding of the unitand the largely remote handling ofthe containers ensures that the ac-cumulated dose received by the crewremained low. While processing slur-ries with an activity of about 1.48 E+10 Bq/m with a nuclide distributionof 14% Cs-134, 33%Cs-137, 36%Co-60, and 5% Mn-54, the measured

dose rates were < 3 m Rem/hr at thewall surface and < 0.35 m Rem/hr atthe operators position. The averagedose rate was less than 10 m Remper day and per person.

Lost Stirrer In-Drum Mixer

The lost stirrer technique wasemployed by NUKEM to develop a

very highly sophisticated, portableunit that provides a high throughputas well as ease of operability. Thisunit is called MOWA. Althoughdesigned to be portable, NUKEMalso used the MOWA-baseline tobuild a permanent Lost Stirrer In-Drum Mixer facility.

Mobile Waste Conditioning PlantMOWAThe MOWA system (Fig. 5 and 6)features all the advantages of acompact plant, as it can be shippedand stored in a 20 ft-ISO-container.It has a high waste throughput,deals with drums of several sizes (

brochure cement at ion juni 2007

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