Prestressing tendons

A more recent test (DlB-test) utilises a solution containing 5 g/1 804, 0.5 g/1 of CT and lg/1 of SCN (added as potassium salt). This test has the advantage that the test solution is less aggressive and the amount of hydrogen that is developed during the test is comparable with that produced in practice on the surface of prestressing tendons within the ducts in defective conditions. The time to fracture required is 2000 h. All types of steel that caused damage in field, failed in this DIB standard test within 2000 h [6]. 

Protection of prestessing steel. The protection of prestressed tendons from external corrosive agents, in particular from the infiltration of de-icing salts, requires that they are completely surrounded with a protective barrier. 

AR384 1.107 Qualifications for cement grouting for prestressing tendons in containment structures (Rev.l,... 

To provide a moisture seal across the joints to protect the prestressing tendons against corrosion and to prevent leakage at joints during tendon grouting. 

The propagation of elastic waves in a civil engineering structure depends on its geometry and shape as well as on the occurring construction elements. Each material has different properties of wave propagation (velocity, attenuation). Elements like reinforcement bars or prestressing tendons may lead to anisotropy and guided waves. 

It Is considered feasible to eliminate reinforcement and prestressing tendons from the activated zone. Whether or not this option would be adopted in future designs is a matter to be considered at the design stage, taking Into account possible effects on design, plant layout, construction and overall cost. 

Whilst the work of Boothby and Williams has shown that meaningful reductions In the trace element content can be made, albeit at a price. It Is unlikely that complete elimination can be achieved. Additionally, even assuming the elimination of reinforcement and prestressing tendons from the active zone. It would appear from discussions with liner designers that they see no alternative to a steel liner securely fixed to the vessel concrete. There will also always be steel penetrations connected to the liner. Thus the emission of gamma radiation from steel In activated concrete will be a persistant problem to some degree. 

For reasons that have been already stated, the presence of steel, including reinforcement and prestressing tendons, within the activated zone Is a severe disadvantage from the point of view of decommissioning. 

The Heysham II/Torness PCRV design does not contain significant reinforcement close to the reactor cavity. The prestressing tendons. In solid wall steel ducts, are a minimum of 0.5m away from the main liner and are therefore outside the likely activated zone. See figure 6. 

Keep reinforcement and prestressing tendons In discrete regions of the activated zone to localise problems due to activated steel. 

PCRVs are axlsymmetrlc structures with an essentially axlsymmetrlc stress distribution and reinforcement and prestressing tendons must accordingly be regularly spaced out. 

Use of unbonded prestressing tendons in the reactor building shell, together with existing inspection platforms for access to the anchorages, will aid in destressing operations. 

The prestressed concrete vessel has a cavity with a diameter of about 12 and a depth of about 38 m, containing some 3,300 m of water. The concrete vessel is a monolith with a cross-section of about 27 and a height of about 43 m. It is anchored to the foundation mat structure by means of prestressing tendons. The pressure retaining capability of the vessel is ensured by a large number of prestressing tendons - partly horizontal tendons run around the cavity, partly vertical tendons run from the top to the bottom, - and by reinforcement bars. 

Nordin, H. (2004), Strengthening structures with externally prestressed tendons . Technical Report, University of Lulea, Sweden. 

The problems of interface in concrete elements, with classic reinforcement in the form of steel bars and prestressing tendons, are not considered here because they exceed the scope of this book and are widely examined in the manuals on concrete technology and concrete structures. 

Smith, L.M. and Taylor, M.F. The Long term In-Service Performance of Corrosion Protection to Prestressing Tendons in AGR PCPVS, Joint Wano/OECD-NEA Workshop, Civaux, Poitiers, France, 1997. 

However, the Oldbury contractors carried out optimisation studies on the UK Hinkley B and Hunterston B power stations. Slight changes in the vessel parameters were inevitable. This time true helices were adopted for the prestressing tendons rather than the barrelised type adopted for the Oldbury... 

Now the pressure Pq to hold forces due to prestressing tendons, bonded steel reinforcement, liner steel and concrete for specified values of Z, Sp and ean be found by taking first moments about the haunch hinge zone at Z. Referring to the previous equations, the equating moments are... 

The tensile stress in the prestressing tendons exert a normal force on dome which depends on the radius of curvature of the tendons. T endons will have a different curvature which will result in Normal forces that vary through out the dome. 

N = normal force exerted in a direction from prestress Tendon. 

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