2018:18 Procedure for Safety Assessment of Components with Defects

– Handbook Edition 5


SSM and the Swedish nuclear power plant owners have financed Kiwa Inspecta Technology in Sweden to develop a new version of the handbook for assessment of defects. This represents a major update of the former fracture mechanics handbook that was published at SSM as Research 2008:01. The procedure in the handbook is based on the British R6-method where the failure mechanisms fracture and plastic collapse are considered for cracked components of metallic materials by evaluating the stress intensity factor and the plastic limit load. Almost all elements of the handbook are included in a computer based expert code called ISAAC, which also have been revised as part of the project. ISAAC is an acronym for Integrity and SAfety Assessment of Components.


The results of the project have meant that a number of new and updated features are now implemented in the handbook. This includes the following:

  • Implementation of the R6-procedure, Rev. 4
  • Implementation of ASME, section XI, edition 2007.
  • A revised system of safety factors to be used with the R6 procedure.
  • Revised chapters on defect characterization, stress intensity factor solutions for new crack geometries, weld residual stresses and material data including new data for fatigue crack growth and stress corrosion crack growth for nuclear applications.


The SSM regulations SSMFS 2008:13, containing rules for mechanical components in certain nuclear facilities, allows for further operation of a nuclear power plant if cracks are detected in mechanical components without repair or replacement, when it has been demonstrated that sufficient safety margins exist against fracture. Thus, there is a need for tools that can perform reliable safety assessments of components with defects in order to verify that the regulations are fulfilled. The fracture mechanics handbook satisfies this need. Many applied research projects since 2008, financed by SSM and in some cases together with the Swedish nuclear power plant owners, have been used to generate results, which have been included in the handbook and the computer code ISAAC. This includes the following SSM research reports:

  • Research 2009:15, Improvement and Validation of Weld Residual Stress Modelling Procedure.
  • Research 2009:16, Influence of Hardening Model on Weld Residual Stress Distribution.
  • Research 2009:26, Tillämpning av stabil spricktillväxt vid brottmekanisk bedömning av defekter i sega material.
  • Research 2009:27, Analysis Strategy for Fracture Assessment of Defects in Ductile Materials.
  • Research 2011:19, Experimental Evaluation of Influence from Residual Stresses on Crack Initiation and Ductile Crack Growth at High Primary Loads.
  • Research 2012:07, Implementation of the Master Curve Method in ProSACC.
  • Research 2013:01, Validation of Weld Residual Stress Modelling in the NRC International Round Robin Study.
  • Research 2015:03, Brottmekaniska K-lösningar för sprickor i massiv stång med icke-linjärt rotationssymmetriskt spänningstillstånd.
  • Research 2016:35, Säkerhetsvärdering mot plastisk kollaps vid skadetålighetsanalyser.
  • Research 2016:39, Recommended Residual Stress Profiles for Stainless Steel Pipe Welds.
  • Research 2017:03, Inverkan av inre tryck på sprickytan vid gränslastanalyser.
  • Research 2017:16, Stress Intensity Factor Solutions for Circumferential Cracks in Cylindrical Bars under Axisymmetric Loading and Global Bending.