KTA 3206: Vessel Fracture Exclusion (Six-Step Method) Alpha · 2026-09-24

Postulated-crack six-step check of a cylindrical shell per KTA 3206 (2014-11) Annex A 3.1

KTA 3206: Vessel Fracture Exclusion (Six-Step Method)

KTA 3206 is the German nuclear safety standard for showing "fracture exclusion (Bruchausschluss)" in pressure-retaining components of nuclear power plants. This calculator runs the six-step procedure of Annex A 3.1 (Bild A-5) for a cylindrical shell with a postulated axial, inner-surface crack under internal pressure only.

The goal is different from a leak-before-break check: it shows that under Level A/B (operating) loads the crack does not initiate, and under Level C/D (fault) loads it only grows by a limited, stable amount. There is no through-wall or leak-rate step.

The analysis runs these steps:

  1. Take the postulated initial crack a_a, 2c_a (at least the NDE assessment limit of KTA 3201.4).
  2. Take the end-of-life crack a_e = a_a+\Delta a, 2c_e = 2c_a+\Delta 2c from an external fatigue crack growth analysis.
  3. Compute the applied J-integral J_{appl}(a,P) of the axial surface crack (manual solution, Annex B 2.2.2 (3) a), using the tables of F and h_1).
  4. Find the initiation toughness J_i (measured, or from the Charpy upper-shelf energy via Eq. C 2-1).
  5. Find the smallest crack depth a_i at which J_{appl}(a,p_{AB}) \ge J_i under Level A/B pressure.
  6. Find the expected ductile extension \Delta a_{CD} under Level C/D pressure: the first crossing of the material J-R curve and the applied-J curve.

Fracture exclusion is shown when both criteria hold:

  • fa) a_e < a_i — the end-of-life crack is smaller than the smallest initiating crack (no initiation under Level A/B).
  • fb) \Delta a_{CD} exists and is within the validated range of the J-R curve, \Delta a_{CD} \le \Delta a_{max} (only limited, stable extension under Level C/D).

Scope and limits:

  • Cylindrical shell, internal pressure only, axial inner-surface crack (manual solution for an infinitely long flaw — a conservative envelope for a finite surface crack).
  • Nozzle corners, spherical shells/heads, circumferential cracks and loads other than internal pressure are not covered.
  • Valid for 1 \le n \le 10, 0 < a/s \le 0.75, and s/R_i within the table range 1/20 to 1/5 (outside this range, use FEM instead).
  • The material must be on the upper shelf of the impact energy curve; the Charpy correlations do not apply to dissimilar-metal welds.
  • The J-R curve must already account for the component's multiaxiality (KTA 3206, A 3.1 (2) e), C 3 (4)) — this calculator does not apply a multiaxiality correction.

Engineering data

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