PSI - Issue 28

ScienceDirect Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2020) 000–000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2020) 000–000 Available online at www.sciencedirect.com Procedia Structural Integrity 28 (2020) 1918–1929

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1st Virtual European Conference on Fracture A combined CFD and FEM analysis of pressurized thermal shock applied to the probabilistics of cleavage fracture Casper Versteylen a, *, Heleen Uitslag-Doolaard a , Lorenzo Stefanini a , Frederic Blom a a NRG Petten, Westerduinweg 3, 1755 LE Petten. In a nuclear power plant, the integrity of the pressure vessel which contains the primary water is paramount. In case of an accident involving the guillotine break of primary system piping there can be a sudden loss-of-coolant accident (LOCA). During such an incident, the reactor core needs to be cooled for some period after its shut-down (residual heat removal). The emergency core cooling is achieved by the injection of cold water in the still pressurized reactor pressure vessel (RPV). The combination of pressure and thermal stresses provides a complex stress state in the RPV wall: a pressurized thermal shock (PTS). The RPV material is generally a ferritic steel. The critical stress intensity for brittle cleavage fracture depends on the ductile to brittle transition temperature. This complex combination of stresses, absolute temperatures and temperature gradients in combination with radiation damage requires an integral approach for the evaluation of the probability for the occurrence of cleavage fracture. This problem is simulated with a combined CFD and FEM approach. A quarter of the reactor pressure wall including the cooling nozzle is simulated during the 1000 seconds of the cooling transient. This method can accurately predict the thermal profile and the corresponding stress field. This approach is applied to a reactor pressure vessel containing pre-existing semi-elliptical cracks. The stress intensities for every time step, the temperature, the effects of radiation damage, and the material properties of two types of RPV steel; (SA 508gr.3 and SA-508gr.4N) contribute to the probability for a brittle cleavage crack to form. An estimation of the probability for cleavage fracture is made through the Master Curve approach. These probabilities are calculated for different crack locations, sizes, aspect ratios and for two different grades of RPV steel. The influence of these geometric factors and material properties under the influence of radiation have been analysed. The material just below the nozzle is cooled down further and the thermal gradient is more severe. This is reflected in a higher probability for cleavage fracture. The new generation of RPV steel; SA-508gr.4N is very promising for its resistance to radiation induced embrittlement and for its higher strength, both factors leading to a lower probability of cleavage fracture in the reactor pressure vessel. Increasing the safety of the RPV. 1st Virtual European Conference on Fracture A combined CFD and FEM an lysis of pressurized thermal shock applied to the probabilistics of cleavage fracture Casper Versteylen a, *, Heleen Uitslag-Doolaard a , Lorenzo Stefanini a , Frederic Blom a a NRG Petten, Westerduinweg 3, 1755 LE Petten. Abstract In a nuclear power plant, the integrity of the pressure vessel which contains the primary water is paramount. In case of an accident involving the guillotine break of primary system piping there can be a sudden loss-of-coolant accident (LOCA). During such an incident, the reactor core needs to be cooled for some period after its shut-down (residual heat removal). The emergency core cooling is achieved by he injection of cold wat r in the til pressurized reac or ressu e vess l (RPV). The combinati n of pressure a d thermal stresses provid s a complex stres state n the RPV wall: a pressurized thermal shock (PTS). The RPV material is generally a ferritic steel. The critical str ss int nsity f r brittle cleavage frac ure depends on t ductile to brittl transition temperature. This complex combination of stresses, bsolu e temperatures an t mpe ature gradient in combination with r d ati n damage requir s an in egral a proach for the evaluation of the probability for the occurr nce of c eavage fracture. This problem is simulated with a combin d CFD and FEM approach. A quarter of he reactor pressure wall includi g t cool ng nozzle is simulated during the 1000 econds of the cool ng transi nt. This me hod can ccurately predict he thermal profile and he correspond ng stress field. Thi pproach is lied to a reactor pressure vess l c ntain ng p e-existing s mi-elliptical cracks. Th stre s intensitie for every time step, the temperature, the effects of radiation damage, nd the material properties of two types of RPV teel; (SA 508gr.3 and SA-508gr.4N) contribute to the probability for a brittle leavage c ack o form. An estimation of probability for cleavag fracture is made through the Master Curv approach. These probabiliti s are calculat d for different crack locatio s, izes, asp ct atios and for two diff ent grad s o RPV steel. The influence of these geometric factors and material propertie under the influence of radiation have been analysed. The m ter al just below the nozzle is ooled down further nd the t rmal grad ent is more seve e. This is refl cted in a igher probability for cleavage fracture. The new generation of RPV st el; SA-508gr.4N is v ry promising for its resistance to adiation induced embrittlem nt and for its high r streng h, both factors le ding to a lower probability of cl avage f cture in the reactor pres ure vessel. Increasing the safety of the RPV. © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-re iew under responsibility of the European Structural Integrity Society (ESIS) ExCo Abstract

* Corresponding author. E-mail address: Versteylen@nrg.eu

2452-3216 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo  2452-3216 © 2020 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo 2452-3216 © 2020 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo * Corresponding author. E-mail address: Versteylen@nrg.eu