PSI - Issue 23

ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000 – 000 Sci nceDirect Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Procedia Structural Integrity 23 (2019) 589–594

© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the ICMSMF organizers © 201 9 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. Abstract Reactor graphite i used as t e mater al for th graphite stack of Russian RBMK power reactors. Lon -term op ration of the reactor’s graphite stack at hig operat ng tempera ur s (500 - 700)°С and neutron irr diatio leads to a significan degrad tion f th gr phite’s propert s, which m y l mit the lifetime of the entire nuclear power plan . In this paper properti s d gradation mechanisms of graphite materials at different stages of RBMK reactors operation was studied to justify their service life. © 201 9 The Authors. Published by Elsevier B.V. This is an ope access article under h CC BY-NC-ND lic nse (http://creativecommon org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. 9th International Conference on Materials Structure and Micromechanics of Fracture Radiation degradation mechanisms of reactor graphites properties B.A. Gurovich, D.A. Kuleshov, D.A. Maltsev * , O.K. Chugunov, A.S. Frolov, Ya.I. Shtrombakh National Research Center “Kurchatov Institute”, 1, Akademika Kurchatova pl., Moscow, 123182, Russia Abstract Reactor graphite is used as the material for the graphite stack of Russian RBMK power reactors. Long-term operation of the reactor’s graphite stack at high operating temperatures (500 - 700)°С and neutron irradiation leads to a significant degradation of the graphite’s properties, which may limit the lifetime of the entire nuclear power plant. In this paper the properties degradation mechanisms of graphite materials at different stages of RBMK reactors operation was studied to justify their service life. 9th International Conference on Materials Structure and Micromechanics of Fracture Radiation degradation mechanisms of reactor graphites properties B.A. Gurovich, D.A. Kuleshov, D.A. Maltsev * , O.K. Chugunov, A.S. Frolov, Ya.I. Shtrombakh National Research Center “Kurchatov Institute”, 1, Akademika Kurchatova pl., Moscow, 123182, Russia 1. Introduction Reactor graphite is a composite material comprising the coke (filler) and binder particles. There is a porosity of various types between and within these particles, which total fraction can reach 25-27%. The filler and binder regions differ significantly in constituent crystallite average sizes. The typical crystallite size along the c axis in the filler is ~ 40-100 nm [1], while for the binder this size is significantly smaller (~ 3- 10 nm along the с axes). Both the filler and the binder regions consist of regions with different preferential orientation of the crystallites (basic planes) with lenticular (Mrozowski) cracks (Fig. 1а). Another type of porosity occurs due to the release of gaseous products during graphitization (the technological processes of nuclear graphite manufacturing). The complex regularities of dimensional changes and changes of the physical and mechanical properties of reactor graphite under operation are due to the peculiarities of its structure [2-4]. Under irradiation, the gradual closure of the Mrozowski cracks and other pores in the compression regions, which are caused by the crystallites interaction. Thus crystallites compressed along the с axes and stretched along the a axis. This is the shrinkage stage of polycrystalline graphite (fig. 1b). 1. Introduction Reactor graphite is a composite material comprising t e coke (filler) and binder particles. re is a porosity of var u typ s between and within th se particles, which total fraction can reach 25-27%. The fill r and binder region differ sig ificantly in constituent crystallite average sizes. The typical crystallite size along the c axis in is ~ 40-100 nm [1], while for the binder this size is significantly smaller (~ 3- 10 nm along the с axes). Both the filler a d the binder regions onsist of regions with differ nt preferential orientation of th crystallites (basic planes) with lenticular (Mrozowski) cracks (Fig. 1а). Another type of porosity occurs due to the release of gaseous products during graphitization (the t chnological processes of nuclear gr phite manufacturing). The compl x regularities f dimensi nal changes and changes of the physical and mechanical properties of reactor graphite under ope tion are d e t the peculiarities of its tructure [2-4]. Under irradiation, the gradual closure of t e M ozowski cracks and other pores in the compression regions, w ich re caused by the crystallites interaction. Thus crystallit s compressed along the с axes and stretched along the a axis. This is the shrinkage stage of polycrystalline graphite (fig. 1b). Keywords: Nuclear graphite, neutron irradiation, power reactor, graphite, RBMK, fractographic analysis, SEM Keywords: Nuclear graphite, neutron irradiation, power reactor, graphite, RBMK, fractographic analysis, SEM

* Corresponding author. Tel.: +0-000-000-0000 . E-mail address: nrcki@nrcki.ru * Corresponding author. Tel.: +0-000-000-0000 . E-mail address: nrcki@nrcki.ru

2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an ope acces article under CC BY-NC-ND lic nse (http://creativecommon org/licenses/by-nc-nd/4.0/)

Peer-review under responsibility of the scientific committee of the IC MSMF organizers.

2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the ICMSMF organizers 10.1016/j.prostr.2020.01.150