Plenary Lectures Abstract


P-1
Ageing and Life Management Covering Full Life Cycle of NPPs with SNPTC’s Practice
Yikang DOU
Chief Engineer and Research Fellow at Shanghai Power Equipment Research Institute under SNPTC

Abstract

According to Chinese Nuclear Safety Guideline Ageing Management for Nuclear Power Plants (HAD 103/12) published by NNSA in 2012, ageing management should be carried out in all stages of full life cycle of NPPs, including design, construction/manufacture, commissioning, operation including operation license extension (OLE) period and decommissioning. This presentation explains in detail on ageing management activities for all individual stages, combining with practice in Chinese nuclear power development programme. Differing from traditional ageing management practice which focuses only on operational stage, the full life cycle ageing management emphasizes early actions at design and manufacture/construction stage to ensure robustness and health of critical SSCs. Some significant ageing mechanisms for typical SSCs are demonstrated. The presentation also analyses the challenges in implementation of full life cycle ageing management covering not only in safety aspects but also in economic aspects on design conception, modes of construction, manufacture, commissioning, equipment qualification, O&M, licensing maintenance, OLE and decommissioning for NPPs. Some examples based on SNPTC’s practice on full life cycle management for NPPs are illustrated.
E-mail: douyikang@speri.com.cn


P-2
Maintenance Science and Technology for Light Water Reactor Safety and Knowledge Management
Naoto SEKIMURA
Professor at Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo

Abstract

Current status of nuclear power plants in Japan reflecting updated nuclear regulation systems will be summarized. Roadmap for light water reactor safety technology, human resource and knowledge management has been discussed under the collaborative activity between Atomic Energy Society of Japan and the Advisory Committee for Natural Resources and Energy in METI. This roadmap describes wide variety of research topics for near term and long term issues including improved maintenance technology and knowledgebase development after the Fukushima Accident. Operational safety with improved regulatory inspection systems will also be discussed mainly focusing on voluntary improvement of safety by risk management activities by operators
E-mail: sekimura@n.t.u-tokyo.ac.jp


P-3
Enhance Safety of NPPs and Activities of Japan Society of Maintenology
Tadashi NARABAYASHI
Professor at Hokkaido University, and President of Japan Society of Maintenology

Abstract

As the president of Japan Society of Maintenology (JSM), JSM established a Nuclear Regulatory Improvement Meeting (NRIM). The meeting members examined the severe accident process in the 1st 2nd and 3rd units of Fukushima Daiichi NPS, and found the vent by FCVS should be done before water injection into the core. The PCV spray and water injection into the pedestal basement should be also the countermeasures to the severe accident. Countermeasures for an intentional aircraft collision should be installed too.
Upon occurrence of a severe accident (SA), vent gas with radioactive fission products is blown out to a scrubbing pool through numerous venturi nozzles. Mist in steam moves upward to a metal fiber filter through a multi-hole baffle plate. After the mist is removed by that filter, radioactive methyl iodine (CH3I) is captured on the surface of a molecular sieve or AgX, made from zeolite particles with silver coating. A FCVS visualized test facility was installed at Hokkaido University. An AgX filter is used down-stream of the scrubbing pool and metal fiver filter. By using the FCVS technology, we had started to develop a high decontamination air cleaning system to remove multi-nuclides for radiation protection to conduct decommissioning the Fukushima NPP. NRIM proposed improved analysis model of tornado, speed up of restart evaluation process by types of NPP and site conditions, etc. to the Japanese Nuclear Regulatory Authority (NRA).
E-mail: tnaraba@eng.hokudai.ac.jp


P-4
LCF and HCF of Austenitic Stainless Steels – ND-Monitoring of Physical Properties to Predict the SN Curve due to the PHYBAL-Procedure for Lifetime Determination
Gerd DOBMANN
Senior Scientific Consultant and Chair of Nondestructive Testing and Quality Assurance, Saar-University

Abstract

The need to reliably perform a fatigue life assessment is obvious, if we have the ageing infrastructure in our power plants in view. Concerning components manufactured in austenitic stainless steel, in Germany, in PWR, we do not have in the primary circuit, as main cooling line (MCL), an austenitic component. The German design is based on pipes, made from the same steel grade as the reactor pressure vessel (RPV) – but cladded on the inner side by austenitic stainless steel. Therefore, Germany, for instance, has not the NDT inspection problems, other countries have, with the dissimilar metal weld between RPV nozzle and MCL. However, the surge line and the pressurizer spray line are fully made from austenitic stainless steel and they are exposed to thermomechanical fatigue. Concerning their fatigue behavior over lifetime of a NPP, many open questions still exist. Therefore, these steels are in the focus of nuclear safety research.
The material of interest is the metastable steel X6 CrNiTi 1810 (1.4541) or X6 CrNiNb 1810 (1.4550). Both have the characteristic, due to accumulated plastic deformation under fatigue loading at lower temperatures, by phase-transformation from the austenitic fcc--phase, to develop the bcc-’-martensitic phase. As ferromagnetic phase, the -’-martensite is magnetized due to the Villari effect in the gyromagnetic field, and, can be detected by sensitive magnetic sensors. Therefore, it is the objective of NDT, to develop a monitoring technique.
The paper describes fatigue experiments, monitoring the material in the servo-hydraulic fatigue machine and the development of the PHYBAL procedure for physically based life evaluation. This new technology, in contrast to the standardized SN-Curve evaluation, only asks for a small number of specimens. In case of a homogeneous material, only three tests, 1 incremental step test and 2 constant amplitude tests, are required for the estimation of a complete S-N-fatigue curve by calculation.
By monitoring the fatigue tests on the austenitic stainless steel samples with electromagnetic NDT such as eddy current impedance measurement by using a GMR (giant magnetic resistor) as a sensor, in addition, electrical resistance- and temperature-development are monitored. The information is fit in the PHYBAL interpretation model, to calculate SN-Curves. Modeled SN-curves are compared with the experimental-ones, determined according the standard procedure.
E-mail: gerd.dobmann@t-online.de


P-5
Why graphite? A Structural Study from the atomic to macro scales
C. (Katia) PAPPAS
Full Professor and Group Leader of 'Neutron and Positron Methods in Materials', Delft University of Technology

Abstract

X-ray diffraction (XRD) is the standard method for investigating the microscopic structure of bulk graphite. The analysis of XRD patterns, however, is not trivial because the Bragg peaks are asymmetric and broad due to several factors, such as the high penetration depth of X-rays, the fluctuations in lattice spacing and the stacking disorder between the carbon layers. However, it is not easy to properly account for these effects in a standard Rietveld refinement, because disorder in graphite is complex due to the inherent anisotropy of the layered structure. In order to overcome these difficulties, we adopted a model [1], which has been developed for graphite and can account for both X-ray and neutron diffraction patterns [2, 3]. We will discuss the applicability limits of this model as well as the deduced structural parameters for non-irradiated and irradiated graphites [4].
The exploration of the mesoscopic structure of the pores must cover a larger range of length scales and for this purpose we have combined three neutron-based techniques: SANS, Spin Echo SANS (SESANS) and imaging to cover lengths from nm to mm [5]. The results reveal a fractal structure over an extraordinary large scale of lengths that spans 6 orders of magnitude and has fractal dimensions close to 2.5, a case where surface and mass fractal dimensions coincide. This is expected for high disorder, ramification and connectivity of the pore structure, as in the case of percolating clusters and the fractured ranked surfaces, that could serve as a model for Mrozowski cracks.
The combination of the structural information at the atomic and mesoscopic levels allows to understand the effect of irradiation damage and why the modification of the microscopic structural parameters is not directly related to macroscopic observations, such as the dimensional changes.
[1] Shi H. Disordered Carbons and Battery Applications. Simon Frasier University, Ph.D. thesis, (1993); Shi H, Reimers JN, Dahn JR. Structure-refinement program for disordered carbons. J Appl Crystallogr 26, 827–36 (1993);
[2] Z. Zhou, et al. Interpretation of X-ray diffraction patterns of (nuclear) graphite. Carbon 69, 17–24 (2014).
[3] Z. Zhou, Thesis Delft University of Technology (2016) doi: 10.4233/uuid: 72b9197e-28b4-4c3d-9fef-ec56df16da1b
[4] Z. Zhou et al. Influence of neutron irradiation on the microstructure of nuclear graphite: An X-ray diffraction study,
submitted to Journal of Nuclear Materials;
[5] Zhou, Z. et al. From nanopores to macropores: Fractal morphology of graphite. Carbon 541–547 (2016).
doi:10.1016/j.carbon.2015.09.069;
E-mail: c.pappas@tudelft.nl


P-6
MD Study of Radiation Effects in Ti-Al Based Structural Intermetallic Compounds
Roman VOSKOBOINIKOV
Senior Scientist at National Research Centre 'Kurchatov Institute', and Head of Department at National Research Nuclear University MEPhI

Abstract

Collision cascades are the primary source of radiation damage in structural materials subjected to fast particle irradiation. They are formed by the recoil of primary knock-on atoms (PKA) with the energy of more than ~1 keV. The cascade process is characterized by the length and time scale of the order of nm and ps, respectively, which is prohibitive for experimental investigation but it can be studied by molecular dynamics (MD) simulations.
MD simulations were applied to investigate primary damage formation in collision cascades in L10 TiAl and D019 Ti3Al intermetallic compounds over a wide range of temperature, 100K < T < 1200K, and primary knock-on atom energy, 5keV < EPKA < 20keV. At least 24 cascade for each (EPKA, T) set were simulated in order to provide statistical reliability of the results. A thorough analysis of the obtained results was carried out. The number of Frenkel pairs, fraction of Al and Ti vacancies, self-interstitials and anti-sites, typical point defect clusters, cluster per cascade yield, etc. were found as a function of (EPKA, T).
Both intermetallic compounds demonstrate anomalously high resistance against the formation of primary radiation defects. Understanding and controlling energy dissipation in intermetallic compounds may pave the way for new design principles of radiation-tolerant structural materials for nuclear engineering applications.
E-mail: roman.voskoboynikov@gmail.com