Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter January 13, 2022

Analysis of the anticipated transient without scram (ATWS) initiated by emergency power mode through the full scope simulator

Alexandre de Souza Soares ORCID logo and Antonio C. M. Alvim
From the journal Kerntechnik


The integrity of the reactor coolant system is severely challenged as a result of an Emergency Power Mode – ATWS event. The purpose of this paper is to simulate the Anticipated Transient without Scram (ATWS) using the full scope simulator of Angra 2 Nuclear Power Plant with the Emergency Power Case as a precursor event. The results are discussed and will be used to examine the integrity of the reactor coolant system. In addition, the results were compared with the data presented in Final Safety Analysis Report (FSAR – Angra 2) in order to guarantee the validation of the methodology and from there analyze other precursor events of ATWS which presented only plausibility studies in FSAR – Angra 2. In this way, the aim is to provide and develop the knowledge and skill necessaries for control room operating personnel to ensure safe and reliable plant operation and stimulate information in the nuclear area through the academic training of new engineers. In the presented paper the most severe scenario is analyzed in which the Reactor Coolant System reaches its highest level of coolant pressure. This scenario is initiated by the turbine trip jointly with the loss of electric power systems (Emergency Power Mode). In addition, the failure of the reactor shutdown system occurs, i.e., control rods fail to drop into the reactor core. The reactor power is safely reduced through the inherent reactivity feedback of the moderator and fuel, together with an automatic boron injection. Several operational variables were analyzed and their profiles over time are shown in order to provide data and benchmarking references. At the end of the event, it was noted that Reactor shutdown is assured, as is the maintenance of subcriticality. Residual heat removal is ensured.

Corresponding author: Alexandre de Souza Soares, Nuclear Engineering Program – COPPE, COPPE, Federal University of Rio de Janeiro, Av. Horácio Macedo, 2030, 21941-972, Rio de Janeiro, RJ, Brazil, E-mail:

  1. Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: None declared.

  3. Conflict of interest statement: The authors declare no conflicts of interest regarding this article.


Anticipated Transients without Scram for Light Water Reactors. (1978). NUREG-0460, Vol. 1; Staff Report, Division of Systems Safety, Office of Nuclear Reactor Regulation; U.S. Nuclear Regulatory Commission – NRC; Washington, D.C. 20555.Search in Google Scholar

BfS Safety Codes and Guides Translations. (1981). Reaktorsicherheitkommission – RSK (Reactor Safety Commission) Guidelines for Pressurized Water Reactors, 3rd ed., amended 1982, 1984 and 1996.Search in Google Scholar

Bindu, S., Jayanthi, T., SatyaMurty, S.A.V., Swaminathan, P., and Raj, B. (2011). Role of animated human machine interface in nuclear power plant simulation; Indira Gandhi Center for Atomic Research, Kalpakkan, India. Int. J. Simulat. Model., 10–1: 5–16, in Google Scholar

Chen, C.-H., Wang, J.-R., Lin, H.-T., and Shih, C. (2014). ATWS analysis for Maanshan PWR using TRACE/SNAP Code. Ann. Nucl. Energy 72: 1–10, in Google Scholar

Classification, selection and use of nuclear power plant simulators for education and training. Vienna: IAEA-TECDOC-1887, 2019.Search in Google Scholar

Corcuera, P.A. (2003). A full scope nuclear plant training simulator: design and implementation experiences. Spain: University of Cantabria.Search in Google Scholar

Final Safety Analysis Report Angra 2 (FSAR). (2016). Almirante Álvaro Alberto Nuclear Power Plant, Unit 2; Rev. 14.Search in Google Scholar

German Risk Study Nuclear Power Plants – Phase B, A Summary. (1990). “Gesellschaft fur Reaktorsicherheit (GRS) mbH”; GRS-74.Search in Google Scholar

Gűnter, G. (2001). Code System S-RELAP/NLPAN2 user’s guideline, Siemens Work Report SNP NDS1/2001/01/e2005 Rev. 02.Search in Google Scholar

ILK statement on requirements on Anticipated Transients without Scram; ILK-20E; 2005.Search in Google Scholar

Kliem, S., Mittag, S., Rohde, U., and Weiß, F.-P. (2009). ATWS analysis for PWR using the coupled code system DYN3D/ATHLET. Ann. Nucl. Energy 36: 1230–1234, in Google Scholar

Kraftwerk Union Aktiengeseilschaft/KWU. (1984). Nuclebrás simulator manual – plant: Angra 2 (PWR-1300 MW).Search in Google Scholar

Lee, W.J. and Yun, D.J. (2001) Safety significance of inherent moderator density reactivity feedback during ATWS. In: Proceedings of the Korea Nuclear Society Autumn Meeting; (pp. CD-ROM). Republic of Korea.Search in Google Scholar

Leineman, K., Meyder, R., Schanauder, H., and Smidt, D. (2017). A new in-depth training concept for nuclear power plant operators. Nucl. Technol. 71: 125–130, in Google Scholar

McFadelen, J.H., Narum, R.E., Peterson, C.E., Noble, C., Farman, R.F., McClure, J.A., Paulsen, M.P., Richert, K.D., Hughes, E.D., and Gose, G.C. (1988). RETRAN-02 – a program for transient thermal-hydraulic analysis of complex fluid flow systems, NP-1850-CCM-A. EPRI.Search in Google Scholar

Naser, J.A., Sehgal, B.R., and Agee, L.J. (1981). Analysis of pressurizer water reactor Anticipated Transient without Scram transients with RETRAN-02. Nucl. Technol. 54: 311–321, in Google Scholar

Nuclear Power Plant Simulator for Use in Operator Training and Examination. (2009). ANSI/ANS-3.5-2009 – American Nuclear society Standards Committee/Working group ANS-3.5, Illinois.Search in Google Scholar

Oelman, K. (2001). NLOOP Code Manual of Angra Specific Version NLPAN2, Framatome Work Report NDS1/2001/en/0214.Search in Google Scholar

Parzer, I. and Kljenak, I. (2005). ATWS thermal-hydraulic analysis for Krsko full scope simulator Validation. In: International Conference Nuclear Energy for New Europe 2005. Bled, Slovenia, pp. 014.1–014.10, September 5–8.Search in Google Scholar

Plant Operation Manual. (2018a). Angra 2 NPP/eletrobrás Termonuclear SA (ETN) – Emergency Power Case, Vol. II, Class S, Part 2, Chapter 4.4. Section 2; Rev. 24, pp. 1–2.Search in Google Scholar

Plant Operation Manual. (2018b). Angra 2 NPP/Eletrobrás Termonuclear SA (ETN) – monitoring safety functions, Vol. II, Class S, Part 3, Chapter 1.2, Section 3; Rev. 7, p.2.Search in Google Scholar

Rebollo, M.J., Queral, C., Fernández-Cosials, K., Sánchez-Torrijos, J., and Posada, J.M. (2019). Development of phenomena identification ranking table for LONF-ATWS sequences in a Westinghouse PWR. Ann. Nucl. Energy 131: 156–170, in Google Scholar

Swaton, E., Neboyan, V., and Lederman, L. (1987). Human factors in the operation of nuclear power plants – improving the way man and machines work together. Nucl. Power Saf. 29: 27–30.Search in Google Scholar

Technical Report on Anticipated Transients without Scram for Water-Cooled Power Reactors (1973). Regulatory staff United States Atomic Energy Commission – US-AEC, Washington, D.C. 20545.Search in Google Scholar

Use of Control Room Simulators for Training of Nuclear Power Plant Personnel. Vienna: IAEA-TECDOC-1411, 2004.Search in Google Scholar

Zimmermann, M.A. (1992). Transient analysis of the MSIV-ATWS in a 1000 MW (thermal) BWR-4. Nucl. Technol. 100: 184–192, in Google Scholar

Received: 2021-08-16
Published Online: 2022-01-13
Published in Print: 2022-04-26

© 2021 Walter de Gruyter GmbH, Berlin/Boston