Improved methodology for generation of axial flux shapes in digital core protection systems Gyu-Cheon Lee a, *, Won-Pil Baek b , Soon Heung Chang c a Korea Power Engineering Company, Inc.,150 Dukjin, Yuseong, Daejeon, South Korea b Korea Atomic Energy Research Institute, 150 Dukjin, Yuseong, Daejeon, South Korea c Korea Advanced Institute of Science and Technology, 373-1 Gusung, Yuseong, Daejeon, South Korea Received 17 April 2001; received in revised form 22 June 2001; accepted 22 June 2001 Abstract An improved method of axial flux shape (AFS) generation for digital core protection sys- tems of pressurized water reactors is presented in this paper using an artificial neural network (ANN) technique—a feedforward network trained by backpropagation. It generates 20-node axial power shapes based on the information from three ex-core detectors. In developing the method, a total of 7173 axial flux shapes are generated from ROCS code simulation for training and testing of the ANN. The ANN trained 200 data predicts the remaining data with the average rootmeansquareerrorofabout3%.Thedevelopedmethodisalsotestedwiththerealplantdata measured during normal operation of Yonggwang Unit 4. The RMS errors in the range of 0.9  2.1% are about twice as accurate as the cubic spline approximation method currently used in the plant. The developed method would contribute to solve the drawback of the current method as it shows reasonable accuracy over wide range of core conditions. # 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction A nuclear power plant should be operated by maintaining a sufficient margin from acceptable fuel design limits in terms of departure from nucleate boiling ratio and local power density; this is usually achieved by plant monitoring systems and pro- tection systems. Annals of Nuclear Energy 29 (2002) 805–819 www.elsevier.com/locate/anucene 0306-4549/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0306-4549(01)00076-7 * Corresponding author. Tel.: +82-42-868-8750; fax: +82-42-861-1485. E-mail address: gclee@ns.kopec.co.kr (G.-C. Lee).