Validation of the RELAP5 Model of Ringhals 4 against a Load Step Test at Uprated Power

Report, 2015

ABSTRACT After finishing the large component replacement project of the steam generators and the pressurizer, the Unit 4 of the Ringhals Nuclear Power Plant was operated in test mode between 2011 and 2014. In order to reach the ultimate goal of power uprate, and obtain a license for operation at the new nominal conditions, a series of tests had to be accomplished. The R4-QP-101 maneuverability test was performed on 2015-03-03. The test was focusing on evaluation of the system responses for ± 10 % perturbances in the load. The data collected during test provided a good opportunity for verification of the full plant model, which is being developed for the RELAP5/Mod3.3 Patch04 computer code, with incorporation of the new component models. The present Scientific Report introduces the test procedure and shows an overview on the key parameters that are utilized. There is a brief summary given on the applicability field of the computer code. Preparation of the input deck and the nodalization of the primary and secondary sides are touched upon. Strategies applied for achievement of steady-state conditions are addressed in the document. The steady-state results are presented in plotted format, demonstrating how the control system brought the entire unit to stable conditions. The calculated steady-state parameters were very close to the measured plant data, before the transient initiation. A chapter summarizes the results of the validation study using the transient data to simulate the startup test. Quantification of simulation accuracy has proven that the stand-alone RELAP5 thermal-hydraulic model is capable of reproduction of the key features and events of the test. Sufficiently good agreement between the measured and simulated data resulted in a successful verification of the plant model. The Ringhals 4 model is suitable for analysis of other types of transients already in its current state of development. Nevertheless, further refinement in the input is planned as soon as new test data will be available. Keywords: Ringhals 4, Load Step, RELAP5, code validation