FI9800067 LAPPEENRANNAN TEKNILLINEN KORKEAKOULU UDK 621.1 LAPPEENRANTA UNIVERSITY OF TEHCNOLOGY 621.039 621.311.25 TIETEELLISIA JULKAISUJA RESEARCH PAPERS 43 THIRD INTERNATIONAL SEMINAR ON HORIZONTAL STEAM GENERATORS LAPPEENRANTA 1995 ISBN 951-763-942-2 ISSN 0356-8210 THIRD INTERNATIONAL SEMINAR ON HORIZONTAL STEAM GENERATORS October 18-20, 1994, Lappeenranta, Finland LTKK W ENERGY WO 1 THIRD INTERNATIONAL SEMINAR ON HORIZONTAL STEAM GENERATORS 18 — 20 October 1994, Lappeenranta, Finland PREFACE Insufficient understanding of realistic thermal hydraulic behaviour of the horizontal steam generators was recognised few years ago when performing safety analyses for VVER reactors. To improve the situation, Finnish nuclear organisations took an initiative to start international cooperation to gather existing experimental and theoretical knowledge of the behaviour of horizontal steam generators under normal operation, transient and accident conditions. Consequently, two International Seminars of Horizontal Steam Generator Modelling were arranged in March 1991 and September 1992 in Lappeenranta, Finland. The seminars concentrated on thermal hydraulic experiments and analytical modelling of the flow behaviour both in the primary side and in the secondary side. The experience from these seminars was most encouraging. New experimental results, comparisons of existing experimental facilities and approaches to calculational modelling were presented. Particularly, the participants experienced the seminars as a useful forum for fruitful discussions. In the final discussions of the second seminar, a common agreement was that continuation of cooperation would be beneficial, and that the scope of the seminars could be enwidened to structural and aging issues. A general feeling among the participants was that it might be very beneficial to bring structural and thermal hydraulic experts together in the next seminar, since difficulties in governing the interface of these areas were detected. The third seminar consisted of six sessions. The topics were thermal hydraulic experiments and analyses, primary collector integrity, management of primary-to-secondary leakage accidents, feedwater collector replacement and discussion of WER-440 steam generator safety issues. As previously, the organisers were I VO International Ltd, Lappeenranta University of Technology (LTKK) and VTT Energy, but now in collaboration with the International Atomic Energy Agency (IAEA). Session I demonstrated that the experimental basis of the thermal hydraulic behavior is not yet sufficiently wide. New results were available only from two integral facilities, i.e. Finnish PACTEL and Hungarian PMK. The PACTEL results with a new steam generator are encouraging, and the experiments will continue. The theoretically predicted flow reversal in the lower tube bundle was now clearly found in the PACTEL experiments. The discussion also indicated that the same would be true for the PMK2 experiments. Dr. S.A. Logvinov of Gidropress discussed the separate effect experiments directed to study the flow distribution in the feedwater distributor of PGV-440. The results help to explain the corrosion-erosion mechanism, which has been found to cause damage to the distributor. Another paper was presented concerning the Czech results of the influence of \ 11 the new feedwater distributor on the impurity distribution. Session II of thermal hydraulic analyses gathered the most papers. The calculational efforts should meet two clearly different objectives. First, the modelling capability of the system codes should be developed to such a level that would satisfy the need to calculate the steam generator behaviour during all conditions, and particularly during transient and accident conditions. Secondly, there is a need for more accurate flow calculations to predict the fluid flow conditions on the steam generator secondary side. To do this, 3-D calculation codes have been developed. Such calculations were deemed to be of a crucial importance for determining thermal hydraulic boundary conditions for the structural evaluations of any proposed design changes. Good examples of such changes are the primary collector replacements and lifetime definitions, and feedwater distributor replacements. The applications of system codes RELAP5, ATHLET, CATHARE, AFROS and DINAMIKA were presented. This work is going on in all the participating countries. The main issues of code application are whether the 1-D nodalization model is sufficient, how detailed nodalization is required, and how to obtain relevant data for validation and assessment. It was pointed out that the most significant resolution of nodalization problems is tailoring according to the application. The safety analyzer should understand well the role and importance of the model from the viewpoint of the specific application. Too detailed models may become unpractically large for the computer capacity. On the other hand, too simple models may give totally wrong picture of the process. The design calculation codes and models were discussed in six papers. The lack of sufficient experimental data to support the development was again recognized here. Some help to the situation can be expected, since a steam generator data bank is being collected in Russia as presented by Dr. Vasiljeva. In the near future this data bank will be made available, and it should be useful for the model development and validation purposes. Primary collector integrity was a topic of Session III. The main issues are the thermal loadings of the PGV-4 (WER-440) primary collector, and the integrity of the tube connection part of the cold primary collector of PGV-1000. Thermal hydraulic conditions as well as plant operations have a strong influence on these integrity issues. A large leakage accident from the primary-to-secondary side (PRISE) is possible in the horizontal VVER steam generators. The break can be a lift-up of the primary collector cover, or a ductile failure of the collector wall in the area of tubing connections. That is why the large PPRISE accidents (the break area up to 90 —100 cm2) are defined as a design basis accident for the VVER plants e.g. in Finland. Session IV discussed, how such PRISE accidents can be effectively managed. The analysis task is particularly difficult, since the PRISE management relies to a large degree on successful operator actions. The different management concepts require well established analyses, and preferentially also the simulator support. The probability aspects were discussed based on the quantification results of the Loviisa PSA study. A very acute problem of the feedwater distributor experiencing severe erosion-corrosion problems in the PGV-4 was the topics of Session V. Two principally different designs exist for replacing the eroded pipe sections. One is developed by Gidropress of Russia, and it Ill has been installed into six steam generators in the Ukrainian Rovno plant, and into one at Loviisa Unit 2. The design employs the idea of locating the new distributor and of injecting the feedwater through the short nozzles above the tube bundle. The other design has been developed in Czech Republic by Vitkovice. Again the distributor locates above the tube bundle, but the feedwater is injected in the middle of the tube bundle through long nozzles. Such feedwater distribution systems have been installed into sixteen steam generators at Dukovany. A modified version with a mixing chambre has been installed into two steam generators at Bohunice Unit 3. Very active discussion was conducted concerning the practical and theoretical questions. Final Session VI was organized as a panel discussion. The panelists expressed their opinion concerning the prioritization of the VVER steam generator safety issues. The discussion has been summarized by Dr. Strupczewski, the session chairman, in the last paper of these proceedings. The continuation of this Seminar was suggested and recommended by a number of participants. Also, the IAEA is willing to continue the support. The Finnish organizers proposed tentatively to have the next seminar in Lappeenranta in summer 1996. Harri Tuomisto, WO IN Heikki Purhonen, VTT Timo Haapalehto, LTKK Andrzej Strupczewski, IAEA \ IV THIRD INTERNATIONAL SEMINAR ON HORIZONTAL STEAM GENERATORS 18 - 20 October 1994, Lappeenranta, Finland PROGRAMME Tuesday. 18 October 1994 8:30 Registration 9:00 Opening of the Seminar Prof. Heikki Kalli, LTKK 9:15 Aim and Programme of the Seminar Dr. Harri Tuomisto, IVO International Session I THERMAL-HYDRAULIC EXPERIMENTS OF HORIZONTAL STEAM GENERATORS Chair: Dr. N. Trunov, Gidropress, Russia Co-Chair: Prof. H. Kalli, LTKK, Finland 9.30 J. Kouhia, V. Riikonen, H. Purhonen (VTT Energy, Lappeenranta, Finland) PACTEL: Experiments on the Behavior of the New Horizontal Steam Generator 10.00 Gy. Ezsol, L. Szabados, I. Trosztel (AEKI/KFKI, Hungary) PMK-2 Experiment Study on Steam Generator Behaviour 10.30 Coffee Break 11.00 S.A. Logvinov, V.F. Titov (OKB Gidropress, Russia), M. Notaros, I. Lenkei (Paks NPP, Hungary) Thermohydraulics of PGV-4 Water Volume During Damage of the Feedwater Collector Nozzles 11.30 L. Papp (Vitkovice, Czech Republic) Influence of Feedwater and Blowdown Systems on the Mineral Distribution in WWER Steam Generators 12.00 V. Yijola (VTT Energy, Finland) Results of Questionnaire for the Needs of Measured Data for the Steady-State Calculations V 12.15 Discussion on Session I 12.30 Lunch Session Ila THERMAL-HYDRAULIC ANALYSES OF HORIZONTAL STEAM GENERATORS Chair: Mr. S. Savolainen,