Comparative Analysis of Methodological Approaches to the Calculational Determination of the Forces Acting on the VVER-1000 Reactor Support Elements

V. O. Posokh¹, V. V. Inyushev¹, A. S. Koliadiuk¹, A. S. Koshmak¹,
V. O. Dubkovsky²

¹SE “State Scientific Engineering Center for Control System and Emergency Response”, 64/56, Heroiv Stalinhrada ave, Kyiv, 04213, Ukraine
²Odessa National Polytechnic University, 1, Shevchenko ave, Odesa, 65044, Ukraine

DOI: doi.org/10.31717/2311-8253.20.2.2

Abstract

The results of the comparative analysis of two methodological approaches to the calculational determination of the forces acting on the support elements through the reactor vessel from the connected main circulation pipelines and pipelines of the emergency cooling system are provided. First approach is that the stiffness of all reactor support elements (support ring, thrust ring and separating bellows) is taken into account in the beam model (for the first time it was applied in the calculations performed within justification of Khmelnytskyi NPP Unit 1 lifetime extension). The second approach is that only the stiffness of support ring and thrust ring is taken into account in the beam model (was applied, in particular, within justification of Zaporizhzhya NPP Unit 3 lifetime extension). Comparative analysis of the results of the calculation of the reactions of the supports showed that the difference reaches significant values, both in percentage (up to 120 %) and in numerical terms (up to 844 kN • m). In order to assess the significance of the abovementioned results, an assessment of the stress-strain state on the example of the support ring was carried out. The results indicate that the greatest changes with the use of different approaches occur for horizontal forces on the fixator of the support beam. With the use of the second approach, there is an increase in the forces on the fixator by about two times compared with the results obtained using the first approach. This is due to a significant change in the torque acting on the support ring when considering the separating bellows. The obtained results show that the membrane and bending stresses for the first approach of force determination show much lower values. The values for these stress categories are lower by 16-30 % compared to the second approach. This indicates excessive conservatism of the calculated stresses for VVER-1000 reactor support elements in previous works of lifetime extension justification. Such conservatism could increase the resulting value of the accumulated cyclic load, which in turn could impose a restriction on the reassignment of the allowable number of load cycles.

Keywords: reactor support elements, reactor vessel, lifetime extension, calculational substantiation of safe operation, stiffness characteristics.

References

1. Posokh V. O., Inyushev V. V., Kolyadyuk A. S., Dubkovsky V. O. (2019). [Analysis of existing approaches to the calculated substantiation of the reactor support elements safe operation]. Yaderna energetyka ta dovkillia [Nuclear Power and the Environment], vol. 15, no. 3, pp. 36-41. (in Ukr.)

2. Posokh V. O., Vasilchenko V. M., Kolyadyuk A. S., Dubkovsky V. O. (2019). [Determination of stiffness characteristics for WWER-1000 support components]. Yaderna ta radiatsiina bezpeka [Nuclear and Radiation Safety], vol. 84, no. 4, pp. 12-17. (in Ukr.)

3. Posokh V. O. [Methodological approaches to determining the forces acting on the VVER-1000 reactor support elements under power unit operating loads]. Yaderna energetyka ta dovkillia [Nuclear Power and the Environment], vol. 16, no. 1, pp. 3-9. (in Ukr.)

4. 1160.01.02.000 SB. Support ring. Assembly drawings. 1981, 4 p. (in Russ.)

5. PNAE G-7-002-86. Standards for strength calculation of equipment and pipelines of nuclear power plants [introduced with changes on 07/01/1987]. Moscow: Energoatomizdat, 1989, 525 p. (in Russ.)

6. Posokh V. O., Oborskyi I. O., Kurov V. O. (2016). [Approaches to the assessment of cyclic strength of NPPs pipelines and equipment by program complex APM Structure 3D]. Yaderna energetyka ta dovkillia [Nuclear Power and the Environment], vol. 8, no. 2, pp. 4-14. (in Russ.)

7. Posokh V. O., Bakhtina K. V., Kurov V. O. (2017). [Choice of a method for determining the cyclic loading parameters for calculating the accumulated and predicted damage of NPP equipment elements]. Yaderna energetyka ta dovkillia [Nuclear Power and the Environment], vol. 9, no. 1, pp. 4-12. (in Russ.)

Full Text (PDF)