Izvestiya vuzov. Yadernaya Energetika

The peer-reviewed scientific and technology journal. ISSN: 0204-3327

Computational and experimental studies on the causes of crack network formation in the area of the heat exchanger tube sheet in the BN-600 reactor

4/04/2015 2015 - #01 Nuclear materials

Vilenskij O.Yu. Krylov A.N. Osipov S.L. Osetrov D.L. Rogozhkin S.A. Margolin B.Z. Prokoshev O.Yu. Pozdnyakov M.L. Gulenko A.G.

DOI: https://doi.org/10.26583/npe.2015.1.06

UDC: 621.039.5:539.4 БН

In order to examine the condition of intermediate sodium-to-sodium heat exchangers (IHX) and to substantiate their operation life extension to 45 years in the BN-600 reactor plant at Beloyarsk NPP Unit 3, one of the six heat exchangers was removed from the reactor in April 2006. Results of inspection showed that there were cracks 7 mm deep maximum on the outer surface of the upper tubesheet and adjacent shell. To predict durability of substantially fatigued metal, a need arose to verify the existing relationship for the threshold stress intensity factor range for the 10Cr18Ni9 steel. To this end, respective testing was conducted on specimens of two structural elements in the IHX – upper tubesheet and protection block. To identify failure mechanisms, fractographic studies were performed on the surface of cracks detected in the tubesheet and made in the specimens. Based upon the studies, a conclusion was made that the failure mechanism for cracks detected on the tubesheet was identical to the mechanism generated in the test specimens. In both the cases, the intergranular failure prevailed that is typical for the material loading level testifying to termination of the crack growth. This result makes it possible to speak about crack initiation and propagation in the IHX tubesheet in the high-cycle fatigue region at a low-level strain ranges and stress intensity factor ranges. An analysis of causes of crack formation showed that the cracks could have formed as a result of the temperature pulsation effect produced by mixing of sodium flows having different temperatures – sodium entering the IHX inlet and sodium coming from the reactor vessel cooling system. Based upon computational analysis results, for all thermal pulsation conditions and crack propagation cross-sections under consideration, the leak-tightness condition is met for the upper tubesheet and IHX outlet chamber shell that divide the primary and secondary coolant circuits. The computational and experimental studies have proved that presence of these cracks does not limit the possibility of service life extension to 45 years for the IHX in the BN-600 reactor plant.

References

  1. Vasil’yev, B.A., Timofeev, A.V., Lyubimov, M.A., Gladkov, V.V., Kaydalov, V.B. Obespechenie rabotosposobnosti zamenyaemogo oborudovaniya reaktornoj ustanovki pri prodlenii sroka e’kspluatacii e’nergobloka BN(600 do 45(ti let. [Ensuring Operability of Reactor Plant Replaceable Equipment while Extending the Service Life of the BN-600 Power Unit to 45 years]. Izvestiya vuzov. Yadernaya Energetika. 2011, no. 1, pp. 44-54 (in Russian).
  2. Ohshima H., Muramatsu T., Kobayashi J., Yamaguchi A. Current status of studies on temperature fluctuation phenomena in LMFRS/ Specialists‘ meeting on «Correlation between material properties and thermohydravlics condition in LMFRs» (Provence, France 22-24 november 1994).
  3. Broek D. Osnovy mexaniki razrushenij. [Elementary Engineering Fracture Mechanics]. Moscow. High school, 1980 (in Russian).
  4. Knott J.F. Osnovy mexaniki razrushenij. [Elementary Engineering Fracture Mechanics]. Moscow. Metallurgy., 1978 (in Russian).
  5. RD EO 1.1.2.09.0714-2007 Metodika rascheta prochnosti osnovnyx e’lementov reaktornyx ustanovok na bystryx nejtronax s natrievym teplonositelem. [Strength Analysis Method for Main Elements of Sodium-Cooled Fast Reactor Plants]. Rosenergoatom Concern Publ., 2007 (in Russian).
  6. RCC-MR Design and construction rules for mechanical components of FBR Nuclear Islands. AFCEN, 2002.
  7. Borishanskij V.M., Kutateladze S.S., Novikov I.I., Fedynsky O.S. Zhidkometallicheskie teplonositeli [Liquid Metal Coolants]. Moscow, Atomizdat Publ., 1976 (in Russian).
  8. Sobolev V.A., Kuzavkov, N.G. Identification of places with fluid temperature fluctuation in BN-600 reactor and reactor system. Specialists’ meeting on «Correlation between material properties and thermohydraulics condition in LMFRs» (Provence, France 22-24 November 1994).
  9. Chellapandi P., Chetal S.C., Baldev Raj. Thermal Striping limits for components cooled fast spectrum reactors. Nuclear Engineering and Design. 2009, pp. 2754-2765.
  10. Metodicheskie rekomendacii MR 125(02(95. Pravila sostavleniya raschetnyx sxem i opredelenie parametrov nagruzhennosti elementov konstrukcij s vyyavlennymi defektami. [Methodical Recommendations MR 125-02-95Regulations for Generating Computational Schemes and Determining Loading Parameters for Structural Elements with Defects Identified]. Moscow, SPA CNIITMASH, NIKIET Publ., 1995 (in Russian).

BN-6002 intermediate heat exchanger computational and experimental studies temperature pulsations stress strained state stress intensity factor multi-cycle fatigue creep cracks