Research Papers: Design and Analysis

A New Methodology for Structural Reliability Assessment of the Heat Exchanger Tubes of WWER Steam Generators

[+] Author and Article Information
Igor Orynyak

G.S. Pisarenko Institute for Problems of Strength
of the National Academy of Sciences of Ukraine,
2, Timiryazevs'ka Street,
Kyiv 01014, Ukraine
e-mail: igor_orinyak@yahoo.com

Maksym Zarazovskii

G.S. Pisarenko Institute for Problems of Strength
of the National Academy of Sciences of Ukraine,
2, Timiryazevs'ka Street,
Kyiv 01014, Ukraine
e-mail: zarazovskiimaxim@ukr.net

Mykhaylo Borodii

G.S. Pisarenko Institute for Problems of Strength
of the National Academy of Sciences of Ukraine,
2, Timiryazevs'ka Street,
Kyiv 01014, Ukraine
e-mail: mborodii@gmail.com

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received April 27, 2016; final manuscript received December 5, 2016; published online February 3, 2017. Assoc. Editor: David L. Rudland.

J. Pressure Vessel Technol 139(3), 031208 (Feb 03, 2017) (9 pages) Paper No: PVT-16-1071; doi: 10.1115/1.4035414 History: Received April 27, 2016; Revised December 05, 2016

A physically and statistically based method for steam generator (SG) heat exchanger tubes (HET) integrity assessment is proposed. The method based is on the stochastic laws of crack dimensions distribution with taking into account its growth, limit load-model of cracked tube, and SG plugging statistics. Based on the history of the tubes, plugging of the specific SG three statistical parameters has to be found: initial number of defects, stochastic parameter of defect depth, and the defect growth rate. The developed method was used for the prediction of HET failure for all Ukrainian SG. It is also used for the justification of pressure reduction of hydrostatic test (HT) for primary circuit of WWER NPPs. It is shown that the pressure reduction from 24.5 to 19.6 MPa for WWER-1000 s and from 19.1 to 15.7 MPa for the WWER-440 s does not practically increase the HET failure probability during operation.

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Fig. 1

General view of WWERs SG (1—“hot” collector (inlet nozzle of reactor coolant); 2—“cold” collector (outlet nozzle); 3—heat exchanger tubes; 4—feed water; 5—out of steam)

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Fig. 2

HET geometry and arrangement, (left and right—for the WWER-440 s and WWER-1000 s, correspondingly)

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Fig. 3

Sludge deposit on SG tubes of WWER-1000 NPPs [6]

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Fig. 4

SCC associated with pitting (South Ukraine NPP) [6]

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Fig. 5

HETs plugging statistiсs of SG #4 of Unit 1 of South Ukraine NPP

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Fig. 6

Schematic diagram of the HT procedure (lines 1 and 2—defect sizes that fail at HT pressure and NOM pressure, correspondingly; line 3 shows the growth of a defect in the time between time two HTs)

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Fig. 7

Critical defect sizes under HT and operation modes for the WWER-1000 SG HETs

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Fig. 8

HET critical defect depth under HT and NOM at certain time of operation (SG #4 of South Ukraine NPP)



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