Consolidation of Scientific and Technological Expertise to Assess the Reliability of Reactor Pressure Vessel Embrittlement Prediction in Particular for the Arctic Area Plant (COBRA)

• Published in: Nuclear Engineering and Design
• Main Authors: BALLESTEROS A., BROS J., DEBARBERIS Luigi, SEVINI Filippo, ERAK D., GEZASHCHENKO S., KRYUKOV A., SHTROMBAKH Y., GOLOSCHAPOV S., PYTKIN Y., ANIKEEV Y., BANYUK G., PLUSCH A., GILLEMOT F., TATAR L., PETROSYAN V., IONOV X.
• Language: English
• Published: ELSEVIER SCIENCE BV 2005
• Subjects: Arctic
• Online Access: https://publications.jrc.ec.europa.eu/repository/handle/JRC31142; https://doi.org/10.1016/j.nucengdes.2004.08.062

The evaluation and prognosis of reactor pressure vessel (RPV) material embrittlement in WWERs and the allowable period of their safe operation are performed on the basis of impact test results of irradiated surveillance specimens. The main problem concerns the irradiation conditions (irradiation temperature, neutron flux and neutron spectrum) of the surveillance specimens that have not been determined yet with the necessary accuracy. These conditions could differ from the actual RPV wall condition. In particular, the key issue is the possible difference between the irradiation temperature of the surveillance specimens and the actual RPV wall temperature. It is recognized that the direct measurement of the irradiation temperature by thermocouples during reactor operation is the only way to obtain reliable information. In addition, the neutron field's parameters in the surveillance specimens location have not been determined yet with the necessary accuracy. The use of state of the art dosimeters can provide high accuracy in the determination of the neutron exposure level. The COBRA project, which started in August 2000 and had a duration of 3 years, was designed to solve the above-mentioned problems. Surveillance capsules were manufactured which contained state of art dosimeters and temperature monitors (melting alloys). In addition, thermocouples were installed throughout the instrumentation channels of the vessel head to measure directly the irradiation temperature in the surveillance position during reactor operation. The selected reactor for the experiment was the Unit 3 of Kola NPP situated in the arctic area of Russia. Irradiation of capsules and online temperature measurements were performed during one fuel cycle. On the base of statistical processing of thermocouples readings, the temperature of irradiated surveillance specimens in WWER-440/213 reactor can be accepted as 269.5 +- 4oC. Uncertainties were evaluated also with experimental work carried out in the WWRSZ research reactor and by finite element ...