TA REG 02.01/03-3 - Embrittlement assessment and validation of embrittlement and re-embrittlement models for 440/213 RPVs (ref AP 7.5.2)

This project was implemented through three separate contracts:

1. Contract 115560 with NRI Rez (EC Consultant)
2. Contract 115556 with ARMS Kiev (Director of Experiment in Ukraine)
3. Contract 76908 with RRCKI Moscow (DoE in Russia)

The description given below summarises the objectives, scope and achievements of the combined project comprising all three contracts. The same description is therefore found under the entries for the other two contracts in this database.

To provide an updated database, including existing surveillance test results as well as new results obtained by testing of reconstructed specimens from broken surveillance specimen halves. The database would be used for upgrading of Charpy V transition curves for further RPV integrity analyses (PTS) in the ongoing twin project TAREG 2.01/00.

To validate the fracture toughness for irradiated surveillance specimens by testing selected reconstituted pre-cracked CV specimens using the Master Curve method. As a result, this upgraded fracture toughness database should be precise and complete enough to be used as input in further analysis (such as the twin project TAREG 2.01/00), aiming at evaluating the safety condition of WER RPVs and the efficiency of mitigation procedures.

To validate the shape of the fracture toughness curve of highly embrittled Russian RPV steel by using the new Russian "Local Approach" test method. The results would be compared to similar test results on the same material but based on the Master Curve method (ASTM E 1921).

To upgrade the knowledge base about the mechanical properties of irradiated RPV austenitic cladding. The Result should include indications about the embrittlement kinetics of the austenitic weld material, and the mechanical influence of the irradiated cladding layer on the integrity of the whole VVER RPVs. The Result should also include useful information for applying the new Russian integrity assessment standard.

Short Tasks review and results

In Task 2 the reconstitution technique for Charpy size specimens from Standard surveillance programmes was successfully qualified in the KINR and this technique was applied in the whole project. This technique used electron beam welding and together with new determination of neutron fluence on individual part of surveillance specimens was able substantially to improve reliability of obtained data. This task was mainly carried out under Contract 115566 in Ukraine.

Tasks 3 and 4 included testing of remained and already tested radioactive surveillance specimens from VVER-440 and VVER-1000 RPVs either in Russia (by RRC KI) or in Ukraine (by KINR) using this qualified technique (RRC KI used the stud welding technique, also qualified by the same methodology). New results on brittle fracture transition temperature from Charpy impact as well as from static fracture toughness testing were obtained. The existing database of irradiation embrittlement of especially VVER-1000 type materials was substantially extended by these tests, as only results obtained on reconstituted specimens could be used for RPV integrity and lifetime evaluation. These Tasks were carried out under Contracts 76908 in Russia and 115556 in Ukraine.

Task 5 was concentrated on the comparison of different approaches to RPV integrity evaluation. For this purpose large (25 mm thick) specimens from trepans from decommissioned RPVs in Novovoronezh-2 and Reactor-37 were manufactured and tested together with Charpy size specimens used in surveillance programmes. Applicability of the Unified Curve and Master Curve approaches has been shown, mainly with respect to surveillance Charpy size specimens. This Task was carried out in RRCKI and CRISM Prometey under Contract 76908.

In Task 6 a series of tests of specimens from highly irradiated austenitic cladding materials were performed. The evaluation of data served for the preparation of the procedure for cladding integrity assessment. As a result of the study J-integral properties were developed for irradiated RPV cladding material. The results were used in the twin project for evaluating the integrity of the cladding in PTS transients. This Task was carried out in CRISM Prometey under Contract 76908.

Final dissemination of results from both twin projects was organized within the Task 7; final dissemination workshop for representatives of Russian and Ukrainian NPPs and regulatory bodies together with both Beneficiaries was held in Pushche-Voditse near Kiev, Ukraine on November 30th to December 1st, 2010. Altogether 52 representatives attended the workshop where 23 presentations were given. These presentations summarized all obtained results with explanation of their use and application to RPV integrity evaluation.

Conclusion

This TAREG 2.01/03 project has been rather complicated to complete mainly due to the connection with its twin TAREG 2.01/00 project. The main reasons for the above mentioned delays were the late commencement of this twin project. This delay again was mainly due to budgetary difficulties in the EC Annual Programming. Nevertheless, the project was very successful and completed fully according to Contract and TOR and maintained a very high scientific level both in Russia and Ukraine. The co-operation between the twin projects was also very good despite the a.m. delays.