NSUF 09-153: High Fluence Embrittlement Database and ATR Irradiation Facility for LWR Vessel Life Extension
Embrittlement of RPV steels over operating periods up to 80 effective full power years, corresponding to a maximum neutron fluence up to 10^20 n/cm2 (E > 1 MeV), is a critical issue that may limit LWR plant life extension. An important unresolved RPV embrittlement issue is predicting transition temperature shifts (TTS) at high fluences (> ˜ 6x10^19 n/cm2), which are well beyond the range of the existing surveillance database. Indeed, there are virtually no low flux irradiation data at these fluence levels. Notably,however, current embrittlement models systematically and significantly under-predict embrittlement (TTS) in the existing high flux test reactor database at high fluence [1]. However, neutron flux has strong and very complex effects on embrittlement; indeed, increasing flux can increase, decrease or leave unaffected the TTS, depending on all the other irradiation and material conditions.Currently no US irradiation facility exists to carry out intermediate flux neutron irradiations pertinent to pressure boundary and other structural materials to resolve these issues. Thus UCSB, in collaboration with ORNL and UCB, propose to develop a new ATR irradiation facility for intermediate flux neutron irradiations in a Small I position [2]. The proposed facility will fill a major hole in the existing RPV embrittlement database at high fluence, as well as providing data for resolving a number of other important embrittlement issues. The proposed Small I facility involves an irradiation capsule that is shielded from thermal neutrons, and instrumented and actively heated to maintain good (<±5°C) temperature control. The capsules will contain more than 2000 specimens in at lease three temperature zones, nominally at 270, 290 and 310 °C. Peak flux levels of ˜ 4.5x10^12 n/cm2-s (10-20 times lower than for most other high fluence data) will produce a fluence of 10^20 n/cm2 in a one-year irradiation. Disc multipurpose coupons, disc compact tension fracture, sub-sized tensile and special purpose specimens will provide mechanical property data, as well as detailed characterization of the irradiation induced microstructures, using state-of-the-art techniques. Critical and scientifically important issues, such as the formation of late blooming phases that result in severe embrittlement in low copper steels, will be explored. The greatly enhanced embrittlment database will be used to develop robust, physically based models to predict TTS to and beyond end of extended life conditions. UCSB and ORNL, with many decades of experience in designing and successfully carrying out major irradiation studies, will collaborate with INL to design and implement the facility. UCSB, ORNL and UCB, who are internationally recognized leaders in various sophisticated characterization studies as well as materials modeling research, will carry out the post irradiation examinations along with their large network of worldwide collaborators. This program will not only provide critical early insight on embrittlement at high fluence, but will also lay a foundation for developing other ATR RPV steel irradiation facilities for longer-term irradiations at even lower and more vessel pertinent neutron fluxes.
Additional Info
| Field | Value |
|---|---|
| Abstract | Embrittlement of RPV steels over operating periods up to 80 effective full power years, corresponding to a maximum neutron fluence up to 10^20 n/cm2 (E > 1 MeV), is a critical issue that may limit LWR plant life extension. An important unresolved RPV embrittlement issue is predicting transition temperature shifts (TTS) at high fluences (> ˜ 6x10^19 n/cm2), which are well beyond the range of the existing surveillance database. Indeed, there are virtually no low flux irradiation data at these fluence levels. Notably,however, current embrittlement models systematically and significantly under-predict embrittlement (TTS) in the existing high flux test reactor database at high fluence [1]. However, neutron flux has strong and very complex effects on embrittlement; indeed, increasing flux can increase, decrease or leave unaffected the TTS, depending on all the other irradiation and material conditions.Currently no US irradiation facility exists to carry out intermediate flux neutron irradiations pertinent to pressure boundary and other structural materials to resolve these issues. Thus UCSB, in collaboration with ORNL and UCB, propose to develop a new ATR irradiation facility for intermediate flux neutron irradiations in a Small I position [2]. The proposed facility will fill a major hole in the existing RPV embrittlement database at high fluence, as well as providing data for resolving a number of other important embrittlement issues. The proposed Small I facility involves an irradiation capsule that is shielded from thermal neutrons, and instrumented and actively heated to maintain good (<±5°C) temperature control. The capsules will contain more than 2000 specimens in at lease three temperature zones, nominally at 270, 290 and 310 °C. Peak flux levels of ˜ 4.5x10^12 n/cm2-s (10-20 times lower than for most other high fluence data) will produce a fluence of 10^20 n/cm2 in a one-year irradiation. Disc multipurpose coupons, disc compact tension fracture, sub-sized tensile and special purpose specimens will provide mechanical property data, as well as detailed characterization of the irradiation induced microstructures, using state-of-the-art techniques. Critical and scientifically important issues, such as the formation of late blooming phases that result in severe embrittlement in low copper steels, will be explored. The greatly enhanced embrittlment database will be used to develop robust, physically based models to predict TTS to and beyond end of extended life conditions. UCSB and ORNL, with many decades of experience in designing and successfully carrying out major irradiation studies, will collaborate with INL to design and implement the facility. UCSB, ORNL and UCB, who are internationally recognized leaders in various sophisticated characterization studies as well as materials modeling research, will carry out the post irradiation examinations along with their large network of worldwide collaborators. This program will not only provide critical early insight on embrittlement at high fluence, but will also lay a foundation for developing other ATR RPV steel irradiation facilities for longer-term irradiations at even lower and more vessel pertinent neutron fluxes. |
| Award Announced Date | 2009-02-04T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Alina Zackrone, Kory Linton |
| Irradiation Facility | None |
| PI | G. Robert Odette |
| PI Email | [email protected] |
| Project Type | Irradiation/PIE |
| RTE Number | 153 |