ML18267A094
| ML18267A094 | |
| Person / Time | |
|---|---|
| Issue date: | 09/24/2018 |
| From: | Robert Tregoning NRC/RES/DE |
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| Download: ML18267A094 (8) | |
Text
This presentation was prepared as an account of work conducted by an agency of the U.S. Government. Neither the U.S.
Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third partys use, or the results of such use, of any information, apparatus, product, or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights. The views expressed in this paper are not necessarily those of the U.S. Nuclear Regulatory Commission.
Effects of Irradiation on Fatigue Life Robert Tregoning Nuclear Regulatory Commission Public Meeting on Environmentally Assisted Fatigue (EAF)
Research and Related ASME Activities Nuclear Regulatory Commission Headquarters September 25, 2018
Background
- Irradiation effects are not considered in ASME Section III fatigue evaluations
- Little current experimental data on irradiation effects for nuclear materials under conditions representative of commercial light-water reactors Most data dates to mid-1970s or earlier Much of the irradiation conducted in fast flux reactors at either higher (> 400oC) or lower (< 100oC) temperatures than service conditions
- Changes in microstructure resulting from irradiation have been observed but not correlated with fatigue life Microstructure and microchemistry changes Cavities and He bubble formation
- Some fatigue tests have been performed Fatigue crack growth rate (FCGR)
Fatigue life (i.e., - N)
September 25, 2018 Public Meeting on EAF and Related ASME Activities 2
Effects of Irradiation on FCGR
- Experimental Breeder Reactor II (EBR-II) Tests Type 304 & 316 SS irradiated at 410oC to 1.2x1022 n/cm2 and tested at 427oC and 593oC 427oC results
- CGRs in irradiated specimens up to factor of 2 higher for K < 44 MPam
- CGRs in irradiated specimens lower for K > 44 MPam 593oC results
- Opposite trends compared to the 427oC results
- Advanced Test Reactor (ATR) Tests Type 304 and 316 SS irradiated at 288oC to 1.8x1021 n/cm2 and tested at 427oC.
Results
- CGRs in irradiated specimens 2 - 4 times lower
- No significant deleterious effects of irradiation in these tests and improved resistance to fatigue cracking observed under some conditions September 25, 2018 Public Meeting on EAF and Related ASME Activities 3
Effects of Irradiation on - N
- Engineering Test Reactor (ETR) Tests Type 347 SS irradiated at 60oC to 5.5x1025 n/m2 and above Tested at room temperature
- Low strain amplitudes ( < 0.35%):
Irradiation appears to increase fatigue life
- High strain amplitudes: Irradiation appears to decrease fatigue life September 25, 2018 Public Meeting on EAF and Related ASME Activities 4
Effects of Irradiation on - N, cont.
- Tests on CW Type 316 SS Tubes Removed from PWR Plant Irradiated to fluences < 1022 n/m2 to > 3x1026 n/m2 Tested in air and PWR-simulated water at 325oC and various strain rates No baseline unirradiated tests for comparison
- Fatigue life for tube specimens decreased by approximately 1.5
- - N relationship of irradiated material appears flatter than the ASME Code mean curve September 25, 2018 Public Meeting on EAF and Related ASME Activities 5
Effects of Irradiation on - N, cont.
- Tests on Solution Annealed Type 304 SS Bars Removed from PWR Plant Irradiated to fluences from 0.5 to 1x1026 n/m2 Tested in air and PWR-simulated water at 325oC and various strain rates No baseline unirradiated tests for comparison
- As with CW 316 results, irradiated life curve appears flatter than ASME mean curve
- Implication is that irradiation may increase fatigue life at low strain amplitudes while decreasing life at higher strain amplitudes September 25, 2018 Public Meeting on EAF and Related ASME Activities 6
Summary
- Effects of irradiation on fatigue crack growth rates (CGRs)
- Conclusive trends cannot be established due to limited LWR-representative data
- No significant increase in FCGRs due to irradiation observed in existing test data
- Decreases in FCGRs due to irradiation observed under some conditions
- Effects of irradiation on fatigue life (i.e., - N)
- Conclusive trends cannot be established due to limited LWR-representative data
- However, consistent trends have been observed in existing test data
- Decreases in fatigue life at higher (i.e., > 0.35 to 0.6%) strain levels
- Increases in fatigue life at low (i.e., < 0.35 to 0.6%) strain levels
- Trends appear consistent with material changes caused by irradiation
- Hardening causes increased tensile strength, leading to increased high cycle fatigue resistance
- Reduced ductility could lead to decreases in low-cycle fatigue life September 25, 2018 Public Meeting on EAF and Related ASME Activities 7
Discussion - Next Steps
- Research Effects of irradiation on fatigue life are one of the least understood of all potential contributing factors to fatigue life Information on any additional past, current, or planned research in this area would be important Relevance/feasibility of using FCR portion of IASCC testing as additional data.
- Implications Any deleterious effects of irradiation on fatigue life will increase with operating time Issue is only relevant to a limited scope of reactor internal components Scoping would be useful to identify components of interest
- Potential resolution Limited test program would be useful in confirming/predicting significant trends Testing representative materials under LWR conditions Initial focus should be on low-cycle fatigue effects and the transition between low-cycle and high-cycle regimes.
Other thoughts?
September 25, 2018 Public Meeting on EAF and Related ASME Activities 8