Technology Reviews

Heavy-Section Steel Technology and Irradiation Programs—Retrospective and Prospective Views

[+] Author and Article Information
Randy K. Nanstad

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6138nanstadrk@ornl.gov

B. Richard Bass

Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6085basssbr@ornl.gov

John G. Merkle

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6151merklejg@ornl.gov

Claud E. Pugh

 ORSA Inc., 9724 Franklin Hill Boulevard, Knoxville, TN 37922pughce@comcast.net

Thomas M. Rosseel

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6151rosseeltm@ornl.gov

Mikhail A. Sokolov

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6151sokolovm@ornl.gov

J. Pressure Vessel Technol 132(6), 064001 (Oct 14, 2010) (20 pages) doi:10.1115/1.4001425 History: Received November 10, 2008; Revised August 18, 2009; Published October 14, 2010; Online October 14, 2010

In 1965, the Atomic Energy Commission, at the advice of the Advisory Committee on Reactor Safeguards, initiated the process that resulted in the establishment of the Heavy Section Steel Technology (HSST) program at Oak Ridge National Laboratory. In 1989, the Heavy-Section Steel Irradiation (HSSI) program, formerly the HSST task on irradiation effects, was formed as a separate program, and in 2007, the HSST/HSSI programs, sponsored by the U.S. Nuclear Regulatory Commission (USNRC), celebrated 40 years of continuous research oriented toward the safety of light-water nuclear reactor pressure vessels (RPVs). This paper presents a summary of results from those programs with a view to future activities. The HSST program was established in 1967 and initially included extensive investigations of heavy-section low-alloy steel plates, forgings, and welds, including metallurgical studies, mechanical properties, fracture toughness (quasi-static and dynamic), fatigue crack-growth, and crack-arrest toughness. Also included were irradiation effects studies, thermal shock analyses, testing of thick-section tensile and fracture specimens, and nondestructive testing. In the subsequent decades, the HSST Program conducted extensive large-scale experiments with intermediate-size vessels (with varying size flaws) pressurized to failure, similar experiments under conditions of thermal shock and even pressurized thermal shock (PTS), wide-plate crack-arrest tests, and biaxial tests with cruciform-shaped specimens. Extensive analytical and numerical studies accompanied these experiments, including the development of computer codes such as the recent Fracture Analysis of Vessels Oak Ridge code currently being used for PTS evaluations. In the absence of radiation damage to the RPVs, fracture of the vessel is improbable. However, it was recognized that exposure to high energy neutrons can result in embrittlement of radiation-sensitive RPV materials. The HSSI Program conducted a series of experiments to assess the effects of neutron irradiation on RPV material behavior, especially fracture toughness. These studies included RPV plates and welds, varying chemical compositions, and fracture toughness specimens up to 101.6 mm (4 in.) thickness. The results of these investigations, in conjunction with results from commercial reactor surveillance programs, are used to develop a methodology for the prediction of radiation effects on RPV materials. Results from the HSST and HSSI programs are used by the USNRC in the evaluation of RPV integrity and regulation of overall nuclear plant safety.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Plot of drop-weight NDT, tensile strength, and hardness through the thickness of a quenched and tempered 305 mm thick plate of SA-533 grade B class 1 steel (9)

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Figure 2

Fracture toughness KIc of a 305 mm thick plate of SA-533 grade B class 1 steel. Specimens up to 305 mm thickness were tested (10).

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Figure 3

ITV tested at 88°C(190°F) on the CVN ductile shelf that failed by ductile shear fracture (5)

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Figure 4

ITV tested at 0°C(32°F) low in the transition region that failed in a brittle manner by cleavage fracture (5)

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Figure 5

Schematic diagram showing test conditions for the ITV experiments relative to CVN energy versus temperature (5). Note that V-6 and V-8A both experienced ductile tearing and ductile shear fracture but the V-8A experiment was specifically focused on ductile tearing predictability.

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Figure 6

Schematic diagram depicting the conditions during an overcooling accident (24-25)

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Figure 7

Diagram showing the stress intensity relative to the distributions of temperature, stress, and fluence compared with the initiation and arrest fracture toughness of the steel during a large-break loss-of-cooling accident (24-25)

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Figure 8

Crack-arrest results from TSE tests relative to the KIR curve (24-25)

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Figure 9

Crack-arrest results from PTSE-1 experiments with those from the TSE experiments and the HSST wide-plate crack-arrest tests, relative to the KIR curve (26)

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Figure 10

Photo of wastage cavity in the vicinity of a control rod drive nozzle in the Davis–Besse reactor pressure vessel head (34)

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Figure 11

Effects of radiation embrittlement on restriction of the operating envelope for an RPV with a radiation-sensitive steel

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Figure 12

Dynamic fracture toughness KId versus temperature in the unirradiated and irradiated conditions for A533B-1 steel, HSST plate 02 (0.14 wt % Cu)(65)

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Figure 13

J-integral versus crack extension for 4TC(T) specimens of HSSI weld 61W irradiated at 288°C to a fluence of ∼1.2×1019 n/cm2(>1 MeV) and tested at 200°C(66)

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Figure 14

Fracture toughness of weld 71W irradiated at 288°C and to 2×1019 n/cm2(>1 MeV). This result demonstrates the low radiation sensitivity of weld metals with low copper and typical nickel contents (70-71).

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Figure 15

Comparison of mean fracture toughness and crack-arrest toughness versus normalized temperature for welds 72W and 73W in the (a) unirradiated and (b) irradiated conditions (72-73)

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Figure 16

Mean curves fit to the unirradiated and irradiated KJc data versus temperature normalized to the RTNDT for HSSI weld 73W (74)

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Figure 17

Twenty-five separate CVN impact curves from the Midland unit 1 low upper-shelf welds, showing large variations in 41 J transition temperatures and upper-shelf energies (85)

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Figure 18

Fracture toughness KJc results for the Midland beltline weld in the unirradiated condition, showing that (a) the master curve from tests of six 0.5TC(T) specimens provides a good representation of T0 for (b) the data from larger compact specimens to 4T size (85-86)

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Figure 19

Fracture toughness KJc data from Midland beltline weld showing that indexing of the ASME KIc curve to RTNDT for low upper-shelf welds is extremely conservative (85-86)

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Figure 20

Fracture toughness KJc median values versus T-T0 from tests of Midland beltline weld showing that the results follow the master curve shape for both unirradiated and irradiated conditions (86-87)

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Figure 21

Fracture toughness KJc data for KS-01 weld in the unirradiated and irradiated conditions, showing the master curve fits to each data set (89)

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Figure 22

Median KJc values for temper embrittled A302B (mod) steel after normalization to 1T equivalence compared with master curve based on data at the three lowest test temperatures (90)

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Figure 23

Comparison of master curve reference temperature T0 values from compact and PCVN specimens for various RPV steels (93)

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Figure 24

Atom maps of the neutron irradiated VVER-1000 low-copper weld material showing some ultrafine manganese-, nickel-, and silicon-enriched precipitates (arrowed) (101)



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