Neutron Absorbing Stainless Steel
NAS 8R10
Made by adding natural boron to austenitic stainless steel, NAS 8R10 provides strong shielding action against neutrons for use in nuclear reactors. The primary application of NAS 8R10 is storage racks for spent fuel. The continuous casting process results in minute amounts of boron dispersed throughout the structure. The elongation property is improved over conventional stainless steels. Nippon Yakin supplies this product in plate form.
Plate
Physical Properties
| Specific heat (J/kg･K) | 25–100℃ | 500 |
| Specific resistivity (μΩ･cm) | 79 | |
| Thermal conductivity (W/m･K) | 25–100℃ | 13 |
| 25–200℃ | 17 | |
| 25–300℃ | 21 | |
| 25–400℃ | 21 | |
| 25–500℃ | 25 | |
| Coefficient of thermal expansion (10-6/℃) | 25–100℃ | 16.7 |
| 25–800℃ | 20.0 | |
| Young's modulus (MPa) | 25℃ | 221000 (22.1 x 104) |
| Ferromagnetism | Yes | |
Mechanical Properties
| 0.2% proof stress (N/mm2) |
Tensile strength (N/mm2) |
Elongation (%) |
Hardness | |
|---|---|---|---|---|
| (HRB) | (HB) | |||
| > 204 | > 519 | 26 | < 100 | < 217 |
Workability
At room temperature, NAS 8R10 can be bent up to 90° with the inner diameter twice its thickness. When bending the surface perpendicular to a bent line, polishing with a 320-grit abrasive is required. Cutting can be carried out in a similar manner to SUS 304 by using a slow speed and cutting notches somewhat deep. Set the cutting tool 2 to 3° more acute than usual.
Weldability
Both shielded metal arc welding and TIG welding can be carried out on NAS 8R10 in a manner similar to SUS 304. We recommend D308 or D308L for the welding consumable.
Pickling
To remove thicker surface scales, pickle in a warm solution of 10 to 25 percent nitric acid and 1 to 4 percent hydrofluoric acid. For thinner scales, use 12 to 15 percent nitric acid and 1 percent hydrofluoric acid. Overpickling occurs more readily in NAS 8R10 than SUS 304, so care should be taken.
Features
Natural boron includes approximately 20 percent of B10, which absorbs neutrons. After absorbing a neutron, B10 changes to B11 as shown in the following formula:
- B10 + n0 → B11
The higher the concentration of boron in steel, the better the ability to absorb neutrons. Adding 1 percent boron to stainless steel provides about three times the shielding effect against neutrons as compared to no boron.
Dependence of neutron shielding on boron content
