Plant Materials DOE-HDBK-1017/2-93 EFFECT DUE TO NEUTRON CAPTURE TABLE  2 Effect of  Fast-Neutron  Irradiation  on  the Mechanical Properties  of  Metals Integrated Radiation Tensile Yield Fast Flux Temperature Strength Strength Elongation Material (NVT) (C) (MPa) (MPa) (%) Austenitic SS     0 ------    576 235       65   Type 304 1.2 x 10²¹    100 720 663       42 Low Carbon     0       ------      517 276       25   steel 2.0 x 10¹⁹     80 676 634        6   A-212 (.2%C) 1.0 x 10²⁰     80 800 752        4 2.0 x 10¹⁹    293 703 524        9 2.0 x 10¹⁹    404 579 293       14 Aluminum     0 ------      124   65     28.8   6061-0 1.0 x 10²⁰     66 257 177     22.4 Aluminum     0 ------    310 265     17.5   6061-T6 1.0 x 10²⁰     66 349 306     16.2 Zircaloy-2     0 ------      276 155       13 1.0 x 10²⁰    138 310 279        4 One of the areas of the reactor vessel that is of most concern is the beltline region.  The Nuclear Regulatory   Commission   requires   that   a   reactor   vessel   material   surveillance   program   be conducted (in  accordance with  ASTM standards)  in water-cooled  power reactors.   Specimens of  steel  used  in  the  pressure  vessel  must  be  placed  inside  the  vessel  located  near  the  inside vessel   wall   in   the   beltline   region,   so   that   the   neutron   flux   received   by   the   specimens approximates that received by the vessel inner surface, and the thermal environment is as close as  possible  to  that  of  the  vessel  inner  surface.    The  specimens  are  withdrawn  at  prescribed intervals  during  the  reactor  lifetime and  are  subjected  to  impact  tests  to  determine new  NDT temperatures.  Figure 5 shows the increase in NDT temperature for a representative group of low carbon  steel alloys  irradiated at  temperatures  below  232C.   Many  current reactors  have core pressure vessel wall temperatures in the range of 200C to 290C, so that an increase in NDT is of very real concern. Irradiation frequently decreases the density of a metal over a certain temperature range, so that a specimen exhibits an increase in volume or swelling.  The swelling of stainless steel structural components  and  fuel rod  cladding,  resulting  from  fast  neutron  irradiation  at  the  temperatures existing in fast reactors, is a matter of great concern in fast reactors.   The swelling can cause changes in the dimensions of the coolant channels and also interfere with the free movement of control elements. Rev. 0 Page 41 MS-05