Fast neutron doses

Kelly, B.T. and Brocklehurst J.E., Dimensional changes of pyrolytic graphite at very high fast neutron doses. In Proc. Fifth SCI Conf. on Industrial Carbons and Graphites, SCI London, (1979, pp. 892 897. 

Gy, single fast neutron doses Shoot growth inhibited by >85% 3... 

Furthermore, one may think of radiation influencing the chemical stability of the solid. There is no experimental evidence for any of these effects [H2]. In all test procedures a long-term dose has been simulated in a short time, which will probably rather enhance the effects. The apparent radiation stability should be not too surprising, bearing in mind that an alpha dose of 10 /cm over 100 years is a rather modest one compared to the fast-neutron doses to which materials in a nuclear reactor are exposed. 

Figure 9. Calibration curve (A) of PSII particles from Spinacea oleracea exposed to gamma r ( Cs dose rate 1.2mGy/h)and(B) fast neutrons (dose rate 1.26 mGy/h)-JRC,Ispra, (IT). The temperature and pH were highly controlled. Ai/Ac ratio of area irradiated /control...

Fig. 2. Reduced transition temperature as a function of fast-neutron dose for various superconductors. (From Sweedler [ ].)...

Fast neutron doses were measured by counting the Mn activity on the cube samples through the RPV wall thickness. The doses obtained were in good agreement with those predicted by the MCBEND code. Chemical analysis of weld metal from all four layers showed remarkable consistency in composition both along and through the weld. Table 7.5 shows that the four weld compositions were similar and compared favourably with the weld compositions obtained from other vessel cut-outs and surveillance... 

Figure 4. Fast neutron dose rate in water at the ORNL lid tank. Circles are experimental points, curve is predicted by moment method. According to D. R. Otis, as quoted by H. Goldstein [2].

Measurements of fast neutron dose in water have also been made with an isotropic, monoenergetic (14.1 Mev) source [7]. For penetrations up to six mean free paths the experimental results are about 15% higher than the results of a moment calculation. The discrepancy is presumably due to the uncertainty as to the scattering cross sections for oxygen which must be fed into the calculation. 

The units of thermal neutron flux are (neutrons cm 2 sec l watt ), those of gamma ray dose rate are (ergs-grgj.j p jj g-i hr l watt i), and those of fast neutron dose are... 

Early irradiation results on BeO showed crumbling of the material after a fast flux dose of 3 x 10 nvt (>1 MeV) at 100°C. More recent work on fine-grain BeO with some additives has shown that the material can withstand a fast neutron dose of about 2 x 10 nvt at 400°C and greater than 10 nvt at 800°C. Under the latter conditions, the volume change is typically around 1 % at a fast neutron exposure of 10 nvt (32). 

Detector type Relative efficiency (%) Threshold fast neutron dose (cm )... 

The large water volume between the core and the wall leads to a very low fast-neutron dose over the RPV wall. 

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