Radioactive changes in the moderator material, zirconium hydrate, during NRE oper­ation in the engine regime (1,000 s) are insignificant. In the power regime after the irradiation of zirconium hydride in a reactor by the integral neutron flux of the order of

Fig. 5.7 Relative length change of graphite samples of various grade: RBMK (7), VPG (2), MPG 6 (3), irradi­ated under neutron fluence at temperatures 1,570-1,770 K.

■ • A Samples are cutting per­pendicularly to compaction axis; □, О, Д Samples are cutting in parallel direction to compaction axes; 1, 2, 3 measurements after irradia­tion; 4 measurements during irradiation

1021 cm-2, hydride swelling by 1.5 % is possible [13]. The temperature dependence of the zirconium hydride swelling is nonmonotonic. The minimum of swelling is observed at 550K and at 800 K is the maximum. The electric resistance changed on 7 % after 3,000h of irradiation by a fast neutron flux with the density 3-1020 cm-2 at 855K [14]. The heat conduction of ZrH1,8 irradiated by a fast neutron flux with the density 3.2-1021 cm-2 at 320 K decreased from 31 to 18Wm-K-1 [14]. As awhole, the results of irradiative studies suggest that the efficiency of the HRA in the NRE in the engine and energy regimes is retained.