LAUSR

Abstract Fast reactor cores employ a large number of sub-assemblies for neutron and gamma shielding constituting more than 60% of the core volume. Use of effective and economical shielding materials can significantly improve the safety and cost competitiveness of fast reactors. Ferroboron has been identified as an efficient neutron shielding material for deployment in future commercial breeder reactors in India that can lead to significant cost savings. After successful shielding experiments and out-of-pile compatibility tests, a SS 304L clad irradiation capsule containing ferroboron powder has been subjected to an accelerated irradiation test in Fast Breeder Test Reactor (FBTR) to a peak neutron fluence of 8.18E21 n/cm2 for evaluating its in-reactor performance. Results of Post Irradiation Examinations carried out on the irradiation capsule to assess the various performance parameters such as slumping of ferroboron stack, helium release and chemical interaction of SS 304L with ferroboron are reported here. The examinations have indicated that extent of slumping is less than 1% and pressure build up due to helium release is 0.17 MPa (at room temperature), which are well within the permissible limits. A maximum clad wastage of 20% of wall thickness has been observed due to chemical interaction with lithium produced from (n,α) reaction. The irradiation performance assessment of ferroboron indicates its suitability for in-core shielding application in fast reactors.