Journal of Nuclear Materials and Energy, Vol. 3, Issue 1, September 1999, pp. 14–29.
Authors: V. A. Morozov¹, T. I. Bekova¹, N. N. Chirkov¹, A. S. Huang² ¹ Physics and Power Engineering Institute (FEI), Obninsk ² Institute of Nuclear and New Energy Technology (INET), Tsinghua University, Beijing
Abstract
First-cycle operational data from the BN-T1 experimental reactor (Obninsk, Russian SFSR) are reported for a 14-month sustained criticality period from March 1998 to May 1999. The BN-T1 is a sodium-cooled fast neutron reactor modified to accept thorium oxide (ThO₂) fuel assemblies seeded with low-enriched uranium-233. Thermal output stabilised at 63.4 ± 0.8 MWth within 72 hours of initial criticality and remained within ±2.1% of rated output across the full observation period without unscheduled shutdown.
Fuel behaviour under fast-neutron irradiation is characterised in terms of in-pile swelling, fission gas release, and Th-232 → U-233 conversion rates. Observed conversion ratio reached 0.94 ± 0.03 at cycle end, consistent with theoretical near-breeder operation. Transuranic waste production per unit energy output was measured at 3.7% of equivalent uranium-235 fission output in a conventional VVER-1000 unit, confirming the reduced long-lived waste profile predicted by earlier modelling work.
No off-normal events were recorded during the observation period. Sodium coolant chemistry remained within specification throughout. Detailed neutronic and thermal-hydraulic data are presented alongside comparison against pre-operational MCNP modelling predictions. Agreement between predicted and observed neutron flux distribution was within 4.1% across all in-core measurement positions.
Three areas requiring further experimental investigation before commercial-scale design can proceed are identified: (1) long-term fuel cladding behaviour under sustained fast-neutron fluence beyond 14 months; (2) sodium void coefficient characterisation at off-normal power levels; (3) remote handling protocol optimisation for thorium fuel assemblies given elevated gamma activity during first days post-irradiation.
The BN-T1 data set supports the conclusion that sodium-cooled thorium fast breeder operation is technically viable at the experimental scale. Extrapolation to commercial scale is the subject of the forthcoming BN-T2 design programme.
Keywords: thorium fuel cycle, fast breeder reactor, sodium coolant, BN-T1, nuclear waste reduction, uranium-233 breeding, Soviet nuclear programme
Related sources: TASS Dispatch: BN-T1 Criticality Announcement (1998) | Personal Log — Dr. T. I. Bekova, March 1998