Browsing by Author "Metcalf, P"

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    OPAL engineering early modifications relating to AOC: loss of offsite power (LOOP)
    (International Group On Research Reactors, 2010-09-19) Metcalf, P; Humphrey, C
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    OPAL engineering strategies to manage neutron guide seal leaks
    (European Nuclear Society, 2012-03-18) Humphrey, C; Metcalf, P
    In the first two years following hot commissioning of the OPAL Reactor in 2006 light water leaks were detected in all five (5) bellows leak detection chambers of helium guide cooling system. These seals from part of the primary LOCA barrier for the reactor pool. To date no water has been detected past the double metallic C-seals of the neutron beam assemblies into the assembly boxes. This paper reports strategies implemented by the OPAL Engineering group to manage current leak rates and deal with any future escalation leaks. These include: changes to the reactor control and monitoring system to enable ongoing reactor operation, automation of drainage operation, installation of pool water leak recycling system, design provisions for helium back pressurisation and in-pool mechanical collar seals. The system approved and implemented on the reactor ensure that leaked water is drained from the inter seal void space to limit pressure on the inner seal. The system includes remote real time indication and warning of leak rates and is capable of handling leak rates up to 0.5 m3/h. By automatically recycling water drainage, the system reduced plant radioactive liquid waste discharges and operator dose rates to ALARA.
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    Zener double exchange from local valence fluctuations in magnetite
    (American Physical Society, 2007-12-14) McQueeney, RJ; Yethiraj, M; Chang, S; Montfrooij, W; Perring, TG; Honig, JM; Metcalf, P
    Magnetite (Fe3O4) is a mixed valent system where electronic conductivity occurs on the B site (octahedral) iron sublattice of the spinel structure. Below Tv=123 K, a metal-insulator transition occurs which is argued to arise from the charge ordering of 2+ and 3+ iron valences on the B sites (Verwey transition). Inelastic neutron scattering measurements show that optical spin waves propagating on the B site sublattice (similar to 80 meV) are shifted upwards in energy above Tv due to the occurrence of B-B ferromagnetic double exchange in the mixed valent phase. The double exchange interaction affects only spin waves of Δ5 symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by short-range electron correlations above Tv. © 2007, American Physical Society