This paper characterises the residual stress in nuclear reactor pressure vessel steel clad with nickel-based alloy and investigates the interaction between residual and thermal stresses during thermal shock. Residual stress measurements were made on two plates of SA508 Grade 4N steel, clad with Alloy 82 nickel-based alloy. The techniques used to measure the residual stresses were: deep hole drilling, centre hole drilling, and the contour method. One plate was as-welded, the other post-weld heat-treated. The post-weld heat-treated plate was subjected to thermal shock by heating it up and then spraying the surface of the cladding with cold water. The residual stress was measured again afterwards. A finite element simulation was made to investigate the physical mechanisms causing residual stress redistribution during thermal shock. Thermal shock caused significant residual stress redistribution in the cladding due to elastic-plastic interaction between the thermal stress and the cladding residual stress. The results demonstrate that an assessment of the safety of a reactor pressure vessel during thermal shock could be conservative for small surface defects if it is assumed that residual and thermal stresses combine elastically.

Aims and method The Maintaining Adherence Programme (MAP) is a new model of care for patients with schizophrenia, schizoaffective disorder and bipolar affective disorder which aims to encourage adherence and prevent relapse. This evaluation, conducted by retrospective and prospective data collection (including patient questionnaires and staff interviews), aimed to describe MAP's impact on healthcare resource use, clinical measures and patient and staff satisfaction, following its implementation in a university National Health Service (NHS) foundation trust in England. We included 143 consenting patients who entered MAP before 31 March 2012.Results In-patient bed days and non-MAP NHS costs reduced significantly in the 18 months post-MAP entry. At 15–18 months post-MAP, Medication Adherence Rating Scale scores had improved significantly from baseline and there was a shift towards less severe clinician-rated disease categories. Based on patient surveys, 96% would recommend MAP to friends, and staff were also overwhelmingly positive about the service.Clinical implications MAP was associated with reduced cost of treatment, improvements in clinical outcomes and very high patient and staff satisfaction.

Nuclear reactor pressure vessels must be able to withstand thermal shock due to emergency cooling during a loss of coolant accident. Demonstrating structural integrity during thermal shock is difficult due to the complex interaction between thermal stress, residual stress, and stress caused by internal pressure. Finite element and analytic approaches exist to calculate the combined stress, but validation is limited. This study describes an experiment which aims to measure stress in a slice of clad reactor pressure vessel during thermal shock using time-resolved synchrotron X-ray diffraction. A test rig was designed to subject specimens to thermal shock, whilst simultaneously enabling synchrotron X-ray diffraction measurements of strain. The specimens were extracted from a block of SA508 Grade 4N reactor pressure vessel steel clad with Alloy 82 nickel-base alloy. Surface cracks were machined in the cladding. Electric heaters heat the specimens to 350°C and then the surface of the cladding is quenched in a bath of cold water, representing thermal shock. Six specimens were subjected to thermal shock on beamline I12 at Diamond Light Source, the UK’s national synchrotron X-ray facility. Time-resolved strain was measured during thermal shock at a single point close to the crack tip at a sample rate of 30 Hz. Hence, stress intensity factor vs time was calculated assuming K-controlled near-tip stress fields. This work describes the experimental method and presents some key results from a preliminary analysis of the data.

No abstract

Residual and thermal stresses have a considerable effect on the process of brittle fracture. In addition to this, the effect of these stresses on elastic-plastic fracture is known to be significant. This is accounted for in structural integrity assessment methodologies such as R6 Rev 4 and BS 7910:2013 by introducing factors representing the interaction between primary and secondary stresses (those that do and do not contribute towards plastic collapse, respectively). The initiation of ductile tearing in a ferritic pressure vessel steel was studied experimentally. Energy-dispersive X-ray diffraction was used to determine lattice strains in the vicinity of a crack tip in modified compact tension specimens at incremental loading steps until the initiation of ductile tearing. The X-ray diffraction measurements allowed the stress field to be evaluated with a high spatial resolution. At the same time, the pattern of total strain at the surface of the specimen was observed using digital image correlation. Prior to the experiment, two samples were subjected to localised out-of-plane compression ahead of the crack tip to introduce a residual stress field and hence significant crack loading in the absence of external load. Stress and strain field data for cracked specimens, with and without a pre-existing residual stress field, indicated significant differences in the development of plastic strain up to the point of tearing initiation. It is shown that this can only be explained when both residual stress and prior material hardening are taken into account.