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Experiments have been performed on a Zircaloy-2 sheet material to evaluate nanoindentation as a technique for measuring the Young’s modulus and hardness of the nuclear material. Room temperature transverse and longitudinal mechanical properties of an unirradiated Zircaloy-2 sheet material were measured with nanoindentation. The results were compared with those of tensile testing and Vickers microindentation obtained on the same material. Anisotropy evaluated with the conventional methods of microhardness measurement and tensile testing could be accurately confirmed by the nanoindentation measurement technique. The results show that the nanoindentation technique can be used to measure the Young’s modulus and hardness of small-volume samples of the material. The constraint factor, employed for converting hardness to yield strength, has also been determined and is reported for the material.

A single hydride platelet and the matrix material next to it in a Zircaloy-2 cladding have been targeted for hardness, H, and Young’s modulus, E, measurement using nanoindentation. The results were compared with those obtained in the matrix material far away from the hydride. The results show that hardness and Young’s modulus in the hydride are higher than those of the matrix adjacent to the hydride, which are the same as those of the matrix far away from the hydride.

At the Studsvik research reactor R2, a Boiling Capsule (BOCA) is used for long-term irradiation of BWR and PWR fuel rods. The BOCA experiment consists of a pressurised container that can hold a number of fuel rods in a bundle type configuration. The water flow inside the tube is driven by natural circulation. The coolant flow rate is not normally measured in the BOCA rig. Only thermocouples, measuring the water temperature at pertinent locations, are located inside the pressure tube. To confirm calculated values of the flow rate, transit time determination through the cross-correlation technique has been implemented. Campaigns of noise measurements have been performed at five different occasions. The measurement campaigns have included ∼10 thermocouples at 3–4 different power levels. The results for the flow rate range between 0.15 and 0.35 m/s depending on reactor power level. The statistical accuracy of the results has also been evaluated. This paper shows that signal processing of thermocouple signals can be used to obtain rather accurate values of the flow rate in BOCA.

During the last 15 years, the problem of BWR instabilities has attracted the attention of a number of researchers. In 1996, an unusual instability event occurred at Forsmark-1 in which superimposed on the classical, fundamental spatial mode oscillations, there were relatively large-amplitude, highly localised oscillations. Subsequent time-series analysis of the local power range monitor (LPRM) signals resulted in very different decay ratios for the two sides of the core (from ≈0.2 to ≈1.0), an inexplicable result. Furthermore, noise analysis-based localisation techniques pointed towards the existence of two strong ‘perturbation sources’ in the two halves of the core, one of them coinciding with the radial position of an unseated bundle. Motivated by these findings and the fact that as was found later, at least one bundle was unseated, the code RAMONA3-12 was used in order to try to simulate these experimental findings, by assuming that in some bundles, there are relatively large amplitude thermohydraulic perturbations. These perturbations (which are in fact density wave oscillations) were excited by modifying the inlet loss coefficients of the bundles in question.

The neutron noise, induced by a rod manoeuvring experiment in a pressurized water reactor, has been calculated by the incore fuel management code SIMULATE. The space- and frequency-dependent noise in the thermal group was calculated through the adiabatic approximation in three dimensions and two-group theory, with the spatial resolution of the nodal model underlying the SIMULATE algorithm. The calculated spatial noise profiles were interpreted on physical terms. They were also compared with model calculations in a 2-D one-group model, where various approximations as well as the full space-dependent response could be calculated. The adiabatic results obtained with SIMULATE can be regarded as reliable for sub-plateau frequencies (below 0.1 Hz).

In a previous publication, a 2-D reactor model was introduced which contained a partially inserted thin absorber. Both the static flux, as well as the noise induced by the vertical oscillations of the rod were calculated by analytical methods. In this paper the validity of certain reactor kinetic approximations of the dynamical problem are investigated in the same reactor model. The induced noise is calculated in the adiabatic and in the plateau frequency approximation and compared with the exact solution. The significance of these two approximations is that they can be applied with existing core calculation codes either directly, or with minor modifications.

We have performed laboratory measurements of the neutron flux and its gradient in a static model experiment, similar to a model problem proposed in Pazsit (Ann. Nucl. Energy 24 (1997) 1257). The experimental system consists of a radioactive neutron source located in a water tank. The measurements are performed using a recently developed very small optical fibre detector. The measured values of the flux and its gradient are then used to test the possibility of localising the source. The results show that it is possible to measure the flux on the circumference of a circle and from this calculate the flux gradient vector. Then, by comparison of the measured quantities with corresponding MCNP calculations, both the direction and the distance to the source are found and thus the position of the source can be determined.

The spatial dependence of thermal and fast neutron flux was measured axially in the core of a 1 MW research reactor. The measurements were made by a thin optical fibre detector with a neutron sensitive ZnS(Ag) scintillation tip. For thermal neutrons 6 Li was used, whereas for fast neutrons 232 Th was used as neutron converter. The spatial dependence was measured by moving the fibre axially with a uniform speed. The measurement takes a few minutes, compared to up to 10 h with the conventional wire activation method. Comparison with traditional measurements shows a good agreement.

In conceptual and model studies of neutron noise and diagnostics, and even in most practical applications, simple homogeneous reactor models have been used so far, in which closed form analytical solutions are possible. In this paper a less trivial, axially non-homogeneous reactor model is used. In this model both the static flux and the noise equations can still be solved by analytical methods. The model consists of a 2-D homogeneous rectangular core in which a δ-function (Feinberg-Galanin) control rod is inserted partially. Solution of both the static flux and the dynamic equations (the latter corresponding to a rod manoeuvring experiment in which the rod is moved up and down periodically) can be given by two different analytical methodologies. Both are calculated and discussed in the paper. This model will be used later in concrete diagnostic applications as well as in studies of reactor kinetic approximations.

The flux of 14.1 MeV neutrons was measured with high spatial resolution in the vicinity of the target of a D–T neutron generator. The measurements were made by a thin optical fibre detector with a ZnS(Ag) scintillation tip mixed with a 232 Th neutron converter. The detector concept was originally developed at Nagoya University. The flux of 14.1 MeV neutrons could be measured with a spatial resolution of about 1 mm. The position of the impact area of the deuterium beam on the target surface was determined by the method as an application. A simple model for the calculation of the space dependence of the flux was developed, and it was shown to agree very well with the measurements. With the help of the model, both the vertical and horizontal position of the beam impact area centre can be determined from one single measurement through parameter fitting.

Diagnostics of core-barrel motion, and notably that of beam mode vibrations, has been usually performed by two distinct concepts. One strategy is to perform a qualitative analysis in the time domain, using descriptors such as vibration trajectory, probability distributions etc. This approach is rather realistic in the sense that it allows for general anisotropic pendular vibrations. The other strategy is to use frequency analysis with the goal of quantifying certain vibration properties. However, this second approach could so far handle only isotropic and unidirectional vibrations. In this paper we propose a unification of these two approaches by introducing a model by which general anisotropic vibrations can be quantified in the frequency domain. However, when separating the noise components prior to the frequency analysis, we suggest the use of symmetry properties of the noise in the time domain, based on reactor physics assumptions, as opposed to the earlier methods that use statistical independence of the components. Due to the unified approach, a combination of time and frequency domain analysis methods can be used for presentation and maximum information extraction.

Tomographic methods applied to soft X-rays emitted from a fusion plasma have long been used to diagnose and interpret magnetohydrodynamic and other plasma activities. However, fluctuation analysis has recently been proposed as a complementary method to tomography. The novelty of the suggested method is that the various modes can be determined without tomographic inversion. This paper reports on the results of correlation and spectral analysis of soft X-ray data. The seven measurements analyzed were made by the Joint European Torus (JET) Joint Undertaking using their old soft X-ray measurement system. Auto power spectral densities and phase relations were evaluated from the measured signals as functions of the lines of sight. The fundamental mode m = n = 1 was identified in several measurements. The corresponding frequency and toroidal rotation velocity were determined. Higher order modes were also observed and identified. Furthermore, simple model calculations were performed and the results compared with evaluated auto-spectra.

Separation of various flux oscillation modes in boiling water reactor (BWR) noise measurements, based on flux factorization techniques (i.e., using orthogonality relations via integrals over the whole core), have been attempted in the past but without much success. One such example is the attempt made in 1990 in connection with the measurements in the Swedish Ringhals Unit 1 (Ringhals-1) BWR where both global (fundamental-mode) and regional (first-azimuthal-mode) oscillations were observed. Shown here is the reason for the failure of the earlier separation methods, that is, the presence of the local component of the noise with its known axial correlation properties. This component has been ignored in all BWR instability work so far. Further because of the approximation of the factorization integral by a finite sum, cross-correlations between all detectors will appear in the autocorrelation of the factorized detector signals. Taking into account the properties of both the noise structure and the approximate factorization, elaboration of factorization-based flux decomposition is possible. A phenomenological BWR noise model is used here in support of the decomposition technique. The model is also used to explain the success or failure ofprevious methods. The general factorization method proposed is demonstrated in various examples using the Ringhals-1 measurement data. In particular, the global and regional decay ratios are determined in a consistent way that is more general than the alternative methods used so far.

In two previous papers the neutron noise, induced by small vibrations of a strong absorber, was treated (Pazsit 1984, 1988). In these, two different rod models and corresponding different linearization procedures were used. The first, called the Feinberg-Galanin-Williams (FGW) model, uses a δ-function approximation of both the static and the vibrating rod. This model corresponds to preserving the static boundary condition (logarithmic derivative) at the surface of the moving rod. The second, a perturbative approach called the ϵd model, starts with a finite absorber and represents the vibration by two stationary absorbing layers with strengths fluctuating in opposite phase. It was found that these two models lead to differing results, indicating a contradiction. In this paper we show that the reason for this contradiction is that the previous results based on the ϵd model are in error. The error is due to the fact that the effect of the static rod was neglected in the Green's function. The correct ϵd result is calculated here in both one and two dimensions and is shown to be equivalent to the FGW results. This serves also as a confirmation of the two-dimensional FGW result which had earlier been derived only by heuristic arguments.