Joakim K.-H. Karlsson

• Ph.D
• Senior Researcher at Studsvik Nuclear AB

One concern during the interim dry storage of spent fuel is hydride reorientation and its effect on cladding integrity. Previous studies with liner cladding show that a low-alloyed zirconium liner will act as a sink for hydrogen and, given sufficient time, hydrogen in solid solution will migrate toward the liner, leaving less hydrogen available for...

In a cooperation between Kernkraftwerk Brunsbüttel (KKB), which is a boiling water reactor (BWR), and Studsvik Nuclear AB, a post-irradiation examination (PIE) project is carried out on 13 Special Fuel Rods at the Studsvik Hot Cell Laboratory. The rods are considered Special Fuel Rods because different defects occurred in these rods during operatio...

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 hig...

The Studsvik Cladding Integrity Project (SCIP) is an OECD/NEA multilateral international research program. SCIP III is a five-year experimental program carried out from 2014 to 2019 focused on fuel behavior in LOCA and overheating transients. The program brings together 32 organizations in 14 countries in a joint research effort. In SCIP, modelling...

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 compare...

The NEA Working Group on Fuel Safety (WGFS) is promoting the understanding of fuel-safety issues by assessing the technical basis for current safety criteria and their applicability to high burnup and to new fuel designs and materials. The group aims at facilitating international convergence in this area, including the review of experimental approa...

A modified burst test (MBT) was used in an extensive test program to characterize fuel cladding failure behavior under rapid loading conditions. The MBT differs from a normal burst test with the use of a driver tube to simulate the expansion of a fuel pellet, thereby producing a partial strain driven deformation condition similar to that of a fuel...

The topic of pellet cladding interaction (PCI) in light water reactor (LWR) fuel rods is reviewed and further explored in this paper by considering the mitigating effect of slow ramps. To that end, a number of PCI mitigating mechanisms were considered in relation to several failure criteria, including peak stress, strain energy density and other cu...

Fuel pins from advanced gas cooled reactors in the UK have been transported to the Studsvik hot cell facility in Sweden for post-irradiation examinations (PIE). The examination program has included visual inspections and length measurements, axial and rotational gamma scans including burnup determination, pin puncturing and fission gas analysis. Th...

Traditionally, power ramp tests are carried out under coolant conditions representative for normal power operation, i.e. typically 286 ºC for BWR conditions. However, power ramps can hypothetically also occur in a BWR at low temperature during reactor start-up. During such transients, for example anticipated operating occurrences (AOOs) such as con...

Secondary cladding defects in LWR fuel can cause large releases of uranium and fission products to the primary coolant. By its very nature, it is impossible to verify the failed fuel performance of new fuel designs in real power reactors using the lead fuel assembly approach, since fuel failures have a very low rate of occurrence. However, such te...

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 m...

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 an...

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 noda...

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 investig...

We have performed laboratory measurements of the neutron flux and its gradient in a static model experiment, similar to a model problem proposed in Pázsit (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...

A method is elaborated and used for the localisation of a channel type instability in a boiling water reactor (BWR) by neutron noise techniques. Localisation means determining the radial position(s) of the fuel channel(s) in which the instability phenomenon occurs. The problem and its solution show clear resemblance to that of the localisation of v...

The spatial dependence of thermal and fast neutron flux was measured axially in the core of a 1MW research reactor. The measurements were made by a thin optical fibre detector with a neutron sensitive ZnS(Ag) scintillation tip. For thermal neutrons 6Li was used, whereas for fast neutrons 232Th was used as neutron converter. The spatial dependence w...

It is well known that after one of the spatial harmonics of a boiling water reactor (BWR) is driven toward limit-cycle oscillations with a decay ratio very close to 1, the nonlinear behavior of the system starts to manifest itself, and a series of resonances appears at frequencies that are multiples of the characteristic oscillation frequency (comm...

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 equa...

An overview of several problems in reactor noise is given. Three relatively different areas are covered, including the use of analytical calculations of the neutron noise in simple reactor models, some aspects of boiling water reactor (BWR) stability and diagnostics of core barrel motion in pressurized water reactors (PWRs).

The flux of 14.1MeV 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 232Th neutron converter. The detector concept was originally developed at Nagoya University. The flux of 14.1MeV ne...

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 gener...

An heuristic approach has been adopted to obtain empirical scaling formulas for the dependence of neutron emission on predefined machine parameters, such as applied auxiliary heating power, plasma current IP, and toroidal magnetic field BT. The results are intended to be used to predict the neutron emission before each discharge. These formulas are...

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...

In two previous papers the neutron noise, induced by small vibrations of a strong absorber, was treated (Pázsit 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 vibrat...

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 witho...

A neutron spectrometer consisting of a number of square shaped hydrogen based scintillating fibres is described. The considered design will have an efficiency of 3·10-3 cm2 for 14-MeV neutrons and is suitable for measurements of energy spectra of collimated fluxes ranging from 106 to 108 n/(cm2s). The energy resolution is ≅ 3.3% (FWHM) which permit...