Dounreay Fast Reactor Research Articles

Calculation of relative displacement damage rates in differing reactor types

A number of materials not necessarily destined for use in fast reactors, in which atomic displacements are the main damage mechanism under observation, are presently being irradiated in the Dounreay Fast Reactor. In this paper it is shown that, if it can be accepted that the ratio of atomic displacement rate in the test reactor to displacement rate in the parent reactor is an acceptable parameter for comparison purposes, then the atomic displacement energy and the electronic cut off energy of a material are not critical parameters in the derivation of this ratio. It is also shown that, if the equivalent fission flux concept is used to describe reactor spectra, it can lead to appreciable errors in deriving the damage ratio, but that integration over the real spectrum is unnecessary below about 0·1 MeV.

Lattice parameter and dimensional changes in graphite irradiated between 300 and 1350°C

The changes in lattice parameters and dimensions of graphite irradiated in the range 300–650°C up to a dose of 5 × 10 21 n.cm −2 have been attributed to four types of radiation defect. These are vacant lattice sites, interstitial loops, vacancy lines and vacancy loops. Evidence for the occurrence of these defects is discussed and their concentrations are determined from the experimental data. The values obtained are used to check theories of the nucleation and growth of interstitial loops and vacancy lines. Graphite has also been irradiated to high doses in this temperature range in the Dounreay Fast Reactor and at higher temperatures to somewhat lower doses in the reactor PLUTO at Harwell. Quantitative analysis is not possible under these conditions but qualitative interpretations of the behaviour are put forward.

66. Lattice parameter and dimensional changes in graphite irradiated between 300 and 1350°C

Abstract The changes in lattice parameters and dimensions of graphite irradiated in the range 300–650°C up to a dose of 5 × 10 21 n.cm −2 have been attributed to four types of radiation defect. These are vacant lattice sites, interstitial loops, vacancy lines and vacancy loops. Evidence for the occurrence of these defects is discussed and their concentrations are determined from the experimental data. The values obtained are used to check theories of the nucleation and growth of interstitial loops and vacancy lines. Graphite has also been irradiated to high doses in this temperature range in the Dounreay Fast Reactor and at higher temperatures to somewhat lower doses in the reactor PLUTO at Harwell. Quantitative analysis is not possible under these conditions but qualitative interpretations of the behaviour are put forward.

Voids in Irradiated Stainless Steel

DURING development work on fuel elements for fast reactor applications, electron microscope examination by the thin foil technique has been carried out on samples of stainless steel irradiated in the Dounreay Fast Reactor, either in the form of cladding on experimental fuel elements or as specimens intended for mechanical property tests. The steel had a composition falling within the American Iron and Steel Institute type 316 specification as shown by the analysis given in Table 1.

Determination of dose and temperature in graphite irradiation experiments in the dounreay fast reactor

Two graphite irradiation experiments have been performed in a pitch 30 position of the Dounreay Fast Reactor core. The changes in dimensions and thermal conductivity of the graphite in these experiments have been correlated with similar changes produced by irradiations in the Harwell Reactor Dido at known temperatures. This allows the determination of the relation between the damaging power of the neutron spectrum in this D.F.R. position with that of the Dido spectrum. The relation is expressed in terms of the fast-neutron flux in the two reactors, using the reaction 58Ni (n, p) 58Co. To produce the same state of damage in graphite, the fast-neutron dose required in Didois about twice that in the D.F.R. position investigated. In the D.F.R. experiments silicon carbide specimens were included with the object of estimating irradiation temperatures. It is concluded, from the results of measurements made on these specimens and from a comparison of D.F.R. and dido data, that an equivalent temperature correction is necessary for dimensional changes over the full range of temperatures covered by the D.F.R. experiments. It cannot be concluded whether a similar correction is necessary for thermal conductivity changes for D.F.R. irradiation temperatures above 600°C.

Dimensional changes and radiation creep of graphite at very high neutron doses

The paper presents the results of graphite irradiations carried out in the Dounreay Fast Reactor. The use of this reactor for graphite irradiations is advantageous for several reasons. The total neutron flux is very high, practically all the neutrons have energies capable of producing damage in graphite and there is a very long fuel cycle. These circumstances have enabled experiments to be carried out to a maximum dose of ~3.8 × 10 22 n.cm −2 in the course of a few months at temperatures in the range 260–500°C. The results are discussed in terms of current theories of dimensional changes and radiation creep; the dimensional changes follow the trends expected but a high tensile creep strain (> 2%) is observed.

Measurement of gamma heating in D.F.R.

A series of experiments has been carried out in the Dounreay Fast Reactor at power levels from 1 to 60 MW to measure the gamma heating (total energy deposition) in materials such as tungsten and stainless steel. Most of the measurements were made in the first row of the breeder and in this position the mean value for the gamma heating in stainless steel was found to be 28 mW/g·MW ± 15%. Several different calorimeter designs are discussed, the electrical calibration procedure is outlined; one standard type and the novel twin bulb differential calorimeter are described in detail.

A calorimetric determination of fission product heating in fast reactor plutonium fuel

Fission product heating in plutonium irradiated in the Dounreay Fast Reactor has been measured using a Calvet microcalorimeter. By use of small, lightly canned samples and a γ-absorber, the β- and γ-power contributions were measured separately over a range of decay times between 40 and 150 days after shutdown.

Dimensional Changes and Radiation Creep in Graphite at Very High Neutron Doses

RADIATION creep1–4 is the deformation produced by the combined effect of stress and irradiation in a nuclear reactor. In graphite, radiation creep consists of a permanent set, transient creep, and steady-state creep. The permanent set and transient creep are comparable with the elastic strain and it is normally assumed that the steady-state creep is proportional to the stress and the total neutron dose. It is of some interest to know whether the steady-state creep can become large compared with the elastic strain. The initial creep rate is such that this requires a fast neutron dose of ∼ 1022 n cm−2. Such neutron doses can be obtained in the course of a few months in the Dounreay Fast Reactor, at the centre of which the neutron flux is ∼ 2.5 × 1015 n cm2. Graphite samples have been irradiated in the fast reactor under stress and creep strains of several per cent have been obtained. The elastic strain at breaking in tension is ∼ 0.1 per cent.

A correlator for investigating random fluctuations in nuclear power reactors

In nominally steady operation of a nuclear power reactor small fluctuations are observed in various parameters, e.g. reactor power, coolant flow and temperature. The cross-correlation between simultaneous recordings of these fluctuations can give information on the kinetics of the reactor system without disturbing its normal operation. An apparatus has been built to explore the practical possibilities of the technique and this paper describes its design principles, practical implementation and the results of tests. Some typical results obtained on the Dounreay Fast Reactor are also given. The equipment records the fluctuations in four channels on magnetic tape, the correlation functions being obtained subsequently by analogue computing techniques in an accelerated time scale. A novel feature is the use of a continuously-rotating magnetic drum with multiple heads to delay one signal relative to another. Delays equivalent to 25 seconds in recording time can be obtained, the smallest delay being 0.05 second. Tests with sinusoidal signals show that frequencies can be measured to better than 2% and the r.m.s. error of all points on the correlation curve is less than 2% of full scale. These errors are shown to be considerably less than the statistical errors due to the finite recording time.

The rhometer: a continuous impurity monitor for liquid metal circuits

The rhometer uses the change in resistivity with impurity content of liquid metals, mainly sodium and sodium-potassium alloy, to measure the amount of impurities, such as oxide and hydride, etc., down to a few parts per million. It is a 'non-contact' or electrodeless instrument, in that the liquid metal through a toroidal pipe which forms one turn of a 50-c/s transformer. The output from this transformer is fed to a phase-sensitive rectifier, and changes in resistivity are then indicated on a standard chart recorder. A special circuit compensates for changes in resistivity caused by changes in temperature of the liquid metal. Operating experience with the rhometer in the primary coolant circuits of the Dounreay Fast Reactor is described in detail, and some possible future trends in the further development of the instrument are briefly discussed.

Noise measurements in the Dounreay fast reactor

Noise measurements in the Dounreay fast reactor

Nuclear Engineering Monographs—Fast Reactors

By R. G. Palmer and A. Platt London: Temple Press Ltd. Pp. x + 93. Price 12s. 6d. The prospect of making efficient use of the plutonium produced in thermal reactors by utilizing it in the fuel elements of fast power reactors, with their potential ability to produce more plutonium than is consumed, has led to a considerable effort being devoted to the development of these systems. In this monograph the authors, who are actively engaged on the Dounreay Fast Reactor, have presented a broad outline of the main trends in the development of, and the techniques applied in, the fast reactor field.

Resistivity monitor to indicate oxide content of sodium

The electrical resistivity of sodium or sodium-potassium is continuously measured whilst flowing at operating temperature in a pipe, to provide an indication of impurity level, particularly oxygen, and thus to enable progress of clean-up in liquid-metal loops to be followed and to give assurance that high purity is achieved and maintained. The meter is designed to be sensitive to a change of one part in 106 in oxygen level, corresponding to a change in resistivity of about one part in 104. A change in liquid-metal temperature of only 0.04° C will also produce this effect, and hence temperature compensation and achieving high stability are the chief problems of the design. Two types of resistivity meter are described, both of which have been installed in the Dounreay fast reactor. Tests indicate that the design objective has been achieved and the value of the meter as an impurity monitor has been proved.