Zero Power Experiments

Before installing the reactor core into the ship a zero power experiment was performed in the critical facility ANEX at Geesthacht 16). This experiment 17) was carried out for the following reasons  

checking the actual assembly of the core comprising fuel rods of four different enrichments and poison rods of two densities, 

time-saving for the loading and zero power tests to be carried out on board the Otto Hahn,  

providing data on the radiation intensities in the innermost part of the shielding. These data were to be completed later by measurements throughout the shielding outside the pressure vessel with the reactor at power 18). 

The first reason was the most important. The conflicting demands of long operational life and the stuck-rod condition admitted only a small margin of possible fuel enrichments 19). The check of the stuck-rod safety was the foremost concern because the theoretically predicted value of k ff for one of the outer control rods withdrawn was very close to one due to the relatively large region of a control rod free square element combined with a triangular corner element. Further matters for consideration were the excess reactivity of the core with all control rods withdrawn, the worth of the control rods, and the reliability of the methods used to calculate the power distribution 20). 

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D. J. PELLARIN. N. P. BAUMANN. J. L. CRANDALL, G. F. O NEILL, and R. M. SATTERFIELD, Zero Power Experiments with U-Enriched Thoria and Thorium Metal Lattices for the HWOCR." DP-1125, E. I. du Pont de Nemours and Co., Savannah River Laboratory (to be published 1968). 

Performance of a zero power experiment with one module in a nuclear experimental facility ... 

Performance of zero power experiment with a single-module at a critical facility Construction of a single-module prototype. 

One part of the FDR zero power experiments consisted of measuring the neutron flux distribution in three dimensions. For this task aluminum tubes were inserted in the experimental quarter of the core parallel to the fuel rods (Fig. 12) inside these tubes semiconductor detectors with Li converter foils could be moved up and down. The a-particles emerging from the reactions Li (n,a) H induce pulses in the biased circuits of the semiconductors, these pulses being counted in a counting device 34). The measurements all over one quarter of the core resulted in an experimental Li absorption rate distribution (20, 34). 

Anything raised to the zero power yields T, therefore, this is a zero-order reaction for B. We can perform a similar procedure in experiments 3 and 1 to determine the reaction order for A. Since [B] is constant in experiments 3 and 1, we can cancel it ... 

Let us now examine the two minor disadvantages of the laser time-resolved experiments which we mentioned briefly. The low radical concentration normally encountered in such experiments makes evaluation of E-A-type polarization difficult. In fact, even when the radical concentration is not a problem, as in pulse radiolysis study, the time profile has to be fitted to obtain the enhancement factor (124). Another aspect in the time-resolved study is that the experiments have to be repeated at different microwave power levels, as the true intrinsic P or V can only be obtained by extrapolation to zero power. Ironically, these two problems can be overcome readily in semi-steady-state experiments using a conventional slow-response spectrometer. 

Evaluation of Integral Physics Experiments in Fast Zero Power Facilities Edgar Kiefhaber... 

The preparation of cross sections for control rod absorbers requires a special treatment due to the very high coupling of the heterogeneous control rod structure to the surrounding core cells. The method used is the reactivity equivalence method [9] which has been validated on the BALZAC IH experiments performed in the MASURCA zero-power critical mock-up in Cadarache [9]. This method uses the Sn transport option of the BISTRO code and its associated perturbation modules. The validity of such an approach for control rods has been evaluated not only for the reactivity variation of the control rod but also for the absorption rates in the control rod and the surrounding core regions. 

Concerning the R D for the CEFR, besides the facilities already prepared, for danonstradmi of thermohydraulic characterisdes of natural convection, a water simulation reactor pool fidliiy in about one third scale is planned, in order to prepare the reactin pl cs expoiments for its start-up, the zero power fast neutron facility with 50kg U-235 has been restored, for endurence testing of core subassemblies and getting some sodium loop operation experiences, Italian ESPRESSO and CEDI are unda reconstraction in our lab. 

A neutron zero power facility with only SOkg U-235 has been built up in 1970, then moved to the South-West center of Reactor Engineering in Sichuan P rovince. Basic zero power physics experiments have been done at diis facility including critical parameter measurements, fission rates, neutron flux distribution, neutron spectrum, material reactivity etc. in 1988, it was removed to ClAE again, and now it has been rebuilt and will be used for proving of the neutronics experiment medtods which will be served to CEFR first start-up and to primary test for die neutronic and other radiation detectors. It is considered also it will be valuable to the evaluation of some specimen nuclear cross section using its hard spectrum. 

Zero Fow r Test Studies on Martin Power Reactor, bg IF. . Otmeifer and B. B. Roeenthcd (MARTIN),. Ejqpodmental results have bem obtained from die Zero FOwm Test performed on the Ma n Power Reactor core The reactor is a heterogdious water-moderated, fully enriched core using tubular fuel elements. The core is cylindrical in shape and contains approximately 18.6 kilograms of U-235 with a total reactivity of about 15%. In the core are six Y shaped rods which are prototypes of the control rods in the Martin Power Reactor. The Zero Power Test reactor is controlled by three blade-shaped control rods (critical experiment rods). In addition, two or three "Y shaped rods used for safety depending on experimental requirements. 

Although the logistic problems involved with rl8 000 fuel pieces and 600 000 pieces of depleted uranium, canned sodium, Iron oxide, uranium oxide, etc., are significant, extension of many years experience with the smaller facility Zero Power Reactor 3 (ZPR-3) indicates that safe and efficient operation of ZPPR can be achieved. 

A series of fast reactor critical experiments at the zero-power plutonium reactor (ZPPK) is providing benchmark physics data for both conventional and heterogeneous LMi BKs in tlie 600- to 700-MW(e) size class, this data base is similar to one established by an earlier series related to fast reactors of 3S0-MW(e) size. This paper discusses the scope of the program, outlines the measurements being emphasized, and presents some results from the conventional core experiments. 

Chemists first tried using domestic kitchen microwave ovens to speed up chemical reactions. They found that they were able to accelerate reactions, increase yields, and initiate otherwise impossible reactions. The results were often unsatisfactory, however, owing to uneven heating, lack of reproducibility, and the possibility of explosions. The power output of a typical kitchen microwave oven carmot be adjusted. The oven cycles between periods of full power and periods of zero power. This means that the amoimt of microwave energy being transmitted into an experiment cannot be controlled precisely. 

Provision has been made in the Winfrlth reactor for the insertion of flux measuring wires along the axes of the fuel elements. Wires may be loaded or withdrawn with the reactor on power. Copper wires were used during the zero energy experiments to check the radial and axial neutron flux distribution. 

The time scale which is employed for the radiation experiments is cumulative time with the reactor at power. During exposure of a given experiment, the reactor was frequently at zero power for appreciable periods. It has been observed in autoclave experiments that a penetration of from 0.005 to 0.01 mil takes place after shutdown and that, following this, corrosion essentially stops until power operation is resumed. The corrosion which takes place during shutdown appears to delay the onset of attack when irradiation is reinstituted the amount of delay about balances off the additional attack which occurs during shutdown. In view of this behavior, the practice has been adopted of using radiation time only in calculating corro.sion rates [5.3]. 

Here, An0 is the population difference at equilibrium, prior to the time that the microwave power is turned on. Equation (22) shows that the population difference decreases exponentially to zero with increasing time. This is important because the power absorption, which is ultimately measured in the ESR experiment, is related to this population difference by the equation... 

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