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Reactor Temperature Control

#3780


Modernization of Metrological Security of Reactor Thermometry Taking into Account Quality of Thermal Contact Between Thermocouple and Object and Degradation of its Characteristics at Irradiation

Tech Area / Field

  • FIR-INS/Nuclear Instrumentation/Fission Reactors
  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors
  • NNE-HCS/Heating and Cooling Systems/Non-Nuclear Energy

Status
3 Approved without Funding

Registration date
20.06.2007

Leading Institute
NPO Lutch, Russia, Moscow reg., Podolsk

Supporting institutes

  • Novovoronezhskaya NPP, Russia, Voronezh reg., Voronezh\nMIFI, Russia, Moscow\nOKB Gidropress, Russia, Moscow reg., Podolsk

Collaborators

  • Fortum Nuclear Services Ltd, Finland, Espoo\nSCK-CEN, Belgium, Mol

Project summary

Metrological security of temperature measurements by contact methods, allowing to define true significances of measured temperatures, in the objects of nuclear energy is one of conditions of economic and safe operation of atomic power stations. However, traditionally applied settlement methods of definition cannot provide with true of temperature required accuracy as they do not provide the adequate account of additional heating of the thermocouple with intensive nuclear radiation at the presence of contact thermal resistance between the sensitive element and object and as well as degradation changes of graduation characteristics of the thermocouple, which are caused by transmutation of nucleuses of thermo-electrode materials and by imperfection of their structure under action of neutrons.

Meanwhile, according to our researches the variations of a thermal resistance contact of the sensor with the object in the channel of the first PWR contour while in service cause an overstating of indications of temperature measuring instruments of up to ~2К, and in situations of poor-quality installation - of up to 5 ч 6 К, when a tolerable uncertainty of results is 1К. The situation with measurement of temperature of a fuel element (FE) cooled cladding during the work on safety of the atomic power station with PWR, conducted both on stands and research reactors, is even more critical. In experiments of EDB "Gidropress" at the stand of critical thermal currents the temperature uncertainty reached several hundreds of degrees at the level of 10К permissible by TC IAEA.

Data, presented in the literature, on the change of thermoelectric properties of a thermocouple during its long operation in the power nuclear reactor are in poor agreement among themselves, that fact excludes their practical application for finding true of temperature.

We have studied the above mentioned problems during the work on tests of FEs of the nuclear rocket engine on high-flow reactors, where the account of influence of effect of radiation to a signal of the thermocouple has appeared obligatory. The researches on change of thermocouple EMF for great fluencies (~1022 neutr./cm2) of thermal neutrons have been also carried out.

In the proposed project the authors introduce their developed patented special methods of a pulse thermal effect on the thermocouple, which is in the working reactor of the atomic power station, and the subsequent analysis of the response of the thermocouple. The quantitative characteristic of the thermal contact (a factor of thermal inertia of a thermocouple in the measurement position) allowing to calculate the amendment for reception of an exact temperature significance with the help of the formulas, developed by the authors, is defined by the characteristic of the response which is specific for a concrete measuring problem.

Finishing of the given developments up to a level of large-scale introduction into the contact thermometry of NPP reactors is the basic purpose of our project – offer to the ISTC.

As a result of fulfillment of the project there will be developed:

  1. complex of calculation models, which allows to provide the adequate account of the above listed factors, and these models are the theoretical basis of metrological maintenance of temperature measurements inside of NPP reactors;
  2. calculation and experimental models of degradation degree of calibrating characteristics of thermocouples;
  3. equipment allowing to probe a contact thermal resistance of the thermocouples fixed in the reactor and to define its impact to uncertainty of measurement results at stationary and dynamic modes of operation.

Using the offered developments makes it possible to carry out the following work at NPP:
  1. estimation of admissible limits for an increase of rated reactor power;
  2. substantiation of admissible borders for maneuverability of reactor installations;
  3. estimation of a stock before the heat exchange crisis on the basis of the analysis of derivatives of coolant temperature increase.

The offered project corresponds to ISTC purposes as, except for attraction of scientists and experts from the area of development of arms to development of civil production, the results of work above the project will introduce a substantial contribution to increase of power efficiency, reliability and safety of nuclear power reactors.


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