Residual power determination of the fissionable fuel.

Stremy, Maximilian ; Elias, Andrej ; Kopcek, Michal 等

1. INTRODUCTION

Slovak and international nuclear regulatory standards are focused to the observance of the safety rules by the manipulation with the fissionable fuel (Regulations for the Safe transport of Radioactive Material, 1996). Applied procedures, methods and programs are approved by the competent institutions following nuclear standards and regulations, but one of the basic principles of the legislative is the duplicate proofing of all reliability and safety parameters of the systems used in nuclear power engineering (Schreiber et al., 2008). Due to this principle originated this project and proposed solution of the residual power determination with help of the mathematical model.

During the transport procedure of the burned-out fissionable fuel (BFF) is necessary to monitor values of some potentially dangerous parameters, e.g. radioactivity, quantity of free neutrons, residual power etc. The biggest problem is to evaluate the quantity of the residual power of the BFF, because the available methods are very inaccurate. Therefore the main aim of this whole project is to verify the accuracy of computations and the residual power real data acquirement of the BFF, which is transported using the type C30 transfer container. The residual power is world widely standard designated using the theoretical nuclear--physic computation. For the verification of computed values is necessary to prove the residual power using experimental measurement and measured values evaluation by the mathematical model. Solution described in the article is the new one and original not only in SR, but even on the international level.

2. BFF TRANSPORTING AND SAFETY LIMITS

After the isolating burned-out fissionable fuel from the nuclear reactor, there are still running some nuclear reactions, which are effecting the heat energy creating. Knowledge of the residual power is therefore important for the BFF safety stocking and transporting.

By the transportation the BFF signed VVER 440 is enclosed and sealed in the safety containter C30.

By the reason of the keeping the limit values of the heat the residual power of the transported BFF cannot overreach the 24kW and the residual power of the each fuel tube has to be below 605W. To achieve the standard safety limits for the radioactivity, total activity of the transporting BFF has to be less than 2,35.1017 Bq.

3. PROPOSED METHODOLOGY

Main goal of the methodology is the proposition of the new approach for the residual power determination of BFF in containers. The proposed methodology is applied by the experimental determination of this parameter and results are compared with the normally used determination method based on the combination of the nuclear and physical computations from the power ratio.

The methodology realization consists of the following parts:

1) Development of the mathematical model of the container represented like the heat system expressed in the form applicable for the computing determinations of the residual power from the measured and known parameters. Mathematical model allows the computation of the BFF residual power in transported container with the relevant input and watched parameters.

2) Specification of the measurement method and computation method of the relevant parameters (e.g. heat transfer coefficient, temperatures etc.) required for the mathematical model.

3) Realization of the systems for the experimental measurement. For the parameters measuring is necessary to project and implement specific software systems (e.g. SCADA), tools and also to proceed few modifications on the BFF container according to the results of the part 2.

4) Execution of the experimental measurements and their evaluation.

On the basis of the experiment results will be implemented the final version of the methodology.

4. MATHEMATICAL MODEL

Methodology of the measurement of the main physical quantities and algorithm for the computation of the BFF residual power are based on the mathematical model. Model is based on the law of conservation of energy adapted to the problem of the BFF container (Incropera & DeWitt, 1996). After the needful mathematical operations the equation for the residual power determination is (Barton & Tanuska, 2008):

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (1)

where S--surface area of the container

a--mean value of the heat transfer coefficient

Te--outside temperature

[T.sub.i]--initial temperature of the container

K--heat capacity of the container

P--residual power

Mathematical model describes the time dependency of the outer wall of the container on the BFF residual power and cooling method. Computation of the residual power from the measured heat values requires the constant temperature and flow method of the cooling medium around the container with the BFF. Representation of the mathematical model is implemented in the math and engineering software called Maple and used for the computation of experiment results from the measured values.

5. MEASURING AND DATA PROCESSING

5.1 Measurement system

About one hundred temperature sensors PT100 (for purpose of the fuel residual power measurement) were systematically placed on the outer casing of the container C30 according to the beforehand prepared allocation pattern. For the data acquisition in the measurement system are used the Advantech ADAM 4015 modules, which are able to communicate with the master system using the ModBus/ASCII protocol over the EIA-485 industrial bus. Every ADAM 4015 provides the connection with six resistive temperature sensors, which are interconnected by the three--wire connection to compensate the disturbances caused by the cable lengths. The lengths of the cables are minimized thanks to the strategic placement of the ADAM 4015 modules in the space around the container. These steps should eliminate the influence of unwanted noises superposed on the measured value.

One of the acquired parameters is the reference temperature inside of the container measured by the precise thermometer CHUB E4--because of this we are able to satisfy the requirements for stabilization. The CHUB E4 is connected to the PC through the COM port.

Seeing that the directly measurement of the delivered electrical power is not possible, we are measuring the delivered voltage and compute the power using the following equation (Kopcek & Elias, 2008):

P = [U.sup.2]/R (2)

where P--delivered electrical power, U--delivered voltage, R--resistance of the heating elements group

Voltage measuring devices are three industrial voltmeters Orbit Merret OM352AC (one for each phase) with the ModBus/ASCII communication protocol, which gives us the opportunity to connect them to the same network as the ADAM 4015 modules.

Three thyristor units CD3000M are used for the electrical power control and also as the heating element--to each thyristor unit are linked four resistive heat elements with power about 2kW. These units are communicating through the EIA-485 industrial bus with the ModBus/RTU protocol. The Thyristor units CD3000M are able to switch the currents in wide range from 15A to 110A, because of this we have a wide spectrum of the electrical power control.

5.2 System network

Gateway module ADAM4570 realizes the conversion between the network interface (Ethernet) and the industrial bus EIA-485 to enable simple connection of the control computer. Ethernet gives us the possibility to use the wireless connection between the control and supervisory computer. The communication is realized using the TCP/IP protocol on the Ethernet level and the ModBus protocol on the EIA-485 level.

[FIGURE 1 OMITTED]

5.3 SCADA system

SCADA system in Delphi was developed for the experiment execution, data acquisition and their presentation to:

* Control the container heating using the resistive heating elements during the residual power simulation (measured values are the container surface temperatures).

* Capture and store the measured values in predefined scan period during the experiment with electrical heating and measurement with real BFF.

* Visualize the measured values from separate sensors by the table and by the graph.

* Export the measured values for further computations and much more.

The communication with the hardware modules is realized using the virtual serial port, which sends the requests and receives the answers through the ADAM4570 module. The communication between the control and the supervisory part of the SCADA system is made by the means of MySQL database server.

6. CONCLUSION

Experimental measurements are being executed at this time. After the successful evaluation and validation of the experiment results (using the implemented SCADA system and mathematical model) will be the methodology finalized and implemented into the practise to provide the duplicate proving of the reliability and safety parameters by the BFF transporting.

7. REFERENCES

Barton, S. & Tanuska, P. (2008). Determination of the residual power of the fissionable fuel, Available from: http://www.mtf.stuba.sk/docs//internetovy_casopis/2008/8/ barton.pdf Accessed: 2009-04-28

Incropera, F. P. & DeWitt, D. P. (1996). Fundamentals of Heat and Mass transfer, JohnWiley, ISBN 0471386502, New York.

Kopcek, M. & Elias, A. (2008). Scada system development as a supportive tool for the measuring of residual power of burned--out nuclear fuel Available from: http://www.mtf.stuba.sk/docs//internetovy_casopis/2008/8/ kopcek.pdf Accessed: 2009-04-28

Regulations for the Safe transport of Radioactive Material, In: Safety Standards Series no. ST-1 IAEA, Vienna, 1996.

Schreiber, P. ; Tanuska, P. ; Vazan, P. & Bozik, M. (2008). The methodology proposal basis of spent fuel containers nuclear safety, Available from: http://www.mtf.stuba.sk/docs//internetovy_casopis/2008/8/s chreiber.pdf Accessed: 2009-04-28