Axial void fraction distribution measurement method and neutron multiplication factor evaluating method

Abstract

A first intensity Az expressed as Az=az×Eα, a first reference intensity Ao expressed as Ao=ao×Eα, a second intensity Bz expressed as Bz=bz×E, and a second reference intensity Bo=bo×E, are evaluated. The first intensity and the first reference intensity are of radioactive nuclides generated by a neutron capture reaction of a heavy nuclide or a fission product nuclide. The second intensity and the second reference intensity are of radioactive fission product nuclides except nuclides generated by a neutron capture reaction. The reference intensities are measured where the void fraction is known. Also a correlation curve of (az / ao) and a void fraction is evaluated. Finally an axial void fraction distribution is evaluated based on the value of (az / ao) and the correlation curve.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No.2005-143884, filed on May 17, 2005; the entire content of which is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] The present invention relates to a measurement method of an axial void fraction distribution in a core of a boiling water reactor (BWR), and also to an evaluating method of a neutron multiplication factor of a fuel assembly to be contained in a container apparatus. [0003] In a BWR, cooling water is heated and boiled in a reactor core as it flows from the bottom of the core to the top of the core. So, a void fraction that is a ratio of the bubbles to space where the cooling water flows in a channel box, increases as the cooling water flows from the upstream (the bottom of the core) to the downstream (the top of the core). [0004] The void fraction significantly affects core characteristics such a...

AI Technical Summary

Benefits of technology

[0023] The above and other features and advantage of the present invention will become apparent from the discussion herein below of specific, illustrative embodiments thereof presented in conjunction with accompanying drawings, in which:

[0024]FIG. 1 is a flow chart of an axial void fraction distribution measurement method according to the first embodiment of the present invention;

[0025]FIG. 2 is a flow chart of an axial void fraction distribution evaluation method according to the second embodiment of the present invention;

[0026]FIG. 3 is a flow chart of an axial void fraction distribution evaluation method according to the third embodiment of the present invention;

[0027]FIG. 4 is a flow chart of an axial void fraction distribution method according to the fourth embodiment of the present invention;

[0028]FIG. 5 is a flow chart of the neutron emission rate technique according to the fourth embodiment;

Problems solved by technology

However, no report has been made on an actual measurement of the void fraction distribution in the core of a commercial BWR because of lack of feasible measurement technique.

The above-described technique is hard to apply to an operating nuclear reactor, because it employs Cd having a low melting point that might harm structure materials of the operating reactor.

As described above, while the axial void fraction distribution is very important for a BWR, no technique has been available for actual measurement of an axial void fraction distribution in an operating commercial nuclear reactor.

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