Patent Number: 051924919
Section: summary

The invention relates to an apparatus for the neutron-radiography testing of a boiling water reactor control element disposed in a water pond, including a hood which has an open bottom, which fits over the control element and which is kept free of water, a neutron source, a collimator and a film cassette which lie in one measurement plane. In generally known apparatuses of this type, the film cassette is disposed outside the hood and is therefore surrounded by water. Although the film cassette is pressed against the hood with a certain force, a film of water remains between the film cassette and the hood wall, in particular in the vicinity of corners and peripheral zones of end surfaces of the cassette, which falsifies test results as a result of scattered neutrons. The film cassette contact pressure which is necessary may furthermore result in undesirable permanent deformations. The solid hood wall disposed between the control element and the film cassette increases the distance between the image plane and the control element which, with a divergent collimator, produces an increase in the geometrical lack of sharpness at the image plane and in an increase in the image size. The hood configuration mentioned above furthermore results in an attenuation of the neutron fluxes as a result of neutron absorption and leads to additional neutron scatterings. It is accordingly an object of the invention to provide an apparatus for the neutron-radiography testing of a boiling water reactor control element, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and with the aid of which the image quality can be substantially improved. With the foregoing and other objects in view there is provided, in accordance with the invention, in a boiling water reactor having a control element disposed in a water pond, an apparatus for the neutron-radiography testing of the control element, comprising a film cassette having a recording area or film area, a water-free hood fitting over the control element, the hood having an open bottom and a wall facing or being adjacent the film cassette, the wall having an opening formed therein with a cross section corresponding to the recording area, a holding device fitting over the opening for receiving the film cassette, the holding device having a downwardly open side extended below the opening through which the film cassette is to be introduced into the holding device, a neutron source, and a collimator, the neutron source, the collimator and the film cassette lying in one measurement plane. The internal space of the hood that is kept free of water by air pressure extends to the holding device. After the film cassette has been introduced into the water-free space from below, the air flowing past the film cassette ensures a water-free film area even before the test position is reached. Due to the opening, the film cassette approaches to the hood wall or a film of water being eliminated. In accordance with another feature of the invention, the holding device has a skimmer past which the surface of the film cassette adjacent the hood can be fed. In accordance with a further feature of the invention, there is provided a coupling piece projecting from the film cassette, a coupling rod, and a detachable coupling link interconnecting the coupling piece and the coupling rod. Through the use of the coupling rod, the film cassette can be readily introduced into the holding device from outside the water pond. In accordance with a concomitant feature of the invention, the holding device has a guide surface with an upper end, a stop for the film cassette adjoining the upper end, and a locking device holding the film cassette in a test position. This is done in order to achieve a precise positioning of the film cassette. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in an apparatus for the neutron-radiography testing of a boiling water reactor control element, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.