Tungsten Shielding Block for Active Detector

The inspection of 235U abundance and homogeneity of nuclear fuel rods is a very important quality control link to ensure the safe and reliable operation of nuclear fuel rods in nuclear power plants. The purpose is to avoid the hot spots caused by uneven 235U enrichment at any location during the operation of nuclear fuel rods. These hot spots may cause fuel rod rupture, contaminate coolant and cause shutdown. Therefore, the enrichment and uniformity of 235U fuel rod must be checked by 100%.

There are two methods to detect the enrichment and homogeneity of nuclear fuel rod 235U: active detection and passive detection. Active detection uses 252Cf neutron source to activate 235U isotope in fuel element UO 2 pellet and cause it to fission, which radiates a strong 185.7KeV gamma ray, and then uses gamma ray detector to measure. This method not only has high spatial resolution, but also greatly improves the detection speed. Generally, when 252Cf neutron source is 1200ugh, the single channel detection speed can reach 5m/min. In the detection process, the radiation source needs to be shielded.

Tungsten is a kind of high density metal material, which can be used in shielding parts of nuclear power plants. Of course, it is also used in tungsten shielding blocks of active detectors. In the relevant data, Xiaobian found that tungsten shielding block includes tungsten shielding body, with through holes, through holes with guide tubes, in tungsten shielding body with square holes perpendicular to the through holes, square holes with height adjustment block at the bottom, and tungsten shielding body with cylindrical holes at the top.

The shielding tungsten block of active detection can completely surround the crystal part of the detector. It can shield not only the influence of 252Cf neutron source on the detector, but also the interference of fuel rods in other channels. The square hole in the center of the shielding tungsten block can also play a collimating role in the detection signal, which greatly improves the resolution of the detector. Shielding the cylindrical hole at the upper end of the tungsten block can make the detector photoelectric.

The receiving part of the multiplier tube is also shielded, which greatly reduces the external interference to the measured signal. The nylon guide tube installed in the center of tungsten shield can guide the fuel rod, make the fuel rod pass through the center of the detector quickly, and protect the crystal part of the detector. The height adjusting block installed at the lower end of the tungsten shield can adjust the height of the detector, make the central hole of the detector consistent with the central hole of the shield tungsten block, and ensure the smooth passage of the fuel rod.

Using tungsten block to shield active detector not only has better shielding effect, but also can collimate the radiation source. It occupies very little space and has great application space.

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