Patent Number: 047909765
Section: description

Referring now to the drawing and first, particularly, to FIG. 1 thereof, there are provided, in a reactor pressure vessel 1 of a boiling water reactor, dry PDD lances 2 only one of which is shown which contain detectors for measuring neutron flux density, the PDD lances 2 being arranged in a reactor core 11. These detectors are connected via cables to a computer which processes the measured values of 100 to 200 detectors. In one dry PDD lance 2, four detectors are arranged above one another. They are first surrounded by pressure-tight dry thimble tubes and fastened to a so-called calibrating tube. An enclosing upper support tube 21 has a cross section in the shape of a clover leaf, as is shown in FIG. 3. The dry lance 2 with its relatively large cross-sectional area can thereby be inserted into the narrow water gap of the core grid 12. In the interest of simplification, as aforementioned, only one dry PDD lance 2 is shown in the reactor pressure vessel 1 of FIG. 1. The lance 2 is inserted into the opened reactor pressure vessel 1 from above. The upper end of the lance 2 is held in the upper core grid plate 14 by an upwardly spring-loaded latching pin 23 according to FIG. 2. Below the lower core grid plate 15, the lance 2 is surrounded, according to FIGS. 4 and 5, by a lower support tube 24 of circular cross section which is joined by a sleeve 26 to the upper tube 21. In the bottom of the reator pressure vessel 1, a lance-housing tube 16 is arranged in a pressure-proof manner, according to FIG. 1, for receiving therein the lance 2, as shown in FIG. 5. Thereat, a lance feedthrough or passageway 22, together with the lance 2, in accordance with FIG. 6 extends through an end flange 13 from the lance housing tube 16 in a pressure proof manner and threadedly secured or bolted. Deposits are formed during the operating period in the reactor vessel 1 and also penetrate into the lance-housing tube 16 as well as into the region of the end flange 13 and the lance feedthrough 22. To reduce the radiation in the accessible area underneath the reactor pressure vessel 1, the lance 2 is lifted by the device 3 according to the invention as shown in FIGS. 7A and 7B, is flushed out or rinsed and, because of the cloverleaf profile of the upper protection tube 21, is subsequently realigned and seated with the lance feedthrough 22, seated by an enlargement 2a thereof; in the sealing seat 13a of the end flange 13. The inventive device 3 for mounting dry lances 2 and for flushing out the lance housing tubes 16 has a tubular housing 31 which surround with radial clearance the part of the lance 2 protruding from the end flange 13 at the reactor pressure vessel 1 and which is protected thereat by a lance protection tube 25. The device 3 is guided over the lance protection tube 25 from below and is fastened to the end flange 13 in a pressure-proof manner. In the housing 31 of the device 3, a piston 32 is arranged movably and rotatably underneath the lance 2. To the piston 32, there is fastened an entrainer pin 321 which snaps into a slot 251 formed in the lance protection tube 25 when the piston 32 is lifted and turned by hand. Accurately aligned therewith, a spherical piece 27 which engages a marking slot 28 in the lance feedthrough 22 is formed in the upper end of the lance protection tube 25. The motions of the piston 32 are thereby transmitted exactly to the lance 2. In the piston 32 there is formed, in the axis of the device 3, a passage 322 for reactor water which can be closed off by a ball valve 33. The piston 32 is supported on a shoulder 323 by a cap screw 34 which cooperates with a thread on the outside surface of the housing 31. By turning the cap screw 34, the piston 32 and the lance 2 connected thereto are lifted out of the sealing seat in the end flange 13. Reactor water thereby flows through the gap between the lance feedthrough 22 and the end flange 13 into the space between the lance protection tube 25 and the housing 31 of the device 3. In this manner, the lance-housing tube 16 and the sealing region of the end flange 13 are flushed out or rinsed and freed of deposits. The water is conducted through the passage 322 formed in the piston 32 and drained intermittently at the ball valve 33. Firingly adhering impurities are thereby also separated. The flow of water is controlled by the ball valve 33 until only clear water flows off. Dry PDD lances must not be twisted during the flushing or rinsing because they would otherwise damage adjacent fuel channels of the core grid 12 when the core 11 is fully loaded. The lance 2 is therefore accurately aligned relative to the core grid 12 by the device 3 according to the invention. To this end, a folding lever 35, which is arrangeable parallel to the housing 31 for facilitating the transport of the device 3, is disposed on the piston 32 of the device 3. This pointer-like folding lever 35 which is elongatable telescopically is folded into a position perpendicular to the housing 31 of the device 3 for exactly aligning the dry lance 2. Via this long lever arm, the lance 2 is aligned accurately relative to the geometry of the reactor core 11, including outstanding calibration points on the underside of the reactor. The lance 2 is then deposited in its sealing seat by turning the cap screw 34 and lowering the piston 32. After draining the device 3 at the ball valve 33 and checking for tightness, the device 3 according to the invention and the lance protection tube 25 are disassembled, and the lance 2 is secured by a nut. The device 3 is immediately ready for reuse elsewhere. For better handling of the device 3 and for assembly without an additional tool, handles 36 and 37 are formed on the housing 31 and on the cap screw 34, respectively. With the aforedescribed device 3, an exact alignment of the dry PDD lance 2 as well as a flushing out of lance-housing tubes 16 which contain dry or wet PDD lances can be performed for the first time with the reactor cover closed and the core 11 flooded. The foregoing is a description corresponding, in substance, to German application No. P 35 28 723.3, dated Aug. 9, 1985, International priority of which is being claimed for the instant application, and which is hereby made part of this application. Any material discrepancies between the foregoing specification and the specification of the aforementioned corresponding German application are to be resolved in favor of the latter .