Patent Number: 052290654
Section: claims

1. Method for measuring the temperature of the primary coolant fluid of a nuclear reactor comprising a pressure vessel in which is arranged the core of the reactor and a primary circuit having at least one loop on which is arranged a steam generator, and which comprises pipes (16, 55) in which the primary coolant fluid of the reactor circulates, one of said pipes being a hot leg (16), another of said pipes being a cold leg (55), connecting the pressure vessel to the steam generator, and another pipe, or the cold leg (55), ensuring the return of the coolant fluid coming from the steam generator into the pressure vessel, said method comprising the steps of (a) sampling coolant fluid from a substantially horizontal part of the hot leg (16) at at least three points (19, 20, 21) distributed at the periphery of a straight section of the hot leg (16), in such a way that at least one of the sampling points (20, 21), or lower sampling point, is situated beneath the axis (17) of the hot leg (16);  (b) measuring the temperature of the coolant water sampled at each of the sampling points (19, 20, 21) at its outlet from the hot leg (16); and  (c) reintroducing the coolant fluid into the hot leg (16) at a point (22) situated in a position substantially diametrically opposite one of the lower sampling points (20, 21), on the straight section of the hot leg (16).  (a) at least three devices for sampling coolant fluid, traversing the wall of a substantially horizontal part of the hot leg (16) and distributed at the periphery of a straight section of said hot leg so that at least one of the sampling devices (20, 21) is situated beneath the axis (17) of the hot leg (16); and  (b) an element (22) for reintroducing coolant fluid into the hot leg (16), arranged in a position substantially diametrically opposite one of the sampling devices situated beneath the axis (17) of the hot leg (16) and pipes (24, 25, 26) connecting each of the sampling devices (19, 20, 21) to the reintroduction element (22). 2. Method according to claim 1, wherein the coolant fluid is sampled at three points (19, 20, 21) arranged at 120.degree. to one another about the axis (17) of the hot leg (16), in a straight section of said hot leg (16). 3. Method according to claim 1, wherein the temperature of the coolant fluid is measured at a point (56) situated in the vicinity of the upper part of the cold leg (55) of the primary circuit. 4. Method according to claim 1, wherein the mean of the temperatures measured at each of the sampling points (19, 20, 21) of the hot leg (16) is calculated by electronic means. 5. Method according to claim 1, wherein the temperature of the coolant water reintroduced into the hot leg (16) is measured at the point situated in a position substantially diametrically opposite one of the lower sampling points (20, 21), and the temperature of the coolant water reintroduced at the reintroduction point (22) is compared with the mean of the temperatures measured at said three sampling points (19, 20, 21). 6. Device for measuring the temperature of the primary coolant fluid of a nuclear reactor comprising a pressure vessel in which is arranged the core of the reactor and a primary circuit having at least one loop on which is arranged a steam generator, and which comprises pipes (16, 55) in which the primary coolant fluid of the reactor circulates, one of said pipes being a hot leg (16), connecting the pressure vessel to the steam generator, and another of said pipes being a cold leg (55), ensuring the return of the coolant fluid coming from the steam generator into the pressure vessel, said device comprising 7. Device according to claim 6, wherein each of the sampling devices (19, 20, 21) is in the form of a scoop comprising a part in the form of a glove finger fixed in an opening (28) traversing the wall of the hot leg (16) and having, in its part situated inside the hot leg (16), openings (31) traversing its wall and opening out into a central channel (32), and a projection (34) comprising an internal bore (36) communicating with the central channel (32) of the part in the form of a glove finger, in which projection is fixed a temperature-measuring probe (39) carried by a support (38) ensuring the sealed closure of the bore of the projection (34) fixed to the outer surface of the hot leg (16), said projection comprising a channel (41) opening out into its bore (36) and brought into communication with a pipe (24) connected at its other end to the reintroduction element (22). 8. Device according to claim 6 or 7, wherein the reintroduction element (22) consists of a projection (46) fixed to the outer surface of the hot leg (16) in the region of an opening (45) traversing the wall of the hot leg (16) and comprising a bore (48) communicating with the opening (45) in which is fixed a temperature probe (51) on a support (50) ensuring the sealed closure, towards the outside, of the bore (48) of the projection (46), said projection (46) comprising at least three radial channels (52) opening out into the bore (48) of the projection (46), each of said channels communicating with a pipe (24, 25, 26) connected to a sampling device (19, 20, 21). 9. Device according to claim 8, wherein the support (50) arranged in the bore (48) of the projection (46) of the reintroduction element (22) is replaced by a plug closing the bore (48) of the projection (46). 10. Device according to claim 7, wherein the reintroduction element (22) consists of a projection (46) fixed to the outer surface of the hot leg (16) in the region of an opening (45) traversing the wall of the hot leg (16) and comprising a bore (48) communicating with the opening (45) in which is fixed a temperature probe (51) on a support (50) ensuring the sealed closure, towards the outside, of the bore (48) of the projection (46), the projection (46) furthermore comprising at least three channels (51) of radial direction opening out into the bore (48) of the projection (46), each communicating with a pipe (24, 25, 26) connected to a sampling device (19, 20, 21).