Abstract: A transiently unstable state of a boiling-water reactor is damped by measuring the oscillating neutron flux and, after a first threshold value is exceeded over a plurality of oscillation periods, the rate of increase of the oscillation is determined. Depending on the slope of the increase, and after a further threshold value (in particular one dependent on the rate of increase) for the oscillating flux is exceeded, a selection is made which one of various stabilization strategies for damping the oscillation should be triggered before a SCRAM becomes necessary. A hierarchy of stabilization strategies is available: blocking a power increase, for instance, in the control system, controlled slow reduction of the power, or rapid power reduction by a "partial SCRAM". The monitoring of the unstable state is effected with a system of sensors strategically distributed throughout the core and which redundantly measure the flux in one region of the core.

Abstract: An in-core monitor protector intended for use during in-vessel services while work is being performed in the reactor core region of a BWR. The purpose of the protector is to prevent damage to or displacement of the in-core monitors, which could be caused by the installation or removal of various types of equipment through the top guide of the core during an outage. This protection is accomplished by partly surrounding the in-core monitor with the protector. The primary component is an aluminum channel of such size as to surround the monitor on three sides and of such length as to extend from the bottom of the top guide to the top of the fuel support castings. The closed sides of the channel prevent direct contact between servicing tools and the monitor. A top subassembly is used to secure the protector to the top guide. A bottom subassembly is used to secure the protector to the fuel support castings.

Abstract: A method of monitoring neutron flex detectors in a nuclear reactor in a neural network is provided. The network comprises an input layer which receives a number of input signals corresponding to values of a measured signal at different times and an output layer which is adapted to deliver a number of state signals. The network is taught to identify a number of different trends of the measured signal such that the state signals indicate the trends, by supplying the network with a plurality of input signals which have known state signals. The network is then supplied with input signals which correspond to values of a measured signal taken at different times from a supervised detector. Also, input signals corresponding to values of measured signals taken at different times from a reference detector are supplied to the network. Next, state signals for the supervised detector and for the reference detectors are calculated and whether the supervised detector is defective is determined based on the state signals.

Abstract: A switching circuit especially suitable for protecting electronic components such as integrated circuits (2) from the harmful effects of ionizing radiation. The circuit comprises two switches for isolating the component (2) from its power supply, the switches conveniently being NPN transistors (TR1, TR2) and being connected either side of a decoupling capacitor (3) associated with a component (2). Because the capacitor (3) is allowed to retain its charge during power-off, no time is lost in recharging it once the power supply has been resumed.

Abstract: A neutron particle measuring apparatus includes a neutron converter to generate alpha rays in response to incidence of neutron, a scintillator to receive as input the alpha rays generated from the neutron converter so as to emit and transmit scintillation, two photoreceptive portions to receive the scintillation through different transmitting paths, and a signal processing portion to measure a neutron distribution depending upon times at which the scintillation can reach the photoreceptive portions according to a time-of-flight method. The single particle measuring apparatus can be used to measure the neutron distribution in the vicinity of a nuclear reactor in a nuclear power plant.

Abstract: A self-powered fixed incore detector for a nuclear reactor has a neutron sensitive emitter element having a low neutron absorption cross section, such as a vanadium element, which extends the length of the active fuel region and generates a full length signal representative of full length power. A number of gamma sensitive emitter elements, preferably platinum but alternatively zirconium, cerium, tantalum, or osmium elements, provide sequentially increasing overlap with the neutron sensitive emitter element to define axial regions of the active fuel region and generate apportioning signals. The portion of the full length signal generated by the neutron sensitive emitter element attributable to each of the axial regions of the core are determined from ratios of the apportioning signals generated by the gamma sensitive elements.

Abstract: A method for determining the core flow rate from pump differential pressure method equations and a heat balance equation for determining the temperature and density of the reactor water in the downcomer and lower plenum region. The measured reactor water temperature is used only as an initial estimate for this new method. This allows the first estimate of the core flow to be determined based upon the reactor water density that corresponds to this temperature and the pump differential pressure and pump rotational speed measurements. Then, with this intial core flow measurement value, and other available plant measurements and assumed nominal values for the heat balance equation, revised values for the reactor water temperature and density can be calculated. Using a standard numerical method, such as the successive approximation technique, a more accurate estimate for the reactor water density can be obtained.

Abstract: An apparatus for carrying out a surveillance program to monitor the neutron fluence and its effect on vessel materials at a position in the annular space between the pressure vessel and core shroud of a boiling water reactor for the purpose of monitoring vessel embrittlement. The apparatus includes an offset capsule holder assembly which fits in an existing capsule holder attached to the inner surface of the pressure vessel wall. The offset capsule holder assembly positions a new capsule holder radially closer to the core, by an amount determined by neutron transport calculations. The new capsule holder is geometrically identical to the original, or a "replacement in kind", allowing the original surveillance capsules to be immediately reinstalled. With the water moderator in the downcomer annulus, the fluence rate increases significantly when the surveillance capsule is moved radially inward from the pressure vessel inside surface toward the core.

Abstract: The tube to be replaced is extracted and an internal surface of the bottom head (1b) is then machined around the through opening (10), a hollow shell (20) is attached and fixed on the machined surface (15) of the bottom head (1b), around the through opening (10), by welding along a peripheral edge (19), the hollow shell is bored in order to produce a passage hole (24) through its wall, in extension of the through opening (10) and a welding bevel (23). A replacement through-tube (18) is fixed on the wall of the hollow shell (20) by depositing a welding metal (25) in the bevel (23). The invention applies in particular to the replacement of vessel bottom head penetrations of a pressurized water nuclear reactor.

Abstract: A reactor protection system having four divisions, with quad redundant sensors for each scram parameter providing input to four independent microprocessor-based electronic chassis. Each electronic chassis acquires the scram parameter data from its own sensor, digitizes the information, and then transmits the sensor reading to the other three electronic chassis via optical fibers. To increase system availability and reduce false scrams, the reactor protection system employs two levels of voting on a need for reactor scram. The electronic chassis perform software divisional data processing, vote 2/3 with spare based upon information from all four sensors, and send the divisional scram signals to the hardware logic panel, which performs a 2/4 division vote on whether or not to initiate a reactor scram. Each chassis makes a divisional scram decision based on data from all sensors. Each division performs independently of the others (asynchronous operation).

Abstract: A computer-based power oscillation detection system and method for detecting, monitoring and indicating thermal-hydraulic stability margin in a nuclear reactor is provided. A group of neutron flux detectors is distributed throughout the reactor core, in contiguous relation to the reactor fuel assemblies, with each flux detector providing an output signal indicative of the power density of the portion of the core adjacent to the detector. A computer-based system processes the detector output signals utilizing a period based algorithm that employs an oscillation detection counting function wherein a count corresponding to the level of periodicity of the signal is determined. Since a representative oscillation count for each reactor stability state usually only occurs on the order of several minutes for a single detector signal, a unique simulated decay ratio algorithm reduces the time required to obtain a representative count by processing the group of detector signals spread throughout the core.

Abstract: During shutdown of the nuclear reactor, the closure head of the vessel having been dismounted and the vessel (3) and the pool of the reactor both being filled with water, an inner zone of the penetration tube (6) for penetrating the bottom head of the vessel (3) is isolated between two seals (39,42), from the upper level of the pool. An electrolyte is caused to flow in the isolated zone inside the penetration tube (6) and a current is passed through the electrolyte in order to deposit a metallic electroplating layer onto the inner surface of the penetration tube (6) in the isolated zone. The metallic layer is preferably a layer of nickel of a thickness of approximately 0.1 mm.

Abstract: Excore detector measurements are used to generate on-line absolute reactor power in a pressurized water reactor (PWR) by calibrating detector current measurements to the reactor thermal power calculation made at a base time early in reactor cycle while the thermal reactor power measurement is still accurate. Measurements are also made at the base time of the three-dimensional core power distribution and the core inlet temperature. Present core power measurements are then made by measuring the present excore detector current, the most recent three-dimensional core power distribution and the present core inlet temperature. The present core power is then calculated as the ratio of the present detector current to the detector current at the base time multiplied by the reactor thermal power measurement at the base time.

Abstract: A method and an apparatus for testing, repairing or exchanging nozzles of the bottom of a reactor pressure vessel include inserting individual shielding containers into the reactor pressure vessel. Shafts pass through a shielding container and water-filled cartridges can be inserted into the shafts. Tubes for receiving probes of an in-core instrumentation are embedded into bottom plates of the remaining shielding containers and into bottoms of the cartridges. After removing a cartridge, a carrier for working tools can be introduced into the shaft. In this way the radioactive loading is considerably reduced by the probes inside or outside the reactor pressure vessel.

Abstract: A method and a device for detecting oscillations in the core of a boiling-water nuclear reactor (BWR) comprising a plurality of neutron detectors, wherein instability is detected based on oscillations in the output signals of the neutron detectors. For each one of a number of selected neutron detectors, oscillations in the output signals of the neutron detectors are detected. The oscillations are detected on the basis of an oscillation signal (SS) which indicates that an oscillation criterion is fulfilled. An alarm signal for remaining oscillations Ka is generated if the oscillation signal (SS) remains during one delay interval (T3). A first alarm signal (LR) is generated if the oscillation signal (SS) indicates that the oscillation criterion is fulfilled at least once, during each of a predetermined number of consecutive alarm intervals (T1).

Abstract: An apparatus for measuring the power of a nuclear reactor having a sensor assembly disposed in a core section inside the nuclear reactor. The sensor assembly includes a cover tube made of metal and press-fitted on the outer surface of a rod-shaped core tube made of metal, a plurality of annular gaps defined between the cover tube and the core tube at different positions spaced from each other in the axial direction of the core tube, a plurality of axial grooves formed in the core tube while opening on the outer surface of the core tube and extending in the axial direction of the core tube, and a plurality of temperature sensors individually guided in the axial grooves and disposed on the core tube. The temperature sensors of the sensor assembly detect temperature distribution in portions of the core tube which face the annular gaps so as to measure the power of the nuclear reactor.

Abstract: A pressurizer vessel of a nuclear power plant contains a liquid and steam both of which function to maintain pressure in a reactor coolant system. A heater support assembly is disposed in an interior portion of the pressurizer vessel and receive a plurality of heaters which are matingly fitted with the heater support assembly for heating the liquid. A temperature detector is operatively connected to the heater support assembly in a structural arrangement which allows for measuring the temperature of the liquid at a plurality of preselected elevations. The temperature detector further includes temperature measuring means for measuring a plurality of temperature readings of the liquid at preselected elevations of the liquid.

Abstract: In a transversing incore probe system including a probe connected to a helix cable that is advanced into a drive assembly and is kept under high tension by a spring biased reel, a safety device is provided by a brake tool including a clamping assembly for clamping the brake tool in a fixed position relative to the reel, a head connected to the clamping assembly for releasable engagement with an outside circumferential surface of the reel, and a threaded shaft connected to the head and received within the clamping assembly for advancing the head toward and withdrawing the head from the reel.

Abstract: A system for monitoring power, particularly a power distribution, of a nuclear reactor includes a plurality of neutron flux measuring units disposed in a core of the nuclear reactor for measuring neutron flux in the core and generating neutron flux signals. A unit, generally constructed by a process computer, for calculating a neutron flux distribution in the core in response to the neutron flux detection signals from the neutron flux measuring units, is provided. A unit for calculating a higher mode of the neutron flux distribution in accordance with results of calculations performed by the neutron flux distribution calculating unit, is provided. A filter calculating unit is provided for obtaining a filter for extracting characteristics of change of the neutron flux detection signal in response to the neutron flux detection signal and an input/output unit for transmitting the neutron flux detection signal filtered by the filter obtained by the filter calculating unit.

Abstract: An automated monitoring system and method of operation is provided for a nuclear reactor having a pressure vessel containing a reactor core for boiling water to generate steam. A plurality of monitors provide signals for respective monitoring parameters for monitoring operation of the reactor, and a computer includes a data base therein containing predetermined setpoints for the monitoring parameters. The computer identifies abnormal and normal behavior of the monitoring parameters based on the data base, and determines the cause of abnormal behavior of the monitoring parameters using artificial intelligence. A warning is also provided to identify the cause of the monitoring parameter abnormal behavior. And, automatic mitigation action may also be effected.

Abstract: Vibration dampener for dampening vibration of a tubular member, such as an instrumentation tube of the type found in nuclear reactor pressure vessels. The instrumentation tube is received in an outer tubular member, such as a guide thimble tube. The vibration dampener comprises an annular sleeve which is attachable to the inside surface of the guide thimble tube and which is sized to surround the instrumentation tube. Dimples are attached to the interior wall of the sleeve for radially supporting the instrumentation tube. The wall of the sleeve has a flexible spring member, which is formed from the wall, disposed opposite the dimples for biasing the instrumentation tube into abutment with the dimples. Flow-induced vibration of the instrumentation tube will cause it to move out of contact with the dimples and further engage the spring member, which will flex a predetermined amount and exert a reactive force against the instrumentation tube to restrain its movement.

Abstract: The thimble (10) is introduced into a guidance duct consisting of a guidance tube (5) joining a measurement room (3) to the vessel (1) of the nuclear reactor, a vertical channel passing through the lower internals (14) of the reactor beneath the core (12) and a tube guide (17) of an assembly of the core (12). The closed end of the thimble penetrates into the tube guide of the fuel assembly as far as a defined level. The position of the thimble (10) is modified along the axis of the guidance duct, between two periods of use of the thimble in the nuclear reactor, so as to modify the position of the heavy wear zones of the wall of the thimble (10) with respect to the guidance duct. Preferably, the axial position of the thimble (10) is adjusted by using an extension of the thimble fixed to a seal (8) of the guidance duct and into which the end of the thimble is screwed.

Abstract: The device comprises a mobile probe which can be displaced inside thimbles. A plurality of ducts (20) for the passage and support of a thimble are disposed in the partitioning (6) of the reactor, around the core (4) along an axial direction and substantially over the entire height of the core. The ducts (20) are distributed circumferentially around the core (4). A plurality of feed-through sleeves in the cover of the vessel are each disposed along the axial extension of a duct (20) for the passage of a thimble. Guide columns each disposed along the axial extension of a duct and each engaged in a feed-through sleeve in the cover of the vessel form, with the corresponding duct (20) and feed-through sleeve, a channel for the reception of a thimble. An arrangement for the guidance, displacement, switching and parking of the mobile probe is disposed outside the vessel (1) and fixed on to the cover of the vessel.

Abstract: A radiation gauge is provided which comprises a casing having an evacuated inside, a pair of electrode plates contained within the casing, and an insulating material of aluminum oxide disposed between the pair of electrode plates, the insulating material undergoing an induced conduction phenomenon when ionizing radiation is illuminated thereon, whereby intensity of ionizing radiation can be measured based on the induced conduction phenomenon of the insulating material.

Abstract: Instrumentation for nuclear reactor head-mounted incore instrumentation systems fabricated of low nuclear cross section materials (i.e., zirconium or titanium). The instrumentation emits less radiation than that fabricated of conventional materials.

Abstract: An improved method for repair of incore-instrumentation-housing and related defects in a nuclear reactor system involves three stages, each with ultrasonically assisted inspections. In the first stage, a defective incore housing is removed and the exposed area and aperture at the former location of the incore housing is ultrasonically inspected using an ultrasonic probe with a tiltable disk-shaped head that self-conforms to the local contour of the reactor vessel bottom. In the second stage, a weld buildup is formed. The reactor is then sealed and the weld buildup is machined to define an aperture therethrough. The weld buildup is then ultrasonically inspected with a second probe with a centering member that is stationary as the probe body is moved vertically relative to it. In the third stage, a J-prep is formed. A new incore housing is inserted through the weld buildup aperture. The new incore housing is welded at the J-prep. The J-weld is ultrasonically inspected using a third ultrasonic probe.

Abstract: A nuclear reactor is provided having a generally cylindrical reactor vessel disposed within an opening in a primary shield. The opening in the primary shield is defined by a plurality of generally planar side walls forming a generally polyhedral-shaped opening. The reactor vessel is supported within the opening in the primary shield by reactor vessel supports which are in communication and aligned with central portions of some of the side walls. The reactor vessel is connected to the central portions of the reactor vessel supports. A thermal insulation polyhedron formed from a plurality of slidably insertable and removable generally planar insulation panels substantially surrounds at least a portion of the reactor vessel and is disposed between the reactor vessel and the side walls of the primary shield. The shape of the insulation polyhedron generally corresponds to the shape of the opening in the primary shield.

Abstract: A nuclear fuel assembly for a pressurized water nuclear reactor has a spring and dimple structure formed in a non-radioactive insert tube placed in the top of a sensor receiving instrumentation tube thimble disposed in the fuel assembly and attached at a top nozzle, a bottom nozzle, and intermediate grids. The instrumentation tube thimble is open at the top, where the sensor or its connection extends through the cooling water for coupling to a sensor signal processor. The spring and dimple insert tube is mounted within the instrumentation tube thimble and extends downwardly adjacent the top. The springs and dimples restrain the sensor and its connections against lateral displacement causing impact with the instrumentation tube thimble due to the strong axial flow of cooling water. The instrumentation tube has a stainless steel outer sleeve and a zirconium alloy inner sleeve below the insert tube adjacent the top. The insert tube is relatively non-radioactivated inconel alloy.

Abstract: Segmented instrumentation tube including a locking sleeve for interlocking the segments of the instrumentation tube, so that the threaded ends of the instrumentation tube do not unthread when subjected to vibration, such an instrumentation tube being suitable for use in a nuclear reactor pressure vessel. The instrumentation tube has a first member having a threaded end portion that has a plurality of first holes circumferentially around the outside surface thereof. The instrumentation tube also has a second member having a threaded end portion that has a plurality of second holes circumferentially around the outside surface thereof. The threads of the second member are caused to threadably engage the threads of the first member for defining a threaded joint therebetween. A sleeve having an inside surface surrounds the end portion of the first member and the end portion of the second member and thus surrounds the threaded joint.

Abstract: The present invention is a detector assembly for a nuclear reactor which includes platinum detector segments (30-40) axially distributed end to end within a reactor assembly and vanadium detector segments (42-52) spatially congruent in the same assembly. The vanadium detectors calibrate the platinum detector signals to remove the flux contributions of fission products. A full length vanadium detector (62) and a full length platinum detector (90) can be substituted and used to determine the compensation for the platinum detector segments (30-40). The compensated platinum detector signals, wherein compensation consists of isolating that portion of the total platinum detector signal that is directly proportional to the current local heat deposition rate in the reactor fuel, can be used for reactor core protection purposes.

Abstract: Apparatus for monitoring the neutron flux of a nuclear reactor in biological protection concrete (6) surrounding the vessel (4) containing the reactor core (2) and having, in vertical shafts (8 to 22) located in the concrete in the vicinity of said vessel (4), a certain number of neutron detecting devices, characterized in that each shaft is provided with a central, aluminium housing tube (24) and several peripheral, aluminium tubes (28), the central tube (24) being reserved for the housing of the boron deposit proportional counter and the peripheral tubes for the housing of the fission chambers, each maintained at a different height by support means connected to the tubes.

Abstract: The present invention is a system which determines nuclear reactor control rod axial position using a deviation signature database generated from a current or reference signal pattern produced by one or more strings of axially dispersed fixed incore detector sections in the reactor core. The deviation signature database is produced by assuming deviant axial positions for the control rods in the core, calculating expected detector signals for the assumed positions and storing the deviation of expected signals from a calibration reference along with corresponding assumed rod positions. The signature database is periodically updated to take into account changed core conditions. When a change in detector responses is detected the system performs a signature analysis of the deviations in the signature database using the current deviation from the reference to search for the closest match.

Abstract: An improved method for monitoring the parameters of a nuclear core reactor, analyzing the monitored parameters using modified two neutron group diffusion equations that have been subjected to space-time factorization such that the factorized shape functions are approximated, and determining the core neutronics in constant time steps, for example, about 0.25 seconds, thereby to provide analysis and simulations in full range of core neutronics in real-time continuously.

Abstract: A plurality of neutron flux sensors (44,46,48,50) and a corresponding plurality of gamma flux sensors (62,64,66,68) are distributed throughout axial zones (24,26,28,30) of the core (14) at the same or closely proximate locations. A steady state comparison, or bias, between the signals of a given neutron/gamma sensor pair are monitored (314, 316), and a divergence (or convergence) can readily be detected through simple signal filtering, to detect a shift in the bias. The pattern of significant convergence and divergence throughout the core, is indicative of the thermal hydraulic stability of the core.

Abstract: A device for restricting the motion of a thimble tube in a nuclear reactor during normal reactor operating conditions. A cylindrical sleeve open at each end has upper, middle, and lower sections. The upper section has an over-expanded area adjacent the top end to aid in proper positioning in the lower core support plate. The middle section is formed from inner and outer sections attached at their ends and formed from material having different coefficients of thermal expansion. The inner portion of the middle section moves from a first normal relaxed state during cold conditions in the reactor to a second flexed state during hot conditions in the reactor to provide a clamping action on the thimble tube received by the sleeve. A baffle in the lower section reduces coolant flow velocity and pressure through the sleeve.

Abstract: An instrument thimble tube shroud is disclosed which has a central cup surrounding an instrument thimble tube to prevent fluid flow about the thimble tube from causing excessive vibration and wear. A plurality of arms extend radially from the cup and have locking pads disposed at the end of each arm, springs extending from the pads engaging recesses in an adjacent fuel assembly nozzle to lock the shroud in position and prevent movement of the shroud or rotation due to aggressive fluid flow. Utilizing the inventive shroud prevents vibration and damage to the instrument thimble tube passing therethrough, enhancing life of the instrumentation and allowing continued observation of dynamics within a nuclear reactor.

Abstract: A neutron detection device is housed in a metal enclosure containing a first detector with a high-sensitivity fission chamber, and a second detector having a low-sensitivity fission chamber and a boron-lined ionization chamber compensated for gamma radiation. The detection device is useful for extended range measurement of the neutron fluence rate outside the core of a nuclear reactor.

Abstract: In a nuclear reactor wherein a plurality of neutron detectors are arranged vertically and at equal azimuth angles around a core of the nuclear reactor, thereby to measure a vertical power profile with a core of the reactor core, the improvement comprising dividing the core into sectors at respective azimuth angles confronting the neutron detectors, usingg the output signal of the partial detectors included in each of the neutron detectors for measuring a vertical reactor power profile of the azimuthal sector of the core confronting the corresponding neutron detector, and averaging the vertical profiles of the respective azimuthal parts with respect to the azimuth angles to measure the vertical reactor power profile of the reactor.

Abstract: Fine and coarse resolvers are used to detect the length of cable withdrawn from a spool to provide an indication of the position of a neutron flux detector at the end of the cable. The position indicated by the resolvers when the neutron flux detector passes a withdrawn limit switch is stored in nonvolatile memory as an offset when the cable is first installed in a flux mapping system. Thereafter, the position indicated by the resolvers, each time the neutron flux detector passes the withdraw limit switch, is compared to the offset. If the difference between the two is significant, a warning is generated, but operation of the flux mapping system continues. During movement of the flux detector, the change in position between two readings of the resolvers is divided by an amount of time measured by a programmable interval timer to determine average speed. A warning is generated if the average speed is outside an expected range. The expected range may vary depending upon the position of the detector.

Abstract: A plurality of flux map sequences are stored in nonvolatile memory to control a flux mapping operation in a nuclear reactor. The flux map sequences are accessed by a host controller which receives instructions from either a local man machine interface or a remote man machine interface. A system control unit determines which of the man machine interfaces is active and also provides the ability to select manual control of detector drivers. A selected flux map sequence is displayed and can be modified and then restored or executed. The modifications to the flux map sequence may include deleting a detector driver from the flux mapping operation and then automatically redistributing the thimbles originally used by the deleted detector driver to be used by the remaining detector drivers.

Abstract: To stabilize boiling water reactors against neutron flux oscillations caused by thermal-hydraulic instabilities, random core-wide reactivity perturbations are induced in the reactor either to suppress the onset of asymmetric (regional) mode oscillations or, in response to the detection of asymmetric mode oscillations, to stabilize the reactor in a symmetric (core-wide) oscillation mode. The reactivity perturbations are produced by effecting random changes in dome pressure, core flow or coolant enthalpy.

Abstract: An excore neutron flux power level detector assembly includes a neutron flux detector subassembly and a moderator subassembly having the form of a dual-wall canister of annular cross-section for receiving the detector subassembly in coaxial and telescoping relationship therein and having moderator material, preferably high density polyethylene, in the annular space between the dual-walls thereof for converting epithermal neutrons in leakage flux from a nuclear reactor to thermal neutrons having a power level detectable by the flux detector subassembly. Insulating spacer elements affixed concentrically about and axially displaced along the surface of the cylindrical housing of the detector provide lateral, structural support and spacing therebetween and electrical insulation of the detector subassembly from the moderator subassembly.

Abstract: The invention makes it possible to measure the degree of radioactive radiation emitted by large pieces. It includes two large gamma ray detectors (12A, 12B) placed opposite each other and whose spacing is adjustable. They are completed by a photoelectron multiplier (14A, 14B). The piece (2) to be measured is suspended so as to be brought between the two detectors (12A, 12B). The positioning of these detectors is obtained with the aid of a computer and a system (22) for recognizing the shape of the piece (2) functioning with the aid of optical clip-on lenses. The fact that the two detectors are position-adjustable makes it possible to take account of the shape of the piece to be measured. An application is the recovery of materials originating from nuclear installations with the view to re-using the materials.

Abstract: A thimble tube for use in a guide the in a nuclear reactor. The thimble tube is an elongated hollow tube having one end closed. The portion of the tube that extends into the reactor is formed from a plurality of sections attached to each other to form the tube in an alternating fashion along the width and length of the tube. The sections are formed from materials having different coefficients of thermal expansion. This causes the thimble tube to warp into supporting contact with the interior of the guide tube at normal reactor operating temperature.

Abstract: A method of measuring reactivity of a nuclear reactor includes automatic normalization. Normalization is achieved by determining the ratio of a linear amplifier used to form an analog detection signal, before and after a range change has taken place. A normalization factor is calculated according to this ratio which is applied to a delay neutral precursor concentration used for calculating the reactivity period.

Abstract: A system for measuring the power distribution in a reactor core includes a plurality of gamma detectors disposed outside of the reactor vessel which houses the reactor core. The gamma detectors correspond in number to the number of instrumentation tubes in the fuel assemblies in the reactor core to be sampled. A first plurality of separate flow branches connect the instrumentation tubes with the gamma detectors for routing the flow of coolant from the instrumentation tubes to the gamma detectors so that the gamma detectors can measure the .sup.16 N decay gamma activity in the respective instrumentation tubes of the fuel assemblies. A second plurality of separate flow branches connect a cold leg of the reactor coolant system with the gamma detectors for routing the flow of coolant from the cold leg to the gamma detectors so that the gamma detectors can measure the background gamma activity in the respective instrumentation tubes of the fuel assemblies.

Abstract: In-core nuclear instrumentation for a fast breeder reactor includes a neutron flux measuring unit disposed in a control rod assembly, whereby it is possible to measure a change in in-core neutron flux reliably and highly accurately without requiring a major modification in core design.

Abstract: A detector path insertion verification system for use with flux mapping of a pressurized water nuclear reactor uses a transfer insertion switch at the input of each multiple-path selector to detect insertion of a detector into the multiple-path selector. No insertion switches are used at the output of the multiple-path selectors; instead software is used to verify the position of the multiple-path selectors. The sensed actual position of each multiple-path selector is monitored as the multiple-path selector is rotated to verify that the sensed actual position passes through the expected sequence of positions in an expected amount of time. The multiple-path selectors are rotated until a sensed actual position is equal to a desired position and rotation is stopped. After the passage of a short period of time, the actual and desired positions are again compared and if equal, insertion is begun.

Abstract: A preferred embodiment of the present invention provides an incore instrumentation system for detecting conditions, e.g., neutron flux density, within the core of a pressurized water nuclear reactor (PWR). The instrumentation system includes a plurality of long straight thimbles (52), containing fixed incore detectors, which are inserted through the top closure head (18) of the PWR. The invention meets today's principal utility, EPRI, DOE and NRC requirements and preferences, including no bottom RV head penetrations and the use of fixed incore instrumentation. In addition, an instrumentation system according to the invention is mechanically simple with a straight core insertion/removal path that does not conflict with or add significant complexity to the reactor internals.

Abstract: A flux mapping system for a nuclear reactor uses a detector having an outer diameter approximately fifteen percent smaller than the inner diameter of distribution tubing through which it passes and a length less than eight percent of the minimum bend radius of the tubing. Frictionless limit switches are used in the flux mapping system to further reduce friction against cables which drive the detectors through the distribution tubing. In combination, these dimensions and switch changes result in a fifty percent improvement in driving force at the thimbles into the core of the nuclear reactor.