Induced nuclear reactions: processes – systems – and elements – Testing – sensing – measuring – or detecting a fission reactor...
Reexamination Certificate
1998-07-28
2001-04-17
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Testing, sensing, measuring, or detecting a fission reactor...
C376S247000, C376S258000, C376S259000
Reexamination Certificate
active
06219398
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved heated junction thermocouple cable arrangement for use with a nuclear reactor heated junction thermocouple level measurement system.
BACKGROUND OF THE INVENTION
When a pressurized water nuclear reactor is first activated after a shutdown, the reactor vessel is completely filled with a fluid coolant such as water. During nuclear reactor operation, the fluid coolant is circulated through the core to remove the generated heat. During normal reactor operation the coolant remains in a liquid state as it passes through the core. During abnormal operation, such as when there is a leak in the coolant system, the fluid coolant within the reactor vessel may change state to become a two-phase mixture of liquid and gas.
A heated junction thermocouple level measurement system with a plurality of sensors is placed within the reactor vessel and located in the upper guide structure. Each sensor includes a heated thermocouple, an unheated thermocouple, and a heater coil. The system is used to determine if liquid coolant is present above the reactor core at the level of each sensor.
Typically, a heated junction thermocouple level measurement system has eight completely separate sensors. The sensors are typically vertically spaced by equal increments in the reactor vessel between the fuel alignment plate and the reactor vessel head to give a coolant level indication over the entire height above the reactor core.
Five separate wires must be connected to each sensor to provide the measurements from the thermocouples and to provide electricity to the coil heater.
The forty wires making up the eight sensors engage the reactor vessel wall by means of a penetration connector. The five wires associated with each of the eight sensors are typically combined into a single cable. Preferably, the cable is mineral insulated, meaning that the cable is manufactured from completely inorganic material. Typically, the cable includes a copper-lined stainless steel sheath and conductors insulated with a mineral oxide such as silicon dioxide. Such components help ensure that the cable is able to withstand the effects of extremely high temperatures such as those associated with nuclear combustion and is still fully usable afterwards.
The eight sensors are then connected to a heated junction thermocouple probe by means of one or more containment, bridge, and head lift rig cables. A containment conduit containing containment cable engages the penetration connector. A bridge conduit engages the containment conduit. A head lift rig conduit engages the bridge conduit. Finally, the probe engages the head lift rig conduit. The cables provide the necessary power for the eight heaters and connect the other wires to signal processing and display equipment.
In one prior art embodiment, eight separate containment, bridge and head lift rig cables are used for each of the sensors. In a second prior art embodiment only one each of a containment, bridge, and head lift conduit are used.
Each free end of the conduits includes a connector adapted to engage a mating connector. A total of 40 pins or sockets are required at each conduit end to connect the forty different wires from each of the sensors with the heated junction thermocouple probe.
There are a number of significant drawbacks with the current heated junction thermocouple cable arrangement. The requirement of having forty separate wires requires either the use of individual very large and unmanageable containment, bridge, and head lift conduits or a significant number of smaller conduits, each of which each must be separately manipulated and located. Problems with cable labeling and clutter are greatly increased when multiple conduits are used. Yet, the ability to be able to easily manipulate and locate the heated junction thermocouple cable arrangement is of critical importance during reactor refueling when time spent in the so-called “hot” region of the reactor vessel must be minimized.
There are also significant drawbacks associated with requiring forty pins and sockets to mate the various wires with corresponding conduits. There is a constant trade off between connector size and the number of pins. As connectors become smaller, so do problems with pin and socket reliability. For example, it becomes easier to bend or distort the pins when handling the connectors or when mating or separating the connectors. Also, it is not often possible to easily replace a connector with damaged pins. This is particularly true if the number of circuits passing through the connector is large or if the shell is hermetically sealed to the interfacing instrument or conduit. However, if connectors are too big, the ability to move the associated conduits is compromised. Both damaged pins and bulky conduits also undesirably increase time spent in the “hot” zone of the reactor vessel.
There are also issues raised by having eight independent cables, each cable having the five wires discussed above. The connectors are very small and are easily damaged during the disconnection and connection process. Combining power wires with sensor wires in the same cable increases the potential for electrical interference with the sensor signals carried by the remaining three wires in the cable. Further, the need for additional insulation in each cable for increased insulation resistance adds to the bulk of the cable and the difficulty in handling the cables.
SUMMARY OF THE INVENTION
The present invention is directed to a nuclear reactor heated junction thermocouple level measurement system having a plurality of sensors. Each sensor includes both an unheated thermocouple and a heated thermocouple. A heater coil is placed adjacent the heated thermocouple. There is a distinct thermocouple conductor of a first polarity associated with each thermocouple and a thermocouple conductor of the opposite polarity shared between the thermocouples. Two power conductors are used to supply electricity to the heater coil.
There is a plurality of thermocouple sensor cables, each of the sensor cables associated with the thermocouples of a single sensor. There is also a plurality of power cables. A power cable provides electricity to more than one heater coil, the heater coils associated with a power cable ganged in parallel such that if one heater coil fails, the rest still receive power.
By having a power cable separate from a sensor cable, prior art problems associated with the power conductors potentially affecting the sensor signals carried from the thermocouples are eliminated.
In a preferred embodiment, all of the power cables and sensor cables are received in a single flexible metal conduit. For the same number of sensors, the reduction in the number of wires providing power to the heater coils provides a number of significant advantages. A smaller conduit is more manageable than either eight conduits of five wires each or a single conduit with the eight five-wire cables contained in the flexible sheath known in the prior art. Opposite ends of a conduit include a connector having either pins or sockets. Pins may be easily bent or distorted. The likelihood of damage to the pins is reduced if the number of pins is reduced.
In a preferred embodiment of the invention, there are eight sensors associated with a heated junction thermocouple sensor. Two pairs of power wires are associated with two sets of four heater coils and three sensor wires are associated with each of the sensors. Thus, penetration connectors to containment cable and to the bridge and head rig cables have either 28 sockets or pins. A containment conduit having connectors at either end engages the penetration connector. A bridge conduit having connectors at either end engages the containment conduit. A head lift rig conduit having connectors at either end engages both the bridge conduit and an existing heated junction thermocouple probe. The head lift rig conduit acts as a transition conduit having 28 pins or sockets in the connector engaging the bridge conduit and 40 pins or sockets in the conn
Fittz John H.
Mauldin Robert H.
Carone Michael J.
CE Nuclear Power LLC
Keith Jack
Rader Fishman & Grauer
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