Patent Number: 
Section: description

A transponder card for a nuclear reactor control rod drive control system is described below in more detail. The transponder card permits continued system operation in the event of a failure of transponder card circuitry that controls the movement of the control rods. The transponder card is configured to detect failures of its rod control circuitry and prevent inadvertent incremental rod insertion without depending on the Rod Control system to remove power from the transponder card. Further, the transponder card can announce to the Rod Control system via a bit on a serial data word that the transponder card has detected a defect in itself. Referring to the drawings, FIG. 1 is a sectional view, with parts cut away, of a boiling water nuclear reactor pressure vessel (RPV) 10. RPV 10 has a generally cylindrical shape and is closed at one end by a bottom head 12 and at its other end by a removable top head 14. A side wall 16 extends from bottom head 12 to top head 14. Side wall 16 includes a top flange 18. Top head 14 is attached to top flange 18. A cylindrically shaped core shroud 20 surrounds a reactor core 22. Shroud 20 is supported at one end by a shroud support 24 and includes an opposed removable shroud head 26. An annulus 28 is formed between shroud 20 and side wall 16. A pump deck 30, which has a ring shape, extends between shroud support 24 and RPV side wall 16. Pump deck 30 includes a plurality of circular openings 32, with each opening housing a jet pump 34. Jet pumps 34 are circumferentially distributed around core shroud 20. An inlet riser pipe 36 is coupled to two jet pumps 34 by a transition assembly 38. Each jet pump 34 includes an inlet mixer 40, and a diffuser 42. Inlet riser 36 and two connected jet pumps 34 form a jet pump assembly 44. Heat is generated within core 22, which includes fuel bundles 46 of fissionable material. Water circulated up through core 22 is at least partially converted to steam. Steam separators 48 separates steam from water, which is recirculated. Steam dryers 50 remove residual water from the steam. The steam exits RPV 10 through a steam outlet 52 near vessel top head 14. The amount of heat generated in core 22 is regulated by inserting and withdrawing a plurality of control rods 54 of neutron absorbing material, for example, hafnium. To the extent that control rod 54 is inserted into fuel bundle 46, it absorbs neutrons that would otherwise be available to promote the chain reaction which generates heat in core 22. Control rod 54 couples with a control rod drive (CRD) 58 which moves control rod 54 relative to a core plate 64 and fuel bundles 46. CRD 58 extends through bottom head 12 and is enclosed in a control rod drive housing 66. A control rod guide tube 56 extends vertically from control rod drive mechanism housing 66 to core plate 64. Control rod guide tubes 56 restrict non-vertical motion of control rods 54 during control rod 54 insertion and withdrawal. FIG. 2 is a simplified block diagram of a control rod drive control system (RDCS) 70 in accordance with an embodiment of the present invention. RDCS 70 includes central rod processing circuitry or control processor 72 that is operationally coupled to a branch amplifier card 74 that is operationally coupled to a transponder card 76. Particularly, in one embodiment, branch amplifier card 74 and transponder card 76 are operationally coupled to control processor 72 via serial digital electronic communication. Branch amplifier card 74 and transponder card 76 are part of a hydraulic control unit (HCU) 78. HCU 78 includes a plurality of transponder cards 76 arranged in clusters of several transponder cards 76 coupled to a branch amplifier card 74. Branch amplifier card 74 serves, in part, to distribute command (CMD) words it receives from central rod processing circuitry 72 to transponder cards 76 within its cluster and to the next downstream branch amplifier card 74. In a reverse manner, acknowledge (ACK) words are routed within a cluster to the cluster""s branch amplifier card 74. Each branch amplifier card 74, in turn, routes the ACK work to a branch amplifier card 74 further upstream and back to control processor 72. With reference to FIG. 3, in an exemplary embodiment, RDCS 70 enables a plant operator to select and maneuver control rods and display rod positions at all times. It includes a set of components, both in the control room and inside the containment, that generate, check and distribute digital electronic messages (xe2x80x9cwordsxe2x80x9d) sent from an operator""s console 80 to hydraulic control units 82 and from rod position probes 84 back to console 80. A general overview of the operation of the RDCS 70 is as follows. The plant operator selects the rod or rods to move at rod interface system (RIS) bench-board console 80. Request words are sent to two redundant rod action control system (RACS) cabinets 86 and 88. Each RACS cabinet 86 and 88 independently evaluates the operator""s request to insure that the desired rod motion will result in a permissible control rod pattern. Validated requests are transmitted to a rod drive system (RDS) cabinet 90. RDS cabinet 90 compares the validated rod movement commands from the two RACS cabinets 86 and 88 and, if they agree, sends CMD words to a set of hydraulic control rod drive units 78 via clusters of branch junction amplifier cards 74 and transponder cards 76. A plurality of position probes 94 underneath pressure vessel 10 measure control rod 54 positions and send probe word messages to two redundant rod position multiplexer (MUX) cabinets 96 and 98. RACS cabinets 86 and 88 independently compare measured rod positions against allowed rod pattern configurations. RACS cabinets 86 and 88 send position information to RDS cabinet 90 for further transmittal to an operator""s display 100 on RIS console 80. RDS cabinet 90 sends position data to a plant process computer (not shown) by means of Process words sent via a computer interface module 102. HCU transponder card 76 is configured to receive and buffer CMD words on to downstream transponder cards 76 in the same cluster. Transponder card 76 is also configured to compare a command address embedded in the CMD word with the transponder card""s own unique identification card address. If the addresses compare (agree), then the command bits of the CMD word are decoded and the appropriate directional control valve solenoid 92 is energized. Transponder card 76 is also configured to transmit its own ACK word to the next upstream transponder card 76. If the addresses do not compare, then transponder card 76 passes any signal on the ACK input to the ACK output. Each transponder card 76 also is configured to generate valve activity bits based on its monitoring of HCU directional control valve solenoid circuits for continuity and energization. Further, each transponder card is configured to generate an ACK word composed of an identification card address, directional valve activity bits, HCU status bits, and transponder trouble bits. Each transponder 76 is configured to receive as input CMD words from the upstream transponder card or a branch amplifier card 74, ACK words from the downstream transponder card, and HCU 78 status. HCU 76 status includes: Both scram valves not fully closed Scram accumulator trouble (N2 gas pressure low or water on the gas side of the accumulator piston) Both scram test switches not in xe2x80x9cNormalxe2x80x9d AC voltage from the downstream transponder card Each transponder card 76 is configured to output CMD words to the downstream transponder and ACK words to the upstream transponder or branch amplifier card. Further, each transponder card 76 is configured to output switched AC voltage to the directional control valve solenoids and AC voltage to the downstream voltage. Any suitable AC voltage can be used, for example, 120 volts AC at 60 Hz or 12 volts AC at 50 Hz. Of course, AC voltages higher or lower than 120 volts AC can be used. The CMD word is composed of a 32-bit serial word transmitted as a serial data stream. This data stream can be divided into 8 defined sections. The data bit transmission rate is 312.5 kHz (3.2 xcexcs), which results in a 102.4 xcexcs of total word length. FIG. 4 shows an exemplary embodiment of a CMD word and Table I provides the description of the CMD word shown in FIG. 4. The Received Synchronization prime is sent prior to CMD Synchronization bit. The state of prime bits is xe2x80x9c1xe2x80x9d. The CMD Synchronization bit is set at xe2x80x9c0xe2x80x9d state. When the transponder card receives this bit, it indicates that the row address will be received on the next bit. Each Transponder has its own ID number corresponding to the plant arrangement of HCUs. Each ID number is composed by row and column address corresponding to the X and Y coordinates of the plant arrangement. The Space bit is sent to separate the ID number from command bits. The state of space bit is set at xe2x80x9c0xe2x80x9d. When the ID number matches with a particular transponder, the ACK word is generated at this point. The Withdraw Supply and Insert/Withdraw Exhaust bits of the CMD word are dynamically encoded. When the Transponder receives command bits for HCU directional control valve activation, the succeeding word""s command bits are required to be encoded with the complement of previous word""s command bits. If the succeeding word""s command bits are not encoded as complement of previous command bits, the activated control valve will be timed out (de-energized). Table II shows the logical values of the command bit that cause the activation to occur. The Margin set of bits is set at xe2x80x9c0xe2x80x9d state, and is sent prior to the received synchronization bits. The purpose of the margin bits is to permit the transponder card to complete the transmission of the ACK word. The ACK word is also composed of a 32-bit serial data stream. This data stream can be divided into eight sections. The data transmission rate is 312.5 kHz (3.2 xcexcs), which results in 102.4 xcexcs of total word length. FIG. 5 shows an exemplary embodiment of an ACK word and Table III provides the description of the ACK word shown in FIG. 5. In conjunction with the Synchronization bit, the Transmitted Synchronization Prime Bits serves to provide a means for the receiving circuitry to synchronize its reception to the word being received in order to interpret the bit meanings correctly. Ten consecutive xe2x80x9c1xe2x80x9d states are required to synchronize the receiving circuitry. The ACK Synchronization bit is set at xe2x80x9c0xe2x80x9d. This bit in conjunction with the Transmitted Synchronization Prime is used to synchronize the receiving circuitry to the word being received. Each Transponder has its own ID number corresponding to the plant arrangement of HCUs. Each ID number is composed by row and column address corresponding to the X and Y coordinates of the plant arrangement. The Space bit is sent to separate the ID number from the Directional Valve Status Bits. The state of space bit is set at xe2x80x9c0xe2x80x9d. The Direction Valve Status Bits contains four bits, and provides the activation status of directional valves. The status of each valve is given by the following two equations. SET (xe2x80x9c1xe2x80x9d State)=(Input power is above AC peak) AND (solenoid valve circuitry has continuity) AND (solenoid valve is de-energized) RESET (xe2x80x9c0xe2x80x9d State)=(Input power is near 0 volt) OR (solenoid valve circuitry is opened) OR (solenoid valve is energized) The HCU status contains three bits, and provides the test switch, HCU accumulator pressure and scram valve position. The Transponder removes power to the solenoid and sets the Transponder Trouble flag to xe2x80x9c1xe2x80x9d if the Transponder detects energization of a directional control solenoid without an appropriate command. HCU transponder card 76 includes a self-testing function that uses solid-state relays in each of the valve control circuits to interrupt the current through the directional valve solenoids if the self-testing circuitry detects a disagreement between the valve monitoring circuitry and the command word received by the card. In other words, if the valve is energized with no command, the self-test circuitry removes power to the valve solenoid after a short time delay by turning off the solid-state relay that is in series with the valve current path. Once the HCU Transponder self-test circuitry detects an agreement between the CMD word and the valve activity, the solid-state relay will again be energized and allow the transponder to operate properly. An Analyzer Card in central rod processing circuitry 72 interrogates the HCU Transponder at intervals as part of a self-testing program. Failure of a Transponder to encode a proper ACK word is detected immediately in the control room and indicated through an annunciation window alarm. The self-test feature of the HCU Transponder 76 detects and prevents operation of a control rod directional control solenoid without an appropriate command from the Rod Drive Control System. A secondary self-test feature of the HCU Transponder is to detect most single component failure modes that would prevent activation of the back-up solenoid de-energization circuitry. HCU Transponder 76 removes power to the solenoid and sets the xe2x80x9cTransponder Troublexe2x80x9d flag (serial word bit) to a logic xe2x80x9conexe2x80x9d if HCU transponder 76 detects energization of a directional control solenoid without an appropriate command. The xe2x80x9cTransponder Troublexe2x80x9d flag occupies the two-bit locations reserved for the Pn and Pp bits added to the Acknowledge word by branch amplifier card 74. If a momentary short turns on the valve control solenoid but is subsequently removed, transponder 76 will remove power to the valve circuit by dc-energizing the solid state relay. Every two minutes, the Analyzer Card will retest the failed Transponder Card. Retesting of the valve control solenoid by the Analyzer Card will provide an agreement between the disconnected state of the valve control monitoring circuitry (appears to the valve monitoring circuitry as energized) and the Analyzer xe2x80x9ctestxe2x80x9d Command word. The self-test circuitry in transponder 76 will again energize the solid-state relay and permit the transponder control circuitry to energize the directional valve solenoid upon command. With control returned to the valve energization circuitry, transponder 76 again operates in a normal manner. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.