ML18051A907

Inadequate Core Cooling Instrumentation Sys.

ML18051A907
Person / Time
Site:	Palisades
Issue date:	05/31/1984
From:	CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
Shared Package
ML18051A906	List: ML18051A905 ML18051A907
References
GL-82-28, NUDOCS 8406060116
Download: ML18051A907 (19)

Text

ATTACHMENT Consumers Power Company Palisades Plant - Docket 50-255 INADEQUATE CORE COOLING INSTRUMENTATION SYSTEM May 31, 1984

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p PDR 18 Pages OC0584-0019C-NL02

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• PROPOSED ICCI SYSTEM FOR PALISADES The following summary describes the proposed ICCI modifications for the Palisades Plant in response to NRC generic letter 82-28 and NUREG-0737.

This information supersedes earlier submittals to reflect a change from the originally proposed Westinghouse Differential Pressure method for reactor vessel level, to a differential thermocouple approach utilizing RADCAL probes. The modifications will consist of the following basic items:

1. Installation of a redundant Reactor Vessel Level Indication System (RVLIS), including:

0 Insertion of two RADCAL Level Instrument (RLI) probes into existing incore instrument guide tubes. These RGT probes will extend from near the top dome of the reactor head down to the top of the reactor core, and contain discrete level sensors at eight locations along the probe length.

0 Replacement of reactor head instrument flanges to accom-modate the two RLI probes.

0 Installation of Class lE cables from the reactor head to Control Room, via separate containment penetrations.

0 Installation of a qualified and redundant readout system in the Control Room. This system will also provide qualified readout from 16 upgraded core exit thermo-couples, and provide interface to an existing computer-based SPDS system.

0 Modifications to the existing SPDS ("Critical Function Monitor") to provide the required "primary display" readout capabilities for ICCI. This will include input changes, software development, and possibly a computer upgrading.

2. Upgrading of 16 existing core*exit thermocouple (CET) signals:

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2 0

Qualification or replacement of existing cables within containment.

0 Replacement of existing cable connectors within contain-ment with LOCA-qualified connectors.

0 Rerouting of these CET signals from an existing data-logger to the new RVLIS display system.

0 SPDS changes to provide the "primary display" require-ment, as noted above.

3. Upgrading of the existing subcooled margin monitor (SMM) channels:

0 Replacement of input temperature transmitters to extend the operating range to meet NUREG-0737 requirements, from the existing 515-615°F range.

0 Modifications of existing SMM units to provide the extended range.

0 SPDS changes to provide the "primary display" require-ment. Qualified backup display will remain to be the existing digital display on the main Control Room panels.

The format of the following submittal is in accordance with Appendix A of NRC generic letter 82-28 dated 12/10/82.

1. Description of the proposed final system, including:

A. a final design description of additional instrumentation and displays:

Reactor Vessel Level Instrumentation The reactor vessel instrumentation system will be based on RADCAL Level Instrument (RLI) probes inserted into existing instrument guide tubes. Two of the 45 present incore probes will be abandoned to accommodate them. Each RLI installation will be an independent channel (two channels total), extend-OC0584-0019A-NL02

3 ing to just above the fuel assemblies. Figure 1 depicts a single channel arrangement (the final choice of one or two RLI probes per channel will depend on flange considerations).

Each channel contains eight level sensors. The four sensors located above the control rod shroud are spaced approximately six-inches apart to provide high resolution and early warning of dropping level. The four (4) sensors distributed along the length of the UGS are spaced approximately four-feet apart.

Display will be provided in the Control Room by new display modules and through the existing Critical Function Monitoring System (SPDS). Level indicating LED display lights will be colored and arranged for optimum operator information, with backup recording also provided. A test arrangement will utilize an integral heater wire in each probe for periodic checkout of each level sensor, complete through display. The display system shown in Figure 1 also will provide isolated outputs to an existing SPDS system for computer-graphics display to the Control Room, as well as TSC and EOF emergency facilities.

Core Exit Thermocouples Sixteen existing core exit thermocouples (CET) will be up-graded to meet the requirements of NUREG-0737. The existing incore/thermocouple probes will continue to be used; however, the readout of these thermocouples will be changed to record-ers in the new RVLIS display units depicted in Figure 1.

These recorders may include digital readout if such qualified units are available. Range of CET readouts will be 0-2300°F.

Isolated and processed output signals will be fed to the existing SPDS/CFM system for computer-graphics display to meet the "primary display" requirements. This will provide flexi-ble display of CET data to the Control Room and remote emer-gency facilities.

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• 4 Subcooled Margin Monitor The existing subcooled margin monitors will be upgraded to meet NUREG-0737 requirements. This will require replacement of the present temperature inputs (515-615°F) with wide-range transmitters. Also, the existing SMM units will require internal modification for wider range calculation. Qualified digital display will remain on the main Control Room panel, which is readable from the rear area where RVLIS displays will be located.

B. Detailed description of existing instrumentation systems:

Reactor Vessel Level Instrumentation There is no present instrumentation.

Core Exit Thermocouples The Palisades reactor contains 45 distributed core exit thermocouples, radially located as shown in Figure 2. These CETs are at the upper end of top entry incore probes, also containing self powered incore flux detectors. The CET and flux signals from each probe are fed through a common cable to the control room. The 45 cables share a common path via two adjacent containment penetration units to the input cabinet of a datalogger. Readout on the datalogger typewriter is hourly or by operator demand.

Subcooling Margin Monitor The subcooling margin monitor is a two-channel Class lE system supplied by Combustion Engineering with digital readouts on.

the main control panels located as shown on Figure 3.

Operating range is 515 to 615°F.

Critical Function Monitor System This computer-based system was recently installed at Palisades to provide the SPDS function required by the NRC.

It is fully capable of the trending and display functions OC0584-0019A-NL02

• 5 for ICCI as required by NUREG-0737. Output CRT displays are located in the Control Room, as well as the TSC and EOF emergency facilities and at the Company General Office.

Although not fully qualified as a Class lE system, it is provided with backup battery power and is expected to be highly reliable.

C. Description of completed or planned modification:

Reactor Vessel Level Instrumentation Reactor incores will be removed from two locations. In their place will be inserted two RLI probes. This will require fabrication of new instrument tube flanges and the machining of flow slots in the incore tubes. Each RLI probe terminates above the reactor vessel head in a multi-pin qualified connec-tor. Qualified signal cable will be routed from these two connectors to existing separate containment penetrations and then to the Control Room. The cables will terminate at a qualified Control Room display module (Figure 1) located in Control Room P~nel C-llA (see Figure 3 for location of C-llA).

Signals also will be routed to the existing Critical Function Monitoring system (Safety Parameter Display System) through an isolation device.

Core Exit Thermocouples The existing core exit thermocouples/flux monitor incores will be unchanged. The cable connectors for the 16 CETs to be upgraded will be replaced with qualified connectors. The 16 signal cables will be disconnected from the present datalogger and connected to the signal processing units located in the reactor vessel level monitoring system modules (Figure 4).

These modules contain the backup display units for the CET.

The primary display is provided by the Critical Function OC0584-0019A-NL02

• 6 Monitoring System. Software and hardware changes for the CFM will be necessary to accept the CET signal.

Subcooling Margin Monitor The existing subcooling margin monitor will be upgraded through software changes to its microprocessor and replacement of input temperature and pressure transmitters with units of extended range.

2. A design analysis and evaluation of inventory trend instrumenta-tion, and test data to support design in Item 1:

Reactor Vessel Level Instrumentation The proposed RVLIS is based on the use of a RADCAL Level Instru-ment (RLI) that is nearly identical to the earlier developed RADCAL gamma thermometer used for incore power monitoring. This probe was developed by Scandpower in the mid-1970 period and has many reactor years of service. The design was described in a topical report, number SCP-OlA, Rev 4, submittal to and approved by the NRC in August 1982. The application of this probe at Palisades will be similar to that proposed for both ANO plants, and subsequently issued satisfactory safety evaluations by NRC.

Once installed in the Palisades vessel, no further movement will be necessary during refuelings. This will enhance the basic rugged design of the probe to ensure continued reliability and minimum system maintenance.

Installation at Palisades will utilize two of the 45 existing instrument guide tubes, which penetrate the reactor head approxi-mately three-feet below the dome and follow a two-bend path down to the top of the core. The guide tubes are firmly attached to the Upper Guide Structure (UGS) at several locations. Flow holes will be opened at appropriate points to allow the guide tubes to function properly as manometers. Figure 5 illustrates the approx-OC0584-0019A-NL02

7 imately path of guide tubes and sensor locations in the Palisades Reactor.

Eight discrete level sensor points will be included within each of the two redundant RLI probes, axially located to provide optimum level indication. Four points will be located in the upper head region within the straight portion of the guide tube above the UGS. This will provide early warning of dropping coolant with an approximate six-inch spacing, giving higher resolution in this critical region. The other four sensors will be located within the 12-foot vertical run through the UGS, to warn of potential core uncovery. These upper and lower regions will be hydraulical-ly isolated within the guide tube manometer. Reactor coolant flow in the lower region will preclude the use of the four sensors in the UGS with pumps running. The four sensors in the upper region will be functional with coolant pumps running or not. Note that there is no plenum separation within the Palisades reactor vessel; ie, the only water barrier between the core and head dome is the control rod shrouds forming the UGS.

The output signal will be a differential thermocouple voltage between the heated and unheated T/C points at each sensor loca-tion. Signal transmission to the Control Room can thus utilize normal copper wiring, which deletes the errors associated with T/C wiring junctions and reference boxes. The readout method will utilize an arrangement of lights to provide the operator with a simple and understandable display, backed up by trend recorders.

In evaluating this method for Palisades application, the design of the system points to several advantages:

1. Early warning of coolant loss in the reactor head region, with or without pumps running;

2. No density correction is required;

3. An easily detectable signal change; OC0584-0019A-NL02

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4. The proven rugged design and lack of refueling movement should provide good probe reliability; 5.- Straightforward signal transmission and readout.

Test data to support design of the RLI probe will be provided by the confirmatory/qualification test program conducted by ORNL for Arkansas Power & Light. These tests include a complete series of LOCA simulations for above-core RLI probe performance evaluations.

Subcooled Margin Monitors Subcooled margin monitoring is not considered to be inventory trend instrumentation. This system provides early warning of approach to boiling conditions, utilizing qualified equipment previously reviewed by the NRC.

Core Exit Thermocouples Core exit thermocouples provide inventory trending only through approximation of core uncovery relative to superheated conditions at core exit. Existing incore probes will be used as inputs to strip chart recorders and, if qualified units are available, digital readouts. Thermocouples are chromel-alumel type with the standard accuracy and range of C/A devices. Readout will cover the required 0-2300°F range with an expected overall accuracy of 1% to 2% of reading. No specific tests are planned to support the CET modifications.

3. Description of tests planned and results of tests completed for evaluation, qualification and calibration of additional instru-mentation:

Reactor Vessel Head Level A program has been conducted by Arkansas Power & Light Company (AP&L) and Technology for Energy Corporation (TEC) at Oak Ridge National Laboratories to demonstrate RADCAL gamma thermometers as level measuring devices. Preliminary results of the above-core OC0584-0019A-NL02 I

1_*~--

9 level testing program appear very satisfactory. AP&L will be submitting them to the NRC in the near future. Consumers Power Company, through arrangements made by TEC will have access to the test program results. Program objectives were discussed in the AP&L submittal to the NRC dated April 14, 1984.

In addition to this testing, TEC has conducted testing at their facilities that demonstrate that a gamma thermometer level device can be inserted into a mockup of a Palisades incore tube and maintain its functionality.

Along with functional testing, environmental and qualifications testing will be addressed. Environmental qualification will be documented by design and operational experience. These probes have had many years of in-reactor service as a power measuring device. Since the construction of a probe for level detection is similar to that of probes used for power monitoring, we feel sufficient information exists for qualification. Since the probe is essentially a solid rod, seismic qualification will be achieved by analysis. The simplicity of design will allow the use of straightforward analytical techniques.

The signal transmission and processing systems up to and including the isolators will be comprised of components which are currently available and qualified. No electronic systems are to be located inside the containment building, thus simplifying the environmen-tal qualification required.

Formal Consumers Power Company preoperational checkout, calibra-tion and system evaluation procedures will be conducted and documented on this equipment. In addition the equipment supplier will conduct functional and electrical checks prior to installa-tion of the level sensor and electrical checks after installation.

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10 Core Exit Thermocouples (CET) qualification testing, analysis or operating experience will be used on components of the 16 modified core exit thermocouples that presently are not qualified. Quali-fication efforts would be conducted according to the Palisades Plant qualification program. The modified CETs will be checked out through a formal preoperational testing program. Component checkout, calibration and overall system performance evaluation will be conducted and documented.

Subcooling Margin Monitor This system presently is being qualified under our EEQ program.

Modifications to the system will be with appropriately qualified components. The modified subcooled margin monitor also will be checked out in a formal preoperational testing program.

4. Provide a table or descri.ption covering the evaluation of confor-mance with NUREG-0737, II.F.2, Attachment 1, and Appendix B (to be reviewed on a plant specific basis):

Reactor Vessel Head Level (II.F.2, Appendix B Format)

1) Environmental Qualification - The Reactor Level Instrument (RLI) probes, signal transmission and signal processing system up to and including the isolators will be seismically and environmentally qualified. For the RLI probe, environmental qualification will be demonstrated by analysis and operational experience. These probes have had many years of in-reactor service as a power-measuring device. Since the construction of a probe for level measurement is similar, it is believed that sufficient information exists for the qualification of gamma thermometer as level monitors.

The signal transmission and processing system up to and OC0584-0019A-NL02

11 including the isolators will be comprised of components which currently are available and qualified. No electronic systems are to be located inside containment, thus simplifying the environmental qualification effort.

The display of reactor vessel head level information will be provided by the CFM/SPDS computer and with new backup display modules. Both are located in a mild environment. The CFM is not lE qualified. The backup display will be qualified to IEEE-323 (1974) and lEEE-344 (1975).

2) Single Failure Analysis - The two RLI probes will be physical-ly separated at the reactor head. Cable routing will be separately run through the north and south containment pene-tration areas to the Control Room. Readout modules will be adequately separated on right and left sides of panel Cll-A.

Signal isolation will be provided before the common CFM/SPDS primary display unit. Thus, the entire RVLIS installation will meet separation criteria of safety-related equipment.

Further single failure analysis will be done as the detailed design develops.

3) Class lE Power Source - All portions of the system will be provided with Class lE power with the exception of the CFM/

SPDS computer. This computer has its own inverter power supply and is battery backed for reliability.

4) Availability Prior To An Accident - The reactor vessel level indication system will be available prior to an accident.

Because the system is composed of two redundant channels, one channel may temporarily be removed from service for surveil-lance, calibration or maintenance while the other channel remains in service.

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5) Quality Assurance - Consumers Power Company's quality assur-ance program, as documented in the Quality Assurance Manual, CPC-2A, Rev 1, complies with the referenced Regulatory Guides, except for 1.28. Our program complies with R.G. 1.33 and thus, meets the intent of R.G. 1.28.

6) Continuous Indications - RVLIS information will be continuous-ly available for selected display on the CFM/SPDS computer graphics. The qualified backup readout will continuously display levels on both an LED light panel and recorders.

7) Recording of Instrument Outputs - Direct recording of all eight sensors from each probe will be available on the quali-fied backup display modules. Also, the trending capabilities of the CFM/SPDS computer will be utilized.

8) Identification of Instruments - As shown on Figure 1, the qualified backup display module will contain two indicating lights and one chart recorder trace for each of the eight sensors in both probes. The two lights will indicate whether the level sensor point is covered (green light on) or uncov-ered (red light on). The recorder trace will show an offset as reactor coolant passes the sensor point. These displays will be arranged in an easily identifiable panel front.

The primary display will collect the ICCI instrument outputs into a logical graphics display under keyboard entry selection.

9) Isolation - The RVIS signals will be isolated from all other systems through the qualified backup display readouts, and qualified signal isolation will be provided prior to signal OC0584-0019A-NL02

13 feed to the primary display computer system.

Core Exit Thermocouples The following summary responds to II.F.2, Attachment I of generic letter 82-28.

1) Figure 2 provides a core map for Palisades showing locations of the 16 core exit thermocouples to be upgraded for ICCI.

2) The CFM/SPDS computer based system will be used as the ICCI "primary display":

a) A CRT display will be available for keyboard selection of a spatially oriented core map showing CET temperature readings.

b) The readout system will have a range of 0-2300°F.

c) The normal CFM/SPDS alarm system will be used to annunci-ate high temperature conditions. Although not programmed at this time, the system is fully capable of signal diagnosis to detect faulty readings.

d) The primary display computer readout is in the center of the Control Room, about 20 feet from the panel where the qualified backup display will be located. Figure 3 shows relative locations.

3) Backup display of subcooled margin monitors will be the existing digital readouts on the front main Control Room panels. They are readable from the rear of the Control Room.

Backup display of RVLIS and CET will be provided on redundant new panels as illustrated in Figure 1 and located as shown on OC0584-0019A-NL02

14 Figure 3. Chart records (and possibly digital display) will continuously monitor each of the 16 CET signals, over a range of 0-2300°F. Operability may be checked by direct observation and comparison for uniform output during normal plant operation.

RVLIS display is described earlier in this submittal.

4) The primary and backup CET displays have been described earlier in this submittal. Operators will normally use the computer graphics output of the primary display for overall diagnosis of core exit conditions and average or high tempera-ture analysis i~ specific areas, as well as trended data.

Backup display will provide both real time and trended infor-mation on individual CETs, to augment or back up the primary display.

Use of CET data for operator action will be based on EOPs not presently written. Operators will be thoroughly trained in the use of ICCI prior to its final implementation.

5) Control Room design task analysis has not been completed at this time. Modifications for ICCI will be factored into final task analysis results.

Based on our review at this time, the upgraded CET system will meet the criteria of NUREG-0737, Item II.F.2, Attachment 1, and Appendix B with the following deviation:

Under single failure criteria of Appendix B, the physical separation requirement will not be met by our proposed modif i-cations for CET cable runs to the Control Room. Cable instal-lation details and justification were provided in our letter of January 30, 1984 in response to your review question number OC0584-0019A-NL02

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5. We continue to feel the cost and personnel exposure to install new cable runs, including new containment penetra-tions, are not justified by the risk improvement from separa-tion of cables for this system.

6) lE power will be provided for both channels of the qualified backup display modules used to read out all 16 upgraded CETs.

The only tie to non-lE equipment will be the primary display, for which qualified signal isolation will be provided.

The power supply for the primary display consists of an inverter-battery system fed from non-lE power.

The clear delinearization point will be at the signal isola-tion devices separating the qualified backup display and primary display computer systems.

7) Core exit thermocouple instrumentation will be environmentally qualified up to the signal isolation devices feeding the primary display system.

Subcooled Margin Monitors (II.F.2, Appendix B Format)

1) Environmental Qualification - The SMM channels will meet this criteria.

2) Single Failure Analysis - The SMM channels will meet this criteria.

3) Class lE Power - The SMM channels are supplied from redundant Class lE power.

4) Availability Prior to an Accident - Present Technical Specifi-cation requirements for at least one operable channel will assure this availability.

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5) Quality Assurance - See RVLIS response above.

6) Continuous Indication - Digital readout of the SMM micropro-cessor is updated continuously as output changes. Trending of this output will be provided by the primary display computer system.

7) Recording of Instruments - SMM output will be trended by the primary display computer system. No backup strip chart record-ing is proposed for this portion of ICCI.

8) Identification of Instruments - The SMM digital readouts are prominently displayed on the main control panels along with other critical NSS parameters. Readout on the primary display computer graphics will be incorporated with other ICCI indica-tions to assure easy identification.

9) Isolation - Qualified signal isolation will be provided between the SMM modules and the primary display computer system.

5. Describe computer, software, and display functions associated with ICC monitoring in the plant:

The signals from all three portions of ICCI will be fed to the existing CFM/SPDS computer system to provide computer graphics display under keyboard selection. Although exact details are not available at this time, display formats will be developed to provide the operator with a human factored, unambiguous indication from ICC inputs.

CET display will follow a core map concept with additional indica-tion of quadrant average and high point temperatures. Core inlet conditions may be combined with CET data to provide quadrant core enthalpy rise. Normal alarming, signal processing, and trending OC0584-0019A-NL02

• 17 capabilities of the computer will be utilized.

RVLIS display will be a straight presentation of the redundant level probe information, enhanced as necessary to provide compari-son of level with vessel physical configuration. Computer capa-bilities will be utilized to ensure data validity, such as pump on/off conditions, and trending.

Subcooled margin display is expected to be only a numerical output on appropriate ICCI display formats, plus trending.

6. Provide a proposed schedule for installation, testing and calibra-tion, and implementation of any proposed new instrumentation or information displays:

Response: Figure 6 shows the projected schedule for installation of the new RVLIS components and upgrading of existing CET and SMM equipment. Final installation and testing will take place during the next scheduled refueling outage, now expected to start in November 1985. Implementation dates shown are based on estimated periods for functional testing and final NRC approval of the system and operating guidelines.

Attainment of this schedule will be contingent upon NRC approval of the RADCAL gamma thermometer test results now being completed at ORNL.

7. Describe guidelines for use of reactor coolant inventory tracking system, and analysis used to develop procedures.

Response: Technical guidelines developed through the CE Owners Group, along with the results from the RGT probe test program at ORNL, will be used to develop plant-specific guidelines for ICCI system use. Guidelines for Palisades will be provided for your OC0584-0019A-NL02

18 review when available.

8. Operator instructions in current emergency operating procedures for ICC and how these procedures will be modified when final monitoring system is implemented:

Following guidelines to recognize void formation and small LOCA potentials for ICC, the current EOPs instruct operators to verify operation of emergency safeguards equipment, to use the reactor head vents if non-comdensible gases are presnet, and to open pressurizer PORVs to allow increased high pressure safety injection flow if natural circulation cannot be established or of steam generator cooling is not availabe when needed. These instructions will be modified after ICCI implementation based on plant-specific guidelines developed from the generic CEOG technical guidelines.

9. Provide a schedule for additional submittals required:

1. Final results of the RADCAL probe qualification tests conduct-ed by ORNL are now expected to be submitted by Arkansas Power

& Light in July 1984.

2. Plant-specific technical guidelines for ICCI use at Palisades will be submitted for your review by September 1984.

3. Final implementation letter will be submitted four months after installation. The present expected schedule is shown on Figure 6 attached.

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