ML17212A213

Forwards Conceptual Design Description of Reactor Vessel Level Monitoring Sys Developed by C-E Owners Group Which Utilizes Heated Junction Thermocouples.Pending Final Confirmation,Util Intends to Install Sys at Plant

ML17212A213
Person / Time
Site:	Saint Lucie
Issue date:	06/19/1981
From:	Robert E. Uhrig FLORIDA POWER & LIGHT CO.
To:	Eisenhut D Office of Nuclear Reactor Regulation
References
L-81-254, NUDOCS 8106230212
Download: ML17212A213 (22)

Text

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SUBJECT':: .o reactor>> vessel level monitoeing, sys~,dehelaped by C El pwner s,,gr l) zes. heated' unctionI,ther mocoupl es.Pending. final oup.which't'i confir mationiutil intends to. install~ sys at~ plant;"

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FLORIDA POWER & LIGHT COMPANY June 19, 1981 L-81-254 Office of Nuclear Reactor Regulation Attention: Mr. Darrell G. Eisenhut, Director Division of Licensing U. S. Regulatory Commission Washington, D. C. 20555

Dear Mr. Eisenhut:

Re: St. Lucie Unit 1 Docket No. 50-335 Post-TMI Requirements-Reactor Vessel Level Monitorin S stem Our letter L-81-234, dated June 1, 1981 described our schedule for purchasing and installing a Reactor Vessel Level Monitoring System (RVLMS). Recent discussions with the NRC Staff indicate that a more complete design description would be required to allow the finalization of the Staff's review. Please find attached a conceptual design description of the RVLMS developed by the C-E Owners Group which utilizes heated junction thermocouples. Pending final design confirmation and the satisfactory completion of testing, we intend to install this system at St. Lucie Unit l.

Very truly yours, CD

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REACTOR VESSEL LEVEL MONITORING SYSTEM RVLMS SYSTEM CONCEPTUAL DESIGN DESCRIPTION The conceptual design of the RVLMS is described in the following sections:

l. Sensors Design

2. Signal Processing Design

3. Display Design

4. System Verification Testing

5. System qualification

6. Operating Instructions Figure 3-1 is a functional block diagram for the RVLMS. The instrument system consists of two safety grade channels from sensors through signal processing equipment. The outputs of processing equipment systems feed-ing the primary display are isolated to separate safety grade and non-safety grade systems. Channelized safety grade backup displays are in-cluded for each instrument system. The following sections present de-tails of the conceptual design.

1. SENSOR DESIGN The RVLMS measures reactor coolant liquid inventory with discrete heated junc ti on thermocoupl e (HJTC) sensors 1 oca ted at di fferent level s wi thin a separator tube ranging from the top of the core to the reactor vessel head. The basic principle of system operation is the detection of a temperature difference between adjacent heated and unhea'ted thermocouples.

As pictured in Figure 3-2, the HJTC sensor consists of a Chromel-Alumel thermocouple near a heater (or heated junction) and another Chromel-Alumel

0 thermocouple positioned away from the heater (or unheated junction).

In a fluid with relatively poor heat transfer properties, the tempera-ture difference between the thermocouples is large.

Two design features ensure proper operation under all thermal-hydraulic conditions. First, each HJTC is shielded to avoid overcooling due to direct water contact during two phase fluid conditions. The HJTC with the splash shield is referred to as the HJTC sensor (See Figure 3-2).

Second, a string of HJTC sensors is enclosed in a tube that separates the liquid and gas phases that surround it. .

The separator tube creates a collapsed liquid level that the HJTC sensors measure. This collapsed liquid level is directly related to the average liquid fraction of the fluid in the reactor head volume above the fuel alignment plate. This mode of direct in-vessel sensing reduces spurious effects due to pressure, fluid properties, and non-homogeneities of the fluid medium. The string of HJTC sensors and the separator tube is referred to as the HJTC instrument.

The HJTC System is composed of two channels of HJTC instruments. Each HJTC instrument is manufactured into a probe assembly. The probe assembly includes eight (8) HJTC sensors, a 'seal plug, and electrical connectors (Figure 3-3). The eight (8) HJTC sensors are electrically .=

independent and located at eight levels from the reactor'essel head to the fuel alignment plate.

The probe assembly is housed in a stainless steel structure that pro-tects the sensors from flow loads and serves as the guide path for .

the sensors..'nstallation arrangements have been developed for each C-E reactor vessel including St. Lucie Unit l. Installation details will be provided in future documentation.

2. SIGNAL PROCESSING E(}UIPMENT DESIGN The processing equi pment of the RYLNS is. presently being developed.

The processing equipment portion will be composed of a combination of new and existing equipment. The design objective for the equipment is to address the NUREG-0737 criteria, including the cri teria of Attachment 1 to II.F.2 and Appendix A. The following description present functional and general hardware design criteria.

The processing hardware:wil.l be configured to provide information to.

3 the displays..described. in Section 3.. The processing equipment includes operator interfaces for equipment testing,, setup, and maintenance...

1 The descripti.ons .are for each of. the. two separate. channels. The outputs of the sensors will be transmitted to the processor, all of which is outside of containment, using qualified cable systems.

The processing for the HJTC instrumentation will have surye'illance testing and diagnostic capabilities. Automatic on-line surveillance tests will continuously check for specified hardware and software t

mal functions. The on-line automatic surveillance tests as a minimum

will indicate inputs that are out of range ahd computer hardware mal-function's. The malfunctions wi ll be indicated through the operator interface.

The processing equipment for the RVLNS performs the following func-tions:

1. Determine if liquid inventory exists at the HJTC posi-tions.

The heated and unheated thermocouples in the HJTC are connected in such a way that absolute and differential temperature signals are available. This is shown in Figure 3-4 ~ Mhen water surrounds the thermocouples, their temperature and voltage output are approximately equal. V( C) on Figure 3-4 is, therefore, approxi-mately zero. In the absence of liquid, the thermocouple temperatures and output voltages become unequal, causing V(< C) to rise. Mhen V(> C) of the individual HJTC rises above a predetermined setpoint, liquid inventory does not exist at this HJTC position.

2. Determine the maximum upper plenum/head fluid temperature from the unheated thermocouples. (The temperature processing range is from 100'F to 1800'F).

3: Process all inputs and calculated outputs for display.

4. Provide an alarm output when any of the.HJTC..detects the absence of liquid level.

5. Provide control of heater power for proper HJTC out-put signal level. Figure 3-5 shows a single channel conceptual design which includes the heater power controller.

3. DISPLAY DESIGN The RVLNS instrument outputs will be displayed in the control room.

and technical support center. All displays are designed to be con-sistent'with the criteria in NUREG-0737 Action Item II.F.2, II.F.2 , and Appendix A.

The following information is anticipated to be displayed:

1. Two channels of 8 discrete HJTC positions indicating liquid inventory above the fuel alignment plate.

'2. Maximum unheated junction temperature of each of the two channels.

3. Unheated junction temperature at each discrete location.

4. f SYSTEM VERI ICATION TESTING

'his section describes tests and operational experience with RVLMS instruments.

4.1 HJTC SYSTEM SENSORS The HJTC System is a new system developed to indicate liquid in-ventory above the core. Since it is a new system, extensive test-ing has been performed and further tests are planned to assure that the HJTC Syst'm will operate to unambiguously indicate liquid inventory above the core.

The testing is divided into three phases:

Phase 1 Proof of Principle Testing Phase 2 - Design Development Testing Phase 3 - Prototype Testing The,-first 4

.phase .consisted of a series of five tests, which have .

been .completed. The testing demonstrated the capability of the HJTC instrument design to measure liquid level in simulated re-l actor vessel thermal-hydraulic conditions (including accident conditions).

TEST 1 Autoclave test to show HJTC (thermocouples only) response to water or steam.

In April 1980, a conceptual test was performed with two thermocouples in s

t one sheath with one thermocouple as a heater and the other thermocouple as the inventory sensor. This configuration was placed in an autoclave (pressure vessel with the capabilities to adjust temperature and pressure).

The thermocouples were exposed to water and then steam environments. The results demonstrated a significant output diff'erence between steam and water conditions for a given heater. power level.

TEST 2 Two'phase flow test to show bare HJTC sensitivity'o voids.

In June 1980, a HJTC.of the present differential thermocouple design.

was placed into the Advanced Instrumentation for Ref lood "Studies (AIRS) test facility,, a low pressure two phase flow test facility. at Oak Ridge National Laboratory (ORNL). The HJTC was exposed to void fractions at various heater power levels. The results demonstrated that the bare HJTC output was virtually the same in two phase liquid as in subcooled liquid. The HJTC did generate a significant output in 100Ã'quality steam.

TEST 3 Atmospheric air-water test to shovI the e'ffect of a splash shield.

A splash shield was designed to increase the sensitivity. to voids. The splash shield prevents direct contact with the liquid in'the two phase fluid. The HJTC output changed at intermediate void fraction two phase fluid. The results demonstrated.that the HJTC sensor (heated junction thermocouple with the splash shield) sensed intermediate void fraction fluid conditions.

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TEST 4 High pressure boil-off test to show HJTC sensor response to reactor thermal-hydraulic conditions.

In September -1980, a=- C-E HJTC sensor (HJTC with splash shield) was installed and tested at-the ORNL Thermal-Hydraulics Test Facility (THTF)., The device is still installed and avilable for further tests at ORNL. The HJTC sensor was subjected to various two phase fluid conditions at reactor temperatures and pressures. The results r

verified that the HJTC sensor. is a device that can sense liquid inventory under normal and accident reactor vessel high pressure and temperature two phase conditions.

TEST 5 Atmospheric air-water test to show the effect of a separator tube A separator tube was added to the HJTC design to form a collapsed liquid level so that the HJTC sensor'irectly measures liquid inventory under. all simulated two phase conditions. In October, 1980, atmospheric air-water tests were performed with HJTC sensor and the separator tube. The results demonstrated that the separator tube did form a collapsed liquid level and the HJTC output did accurately indicate liquid .inventory. This test verified that the HJTC instrument, which includes the HJTC, the splash shield, and the separator tube, is a viable measuring device for liquid inventory.

The Phase 2 test program consisted of high pressure and temperature e

tests on the HJTC instrument. .Testing,was recently conducted and in all cases the instrument performed as designed. A full test report f

is due to be issued in July of 1981.

The Phase 3 test program will consist of high temperature and pressure testing of the manufactured prototype system HJTC probe assembly and processing electronics. Verification of the HJTC system prototype will be the goal of this test program.'he Phase 3 test program is expected to be completed by the end of 1981.

4.2 PROCESSING AND DISPLAYS The final processing and display design for the RVLNS has not been completed. As the design effort proceeds, design evaluations will be performed prior to installation. Correct implementation of the soft-ware and hardware will be included and documented as part of .the design effort.

5. SYSTEM UAL IF I CATION The qualification program for the RVLMS instrumentation has not been completely defin'ed. However, plans are being developed based on the following three categories of RVLNS instrumentation:

1. Sensor instrumentation within the pressure vessel.

2. Instrumentation components and systems which extend from the primary pressure boundary up to and including the primary display isolator and including the backup displays.

, 3. Instrumentation systems which comprise the primary display equipment.

A preliminary outline of a qualification program for each classification is given below.

The in-vessel sensors will meet the NUREG-0737, Appendix A guide to install the best equipment available consistent with qualification and schedular requirements. Design of the equipment will be consistent with the guidelines of Appendix A as well as the clarification and Attachment I to Item II. F.2 in NUREG-0737. Specifically, instrumentation will be designed such that they meet appropriate stress criteria when subjected to normal and design basis accident loadings. Yerification testing will be conducted to confirm operation at LOCA (as defined by C-E) pressure and temperature conditions. Seismic testing to safe shutdown conditions will verify function after being subjected to the seismic loadings.

The out-of-vessel instrumentation system, up to and including the TSC display isolator, and the control room displays will be environ-mentally qualified in accordance with IEE-323-1974.

Plant-specific containment temperature and pressure design profiles will be utilized where appropriate in these tests. This equipment will also be seismically qualified.

6. OPERATING INSTRUCTIONS Guidelines for reactor operators to use the RYLMS and take corrective action have been developed by the C-E Owners Group and submitted to NRC for review via letter dated December 10, 1980 from the C-E Owner's Group."C-E Generic-Emergency Procedure Guidelines". These guidelines E

have been used to review and revise the plant emergency procedures for St. Lucie Unit l.

The C-E Owners Group is defining a program for development of further emergency procedure guidelines and operator training materials associated with the RVLMS described. This program is expected to provide these guidelines and training materials during 1981. A more specific schedule is subject to finalization of the RVLHS design, specifically the instrument displays.

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SENSORS PROCESSING DISPLAY ISOLATION iSC.

DISPLAY QGt4YR,O'4 Q,age, SENSORS PROCESSING OISI'LAY Cllht/ttfL 0 FIGURE 3-1 IHSTRUtlEttTS FUNCTIONAL BLOCK DIAGRAH

FIELD SPLASII Sll FIGURE 3-2 IIJTC -SENSOR - IIJTClSPLASII SIIIELD

ELECTRICAL CONNECTORS SEPARATOR TUBE (OtJE PER SEttSOR)

SEAL PLUG ltJTC SENSOR

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tNCQt",EL COPPER CHROMED ALU>i'/ED ALUA1EL CHROMEL COPPER V V -'>} ACTUAL TENPERATURE, UNHEATED JUNCTION V (C- 8} " ACTUAL TEMPERATUREr HEATED JUNCTiON

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Y (A- C) ~ OtFFERENTIAL TEMPERATURE FIGURE 3-4 ELECTR1CAL DlAGRAM OF H. J. T. C.

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SENSOR 1

~ SIGNAL PROCESSOR PRINARY DISPLAY THROUGH LOGIC ANO CHANNFL BACKVP SENSOR 8 CONTROLS D I SPLAY ALARM POVlER FEEDSACK SIGNAL POWER POlrtlER CONTROL SIGNAL HEATER POVNER CONTROLLER POWER TO HEATERS FIGURE 3-5 HJTC SYSTiiIiPROCESS liNG CGNFIGURATIOi'I (OOC CHA WFL SHOWj"