ML20054F070

Bryon/Braidwood Stations - Units 1 & 2,Inadequate Core Cooling Detection Sys Summary Status Rept

ML20054F070
Person / Time
Site:	Byron, Braidwood, 05000000
Issue date:	04/30/1982
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML20054F066	List: ML20054F065 ML20054F070
References
NUDOCS 8206150188
Download: ML20054F070 (29)

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BYRON /BRAIDWOOD STATIONS - UNITS 1 AND 2 INADEQUATE COT .dG DETECTION SYSTEM

SUMMARY

STATUS REPORT I l

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TABLEOFCONTE!h Section Title Page.

1.0 INTRODUCTION

E.31-4 1.1 Surgmary of Activities E.31-f.

1.2 Basis for ICC Instrument Selection E.31-

1. 3 Description of Event Progression E. 31-(p .

1,4 Summary of Sensor Evaluations E.31-f I

2.0 SYSTE;f FUNCTIONS DESCRIPTION E.31-30 f

2.1 Subcooling and Saturation E.31-10 2.2 Coolant Level Measurement in Reactor Vessel E.31-l10 2.3 Fuel Cladding !!catup E.31 'll 3.0 SYSTEM DESIGN DESCRIPTION E.31-12 3.1 Sensors Design E . 31 -12 3.2 Signal Processing and Display Equipment Design E. 31 -l19 I

4.0 SYSTEM VERIFICATION TESTING E.31225 l

4.1 Pressure Sensors E. 31- 26 4.2 HJTC System Sensors and Processing E.31426 4.3 Core Exit Thermocouples E.31 27 1

5.0 SYSTF3! QUALIFICATION E.31-28 6.0 OPERATING INSTRUCTIONS E.31229 l

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1.0 INTRODUCTION

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I 1.1 SUFNWRY 'CTl ACTIVITIES ,

This report responds ~ to the requirements in Section II.F.2 of NUREC-0737

-(Ref. 1). The report describes the status of design and development (

activities being conducted by the.C-E Owners Group as supplemented by [

plant specific ef forts by Commonwealth Edison Company to define and implement a system of instrumentation to be used to detect inadequate core cooling (ICC). . The report also provides information specific to [

Byron /Braidwood Units 1 and 2 in order to demonstrate the applicability t of the generic activity to Byron /Braidwood Units 1 a'nd 2. {

Results of initial studies-by the C-E Owners Croup are documented in rep, orts CEN-117 (Ref.G 2) and CEN-125 (Ref. 3). All studies have been based on the requirement to indicate the approach to, the existence of, an i. the recovery from ICC.

l The,ICC system selected was specifically based on the results presented.in The basis for the instruments selected is summa'rized J"CEN-185 (Reference 5).

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1.2 BASES FOR ICC/ INSTRUMENT SEI.ECTION r

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- -The ICC instrumentation sensor package described herein is designed to:d'

1) \ ~pr, ovide the operator with an advanced warning of the approach to IC

2) cover the full range of ICC from normal operation to complete core

'uncovery.

The .ICC detection system that employs this sensor package and displays. !

trends and logs the sensor outputs, enabling the reactor operator to monitor system conditions associated with tne approach to and tne recovery t' rom ICC.

1.3. DESCRIPTION OF ICC EVENT PROGRESSION The instrument sensor package for ICC detection provides the reactor operator a continuous indication of the thermal-hydraulic state within the Reactor Pressure Vessel (RPV) during the progression of an event leading to andf away from ICC. The progression towards and away from ICC can be divided into intervals based on physical processes occurring within the RPV. These are characterized as follows:

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BfB-FSAR Intervals Associated with the Approach to TCC Interval 1 Loss of fluid subcooling prior to the first occurrence of satura-tion conditions in the coolant.

Interval 2 Decreasing coolant inventory within the upper plenum, (trom the top of the vessel to the top of the active fuel).l Interval 3 Increasing core exit temperature produced by uncovery of the core resulting from the drop in level of the mixture of vapor bubbles and liquid below the top of the active fuel. '

Intervals Associated with Recovery f rom ICC 4

Interval 4a Decreasing core exit temperature resulting from the rising of the mixture level within the core. .

Interval 4b Increasing inventory above the fuel.  !

i Interval 4c Establishment of saturation conditions followed by an increase in ,

fluid subcooling. i i

These intervals encompass all possible coolant states associate'd with any ICC even t progression. Intervals 1 thru 3 refer to fluid situations that occur during the approach to ICC. Intervals 4a, 4b and 4c refer to fluid situations which occur during the recovery f rom ICC.

6 In order to provide indicators during the entire progression of an event , an ICC instrument system should consist of instruments which provide at least one appropriate indicator for each of the physical intervals described above.

Applying this description of the " approach to", and " recovery f rom" ICC to ICC instrument selection:

1) provides assurance that the selected ICC system detects the entire progression. ,

2) demonstrates the extent of instrument diversity or redundancy; which is possible with the available instrumenta.

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Furthermore, by defining the ICC progression on a physical basis the general labels of ' approach to", and " recovery f rom" ICC can now be assoe1.4,t ed wI:h specific physically measurable processes. (See Section 1.3.1 anct 1. 3. 3)

The 'nadequate core cooling instrument sensor package consists of (3) Reactor coolant loop and pressurizer pressure sensors, (2) re.etor vessel level monitors employing the HJTC concept and (3) co re ex i t .thermo-couples. The signals f rom the temperature and pressure sensors cart be cor.bined to indicate the loss of subcooling and occurrence of saturation (Interval 11 and the achievement of a subcooled condition following core recovery (Interval 4c). The reactor vessel level monitors provide informatihn to the

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1 B/B-FSAR operator on the decreasing liquid inventory in the reactor pressure vessel (RPV) regions above the fuel alignment plate, as well as the increasing RPV liquid inventory above the fuel alignment plate following core recovery (Interval 2 and 4b) . The core exit thermocouples (CETs) monitor the increasing steam temperatures associated with core uncovery and the decreasing steam temperatures associated with core recovery (Interval 3 and 4a).

1.3.1 Advanced Warning Of The Approach To ICC The ICC instrunentation provides the operator with an advanced warning of the approach to ICC by providing indications of:

1) the loss of subcooling and occurrence of saturation (Interval 1) with a saturation meter receiving input from primary system temperature and pressure sensors.

2) the loss of inventory in the RPV (Interval 2) with the RVLMS.

3) the increasing core coolant exit temperature (Interval 3 ) with CETs.

It should be noted that the RVLMS measures inventory (collopsed liquid level) rather than two-phase level. This measurement provides the operator with an advanced indication of the coolant level should conditions arise to cause the two-phase froth to collapse via system overpressurization, or the loss of operating reactor coolant pumps.

1.3.2 Application Of The ICC Detection Ins truments Following an event leading to ICC the ICC detection instruments will provide information to the reactor operator so that he may:

1) verify that the core heat removal safety function is being met.

2) establish the potential for fission product release.

ICC instrumentation indications will be used to support the operator in helping to verify that the core heat removal safety function is being met. ICC instrumentation indications availabic to the operator are (1) a decreasing core exit steam superheat, (2) an increasing Inventory above the fuel alignment plate or (3) an increasing subcooling in the RPV or RCS piping.

The operator is informed about the progression of an event by both static and trend displays. The trending of ICC information enables the operator to quickly assess the success of automatically or manually perfonned mit inat inn actions. A chart indicating the ICC instrumentation t rending during the variou's ICC progression intervals associated with the approach to and recovery fron ICC is presented in Table 1-1.

E.31-6

TABLE l-1 ICC STATUS AS AVAILABLE TO THE OPERATOR FROM ICC INSTRUMENTATION TRENDING i

I. APPROACHING AN ICC. CONDITION SUBCOOLING MEA- WATER INVENTORY MEA- COOLANT SUPERHEAT 1

INTERVAL SURED BY SMM SURED BY HJTC PROBE MEASURED BY CET 4

1 DECREASING CONSTANT CONSTANT 2 CONSTANT DECREASING CONSTANT

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• M Nto w II. RECEDING FROM AN ICC CONDITION 4

- m b SUBCOOLING MEA- WATER INVENTORY MEA- COOLANT SUPERHEAT $

INTERVAL SURED BY SMM SURED BY HJTC PROBE MEASURED BY CET 4

4a CONSTANT CONSTANT DECREASING 4b CONSTANT INCREASING CONSTANT 4c INCREASING CONSTANT CONSTANT 4

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1. 3. 3 INSTRUMENT RANCE In the ICC instrumentation sensor package satu ation temperature and water inventory are used as indicators for the approach to and recovery f rom ICC when there is water inventory above the fuel alignment plate. These measure-ments characterize Intervals 1, 2 4b and 4c of the ICC progression.

3 When the two-phase icvel is below the fuel alignment plate, the. measurement of core exit fluid temperature represents a direct indication of the approach to, and recovery f rom ICC (Intervals 3 and 4a). Therefore, the ICC sensor package is sufficient to provide information to the reactor operator on the entire progression of an event with the potential of resulting in ICC.

1.4

SUMMARY

OF SENSOR EVALUATIONS Several sensors have been evaluated for use in an ICC Detect ton Synt em.

Significant conclusions abcut each instrument are given below.

1.4.1 Subcooled Margin Monitor A subcooled Margin Monitor (SIDI), using inputs from existing Resistance Temperature Detectors (RTD) in the hot and cold Icgs and from the pressur-izer pressure sensors, is adequate to detect the initial occurrence of saturation during LOCA events and during loss of heat sink events.

However, the usefulness of the SMM can be significantly increased by using G.e signals f rom the fluid temperature measurements from the HJTCS and the signals from selected core exit thermocouples and by modifying the SMM to calculate and display degrees superheat (up to about 1800*F) in addition to degrees subcooling. The sir,nals from the llJTCS temperature measurements provide information about possible local dif ferences, in t emperat ure between the reactor vessel upper head / upper plenum (location of the itJTCS) and the hot or cold Icgs (location of the wide range RTDs). The core exit thermo-couples respond to the coolant temperature at the core exit and their signal indicates superheat af ter the coolant level drops below the top of the core and, thus, provide an approximate indication of the depth of core uncovery.

E.31-8

B/B-FSAR S With' this implementation, the SMM can be used for detection of the approach to ICC, namely Interval 1 (loss of subcooling) Interval 3 (core uncovery),

Interval 4b (core recovery) and Interval 4c (establishment of saturation conditions). Even with the modifications, the SKM will not be capable of indicating the existence of Interval 2 when the coolant is at saturation conditions and the level is between the top of the vessel and the top of the core.

The recovery interval may occur at low system pressure and temperature.

Since the errors in the existing SMM calculations increase with lower temperature and pressure, required subcooling margins need to be revised for this situation.

1.4.2 Resistance Temperature Detectors (RTD)

The RTD are adequate for sensing the initial occurrence of saturation.

Narrow range RTD are located in the hot and cold leg manifolds and the wide range RTD are located in the hot and cold legs of the reactor coolant piping. Either of the narrow or wide range RTD are suf ficient to, sense saturation for events initiated at power. The wide range RTD are sufficient to sense saturation for events initiated f rom zero power or shutdown conditions.

The RTD range is not adequate ' row ICC indications during core uncovery.

For depressurization LOCA ,cVents, the core may uncover at low pressure, when the saturation temperature is below the lower limit of the RTD.

Initial superheat of the st'eam will therefore not be detected by the RTD.

As the uncovery proceeds., the superheated steam temperature may quickly exceed the upper limit of the RTD range. In order to be useful during the core uncovery interval, the range of RTD would have to be increased to cover a temperature range from 100*F to 1800 F.

1.4.3 Heated Junction Thermocouple System (HJTCS)

The llJTCS is being designed 'to show the liquid inventory of the mixture of liquid and vapor coolant above the core. It is an instrument which shows the approach to ICC and is the only one which functions in Interval 2, namely the period from the initial occurrence of saturation conditions until the start of core uncovery and Interval 4b, the period when inventory is increasing above the! fuel alignment plate.

1.4.4 _ Core Exit Th'ernoccuples The core exit thermoc/ouples are adequate to show the approach to ICC af ter core uncovery for the events analyzed, provided that the signal process [nn and display does not add substantial time delay to the thermal delay at

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B/B-FSAR the thermocouple junction. As mentioned above, the core exit thermo-couples respond to the coolant temperature at the core exit and indicate superheat af ter the core is no longer completely covered by coolant.

Except for a time delay, depending on event, the trend of the change in superheat corresponds to the trend of core uncovery as well as to the accompanying trend of the change in cladding temperature.

2.0 SYSTEM FUNCTIONAL DESCRIPTION In the following sections a functional description of the instruments of the ICC Detection System is given and the function of the instruments is related to the ICC intervals which were described in Section 1.0.

2.1 SUBC00 LING AND SATURATION ,

The parameters measured to detect subcooling and saturation are the RCS coolant temperature and pressure. The measurement range extends f rom the shutdown cooling conditions up to saturation conditions at the pressurizer safety valve setpoint. The response time needs to be such that the operator obtains adequate information during those events which proceed slowly enough for him to observe and to act upon the informat fon.

The information which is derived from the reactor vessel temperature and pressure measurements is the amount of subcooling during the initial approach to saturation conditions and the occurrence of saturation during Interval one. During Interval four, the reestablishment of sub-cooled conditions is obtained.

2.2 COOLANT LEVEL MEASUREMENT IN REACTOR VESSEL The Reactor Coolant System is at saturation conditions until sufficient coolant is lost to lower the two-phase level to the top of the active core. During this interval there are no existing instrumcats which would measure directly the coolant inventory loss. A Reactor Vessel I.evel Monitoring System provides a direct measurement during this period. 'th e parameter which is measured is the collapsed liquid level above the fuel alignment plate. The collapsed level represents the amount of liquid mass which is in the reactor vessel above the core. Measurement of the collapsed water level was selected in preference to measuring two-phase level, because it is a direct indication of the water inventory while the two phase level is determined by water inventory and void fraction.

The collapsed level is obtained over the same temperature and pressure range as the saturation measurements, thereby encompassing all operating and accident conditions where it must function. Also. It is intended to f unction during Interval four, the recovery interval. Therefore, it mont survive the high steam temperature which may occur during the preceding core uncovery interval.

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B/B-FSAR The level range extends from the top of the vessel down to the top of the , ,

fuel alignment plate. The response time is short enough to track the .

level during small break LOCA events. The resolution is suf ficient to I show the initial level drop, the key locations near the hot leg elevation l f

and the lowest levels just above the alignment plate. This provides the operator with adequate indication to track the progression durirg f Intervals two and four and to detect the consequences of his mitigating actions or the functionability of automatic equipment.  ;

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2. 3. FUEL CLADDING HEATUP j The overall intent of ICC detection is understood to be the detection of  :

the potential for fission product release from the reactor fuel. The  !

parameter which is most directly related to the potential for finnion product release is the cladding temperature rather than the uncovery of '

the core by coolant.

Since clad temperature is not directly measured, a paraineter to which .

cladding temperature may be related is measured. This parameter is the fluid temperature at the core exit. Af ter the core becomes uncovered, the fluid leaving the core is superheated steam and the amount of super-heat is related to the fuel length exposed and to the cladding temperature.

The amount of superheat of the. steam leaving the core will be measured by the core exit thermocouples. The time behavior of the superheat tempera-ture is, with the exception of an acceptably small time delay, similar to the time behavior of the cladding temperature. Thus, from the observation of the steam superheat, the behavior of the cladding temperature can be in ferred. Observation of the cladding temperature trends during an accident is considered to be of more value to the operator than information

- on the absolute value of the cladding temperature.

The core exit steam temperature is measured with the thermocouples located

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show that the thermocouples respond suf ficiently fast to the increasing steam temperature.

The required temperature range of the thermocouples extends f rom the lowest saturation temperature at which uncovery may occur up to the maximum core average exit temperature which occurs when the peak clad temperature reaches 2200 F. The required thermocouple range is therefore 200'F to about 1800'F, which is the approximate upper service temperature limit. Thermocouples are expected to function with reduced acci e ecy at even higher temperatures, so the range for processing the thermocouple outpu.t extends to about 2300'F.

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E.31-11

B/B-rSAR 3.0 SYSTEM DESIGN DESCRIPTION The following sensors have been selected as the basic instruments to meet the functional requirements described in section 2.

1. The subcooled margin monitor (SMM) (Reference 1)

2. The heated junction thermocouple UlJTC) system (Reference 2) and

3. The core exit thermocouple (CET) system.

The conceptual design of each ICC instrument is described in this section which addresaes:

1. Sensors design

2. Signal processing and display design Figure 3-1 is 'the functional diagram for the ICC instrument syutems. We IIJTC and CET instrument systems consist of two safety grade channels from sensors through signal processing equipment. The outputs of processing equipment systems feeding the primary display are isolated to separate safety grade and non-safety grade systems. Channelized safety grade bach-up displays are included for the two instrument systems. The SMM instrument system consists of various sensor inputs to the process computer. The generation and display of SMM is done by the process computer and is non-safety grade. The following sections present details of the design.

3.1 SENSORS DESIGN 3.1.1 Subcooled Margin Monitoring System he subcooled margin monitor design configuration being implemented is detailed in Section 3.2.4.1. The SMM includes the maximum unheated junct lon thermocouple temperatures from the top three sensors of each probe (tRITC)

(Sections 3.1.2 and 3.2.2) and the representative core exit thermocouple (CET) temperature (Sections 3.1. 3 and 3.2. 3) . The sensor inputs to the SS1M are:

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Pressurizer Pressure 1700-2 500 psig Reactor Coolant Loop Pressure (Wide Range, RC liot Legs A & C) 0-3000 pain Maximum UllJTC Temperature (f rom IlJTC, processing) 100-1800'I' Rep resenta tive CET Temper.it ure ( f rom C1'.T proce ;n t ne,) 2 00- TlnO" P E.31-12

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B/B-FSAR 3.1.2 Heated Junction Thermocouple (HJTC) Syst*cm, The HJTC system measures reactor coolant liquid inventory with discrete HJTC sensors located at dif ferent levels within a separator tube ranging f rom the top of the core to the reactor vessel head. The basic principle of system operation is the detection of a temperature dif fere nee between adjacent heated and unheated thermocouples.

As pictured in Figure 3-2, the HJTC sensor consists of r, Chromel-Alumel thermocouple near a heater (or heated junction) and another Chromel-Alumel thermocouple positioned away from the heater (or unheated junction). In a fluid with relatively good heat transfer properties, the temperature dif-ference between the adjacent thermocouples is very small. In a fluid with relatively poor heat transfer properties, the temperature dif ference between the thermorouples 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 sennorn measure. This collapsed liquid level is directly reint ed to the average liquid f raction of the fluid in the reactor head volume above the f uel alignment plate. This mode of direct in-vessel sensing reduces spurious effects due to pressure, fluid properties, and non-homogeneities of the fluid med"um. 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 IlJTC instrument is manufactured into a probe assembly. The probe assembly in-cludes 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 vessel head to the fuel alignment plate.

The probe assembly is housed in a stainless steel structure that prot ects the sensors f rom flow loads and serves as the guide path for the sensors.

Figure 3-4 describes the locations of the HJTC probe assemblies. Installa-tion arrangements have been developed for Byron /Braidwood l' nits 1 and 2.

3.1.3 Core Exit Thermocouple (CET) Systen3

• the design of the Byron /Braidwood Units 1 and 2 in-core instrumentation (ICI) system includen 65 Type K (Chromel-Alonel) thermocouples. The thermo-couples are installed into guide tubes which penetrate the reactor venel head and terminate at the exit flow end of selected fuel assemblies.

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270' HJTC HOLDER ASSEMBLY LOCATIONS REACTOR VESSEL PIJsN FIGURE 3-4 E.31-18

B/B-FSAR These core exit thermocouples (CET) monitor the temperature of the reactor coolant as it exits the fuel assemblies. The core locations of the thermo-couples are shown in Figure 3-4A.

FSAR Subsection 4.4.6.1 and Section 7.7 describe the present design of the CET system. The basic design of the CET system will not change for the final ICC detection system; however, modifications will be performed to ur-grade the CET to meet environmental qualification requirements. (See Section 5.0).

The CETs have a usable temperature range from 200*F to up to 2300'F (refererce 4) although accuracy is reduced at temperatures above 1800'F.

The signal processing and display for the CET portion of the ICC detection instrumentation is described in paragraph 3.2.4.3 below.

3.2 SIGNAL PROCESSING AND DISPLAY EQUIPMENT DESIGN The processing and display hardware depicted in Figure 3-1 includes two subsystems of hardware - a qualified, safety related subsystem of ICC inst rumentation and an unqualified, non-safety subsystem of ICC instrumen* -

tion. The equipment subsystems process and display the ICC detection sensor inputs as well as sensor inputs to meet other NRC requirements. The back-up displays for reactor icvel and core exit temperature are safety grade while the primary displays are non-safety grade. Human factors engineering reviews are applied to both types of display. The design objective for the equipment is to address the NUREC-0737, Item II.F.2.

3.2.1 Backup Displays As depicted in Figure 3-1, the backup displays for reactor level and core exit temperature are driven by a two channel system. Both the ll.ITC and CET systems use microprocessor based designs for the signal processing function '

in conjunction with main control room indication, digital and analog, respectively. Each channel will accept and process ICC input signals, and provide outputs to the channel related indicator and the plant process computer. The backup displays are designed to give information to the operator in the remote chance that the primary display becomes inoperable and to confirm primary display information. Specific display descript hans for each ICC detection instrument are included in Section 3.2.4.

3.2.2 Primary Displays The primary displays for ICC detection are generated by the plant process computer using isolated outputs f rom the llJTC and CET processor cabinet s and NSSS protection system cabinets (for pressurizer and reactor coolant loop pressures). The main control room primary displays for ICC detect ion are part of the Safety Parameter Display System (SPDS). A complete de-scription of the SPDS is included in Section E.17 for NUREC-0737, item I.D.2.

A description of specific ICC displays is included in Section 3.2.4.

E.31-19

B/B-FSAR O O O O O O O O O O O O O O O O O O O O O O

'O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O THERMOCOUPLE LOCATION CORE EXIT THERMOCOUPLES CORE LOCATIONS FIGURE 3-4A E.31-20

B/B-FSAR 3.2.3 Cabling Systems

• The in-containment cabling system for the CETs and HJTCs use environmentally qualified cabling and Class IE connectors. Qualified containment penet rat ions route the CET and HJTC signals through the containment wall to the auxiliary building.

Separation of the two CET/HJTC channels is initiated below the missile shield and mainta'ined to the signal processing equipment in accordance with the requirements of Regulatory Guide 1.75. Section 5.0 discusses the qualification testing of the cabling.

The SMM inputs are routed from the sensors to the processing equipment via existing safety grade cabling and containme1t penetrations and signal isolation hardware.

3.2.4 Processing and Display Description The following sections describe the processing and display for each of the ICC detection instruments.

3.2.4.1 Subcooled Margin Monitor The SMM functions performed by the process computer are as fo. lows:

1. Calculate the subcooled margin.

The saturation temperature is calculated from the average pressurizer pressure input (narrow range) unless the pressure is outside of the pressurizer pressure transmitters range in which case the average reactor coolant loop pressure input (wide range) is used. The saturatien pressure is calculated f rom the hottest of three temperature inputs. The three inputs include: 1) average of ten hottest core exit the rmoco upl es ,

2) hottest of the top three sensors of HJTC probe-Channel A, 3) hottest of the top three sensors of HJTC probe-Channel B. The temperature sub-cooled margin is the dif ference between the saturation temperature and the hottest temperature input noted above. The pressure subcooled margin is the difference between saturation pressure and the average pressure input.

2. Process all outputs for display.

The SMM processes the temperature and pressure inputs over the following ranges: CET temperatures from 200 to 2300"F, the unheated HJTC temperaturen f rom 100 to 1800 F, the pressurizer pressures from 1700 to 2500 psig and reactor coolant loop pressure from 0 to 3000 psig. The sa turation temp-erature and pressure are calculated f rom a saturation curve and an interpolation routine.

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B/B-FSAR The following information is presented on the primary display:

1. Pressure margin to saturation

2. Temperature margin to saturation

3. Trends of pressure or tem.crature margin to saturation i

Additional information regarding the primary display, safety parameter display system (SPDS) is included in Section E.17.

Backup displays are not provided for the SR't.

3.2.4.2 Heated Junction Thermocouples - Renetor 1.evel The processing equipment for the HJTC performs the following functions:

1. Determine if liquid inventory exists at the llJTC positions.

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 3-5. When water surrounds the thermocouples, their temperature and voltage output are approximatelv eq ual . V(A-C) n Figure 3-5 is, therefore, approximately zero. In the absence of liquid, the thermocouple temperatures and output voltages become unequal, causing V(A-C) t rise. When V(A-C) of the individual IIJTC rises above predetermined setpoint, liquid inventory does not exist at this HJTC position.

2. Determine the maximum 'spper plenum / head fluid temperature from the top three unheated thermocouples for use and a process computer input for the SMM. (The temperature processing range is f rom 100*F to 1800*F.) This output is an isolated signal.

3. Process all inputs and calculated outputs for display.

4. Provide an alarm output to the plant annunciator system when any of the IIJTC detects the absence of liquid level.

5. Provide control of heater power for proper HJTC output signal level.

Figure 3-6 shows a single channel design which includes the heater power controller.

6. Provide an input to the process computer for % liquid inventory level above the fuel alignment plate. This output is an isolated signal.

The following information is presented on the primary display:

1. Liquid level inventory above the fuel alignment plate.

2. Trends of liquid level inventory. l E . 3 L-2 2

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ALUMEL A

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ELECTRICAL DI AGRAM OF H.J.T.C.

FIGURE 3 5 r

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,5f NSOR I - PRIMARY O! SPLAY

. K R P,UtiH SIGNAL PROCESSOR SEA 3UR a LOGIC AND CHANNEL BACKilP C =

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POWER F0WEA CCNTROL UlGNAL o 4, HEAT POWER CONTROLLER'

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POWER TO

I HEATERS 6

i ll HJTC SYSTEM PROCESSING CONF!GURATION (ONE CHANNEL SHOWN)

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B/B-FSAR Additional information regarding the primary display, safety parameter display syst em (SPDS) is included in Section E.17.

The following information is presented on the backup llJTC display:

1.  % liquid inventory level above the fuel alignment plate derived f rom the eight discrete IIJTC positions.

2. Unheated junction temperature at eight positions.

3. Heated junction tenperature at eight positons.

3.2.4.3 Core Exit Thermocouple System The processing equipment for the CET will perform the following functions:

1. Process all core exit thermocouple inputs. Processing of 33 CET inputs will be performed by Channel A and 32 CET inputs by Channel B.

2. Provide sixteen thermocouple (4 per quadrant) outputs, per channel, to the backup displays.

3. Provide data link outputs to the process computer for all 65 therno-couple inputs. These outputs are isolated signals.

These f unctions are intended to meet the design requirements of NUREC-0737, II.F.2 Attachment 1.

The following information is represented on the primary display.

1. A spacially oriented core map indicating the temperature at each of the CET locations.

2. A core exit temperature representative of the CET inputs.

3. Trends of core exit temperature.

Additional information regarding the primary display, safety pararacter display system (SPDS) can be found in Section E.17.

The f ollowing information is availabic on the backup displays:

1. Selectabic temperatures of 16 core exit thermocouples for each of the Channels A & B.

4.0 SYSTEM VERIFICATION TESTING This section describes tests and operational experience with ICC instrument: .

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B/B-FSAR 4.1 PRESSURE SENSORS The hot and cold leg wide range pressure and the pressurizer pressure sensors are standard NSSS instruments which have well.known resiennes.

No special verification tests have been performed nor are planned for the future. These sensors provide basic, pressure inputs which are considered adequate for use in the SMM and other additional display functions.

4.2 HJTC SYSTEM SENSORS AND PROCESSING The HJTC System is a new system developed to indicate liquid inventury above the core. Since it is a new system, extensive testing has been performed and further tests are planned to assure that the llJTC Synten will operate to unambiguously indicate liquid inventory above the core.

The testing is divided into three phases:

Phase 1 - Proof of Principle Testing (Reference 6)

Phase 2 - Design Development Testing (Reference 7)

Phase 3 - Prototype Testing The first phase consisted of a series of five tests, which have been completed. The testing demonstrated the capability of the llJTC instrument design to measure liquid 1cvel in simulated reactor vessel thermal-hydraulic conditions (including accident conditions).

Test I Autoclave test to show HJTC (thermocouples only) response to water or steam.

In April 1980, a conceptual test was performed with two thernocouples in one sheath with one thermocouple as a heater and the other thernocouple as the inventory sensor. This configuration was placed In an autoclave (pressure vessel with the capabilities to adjust temperature and prennure).

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

, Test 2 Two phase flow test to show bare IIJTC sensitivity to voids.

In June 1980, a HJTC (of the present dif ferential thermocouple design) j was placed into the Advanced Instrun:entation for Reflood Studies (All:S) 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 llJTC output was virtually the same in two phase liquid as in subcooled liquid. The HJTC did generate a significant output in 100% quality l steam.

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,7est 3 Atmospheric air-water test to show the effect of a splush shield A splash shield vac designed to increase the sensitivity to voids. The splash shield prevents direct contact with the liquid in the two phase fluid. The llJTC output changed at internediate void fraction two phaw fluid. The results demonstrated that the HJTC sensor (heated junction thermocouple with the splash shicid) sensed intermediate void fraction fluid conditions.

Test 4 liigh pressure boil-off test to show IlJTC sensor response to reactor thermal-hydraulic conditions In September 1980, a C-E !!JTC sensor (l!JTC with splash shield) was installed and tested at the ORNL Thermal-llydraulics Test Facility (TllTF).

The !!JTC sensor was subjected to various two phase fluid conditions at reactor temperatures and pressures. The results verified that the llJTC sensor is a device that can sense liquid inventory under normal and accident reactor vessel high pressure and temperature two phase condi-tions.

Test 5 Atmospheric air-water tes t to show the effect of a separator tubc A separator tube was added to the llJTC design to form a collapsed liquid Icvel so that the HJTC sensor directly measures liquid inventory under all simulated two phase conditions. In October, 1980, atmospheric air-water tes ts were performed with IlJTC sensor and the separator tube. The results demonstrated that the separator tube did form a collapsed liquid level and the llJTC output did accurately indicate liquid inventory.

This tes t verified diat the llJTC ins trument, which includes the llJTC, the splash shield, and the separator tube, is a viable measuring device for liquid inventory.

The Phase 2 test program consisted of a series of steady state and transient tests under single phase and two phase fluid conditions with an liJTC probe assembly. Fluid conditions that the probe might be opposed to were simulated.

The Phase 2 tests verified that the !!JTC probe assembly is capabic of m< asuring water inventory in a reactor vessel.

The Phase 3 test program will consist of high temperature and pressure testing of the manufactured prototype system !!JTC probe assembly and processing electronics. Verification of the llJTC system prototype will be the goal of this tes t program. The Phase 3 test report will he published in 1982.

4.3 CORE EXIT THERMOCOUPLES

, i No verification testing of the CETs is planned. A study at ORNL was performed to tes t the response of CETs under simulated accident conditions (Re ference 4). This test showed that the instruments remained functional up to 2300*F. This test along with previous reactor operating experience verifies the response of CETs.

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B/B-FSAR 5.0 SYSTEM QUALIFICATION The qualification program for the ICC detection system instrumentation has not been completely defined. However, plans are being developed based on the following categories of ICC 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.

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

The in-vessel sensors will meet the NUREC-0737, Appendix B guide to install the best equipment available consistent with qualification and schedular reqairements. Design of the equipment will be consistent with the guidelines of Appendix B as well as the clarification and Attachment I to Item II.F.2 in NUREG-0737. Specifically, instrumentation will he designed such that they meet appropriate stress criteria when subjected to normal and design basis accident loadings. Seismic qualification to safe shutdown conditions will verify function af ter being sub jected to the scismic loadings.

The out-of-vessel instrumentation system, up to and including the primary display isolator, and the backup displays will be environmentally quallfled in accordance with IEEE-323-1974. Plant-specific containment temperature and pressure design profiles will be used where appropriate in these tests. This equipment will also be scismically qualified according to IEEE-STD-344-19 7 5. CEN-99(S), " Seismic Qualification of NSSS Supplied Instrumentation Equipment, Combustion Engineering, Inc." (August 1978) describes the methods used to meet the criteria of this document for the heated junction thermocouple system.

Consistent with Appendix B of NUREG-0737, the out-of-vessel equipment under procurement is the best availabic equipment and will be qu.111rled to meet the requirements of NUREG-0588.

The primary display will not be designed as a Class IE systen, but will be designed for high reliability; thus it will not be quall fled environ-mentally or seismically to Class IE requirements nor will it meet the single failure criteria of Appendix B. Item 2. Post-accident maintenance accessibility will be included in the design. The quality assurance provisions of Appendix B, Item 5 do not apply to the primary display according to NUREC-0737, llowever , the computer driven primary display system will be separated from the Class IE sensors, processing and back-up display equipment by means of isolation devices which will be qualified to Class IE criteria.

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• B/B-TSAR Verification and Validation of the SPDS sof tware for the primary ICC display will be performed. Additional information regarding the SPDS can be found in Section E.17. ,

6.0 OPERATING INSTRUCTIONS Plant specific emergeacy operating procedures for use of the information from the ICC instrumentation system will be developed taking into account recommendations f rom the C-E generic procedures and f rom the West inghouse Owners Group Ceneric Procedures. The Byron /Braidwood operator training program will be modified to include material associated with the use of the ICC Instrumentation system.

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. I, b/B-FSAR REFERENCES

1. NUREC-0737, " Clarification of 1M1 Actio$ Plan Requirements," U.S.

Nuclear Regulatory Commission, Novemb.er,' 1980. )

. 2. CEN-117, " Inadequate Core Ccoling - A Response to NRC I E Bulletin 79-06C, Item 5 for Combustion Enginc'cring Nuclear Steam Supply Systems," Combustion Engineering, October,19

- .i 79.

3. CEN-125, " Input for Response to NRC Lessons Learned Requirements for Combustion Engineering Nuclear Steam '

Supply Systems," Combustion Engineering, December,1979. x

4. Anderson, R. L. , Banda, L. A. , Cain.' D. C. , "Incore Thermocouple Performance Undet Simulated Accident Conditions," IEEE Nuclear Science Symposium, V't. 28, No. 1 Page 773, Figure 81.

5. CEN-185, " Documentation of Inadequate Core Cooling Instrumentation for Combustion Engineering Nuclear Steam Supply Systems," Combustion Engineering, September,1981.

6. CEN-185, Sup.1, "HJTC Phase 1 Test Report," Combustion Engineering, Nov ember, 1981.

7. CEN-185P, Sup. 2-P, "HJTC Phase 2 Test Report," Combustion Engineering, November, 1981.

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