0 f

.

O

.

INADEQUATE CORE COOLING DETECTION SYSTEM

SUMMARY STATUS REPORT

.

1

December, 1930

.- * *'uo 39H . -.

, .

.

TABLE OF CONTENTS

Section Title Page

1.0 INTRODUCTION 1-1

1.1 Summary of Activities 1-1

1.2 Definition of ICC 17

1.3 Description of Event Progression 1-31.4 Summary of Sensor Evaluations 1-3

2.0 SYSTEM FUNCTIONAL DESCRIPTION 2-12.1 Subcooling and Saturation 2-1

2.2 Coolant Level Measurement in ReactorVessel 2-1

2.3 Fuel Cladding Heatup 2-23.0 SYSTEM CONCEPTUAL DESIGN DESCRIPTION 3-1

3.1 Sensors Design 3-1

3.2 Signal Processing Equipment Design 3-43.3 Display Design 3-7

4.0 SYSTEM VERIFICATION TESTING 4-14.1 RTD and Press 0rizer Pressure Sensors 4-1

4.2 HJTC System Sensors and Processing 4-1

4.3 Core Exit Thermocouples 4-44.4 Processing and Displays 4-4

5.0 SYSTEM QUALIFICATION 5-16.0 OPERATING INSTRUCTIONS 6-1 -

_ - _ _ _ _ - _ _ _ _ - _ _ _ _ _ _ _____

. o

.

1.0 INTRODUCTION

1.1 Sul+1ARY OF ACTIVITIES

This rem.rt responds to the requirements in Section II.F.2 of NUREG-0737 (Ref.1).The report describes the status of desier and development activities being conductedby the C-E Owners Group to define a system of instrumentation to be used to de-tect inadequate core cooling (ICC). The report also provides information specificto the Palisades Plant in order to demonstrate the applicability of the genericactivity to the Palisades Plant.

Results of initial studies by the C-E Owners Group are documented in reports CEN-ll7

(Ref. 2) and CEN-125 (Ref. 3). These results were referenced in a letter fromConsumers Power Company dated 12/27/79. All studies have been based on the require-

ment to indicate the approach to, the existence of and the recovery from ICC.

A three step process is being used to define the ICC Detection System. Fi rs t ,

a definition for the state of ICC has been selected. Second, typical accidentevents which progress toward the defined state of ICC have been analyzed. Third,instruments which indicate the progression of these events have been selectedand evaluated.

Based on initial evaluations of a variety of instruments, an ICC Detection Systemhas been defined. This system is judged to be technically sufficient for ICCdetection. However, this system is not uniquely necessary, and functions of itsvarious ccmponents may be perfonned by alternative components. This system isdescribed in Section 3. Further developments are necessary before the systemcan be implemented and these are planned as described throughout this report.

1.2 DEFINITION OF ICC

| The definition of ICC and the functional requirements for the ICC DetectionSystem have been established within the bounds of the following core conditions:

1-1

-. . -- - -

i .

.

1. The reactor is tripped so only decay power is considered.

2. The coolant level falls below the top of the core, which can occuronly with a loss of coolant mass from the Reactor Coolant System (RCS).

3. The event proceeds slowly enough so that the operator has time to observeand to make use of the instrument displays.

These conditions provide the boundaries for a range of sizes of small breakloss of coolant accident (LOCA) caused by either RCS ruptures or primaryco.lant expansion.

The following definitions of ICC have been considered:

1. First occurrence of saturation.

2. Core uncovery.

.

3. Fuel clad temperature of 9000F (below which return to normal operation maybe permissible).

4. Fuel clad temperature of 11000F (below t?.i h clad rupture in not expectedt

to occur).

5. Fuel clad temperature of 22000F (which is the licensing limit for designbasis events using approved analytical models).

It has been concluced that the events can progress too rapidly for the instrumen-tation to reliably display the approach of ICC if one of the first four defini-tions is used. Therefore, it is concluded that definition 5, a fuel clad

0temperature of 2200 F, should be selected as the criterion for existence of ICC.

1-2

- _ -_. . _ - - , __ __. , . . _

. .

.

1.3 DESCRIPTION OF EVENT PROGRESSION

A typical small break LOCA illusf. rates the progression of an event which causesthe approach to ICC. Figure 1-1 shows a representative behavior for the twophase mixture level and the RCS pressure vs. time for the event. The eventprogression is divided into four intervals which are shown in Figure 1-1 andare defined in Table 1-1.

1.4 SUMMARY OF SENSOR EVALUATIONS

Several sensors have been evaluated for use in an ICC Detection System. Theinstruments considered are listed in Table 1-2, where their capabilities aresunnarized. Significant conclusions about each instrument are given below.

1.4.1 Subcooled Margin Monitor

The Subcooled Margin Monitor (SMM), using input from existing ResistanceTemperature Detectors (RTO) in the hot and cold legs and from.the press"rizerpressure sensors, is adequate to detect the initial occurrence of saturation

during LOCA events and Juring loss of heat sink events.

The usefulness of the SMM can be significantly increased by also feeding intoit the signals from the fluid temperature measurements from the Reactor VesselLevel Monitoring System (RVLMS) and the signals from selected core exit thermo-

,

! couples and by modifying the SMM to calculate and display degrees superheat(up to about 18000F) in addition to degrees subcooling. The signals from the

,

|.

RVLMS temperature measurements provide information about possible local

differences in temperature between the reactor vessel upper head / upper;

plenum (location of the RVLMS) and the hot or cold legs (location of the

RTDs). The core erit thermocouples respond to the coolant temperature atI the core exit and their signal indicates superheat af ter the coolant level

drops below the top of the core and, thus, provide un approximate indicationof the depth of core uncovery.

i 1-3

- . - . -. - - .. - . _ - . . . ... - . .. --.-. .. - . . - .

.. .

t

!. .

.

With these modifications, che SMM can be used for detection. of the approachto ICC, namely Interval *. (loss of subcooling), Interval 3 (core uncove y)and Interval 4 (core recovery). Even with the modifications, the SMM will

not be capable of indicating the existence of Interval 2 when tne coolantis at saturation conditions and the level is between the top of the vesseldnd 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 lowertemperature and pressure, required subcooling margins need to be revisedfor this situation.

l 4.2 Resistance Temcerature Dete'ctors (RTD)

The RTD are adequate for sensing the initial occurrence of .s_aturation. Thehot leg RTD range is sufficient to sense saturation for events initiatedat power. The cold leg RTD, which have a wider' range, are sufficient tosense saturation for events initiated from zero power or shutdown conditions.

The, RTD range is not adequate for ICC indications during core uncovery. For

cepressurization LOCA events, the core may uncover at low pressure, when the~

saturation temperature is below the lower limit of the hot leg RTD. Ini tialsuperheat of the steam will therefore not be detected'by the hot leg RTD. Asthe uncovery proceeds, the superheated steam temperature aay quickly exceedthe upper limit of the RTD range. In order to be useful during the coreuncovery interval, the range of RTD would need to be increased to cover a

U Utemperature range from 100 F to 1800 F.

1.4.3 Reactor Vessel Level Monitoring . System

The Reactor Vessel Level Monitoring System (RVLMS) is being designed to showthe liquid inventory of the mixture of liquid and vapor coolant above thecore. It is an instrument which shows the approach to ICC and is the onlyone which functirns in Intervai 2, namely the period from the initial occurrenceof saturation conditions until the start of core uncovery.

1-4

_.. -. . . - . - . . . - .

(a f

.

1.4.4 Core Exit Thermoccuoles

The core exit thermocouples are adequate to show the approach to ICC after coreuncovery for the events analyzed provided that the signal processing and displaydoes not add substantial time delay to the thermal delay at the thermocouple:

junction. As mentioned above, the core exit thermocouples respond to thecoolant temperature at the core exit and indicate superneat after the core isno longer completely covered by coolant. Except for a time delay of about200 to 400 sec, depending on event, the trend of the change in superheatcorrespcnds to the trend of ctre uncovery as well as to the accompanying trendof the change in cladding temperature,

1.4.5 Self Powered Neutron Detectors (SPND).

The SPND yield a signal caused by high temperature as the two-phase levelfalls below the elevation of 'he SPND. However, testing is required toidentify the phenomena responsible for the anomalous behavior of the SPNDat TMI-2. At the present, their use is limited to low temperature events

(less than 1000*F clad temperature) or to only the initial uncovery portionof an event.

1.4.6 Ex-Core Neutron Detectors

Existing source range neutron detectors are sensitive enough to respond tothe formation of coolant voids within the vessel during the events analyzed.However, the signal magnitude is ambiguous because of the effects of varyingboron concentration and deuterium concentration in the reactor coolant.

A stack of ex-core detectors gives less ambiguous information on voids andlevel in the vessel. The relative shape of the axial distribution of signals

,

from a stack of five detectors shows promise as an ICC indicator, but additionaldevelopment would be needed.

1-5

-- - . . . - . .. . .- - - . . - _ - .- -

__ . _ _ _ _ _ _ _ _ _ _ . . . . _ _ _ _ . _

. .

.

1.4.7 in-Core Thermccoucles'

It appears in general feasible that in-core thermoco_ les could be added to or sub-stituted for some SPND in the in-core instrument string. They would respond more

quickiy to gore uncovery than the core-exit thermocouples. Also, due to thermalradiation from the fuel rods they see temperatures closer to the cladding tem-peratures than to the steam temperature seen by the core exit thermocouples.

'

For top mounted in-core instrumentation, the core exit thermocouples may survivelonger for deep uncovery events because the thermocouples and their leads seeonly core exit steam temperature which is less than the fuel clad temperature.For bottem mounted in-core instrumentation, those in-core thermocouples which

1e located below the two-phase level will survive longer than the core exitr.hermoccupies because the core exit thermocouple leads past''down through thehigh temperature region during core uncovery.

Using a synthesis approach, sim.ilar to the one described for core exit thermo-

| couples, it is expected that the in-core thermocouple temperature can be related

more directly to the adjatant fuel clad temperature than is possible with a syn-thesis which uses core-exit thermocouples. However, additional work would be

( required to study the temperature response of in-core thermocouples as well asto develop the mechanical design for incorporating the thermocouples into thein-core instrument string and to develop a synthesis method for calculatingfuel cladding temperatures.

||

l-6

__ _ _ __ _ ___ _ _ _ _ . _ _ _ . _ _ ~ _ . ,

_ _ . _

.

.

Table 1-1.

Definition of Intecvals in ICC Event progression

Interval No. ICC phase Bounding parameter Description

-1

; 1 Approach to Reduction in RCS subcooling Depressurization of RCS to satura-untii saturation occurs. tion pressure at hot leg temperature

or heatup to saturation temperature'

j at safety valve pressure.!

|

2 Approach to Falling two phase mixture level in Net loss of coolant mass from RCS

upper plenum, down to top of active accompanied by boiling from continuedfuel. depressurization and/or decay power.

,

1 3 Approach to Two phase level falls from top Two phase level drops in core causingand/or of active fuel until mininom clad heatup and producing superheatedExistence of level during event progression steam at core exit.

occurs or until 2200"F clad: tanperature occurs.

,

4

4 Recovery from Two phase level rises above top Coolant addition by ECCS raises levelof core. and quenches fuel. ICC progression

'

is defined to tenninate when vesselis full or when stable, controllable

'

conditions exist.

&

4

e

*be. w t.J had had b.J@ esu O' ** > 2 w > O V W 3 2w> Ew> E5 *2 ==| a y c as w I = w %.4 = 3 6 =3 *=.|=. 3Z- O

i u .,

$ $wa <*w $ - =>%D w < w wCi,C,e= =

8 g w -> - > C-> -

3 o >

a u ~1 :,.=

w c. -C

_ -A 3y,

5 .>a;& ^ C E@C 3^Cu 5C 3 A 3

- .,,,*

r.,. - w :-w -wLa- n s,,e = w * n ad :Hd NO y l' -

E.,a E w = E w

- J. 5 <ws <ws E w =.4-- E a a <

m E .s==

,g '-E

- x.G= < - ac

=m= <g M - GE

eT, e tad 3 ==8

w w z eav- ar =-I = -a_ - X -

- -s M5

- -

*** -g * 5< < <4 < 5 4 E 5=*D 3 D 6 D w w b : % Cww === ='

n- = w w r T w g

,E - - g == x d .e== =

- =-= === zo== M -

Q w .J C s,adW *= san m ==g. 3 med 4 % .4 ed sed == 3 *

E C3 a > 3 ned C 3m O3 M

2 end was 6.d as d had had an == d- M ==

C.)# 4ml 2 .ms b O w 3 .s s M ==

2 3 a= g E s== .ms 3 @- w== M * * had end W - >= hmA AE6 h.d

-* mwo a=5= n#9 G *= Z w M ma'm Qg O wtC - =2 *= wg> z o -

ca- z - E e == c g I cc - cC w-O w, .ns ' M *C and 6 - - .ms 2M 2.-

C E > > z3 32- .e =o H m. > %Eu %==y =

C O == .a -. Z -- 3 - < OC =-E w.d CO3 c2 cc =i.* O-E w CE = w w a - * y 6,

= 3.s =3= g #, wt,g >=a2=* == n= e'. eC > 2 O eC 2.

- 33=1>. w= *=d.adm. y.z 3 E =.d= 2Aw s.4 z > E = - - <e s~ m

- - .,w <<= < -5 mw - -C v.h. E>=>= . e s = .C <

== .C Z ".m .s < . == 3 3 .e.-

;,,8= g aC O w=.QaC g w .g .a g =2

8= *-2E n -eGm.A

.d *Cs .x,. :.= =3 2 ==2.d == m. =.e s. 'wa=5 W=2

g A .e.- = * * - 3 w ed b.JZ. c=oi w e o E O2<sa

aC eQ

- -% < m

eC C == d =, aC - - == aC== } Q ==3.,==~==3=, * J cc a= w w w =d ew

= aC 3 - = w .J w e.,d 4 .

p,h D =E. w z _2 .g w= =.www (we m,

@whC, We.-. a.d d m. 2 .>a - g8 c.-C. z- - - s

-- C|E .,e 3 O e == w ==aC .13 ., == aC 3 == *Ew i.d . .-

3 == w 2 .w fa.E.=' E" '5' C.s

==wZ EIQ*=

"c"i d.== *N *".e= "N"** ==

== had a== *==*C . = . , n,.== = = = =

3 e == c == N.s >=*C @2*ned , EN C -J y w'

8 Z .= z* == nmJ had snJ= == i,p.= < b 8= C

== aC 3 3 O y w,,,,

Q ==W w = w w -| w w - = w wJ = -j w-<, - w=

2.s Q *C w == 6 a3 w w knJ ee 6==g 33

== E3 C CM -

.4 Je

,,e=A g g,

.J8= .

I dI f f I < %w E,

Ib E w w'"E v v v 5

w -

Ea, s s a--

e.S whan 6,

y - -z.,o

z =- 6/1 =e n=- O a

5 .=.2e 5 .m.

cr wz - w - - - ..c: ac ,w e we e e vi w-- m -aum -= a == == == Z.

5 a=C== w M M C3e

=M M M5% w we w w w ww

..-

Y

E5 -0= (m) dHE%

- w w-*EE an. g

.b MO M one.d.

====

3 e.d r - ,,,,,w wa-

.a .

ha8 =d C 2me d'g ya

un a=Da $g 2 y

$ t.E a -z - w -

-E< w==5=8 W3

.uI @_ a ,- = m -

*I M 3 EO.d

- 6ad == *3

5 3 5 5 Y E ."1O 3 %J 3=g X t#9 *'= w

*= .

a 5 =w -.=s'' w ct H w

5 .

U s.d + .,dy- ad

8 *,-.

K C- g- -

6s . 5wa

* .d == e *w<ww w a w

G <5"'''

a

x g .M., .5 moa wo a w - e w-

1-8

_ .-_ _ _ _ _ - - ._ _ _ _ _ ._- . _ . . . _ _ _ _ _ . . -

_.

_

, .

.

INTERVAL NLitSSR

2 _ 3 'r a r ----" -1- :

-- - ~'36- 2400

[) .

1600/

\/ \2000-

30 -

1400_

| \! k

- 160024 '"

=-

e i N / \ e_~: =.

1 00 g/ TCP OF CORE

-

!1.

' t-2 \ ?

r 1200 < E"-

E IS --

(- 5~

- :-E / 1000 gE _ HOTROD -

f PEAK CLAD TEMP yI \--

\[ 800-

12 --

/ \if k BO ROM 0F CORE - S02

I __ i

| / w if -

400-

6 .

'

-

(,_,,,_CO RE

,

EXIT TE!!P'/ - 600

V \\, . _ _ _-

I I I \ I J 0_

0

0 800 1600 2400 3200 4000

TI!E AFTER BREAK, SECONDS

|

FIGURE l-1

DEFINITION OF INTERVALS IN EVENT PROGRESSION

.-. . . _ . .-_ . _ _ . - _ - . - - - - . -

|. .

|

.

2.0 SYSTEM FUNCTIONAL DESCRIpTICN

In the following sections a functional description of the instruments of theICC Detection Sys. tem is given and the function of the instruments is related to theICC intervals which were described in Section 1.0.

2.1 SUSC00 LING AND SATURATION

The parameters measured to detect subcooling and saturation are the RCS coolanttemperature and the pressurizer pressure. Temperature is measured in the hotlegs for typical LOCA type events and is measured in the vessel upper head regionfor cooldown events. The measurement range extends from the shutdown coolingconditions up to saturation conditions at the pressurizer safety valve setpoint.The response time needs to be such that the operator obtains adequate informationduring those events which proceed slowly enough for him to observe and to actupon the information from the instrument display. Plant specific analyses forPalisades may need to be performed for a selection of small break LOCA events in

order to establish the required response times. Generic analyses done to dateshow that existing or planned instruments have adequate range and response.

The information whicn is derived from the reactor vessel temperature and pressuremeasurements is the amount of subccoling during the initial approach to saturationconditions and the occurrence of saturation during Interval 1. During Interval 4,the reestablishment of subcooled conditions is obtained.

2.2 COOLANT LEVEL MEASUREMENT IN REACTOR VESSEL

The Reactor Coolant System is at saturation conditions until sufficientcoolant is lost to lower the two-phase level to the top of the active core.During tnis interval there are no existing instruments which would measure

A Reactor Vessel Le' el Monitc.ing System provides adirectly the coolant inventory loss. v

direct measurement during this period. The parameter which is measured is thecollapsed liquid level above the fuel alignment plate. The collapsed levelrepresents the amount of liquid mass which is in the reactor vessel above thecore. Measurement of the collapsed water level was selected in pr eference to

2-1

-. _ _. _ . . - . . ._- - -. - _ _ _ . - - . .

. .

.

measuring two-phase level, because it is a direct indication of the water inventorywnile the two/ phase level is determined by water inventory and void fraction.

The collapsed level is obtained over the t'me temperature and pretsure range asthe saturation measurements, thereby encompassing all operating and accidentconditions where it must function. Also, it is intended to function duringInterval 4, the recovery interval. Therefore it must survive the high steamtemperature which may occur during the preceeding core uncovery interval.

The level range extends frem the top of the vessel down to the top of the fuelalignment plate. The response time is short enough to track the level duringsmall break LOCA event 3. The resolution is sufficient to show the initial' leveldrop, the key locations near the hot leg elevation and the lowest levels justabove the alignment plate. This provides the operator with adequate indicationto track the progression during Intervals 2 and 4 and to detect the consequencesof his mitigating actions or the functionability of autcmatic equipment.

2.3 FUEL CLADDING HEATUP

The overall intent of ICC detection is understood to be the detection of thepotential for fission product release from the reactor fuel. The parameter

wnich is most directly related to the potential for fission product release is thecladding temperature rather than the uncovery of the core by coolant.

Since clad temperature is not directly measured, a parameter to which claddingtemperature may be related is measured. This parameter is the fluid temperatureat the core exit. After the core becomes uncovered; the fluid leaving the coreis superheated steam and the amount of superheat is related to the fuel lengthexposed and to the cladding temperature.

The amount of superheat of the steam leaving the core will be measured by thel core exit thermocouples. The time behavior of the superheat temperature is, with

the exception of an acceptably small time delay, similar to the time -

|

2-2

,_ ~ - _ - . _ _ . . . - - _ _ _ - , , - _ _ . - - - - . _ . , _ _ - . , _ - - _-. ~ . - - _ - _ - _ . . , - _ - ---

. .

.

behavior of the cladding temperature. Thus, from the observaticn of the steam

superheat, the behavior of the cladding temperature can be inferred. Observationof the cladding temperature trends during an accident is considered to be ofmore value to the operator than information en the absolute value of the claddingtemperature.

The core exit steam temperature is measured with the thereccouples included inthe In-Core Instrument (ICI) string. They are located inside the ICI supporttube, at an elevation a few inches above the fuel alignment plate. Generic

calculations of a similar installation for representative uncovery events show-hat the thermocouples respond sufficiently fast to the increasing steam tem-perature. Plant specific calculations on the Palisades configuration may needto be made to verify this response.

The required temperature range of the thermocouples extends from the lowest satura-tion 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 accuracy at even higher temperatures, 7 the range for

0processing the thermocouple output extends to about 2300 F.|

|1

|

|

!!

. .

.

2-3

-_ __ - _ , - - . _ _ _ - __ . - _ - . , ,

. .

.

3.0 SYSTEM CONCEPTUAL DESIGN DESCRIPTION

The following sensors have been selected as the basic instruments to meet thefunctional requirements described in Section 2. '

1. the Subcooled Margin Monitor (Sit) (Ref.1),2. the Heated Junction Thermocouple (HJTC) System (Ref. 3), and3. the Core Exit Thermocouple (CET) System.

The conceptual design of each ICC instrument is described in this sectionwhich addresses:

,

1. sensors design

2. signal processing desige3. display design.

Figure 3-1 is a functional block diagram for the ICC instrument systems. Eachinstrument system consists of two safety grade channels from sensors throughsignal processing equipment. The outputs of processing equipment systems feedingthe primary display are isolated to separate safety grade and non-safety gradesystems. Channelized safety grade backup displays are included for eachinstrument system. The following sections present details of the conceptualdesign.

!

3.1. SENSORS DESIGN

3.1.1 Subcooled Margin Monitoring System

The subcooled margin monitor requires reactor coolant system temperature andpressure inputs to determine saturation margin. Each of the two SMM channelsare expected to use the following sensors:

1. two cold leg resistance temperature detectors (RTDs)

| 2. one hot let RTD3. one pressurizer instrument

|

3-1

|

- - -- _ . . ..

i. .

.

4. one HJTC System thermocouple (maximun HJTC System unheated jur:ction

temperature from one channel)

5. one core exit thermocouple (maximum CET temperature of one channel)

The RTDs are the wide range element of a dual RTD design. The RTDs are locatedwithin wells which protrude through the pipe wall into the coolant flow.The RTD output is connected to a transmitter located outside containment. The

0RTD temperature range is from 100 F to 7000F.

The pressurizer pressure sensors are of a force balance design obtaining thepres;ure input from taps on the pressurizer in the steam volume. The sensorand transmitter functions are perfomed in one piece of squipment locatedinside containment. The pressure range is from 0 psia to 2500 psia. Thesesensors also provide the process inputs for the Reactor Protection System lowpressurizer pressure trip.

3.1.2 Heated Junction Therinocouole (HJTC) System

The HJTC System measures reactor coolant liquid inventory with discrete HJTC~

sensors located at differcat levels within a separator tube ranging from thetop of the core to the reactor vessel head. The basic principle of systemoperation is the detection of a temperature difference between adjacent heatedand unheated thermocouples.

|As pictured in Figure 3-2, the HJTC sensor consists of a Chromel-Alumelthermoccuple ne.ar a heater (or heated junction) and another Chromel-Alumelthermocouple positioned away from the heater' (or unheated junction). In a fluid

with relatively g000 imat transfer properties, the temperature differencebetween the adjacent thermocouples is very small. In a fluid with relatively

poor heat transfer properti.es, the temperature difference between the themocouplesis large.

Two design features ensure proper operation under all themal-hydraulic conditions.First, each HJTC is shielded to avoid overcooling due to direct water contactduring two phase fluid conditions. The HJTC with the splash shield is referred

3-2, _

!

. .

.

to as the HJTC sensor (See Figure 3-2). Second, a string ofHJTC sensors is enclosed in a tube that separates the liquidand gas phases that surround it.

The separator tube creates a collapsed liquid level that theHJTC sensors measure. This collapsed liquid level is directlyi

related to the average liquid fraction of the fluid in thereactor head volume above the fuel alignment plate. Thismode of direct in-vessel sensing reduces spurious effectsdue to pressure, fluid properties, and non-homogeneities ofthe fluid medium. The string of HJTC sensors' and the separatortube is referred to as the HJTC instrument.

.

The HJTC System is composed of two channels of HJTC instru-

ments. Each HJTC instrument is manufactured into a probeassembly. The probe assembly includes eight (8)-NJTC 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 thatprotects the sensors from flow loads and serves as the guide pathfor the sensors. Installation arrangements have been developedfor each C-E reactor vessel including Palisades. Installation detailswill be provided in future documentation if Consumers Power Companydecides to install the HJTC System.

3.1.3 Core Exit Thermocouples (CET) System

~

The Palisades Plant reactor contains 45 thermocouples that aretop mounted and placed above the fuel assemblies above the fuelalignment plate. Figure 3-4 shows the CET locations. Thethermocouples are Type K (Chromel-Alumel) and are connected inthe same Incore Instrumentation (ICI) cabling as the fixed incoreneutron detectors. The thermocouples monitor the temperature

3-3

. - .

. .

of the reactor coolant as it exits the fuel assemblies.The junction of each themocouple is located above thefuel assembly inside a structure which supports and shieldsthe instrument string from flow forces in the outlet plenumregion.

,

The basic design of the CETs will not change for the ICCDetection System. However, design modifications must be madeto meet the qualification requirements (See Section 5.0).The CETs have a maximum usable temperature range from

01000F to approximately 1800 F (Reference 6).'

3.2 SIGNAL PROCESSING EQUIPMENT DESIGN

The processing equipment of the ICC instruments is presentlybeing developed. The processing equipment portion will be composedof a combination of new and existing equipment. The design objectivefor the equipment is to address ~the NUREG-0737 criteria, including thecriteria of Attachment 1 to II.F.2 and Appendix A. The followingdescription present functional and general hardware designcriteria in terms of the three instrument systems described inSection 3.1.

Tlie processing hardware will be confioured to orovideinformation to the displays described in Section 3.3. The

,

processing equipment includes operator interfaces for equipment'

testing, setup, and maintenance. The descriptions are for each

| of the two separate channels.|

All three ICC instrument systems will have similar sensor inputprocessing. The outputs of the sensors will be transmitted tothe processor, all of which is outside of containment, using

| qualified cable systems.

!

3-4

--. _. _

. -_

-, o

.

The processing for the ICC instrumentation will he<e' surveillancetesting and diagnostic capabilities. Automatic on-line surveil-

I lance tests will continuously check for specified hardware andsoftware malfunctions. The on-line automatic surveillance testsas a minimum will indicate inputs that are out of range andcomputer hardware malfunctions. The malfunctions will be indicatedthrough the operator interface. A manual on-line diagnostic

i

capability will be incorporated to aid the operator in locatingthe source of these malfunctions.

'. 3. 2.1 Subcooled Margin Monitoring System

The SMM processing equipment will perform the following :

Ifunctions:

1. Calculate the subcooled margin.

The saturation temperature is calculated from the-

minimum pressure input and the saturation pressure iscalculated from the maximum temperature input (fc3Section3.1). The temperature subcooled margh? 14 thedifference between saturation temperatgrt tab themaximum temperature input. The pressure subcooled

margin is the difference between t?5:rvdon pressureand the minimum pressure input. ing 9.MM will indicate

superheated conditions.

' 2. Process all out;p+.t fdf r.itplay.

3. Provide an alarm output when subi;ooled margin reaches a

preselected salpoint.

The EMN ;J?! A;r.c' the temperature and pressure inputs over0 0the input range of the sensors -- CET from 100 F to 1800 F,

ths g|Tr from 100*F to 1800*F, the RTDs from 0*F to 710*F.

3-5

. ...--- - .. . . .. - . , . . - . - - - - _ . --

- . ..

.

and the precrure from 0 psia to 3200 psia. The saturationtemperature and pressure are calculated from a saturationcurve derived from the 1967 ASME steam tables and an inter-polation routine.

3.2.2 HJTC System

The processing equipment for the HJTC performs the followingfunctions :

1. Determine if liquid inventory exists at'the HJTCpositions.

I

The heated and unheated themocouples in the HJTC are

connected in such a way that absolute and differentialtemperature signals are available. This is shown in

' ~

Figure 3-5. When water surrounds the thennocouples,

their temperature and voltage output are approximately

equal. \(A-C) n Figure 3-5 is, therefore, approximatelyzero. In the absence of liquid, the thermocoupletemperatures and output voltages become unequal,

causing V(A-C) to rise. When V(A-C) of the individualHJTC rises above a predetermined setpoint, liquidinventory does not exist at this HJTC position.

2. Determine the maximum upper plenu.n/ head fluid temperature

from the unheated thermocouples for use as an input to

the SMM. (The temperature processing range is from

100*F to 1800*F.)

|

3. Process all inputs and calculated outputs for display.i

4. Provide an alarm output to the plant annunciator systemwhen any of the HJTC detects the absence of liquid

level.|

f

( 3-6,

, .. , _ . . - . . . _ . . , - . . , .,..

. .

.

5. provide control of heater power for proper.HJTC outputsignal level. Figure 3-6 shows a single channel conceptualdesign which includes the heater power controller.

3.2.3 Core Exit Thermocouple System

The processing equipment for the CET will perform thefollowing functions:

1. Process all core exit thermocouple inputs for display.Half of the available CET inputs will be processed in eachchannel.

2. provide an alarm output to the plant annunciator systemwhen the temperature from any of the CET's exceeds apreselected setpoint.

3. Detennine the maximum CET temperature to be supplied to

the Stei. The processed temperature range will be from

100*F to 2300*F.

These functions are intended to meet the design requirementsof NUREG-0737, II.F.2 Attacnment 1. The display sectionwill describe the display design for the CET system.

i

3.3 DISPLAY DESIGNI

The ICC instrument outputs will be displayed through a human

engineered cathode ray tube (CRT) based primary disolav andseparate backup displays. The ' Critical Function Monitor (CFM) System

(Ref. 7) is being considered as the primary display for the ICC

| instrument outputs. As shown in Figure 3-1, each channel of the

| ICC Instrument system will also have safety grade backup displays.l Both primary and backup displays are intended to be designed consistent

with the criteria in NUREG-0737 Action Item II.F.2, II.F.2 Attachment 1,

and Appendix A. The following description presents the conceptualI design for display.

3-7

(.

. _ _ _ _ _ _ - _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

.

.

The CFM System is a dedicated, computer based display system thatmonitors s, f tical olant functions:

1. Core reactivity control2. Core heat removal control3. RCS inventory control4. RCS pressure control

5. RCS heat removal control

6. Containment pressure / temperature control

7. Containment isolation!

If any of the critical functions are violated, (by exceedinglogic setpoints) a Critical Function Alarm (CFA) is initiated.The ICC instruments outputs will be incorporated in this critical

function alarm logic.

The CFM displays data on four cathode ray tubes. The datahas three levels of information:

i

Level 1 Critical functions status (very general)Level 2 System overview (general, on system)

Level 3 System detail (specific information)

This hierarchy allows the operator to progress from an overall

l system view to a detailed diagnostic view. The ICC instrument.

i outputs will be incorporated in all three levels of disolay. The|

|detailed ICC information is anticipated to be displayed on the

| Level 3 display. Trending displays are also available with the

| CFM.

!|

| 3-8

i~~

- . . _

. .

.

Each channel of backup display will present the most reliablebasic information for each of the ICC instrument systems. These

displays will be human engineered to give the operator clearunambiguous indications. The backup displays are designed:

1. to give primary instrument indications in the remote chancethat the primary display becomes inoperable.

2. to provide confirmatory indications to the primary display.3. to aid in surveillance tests and diagnostics.

The following sections present details on the display for each ofthe instrument systems as presently conceived.

3.3.1 Subcooled Margin Monitor Display.

The following information is anticipated to be presented onthe primary display:

'

1. Pressure margin to saturation.2. Temperature margin to saturation.

3. Maximum temperature and source (i.e., HJTC, RTD, or

CET)

4. Minimum pressure

The following information is anticipated to be presented onthe backup displays:

1. Pressure margin to saturation

2. Temperature margin to saturation

3. Temperature inputs

4. Pressure inputs

3-9 ).

__ . _ - - _ _ _ - -

, ..

.

3.3.2 Heated Junction Thermocouple System Display

The following information is anticipated to be displayed onthe primary display:

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

2. Maximum unheated junction temperature of each of thetwo channels which is provided to the SMM.

The following information is anticipated to be displayed anthe backup displays:

1. Liquid inventory level above the fuel alignment platederived from the 8 discrete HJTC positions

2. Unheated junction temperature at the 8 positions3. Heated junction temperature 6t the 8 positions

.

3:3.3 Core Exit Thermocouple System Display

The following information is anticipated to be displayed onthe primary display:

1. A spatially oriented core map indicating the temperatureat each of the CET locations.

2. A selective reading of CET temperature

At least the maximum CET temperature of each of the two.

'

channels which is provided to the SMM will be presented.The backup displays are anticipated to display atleast four CET from each quadrant with an identificationnumber for each CET temperature.

3-10

4

..

.

Y YY YRA' AL

P MP PIS S

^I RI ^ID PD D.

-

_ M_ A

RG

. N A_ O I

_ I DT

. U O KA_ CL

O OS LI B

L- A_- N

1 O- I

3 T_ , CE NR UGG U FNN GI

I I SSS F TSS NEE ECC MOO UR_ R RP_ P T

SA B N

I

L LE E CN N CN N I

AlAli i

C C

_

-

S SR RO O_

_ S S_ N N

E E_

S S__

Y

, l

_ _ _ _ _ _ _ _ _ _ _ ____ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ , _ _ _ _ _ _ - _ - - - _ _ -

.

$ 4

.

.

i I

f""^*** r/c tamr,,,,

|W

[g: g;["[~~ %%w&gy%. y,

\M o S,-- ,.

' ,_ _

.

SPLASil Sil! ELD-_

lt

|

|4

!FIGURE 3-2

IlJTC SENSOR - IlJ1C/SPLASil SilIELD!

',

t

4

1

1

1I

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ ._ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ - _ _ _ _ _ _ - _ _ _ _ _-_ _ _ _ _ _ .

: .

.

.

i

!

..

ELECTRICAL CONNECTORS' SEPARATOR TWdi

(ONE PER SENSOR)

i

i~~ k' #

| 1h o , -- ,,E o. ,-

m-- p-: <?

= . .,.. .. .--

;___ m__ m

! L ). y

! SEAL PLUGHJTC SENSOR

i

f

!

FIGURE 3-3

) IIEATED JUNCTION TilERH0C00PLE

PROBE ASSEMBLY

,

i

1

4

.. . . - ._ ._. _ _

, .

e

.

FIGURE 3-4>h

PALISADh5 FIRiT D

D

FIXED IN-CORE INSTRUMENTATION LOCATIONSN

A B D EFG HI J KLM .N P Q RST YWX Z

l I I I I' '

1 | O| s

1 1

,. - - - .'. - - .;. -- g-eit | it |e 3 g 22 j g3

' - 3

4{G.. - ---n[-}3[ |

i( O f4 4

1 let d 401 M5 5

s ...,- - n -

.T..-- yG |j

O|[n - - s, - -a

||G }O ||| O . |

O(j,

3

s ' O -l---@---.'|.h--:l'

s il 'O O ' -ai i

,b #-' , - -;.TJ- 3;.i - -e

| | O|iO! +|Ol|',--

..

ic 'O ' '

O|| O 7'10

| 11 u i i'

i,+ t - - .t..,-i l4 --a!.;s

,e

-

G '' O T T,-

1,- -

g | =..;,-, e ..z .

| '3 O 'l O O O 13'

|' I I | |'@u 4 I1 1 0.1. - #..--I .t. Oa@

'

i s. -.- . , - ,- ., ,' - _is','O | O ( 'O 'T' 'TY Y16

| | '|16

{ O[| | ,4| |

17 6 0 174.,, - - 4. .m % ,,- - s. ,,- -- ,

,. ,- - , .# O- ~,,p O4is ie

.T T O|0 T T O fis ' isI | | |

20 0 201 i i.

5.$- -$| I- - '7.|- -- - --~3M 21| 21

O h- | 0'

22 ' ' ' 22

@ | I @'

23 0 23|# | | l l I* c i.

| A BCD EFG HIJ KLM NPQ RST YWI 2I

~~ .

Ex - Core Nuclear Detecter h in - Core Detector with ID r.trater n(10cetectors)

All in - core instrtrents c:ntain

5 rncdite cetectors and?

i 1 outlet thermoccuple|

3-14._ _ _ _ _ _ _ _ _ _ . _ _ . _ . , _ _ . ._ . , _ _ _ _ _ ._._ _ , _ _ _ _ _ _ _ . . . . _

. ..

.

COPPER INCONELi

(+) : m:

CHROMEL ALUMEL, ,

A 1ELB ,

CHROMEL

|'

COPPER,

||

| V (A B) = ACTUAL TEMPERATURE, UNHEATE.D JUNCTIONV (C.B) = ACTUAL TEMPERATURES HEATED JUNCTIONV (A C) = DIFFERENTIAL TEMPERATURE

|

;

i

FIGURE 3-5

ELECTRIC A L DI AG R AM OF H.J. T.,C.

3-15

O e

.

SENSOR 1 C. ?

THROUGH ,i SIGNAL PROCESSOR --> PRIMARY DISPLAYSENSOR 8 e LOGIC AND CHANNEL B6CKUP

CONTROLS = DISPLAYa

* ALARM

A

f

POWERFEEDBACKSIGNAL POWER

CONTROLSIGNAL

ll U

HEATERPOWER

CONTROLLER

||,

|,

i U

| POWER TOHEATERS

FIGORE3-6

HJTC SYSTEM PROCESSING CONFIGURATION(ONE CHANNEL SHOWN)

3-16

-- . -. -. . . - _ . . _ _ - _ _ - . _ _ _ _ _ , . - _ - . . . . . . - _ . _ _ . . - .-- .. . - . . . _ . . - . . , . _ _ . . . - . .

. o .

.

4.0 SYSTEM VERIFICATION TESTING

This section describes tests and operational expurience with ICCsystem instruments.

l

4.1 RTD AND PRESSURIZER PRESSURE SENSORS

The hot and cold leg RTD temperature sensors and the pressurizerpressure sensors are standard NSSS instruments which have well

known responses. No special verification tests have been per-formed nor are planned for the future. These sensors providebasic, reliable temperature and pressure inputs which are con-sidered adequate for use in the SMM and other additioTial displayfunctions.

I

4.2 HJTC SYSTEM SENSORS AND PROCESSING -

The HJTC System is a new system developed to indicate liquidinventory above the core. Since it is a new system, extensive ;

testing has been perfonned and further tests are planned to assurethat the HJTC System 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 Developmer.t Testing

Phase 3 - Prototype Testing

The first phase consisted of a series of five tests, which havebeen completed. The testing demonstrated the capability of the

!4

1

4-1

I. _ _ _ . . . - . , - . - -

.o .

.

HJTC instrument design to measure liquid level in simulatedreactor vessel thermal-hydraulic conditions (including accident

conditions).

Test 1 Autoclave test to show HJTC (themocouples only)_

response to water or steam.

In April 1980, a conceptual test was performed with two themocouplesin one sheath with one thermocouple as a heater and the otherthermocouple as the inventory senser. This configuration wasplaced in an autoclave (pressure vessel with the capabilities toadjust temperature and pressure). The thermocouples were exposed

to water and then steam environments. The results demonstrated asignificant output difference between steam and water conditionsfor a given heater power level.

Test 2 Two phase flow test to show bare HJTC sensitivity tovoids.

,

In June 1980, a HJTC (of the present differential themocoupledesign) was placed into the Advanced Instrumentation for RefloodStudies (AIRS) test facility, a low pressure two phase flow testfacility at Oak Ridge National Laboratory (ORNL). The HJTC wasexposed to void fractions at various heater power levels. The

|results demonstrated that the bare HJTC output was virtually the

l same in two phase liquid as in subcooled liquid. The HJTC did

| generate a significant output in 100% quality steam. ,

|Test 3 Atmospheric air-water test to show the effect of a splash

shield

A splash shield was designed to increase the sensitivity tovoids. The splash shield prevents direct contact with the liquidin the two phase fluid. The HJTC output changed at intermediate

|

4-2

__

,.

.

void' fraction two phase fluid. The results demonstrated that theHJTC sensor (heated junction thermocouple with the splash shield)

sensed intermediate void fraction fluid _ conditions.

Test 4 High pressure boil-off test to show HJTC sensor responseto reactor thermal-hydraulic conditiins.

In September 1980, a C-E HJTC sensor (HJTC with splash shield)

was installed and tested at the ORNL Therm'al-Hydraulics Test Facility

(THTF). The device is still installed and available for furthertests at ORNL. The HJTC sensor was subjected to various two

phase fluid conditions at reactor temperatures and pressures.The results verified that the HJTC sensor is a device that cansense liquid inventory under norm'al'and accident reactor vessel high pressureand temperature two phase conditions.

Test 5_ Atmospheric air-water test to show the effect of a

| separator tube

l*

A separator tube was added to the HJTC design to form a collapsedliquid level so that tnc HJTC sensor directly measures liquidinventory under all simulated two phase conditions. In October,

1980, atmospheric air-water tests were performed with HJTC sensorand the separator tube. The results demonstrated that the separator

,

tube did form a collapsed liquid level;and the HJTC output didaccurately indicate liquid inventory. This test verified that theHJTC 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 will consist of high pressure and tempera-ture tests on the HJTC instrument. These tests will provideinput for the C-E HJTC instrument design and manufacturingeffort. The Phase 2 test program is expected to be completed in

early 1981.

.

4-3

_ _ _ _ , _ __ _ , _ _ ,, _ _ , _ _ - - __

.

. , .

.

The Phase 3 test program will consist of high temperature andpressure testing of the manufactured prototype system HJTC probeassembly and processing electronics. Verification of the HJTCsystem prototype will be the goal of this test program. The4

Phase 3 test program is expected to be completed by the end of1981.

4.3 CORE EXIT THERMOCOUPLES

No verification testing of the CETs is planned. A study at ORF.was performed to test the response of CETs under simulated acci-

dent conditions (Reference 6). This te'st showed that the instru-ments remained functional up to 2300 F. This test along withprevious reactor operating experience verify the response df CETs.

4.4 PROCESSING AND DISPLAYS

.

The final processing and display design for the ICC detectionsystem has not been completed. As the design effort proceeds,design evaluations will be performed prior to installation.Correct implementation of the sof tware and hardware will beincluded and documented as part of the design effort.

h _h

.. - _.- . _ . . . . _ , ---_. _- -.

, .

5.0 SYSTEM QUA!.IFICATION

The qualification program for the ICC Detection System instrumentationhas not been completely defined. However, plans are being developedbased on the following three categories of ICC instrumentation:

1. Jensor instrumentation within the pressure vessel.

2. Instrumentation components and systems which extend from the

primary pressure boundary up to and including the primary displayisolator and including the backup displays.

3. Instrumentation systems which comprise the primary displayequipment.

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

The in-vessel sensors will meet the NUREG-0737, Appendix A

guide to install the best equipment available consistentwith qualification and schedular requirements. Design of the equipmentwill be consistent with the guidelines of Appendix A as well as theclarification and Attachment 1 to Item II.F.2 in NUREG-0737. Specifically,instrumentation will be designed such that they meet appropriate stresscriteria when subjected to normal and design basis accident loadings.Verification testing will be conducted to confinn operation at DBA(as defined by C-E) pressure and temperature conditions. Seismictesting to safe shutdown conditions will verify function after beingsubjected to the seismic loadings.

The cut-of-vessel instrumentation system, up to and including theprimary display isolator, and the backup displays will be environmentallyqualified in accordance with IEEE-323-1974 as interpreted by Combustion

. Engineering Document, CENPD-255, " Qualification of Combustion Engineering

Class 1E Instruments." This document describes the method which willbe used to qualify out-of-vessel Class lE equipment.

5-1

- - .

e

Plant-specific containment temperature and pressure design profileswill be utilized where appropriate in these tests. This equipmentwill also be seismically qualified according to IEEE-STD-344-1975.CENPD-182, " Seismic Qualification of C-E Instrumentation Equipment,"

describes the methods used to meet the criteria of this document.

The primary display will not be designed as a Class lE system, butwill be designed for high reliability; thus it will not be qualifiedenvironmentally or seismically to Class lE requirements nor will itmeet the single failure criteria of Appendix A, Item 2. Post-accidentmaintenance accessibility will be included in the design. The qualityassurance provisions of Appendix A, Item 5 do not apply to the primarydisplay according to NUREG-0737. However, the computer driven primarydisplay system will be separated from the Class lE sensors, processingand backup display equipment by means of an isolation device whichwill be qualified to Class lE criteria.

|

||

||

:

5-2,

!

. -.

.

* 6.0 OPERATING INSTRUCTIONS

Guidelines for reactor operators to use to detect ICC and takecorrective action has been developed by the C-E Owners Group andsubmitted to NRC for review (Ref. 8). These guidelines havebeen used to review and revise the plant emergency procedures for(Plan Neme). In addition, the C-E Owners Group has developedreactor operator training materials concerning ICC.

The C-E Owners Group is defining a program for development of furtheremergency procedure guidelines and operator training materialsassociated with the ICC Detection System described in Section 3.This program is expected to provide these guidelines and trainingmaterials during 1981. A more specific schedule is subject tofinalization of the ICC Detection System design, specificallythe instrument displays.

6-1-

._. _

. ., o

|

|*

|

REFERENCES.

1. NUREG-0737, " Clarification of TMI Action Plan Requirements,"U. S. Nuclear Regulatory Commission, November,1980.

'

|

2. CEN-ll7, " Inadequate Core Cooling - A Response to NRC I E Bulletin79-06C, Item 5 for Combustion Engineering Nuclear Steam SupplySystems," Combustion Engineering, October,1979.

3. CEN-125, " Input for Response to NRC Lessons Learned Requirementsfor Combustion Engineering Nuclear Steam Supply Systems," CombustionEngineering, December,1979.

4. C-E Proposal No.1579 SP, "C-E PWR Subcooled Margin Monitor," September,1979.

5. C-E Proposal No. 2580 SP, " Heated Junction Thermocouple System,"September,1980.

,

i

i 6. Anderson, R. L. , Banda, L. A. , Cain, D. G. , "Incore ThermocouplePerformance Under Simulated Accident Conditions", presented at IEEESymposium, November,1980.

7. C-E Paper TIS-6649, " Operational Aids to Improve the Man-MachineInteraction in a Nuclear Power Plant," Presented at American NuclearSociety Annual Meeting, Las Vegas, Nevada, June 8-12, 1980.

8. Letter C-E Owners Group to NRC, "C-E Generic Emergency ProcedureGuidelines," December 10, 1980.

i

!

.>