2chp11-06

Koeberg Safety Analysis Report

Part II Chapter 11 Section 6 Revision 4

2chp11-06.doc © Eskom 2003

CONTENTS

II-11.6 OTHER INSTRUMENTATION AND CONTROL SYSTEMS.......................................3

II-11.6.1 General .......................................................................................................................3

II-11.6.2 Control System Interlocks...........................................................................................3

II-11.6.2.1 General .......................................................................................................................3

II-11.6.2.2 Automatic Turbine Generator Runback ......................................................................4

II-11.6.3 In-Core Instrumentation (RIC) ....................................................................................4

II-11.6.3.1 General .......................................................................................................................4

II-11.6.3.1.1 Neutron flux measurements........................................................................................4

II-11.6.3.1.2 Temperature measurements ......................................................................................5

II-11.6.3.2 Thermocouples ...........................................................................................................6

II-11.6.3.3 In-Core Neutron Flux Measurement ...........................................................................7

II-11.6.3.3.1 Description..................................................................................................................7

II-11.6.3.3.2 Operation ....................................................................................................................9

II-11.6.3.3.3 Mapping Modes ........................................................................................................10

II-11.6.3.3.4 Equipment characteristics.........................................................................................11

II-11.6.3.3.5 Output signals...........................................................................................................12

II-11.6.3.3.6 RIC Thermocouples during Drain-down ...................................................................12

II-11.6.4 Boron Concentration Measurement..........................................................................12

II-11.6.5 Detection of Large Cladding Ruptures......................................................................12

II-11.6.5.1 General .....................................................................................................................12

II-11.6.5.2 Large cladding ruptures ............................................................................................13

II-11.6.6 Neutron Flux Surveillance System............................................................................13

II-11.6.6.1 Radial Tilt Surveillance .............................................................................................13

II-11.6.6.1.1 Function (see Figure F-II-11.6-4)..............................................................................13

II-11.6.6.1.2 Comparator channel .................................................................................................14

II-11.6.6.2 Axial Flux Difference.................................................................................................14

II-11.6.6.2.1 Function ....................................................................................................................14

II-11.6.6.2.2 Axial flux difference monitoring.................................................................................14

II-11.6.7 Core Cooling Monitor................................................................................................16

REFERENCES ................................................................................................................................19




TABLES

Table T-II-11.6-1: Plant Control System Interlocks ..........................................................................17

FIGURES

Figure F-II-11.6-1 Control system interlocks

Figure F-II-11.6-2 In-core instrumentation system - RIC

Figure F-II-11.6-3 Power range channel block diagram

Figure F-II-11.6-4 Comparator channel

Figure F-II-11.6-5 Axial power difference

Figure F-II-11.6-6 Flux difference channel




II-11.6 OTHER INSTRUMENTATION AND CONTROL SYSTEMS

II-11.6.1 General

The general design objectives (see References 1 and 2) of the controlsystems are:

♦ to establish and maintain power equilibrium between reactor coolant andthe secondary system during steady-state unit operation,

♦ to constrain operational transients to avoid a spurious unit trip and re-establish steady-state unit operation,

♦ to provide the reactor operator with monitoring instrumentation thatindicates required control parameters of the systems and provides theoperator with the capability of assuming manual control of the systems.

The instrumentation systems discussed in this section are:

♦ control system interlocks,

♦ in-core instrumentation,

♦ boron concentration measurement,

♦ neutron flux surveillance system (safety related).

II-11.6.2 Control System Interlocks

II-11.6.2.1 General

These interlocks are designed to assist normal control channels to reduceinstances requiring reactor protection system action.

The interlocks are based on parameters relating to:

♦ reactor power, and

♦ turbine load.

A list of unit control interlocks, along with the description of their derivationsand functions, is presented in Table T-II-11.6-1. These interlocks aredesignated by the prefix "C". The development of these logic functions isshown in the functional diagrams (in Section II-11.5).

Control system interlocks have the following functions (seeFigure F-II-11.6-1):




♦ prevent further withdrawal of the control bank “D” when a Departure fromNucleate Boiling Ratio (DNBR) limit or a linear power (kW/m) limit isapproached (see Subsection II-11.4.2.1.1.4),

♦ initiate automatic turbine generator runback when approaching coreovertemperature or overpower conditions (see Subsection II-11.6.2.2),

♦ unblock steam dump valves when the rate of load rejection exceeds apreset value as measured by turbine first stage pressure (seeSubsection II-11.4.2.3.1).

II-11.6.2.2 Automatic Turbine Generator Runback

Automatic turbine generator runback is initiated by an approach to anoverpower or overtemperature condition (C3 or C4). This helps avoidoperating conditions leading to a reactor trip. Each C3 or C4 signal pulsereduces turbine generator load by 5%. Since pulses are generated every 30seconds and last 1.2 seconds, the average runback capability is 10% perminute.

II-11.6.3 In-Core Instrumentation (RIC)

II-11.6.3.1 General

In-core instrumentation supplies:

♦ data on neutron flux distribution in the core,

♦ fuel assembly coolant temperatures at selected core locations,

♦ an indication of saturation temperature margin between the saturationtemperature of the primary water and,

• hot leg temperatures,

• thermocouple temperatures.

II-11.6.3.1.1 Neutron flux measurements

Flux measurement data obtained from each selected thimble is plotted onstrip chart recorders for direct indication of axial neutron flux distribution. Thisdata is also an analogue input to the unit computer. After initial formatting,the data is extracted from the unit computer for subsequent three-dimensional flux mapping by other computers.

♦ Use during normal reactor operation




During normal unit operation, in-core instrumentation does the following:

• compares actual power distribution with predicted values,

• provides input to the unit computer for burn-up, power distribution,DNBR, and other calculations,

• verifies ex-core instrumentation response,

• detects abnormal core conditions.

♦ Use during test operation

In-core instrumentation is also of importance when core physics tests arebeing run.

Instrument data is used to:

• verify that Beginning Of Life (BOL) power distribution agrees with thepredicted values,

• check the hot spot factor used in accident studies,

• calibrate ex-core power range detectors,

• detect misplaced fuel assemblies. (i.e. errors in core loading).

For detailed description of in-core flux measurement seeSubsection II-11.6.3.3.

II-11.6.3.1.2 Temperature measurements

The temperature system includes a core cooling monitor which continuouslychecks the difference between the saturation temperature and the core exittemperature. The core cooling monitor is intended for use at power andduring a reactor shutdown and to monitor the adequacy of core coolingduring and after an accident. Temperature measurements are alsoprocessed by the unit computer.

The temperature data detects or confirms radial tilt and Rod Cluster ControlAssembly (RCCA) or RCCA bank misalignments.

a) Safety evaluation

The core instrumentation is only in service on an intermittent basis.Moreover, there is a significant delay between the time the measurementis taken and the time the data becomes useable.




The temperature measurements do not participate in the safety of theunit. However, in the event of an accident, the system will continuouslyprovide temperature measurements up to 1 250ºC. This allows theoperator to follow the evolution of the core exit temperatures both duringand after the accident.

Although the system is not safety related, in-core instrumentation doesplay an important indirect part in unit safety. It verifies that sufficientmargins exist with respect to design and accident studies and detectsabnormal operating conditions such as RCCA or RCCA bankmisalignment, fuel misloading, etc.

In the event that the neutron flux instrumentation is inoperable, thereactor can continue to operate normally until a full or partial flux map isrequired by the Operating Technical Specifications (see Reference 6).

II-11.6.3.2 Thermocouples

A representative indication of core exit temperatures is measured by up to 51thermocouples, located in fuel assembly coolant exit channels. Thesethermocouples use chromel-alumel hot junctions. They are clad withstainless steel and insulated with aluminium oxide.

Thermocouple characteristics are:

outside diameter: 3.17 mm,

length: 6.5 - 9.2 m,

measurement span (working range): ambient to 370ºC,

measurement span (accident conditions) ambient to 1 250ºC,

accuracy: ± 1.1ºC (0 - 275ºC),± 0.375% (275 - 1 250ºC),

repeatability: (variation between thethe detectors) 0.8ºC (200 - 370ºC),

insulation resistance: >5 x 106 ohms (to 370ºC).

The thermocouples are routed in conduits which pass through the reactorvessel head and through the support columns and terminate above the uppercore plate.

At a point just above the upper core plate, the hot junction of eachthermocouple is guided to the flow path from the given fuel assembly.




The conduits pass through and are supported by the thermocouple columnswhich are mounted on the upper support plate and provided with sealassemblies to the vessel head penetrations. Compression type fittings fix thethermocouples in position and provide the pressure boundaries between thethermocouples sheaths and the conduits.

There are four thermocouple columns. Each thermocouple column carries 13conduits. One conduit is provided as a spare.

A connector enables connection of the thermocouples with an extensioncable of identical thermoelectric materials running to the cold junction box.Each cable is routed along the vessel head lifting rig members and the cablebridge to the connector plate.

From the connector plate, signals are transmitted by extension cable to theelectrical penetrations.

From the electrical penetrations the cables are grouped in four bundles androuted to the junction boxes.

From the cold junction boxes, electrical signals are transmitted by coppercables to the core cooling monitor. The electrical signals are processed bythis core cooling monitoring system and then sent to the unit computer and tothe RIC recorder located in the RIC cabinet.

The core cooling monitor processes the above data and defines thesaturation temperature and the margin between saturation temperature andRIC temperature which is indicated on a remote display located on P9 controldesk (see Reference 5). The temperature threshold alarms are automaticallyinhibited above P10 (10% Pn).

II-11.6.3.3 In-Core Neutron Flux Measurement

II-11.6.3.3.1 Description

In-core neutron fluxes are measured in 50 selected fuel assemblies by fivemovable miniature neutron detectors. The layout is shown inFigure F-II-11.6-2. A mechanical description is given inSubsection II-3.3.10.

During normal reactor operation, the instrument thimbles are in their guidetubes, which run from the reactor vessel bottom head through the primaryshield to the high pressure seal located in the in-core instrumentation room.

During refuelling, instrument thimbles are withdrawn beyond the lower coreplate so as not to interfere with loading operations.




Each detector is connected to a drive cable, which is inserted or withdrawnfrom the core by a drive unit. The drive unit consists of a gear wheel, two-speed bi-directional electric motor, cable storage reel, and a sensor givingcontinuous indication of the gear wheel angular position and consequently ofthe detector position.

Selection of thimbles is made by three banks of rotary path selectors.

The first bank of five "group" selectors allows the selection of a path leadingto either:

♦ the normal path group,

♦ the alternate path group,

♦ the cross-calibration path group,

♦ the storage path, which routes the detector and drive cable to a shieldedarea when servicing is required.

The second bank of five "path group" selectors allows selection of a pathleading to the normal ten-path selector.

The third bank of ten "path" selectors consists of ten-path selectors directingthe detector to one of ten possible thimbles.

The neutron flux is measured by the miniature detector and its electricalsignal is transmitted to its respective channel.

The electrical connections linking the detector to the measurement circuitconsist of:

♦ stainless steel sheathed coaxial cable running through the hollow helical-wrap drive cables,

♦ a sliding brush contact at the cable storage reel,

♦ a standard coaxial cable running through a containment electricalpenetration to the terminal cabinets.

Measurement circuit equipment includes a dc power source for detectorsupply and two current-measuring shunts. The circuit is in series with thedetector and the detector power supply. One of the shunts feeds a strip chartanalogue recorder; the other is connected to the unit computer.




The entire drive/transfer system can be isolated by motor-operated valves(backed up by manual isolation valves) located at the bottom end of thethimble guide tubes, just beyond the primary shield. These isolation valvesare opened just prior to introduction of the detectors into the core. They serveto prevent flow of reactor coolant into the instrumentation room, should athimble leak or rupture occur. Leak detectors, mounted between manual andmotor-operated valves prevent valve opening if reactor coolant is detected.

The protection is backed up by ball check valves (bead valves) which ensurea rapid isolation in the event of a leak occurring during flux mapping when thedetectors are being withdrawn. They are linked to the leak detectors fittedupstream, which prevent the motor-operated valves from opening if water ispresent.

All equipment is controlled from cabinets situated in the computer room.

Each detection channel is connected to a separate flux measurementcabinet. All five cabinets are grouped together near the control room, alongwith one cabinet housing power supply, synchronizing circuits, commoncircuits and one cabinet housing in-core temperature recorders.

Each flux measurement cabinet contains electromechanical relay circuitry, adecoder for signals received from the detector position sensor (the decoderserves as a motor controller), a flux measurement module, a recorder, and acontrol panel.

II-11.6.3.3.2 Operation

Detectors are inserted at high speed until they reach the bottom of the core.They then traverse the length of the core at low speed while the axial fluxdistribution along the fuel assembly is logged. The drive unit position sensorsprovide the control system with data indicating precise detector location.

The following general sequence is used in flux mapping:

♦ individual paths are selected by using group, path-group, and pathselector switches,

♦ isolation valves open automatically provided no leaks have beendetected,

♦ detectors are driven at high speed to positions at the bottom of the coreand are stopped automatically,

♦ detectors are then driven at low speed up to the top of the core and arestopped automatically,




♦ detectors are withdrawn at low speed to positions below the core and arestopped automatically,

♦ detectors are withdrawn at high speed to the drive unit actuating thewithdrawal limit switches,

♦ isolation valves automatically close.

The trend recorders run as long as the detector is traversing the core.Recorder readout and computer input of the axial flux distribution is obtainedover the full length of the selected fuel assembly.

To obtain a full core flux map, a reference fuel assembly is scannedsequentially by all five detectors for cross calibration purposes. All fifty fuelassemblies are then scanned five at a time using the automaticsynchronization circuit in the control system. Automatic scan speed anddirection sequencing, programmed sequencing of fuel assemblies to bescanned, and synchronization of detector movement enable mapping to beperformed with a minimum of operator action.

Back-up capability is provided to ensure automatic mapping even if adetection channel becomes inoperable due to failure of a channel component(detector, measurement channel, drive unit or path group selector). The tenpaths normally handled by the channel are scanned by the adjoining channelby rotating the "group" and "path group" selectors to the alternate positions.

Full manual and partial automatic operating capabilities are provided inaddition to the normal operating mode.

During the period that this facility is not used and especially when humanactivity is being carried out in the room that contains the electro-mechanicalequipment, the five detectors can be routed beforehand to a protective leadcask located in the reactor pit underneath the vessel.

II-11.6.3.3.3 Mapping Modes

There are manual and automatic scanning modes. In the manual mode, alloperating instructions are given by the operator.

The more frequently used mode of operation is automatic and ischaracterized by continuous discrete sequencing of detector speed anddirection, based on preselected points.

The following points are programmed for each path:

♦ point A, at the bottom of the core where the detector switches over to lowspeed,




♦ point B, at the top of the core where the detector reverses direction.

Two types of automatic scanning are possible:

♦ individual scanning using each detection channel discretely,

♦ synchronized scanning using the five detectors simultaneously, with thescanning of the different flux chambers preprogrammed.

An individual scan takes approximately 10 minutes. A full core map usingautomatic synchronized scanning requires approximately 2.5 h (100 minutesfor performing 50 axial scans plus an additional 50 minutes for running eachdetector through the reference thimble for cross-calibration).

II-11.6.3.3.4 Equipment characteristics

♦ detector travel speed

• low speed: 1.5 m/min,

• high speed: 9 m/min,

♦ storage reel take-up capacity: 35 m,

♦ position indication reproducibility: ±2 mm,

♦ measurement chamber type: RTC model CFUF 43, fission,

♦ outside diameter: 4.7 mm,

♦ active length: 27 mm,

♦ voltage rating: 50 - 200 V,

♦ thermal neutron sensitivity: 10-17 A/neutron/cm2.s,

♦ gamma radiation sensitivity: 2.3 x 10-12 A/Gy/h,

♦ linearity: better than 3%,

♦ loss of sensitivity: less than 10% for an integrated flux of1020 neutron/cm2.s stationary at 320ºC,

♦ measurement current variation: 1 µA to 1.5 mA corresponding to1011 neutron/cm2.s and rated full power respectively.

1785




II-11.6.3.3.5 Output signals

Flux measurement chamber output signals are fed to the unit computer andto strip chart recorders (one per detector).

The recorder starts up automatically when scanning begins.

A digital readout on the control cabinets located near the control room givesdetector position. Position signals are used to initiate scan and control scansequencing. The cabinets include a mimic panel, which provides an overallview of detector operations.

II-11.6.3.3.6 RIC Thermocouples during Drain-down

At refuelling outages, at least two RIC thermocouples (one on Train A, oneon Train B) remain in place whilst draining down to vessel flange level. Thisprovides the operators with indication of the vessel coolant temperature.

II-11.6.4 Boron Concentration Measurement

Reactor coolant system (RCP) boric acid concentration is measured bymeans of continuous sampling taken from the hot leg of RCP loop No 2 orNo 3.

The boron measurement system is located in the nuclear auxiliary buildingsampling area. It consists of a long half-life neutron source and a neutrondetector. The neutron flux measured by the instrument is proportional to theboron concentration of the sample flowing past the source.

The measurement range is 0 to 3 000 mg B/kg and an automatic controlsystem ensures continuous operation.

Boron meter output signals are transmitted at periodic intervals to acontinuous strip chart recorder and a digital readout in the control room andto the unit computer for use in reactivity calculations.

Because of the importance of boric acid concentration measurements duringcold shutdown, a routine monitoring capability is provided, with provision forinstrument recalibration if required.

Boric acid concentrations are measured in the laboratory in the event that theboron meter is not functioning. One boron meter is provided per reactor.

II-11.6.5 Detection of Large Cladding Ruptures

II-11.6.5.1 General

Not used.




II-11.6.5.2 Large cladding ruptures

A rapid increase in primary coolant water contamination may indicate a largecladding rupture. A continuous gamma activity measurement is performed bymeans of an ionisation counter (KRT 001 MA) positioned directly on theletdown line of the volume control circuit.

The alarms for exceeding the activity set point are sent to the control roomand to the unit computer.

II-11.6.6 Neutron Flux Surveillance System

The flux surveillance system is part of the nuclear instrumentation system(RPN).

Flux surveillance is based on monitoring two parameters derived from thefour power range instrument channels (see Figure F-II-11.6-3):

♦ radial tilt,

♦ axial flux difference.

II-11.6.6.1 Radial Tilt Surveillance

II-11.6.6.1.1 Function (see Figure F-II-11.6-4)

Radial tilt surveillance monitors the radial power distribution betweensuccessive flux mappings. unit power capability studies are based on pre-established (design) total enthalpy rise and radial peaking factors (F∆H andFxy, respectively).

Detailed power distribution determinations using flux maps are performedduring startup testing and on a monthly basis and serve to ensure that theenthalpy rise and radial peaking factors remain below design values.

Radial tilt surveillance instrumentation uses a comparator circuit to monitorthe deviation of individual detectors from the average map as a means ofensuring that enthalpy rise and radial peaking factors have not increasedsignificantly.

A skewed radial distribution (e.g., resulting from a minor asymmetry in fuelloading) is allowed as long as enthalpy rise and radial peaking factors shownon flux maps remain within acceptable limits.

Circuit fault detection capability is provided.




II-11.6.6.1.2 Comparator channel

The comparator channel receives separate top and bottom power rangesignals from each of the four power range channels.

A flux deviation alarm circuit is provided for each of the following:

♦ high flux deviation of any upper ion chamber signal from the average ofall the upper ion chamber signals (inhibited when all power rangechannels are below 50% Pn),

♦ high flux deviation of any lower ion chamber signal from the average ofall the lower ion chamber signals (inhibited when all power rangechannels are below 50% Pn),

♦ high flux deviation of any channel (top plus bottom) with respect to any ofthe other three. This function is to indicate possible single channel failure.

Only one power range channel at a time can be inhibited for testing orfollowing a failure without requiring a change in the alarm setpoint. Thecomparator channel then only uses the three remaining power rangechannels.

II-11.6.6.2 Axial Flux Difference

II-11.6.6.2.1 Function

Axial flux difference monitoring, as the name indicates, is used to detectdeviations in axial power distribution from target values. Detection isperformed by comparing the power range upper ion chamber signals with thepower range lower ion chamber signals.

At any power level equal to or greater than 15% Pn, the flux difference mustbe maintained within the CD band (see Figure F-II-11.6-5) on either side ofthe target axial power distribution value and ideally within the AB band. Axialflux difference alarms will occur if either of these limits is exceeded.

No limit on axial flux difference is set when reactor power is below 15% Pn.Overall operating guidelines governing control of reactor power are given inReference 3.

II-11.6.6.2.2 Axial flux difference monitoring

The axial flux difference monitoring circuit (see Figure F-II-11.6-6) assists theoperator in ensuring that the axial power distribution remains within targetvalues.




The following instrumentation is provided in the control room:

♦ an axial flux difference indicator for each power range channel (fourreadouts: range: -20 to +20% Pn),

♦ an axial flux difference chart recorder (range: -50 to +50% Pn),

♦ a digital readout showing elapsed time during which the CD limits havebeen exceeded over the preceding twelve hours period (range0 to 99 minutes),

♦ a chart recorder showing the measured-to-reference flux differenceselectable for each power range channel (wide range: -40 to +40% Pn;narrow range: -5 to +5% Pn),

♦ an alarm for each of the following conditions:

• axial flux difference out of AB limits (3/4 logic),

• axial flux difference out of CD limits (3/4 logic),

• axial flux difference out of CD limits for more than one hour over thepreceding 12 hours period (3/4 logic).

Alarms are inhibited for reactor power levels less than 15% Pn, where Pn =unit nominal power.

The output signals of the four upper and four lower ion chambers are fedthrough isolation amplifiers to a differential amplifier located in the axial fluxdifference monitoring circuit.

The differential amplifier, which is provided with adjustable gain control, givesas an output the axial flux difference. The output of the differential amplifier istransmitted to axial flux difference recorders and indicators.

Each average flux signal from the isolation amplifier of the power rangechannels feeds a function generator which produces the axial flux differencereference value.

The axial flux difference and the axial flux difference reference value are fedto a summing amplifier, which gives as an output the measured-to-referencedifference. This is transmitted to comparators and recorders. Thesecomparator outputs are validated only for an average flux greater than15% Pn.




II-11.6.7 Core Cooling Monitor

The wide range hot leg temperature loops are qualified for post-accidentoperating conditions and give an accurate picture of the coolant as it leavesthe core.

The core cooling monitor also receives primary pressure signals fromsensors located on the RRA hot leg connections. These sensors are alsoqualified for post-accident conditions. In addition, the core cooling monitoralso receives pressurizer pressure signals, these being used to validate theprimary pressure measurements.

The core cooling monitor receives 220 Vac power supplies from LNA (Train A)and LND (Train B).




TABLE T-II-11.6-1: PLANT CONTROL SYSTEM INTERLOCKS

Designation Derivation FunctionC1

C2

C3

C4

C5

C7A

C7B

C8*

C9

C11

1/2 neutron flux (intermediate range)above setpoint

1/4 neutron flux (power range) abovesetpoint

2/3 loops overtemperature ∆T within 3 %of protection setpoint

2/3 loops overpower ∆T within 3 % ofprotection setpoint

1/2 turbine first stage pressure belowsetpoint

1/1 negative time derivative of turbine firststage pressure (decrease only) above15 % Pn / 2s

1/1 negative time derivative of turbine firststage pressure (decrease only) above50 % Pn / 2s

Turbine trip, 2/3 turbine stop valvesclosed (signal generated by measurementof stop valve solenoid current and valvelimit switch position)

Condenser pressure below setpoint andde-superheating water pressure abovesetpoint

1/1 bank D control rod position abovesetpoint

Blocks automatic and manual control rodwithdrawal (if P10 present)Inhibits the improved flux rate protectiontrip (ie, pump speed and Tavg)**

Blocks automatic and manual control rodwithdrawal

Blocks automatic and manual control rodwithdrawalActuates turbine runback via loadreference

Blocks automatic and manual control rodwithdrawalActuates turbine runback via loadreference

Blocks automatic control rod withdrawal

Makes first two groups of condensersteam dump valves available. The twoother groups remain unavailable

Makes remaining condenser steam dumpvalves available

Trips the reactor if the condenser isunavailable and power is greater than40 % Pn (P16)

Allows steam dump to condenser

Blocks automatic and manual control rodwithdrawal

*One of C8’s original functions (steam dump interlock) has been taken over by P4.** Unit 1 only




REFERENCES

1) DSE RPNKBA 12 17 RPN 001.

2) DSE RGLKBA 12 17 RGL 001.

3) Operating Procedure F.RRC-RPR-RPN "NSSS Reactor controloperation"KWB-F.RRC-RPR-RPN.

4) DSE RICKBA 12 17 RIC 001.

5) DSE RIC Chapter 4KBA 12 17 RIC 004.

6) Operating Technical Specifications OPS 7030.

2chp11-06

Documents

large cladding ruptures

radial peaking factors

axial flux distribution

strip chart recorders

axial flux difference

core exit temperatures

power range channels

high flux deviation