IRM

Question 1

What is the purpose of IRMs?

Answer 1

Monitor and record core neutron flux levels between startup range and power range during startup and shutdown.

Provides trips to protect against rapid reactor power increase that can cause fuel damage from single operator error or equipment malfunction

Question 2

What is the IRM Detector?

Answer 2

Ionization Range Fission Chamber (Ion Chamber)

Question 3

How Many IRMs are there? Per Channel? What system do they feed?

Answer 3

8 total - 4 per channel - 11-14 feed RPS A; 15-18 feed RPS B

Question 4

What is the IRM detector coating? Fill Gas? Operating Voltage?

Answer 4

1.25mg of Uranium Oxide
17.7 psia of Argon Gas
100Vdc

Question 5

What is the power supply for the IRM Drive Unit?
Rod Matrix?
HV Supply?

Answer 5

Drive Unit - A - 28-1; B - 29-1
Rod Matrix (same as SRM) - IB
HV Supply - 24/48vdc - 2A - 11-14 ; 2B - 15-18

Question 6

What is the IRM Voltage Pre-amplifier?

Answer 6

Amplifies low level signal from detector to overcome noise to pass only portions of detector signal necessary for proper operation

Question 7

How many IRM detector ranges are there and what frequencies do they operate at?

Answer 7

10:
1-6 at 8-16kHz
7-10 at 300 - 600kHz

Question 8

What caution must be taken when switching from IRM range 6 to 7?

Answer 8

There is a deadband between the two ranges - may cause a half scram - some operators bypass the halfscram during this switch from 6 to 7

Question 9

What is the IRM attenuator?

Answer 9

Adjusts the gain of the IRM channel according to the range set by the range switch. Resistors set the gain of the voltage divider. Receives signal from the calibrate and diode logic matrix to adjust the gain.

Question 10

What is the IRM Calibration and Diode Logic Unit?

Answer 10

Receives signal from range switches to relay information to other components - ranges from range switches are linear (SRMs are logarithmic)

Sends signal to voltage pre-amplifier to allow pre-amp to select proper frequency ranges
Sends signal to attenuator to adjust gain properly
aids in calibration of IRMs with mode switch operation

Question 11

What is the IRM Inverter?

Answer 11

Inverts the signal from the attenuator - produces a signal of the same size, but inverse from the input signal
Allows for Mean square circuitry to work because it can only square positive signals.
Positive signals bypass inverter. Inverted negative signal and positive signal superposition at the mean square analog circuit.

Question 12

What is the IRM Mean Square Analog Circuit?

Answer 12

USED TO make gamma signals negligible so only Neutron flux is counted

Produces a signal proportional to only the core neutron flux
2 input signals: 1) from attenuator (positive signals) 2) inverted negative signals from inverter - superimposes them
Squares only the positive portions of both to provide input signal
By squaring, smaller gamma inputs are essentially eliminated

Question 13

What is the Output Amplifier?

Answer 13

Converts current output from mean square analog circuit to voltage to be used for meters and trip units

Question 14

What are the scales of the Output Meters and Recorder ranges? Which range uses which scale?

Answer 14

0-40 scale used by odd ranges (1,3,5,7,9)

0-125 scale used by even ranges (2,4,6,8,10)

Question 15

Which two IRM ranges provide a direct relationship of MWth?

Answer 15

7&8 read it straight -
a reading of 20 on 7 is 20MWth
a reading of 60 on 8 is 60 MWth

Question 16

How do the odd and even IRM ranges relate to the next higher odd/even range?

Answer 16

Between each odd/even range and the next highest odd/even range there is a factor of 10 difference

Question 17

How is IRM Range 10 calibrated?

Answer 17

reading of 100 equals 1000MWth (33.3% power)

Question 18

How do the odd and next sequential even IRM range relate?

Answer 18

An odd and next sequential even range (1 and 2, 3 and 4, etc.) have the same range/amplification, but output is displayed on a different scale:
0-40 vs 0-125

Question 19

What are the power suppllies for the IRMs?

Answer 19

11-14 - powerd by 24/48VDC A - feed to RPS A

15-18 powered by 24/48 VDC B - feed into RPS B

Question 20

What are the IRM recorders powered by?

Answer 20

11-14 recorders - ESS

15-18 recorders - IB

Question 21

What happens on a loss of power to IRM?

Answer 21

causes Half-scram

Question 22

What are the alarms/Trip signals for IRMs?

Answer 22

IRM HI
IRM INOP
IRM Downscale
Detector Wrong Position
IRM HI-HI

Question 23

What signal causes IRM INOP? what is result?

Answer 23

Function switch not in operate
HV Low
Module Unplugged

Bypassed when Rx in RUN
Causes Rod Block - can by bypassed with INOP INHIBIT Switch
Causes Scram signal - can be bypassed by INOP INHIBIT Switch

Question 24

What is the IRM Downscale Signal and Result?

Answer 24

Setpoint of 8/125 - Rod out block - bypassed on range 1 or Rx in RUN

Question 25

What is IRM HI Signal and Result?

Answer 25

Setpoint of 105/125 - Rod Block - Bypassed when Rx in Run

Question 26

What is IRM HI-HI Signal and Result?

Answer 26

117/125 - SCRAM - Bypassed when Rx in RUN AND companion APRM not downscale

Question 27

What is IRM Retract Permit (Detector Wrong Position) signal and result?

Answer 27

IRM not fully inserted OR Rx mode switch not in Run Rod Out Block if one of these not met

Question 28

What happens to IRM with loss of 24/48vdc?

Answer 28

Division local indication fail to zero Division status lights off RPS Division 1/2 scram Division Rod Block Division meters and recorders go downscale

Question 29

What happens to IRM with loss of ESS?

Answer 29

11 - 14 recorders lose power | Meters have no effect, recorders fail as-is

Question 30

What is IRM impact of loss of IB?

Answer 30

``` 15-18 Recorders lose power Detector drive select matrix control lost Meters not impacted Recorders Fail as is ```

Question 31

What is IRM effect of lost Div. MCC (28-1/29-1)?

Answer 31

Lost power to move division detector

Question 32

What is impact of IRM detector short circuit?

Answer 32

Max current through circuit - meters and recorders fail upscale

Question 33

What is IRM impact of range switch misposition?

Answer 33

May cause downscale alarm or upscale HI or HI-HI alarm depending on direction of switch operation

Question 34

What happens on a complete loss of IRM system?

Answer 34

ROd blocks and FULL SCRAM if not in RUN - bypassed if in RUN

Question 35

How many IRMs are REQUIRED (how many may be bypassed) per RPS Subsystem?

Answer 35

3 are required - 1 may be bypassed (DEPENDING ON MODE)

Question 36

What impact do radios have on IRMs/SRMS?

Answer 36

cabinet on DW Mezz is radio sensitive and may cause spurious scram

Question 37

Where is the IRM reset switch for seal in trip lights?

Answer 37

on front of IRM drawer.