Sro Excore Nis

Front 1

Question 1. What are the three primary functions of the excore nuclear instrumentation system?

Back 1

1. Provide core protection by monitoring neutron leakage from the core. 2. Generate control functions and alarms. 3. Provide power indication during an accident.

Front 2

List the three ranges of excore nuclear instrumentation provided by Westinghouse.

Back 2

1. Source Range 2. Intermediate Range 3. Power Range

Front 3

Question 1: Describe the characteristics of the source range NI detectors.

Back 3

Answer 1: Gas filled detector operating in proportional region. Sensitive to neutrons and gammas. Measures ~31 inches in length.

Front 4

Question 2: Explain the operation of the source range NI detectors.

Back 4

Answer 2: High voltage applied to detector's center electrode. Gas amplification allows small radiation to generate current pulses large enough to be easily detected. Uses Boron Triflouride (BF3) gas. Gamma pulses are significantly smaller than neutron pulses. Gamma pulses are filtered out. Circuitry measures neutron flux level by counting current pulses.

Front 5

1. State the function of each of the following source range components: a. Preamplifier - boosts detector output signal from low in the milli-volt range to high in the milli-volt range. b. Discriminator - Electrically gates pulses of heights below certain levels c. Pulse shaper - Shapes pulses into a square wave d. Log pulse integrator - Integrates square wave pulses to provide a DC voltage output proportional to log of input pulse rate e. Level amplifier - Receives input from log pulse integrator and produces a 0 - 10 volt DC output f. Isolation amplifier - Isolates the source range level signal from faults that may occur in remote indicating and recording equipment

Front 6

2. Describe the event(s) that cause the following source range drawer lights to illuminate. A. Loss of detector volts - High voltage supplied to detector is removed or low, setpoint 100 volts below normal B. Level trip - Neutron level has reached trip setpoint of 1E+5 cps C. Level trip bypass - Level trip bypass switch in BYPASS D. High flux at shutdown - Neutron level exceeds 5x shutdown neutron count rate

Front 7

3: What are the four modes of operation of the scaler-timer and what does each do?

Back 7

Answer 3: 1. Display Time - Preset Count: Totalizes and displays amount of time required to make preset number of counts. 2. Display Count - Preset Time: Counts and displays number of input pulses for a preset period, in seconds or minutes 3. Display - Preset Check: Totalizes and displays a preset number of counts 4. Display - Preset Manual: Totalizes and displays the number of input pulses for a time determined by the front panel start/stop pushbuttons.

Front 8

4: Describe the source range trip logic.

Back 8

Answer 4: Initiates reactor trip at 1E+5 cps. Prevents reactor from uncontrollable high power levels caused by high startup rates. Trip may be disabled by use of the trip bypass switch. Manually blocked during a reactor startup after P-6 (either Intermediate Range channel >1E-10 amps). Automatically unblocked when P-6 resets (both Intermediate Range channels < 1E-10 amps). P-10 blocks Source Ranges regardless of P-6 status.

Front 9

5: Describe the source range trip logic.

Back 9

Answer 5: Initiates reactor trip at 1E+5 cps. Prevents reactor from uncontrollable high power levels caused by high startup rates. Trip may be disabled by use of the trip bypass switch. Manually blocked during a reactor startup after P-6 (either Intermediate Range channel >1E-10 amps). Automatically unblocked when P-6 resets (both Intermediate Range channels < 1E-10 amps). P-10 blocks Source Ranges regardless of P-6 status.

Front 10

Question 1: Describe the characteristics of the intermediate range nuclear instrumentation detectors.

Back 10

Answer 1: Nitrogen gas filled detector operating in ionization region. Sensitive to both neutrons and gammas but compensates for gammas (compensated ion chamber). Measures ~18 inches in length.

Front 11

Question 2: Explain the operation of the intermediate range nuclear instrumentation detectors.

Back 11

Answer 2: Consists of "can within a can." Cans are isolated from one another. Each can is nitrogen filled, with inner can volume slightly greater than outer can. Outer can is lined with Boron-10. Therefore, both cans interact with gammas, but only outer can reacts with neutrons. The gamma currents are electrically canceled by use of a compensating voltage applied only to inner can. Gamma current from inner can is subtracted from gamma plus neutron current from outer can. Net result is neutron-only current.

Front 12

1. Describe the control interlock generated by the intermediate range.

Back 12

Answer: C-1 rod stop at current equivalent to 20% of rated thermal power. All outward rod motion stops in both manual and automatic. Blocked simultaneously when intermediate range trip is blocked or when channel is bypassed locally at drawer.

Front 13

2. Describe the possible effect of under compensation during a reactor shutdown.

Back 13

Answer: Under compensation may prevent Source Range channels from automatically unblocking during a reactor shutdown because permissive P-6 would not clear. Source Range channels would need to be manually unblocked.

Front 14

3: Describe the intermediate range trip logic.

Back 14

Answer 3: Reactor trip at current equivalent to 25% rated thermal power unless manually blocked. When 3 of 4 power ranges < 10%, P-10 resets, and intermediate range trip is automatically unblocked.

Front 15

4: Why is over compensation of an intermediate range detector a concern?

Back 15

Answer 4: Gamma induced current in inner can more than compensates for gamma induced current in outer can causing detector to read erroneously low. Indicating less than actual power is non-conservative.

Front 16

Question 1: Describe the characteristics of the power range nuclear instrumentation detectors.

Back 16

Answer 1: Nitrogen gas filled detector operating in ionization region. Lined with Boron-10. In power range it is unnecessary to compensate for gamma because gamma induced current in this range is only one thousandth the magnitude of neutron induced current and proportional to reactor power (uncompensated ion chamber). One power range channel consists of two separate detectors, sharing common center electrode. Each chamber has an ~5 foot sensitive length.

Front 17

Question 2: What is meant by the term "normalized" with regards to the power range excore nuclear instruments? Why is it necessary? How is it determined?

Back 17

Answer 2: 1.Differential flux (i.e., flux in top of core minus flux in bottom of core) equals 0, detector signal strengths are same relative to one another. 2.Takes into account that no two detectors will indicate exactly the same when exposed to the same neutron flux. 3.To determine the normalized values, a secondary calorimetric performed to determine actual reactor power, and an in-core flux map is run to determine core flux distribution.

Front 18

1. Describe the power range trip logic.

Back 18

Answer: 1. Low range high level reactor trip at > 25% on 2/4 channels unless manually blocked above P-10. When 3/4 power ranges < 10%, P-10 is deactivated and low range high flux trip is automatically reinstated. 2. High range high level reactor trip at > 109% on 2/4 channels. Cannot be manually blocked or bypassed. 3. Power range high flux rate reactor trip at +4% with a 2 second time constant.

Front 19

2. Describe the power range controls and permissives.

Back 19

Answer: Controls: C-2 rod stop at 103% on 1/4 channels. Can be manually bypassed on Misc. Control & Indication Panel. Permissives: P-8 (single loop loss of flow) at >48% on 2/4 channels. Automatically blocks single loop loss of flow reactor trip when <48%. P-10 (nuclear at power) at >10% on 2/4 channels. Permissive P-10 is involved in the following circuits: a. Manual block of the Power Range/low range high trip (25%). b. Manual block of the Intermediate Range high level trip (25%) and rod stop (20%). c. Automatic block of high voltage supply to the Source Range. d. Input to P-7 "at power" permissive.

Front 20

3: List the bistable relay drivers that receive a signal from the summing level amplifier.

Back 20

Answer 3: 1. Overpower rod stop (C-2) and alarm 2. Power above P-8 3. Low range high level trip 4. High range level trip 5. Power above P-10 6. High positive rate trip 7. High negative rate trip 8. Power above P-9