In this Nukefact we address the questions under the subsection Reactivity Coefficients. Of the eighty-four questions in the INPO Catalog pertaining to Reactivity Coefficients we find twenty-nine to be technically incorrect, that's 34% wrong folks.
And from the existing technical error it becomes evident that INPO hasn't a clue about the following:
1. the difference between reactivity and reactivity change
2. what a reactivity coefficient really represents
3. the difference between algebraic sign and magnitude
Here too, the sloppiness in structuring the questions and in terminology is truly disturbing ... and appalling.
There should be questions in this section that address the reactivity change from cold to hot caused by the moderator coefficient, and concerning the reactivity change from 500oF to 2000oF caused by the Doppler coefficient, and the reactivity change from 0% to 40% voids caused by the void coefficient
a. void
b. moderator*
c. power
d. doppler
Comment: The asterisk indicates the intended correct answer is choice "b". The moderator coefficient is very specifically defined as being the change in reactivity associated with "a one oF increase in moderator temperature". Restate the question and choices as follows:
Question 1: (revised) The change in reactivity produced by a one oF increase in reactor coolant temperature defines which reactivity coefficient?
a. void
b. moderator*
c. power
d. doppler
Question 2: The moderator temperature coefficient (alpha-T) measures a change in _____________ resulting from a change in __________________.
a. reactivity, moderator temperature*
b. K effective, moderator temperature
c. moderator temperature, reactivity
d. moderator temperature, K effective
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect for the same reason as question #1. In addition, this question is poorly worded. The moderator temperature coefficient does not "measure" anything. Restate the question as follows:
Question 2: (revised)
The moderator temperature coefficient (alpha-T) represents the change in _____________ resulting from a unit increase in __________________.
a. reactivity, moderator temperature*
b. K effective, moderator temperature
c. moderator temperature, reactivity
d. moderator temperature, K effective
Question 3: The moderator temperature coefficient (alpha-T) is expressed in units of
a. Delta-K effective per degree Fahrenheit, moderator
b. Delta-K effective per degree Fahrenheit, moderator and fuel
c. Delta-K/K per degree Fahrenheit, moderator*
d. Delta-K/K per degree Fahrenheit, moderator and fuel
Comment: The asterisk indicates the intended correct answer is choice "c". The answer is technically incorrect because choice "c" is indicated to represent reactivity per oF. Reactivity is not a unit of measure; it is a physical property of the reactor. However, as indicated in previous comments, we believe it is helpful to indicate what the coefficient represents, as long as it's done correctly. A temperature increase causes a reactivity change, not simply reactivity. The coefficient represents delta-rho/oF. Restate the question as follows:
Question 3: (revised) The moderator temperature coefficient (alpha-T) represents
a. Delta-k per degree Fahrenheit increase in moderator temperature
b. Delta-k per degree Fahrenheit increase in moderator and fuel temperature
c. Delta-rho per degree Fahrenheit increase in moderator temperature*
d. Delta-rho per degree Fahrenheit increase in moderator and fuel temperature
Question 6: A one degree Fahrenheit increase in moderator temperature in a reactor with a negative moderator temperature coefficient (alpha-T) will insert
a. negative reactivity resulting in a decrease in core reactivity*
b. positive reactivity resulting in an increase in core reactivity
c. positive reactivity resulting in a decrease in core reactivity
d. negative reactivity resulting in an increase in core reactivity
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect. A one oF increase in moderator temperature will insert a negative reactivity "change", not negative reactivity. In addition, as the question is stated, it cannot be determined whether the reactivity will increase, or decrease. If the initial reactivity is positive, then the magnitude of the positive reactivity will decrease. If the initial reactivity is negative, then the magnitude of the negative reactivity will increase. This is another example of where initial conditions are essential, but have not been provided. Restate the question as follows:
Question 6: (revised) A one degree Fahrenheit increase in moderator temperature in a supercritical reactor with a negative moderator temperature coefficient (alpha-T) will insert
a. negative reactivity change, resulting in a decrease in core reactivity*
b. positive reactivity change, resulting in an increase in core reactivity
c. positive reactivity change, resulting in a decrease in core reactivity
d. negative reactivity change, resulting in an increase in core reactivity
Question 9: If the plant has operated steady-state at 100% power for the past six months, the moderator temperature coefficient (alpha-T) most likely has:
a. changed very little
b. become less negative*
c. become more negative
d. become less negative, turned, and become more negative
Comment: The asterisk indicates the intended correct answer is choice "b". The question is technically incorrect because there are no gradations of negativity. Negative is negative and positive is positive. Restate the question as follows:
Question 9: (revised) If the plant has operated steady-state at 100% power for the past six months, the magnitude of the negative moderator temperature coefficient (alpha-T) will have:
a. changed very little
b. become smaller*
c. become larger
d. become smaller, turned, and become larger
Question 10: The plant is currently at end-of-life in its fuel cycle, and it will be refueled next month. How will the refueled core's moderator temperature coefficient (alpha-T) compare to its present value?
a. will be less negative
b. will be more negative*
c. will not be much different
d. A comparison cannot be made with the available information.
Comment: The asterisk indicates the intended correct answer is choice "b". The question is technically incorrect for the reason given for question #9. Restate the question as follows:
Question 10: (revised) The plant is currently at end-of-life in its fuel cycle, and it will be refueled next month. How will the refueled core's negative moderator temperature coefficient (alpha-T) compare to its present value?
a. smaller in magnitude
b. larger in magnitude*
c. about the same (no change)
d. comparison cannot be made with the available information.
Question 11: Which of the following describes the change in the moderator temperature coefficient (alpha-T) during a plant cooldown?
a. The moderator temperature coefficient continually becomes less negative.*
b. The moderator temperature coefficient continually becomes more negative.
c. The moderator temperature coefficient changes very little during a plant cooldown.
d. The moderator temperature coefficient becomes more negative, then turns, and becomes less negative.
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect for the reason given in question #9. Restate the question as follows:
Question 11: (revised) Which of the following describes the change in the negative moderator temperature coefficient (alpha-T) during a plant cooldown?
a. The moderator temperature coefficient continually decreases in magnitude.*
b. The moderator temperature coefficient continually increases in magnitude.
c. The moderator temperature coefficient changes very little during a plant cooldown.
d. The moderator temperature coefficient becomes smaller, then turns, and becomes larger.
Question 12: The plant is currently at beginning-of-life in its fuel cycle. During plant heatup, the negative moderator temperature coefficient will
a. become less negative
b. become more negative*
c. remain effectively constant
d. become more negative, then turn and become less negative
Comment: The asterisk indicates the intended correct answer is choice "b". The question is technically incorrect for the reason given in question #9. Restate the question as follows:
Question 12: (revised) The plant is currently at beginning-of-life in its fuel cycle. During plant heatup, the negative moderator temperature coefficient will
a. become smaller in magnitude
b. become larger in magnitude*
c. remain effectively constant
d. become smaller, then turn and become larger
Question 13: In regard to the magnitude of change, which one of the following statements describes the response of the moderator temperature coefficient?
a. Below the power range, the moderator temperature coefficient becomes more negative as control rods are withdrawn.
b. The moderator temperature coefficient becomes less negative as fuel temperature increases.
c. In the range of 1 percent to 100 percent power, very little negative reactivity is inserted due to moderator temperature change.*
d. The moderator temperature coefficient becomes negligible below 1 percent power.
Comment: The asterisk indicates the intended correct answer is choice "c". The question is technically incorrect for the same reason as question #9. In addtion, Choice "c" is not an answer to the question. Restate the question as follows:
Question 13: (revised) With regard to the magnitude of change, which one of the following statements describes the response of the negative moderator temperature coefficient in a BWR?
a. Below the power range, the moderator temperature coefficient becomes larger in magnitude as control rods are withdrawn.
b. The moderator temperature coefficient becomes smaller in magnitude as fuel temperature increases.
c. From 1 percent to 100 percent power, very little change occurs in the magnitude of the moderator temperature coefficient because moderator temperature remains relatively constant.*
d. The moderator temperature coefficient becomes negligible below 1 percent power.
Question 14: Which of the following conditions would cause the moderator temperature coefficient of reactivity to become more negative?
a. inserting rods from 50 percent control-rod density to 75 percent rod density*
b. fuel temperature decreases from 1500°F to 1200°F
c. core age increases
d. moderator temperature decreases from 500°F to 450°F
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect for the same reason given for question #9. Restate the question as follows:
Question 14: (revised) Which of the following conditions would cause the negative moderator temperature coefficient of reactivity to become larger?
a. control-rod density increases from 50 percent to 75 percent*
b. fuel temperature decreases from 1500°F to 1200°F
c. core age increases
d. moderator temperature decreases from 500°F to 450°F
Question 17: As the moderator temperature increases, the negative moderator temperature coefficient becomes
a. less negative because the increased neutron velocities require more collisions to thermalize
b. more negative because the microscopic cross section for capture increases
c. less negative because moderator density increases
d. more negative because the slowing-down length increases more*
Comment: The asterisk indicates the intended correct answer is choice "d". The question is technically incorrect for the same reason as question #9. In addition, the correct choice "d" seems to be missing words after "more". Restate the question as follows:
Question 17: (revised) As the moderator temperature increases, the negative moderator temperature coefficient becomes
a. smaller in magnitude because the increased neutron velocities require more collisions to thermalize
b. larger in magnitude because the microscopic cross section for capture increases
c. smaller in magnitude because moderator density increases
d. larger in magnitude because the slowing-down length increases, resulting in greater fast leakage*
Question 21: The reactor is operating at full power following a refueling outage. In comparison to the current moderator temperature coefficient (MTC), the MTC just prior to the refueling was
a. less negative at all coolant temperatures*
b. more negative at all coolant temperatures
c. less negative below approximately 350°F coolant temperature and more negative above approximately 350°F coolant temperature
d. more negative below approximately 350°F coolant temperature and less negative above approximately 350°F coolant temperature
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect for the same reason given in question #9. Restate the question as follows:
Question 21: (revised) The reactor is operating at full power following a refueling outage. In comparison to the current negative moderator temperature coefficient (MTC), the MTC just prior to the refueling was
a. smaller in magnitude at all coolant temperatures*
b. larger in magnitude at all coolant temperatures
c. smaller in magnitude below approximately 350°F coolant temperature and larger in magnitude above approximately 350°F coolant temperature
d. larger in magnitude below approximately 350°F coolant temperature and smaller in magnitude above approximately 350°F coolant temperature
Question 22: The reactor is currently at end-of-life in its fuel cycle, and it will be refueled next month. In comparison to the current moderator temperature coefficient (MTC), the MTC after refueling will be
a. less negative at all coolant temperatures
b. more negative at all coolant temperatures*
c. less negative below approximately 350°F coolant temperature and more negative above approximately 350 °F coolant temperature
d. more negative below approximately 350°F coolant temperature and less negative above approximately 350°F coolant temperature.
Comment: The asterisk indicates the intended correct answer is choice "b". The question is technically incorrect for the same reason given in question #9. Restate the question as follows:
Question 22: (revised) The reactor is currently at end-of-life in its fuel cycle, and it will be refueled next month. In comparison to the current negative moderator temperature coefficient (MTC), the MTC after refueling will be
a. smaller in magnitude at all coolant temperatures
b. larger in magnitude at all coolant temperatures*
c. smaller in magnitude below approximately 350°F coolant temperature and larger in magnitude above approximately 350 °F coolant temperature
d. larger in magnitude below approximately 350°F coolant temperature and smaller in magnitude above approximately 350°F coolant temperature.
Question 39: The Doppler temperature coefficient (alpha-D) measures
a. the change in Keffective due to change in reactor power
b. the change in reactivity due to a change in reactor power
c. the change in Keffective due to a change in the fuel temperature
d. the change in reactivity due to a change in the fuel temperature*
Comment: The asterisk indicates the intended correct answer is choice "d". The question is technically incorrect because, as for the moderator coefficient in question #1, the Doppler coefficient is very specifically defined as being the change in reactivity associated with "a one oF increase in fuel temperature". And, the Doppler coefficient does not "measure" anything. Restate the question and choices as follows:
Question 39: (revised) The Doppler temperature coefficient (alpha-D) represents
a. the change in Keffective due to a 1% increase in reactor power
b. the change in reactivity due to a 1% increase in reactor power
c. the change in Keffective due to a 1 oF increase in the fuel temperature
d. the change in reactivity due to a 1 oF increase in the fuel temperature*
Question 40: The correct units of measure of the Doppler temperature coefficient (alpha-D) are:
a. delta-K/K per °F, fuel temperature*
b. delta-Keffective per °F, fuel temperature
c. delta-K/K per percent reactor power
d. delta-Keffective per percent reactor power
Comment: The asterisk indicates the intended correct answer is choice "a". The answer is technically incorrect because choice "a" is indicated to represent reactivity per oF. Reactivity is not a unit of measure; it is a physical property of the reactor. However, as indicated in the comments on earlier questions, we believe it is helpful to indicate what the coefficient represents, as long as it is done correctly. A temperature increase causes a reactivity change, not simply reactivity. The coefficient represents delta-rho/oF. Restate the question as follows:
Question 40: (revised) The Doppler temperature coefficient (alpha-D) represents:
a. delta-rho per °F, fuel temperature*
b. delta-Keffective per °F, fuel temperature
c. delta-rho per percent reactor power
d. delta-Keffective per percent reactor power
Question 41: The amount of reactivity added to a reactor for each 1 °F change in fuel temperature is referred to as the ______________ temperature coefficient.
a. moderator
b. Doppler*
c. power
d. void
Comment: The asterisk indicates the intended correct answer is choice "b". The question is technically incorrect for the same reason given in question #39. Restate the question as follows:
Question 41: (revised) The reactivity change resulting from a 1 °F increase in fuel temperature is referred to as the ______________ temperature coefficient.
a. moderator
b. Doppler*
c. power
d. void
Question 43: Which of the following phrases defines the Doppler temperature coefficient (alpha-D)?
a. the incremental change in reactivity due to an incremental change in reactor power
b. the total change in reactivity due to a given change in reactor power
c. the incremental change in reactivity due to an incremental change in fuel temperature*
d. the total change in reactivity due to a given change in fuel temperature
Comment: The asterisk indicates the intended correct answer is choice "c". The question is technically incorrect for the same reason given in question # 39. The difference between incremental and total reactivity change, as used in this question, is not understood. Restate the question as follows:
Question 43: (revised) Which one of the following defines the Doppler temperature coefficient (alpha-D)?
a. the incremental change in reactivity due to an 1% increase in reactor power
b. the incremental change in reactivity due to a 1 psig increase in reactor pressure
c. the incremental change in reactivity due to a 1oF increase in fuel temperature*
d. the incremental change in reactivity due to a 1oF decrease in fuel temperature
Question 45: The term Doppler coefficient is defined as the change in reactivity per unit change in
a. overall reactor pressure
b. overall core void volume
c. fuel temperature*
d. moderator temperature
Comment: The asterisk indicates the intended correct answer is choice "c". The question is technically incorrect for the same reason as given in question #1. Restate the question as follows:
Question 45: (revised) The Doppler coefficient is defined as the change in reactivity per
a. 1 psig increase in reactor pressure
b. 1% volume fraction increase in core voids
c. 1 oF increase in fuel temperature*
d. 1 oF increase in moderator temperature
Question 47: The Doppler coefficient of reactivity is the reactivity associated with the
a. heating of U-238*
b. addition of Sm-149 during power changes
c. heating of B-10
d. addition of Pu-239 as the core ages
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect for the same reason as question #3, and because of poor wording. In addition, it is not consistent with other questions that involve the effect of Pu-240 buildup on the Doppler coefficient. Restate the question as follows:
Question 47: (revised) The Doppler coefficient of reactivity represents the reactivity change associated with the
a. heating of U-238 and Pu-240*
b. addition of Sm-149 during power changes
c. heating of B-10 and dysprosium
d. addition of Pu-239 as the core ages
Question 48: Which one of the following describes how the magnitude of the Doppler coefficient of reactivity is affected over core life?
a. It becomes more negative due to the buildup of Pu-240.*
b. It becomes less negative due to the buildup of fission products.
c. It becomes more negative initially due to gadolinium burnout, then less negative due to fuel depletion.
d. It remains essentially constant.
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect for the reason given in question #9. Magnitude does not become more or less negative. Restate the question as follows:
Question 48: (revised) The magnitude of the negative Doppler coefficient of reactivity over core life
a. becomes larger due to the buildup of Pu-240.*
b. becomes smaller due to the buildup of fission products.
c. becomes larger initially due to gadolinium burnout, then smaller due to fuel depletion.
d. remains essentially constant.
Question 50: The void coefficient of reactivity is the change in reactivity produced by a
a. change in the volume fraction of steam bubbles to liquid coolant in the core*
b. unit change in the moderator temperature
c. unit change in the core average exit quality
d. change in the mass fraction of vaporized coolant to liquid coolant in the core
Comment: The asterisk indicates the intended correct answer is choice "a". The question is technically incorrect for the reason given in question #1. Restate the question as follows:
Question 50: (revised) The void coefficient of reactivity is the change in reactivity produced by a
a. 1% increase in the volume fraction of steam bubbles to liquid coolant in the core*
b. 1oF increase in the moderator temperature
c. 1% decrease in the core average exit quality
d. 1% increase in the mass fraction of vaporized coolant in the core