# Nuclear Eng. - Control Rod step requirements

1. Mar 25, 2014

### mudweez0009

How many steps of Bank D rod motion will be required to change power level from 5% to 18%? Assume that the full power Delta T from primary to secondary is 50 degrees F. Assume the moderator temperature coefficient is -5 pcm/degree F. Assume the Bank D rod worth is 5 pcm/step. Neglect fuel temperature changes.

I dont even know what equations to use, nor can I find them anywhere. There is also NO textbook for this class, so everything is done via google search.

2. Mar 26, 2014

### Staff: Mentor

You are not at the stage of needing any equations. I suspect that this problem is one of those where once you understand the question you'll recognize you have the answer; where most of the difficulty lies in just understanding the question.

First you have to master the language of the question. What is "pcm"? What is the significance of transitioning from primary into secondary? (I don't know. I'm asking you to explain.)

3. Mar 26, 2014

### mudweez0009

Btw, I'm not asking for an answer to just simply be given to me, but I do need to stress that I have no clue how to do this. I took a class with zero background in nuclear because it is supposed to be a ramp-up course for non-nuclear engineers. I'm in way over my head, and with no textbook and hardly any online references, going to a forum is my last resort. So if you do know how to do this problem, I would appreciate your guidance.

That said, all I know is that pcm is a unit of reactivity. As to the significance from primary to secondary, I imagine it means the reaction generating heat on the primary side in the reactor transitioning to the steam generator and producing steam for the secondary side. But I think that is getting off track.

4. Mar 27, 2014

### Staff: Mentor

Let's break it down into small mangeable steps. If I can recast the essential part, see how you go with this sub-question ....

All the information you need is contained within the blue box above ^^^^^^

Last edited: Mar 27, 2014
5. Mar 27, 2014

### mudweez0009

Well at full power, the delta T is is 50 deg. I would assume it would change based on power level. But since the problem doesnt give that information, and you are hinting that it doesnt, then I imagine there is a 50 degrees F difference.

In which case, this problem becomes a unit cancellation problem?
If so, we have:
(50 deg) * (-5 pcm/deg) = -250 pcm
(-250 pcm) * (1 step / 5 pcm) = -50 steps.

Does -50 steps make sense? Does that mean the rod is moved out of the core 50 steps in order to increase power from 5% to 18%?

6. Mar 27, 2014

### Staff: Mentor

I'm guessing that the 50°F corresponds to the power level changing from 0% to 100%.

7. Mar 27, 2014

### mudweez0009

I'm sorry to be blunt but do you know how to do this problem or not? Because if not then this isn't productive, and if so, then your subtleties are being lost on me and it's still not productive.. are you trying to work through it with me haha?