February 15, 1952

Everyone was mo st cordial and helpful to me on my recent trip
to the Oak Ridge National Laboratories.

the following conclusions and recommendations which I present
are the result of my discussions with several different people
in both the Y-l2 and X-10 areas and represent a blend of ideas and
information obtained on this trip and modified by my overall
background of our reactor developement. The people with whom I
talked gave me information and ideas freely and generously, but
wee reticent with advice. Therefore, the responsibility for the
recommendations is mine.

1. If the theoretically computed fastest period of a reactor
is of the order of 10 to 50 milliseconds, it is dangerous to
assume that these calculations have thereby ruled out the probability
of going prompt critical. In which case, a negative temperature
will not prevent a disaster.

2. When any new nuclear fuel assembly is being put into
operation for the first time, the maximum rate of control rod
withdrawal should be such that the maxima rate of increase of
reactivity is 1/1000 percent per second. After experience has been
gained concerning its behavior, this rate may be increased to 1/100
percent per second. This implies that our control rod mechanism
should be made to operate at a slower rate of withdrawal than is at
present planned until we are able to judge the wisdom of the faster
rate from personal experience with our reactor's behavior.

3. It may be advantageous to come to criticality by introducing
a rather dry solution of the uranium salt in increments and
watching the multiplication and then add the water moderator in
small amounts until criticality is achieved. The information
obtained from the Co/C versus mass curve needs to be supplemented by
the information that is revealed when the source is removed from the
nearly critical assembly.

4. The value of the rods must be carefully determined in the
process of reaching criticality. That is, at each state of approaching
criticality evaluate the rods before going to the next state.

5. In addition to electrical signal checks at all channels each
day before operation, it is necessary to check each channel by
moving a radioactive source.

6. The Oak Ridge logarithm circuits work quite well and reliably
at least down to 10-10 amperes and the period circuit should afford
5 seconds "e" fold protection down to 1 watt on our reactor. Only
one sensitivity range is needed for this channel.

7. it appears as if our automatic control should work down to
25 watts. There is not much value in automatic operation at lower
levels.

Boron 10 ionization chambers operating at 400 to 600 volts
and at such size that 50 - 100 micro-amperes equals 1010 flux
should be used. It is necessary to flow gas through them continually,
otherwise their calibration will shift. These chambers have carbon
electrodes that have been coated with a boron 10 oil dag and burnt off.
Quartz insulation is advisable.

8. One channel must always "see" the source. This had best be
a U 235 pulse chamber. This chamber feeds into a pre-amplifier, then
into a linear amplifier and discriminator (so that the [gamma] ray back-
ground can be suppressed) then into a scaler and rate meter.

9. Hard tube fail safe trips are thought to be better than
thyratron trips.

10. The nitrate solution appears to be the wisest choice from
the viewpoint of chemical stability.

11. We should build our own equipment which cannot be bought
"of the shelf".

12. Indium foils and film badges should be strategically located
in the reactor room at all times.

13. Each p erson needs.- two slow neutron ionization chambers,
two [gamma] ionization chambers and a film badge.

14. For general monitoring purposes a Cutie Pie is wise. A Zeuto
is used for [alpha] monitoring. Air must be monitored by forceing it
through a piece of filter paper which is measured in a scintillation
counter. A frisker may be a better choice for general personal
monitoring than a head and foot monitor.

15. Our plan for coating a water-proof Geiger counter with
strippable paint and silicone may be all right for a liquid monitor.

16. A thermal flow meter may be desirable in the recombiner
system.

17. A liquid depth guauge based upon using the solution as a
dielectric which rises into a cylindrical condenser and varies
its capacity may work.

A good deal of valuable specific information about apparatus

was obtained which is not appropriate for this letter.

A list of drawings and documents which should be requested
is enclosed.

I enjoyed the trip vary much and believe the information obtained
will save us a good deal of time and money and result in an overall
improvement in our instrumentation.

In view of the fact that secret information was involved in some
of the discussions, I as sending copies of this letter to Dr. Callihan
and Dr. Jordan so as to be sure that I have not inadvertently
included any such information in the letter. To the best of my
knowledge and belief, I have not included any secret information.
However, I will, await a reply from them before releasing this letter
to our general reactor committee.