3. Critical Facilities Tomorrow 
CRITICAL FACILITIES are slated to be- 
come more rather than less important 
in the affairs of the reactor designer. 
As a means of turning out specific de- 
sign information the critical experiment 
is proving superior to its rival, the 
multigroup computing-machine pro- 
gram. Outstanding reactor theorists 
such as B. Spinrad of Argonne and 
M. C. Edlund of Babcock & Wilcox 
state quite frankly that, compared with 
detailed theoretical calculations, the 
reactor design information from critical 
facilities is cheaper and more accurate 
and takes less time to get. 
To date most of the critical experi- 
ments supporting prototype reactor de- 
signs have been done in the national 
laboratories. The future should see 
private industry take over the greatest 
part of the task of developing specific 
design information of this kind; this 
will leave the national laboratories free 
to concentrate on more fundamental 
research. 
In using critical facilities for reactor 
design the industry will very likely 
adopt the strategy used for the Army 
Package Power Reactor (APPR). 
Here critical experiments were per- 
formed in two distinct phases: First a 
highly flexible arrangement was used 
(at ORNL) to establish ‘ball-park”’ 
estimates for the critical mass and the 
reactivity available for control and 
shim. With this information the fuel- 
element design was frozen and a set of 
elements fabricated. These elements 
were assembled together with the actual 
APPR-1 core support structure and 
control-rod drives to form a ‘‘zero- 
power” experiment in Alco Products’ 
critical facility (see p. 53). This sec- 
ond step gave refined figures for the 
critical loading and allowed optimiza- 
tion of core performance. 
For the ball-park phase of critical 
experimentation future private reactor 
designers will need all-purpose facilities 
flexible enough to mock up a wide 
variety of concepts; eventually these 
will include advanced design concepts 
operating at extreme temperatures and 
heat flux. Larger concerns will find it 
profitable to operate their own flexible 
facilities. Others, who cannot justify 
full-time use of a facility, will look to 
organizations like Battelle Memorial 
Institute, Nuclear Development Corp. 
of America (NDA) and Alco Products, 
which are in the business of hiring out 
critical-facility services. 
The second-stage zero-power experi- 
ments will be much more an individual 
problem for each reactor. These ex- 
periments may very well be carried out 
in the reactor vessel itself using as 
much of the actual core structure as can 
be safely frozen. (This has already 
Meet the Prophets 
The predictions on this page 
represent NUCLEONICS’ sum- 
mary of a collective crystal-gazing 
session on the subject of the 
future of critical facilities at- 
tended by Dixon Callihan (ORNL), 
Joel Chastain (Battelle), M. C. 
Edlund (B&W), G. A. Linenberger 
(AGN), John Noakes (Alco), Hugh 
C. Paxton (Los Alamos), W. C. 
Redman (Argonne), D. V. Wil- 
liams (B&W) and Roy Zimmer- 
man (NDA). 
NEW TREND has been introduced by 
Engineering Test Reactor Critical Facility 
shown here. ETRC will be retained as 
permanent part of ETR operation to 
check out proposed test-reactor runs 
been done with EBWR; see NUCLE- 
onics July ’57, 62.) Preferably the 
tests would be conducted at tempera- 
tures and pressures close to the design 
conditions. Since no heat flux is in- 
volved, fuel elements at this stage 
would not have to be real working 
models but only reasonably exact 
facsimiles; much of the fabrication ex- 
pense could be saved by omitting welds 
and using looser tolerances for the 
mock-up elements. 
Another problem that is just begin- 
ning to be studied is that of determining 
core characteristics at very high burnup 
and for recycled fuel. Zero-power- 
type experiments will probably be used 
to get this information; facsimile fuel 
elements containing radioactive fuel 
and fission products may be necessary. 
Beyond the area of reactor design, 
critical facilities will find new applica- 
tions as auxiliary facilities supporting 
routine reactor operations. Perhaps 
the first example of this is the Engineer- 
ing Test Reactor critical facility (see 
figure). The ETRC has been retained 
as a permanent fixture to check out 
scheduled core loadings for the ETR 
before putting them in the ETR itself. 
Similarly every power reactor of the 
future may well come equipped with a 
modest on-site critical assembly to be 
used for routine measurements. These 
might include double-checking new fuel 
elements as they arrive from the manu- 
facturer (presumably the manufacturer 
will have already checked the shipment 
in his own standard critical assembly), 
evaluating the reactivity worth of used 
elements and predicting the effects of 
modifications in core loading. 
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