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Guidelines For Preparing Criticality Safety Evaluations at Department of Energy Non-Reactor Nuclear Facilities
Evaluation Results cont'd - s3007cn10114

6.1.2 SATs D2401 A/B/C/D, D-2402 A/B, D-2403: The CWTS exclusively uses these seven
tanks for storage of fissionable solutions. Each tank can contain approximately 725 liters of liquid
and is nominally 64.24" OD by 87.25" H. These tanks meet design criteria as follows.
Accordingly, CWTS SATs are subcritical for any contingency, including overbatching to 1000 g/l
fissionable solution. (reference Appendix G). All CWTS SATs met the criteria for solution annular thickness of 2.88" +/- 1/8".
Verification using a digital ultrascope at six different heights for each of eight radial positions can
be found in Appendix K. Pure polyethylene with a density of 0.92 g/cc was used in the CWTS SATs. A
certification letter to this effect is in Appendix K. In addition, the Tank Evaluation System (TES)
was used to verify the presence of required polyethylene in these tanks. Reference Appendix K
for TES results. Type 238Z Flex/Boron (silicone based rubber mixed uniformly with Boron Carbide)
manufactured by Reactor Experiments, Inc. was used as the nuclear poison in the CWTS SATs.
An elemental analysis of the Flex/Boron is in Appendix K. In addition, TES was used to verify
the presence-of required nuclear poisons in these tanks. Reference Appendix K for TES results. Since tanks which could be drained to the CWTS were operated at less than 150 g/l Pu
and the highest fissionable solution currently in Building 371 tanks is less than 10 g/l Pu, the
maximum credible solution concentration is 150 g Pu/l. In addition, liquids from other facilities
are to be sampled to contain less than 150 g/l fissionable material, i.e., Pu + U235, before
accepted into Building 371. Thus the 150 g/l fissionable material limit for tanks D-2401 A/B/C/D
can be maintained during collection of liquids. In addition, liquids received by tanks D-2402 A/B
have undergone precipitation to remove fissionable materials and supernate liquid has been
filtered through an R6 filter and three 1-micron bag filters. Caustic liquids are only filtered since
materials are suspended and not dissolved. Overbatching of collection tanks D-2401 A/B/C/D as the result of precipitation due to the
introduction of caustic liquids would not exceed 1000 g Pu/l, thus tanks D-2401 A/B/C/D would
remain subcritical. Reference correspondence in Appendix R. Precipitation in tanks is prevented
by ensuring the receiving tank is empty and isolated from other tanks prior to introduction of
caustic liquids. Also, inlet valves to these tanks are required to be closed when greater than four
liters of caustic is present in any glovebox or room which drains to Criticality Drain System "A".
In addition, caustic liquids are not allowed to be used in decontamination activities in rooms with
drains to Criticality Drain System "A" or disposed in it. Reference the criticality safety evaluation
for Criticality Drain System "A". Overbatching of tanks D-2401 A/B/C/D as the result of plutonium polymer formation
(water added to tanks containing high concentration plutonium nitrate solution) would not exceed
1000 g Pu/l, thus tanks D-2401 A/B/C/D would remain subcritical. Reference correspondence in
Appendix R. This is also judged to bound density increases due to freezing of tank contents.

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