ML20128D575
| ML20128D575 | |
| Person / Time | |
|---|---|
| Site: | 07001359, 07001703 |
| Issue date: | 08/28/1974 |
| From: | Preskitt C INTELCOM INDUSTRIES, INC. |
| To: | Rouse L US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20128D517 | List: |
| References | |
| NUDOCS 8507050146 | |
| Download: ML20128D575 (5) | |
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R AD TECH August 28, 1974 United States Atomic Energy Commission Attn: Mr. L. C. Rouse, Chief Fuel Fabrication and Reprocessing Branch Directorate of Licensing Washington, D. C.
20545 Gentlemen:
In response to requests in your letter of June 19, 1974 authorizing Amendment No. I to SNM-1405 we submit the following experimental info rmation. These data were obtained in loading the suberitical CFX 235 assembly with up to 1261.04 grams of U.
The minimum reactivity
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was determined to be -$8.14 which corresponds to k,gg of. 946 assuming Eeff =. 007.
The reactivity effects of additional shielding or reflectors was determined by covering the 4 inch thick polyethylene reflector with from 4 to 6 inches of additional poly or parafin over 50/o of the area.
The reactivity effect was measured to be negligible with k change of 6p of $0. 01 ( Ak/k = 0. 00007).
The radiation levels around the operating subcritical assembly (k,gg =. 95) were measured with only a portion of the final shielding present. The final shield configuration, which will primarily consist of a concrete block wall, will allow 10 mr/hr or less radiation into the position of the cell where authorized personnel have access. The j
measured radiation levels were not made with the additional concrete l
wall in place, only with the lead and blocks of water-extended-polyester (WEP) mixed with boron that are immediately adjacent to the reflector.
Scaling the measured data, which was taken with a 108p gram 252Cf 252 source in the assembly, to a 1 m gram Cf source we determined the following doses:
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United States Aicmic Energy Commission August 28, 1974 k
Page 2 Dose Y
n Position mr/he mrem /hr 20' from assembly
- 7. 7 18.5 6' from assembly 35.2 120.4 front edge of assembly 315 833 top of assembly 259 93 Assuming the assembly is finally loaded to a reactivity that corresponds to a k,ff of 0 990, these doses should be multiplied by a factor of S. 4 for a system with the same shielding configuration. The additional con-crete shield is expected to be adequate based on these measurements.
The function of the fail-safe features of the Californium Flux Multiplier (CFX and remove the {52{s to shut down the CFX (f. e. scram the safety rods Cf source from the core) if the high level flux trips on either the linear or log channel is exceeded, if the period on the log channel is too short, or if power is lost. In addition, the safety rod drive motors are in series with a low level flux trip that must be exceeded before the safety rods can be withdrawn from the core' to increase the reactivity of the assembly. These features have been checked daily and found to be functional every day that the CFX has been operated. There have been no malfunctions of the fail-safe features during this period.
The effect of accident considerations was experimentally considered by measuring the change in reactivity when the radiography port was completely filled with hi-density polyethylene and the fast neutron activa-tion port with a lucite rod.
This corresponds to flooding of these ports with water.
The reactivity of the system was found to change by 624 --
much less than the $1. 44 needed to go critical with the assembly loaded to a k,ff of 0. 99. The effect of adding 235 U to the central region of the CFX was measured by placing a poly vial of UO i
2 n the central flux trap.
Total amount of 235U was 16. 21 grams. (The maximum amount a standard 2 dram poly vial can hold of 93% enriched UO2 w uld be somewhat less than this, approximately 14 grams). The total change in reactivity was found to be 664 or 4.14 per gram of 235 Again this reactivity change U
is insufficient to cause criticality even at the fullloading of the CFX.
Indeed, all of these effects taken simultaneously are insufficient to cause
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criticality.
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Unit 9d Statan At:mic Enargy Ccmmission August 28, 1974 Page 3
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The thickness of the polyethylene moderator plates were varied to investigate the optimum moderation conditions for fuel loading.
The reactivity results listed below were obtained for the hydrogen to uranium ratios listed.
H/U p($)
511
-8.84 -
426
-8.68 342
-10. 87.
It appears that the broad peak in the optimum hydrogen to uranium ratio for the CFX is slightly less than the 500 to 1 that we had originally calculated.
The final loading of fuel to a k,ff of 0. 990 will be made at a H to U ratio of 426. to 1.
These data substantiate our claim that either the addition (flooding) or loss (disassembly) of moderation will result in a loss of renetivity.
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Dur.ing the initial loading and operating period of the CFX the
- tructural integrating of the components has been found to be adequate.
The technique of applying a small amount of pressure to one end of each fuel box has worked very well in maintaining an absence of voids in the fuel region yet allowing for an efficient fuel loading operation.
At the present k the accurate measurement of the temperature ff coefficient is a very, difficult task since it is expected to be on the order of -1. 6 x 10-4/Co. We would like to defer this measurement until the CFX is loaded to its design value of k,ff = 0 990. The thermal power produced in the CFX was determined from neutron flux measurements to O. 8 watts.
Consequently, the thermal power output at full fuel loading should be approximately 4. 3 watts.
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The additional information requested in your letter is listed below in the same order as the questions.
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- 1) The Cf source drive mechanism assembly drawing is contained in Appendix 2 (RT048J00llA) of the CFX Description and Safety Analysis that was submitted with our license application dated January 24, 1974.
The function of this mechanism is to move the Cf source from a lead
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storage pig located in the WEP shielding to the central core region and back again., During a scram or when the operate key is turned off the Is I
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United States Atomic Energy Commission August 28, 1974
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the source automatically moves to the storage postion. During a scram i
that is caused by a power failure the Cf source may be moved by a manual crank located on top of the assembly above the WEP shielding.
The radiation shielding for the CFX is described above. The 4
remaining component of the shielding is the concrete block wall that will have a surface radiation level of 10 mr/hr or less when the CFX is ope rating.
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- 2) The shutter door of the CFX can be open when the CFX is 7.,
operating. However, the shutter door interlock is in parallel with the interlock on the cell door and the personnel plug interlock.
If either of these interlocks are opened with the shutter door open then the CFX
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will scram. The personnel plug interlock is an adminstrative feature l
that requires all personnel entering the limited acess cell to pull a plug l
and return it for the duration of the stay in the cell.' This adminstrative control is in addition to the access door interlock.
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- 3) There is no automatic control on the safety rods other than the high level flux trips, the period trip and the low level trip. The i
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intent is to load the CFX to a'k,gg of 0 990. This k,gg will be achieved only at the full out position of the safety rods and no further increases can be made by an operator. We have shown that even in the most extreme cases, i. e. insertion of hi-density polyethylene in the ports l
to simulate flooding, or insertion of a sample activation analysis vial t
j, containing pure enriched uranium oxide, the increase in reactivity is less than half that needed to take the system to criticality. Of course, these extreme conditions wS1 be precluded by other controls; however, they do illustrate that the CFX, once it is loaded to its design k,gg, can-not be taken to criticality under any credible operating conditions.
We suggest that.the data and experience obtained to date with the CFX confirms the inherent safety of the system as discussed in our license application. - Therefore, we respectfully request authorization to load the assembly to its design multiplication, k,gg = 0 990.
At that loading we will reconfirm the reactivity effects reported above, and will in addition be able to confirm that the expansion and temper-i>
ature coefficients are within safe limits.
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United States Atomic Energy Commission August 28, 1974
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Page 5 We will be pleased to present any further details required to complete your review, including a technical presentation to your staff in Bethesda if desired.
Sincerely yours,
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C. A. Preskitt Group Vice President CAP /km k.
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