ML20059D842
| ML20059D842 | |
| Person / Time | |
|---|---|
| Site: | Vallecitos Nuclear Center |
| Issue date: | 08/31/1990 |
| From: | Cunningham G GENERAL ELECTRIC CO. |
| To: | Michaels T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9009070203 | |
| Download: ML20059D842 (10) | |
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GE NucIcar Energy ce-nm cnv tvwics Nuow Ce?.ter IO ODX $(*O $?l60f.11 kktd 1%Mit"!Dh. {} [iO%6 August 31, 1990 Document Control Desk Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Attention:
T. S. Michaels
References:
1 License R-33, Docket 50-73, 2
Letter, T. S. Michaels to G. E. Cunningham; January 9,1990.
3 Letter, G. E. Cunningham to T. S. Michaels; March 15, 1990.
Dear Mr. Michaels:
l This letter is in response to several questions resulting from our submittal (Ref. 3) concerning the self-protecting properties of the NTR fuel.
Enclosed is a revised calculation which demonstrates that the fuel is self-protecting during operation and for approximately 29 days after shutdown.
Sincerely, clll:[
G. E. Cunningham Senior Licensing Engineer (415) 862-4330
/ca Enclosure 9009070203 900831 pf8 PDR ADOCK 05000073 p
August 29, 1990 cc:
J.
H.
Cherb G.
E.
Cunningham To: u.
R.
Smith E.
J.
Strain From:
B.
M.
Murray
Subject:
Calculated Dose Rate at 3 Feet From an NTR Fuel Element. Revision 1
Reference:
Murray to Smith, " Calculated Dose Rate at 3 Feet From an NTR Fuel Element", February 14, 1990.
This revi. ion to the referenced letter is to report a different calculated dose rate at three feet in air from an NTR fuel element.
The reason for this revision is to respond to comments from the NRC contracted technical reviewers at INEL.
The INEL people correctly felt that the previous assumption used for the fuel operation history, i.e.,
continuous full power operation for 1108 days immediately prior to the 18 cylic power steps, was nonconservative.
Therefore a model, as shown in Table 1, was set up to more closely represent the actual operating records of the NTR as shown in Table 2.
This model used a total of 95 steps as described below under "Foel Irradiation".
The result of this revised model was to reduce the decay times required to reach 100 Rem /hr. at three feet to approximately 19 days.
Calculations were made using computer codes RIBD which calculates the fission product inventory following periods of fuel irradiation and decay, and ISOSHLD which calculates dose rates at given distances from a described source geometry, to determine the unshielded dose rate at a distance of three feet from the side of an irradiated NTR fuel element.
The results of the calculations are shown on the attached tables and graphs.
The dose rate calculatioas do not take any credit t
for activated hardware or impurities in thu fuel element, only the gamma and bremsstrahlung photons from the 450 fission product isotopes calculated by RIBD.
l The description and valur.s used in the calculational model are given below:
Geometry:
A single fuel element was modeled as a homogenized cylinder of uranium and aluminum, surrounded by a layer of aluminum.
l The fuel cylinder dimensions are 2.68 inches diameter by l
15.16 inchet long.
The surrounding side layerHof aluminum is 0.07 inches chick and the end layer is 0.027 inches j
thick.
The dose rate measurement point is 36 inches from the outer surface of the surrounding shell, at the midplane of the cylinder.
The source volume was divided into 30 radial angles, 30 axial angles and 60 radial elements for the source integration.
'1-
s*
Densitiest The density of the uranium in the source cylinder is 0.18 grams per cubic centimeter.
The density of the aluminum in the source cylinder is 0.94 grams per cubic centimeter.
The density of the aluminum skin is 2.7 grams per cubic centimeter.
Fuel Irradiation:,
The burnup and operating power for a single fuel element was calculated as one sixteenth of the burnup and nominal operating power of the total core, 123 mwd at 30 and 100 kW.
The 95 step power history used for the RIB 0 fission product inventory calculation started with 0.001875 MW (30 kW reactor power) for 365 days folicwed by a shutdown of 1800 days.
The third step was a 0.00625 MW power step for 24 days followed by a 309.8 day shutdown period.
All following pnwer steps were at 0.0625 MW, The fifth power step was for 55.2 days followed by a 294.4 day shutdown.
The seventh power step was for 70.6 days followed by a 285 day shutdown.
The nineth power step was for 81 days followed by a 289.8 day shutdown.
The lith power step was for 75.2 days followed by a 281 day shutdown.
The 13th power step Las for 84 days followed by a 289 day shutdown.
The 15th powar step wss for 76 days followed by a 301.2 day shutdown.
The 17th power step was for 64.8 days followed by a 289.1 day shutdown.
The 19th power step was for 75.9 days followed by a 278.3 day shutdown.
The 21st power step was for 86.7 days followed by a 328.1 day shutdown.
The 23rd power step was for 36.9 days followed by a 323.1 day shutdown.
The 25th power step was for 42.9 days followed by a 328.6 day shutdown.
The 27th power step was for 36.4 days followed by a 323.5 day shutdown.
The 29th power step was for 41.5 days followed by a 338.5 day shutdown.
The 31st power step was for 26.5 days followed by a 337.8 day shutdown.
The 33rd power step was for 28.2 days followed by a 337.9 day shutdown.
The 35th power step was for 27.1 days followed by a 334.2 day shutdown.
The 37th power step was for 30.8 days followed by a 324.5 day shutdown.
The 39th power step was for 40.5 days followed by a 317.4 day shutdown.
The 41st power step was for 48.6 days.followed by a 317.6 day shutdown.
The 43rd power step was for 47.4 days followed by a 27 day shutdown.
The 45th power step was for 4 days followed by a 27 day shutdown, this typical one month power cycle.
This monthly represents a l
power / shutdown cycle is repeated for a total of four months followed by a 0.8 day shutdown.
Next is a daily repeating 0.2 day power operation with a 0.8 day shutdown.
The weekend shutdown lasts for 2.8 days.
This weekly operating cycle is repeated 4.4 times.
This power history resulted in a total power operation time of 1465 days, over a total elrpsed time of 9283 days (25.4 years).
Each power step was equal to the mean actual burnup for the respective 2
1 extended time period.
A table of the steps used as the power history model is attached as TABLE 1.
The recorded NTR power history summary, from which this power step sequence was derived is attached as TABLE 2.
To determine the self protection period, nine decay times following shutdown were chosen; 10, 15, 20, 25, 30, 35, 40, 50, and 60, days.
The other fuel parameters used as RIBD input were:
2 Average thermal neutron flux - 5.6E11 n/cm j,,,,
U 235 absorption cross section - 683 barns.
Initial mass of U 235 (93.17%) in core 3719 graus (3992 grams of uranium total).
U-239 production rate - 3.6E 4 grams per mwd..
..._-...-.... ~ - - - -
s' RADIOACTIVE ISOTOPE BUILDUP AND DECAY, RIBD 1, GE APED version of the-RSIC distributed code RIBD, ccc 137, memorandum SCER 132,
(
gec. 1968.
i-ISHLD01, the GE NE version of the RSIC distributed code ISOSHLD, Kernel Integration. Code Geeeral Purpose Isotope i
Shielding Analysis. CCC 79.
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l 21-Jun-90 O
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ASSUMED NTR FUEL 'LEMENT POWER HISTORY MODEL
=======u=========================
=====
BURNUP =
/ '.375 MWD AT 1.075 AND 6.25 kW. AS OF 6/1/90 OPERATING BURNUP PERIOD PERIOD PCWER, MW TIME, DAYS TOTAL, MWD END DATE APR '90 0.000000 27.O 7.634 04/28/90 APR '90 0.006250 4.0 7.654 05/02/90 MON O.000000 O.B 7.659 05/03/90 O.006250 O.2 7.660 05/03/90 TUES 0.000000 0.8 7.660 05/04/90 O.006250 0.2 7.662 05/04/90 WED O.000000 O.8 7.662 05/05/90 O.006:50 O. 2 7.663 05/05/90 THUR O.000000 O.8 7.663 05/06/90 O.006250 O.2 7.664 05/06/90 FR1 O.000000 O.B 7.664 05/07/90 0.006250 0.2 7.665 05/07/90 SAT / SUN O.000000 2.8 7.665 CS/10/90 MON O.006250 O.2 7.667 05/10/90 0.000000 0.8 7.667 05/11/90 TUES 0.006250 O.2 7.668 05/11/90 C.000000 O. 8 7.668 05/12/90 WED O.006250 0.2 7.669 05/12/90 O.000000 O.8 7.669 05/13/90 I
THUR O.006250 0.2 7.670 05/13/90 0.000000
- 0. 8 7.670 05/14/90 FRI O.006250 C.2 7.672 05/14/90 SAT / SUN O.000000 2.8 7.672 05/17/90 MON O.096250 O. 2 7.673 05/17/90 0.000000 O.8 7.673 05/18/4O TUES 0.006:50
- 0. 2 7.674 05/18/90 l
0.000000 O. 8 7.674 05/19/90 WED O.OO625C O.2 7.675 05/19/90 O.000000 O.8 7.675 05/20/90 THUR O.006250 0.2 7.677 05/20/90 0.000000 0.8 7.677 05/21/90 FRI O.006250 O. 2 7.670 05/21/90 SAT / SUN O.000000 2.8 7.678 05/24/90 MON O.006250 O.2 7.679 05/24/90 t
O.000000 O.8 7.679 05/25/90 TUES 0.006250 O. 2 7.680 05/25/90 0.000000 O.8 7.600 05/26/90 WED O.006250
- 0. 2 7.682 05/26/90 C.000000 O.B 7.682 05/27/90 THUR O.006250 0.2 7.683 05/27/90 O.000000
- 0. 8 7.683
,05/28/90 FRI O.006250 0.2 7.684
'05/28/90 SAT / SUN O.000000
- 2. 8 7.684 05/31/90 MON O.006250 0.2 7.685 05/31/90 C.000000 O. 8 7.685 06/01/90 TUES 0.006200 0.2 7.687 06/01/90 O.000000 O.8 7.687 06/O2/90 TABLE 1'
. 21-Jun-90 RECORDED NTR OPERATING HISTORY
=.....................................................
HOURS AT HOURS AT CALCULATED YEAR 30 kW 100 kW MWD 1960 500 0.63 1961 340 0.43 1962 280 0.35 1963 1228 1.54 1964 1142 1.43 1965 1200 1.50 1966 1200 1.50 1967 1200 1.50 1968 1100
).38 1969 575 575
- 3.11 1970 1325 5.52
.g 1971 1695 7.06 m
1972 1945 8.10 1973 1804 7.52 1974 2015 0.40 1975 1824 7.60 1976 1555 6.48 1977 1821 7,59 1978 2000 8.67 1979 885 3.69 1980 1029 4.29 1981 873 3.64.
1982 995 4.15 1983 635 2.65 1984 677 2.82 1985 650 2.71 1986 740 3,09 1987 973 4,05 1988 1166 4.86 1989 1137 4.74 1990 490 (ASSUMED) 2.04 TOTALS:
8765 HOURS 26889 HOURS 122.99 MWD TABLE 2 r
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8/30/1990-
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. TABLE 3 i
DOSE RATE 3' FROM END OF NTR FUEL ELEMENT VERSUS DECAY TIME i
INITIAL U.235 WEIGHT -
249.5GRANS
'I OPERATING POWER -
.00625MW OPERATING TIME --
9649 DAYS i
CALCULATED DECAY TIME, DAYS. DOSE RATE.-R/h
_1 0
3994 1
158.3 2
123 3~
.109.3 l
4 101.1 5
95.15 10 76.92
'15 66.49 1
20 59.04
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30 49.91
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