ML20051E552
| ML20051E552 | |
| Person / Time | |
|---|---|
| Site: | 05000054 |
| Issue date: | 05/06/1982 |
| From: | Office of Nuclear Reactor Regulation |
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| Shared Package | |
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| References | |
| NUDOCS 8205170030 | |
| Download: ML20051E552 (7) | |
Text
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UNITED STATES g
g NUCLEAR REGULATORY COMMISSION gg
.j WASHINGTON, D. C. 20555 o-a
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SAFETY EVALUATION REPORT FOR UNION CARBIDE REQUEST FOR SINGLE ENCAPULATION FOR IN-CORE 10 DINE PRODUCTION AND INCREASE TO 1000 Ci PER CAPSULE P
Background
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tinion Carbide in a letter dated June 2,1981 and modified January 9,1982 requested a modification to their Technical Specification 3.5.2.c that would change their current double encapsulation of in-core target material to single encapsulation and increase the quantity of iodine per capsule to 1,000 Ci.
The staff requested LANL to review and evaluate the requested amendment.
The complete report is included as Attachment A.
l Safety Evaluation Summary Two accident scenarios were considered by LANL:
1.
A release of the capsule contents while in the core (capsule melt)
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with gaseous iodine transit through 7 m of water.
I 2.
A release from the capsule caused by mechanical damage, material defects, or improper seals with gaseous iodine transit through 3.1 m of water.
l A - Release from Capsule Melt For a target and capsule melt, it was assumed tnat 100% of the iodine will be released to the reactor pool. This felt to be a conservative value because the iodine release value should be must less, inasmuch as the temperature is a relatively low 126*C and that any released iodine would l
'still have to find, reach and traverse'any break or rupture in the capsule.
Water transfer coefficients range from 10-2 to 10-4 for depth between 3m-7m. There appears to be little dependency on rate of iodine injection or size of bubble formed during the release process. There is a large dependency due to the carrier media. The more vapor in contact with the iodine formed, the smaller the transfer coefficient.
Results and Conclusions For the capsule melt scenario, the amount of iodine reaching the surface l
is 10-L 820517003o
' For the capsule damage scenario and the shallowest depth of water [which is the transfer chute], the amount of iodine reaching the surface = 2.5x10-4 Therefore, for the above accident scenarios, the amount of iodine released to. the water = 1,000 Ci Iodine x 10-4 = 0.1 Ci.
Iodine reaching surface of pool '= 0.1 Ci to 0.25 C1.
The iodine that reaches the surface will be:
(1) diluted by the containment building volume (7000 m3)
(2), plate out on the various surfaces for a factor of 2 reduction (3) further reduced by the emergency exhaust system 200 CFM [9.44x10-2 m3/sec]
(4) reduced by absorbtion by the charcoal filters by a factor of approximately 20.
Assuming overall mixing in the containment, the iodine concentration in the containment vessel is 0.1 Ci 7x109 cc =.014 x10-3 uc/cc building following escape from the capsule, and the concentration leaving the charcoal filters is 0.1 Ci x 9.44x10-2,3-sec
= 3.37x10-8 Ci 7x103 m3 x 2x20 sec The concentration of the site boundary using the Union Carbide calculated dispersion factor of 1.8x10 sec m
for a 0-2 hour period = 3.37 x 10-8 Ci x 1.8x10-4 sec sec m
= 6.07x10-12 Ci = 6.0x10-12 uCi m
cc of 10')g0 Appendix B, Table III indic'ates a pemissible offsite concentration 10 CFR uCf. The exposure of a person standing offsite directly in the plume for a continuous 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> period is, therefore, less than that allowed in 10 CFR 20.
Conclusion Though it is recognized that the iodine inventory will be materially increased to 1000 Ci per irradiated capsule, calculations for I-131 concentrations in the event of an incident utilize conservative assumptions, and they indicate an offsite concentration that is only 1/100th of MPC, as delineated in 10 CFR Part 20, Appendix B, Table II.
It is concluded, therefore~, that no significant hazard can accrue from the proposed operations.
Accordingly, the staff concludes that a single encapsulated capsule containing 1000 Ci of iodine can be safely handled in the Union Carbide reactor and that there is reasonable assurance (a) that the activity authorized can be conducted without endangering the health and safety of the public and (b) that such activities will be conducted in compliance with the regulations of the Commission set forth in 10 CFR Chapter 1.
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'APPENDlX b
EVALUATION OF THE UNION CARBIDE REACTOR TECHNICAL SPECIFICATION 3.5.2.c (5) o j'
I.
INTRODUCTION I have evaluated the proposed amendment of a Technical Specification for i
the Union Carbide nuclear reactor, License No. R-81, Docket No. 50-54. " Union Carbide has requested that Technical Specification 3.5.2.c (5) read, "The 131 iodine inventory of a single capsule shall be' limited to 1000 Ci 7
e dose-equivalent." The following documents were reviewed during the evaluation.
o Letter from Union Carbide to the NRC dated June 2, 1981.
)'
131
Subject:
Proposed Change in Technical Specifications to Allow 500 Ci I equivalent for a single capsule.
o Letter from the NRC.to' Union Carbide dated September 19, 1981.
Subject:
Questions about the proposed technical specification change outlined in June 2,1981, letter.-
o Letter;from Union Carbide to the NRC dated October 15, 1981.
Subject:
Answers to questions generated in September 19, 1981, i
letter.
o Letter from Union Carbide to the NRC dated February 9,1982.
Subject:
Proposed change in technical specifications to allow 131 1000 C1 I equivalent for a single capsule.
II.
BACKGROUND 131 In an earlier evaluation (1973) of the allowable I concentrations for the Union Carbide capsules by the NRC staff, they determined "that 131 ~ equivalent be doubly capsules containing more than 70 Curies I
encapsulated to rcduce the probability of occurrence of capsule failure." The following assumotions were made by the NRC staff.
1.
100% of the noble gas and' iodine inventory is released from a capsule.
2.
100% of the noble gases appear in the containment building air.
3.
10% of the iodines appear in the containment air.
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4.
Mixing takes place with only 50% of the building air.
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I With these assumptions, the NRC staff also concluded (and verified by l
131 this study) that "the failure of capsules containing less than 70 Ci 7
aquivalent of fission products will result in onsite personnel exposures that do not exceed those permitted in 10 CFR Part 20."
When assumptions 1 and 3 are combined, the amount of iodine assumed to reach the pool surface is.10% of the capsule inventory, which is an extremely conservative value.
o III.
PROPOSAL EVALUATION We considered two basic scenarios to evaluate this proposed change.
I 1.
A release of the capsule contents while in the core (capsule melt) with gaseous iodine transit through 7 m of water.
2.
A release from the capsule caused by mechanical damage, material defects, or improper seals with gaseous iodine transit through 3.1 m of water.
Long-term release of iodine from the pool surface was not considered to be as important as the immediate release determination, and therefore, it was not factored into the evaluation.
It was also de,termined that the iodine release from the pool will be the predominant f actor in determining the dose received by personnel within and outside the facility.
A.
Release From Capsule Melt The iodines will interact with the molten capsule materials if the capsule is melted during irradiation in the core.
The exact mechanisms are not well understood, but the release is nearly complete.
For the purposes of this study it has been assumed that 100% of the iodine is released from the capsule to the water environment when melting occurs.
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B.
Release From Capsule Mechanical Damage Union Carbide's use of the methodology in the proposed ANS standard 5.4 is unsuitable.
However, it is obvious that the iodine release from a 0
low-temperature, thin-layered oxide at a peak temperature of 126 C is less than 100%. The measurements of fission product release performed by Union Carbide in 1973 are probably some of the best thin-film oxide data available.
There is a question about the appropriateness of the iodine release estimation e
because of the difficulty of making such a measurement.
The estimation of the release fraction for the noble gases (2.5%) is relatively easy to make and is almost surely an upper bound for the release fraction of the iodine.
I am not aware of any case where the iodine release from a material at the temperatures being considered is greater than the release fraction of the noble gases.
Thus, the release fraction for the thin-layered, low-temperature oxide coating is chosen as 2.5%.
It should also be remembered that if capsule integrity is lost in this scenario, the breach should be very small relative to the inside surf ace area of the capsule, and therefore, once the iodine is released from the oxide it must still reach the break in the capsule.
C.
Water Transfer Coefficient I
A number of measurements have been performed -4 to determine the amount j
of iodine transmitted through water under various conditions.
In addition to l
these measurements, several accidents have yielded estimates of iodine 5
transmission through water. These include studies of the TMI accident, the
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i SIL0E accident, and the SL-I accident.
The amount of water between the source point and eir environment (surface of water) ranged from 0.2 m to 7.5 ni.
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Several experiments were performed using actual reactor power excursions, and others were performed using various forms of subsurface iodine injection with different carrier medias. The results indicate transfer coefficients 'of around 10-2 and'10-4 for 3-m and 7-m depths, respectively.
Also, the l
experiments show little if any dependency on rate of injection of iodine or l
size of vapor bubble formed during the injection process.
However, there is i
great dependency on the carrier media used in the injections.
The more vapor
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in contact with the iodine formed, the smaller the transfer coefficient.
IV. RESULTS AND CONCLUSIONS The combination of results in the last section indicates the following 6verall results for the two scenarios considered.
1.
Capsule Melt Scenario.
The amount of iodine reaching the i
surf ace following a capsule melt in the core region is (1.01 (10-4) = 1 x 10-4 2.
Mechanical Damage Scenario. The amount of iodine reaching the surf ace following a loss of capsule integrity in the transfer chute (shallowest de transfer) is (0.025) (10-2) =pth of cao}ule during 2.5 x 10-4 Both of these overall transfer coefficients are very small in comparison with the 0.1' assumed in the 1973 evaluation.
Because Union Carbide has asked for an increase of 15 in capsule inventory for iodine (70 Ci to 1000 Ci), a similar decrease in an overall tranfer coefficient is required.
Both of the scenarios considered give coefficients better than that required, with a built-in safety factor.
Therefore, I see no reason to reject Union Carbide's 131 proposal to increase the single capsule iodine inventory to 1000 Ci 7
equivalent.
G e
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REFERENCES 1.
J. R. Smith, " Iodine Cleanup in a Steam Suppression System," AERE-R.4882, 1957.
2.
W. E. Kessler, et. al., "Snaptran 2/10 A-3 Experiments - Destructive Test Results, 100-17019, 1965.
3.
E. de Monta.ignere, et. al., " Diffusion de L'iode travers l' eau",
CEA-R-3199, 1967.
9 4.
Diffey, H. R., et.'al., " Iodine Clean-up in a Steam Suppression System,"
International Symposium on Fission Product Released and Transport Under Accident Conditions, Oak Ridge, Tennessee, CONF-65047, Vol. 2, ppg. 776-804 (19651.
5.
Letter report to the NRC, August 14, 1980, from A. P. Malinaruskas, D. O.
Campbell and W. R. Stratton,
Subject:
Behavior of Cesium and Iodine in'a LWR following a loss-of-coolant accident.
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