ML19326C344
| ML19326C344 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 03/01/1976 |
| From: | Cavanaugh W ARKANSAS POWER & LIGHT CO. |
| To: | Zieman D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8004220891 | |
| Download: ML19326C344 (6) | |
Text
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I N.C ocmu 196 u.c. NUCLEAA KECULATO :V CCA SiON DOCKET NUM BE R
$ is.m 50-313 NRC DISTRIBUTION pOn PART 50 DOCKET MATERIAL, TJ:
0.L. Ziemann FROM:
^78 Arkansas-Power & Light Co.
3-1 76 Little Rock, Arkansas W. Cavanaugh, III o*78 ajcj',vyg OLETTEm CNOTOM12ED PROP INPUT FORM NUM8ER OF COPIES RECEIVED
} COPY EuNC LAssielE o Om'08NAL dn
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Ltr. re. our ite. of 10-7-75...
Ltr. trans the following.......
Consisting of revision:: to Tech. Specs. with regard to Effects of Thiosulfate Concentration on the Thyroid Dose.....W/ Attached Tables...
(1 Signed & 39 C. Cys. Received)
THIS DOCUMENT CONTAINS Arkansas # 1 PI.ANI NAME*
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SAFETY FOR Ar. TION /INFORMATION ENVIRO qaR 1.c;_76 ASSIGNED AD :
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.b H EL PIN G BUILO ARKANSAS A R K /A N S A S P O W E R & L I G H T C O M P A N Y erH & LOUISl AN A ST AeEr5. LITTLE AoCK. A AK ANS AS 722C3. (501) 371-4000 March 1, 1976
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Director of Nuclear Reactor Regulation r
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l[ u'.s. g' ATTN: Mr. Dennis L. Ziemann, Chief Operating Reactor Branch #2 ug.c U. S. Nuclear Regulatory Commission
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Washington, D. C.
20555 S
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Subject:
Arkansas Power & Light Company
,s Arkansas Nuclear One-Unit 1 Docket No. 50-313 License No. DPR-51 Proposed Technical Specification Changes Gentlemen:
Attached find our evaluation concerning the effect that the reduction in sodium thiosulfate concentration in the Reactor Building Spray System will have on iodine removal capability, as requested by Mr. Bill Converse of your staff. This information is submitted as a supplement to our original request for changes to the technical specifications concerning tank level and chemical concentration limits in the Reactor Building Spray System, as was transmitted on October 7,1975.
Whereby, with this supplemental information, we request those changes as j
were originally proposed in the aforementioned letter.
- l Very truly yo
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f William Cavanaugh II Manager, Nuclear Se es WC:ay Attachment bIbb Q, usueca vioou sour-uriuries sysreu ro.A
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- N 3
Effect of Thiosulfate Concentration on the Thyroid Dose A study was conducted to determine the effect on the thyroid dose of lowering the sodium thiosulfate spray solution concentration, from the design value of 1.0 wt % to the current technical specification value of 0.66 wt %.
The calculation determined the net percentage change in the FSAR two-hour thyroid dose at the exclusion area boundary (EAB) and the 30 day thyroid dose at the low population zone (LPZ).
The calculation was based upon the same assumptions and parameters noted in Chapter 14 of the FSAR except for the iodine fraction values. The old Safety Guide 4 iodine fractions (85% elemental,10% organic, 5% particulate) used originally to calculate the thyroid doses for the Maximum Hypothetical Accident (MHA) in Chapter 14 of the FSAR were replaced by Regulatory Guide 1.4 iodine fractions (91% elemental, 4% organic, 5% particulate).
The iodine removal rate for each iodine species is shown in the attached Table 1 for sprays with different sodium thiosulfate concentration. The removal rates for the elemental and particulate forms of iodine are assumed to be independent of the thiosulfate concentration, because:
a) the chemical reaction rate between thiosulfate and elemental iodine is so fast at these high concentrations (approximately 1000 times greater than required for complete reaction) that the rate of elemental iodine absorption by the spray drops is controlled by the relatively slow diffusion rate of iodine through the gas-film surrounding each drop and is essentially unaffected by several fold changes in the thiosulfate concentration; and, b) the removal rate of particulate iodine is controlled by the physical scrubbing action of the spray drops, and the cheraical action of the thiosulfate has little or no effect.
The chemical reaction rate between thiosulfate and organic iodine is slow enough that the concentration of thiosulfate does have a significant affect on the rate of organic iodine absorption by spray drops. The effect of thiosulfate concentration (c) on the organic iodine re yal rate (A) was calculated using the following empirical relationship.
1 (C /C )
A2"A 2 1 The relative-thyroid doses at the EAB and LPZ were calculated for three
~different spray conditions and are summarized in Table 2.
Case 1 (base case) assumes operation with one spray header, Regulatory Guide 1.4 iodine fractions, and a constant sodium thiosulfate concentration of 1.0 wt% in the spray solution. The spray is turned off after 200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> of operation. Also, the thyroid doses were adjusted to account for 50% of the iodine activity leaking from the containment being processed by a 90%
i efficient penetration room ventilation system.
1
's Case 2 uses the same parameters and assumptions as in Case 1, except the organic iodine removal rate is 0.08124 hr-1 which corresponds to a constant sodium thiosulfate concentration of 0.66 wt % in the spray.
The resultant two-hour and 30-day thyroid doses (as compared to the base case) would increase by 0.51% and 3.2%, respectively.
Case 3 assumes a more realistic approach of calculating the 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 30 day thyroid doses by taking credit for the higher sodium thiosulfate concentration in the spray header during the injection period. After suction is switched to the sump, the spray solution sodium thiosulfate concentration will be at the technical specification value of 0.66 wt %.
A conservative estimate of the sodium thiosulfate concentration in the one header during the 42 minute injection period is 3.0 wt %.
Results of Case S calculation shows that by spraying with a 3.0 wt % sodium thiosulfate solution for the 42 minute injection period followed by a spray containing 0.66 wt % thio results in a two-hour thyroid dose at the EAB which is 0.17% lower than Case 1.
On the other hand, this short spray period with 3.0 wt % thio has very little affect on the 30 day thyroid dose, which still shows an increase of 3.1% compared to Case 1.
Reference (1) " Effectiveness of Sodium Thiosulfate Spray for Iodine Removal", BAW-10024, January 1971, p. 5-24.
6
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Table 1 Effect of Thiosulfate Concentration on Iodine Removal Rates Iodine Removal Rates / Iodine Form Sodium Thiosulfate Concentration (wt%)
Elemental Organic Particulate 1.0 9.533*
0.1000**
0.45 0.66 9.533*
0.08124**
0.45 3.0 9.533*
0.1724**
0.45 i
- Elemental iodine removal rate 105 FH-
=
V Where:
F = spray flow rate,1500 gpm (one header operation)
H = fall height of spray,115 ft V = Free volume of Containment Building, 1.9 X 106 gg3
- The organic iodine removal rate is half of the indicated value after the first 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> due to the lower temperature in the reactor building.
T m,
Table 2 Effect of Thiosulfate Concentration on the Thyroid Doses Iodine Fractions Change in Thyroid Dose C:se Number Elemental Organic Particulate 2 Hour (EAB) 30 Day (LPZ) 1*
0.91 0.04 0.05 2*
0.91 0.04 0.05
+0.51%
+3.2%
3*
0.91 0.04 0.05
-0.17%
+3.1%
- Definition of Cases:
Case 1 - Base case, one header operation, sodium thiosulfate concentratien of 1.0 wt%, sprays turned off after 200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br />, 50% of the iodine leakage from the containment is processed by the penetration room ventilation i
system.
Case 2 - One header operation, sodium thiorulfate concentration of 0.66 wt%,
spray turned off after 200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br />, 50% of the iodine leakage from the containment is processed by the penetration room ve-tilation system.
Case 3
.One header operation, initial 42 minute of spray containing 3.0 wt%
sodium thiosulfate followed by 0.66 wt% sodium thiosulfate spray for 199.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, 50% of the iodine leakage from the containment is processed by the penetration room ventilation system.
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