ML18058B918
| ML18058B918 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 07/08/1993 |
| From: | Rogers D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9307150082 | |
| Download: ML18058B918 (4) | |
Text
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Palisades Nuclear Plant:
27780 Blue Star Memorial Highway, Covert, Ml 49043 July 8, 1993 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 David W. Rogers Plant Safety and Licensing Director DOCKET 50-255 - LICENSE DPR PALISADES PLANT - TECHNICAL SPECIFICATIONS CHANGE REQUEST - DELETION OF HYDRAZINE REQUIREMENTS.
On June 12, 1992, Consumers Power Company (CPCo) requested an amendment to Technical Specifications which would remove the requirements for hydrazine in the Palisades Containment Spray Additive System.
In a follow up telephone conversation on June 16, 1993 the NRC requested additional information on iodine related engineering factors involved in the analyses supporting that Technical Specification change request. This letter provides the requested information.
The engineering factors affecting iodine removal from a post-accident containment atmosphere are: 1) the First Order Removal Coefficients or "iodine removal rates," for Spray Removal and Wall Deposition of Elemental Iodine, and for removal of Particulate Iodine, 2) the Iodine Partition Coefficient, and 3) the Iodine Decontamination Factor. These engineering _factors are used to calculate the concentration of iodine which is to be assumed present in the containment atmosphere following an accident and, therefore, in any leakage from the containment.
The guidance provided for calculation of these engineering factors in the Standard Review Plan (SRP), Section 6.5.2, "Containment Spray as a Fission Product Cleanup System," has changed significantly over the past 15 years. That change in guidance eliminates the effects that the presence of hydrazine had on the calculation of these engineering factors.
We have concluded that, since:
a)
The revised SRP guidance provides no reduction in the calculated concentration of iodine in the post accident containment atmosphere due to the addition of hydrazine, and b)
In those places where CPCo analyses formerly took some credit for the presence of hydrazine, the new methodology results in higher iodine removal rates (without any reference to, or credit taken for, hydrazine) than CPCo's former methodology did with hydrazine, that the requirement for hydrazine may be removed from the Technical Specifications without any adverse effect.
In our June 12, 1992 amendment request, we only discussed the iodine removal rate, since the partition coefficient and decontamination factor used in our calculations had not changed significantly. Since we discussed only the iodine rem.oval rate, the NRC reviewers were uncertain as to the effects of removal of hydrazine requirements on our calculation of the other associated engineering factors.
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Each of the engineering factors is discussed below.
For brevity, those calculational methods and resultant values of the engineering factors which are associated with the MHA analysis of record are referred to as "former"; those associated with SRP Section 6.5.2, Revision 2 methodology are referred to as "revised."
- 1)
Iodine Removal Rates:
2 The iodine removal rates are a measure of the rate at which iodine is removed from the containment atmosphere by surface deposition, or "plate out," and by dissolution in the spray droplets, or "spray washout".
Two distinct removal rates are involved; one for particulate iodine, and one for elemental (gaseous) iodine.
The former iodine removal rates are identical to those used by the NRC in their analyses associated with Amendment 31 (November 7, 1977) to the Palisades Technical Specifications; the revised rates are calculated in accordance with methodology found in Revision 2 of the SRP, Section 6.5.2.
a)
Particulate Iodine Removal Rate:
The former particulate iodine removal rate was 1.0; the revised rate is 4.43.
The difference between these rates is due solely to a change in calculational methodology, and not due to the proposed removal of hydrazine.
Neither former nor revised calculation methodology assigns higher particulate iodine removal rates due to the presence of hydrazine.
The revised rate is unaffected by the proposed removal of the hydrazine Technical Specification requirements.
b)
Elemental Iodine Removal Rates:
Two elemental iodine removal rates were formerly used: a value of 10.0 was used for the period when hydrazine is being added to the containment spray water, and 0.42 for the periods when hydrazine is not being added.
The revised elemental iodine removal rate is 21.3 per hour, whether hydrazine is being added or not.
Spray removal rates calculated in accordance with SRP 6.5.2 Revision 2 are not affected by hydrazine addition to containment sprays.
The spray removal rate for elemental iodine calculated for Palisades using the revised methodology is 20.0. The actual calculated value was higher, but is limited by SRP 6.5.2 Revision 2 to a maximum value of 20.0. The revised methodology also allows credit for wall deposition of elemental iodine, for which a value of 1.3 is appropriate for Palisades.
The resulting total elemental iodine removal rate is 21.3. These updated values for Palisades are valid regardless of whether hydrazine is added to containment sprays or not. Therefore, the revised elemental iodine removal rate is unaffected by the proposed removal of the hydrazine Technical Specification requirements.
- 2)
Iodine Partition Coefficient:
The -partition coefficient is, basically, the ratio of the concentrations of iodine in the containment sump solution and in the containment atmosphere.
The former iodine partition coefficient was 1000: the revised partition coefficient is 1250.
The former partition coefficient value was taken from Figure 6.5.2-1 of 3
SRP 6.5.2, Revision 1 which gives partition coefficients for spray solutions containing sodium hydroxide.
Palisades' operating procedures direct the addition of sodium hydroxide to the ECCS pump suction to maintain the sump solution (and thereby the spray solution) pH between 7 and 8.
Although Table 6~5.2-1 of SRP 6.5.2, Revision 1 allows a partition coefficient of 5000 for solutions containing 50+/-5 ppm of hydrazine, that value was not used in the Palisades calculations.
The text in SRP 6.5.2, Revision 1 describes the values in that table as instantaneous elemental iodine partition coefficients.
The references provided in SRP 6.5.2, Revision 1 present methods for calculating elemental iodine spray removal rates that use an instantaneous partition coefficient.
The partition coefficient which should be used to calculate the iodine decontamination factor, however, is the equilibrium, rather than the instantaneous, coefficient. Hydrazine added to sprays will react with oxygen to form water and nitrogen in the sump solution, and will also decompose to ammonia.
Therefore, the hydrazine would not be present in the long term to enhance iodine retention in the sump solution (or to increase the iodine partition coefficient) and a partition coefficient of 5000 would be inappropriate for calculation of the decontamination factor.
The revised iodine partition coefficient was calculated following the references provided in SRP 6.5.2 Revision 2.
This revised value was taken from Figure 6 of NUREG/CR-4697, "Chemistry and Transport of Iodine in Containment," (Reference 15 of SRP 6.5.2, Revision 2) based on the expected containment sump solution temperature, pH, and iodine concentration for the MHA.
This revised value of 1250 for the equilibrium partition coefficient is valid for Palisades regardless of whether hydrazine is added to containment sprays or not. Therefore, the revised iodine partition coefficient is unaffected by the proposed removal of the hydrazine Technical Specification requirements.
- 3)
Iodine Decontamination Factor:
The iodine decontamination factor (OF) is the maximum amount of iodine that can be credited as removed from the containment atmosphere before an equilibrium is reached.
The iodine DF is based on the partition coefficient, the containment air volume and the containment sump volume, with the partition coefficient being the only variable which is not fixed by the plant physical design.
The former iodine DF was 25.57; the revised DF is 32.51.
The former DF was based on an partition coefficient of 1000 using the equati-0n provided in SRP 6.5.2, Revision 1.
The revised OF is based on an partition coefficient of 1250 using the same equation, which appears in both Revision 1 and Revision 2 of the SRP.
This revised OF of 32.51 is, like the partition coefficient on which it is based, valid for Palisades regardless of whether hydrazine is added to containment sprays or not. Therefore, the revised iodine OF is unaffected by the proposed removal of the hydrazine Technical Specification requirements 4
The table below summarizes the calculated engineering factors for iodine removal for the former and revised MHA analysis.
The effect of hydrazine addition is shown for both sets of values.
As can be seen from the table, the iodine removal rates, partition coefficient and maximum decontamination factor calculated ~sing the "revised" methodology of the 1988 revision to SRP 6.5.2 are greater than those used in the "former" MHA analysis of record in the current Palisades UFSAR.
This improvement occurs without consideration of the addition of hydrazine to containment sprays. Therefore, it can be directly inferred that removal of the hydrazine Technical Specification, requirements at Palisades would have no adverse impact on the radiological consequences of an accident.
Palisades Iodine Engineering Factors FACTOR WITH HYDRAZINE WITHOUT HYDRAZINE Particulate Iodine Revised:
4.43 Revised:
4.43 Removal Rates Former:
1.0 Former
1.0 Elemental Iodine Revised:
21.3 Revised:
21.3 Removal Rates Former:
10.0 Former:
0.42 Partition Revised:
1250 Revised 1250 Coefficients Former:
1000 Former:
1000 Decontamination Revised:
32.51 Revised:
32.51 Factors Former:
25.57 Former 25.57 Representatives of Consumers Power Company are available to meet with the NRC to provide additional explanation, if such a meeting would assist the reviewers.
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David W. Rogers Safety and* Licensing Director CC Administrator, Region III, USNRC Resident Inspector, Palisades At'tachments