ML20198M369
| ML20198M369 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 12/23/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20198M355 | List: |
| References | |
| NUDOCS 9901050320 | |
| Download: ML20198M369 (6) | |
Text
a cuou UNITED STATES a
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s, SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO194 TO FACILITY OPERAT!NG LICENSE NO. NPF-6 ENTERGY OPERATIONS. INC.
ARKANSAS NUCLEAR ONE. UNIT NO. 2 DOCKET NO. 50-368
1.0 INTRODUCTION
By letter dated May 18,1998, as supplemented by letter dated December 8,1998, Entergy Operations, Inc. (the licensee) submitted a request for changes to the Arkansas Nuclear One, Unit No. 2 (ANO-2) Technical Specifications (TS). The requested amendment deletes the ANO-2 TS 3.6.2.2 and 4.6.2.2 requirements for the sodium hydroxide addition system and adds new limiting conditions for operation, action statements, and surveillance requirements for the trisodium phosphate baskets which are to be installed during the next ANO-2 refueling outage (2R13). The licensee proposes to modify the associated bases accordingly.
The information in the December 8,1998, submittal provided clarifying information and did not expand the scope of the original application as initially noticed, or change the staff's proposed no significant hazards determination published in the FederalRegister on October 21,1998 (62 FR 56241).
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2.0 BACKGROUND
In the original design of ANO-2, sodium hydroxide additive was used to control the pH of the containment spray solution in order to enhance removal of e'emental lodine from the post-accident containment atmosphere and prevent stress corrosion cracking of austenitic steel components. The limits on water volumes, boron concentrations, and the sodium hydroxide system resulted in a long term pH value of between 8.8 and 11. At the time the plant was designed it was thought that these high pH values were required to remove elemental lodine.
As more information was gained on iodine removal, it was found that in an iodine free solution the pH could be maintained at much lower values and still be effective in removing elemental iodine.- In addition, it was found that some of the lodine is in a cesium iodide form and could dissolve in water regardless of its pH There was no need, therefore, to control the pH of the spray water as long as it was free of dissolved iodine. However, when iodine containing water is used, as for example, during the recirculation phase spraying, the pH has to be maintained above 7, otherwise reevolution of dissolved iodine will occur. A pH higher than 7 is also necessary to minimize the potential for chloride induced stress corrosion cracking of austenitic 9901050320 981223 DR ADOCK 050003 8
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k l steel components exposed to spray water and minimize evolution of hydrogen from the corrosion of zinc on galvanized surfaces and in zine based paints. These requirements for minimum pH are discussed in Sections 6.1.1 and 6.5.2 of the Standard Review Plan (SRP). In the submittal, the licensee proposes to use borated water with the lowest pH of approximately 4.4 and control the sump water pH above 7 (minimum value of 7.06 and between 7.25 and 8.07 based on the target volumes of trisodium phosphate) using the passive design of baskets containing trisodium phosphate located in the containment sump. The licensee has proposed to locate appropriate controls for the passive system in amended Technical Specification 3/4.6.2.2, " Trisodium Phosphate (TSP)." The associated TS Bases would also be modified.
3.0 EVALUATION 3.1 lodine Removal from Containment Atmosobere The licensee proposes that during the injection phase of the plant response to a loss-of-coolant l
accident (LOCA) (i.e., the water source for emergency core cooling and containment spray
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systems is the refueling water tank), that containment spray will be operated with borated water 1
without sodium hydroxide additive. The pH of this water could be as low as approximately 4.4.
l Using the information currently available on iodine removal and the guidance provided in Section i
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6.5.2 of the SRP, the licensee has demonstrated that this low value of pH would not affect removal rates of elemental and particulate iodine from the post-accident containment atmosphere. These rates are determined by the first-order removal coefficients which are independent of pH and are not affected, therefore, by elimination of the pH controlling additive.
The same applies to the removal coefficient for particulate iodine which is controlled by the j
hydrodynamic characteristics of the sprays.
During the spray recirculation phase, water for the emergency core cooling and containment spray systems will come from the sump and will contain dissolved iodine removed from the containment atmosphere during the injection phase. In a radiation environment, this iodine could be revolatilized and released to the containment atmosphere if the pH of the solution is acidic. In order to prevent this from happening, the pH of the sump solution should be kept above 7. The licensee proposes to control the pH by having greater than 278 cubic feet (approximately 15,000 pounds) of crystalline, hydrated TSP in three baskets located in the sump. This TSP will dissolve as it comes in contact with the spray water and will maintain the long-term pH above 7.06 with the expected TSP loadings resulting in a pH of between 7.25 and 8.07. Under the worst case conditions of minimal TSP dissolution, minimum recirculation flow, and maximum cump inventory and boron concentrations, the pH of the spray water drawn from the sump is expected to remain below 7 for no more than 20 minutes following the start of sump recirculation. As the higher concentration recirculation flow water mixes with the sump solution, the pH at the sump pit will reach its equilibrium within approximately 4 to 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> after the start of sump recirculation. Since the expected sump pH with the TSP baskets differs from the pH values associated with the existing sodium hydroxide addition system, there will be some difference in the amount of iodine removed from the containment atmosphere and in the resulting radiation doses. These doses were, therefore, revised by the licensee.
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. The iodine removal coefficients (A) used by the licensee were found to be reasonable given the planned changes in pH pertaining to the replacement of the sodium hydroxide addition system with the TSP baskets per the methodology described in Section 6.5.2. of the SRP. The change in the total amount of iodine removed from the containment atmosphere is due to a significant effect of the pH on the amount of iodine dissolved in spray solution before it becomes saturated.
Saturation concentration of iodine is determined by equilibrium between its concentrations in the containment atmosphere and the sump water. This equilibrium is determined by a partition coefficient (H) for iodine between air and water which is a function of pH. It is expected, i
therefore, that the decontamination factor (DF), which is a measure of the amount of iodine J
removed from the containment atmosphere, will be decreased for lower values of pH.
l Currently, sodium hydroxide will maintain the sump pH at a value between 8.8 and 11. Using trisodium phosphate this value will change to between 7.0 to 8.1 for equilibrium conditions during recirculation. This represents a marked difference and should be reflected in the decontamination factors used in dose calculations. The licensee calculated a new value for the decontamination factor using the partition coefficient and determined the actual value to be above the maximum value of DF=200 as stated in Section 6.5.2 of the SRP. Therefore, the i
licensee's use of DF=200 for elemental iodine results in a conservative treatment for elemental iodine removal. For particulate iodine, the licensee used a very conservative value of DF=50.
Another reason for maintaining an alkaline solution in the containment sump is to minimize corrosion of metallic surfaces. Chloride induced stress corrosion cracking of austenitic stainless steel components is considerably reduced if the pH of the solution to which the components are exposed is maintained above 7. Short exposure to low pH water during the initial injection phase and the transition period into the recirculation phase will not cause significant stress corrosion cracking. However, extended exposures to pH environments below 7 during long term core cooling operations in the recirculation phase could result in significant damage. Section 6.1.1 of the SRP (Branch Technical Position MTEB 6-1) recommends maintaining the sump pH j
in a 7 to 9.5 range.
Control of the sump pH is also required to minimize hydrogen generation by corrosion of aluminum and zinc on galvanized surfaces and in the organic coatings on containment surfaces.
The TSP chemistry control range for sump pH more closely approximates neutral pH conditions as compared to the 8.8 to 11 range of the current sodium hydroxide pH control system. Thus, a general reduction in the generation of hydrogen from the corrosion of zinc, aluminum, and organic surfaces located inside containment would be realized during long term core cooling as a result of this change. The generation of hydrogen due to the corrosion of zine willincrease with the lower pH values during the initial injection phase. However, due to the limited duration l
associated with the injection phase, this effect would be offset by a considerably smaller l
generation of hydrog 'n experienced during the recirculation phase.
l Based on the above evaluation, the staff concludes that the modifications to implement a passive application of trisodium phosphate pH control for ANO-2, as proposed by the licensee, meets the requirements of General Design Criterion (GDC) 41 for providing a satisfactory means of post-accident containment atmosphere cleanup. The staff further concludes that the proposed revised TSs for surveillance of trisodium phosphate in the containment sump meet the 3
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! i requirements of GDC-42 for inspection of containment atmosphere cleanup systems. Therefore, the staff review concludes that, relative to iodine removal, the licensee's proposed deletion of the
- sodium hydroxide addition system in conjunction with the addition of a passive trisodium j
phosphate containment sump pH control program is acceptable.
3.2 Eauioment Qualification l
j The staff also reviewed the replacement of the sodium hydroxide addition system with the use of trisodium phosphate baskets located on the floor of containment with respect to environmental 3
qualification of electric equipmen'.. The current design of the sodium hydroxide addition system maintains a post-accident injection and recirculation pH range of 8.8 to 11. With trisodium 2
l phosphate control, the pH of spray water during the injection phase could be as low as 4 4.
During the recirculation phase, the pH will be maintained within a range of 7 to 8.1 under j
equilibrium conditions. During the transition from the injection phase to the recirculation phase, 4
the spray water pH could remain below 7 or increase to levels as high as 12 for short periods l
prior to complete mixing of the sump volume. The time period above a pH of 11 was estimated
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to be less then 20 minutes. Due to the timing sequence of the post-accident recovery, the 1
majority of the equipment degradation from containment spray occurs during the recirculation
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i phase when long term core cooling is provided. Since the resulting pH level will be closer to j
neutral, post-LOCA corrosion of containment components will not be increased as a result of the i
j proposed change. The staff reviewed the change in the containment spray pH and agrees that j
envircamental qualification wiH not be affected.
j The lower pH values for containment spray during the injection and recirculation phase that are i
inherent with trisodium phosphate control will affect the radiation levels inside containment. The
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staff has reviewed the proposed modification and concluded that the use of trisodium phosphate wi!! have only a slight impact on post-accident radiation levels. The licensee has indicated that these changes are bounded by the current analysis such that the proposed change will not l
impact the environmental qualification of equipment with respect to radiatior exposure limits.
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Therefore, the staff concludes that the licensee's proposal is acceptable relative to equipment
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qualification.
3.3 Offsite and Control Room Dose Calculations
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The licensee assessed the impact of the elimination of the sodium hydroxide addition system on iodine removal during a LOCA. The licensee determined that iodine removal during the injection phase can still be effectively performed by boric acid sprays without using sodium hydroxide as l
an additive and that long-term iodine retention ;r...ie sumps is assured as long as the equilibrium sump pH levelis maintained above 7. The licensee has performed revised calculations to determine the impact of the changes in the iodine retention characteristics on offsite and control room dose assessments. The licensee revised its treatment of iodine retention along with other inputs and assumptions (e.g., decontairnination factor, sump volume, etc.) such that a general reductions in dose at the exclusion are's boundary (EAB) and low population zone (LPZ) were observed. Control room doses either remained unchanged or experienced slight increases. The calculated control room dose continues to meet the C3 D Wb
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requirements of General Design Criteria (GDC) 19. The staff has reviewed the changes in calculational inputs and assumptions as described in the licensee's submittal dated May 18, 3
1998, as supplemented by letter dated December 8,1998, and found them to be acceptable.
i The staff has assessed the capability of ANO-2 to meet the thyroid dose limits of 10 CFR Part 100 and GDC-19 with the elimination of the sodium hydroxide addition system for iodine.
l As a restf of this assessment, the staff has concluded that the myroid doses would not exceed the dose geidslines presently contained in 10 CFR Part 100 or GDC-19 of 10 CFR Part 50, i
Appendix A for either offsite locations or control room operators. Therefore, the staff finds the proposed TS amendment request acceptable.
l 3.4 Surveillance Reauirements The licensee proposes surveillance requirement 4.6.2.2.a and 4.6.2.2.b to demonstrate the operability of the TSP pH control program on a frequency of at least once per 18 months. TS 4.6.2.2.a verifies that a minimum value of 278 cubic feet of TSP is contained within the three 4
TSP baskets combined to ensure sufficient product is available to maintain pH greater then 7 l
during the recirculation phase. TS 4.6.2.2.b requires that a sample be taken from a TSP basket j
to demonstrate adequate pH adjustment of borated water. The required ratio of TSP to borated water is contained in TS bases 3/4.6.2.2. Location of these parameters in the bases section is i
appropriate as it will allow ratio changes to be performed under the controls of 10 CFR 50.59 as long as the ratio is reflective of a minimum TSP volume of 278 cubic feet. Thus, if changes to the primary system (such as a change in fuel enrichment) results in a required change in boron, j
the test ratio can be adjusted to reflect this change. The boron concentration of the test water will be representative of the maximum possible concentration corresponding to the maximum sump volume following a LOCA. A representative sample of TSP will be added to 1+/- 0.01 liter of borated water without agitation. After four hours, the solution is decanted and the pH verified to be greater than or equal to 7. The test will be performed at a temperature of 120 +/- 5 3
degrees Fahrenheit which is acceptable as it is below the expected temperature of the containment sump following a LOCA in which recirculation would be required. The i
l measurement of the pH of the decanted liquid will be performed at a temperature of 77 +/- 2 degrees Fahrenheit to ensure consistency in the results and the relevance of the indicated value as pH is a function of temperature. Based on the licensee's submitt31 dated May 18,1998, as j
supplemented by letter dated December 8,1998, the staff has concluded that the value for TSP J
volume and approach to measure TSP effectiveness yield conservative results and are, therefore, acceptable.
4.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Arkansas State officbl was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
l The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes i
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. surveillance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there 16 no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (63 FR 56241). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and sdaty of the public will not be endangered by operation in the prcposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Chris Nolan Date: December 23, 1998 i
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