2CAN100703, Unit 2 License Amendment Request for Technical Specification Change Associated with Replacement of Containment Sump Buffer

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Unit 2 License Amendment Request for Technical Specification Change Associated with Replacement of Containment Sump Buffer
ML072890085
Person / Time
Site: Arkansas Nuclear Entergy icon.png
Issue date: 10/05/2007
From: Mitchell T
Entergy Corp, Entergy Operations
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
2CAN100703
Download: ML072890085 (13)
v • d • e


Text

Entergy Entergy Operations, Inc.

1448 S.R. 333 Russellville, AR 72802 Tel 479-858-3110 Timothy G. Mitchell Vice President, Operations Arkansas Nuclear One 2CAN100703 October 5, 2007 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

SUBJECT:

License Amendment Request Technical Specification Change Request Associated with Replacement of Containment Sump Buffer Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6

Dear Sir or Madam:

Pursuant to 10 CFR 50.90, Entergy Operations, Inc. (Entergy) hereby requests an amendment for Arkansas Nuclear One, Unit 2 (ANO-2) to modify the technical specifications to replace the containment buffering agent from trisodium phosphate (TSP) to sodium tetraborate (NaTB) decahydrate. Specifically, this change is to minimize the potential for exacerbating sump screen blockage concerns under post loss-of-coolant accident (LOCA) conditions due to a potential adverse chemical interaction between TSP and certain insulation materials used in containment. Technical Specification (TS) 3.6.2.2 is being revised to utilize NaTB rather than TSP.

The proposed changes have been evaluated in accordance with 10 CFR 50.91 (a)(1) using criteria in 10 CFR 50.92(c) and it has been determined that the changes involve no significant hazards consideration. The bases for these determinations are included in the attached submittal. The proposed changes do not include any new commitments.

Entergy requests approval of the proposed amendment by March 15, 2008, to support implementation activities and operation with the new buffer following completion of the 2R19 refueling outage in spring 2008. Although this request is neither exigent nor emergency, your prompt review is requested.

If you have any questions or require additional information, please contact Natalie Mosher at 479-858-4635.

At

2CAN 100703 Page 2 of 2 I declare under penalty of perjury that the foregoing is true and correct. Executed on October 5, 2007.

TGM/nbm Attachments:

1. Analysis of Proposed Technical Specification Change
2. Proposed Technical Specification Changes (mark-up) cc: Mr. Elmo E. Collins Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P. 0. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Mr. Alan B. Wang MS 0-7 D1 Washington, DC 20555-0001 Mr. Bernard R. Bevill Director Division of Radiation Control and Emergency Management Arkansas Department of Health & Human Services P.O. Box 1437 Slot H-30 Little Rock, AR 72203-1437

Attachment I 2CAN100703 Analysis of Proposed Technical Specification Change to 2CAN 100703 Page 1 of 8

1.0 DESCRIPTION

This letter is a request to amend Operating License No. NPF-6 for Arkansas Nuclear One, Unit 2 (ANO-2) by revising Technical Specification (TS) 3.6.2.2, "Trisodium Phosphate (TSP)". TS 3.6.2.2 currently requires the use of TSP as the buffering agent in the containment sump. Entergy proposes to change the title of the TS to "Containment Sump Buffering Agent" and to replace "TSP" with "Sodium Tetraborate (NaTB) decahydrate" (hereafter referred to as "NaTB" and/or "buffering agent") within TS 3.6.2.2.

The purpose of this change is to minimize the potential for exacerbating sump screen blockage concerns under post loss-of-coolant accident (LOCA) conditions due to a potential adverse chemical interaction between TSP and certain insulation materials used in containment. These changes will maintain the intent of using buffering agents as described in NUREG-1432, Revision 3.1, "Standard Technical Specifications Combustion Engineering Plants." The NUREG-1432, Revision 3.1 Bases specifies the use of TSP "to ensure that iodine, which may be dissolved in the recirculated reactor cooling water following a LOCA, remains in solution. TSP also helps inhibit stress corrosion cracking (SCC) of austenitic stainless steel components in containment during the recirculation phase following an accident." NaTB serves this same function, maintaining the intent of the TS, albeit through the use of a different buffering agent.

2.0 PROPOSED CHANGE

The proposed amendment changes the TS 3.6.2.2 containment sump buffering agent from TSP to NaTB. A marked-up copy of the TS page is included in Attachment 2 of this letter.

The title of TS 3.6.2.2, "Trisodium Phosphate (TSP)", is revised to "Containment Sump Buffering Agent." Limiting Condition for Operation (LCO) 3.6.2.2 is changed to "The buffering agent baskets shall contain > 308 ft3 of sodium tetraborate (NaTB) decahydrate." The TS action is changed to "With the buffering agent not within limits, restore the buffering agent to within limits within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and be in at least HOT SHUTDQWN within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />." Surveillance requirement (SR) 4.6.2.2 is changed as follows:

4.6.2.2 The NaTB shall be demonstrated OPERABLE:

a. At least once per 18 months by verifying that the buffering agent baskets contain > 308 ft 3 of NaTB decahydrate.
b. At least once per 18 months by verifying that a sample from the buffering agent baskets provides adequate pH adjustment of borated water.

to 2CAN 100703 Page 2 of 8

3.0 BACKGROUND

Under LOCA conditions, buffering agents are added to the emergency core cooling system (ECCS) to increase the coolant pH to greater than 7.0. Buffering agent addition is mainly required to reduce release of iodine fission products from the coolant to the containment atmosphere. Thus, pH control is primarily an offsite dose control measure. Increasing the coolant pH also reduces the corrosion rates of most materials in the containment, most notably metal structural members and components. Traditionally, TSP is used as the buffering agent at many plants, including ANO-2. The buffering agent is stored in baskets that become submerged within the containment sump pool (as the post-LOCA water level rises) and release the buffering agent by dissolution.

TSP was initially selected as a post-LOCA buffering agent because of its many favorable characteristics. In particular, it dissolves rapidly and the quantity needed to increase the coolant pH above 7.0 is reasonable. It also has corrosion inhibitor properties beyond its ability to moderate pH. For example, steel corrosion is inhibited through the formation of iron phosphate conversion coatings. In the hydrated form, it has a good storage life, is inexpensive and is readily available.

Under LOCA conditions, calcium could be released into the coolant due to dissolution of calcium-bearing materials. Of particular concern at ANO-2 is the potential release of calcium from calcium-silicate insulation. TSP could react with dissolved calcium to form insoluble calcium phosphates. The resultant calcium phosphate precipitates may collect on fibrous beds and exacerbate flow restrictions within the ECCS at the containment sump screen.

Calcium phosphate precipitation can lead to additional head loss.

The Pressurized Water Reactor Owners Group (PWROG) investigated the ability to reduce or eliminate the risk of calcium phosphate precipitant formation simply by replacing TSP with another chemical that does not react with the materials in containment to form precipitants.

The program tested alternative buffering agents to determine the efficacy of these materials to replace TSP. The results of the PWROG activity were reported in WCAP-16596-NP, Revision 0, "Evaluation of Alternative ECCS Buffering Agents," dated July 2006 (Reference 5). The results of the candidate buffer testing were used to determine the appropriate replacement for TSP at ANO-2. NaTB was selected as the buffering agent to replace TSP at ANO-2.

The buffering agent is stored in stainless steel wire mesh baskets located in the containment on the basement level near the outer wall. The baskets have a maximum combined capacity of 486 ft 3. As the safety injection water fills containment, it dissolves the buffering agent, which resides in baskets on the containment floor. Mixing is achieved as the solution is continuously recirculated.

For the present plant configuration, ANO-2 SAR Section 6.2.2.1.1 (Reference 1) states that adequate quantities of TSP are mixed with the boric acid spray creating a buffered pH solution. SAR Section 6.2.3.3.1.1 (Reference 1) states that during the injection mode, the pH of the spray water will be approximately 4.4, given the maximum refueling water tank boron concentration of 3000 ppm. SAR Section 6.2.3.3.1.2 (Reference 1) indicates that prior to the onset of recirculation, while the sump is filling, the TSP in the three wire mesh baskets in the to 2CAN100703 Page 3 of 8 bottom of containment will be dissolving in the rising sump water. During this time and for a short period after the start of recirculation while additional mixing of the sump occurs, the pH of the sump water will continuously change, assuming different values which will be dependent on the amount of TSP dissolved and the volume of water in the containment sump. The spray pH gradually increases, and will continue to increase to a short-term peak of less than 12, as water with higher than average TSP concentrations reaches the sump pit.

As the higher concentration recirculation flow water returns to and mixes with the sump solution, the pH at the sump pit will fall to its final long-term value. These transient conditions are expected to last only for a short time. The sump pH should be very near its equilibrium value within several hours after the start of sump recirculation. SAR Section 6.2.2.2.1 (Reference 1) states that the TSP is used to raise the pH of the sump fluid to an equilibrium pH of 7.0 or higher. A pH of 7.0 or greater will assure that the iodine washed out of the reactor building atmosphere by the spraying action will not re-evolve from the liquid as it is sprayed back into the building.

The proposed operating condition is analogous to the existing operating condition described above except that NaTB replaces TSP. The pH values described in the SAR remain unchanged. The spray water pH is raised with NaTB, having a minimum manufactured density of 48.7 Ibm/ft3 . A hydrated form is used because of the high humidity in the containment building during normal operation. Since the NaTB is hydrated, it is less likely to absorb large amounts of water from the humid atmosphere and undergoes less physical and chemical change. As with TSP, the NaTB is stored in three wire mesh baskets located in the bottom of containment. The safety injection water dissolves the chemical as it fills the containment sump. Mixing is achieved as the solution is continuously recirculated.

4.0 TECHNICAL ANALYSIS

The proposed change to TS 3.6.2.2, which replaces the use of TSP with NaTB, maintains consistency with the intent of NUREG-1432, Revision 3.1. The basis of LCO 3.5.5 of NUREG-1432, Revision 3.1 specifies the use of the hydrated form of TSP (45-57% moisture) because of high humidity in the containment building during normal operation. However, because the use of TSP has been shown to potentially exacerbate post-LOCA sump screen blockage due to a potential adverse chemical interaction with certain insulation materials used in containment, Entergy has decided to replace the buffering agent chemical employed at ANO-2. Therefore, to preclude the potential for a possible adverse TSP/insulation interaction, Entergy is proposing to replace the TSP with NaTB which has essentially the same buffering agent characteristics as TSP but without the potential adverse consequences.

TS 3.6.2.2 is also revised to replace the volume of TSP required with a revised volume, based on the use of NaTB with a minimum density of 48.7 Ibm/ft3 . The changes to the surveillance requirements (volume of buffering agent) specified in TS 4.6.2.2.b will verify the ability of the NaTB to adjust pH to within the desired range. Because the highest hydrated form of NaTB is being used (NaTB decahydrate), it should not adsorb additional waters of hydration during storage in areas with elevated humidity. Concerning surveillance of the buffering agent volume specified in SR 4.6.2.2.a, the sample size changes from 3.09 +/- 0.05 grams of TSP to 3.07 +/- 0.05 grams of NaTB. The minimum mass of the buffering agent used in post-LOCA analyses is unchanged from the present 6,804 kg and the to 2CAN100703 Page 4 of 8 minimum required density of the buffering agent is now specified as 48.7 Ibm/ft 3 . The TS surveillance requirements are implemented in an onsite procedure by checking level to verify volume for SR 4.6.2.2.a and by performing a buffering test to verify pH for SR 4.6.2.2.b.

NaTB is an acceptable alternative to TSP for use as the ECCS buffering agent at ANO-2.

Use of NaTB could result in a significant reduction in precipitate formation with no adverse side effects as demonstrated by the NRC Integrated Chemical Effects Tests (ICET) with TSP (Reference 3) and NaTB (Reference 4) and the results of the PWROG chemical effects testing in WCAP-16530-NP, Rev. 0, "Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support Generic Safety Issue (GSI)-191," February 2006 (Reference 2), and alternate buffer testing (Reference 5). Additionally:

  • NaTB provides a comparable buffering capacity to TSP with a comparable quantity of buffering agent, so that no modification to the existing buffer delivery scheme is required;
  • No new types of precipitates are formed in the target pH range of 7.0 to 8.0, which is within the range of ANO-2 pH control (Reference 5);

" Corrosion to steel structural materials is comparable to that expected with TSP.

Corrosion to submerged aluminum in NaTB is higher than in TSP for equivalent pH; however, the overall effect of the increased corrosion with NaTB has been factored into the current chemical effects evaluation and addressed in subsequent testing (Reference 5);

" The effect of NaTB on boron solubility has been evaluated and found to be acceptable (Reference 5);

" NaTB has been evaluated for other potential chemical effects as part of the PWROG Program (Reference 5) and the ICET program and was found to be acceptable;

" NaTB is already in use at ice condenser plants and has a long and acceptable track record;

  • NaTB has been approved for use at another PWR (Reference 6) and;
  • Use of NaTB will provide additional dissolved boron for reactivity control.

Under post-LOCA conditions, with current maximum ANO-2 calcium and aluminum loadings, and using the maximum pH as the bounding condition, 67.3 kg and 62.2 kg of sodium aluminum silicate (NaAISi 3O8 ) for TSP and NaTB, respectively, are predicted to form as precipitates. No aluminum oxyhydroxide (AIOOH) is formed with either TSP or NaTB. With TSP, an additional 739.4 kg of calcium phosphate (Ca 3 (PO4) 2) precipitate is generated, compared to no Ca 3(PO4) 2 formation using NaTB. Thus, the use of NaTB rather than TSP results in a net decrease of 92.3% in the quantity of precipitate generated (62.2 kg with NaTB versus 806.7 kg with TSP). The following table provides a summary of the predicted precipitate generation. The analysis and evaluation of debris loadings applicable to ANO-2 continue to be revised and updated. Thus, the values presented here may not represent final to 2CAN 100703 Page 5 of 8 conditions credited for ANO-2; however, they present a comparison of the differences associated with the two buffering agents.

Predicted Chemical Precipitate Formation for ANO-2 Generated Buffering Agent Precipitates TSP NaTB*

NaAISi 3 0 8 (kg) 67.3 62.2 AIOOH (kg) 0.0 0.0 Ca 3(PO4) 2 (kg) 739.4 0.0 Total (kg) 806.7 62.2

  • These values are based on the buffer change and its associated effect on the lower maximum pH.

The design function of the buffering agent storage baskets located in containment does not change. The baskets that currently contain active TSP will utilize NaTB as the buffering agent. NaTB has been approved for use at PWRs utilizing an ice condenser containment building. Although the method for introducing NaTB to the post-accident containment sump pool differs from that at ice condenser plants (dissolving versus released from melting ice),

environmental considerations are not significantly different. Both systems are passive in nature releasing the buffering agent only in the event of a high energy line break inside containment. As reported in WCAP-16596-NP (Reference 5), in the initial test of environmental stability, buffer samples were exposed to a simulated containment environment. After 30 days, clumping was observed in both TSP and NaTB, but both buffers readily dissolved in hot water. On the basis of these results, the stability of NaTB in the containment environment can be considered comparable to or slightly better than that of TSP. The stability of NaTB to radiation exposure has been demonstrated to be satisfactory based on years of use in PWR environments. An assessment of the use of NaTB has concluded that there are no adverse effects on the corrosion of zirconium-based alloys and stainless steel which are used in the fabrication of fuel assemblies and core components; therefore, replacement of the TSP containment buffer with NaTB is not expected to have any detrimental effects on the fuel.

5.0 REGULATORY ANALYSIS

5.1 Applicable Regulatory Requirements/Criteria The changes to ANO-2 Technical Specification (TS) 3.6.2.2 are consistent with the applicable regulatory guidance contained in NUREG 0800, Section 6.5.2, "Containment Spray as a Fission Product Cleanup System." Subsection 11.1 .g specifies that the pH of solutions in the containment sump and additives for reactivity control, fission product removal, or other purposes (boric acid) should be maintained at a level high enough to assure that significant long-term iodine re-evolution does not occur. Long-term iodine retention may be assumed only when the equilibrium sump solution pH, after mixing and dilution with primary coolant to 2CAN 100703 Page 6 of 8 and Emergency Core Cooling System (ECCS) injection, is above 7.0. It was conservatively assumed that borated water sources are at their maximum volume and maximum boric acid concentration in calculating the volume of sodium tetraborate (NaTB) required to achieve recirculation water equilibrium pH > 7.0.

10 CFR 50.49(e)(3) requires the composition of chemicals used to be at least as severe as that resulting from the most limiting mode of plant operation (e.g., containment spray, emergency core cooling, or recirculation from containment sump). 10 CFR 50, Appendix A, General Design Criteria (GDC) 41 requires systems to control fission products which may be released into the reactor containment to be provided to reduce the concentration and quality of fission products released to the environment following postulated accidents. In conclusion, Entergy has determined that the proposed changes do not require any exemptions or relief from regulatory requirements, other than the TS, and does not affect conformance with any GDC differently than described in the Safety Analysis Report.

5.2 No Significant Safety Hazards Consideration Entergy has evaluated whether or not a significant hazards consideration is involved with the proposed amendment by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of Amendment," as discussed below:

1. Does the proposed change involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No.

There are no changes to the design or operation of the plant that could affect system, component, or accident functions as a result of replacing trisodium phosphate (TSP) with sodium tetraborate (NaTB). Buffering agents are used to minimize the potential consequences of an accident and do not represent an accident initiator. Utilizing NaTB as a buffering agent ensures the post-loss-of-coolant accident (LOCA) containment sump mixture will have an equilibrium pH > 7.0. Replacing TSP with NaTB, which achieves comparable pH buffering results, will maintain the iodine retention and corrosion inhibition required by the safety analyses.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Does the proposed change create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No.

No new accident scenarios, failure mechanisms, or single failures are introduced as a result of the proposed change. Structures, systems, and components previously required for mitigation of an event remain capable of fulfilling their intended design function with this change to the TS. The proposed change has no new adverse effects on safety-related systems or components and does not challenge the to 2CAN100703 Page 7 of 8 performance or integrity of safety-related systems. The replacement buffering agent has been evaluated and no new accident scenarios or single failures are introduced.

Therefore, the proposed change does not create the possibility of a new or different kind of accident from any previously evaluated.

3. Does the proposed change involve a significant reduction in a margin of safety?

Response: No.

The safety analyses assume a post-LOCA equilibrium pH > 7.0 to minimize iodine re-evolution and to minimize corrosion of components within containment. Changing the containment sump buffering agent requirement from TSP to NaTB and revising the required volume of NaTB continues to ensure a containment sump equilibrium pH > 7.0. The margin for pH control is not altered by the proposed changes.

Therefore, the proposed change does not involve a significant reduction in a margin of safety.

Based on the above, Entergy concludes that the proposed amendment to replace the containment sump buffering agent requirement for the use of TSP with NaTB presents no significant hazards consideration under the standards set forth in 10 CFR 50.92(c), and, accordingly, a finding of "no significant hazards consideration" is justified.

5.3 Environmental Considerations The proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore pursuant to 10 CFR 51.22(b), no environmental assessment need be prepared in connection with the proposed amendment.

6.0 PRECEDENT NaTB is presently in use at ice condenser plants and has a long and acceptable track record.

Utilization of NaTB in lieu of TSP as a buffering agent at ANO-2 serves an analogous function to its use in ice condenser plants, albeit via a different delivery mechanism (dissolution of granular NaTB versus melting NaTB ice).

By letter dated August 21, 2006, as supplemented by letters dated September 6, 2006, and October 10, 2006, Omaha Public Power District (OPPD) submitted a similar license amendment request for Ft. Calhoun. OPPD requested to replace TSP with NaTB due to minimizing the potential for exacerbating sump screen blockage due to a potential chemical interaction between TSP and certain calcium sources used in containment. In a letter dated November 13, 2006, the NRC approved the use of NaTB at Ft. Calhoun (Reference 6).

to 2CAN 100703 Page 8 of 8 The proposed change for ANO-2 is similar in that both requests replace TSP with NaTB.

Similar to Ft. Calhoun, Entergy is specifying a minimum volume of NaTB. The minimum density of 48.7 Ibm/ft 3 for NaTB ensures that the correct weight of NaTB required for post-accident buffering is available.

7.0 REFERENCES

1. ANO-2 Safety Analysis Report, Section 6.2
2. WCAP-16530-NP, Rev. 0, "Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSI-191," February 2006
3. LA-UR-05-6996, "Integrated Chemical Effects Test: Test #3 Data Report,"

October 2005

4. LA-UR-05-9177, "Integrated Chemical Effects Test Project: Test #5 Data Report,"

January 2006

5. WCAP-16596-NP, Rev. 0, "Evaluation of Alternative Emergency Core Cooling System Buffering Agents," July 2006
6. Letter, Alan B. Wang, NRC, to R.T. Ridenoure, Ft. Calhoun Station, dated November 13, 2006, "Fort Calhoun Station-Unit No. 1-Issuance of Amendment 247 Re: Change of Containment Building Sump Buffering Agent from Trisodium Phosphate to Sodium Tetraborate (TAC No. MD2864)" (ADAMS Accession Number ML063120248)

Attachment 2 2CAN100703 Proposed Technical Specification Changes (mark-up)

CONTAINMENT SYSTEMS CONTAINMENT SUMP BUFFERING AGENTTRISODIUM PHOSPHATE (TSP)

LIMITING CONDITION FOR OPERATION 3.6.2.2 The bufferinq aqentTSP-- baskets shall contain _>3082-7-8 ft3 of sodium tetraborate (NaTB) decahydrateantive TRP.

APPLICABILITY: MODES 1, 2 and 3.

ACTION:

With the buffering a-gentT-&P not within limits, restore the buffering agentT-SP to within limits within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and be in at least HOT SHUTDOWN within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

SURVEILLANCE REQUIREMENTS 4.6.2.2 The buffering agentT-SP shall be demonstrated OPERABLE:

a. At least once Der 18 months bv verifvina that the bufferina aaentTS-P baskets contain >_3082-7-_ft 3 of NaTB decahydrate.eT-&P..
b. At least once per 18 months by verifying that a sample from the buffering aqentT-SP baskets provides adequate pH adjustment of borated water.

ARKANSAS - UNIT 2 3/4 6-12 Amendment No. 4-94,

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