1CAN010904, Deviation from EPRI Guideline - Steam Generator Chemistry Specification
| ML090280575 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/28/2009 |
| From: | James D Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 1CAN010904, NEI 03-08 | |
| Download: ML090280575 (6) | |
Text
Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4619 Dale E. James Manager, Licensing Arkansas Nuclear One 1CAN010904 January 28, 2009 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
SUBJECT:
Deviation from EPRI Guideline - Steam Generator Chemistry Specification Arkansas Nuclear One, Unit 1 Docket No. 50-313 License No. DPR-51
REFERENCES:
- 1. EPRI Report 1008224, Pressurized Water Reactor Secondary Water Chemistry Guidelines, Rev. 6
- 2. NEI 03-08, Guideline for the Management of Materials Issues, April 2007 Addenda, Materials Initiative Guidance, Addendum E, Rev. 3
Dear Sir or Madam:
In accordance with NEI 03-08 (Reference 2), Entergy Operations, Inc. (Entergy) is informing the NRC of a deviation from the EPRI Steam Generator Management Project (SGMP)
(Reference 1) relating to Steam Generator (SG) chemistry for Arkansas Nuclear One, Unit 1 (ANO-1). Addendum E of NEI 03-08 states:
Utilities shall notify the NRC of any approved deviations from Mandatory and Needed guideline elements. This notification is for information; NRC approval or other actions are not expected. The notification shall summarize:
- the guidance being deviated from,
- the justification for the deviation, and
- any actions undertaken in lieu of the guidance.
1CAN010904 Page 2 of 3 Guidance Deviated From During startup from a forced outage on December 22, 2008, Entergy performed a deviation as a result of secondary water chemistry guidelines being exceeded. In accordance with Table 6-4 of the EPRI guidelines (Reference 1), two conditions relative to steam generator control parameters are relevant to this deviation:
- 1. > 250 ppb sodium, chloride, or sulfate between 0 - 15% power If limit is exceeded during power escalation, be in Hot Shutdown within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and cleanup by feed and bleed or drain and refill as appropriate.
- 2. Do not exceed 5% power when > 100 ppb sodium, chloride, or sulfate Justification for Deviation The deviation prevented thermal cycling of the ANO-1 Once-Through Steam Generator (OTSG). Thermal cycles of the relatively new (replaced in 2005) OTSGs has been shown to be detrimental to the tube support plate tie rods. A detailed justification for the deviation is included in Attachment to this submittal. The manufacturer (Areva) expressed concern with remaining in Hot Standby conditions for an extended period of time and approved the deviation with the restrictions depicted in Attachment to this submittal.
The ANO-1 steam generators have experienced tie rod bowing upon cooldown. The cause of this bowing is frictional resistance between the tube support plates and the inner shroud. As the component cools off, the tube support plate(s) lock to the shroud. Due to the difference in material properties, the carbon steel shroud/shell compresses more than the stainless steel support plates and rods. This causes a downward force to be placed on the tie rods resulting in bowing of the rods. Stress to the component in the form of fatigue was viewed as a more severe issue than the short term affects of high caustic conditions with A690 thermally treated material. This condition related to the ANO-1 steam generators was presented to the NRC in a meeting in Rockville, Maryland, on August 27, 2008 (reference NRC meeting notes provided in NRC letter dated December 1, 2008).
Actions Undertaken in lieu of Guidance Document The Moisture-Separator-Reheater (MSR) drain paths to the Main Condenser were opened during the period of deviation. In addition, the period in which the deviation was permitted was strictly controlled and limited. Details of compensatory measures and administrative controls are included in Attachment to this submittal.
1CAN010904 Page 3 of 3 Note that the attached justification is an internal Entergy document and was not written in a manner requesting NRC approval. As stated above, this justification is for informational purposes only.
This letter does not include any new commitments.
If you have any questions or require additional information, please contact Dale James at 479-858-4619.
Sincerely, DEJ/dbb
Attachment:
Technical Justification and Compensatory Measures and Controls for Deviation 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. O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Mr. Alan B. Wang MS O-7 D1 Washington, DC 20555-0001 U. S. Nuclear Regulatory Commission Attn: Allen Hiser MS O-9 H6 Washington, DC 20555-0001
Attachment to 1CAN010904 Technical Justification and Compensatory Measures and Controls for Deviation
Attachment to 1CAN010904 Page 1 of 2 Technical Justification and Compensatory Measures and Controls for Deviation The EPRI Pressurized Water Reactor Secondary Water Chemistry Guidelines, Revision 6, identifies all steam generator control parameters as shall requirements. All control parameters (including all associated action level values, hold values, and monitoring frequencies) require appropriate justification for exceptions when those exceptions are less restrictive or less conservative than those contained in the guidelines. The justification must be appropriately approved and documented.
There are two conditions relative to steam generator control parameters that this deviation addresses:
EPRI Revision 6 Guideline Requirements:
- 1. > 250 ppb sodium, chloride, or sulfate between 0 - 15% power - be in hot shutdown within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> - cleanup by feed and bleed or drain and refill as appropriate
Proposed Deviation:
Escalate power even with greater than 250 ppb sodium, chloride, or sulfate and route moisture separator drains back to condenser. This will be allowed one time due to the concern of thermal cycling of the Once Through Steam Generator (OTSG) tube support plate tie rods if steam generator temperature was reduced to allow tubesheet drains to be used for cleanup. If the steam generator chloride, sulfate and sodium reach 1000 ppb, then power cannot be escalated and cooldown would be required to clean the steam generator impurities.
Steam generator sodium, chloride and sulfate are required to be less than 100 ppb prior to exceeding 15% power.
Justification for Deviation:
Table 6-4 of EPRI Pressurized Water Reactor Secondary Water Chemistry Guidelines -
Revision 6 Mode 1, 0 - 15% Power states for steam generator control parameters (sodium, chloride, and sulfate), if the 250 ppb limit is exceeded during power escalation, be in hot shutdown within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and cleanup by feed-and-bleed or drain and refill as appropriate. The action is required not just during power escalation, but at any time the reactor is critical up to 15% reactor power. The guidelines state on Page 6-10, Bulk water concentration may be controlled by blowdown from the lower tubesheet drains. The Arkansas Nuclear One, Unit 1 (ANO-1) steam generators are configured without steam generator blowdown at normal operating temperature and pressure. The tubesheet drain valves are closed at approximately 435 °F (prior to criticality), which drastically reduces the ability to exchange steam generator bulk water inventory. These drains are isolated due to thermal and reactor startup dose concerns.
Attachment to 1CAN010904 Page 2 of 2 From 0 - 5 % power, the plant is in transient conditions. The Babcock & Wilcox (B&W) plant will increase in reactor power using auxiliary feed until approximately 5% power when the first main feed pump is placed on line. The water level of the OTSGs is very small compared to a recirculating generator. The unit has approximately 35 degrees of super heat so the boiling zone is within the first 12-15 feet vertically of the generator. As mentioned above, the unit does not have blowdown capability above the temperature at which tubesheet drain lines are isolated to the condenser. Therefore, the only mechanisms to reduce contaminant concentrations are dilution (increasing the water inventory) which is limited due to startup procedures, or by use of the sample line which provides an insignificant volume of water removal (~ 1-2 gallons per minute). Therefore, the only way to increase the exchange of steam generator inventory is to drop temperature low enough to open the drain lines that connect to the condenser (~ 435 °F). This requires not only cooldown, but removing a reactor coolant pump from service.
Contaminants in the bulk water would be essentially blown out the main steam line as feed flow increases and reactor power goes up. The contaminants would then go to the condenser where they would be removed with the full flow polishers. Two other items to consider are the affect of thermally cycling the tubes and the wear concerns associated with tube to tubesheet interfaces caused by tube expansion during thermal excursions. Inconel 690TT does not have the wear resistance that the Inconel 600 tubing had with carbon steel supports. Historically, the most significant wear has been associated with heatup and cooldowns due to the difference in thermal expansion of the shell and the tube support plates. Stresses associated with the thermal cycling of tubing have a greater risk of tube damage than the short operating period during which contaminants would be in the steam generator bulk water from 0 to 5%
power.
ANO-1 steam generators were replaced in 2005 (1R-19). The replacement steam generators are of Areva design and designated as Enhanced Once-Through Steam Generators (EOTSG).
The steam generators are constructed of Alloy 690TT tubes that are highly resistant to corrosion degradation. There is also an improvement in boiling stability. These design characteristics improve the overall corrosion resistance of steam generators and their associated internals.
Areva is concerned with staying at hot shutdown conditions for an extended period of time.
They provided correspondence stating that they would agree with a one time increase in power with cleanup performed by routing Moisture-Separator-Reheater (MSR) drains back to the condenser. This was based on the issue of thermal cycling of the OTSG tube support plate tie rods.
This deviation is only applicable for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> from the time of the approval by Areva (12-22-08 at 1121 CST). Once this time period has expired and ANO-1 has not escalated in power, than the unit should be cooled down and steam generator drains opened for cleanup of sodium, chloride, and sulfate to less than 100 ppb.
This deviation is documented under condition report CR-ANO-1-2008-2758.