ML100550127

Replacement Steam Dryer

ML100550127
Person / Time
Site:	Monticello
Issue date:	02/18/2010
From:	O'Connor T Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-MT-1-007
Download: ML100550127 (8)

Text

Xe l n ry20Monticello Nuclear Generating Plant Xcel nergy2807 W County Road 75 February 18, 2010 L-MT-1 0-007 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket 50-263 Renewed License No. DPR-22

Subject:

Monticello Replacement Steam Dryer

References:

1) U.S. Nuclear Regulatory Commission, Regulatory Guide 1.20, "Comprehensive Vibration Assessment Program for Reactor Internals During Preoperational and Initial Startup Testing,"

Revision 3, March 2007.

The purpose of this letter is to inform the Nuclear Regulatory Commission (NRC) of Northern States Power Company, a Minnesota corporation (NSPM), plans to replace the existing Monticello Nuclear Generating Plant's steam dryer. NSPM has completed a preliminary review of regulatory requirements to determine whether or not the steam dryer replacement requires prior NRC review and approval. The preliminary review concludes that the installation of the replacement dryer may be completed under 10 CFR 50.59.

The replacement steam dryer will be provided by Westinghouse and is currently scheduled to be installed during the Spring 2011 refueling outage. NSPM is replacing the steam dryer because the new dryer is a cost effective measure to reduce moisture carryover to < 0.1%. This reduction in moisture carryover helps minimize corrosion products in the reactor coolant loop. The reduced corrosion products minimize high pressure turbine wear, reduces the production and transportation of activated corrosion products, and reduces the volume of radioactive wastes (from Condensate Demineralizer & Reactor Water Cleanup (RWCU) filtering material replacements). These reductions help minimize worker doses. The replacement steam dryer is not required for operation under extended power uprate (EPU) conditions (the EPU License Amendment Request (LAR) is currently under review by the NRC staff (TAC No. MD9990)).

Document Control Desk Page 2 The replacement steam dryer will be designed and analyzed to the latest industry standards, and will meet the criteria in Regulatory Guide (RG) 1.20, Revision 3 (Ref. 1).

A steam dryer is a passive component that has no safety-related function. It does have a passive function (considered important to safety) to maintain its structural integrity during abnormal events.

NSPM has completed a preliminary review of regulatory requirements to determine whether or not the steam dryer replacement requires prior NRC review and approval. 10 CFR 50.59 establishes the criteria to determine whether or not prior NRC review is required. Enclosure 1 discusses how the 10 CFR 50.59 criteria are expected to be addressed upon development of the final evaluation required by 10 CFR 50.59. The review concludes that the installation of the replacement dryer may be completed under 10 CFR 50.59.

Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.

r-/-'T, i~ntf 'ý./JC6" nnor Site Vic esident Montice rNuclear Generating Plant Northern States Power Company-Minnesota Enclosures (1) cc: Administrator, Region III, USNRC Project Manager, Monticello Nuclear Generating Plant, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC Minnesota Department of Commerce

L-MT-1 0-007 ENCLOSURE I Preliminary Regulatory Review

L-MT-1 0-007 Page 1 of 5

==

Introduction:==

NSPM plans to replace the existing steam dryer with a new dryer during the Spring 2011 refueling outage. The purpose of the following review is to determine whether or not prior NRC review and approval of the installation of the replacement dryer is expected to be required. The following is not a 10 CFR 50.59 evaluation; it is a preliminary review which considers the 10 CFR 50.59 criteria and addresses each criterion assuming the conditions which are expected to exist by the Spring 2011 outage. This review also includes additional information that provides confidence that the steam dryer will meet the necessary technical requirements. Prior to steam dryer installation, regulations and plant procedures require that an evaluation in accordance with 10 CFR 50.59 requirements be completed.

Would the replacement steam dryer:

(i)

Result in more than a minimal increase in the frequency of occurrence of an accident previously evaluated in the final safety analysis report (as updated)?

Not Expected A failure of the steam dryer is not an accident initiator in the MNGP USAR, i.e., it is not a component whose failure or malfunction initiates any accident in the USAR. Therefore, the frequencies of occurrence of the accidents in the USAR are not affected.

(ii)

Result in more than a minimal increase in the likelihood of occurrence of a malfunction of a structure, system, or component (SSC) important to safety previously evaluated in the final safety analysis report (as updated)?

Not Expected A steam dryer is a passive, nonsafety-related component. The original steam dryer was not considered important to safety, and was built prior to the issuance of Regulatory Guide 1.20, Rev. 0. The replacement steam dryer's design, analysis and testing are expected to satisfy the criteria in RG 1.20, Rev. 3, and are expected to confirm that the dryer would maintain its structural integrity during accidents (i.e., blowdown pressure loads).

The steam dryer's basic design has been successfully used at 12 European BWRs for over 200 years of operating experience.

Consistent with RG 1.20, Rev. 3:

A vibration assessment program will be implemented in conjunction initial startup testing. The program will consist of vibration and fatigue analyses, a vibration measurement program, an inspection program, and analyses correlating the measured parameters to the calculated results.

L-MT-10-007 Page 2 of 5 The vibration and stress analyses will be performed for steady-state conditions that correspond to initial startup test and normal operating conditions. In addition, the loads analyses will include a main steamline break accident.

" The steam dryer vibration measurement program will verify structural integrity, design and safety margins, and compare the results to the vibration analysis.

The inspection program will include an initial acceptance inspection and an inspection following the initial fuel cycle of operation.

" The results of the vibration and stress analysis, measurement, and inspection programs will be reviewed and correlated to determine the extent to which the test acceptance criteria are satisfied. The results will be summarized in a report.

Analyses are expected to show that the loadings due to the dryer's weight, normal and abnormal event conditions pressure differentials, flow induced vibrations, and from a seismic events are within design allowables. The new steam dryer is expected to have an analyzed stress ratio > 2.0 at full power EPU conditions. Stress ratios > 2.0 will be confirmed by monitoring of instrumentation on main steam lines and on the replacement steam dryer.

The replacement dryer will be made of 316L stainless steel (commonly used in BWRs), which has a proven history, is compatible with the environment and materials within the reactor pressure vessel, and meets the BWRVIP-84 (Reference 1) materials guidelines. Thus, the replacement dryer is not expected to adversely interact with any SSC important to safety.

Therefore, the likelihoods of occurrence of malfunctions of SSCs important to safety, previously evaluated in the MNGP USAR, are not expected to be adversely affected.

(iii)

Result in more than a minimal increase in the consequences of an accident previously evaluated in the final safety analysis report (as updated)?

Not Expected The steam dryer is a passive, nonsafety-related component that performs no accident mitigation function, does not affect any radioactive material source term, is not a radioactive material boundary, and would maintain its structural integrity during accidents. Therefore, no radiological consequence of any accident previously evaluated in the MNGP USAR is affected.

L-MT-10-007 Page 3 of 5 (iv) Result in more than a minimal increase in the consequences of a malfunction of a SSC important to safety previously evaluated in the final safety analysis report (as updated)?

Not Expected The steam dryer is a passive, nonsafety-related component that performs no abnormal event mitigation function, does not affect any radioactive material source term, is not a radioactive material boundary, would maintain its structural integrity during accidents, and is not associated with any malfunction addressed in the MNGP USAR. As the steam dryer is expected to maintain its structural integrity, neither the MSIVs nor any other SSC important to safety is expected to be adversely affected. Therefore, no consequence of any malfunction of a SSC important to safety previously evaluated in the MNGP USAR is affected.

(v) Create a possibility for an accident of a different type than any previously evaluated in the final safety analysis report (as updated)?

Not Expected The only potential event of concern would be a Main Steam Line Break Accident (MSLBA) outside containment, where Main Steam Line Isolation Valve(s) (MSIVs) could potentially fail to isolate due to debris from a steam dryer failure. Analyses are expected to show that the loadings due to the dryer's weight, normal and abnormal event conditions pressure differentials, flow induced vibrations, and from a seismic events are within design allowables. The new dryer is expected to have an analyzed stress ratio >

2.0 at full power EPU conditions. The dryer's design, analysis and testing shall satisfy the criteria in RG 1.20, Rev. 3, and thus, the dryer would maintain its structural integrity during a MSLBA. The new dryer does not allow for a new fission product release path, result in a new fission product barrier failure mode, nor create a new sequence of events that result in significant fuel cladding failures. Therefore, the steam dryer can not create the possibility of an accident of a different type than any previously evaluated.

(vi)

Create a possibility for a malfunction of a SSC important to safety with a different result than any previously evaluated in the final safety analysis report (as updated)?

Not Expected The steam dryer is a passive component that as long as it maintains its structural integrity can not adversely interact with any SSC important to safety. The steam dryer is made of 316L stainless steel and meets the BWRVIP-84 guidelines (Reference 1) for BWR materials, and thus, is

L-MT-10-007 Page 4 of 5 compatible with the environment and materials within the reactor pressure vessel. Analyses are expected to show that the loadings due to the dryer's weight, normal and abnormal event conditions pressure differentials, flow induced vibrations, and from a seismic events are within design allowables.

The dryer will not adversely interact with any SSC important to safety, and does not allow for a new failure mode of a SSC important to safety.

Therefore, the dryer can not create the possibility for a malfunction of a SSC important to safety with a different result than any previously evaluated in the MNGP USAR.

(vii) Result in a design basis limit for a fission product barrier as described in the FSAR (as updated) being exceeded or altered?

Not Expected The steam dryer is not a fission product (i.e., radioactive material) barrier.

The only design basis function potentially associated with a steam dryer is the ability for the MSIVs to isolate the containment during a MSLBA, due to debris from a steam dryer failure preventing the MSIVs to fully close.

However, the dryer's design, analysis and testing shall satisfy the criteria in RG 1.20, Rev. 3, and confirm that the dryer would maintain its structural integrity during a MSLBA. Therefore, the dryer cannot adversely affect any design basis limit of any fission product barrier described in the MNGP USAR.

(viii) Result in a departure from a method of evaluation described in the FSAR (as updated) used in establishing the design bases or in the safety analyses?

Not Expected The steam dryer is a passive, nonsafety-related component, and other than maintaining structural integrity, has no 10 CFR 50.2 design basis nor safety analysis function. However, the dryer will be analyzed using the current industry standard methods, and is expected to meet the applicable criteria in RG 1.20.

In addition, similar to Susquehanna, the Monticello dryer will be instrumented. It will be equipped with strain gages to measure dryer stresses, and their readings analyzed to ensure the stresses are acceptable. Strain gage results will be compared to a Westinghouse acoustic analysis to validate the analysis results. (Note; the acoustic analysis methodology used by Westinghouse was originally developed by Continuum Dynamics Inc.)

Guidance from the NRC accepted version of the Reference 2 EPRI topical report will be used in confirming the integrity of the steam dryer. The steam

L-MT-1 0-007 Page 5 of 5 dryer and Main Steam Lines will be instrumented, monitored and analyzed (as needed) at specific steps during the initial ascension to full EPU power.

The results of the vibration and stress analyses and measurements will be reviewed and correlated with steam dryer instrumentation to ensure that test acceptance criteria are satisfied. During later refueling outages, the steam dryer will be visually inspected to ensure structural integrity is maintained.

Therefore, the combination of analysis methods with confirmation testing, measurements, analysis and inspections used for Monticello is expected to be similar to the analyses performed for the current steam dryer, as reviewed by the NRC during staffs review of NSPM's EPU LAR.

==

Conclusion:==

Based on the above preliminary review; it is concluded that no adverse effect is expected and prior NRC review and approval is not required. The 10 CFR 50.59 required evaluation for the installation and use of the replacement steam dryer is expected to confirm this conclusion.

References:

1.

Electric Power Research Institute, "BWRVIP-84, Vessel and Internals Project Guidelines for Selection and Use of Materials for Repairs to BWR Internal Components," EPRI Report No. 1000248, October 2000.

2.

Electric Power Research Institute, Topical Report, "BWRVIP-182: Guidance for Demonstration of Steam Dryer Integrity for Power Uprate," EPRI Report No. 1016166, (TAC No. MD9427).