IR 05000409/1986005

Insp Rept 50-409/86-05 on 860408-12 & 0528.No Violation Noted.Major Areas Inspected:Hpcs Bundle Reinstallation & Engineering Evaluation of Tube Stress

ML20198S089
Person / Time
Site:	La Crosse File:Dairyland Power Cooperative icon.png
Issue date:	06/05/1986
From:	Dupone S, Dupont S, Rescheske P, Ring M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
Shared Package
ML20198S032	List: IR 05000409/1986005 ML20198S030
References
50-409-86-05, 50-409-86-5, NUDOCS 8606100322
Download: ML20198S089 (8)

Text

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U.S. NUCLEAR REGULATORY COMMISSION

REGION III

Report No. 50-409/86005(DRS)

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Docket No. 50-409 License No. DPR-45 Licensee: Dairyland Power Cooperative 2615 East Avenue - South Lacrosse,_WI 54601 Facility Name: Lacrosse Boiling Water Reactor Inspection At: Lacrosse Site, Genoa, Wisconsin Inspection Conducted: April 8-12 and May 28, 1986 Y *)

Inspectors: S. G. DuPo7 [>kA6 Date '

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ikIsro Dath

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Approved By:

'&td M.A. Ring,7 Chief

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Test Programs Section Da~te Inspection Summary 28 1986 (Reaort No.50-409 Inspection Areas Inspected: on April High 8-12Pressure and May'Cir,e Spray (If)fSTbiridlF~r~e/86005fDRSR instillision and engineering evaluation of tube stress (93700).-

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Results: No violations were -identified.

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8606100322 860605, PDR ADOCK 05000409 G PDR, i

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DETAILS Persons Contacted

+*J. D. Parkyn, Plant Superf9tendent

• P. D. Bronk, Nuclear Engineer

• L. Goodman, Operations Engineer P. E. Gray, Mechanical Maintenance Supervisor

• D. Rybarik, Mechanical Engineer

• H. A. Towsley, Technical Support Engineer

• R. R. Wery, Quality Assurance Supervisor The inspectors also interviewed other licensee personnel during the course of the inspectio * Denotes persons attending the exit meeting of April 10, 198 + Denotes persons attending the exit meeting of May 28, 1986 via telephon . High Pressure Core Spr_ay_jHPCS)_Syst_em_ Bundle

_ Description The HPCS bundle is made up of 72 tubes inserted into the failed-fuel location system tubes (see figures 1 and 2) through tees located in the upper head cavity and are kept concentric along the entire length of the tubes by means of radial spacers. Figure 2 of this report gives the general location of the bundle between the HPCS system tees and the nozzles located above the top of the fuel elements. Below the bottom radial spacer, the HPCS and the failed-fuel location system tubes pass through an outer support tube. Figure 1 shows the configuration of the three concentric tubes (HPCS, Failed-Fuel Location System and outer support tube). The outer support and failed-fuel location system tubes are welded to the HPCS adapte It is important to note that the outer support tube is not welded, but free fitted to the bottom radial spacer. The HPCS nozzle is located within the adapter and is connected to the HPCS flow tub The HPCS tubes protrude beyond the failed-fuel location tubes to discharge through the nozzles directly above each fuel assembl The upper support of the bundle is an annular ring plate with ten parallel bars extending across the plate opening. The 72 tubes are attached to the bars. The bundle is laterally supported between the top of the steam dryer and the top of the core by four radial supports or brackets that are bolted to the thermal shield and fitted about the periphery of one of the tube sheets formed by the lateral flow deflector baffle. Figure 3 shows the location of the radial support bracket. The lateral flow deflector is an integral part of the e combined assembly, consisting of two parallel baffle plates. The deflector primarily produces the water level necessary for efficient natural steam water separation. In addition, it provides radial support for the HPCS bundl .

. Failed-Fuel Location System Although the failed-fuel location system is no longer used for the detection of failed fuel, the failed-fuel location system concentric tubes, which are integral with the HPCS bundle and the support tubes, remain installed in the reactor. The failed-fuel location system was initially installed during the Lacrosse BWR's research phase and was made inoperable when the unit was licensed as a power generating facilit . Chronology of Significant Events The licensee encountered problems during the re-installation of the High Pressure Core Spray (HPCS) bundle into the reactor vessel following refueling. As a result of discussions with the licensee and by direct observation, the inspectors have determined that the sequence of events occurred as follows:

April 3,1986 The licensee was near the end of a refueling outage and was preparing to transfer the HPCS bundle from the storage well to the reactor vessel. An air-flow test which tests for nozzle and tube blockage was completed satisfactorily. The bundle was then lowered (underwater) into the vessel cavity below the flange and apparently caught and tilted. The overhead crane was re-adjusted and the bundle was lowered and assumed to be seate April 4, 1986

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During preparation to bolt down the bundle, the licensee found that it was not fully seated and was unable to seat the bundl '

The bundle was lifted out of the vessel and transferred to the storage well where it was visually inspected by the licensee with a remote camer Four peripheral tubes appeared to be bent inward: two tubes, in the southwest and southeast corners, were bent approximately 5 (degree of angle from the vertical); a northwest and northeast tube were at approximate angles of 20 and 35 , respectively. The Resident NRC inspector was notified of the problem by telephon NOTE: Each of the 72 HPCS tubes consists of three concentric tubes (see Figure 1). The outer. tube actually was " cocked" rather than bent. The two inner tubes were possibly bent, but sufficient information was not available to substantiate thi gril 5-6, 1986 The licensee manufactured a special tool to straighten the tubes. The four tubes were straightened and an air-flow test was satisfactorily performed. The bundle was transferred to the reactor vessel. Attempts to seat the bundle were unsuccessful; a gap of about one-half inch existed l between the vessel flange and the upper support plate of the bundle. The

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bundle was once again returned to the storage well and a visual inspection was performed by the licensee. No problems with the tubes were found; however, there was indication of rubbing between the pads on the bundle and the flow deflector plate support brackets (radial support bracket on Figure 3). It was not known if these rub marks were normal since visual inspections are not regularly performed. Measurements were taken on the brackets which indicated that two of the four brackets were not at the same level on the vessel wal April 7,1986 The licensee took additional measurements on the brackets to verify the previous data. The results indicated that the scutheast bracket was high and the southwest bracket was low when compared with the original design specifications. The significance of these findings has not been determined since measurements and visual inspections are not regularly performe April 8,1986 Two Region-based NRC inspectors arrived on site to follow the problem and the resolutions. The HPCS bundle was transferred to the reactor vesse The licensee attempted to seat the bundle and failed. A one-quarter inch gap existed between the vessel flange and the upper support plate of the bundl April 9, 1986 Further attempts to seat the bundle were unsuccessful, including rotating the bundle 180 . According to the licensee, the bundle appeared to

" wedge" down as it was lowered into the cavity, as if it was dragging or rubbin The licensee used a nuclear-grade lubricant to swab the pads. The objective was to lubricate and to mark where contact was made when the bundle was lowered. The bundle was then lowered, but it did not seat. A visual inspection indicated rub marks. From these findings it was determined that two pads were hanging-up on the brackets and not allowing the bundle to sea Subsequent Action The licensee removed some material from the two pads that were not seating against the radial support brackets and successfully seated the HPCS bundle. The inspectors found this resolution satisfactory and have no further concern with the seating of the bundle. However, the inspectors did have a concern with the possible material stress that could have been associated with the " cocking" of the outer concentric tube and the possible bending of the inner HPCS tube. To resolve this concern, the licensee contacted Southwest Research Institute (SWRI) of San Antonio, Texas to perform an engineering evaluation of the possible stress on the HPCS tube .

4. Engineering Evaluation The licensee requested Southwest Research Institute (SWRI) to perform an engineering evaluation of the possible stress that would have been experienced by the HPCS tube when bent to a 30 angle. SWRI computed that the maximum induced outer fiber strain would not exceed 3 percent. This value was obtained using an elastic-plastic material model and values published in " Irradiation Effects in Cladding and Structural Materials,"

S. H. Bush, ASM, 196 In addition, a residual stress value of 20,000 psi was assumed based upon a strain hardening coefficient of 0.1 and that all of the 3 percent strain was lost during the straightening process. The evaluation, based upon these assumptions and values demonstrated that the 3 percent strain was lower than the published values of 7 to 10 percent strain for 304 stainless material (the HPCS tubes are made up of 304 stainless) at the lifetime neutron exposure experienced by the HPCS bundle. Based upon this evaluation, SWRI concluded that the bounding analysis indicated that the HPCS tube had received no unacceptable damage and that future failure would not occur because of the associated bending of the tub The inspector verified this assumption by reviewing the evaluation and the licensee supplied data to ascertain that the lifetime neutron exposure used during the evaluations was correct. Cased upon the review of the engineering evaluation, the inspectors have no further concerns in this a rea .

5. Exit Interview The inspectors met with licensee representatives (denoted in Paragraph 1)

at the conclusion of the inspection on April 12, 1986, and by telecommunications on May 28, 1986, with Mr. J. D. Parkyn. The inspectors summarized the scope and conclusions of the inspection. The inspectors also discussed the likely informational content of the inspection report with regard to documents or processes reviewed by the inspectors during the inspection. The licensee did not identify any such documents or processes as proprietary. The licensee acknowledged the statements made by the inspectors with respect to the finding .

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