ML20217F318

SER Accepting Relief Request for Approval for Use of Alternate Exam Requirements for Plant Inservice Insp Program

ML20217F318
Person / Time
Site:	Callaway
Issue date:	03/24/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217F316	List: ML20217F312 ML20217F318
References
NUDOCS 9803310344
Download: ML20217F318 (6)

Text

UNhTED STATIS j*-

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WAsHWOTON, D.C. 30806 0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE RFt IEF REQUEST TO THE SECOND TEN YEAR INSERVICE INSPECTION PLAN UNION Fl FCTRIC COMPANY CAI I AWAY PLANT. UNIT 1 DOCKET NO. 50-483

1.0 INTRODUCTION

The technical specifications for the Callaway Plant, Unit 1, state that the inservice inspection of the American Society of Mechanical Engineers (ASME) Code Class 1,2 and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel -

Code and applicable addenda as required by 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Section 50.55a(a)(3) states that altematives to the requirements of paragraph (g) may be used, when i

authorized by the NRC, if (i) the proposed attematives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2 and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examinat;on of components and system pressure tests conducted during the first ten-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) twelve months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable ASME Code,Section XI, for Callaway Power Station, second ten-year inservice inspection (IS)intervalis the 1989 Edition. The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifestions listed therein and subject to Commission approval. -

Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Sectbn XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination, i -9803310344 990324 7 3 PDR ADOCK 05000483 1 .

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2-Q pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose attemative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were '

imposed.

in a' letter dated December 19,1997, Union Electric Company submitted to the NRC its request for approval of an altemative to the Code required examination for Class 1 bolted connectons inside the bioshield during the ninth refueling outage of Callaway Planti The Civil Engineering and Geosciences Branch, Division of Engineering, has reviewed and evaluated the licensee's request for an attemate examination, pursuant to 10 CFR 50.55a(a)(3)(ii).

2.0 DISCUSSION Component Function -

Code Class: 1

Reference:

IWA-5242(a)

Examination Category: B-P ltem Numbers: ~ All item numbers listed under Examination Categories B-P

Description:

Alternate rules for insulation removal during IWA-5000 pressure tests at bolted connections in systems borated for the purpose of controlling reactivity Component Numbers: Bolted connections listed in Table 1 of the li:;onsee's letter of December 19,1997 Code Requirements ASME Section XI,1989 Edition, Paragraph IWA-5242(a) states, "For systems borated for the purpose of controlling reactivity, insulation shall be removed from pressure retaining bolted 3 connections for visual examination VT-2."

Licensee's Basis for Proposed Alternative (As stated)

Authorization is requested for a proposed altemative from the requirement to remove insulation for visual VT-2 examination of bolted connections during a system pressure

- test on systems borated for the purpose of controlling reactivity.- This request proposes

- a one-time attemate examination from the code requirements of IWA-5242(a) for

~ Callaway Refueling Outage 9 on Class 1 boited connections inside the bioshield. Union Electric believes that removal of insulation at bolted connections during Refuel 9 on components inside the bioshleid for the sole purpose of visual examination is impractical

. and will result in hardship and unusual difficulty for the reasons listed below per 10 CFR -

50.55a(a)(3)(i):.

~ 1) - The visual VT-2 examination of the Reactor Coolant System (RCS) is performed following the majority of outage maintenance activities and just prior to reactor -

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criticality. The RCS is at a normal operating temperature and pressure (557'F and 2235 psig) during the pressure test as required by IWA-5000. Performance of a visual VT-2 examination, re-installation of insulation, and disassembly of scaffolding under these conditions is a personnel safety hazard. Performance of the examinations at cold shutdown is the only relief realized by the use of_ Code

" Case N533.

2) All Class 1 bolted connections listed in Table 1 were inspected without insulation in accordance with Code Case N533 during Refueling Outage 8. None of the bolted connections exhibited any evidence of degradation due to boric acid -

corrosion. Where boric acid residue was discovered and bolting removed, no :

rorrosion or gross degradation due to intergranular stress corrosion cracking (IGSCC) was evident on the bolting material.

3) Exposure for all examinations performed in accordance with Code Case N533 from Callaway Refueling Outage 8 totaled 9.2 Person-Rem, with no evidence of degradation discovered. Dose rates for Refueling Outage 9 are expected to be -

higher than in previous outages due to the Axial Offset Anomaly and fuel defects that Callaway is currently experiencing in its reactor core. The projected dose for the nine components listed in Table 1 for Refueling Outage 9 is expected to exceed 7 Person-Rem. This is considered an excessive amount of dose relative

- to the anticipated inspection results.

4) Differential thermal expansion occurs when insulation is removed from a bolted connection that creates a greater chance for leakage. When insulation is removed, the flanges expand at a rate greater than the bolts causing stress on the connection. Once the bolts expand, the stress has caused the equivalent of untorquing the connection. The less tightened connection then has a higher probability ofleaking.

5) Code Class 1 systems borated for the purpose of controlling reactivity are extensive and consist of large systems covering many areas inside the containment bioshield on multiple elevations. Scaffolding will be required to access many of the bolted connections. In addition, many of the bolted connections are located in medium to high radiation areas. Insulation removal combined with scaffolding requirements willincrease outage costs. Refuel 8 craft support of these inspections incurred $43,000 in additional costs despite the limited relief provided by Code Case N533, if the exam were to be performed during the normal VT-2 between Modes 3 and 2 ascending, critical path time will be extended by several hours to accommodate the insulation installation and scaffold removal inside the bioshield wall and throughout containment after the

- examination is complete. Critical path cost is currently estimated at $207,000 per day.

~ Union Electric believes that the established Callaway programs described below in

. addition to the alternative examination proposed below, provide an acceptable level of j;

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safety and quality for bolted connections in systems borated for the purpose of controlling reactivity per 10 CFR 50.55a(a)(3)(ii).

1) in response to NRC Generic Letter 88-05, Union Electric established a program to inspect all boric acid leaks discovered in the containment building and to evaluate the impact of those leaks on carbon steel or low alloy steel components. All evidence of leaks, including boric acid crystals or residue, are inspected and evaluated regardless of whether the leak was discovered at power or during an outage. Issues such as the following are considered in the -

inspection and evaluation: 1) evidence of corrosion or metal degradation,2) effect the leak may have on the pressure boundary,3) possibility of boric acid traveling along the inside of insulation on piping, and 4) possibility of dripping or spraying on other components. Based on Dis evaluation, appropriate corrective actions are initiated to prevent reoccurrence of the leak and to repair, if necessary, any degraded materials or components.

2) In addition to the nondestructive examinations required by ASME Section XI, Union Electric has committed to the bolting examination requirements of NRC Bulletin 82-02. In accordance with this Bulletin, at least two nondestructive examination techniques (e.g., ultrasonic, liquid penetrant, magnetic particle, or visual VT-1) are performed on bolted connections of the following components:

Steam Generator primary manways, Pressurizer primary manway, Pressurizer safety valves, and a total of 22 Reactor Coolant System isolation valves that are greater than 6" NPS. As a minimum, two nondestructive examination techniques are used whenevu the bolted connection of one of the subject components is disassembled for maintenance or other inspection. These additional examinations ensure that degradation mechanisms such as stress corrosion cracking or corrosion do not go undetected in bolted connections critical to reactor safety.

3) All bolted connections on Callaway's Class 1 borated systems inside the bioshield consist of SA-453 Grade 660 for studs and SA-194 Grade 6 or SA-453 Grade 660 for nuts. The stainless steels were designed to be corrosion resistant in corrosive applications. This is substantiated for the 410 stainless steels (SA-194) by documents such as EPRI Report NP-5769 which attests to the resistance of stainless steels to boric acid corrosion. EPRI Report TR-104748 further confirms in section 7.2.1 that the 410 stainless steels are superior to the low alloy and carbon steel bolting materials. 410 stainless steel is an acceptable nut material as the nuts only experience a compressive stress. Tensile stresses l are required for initiation of stress corrosion cracking. Therefore, only studs comprised of 410 stainless steel are potentially susceptible _to stress corrosion cracking. EPRI Report TR-104748 also identifies A-286 (SA-453) as a superior fastening material.- The superalloy was designed for resistivity to acid corros6on 1 environments due to its high nickel and chrome content and the inclusion of molybdenum specifically to inhibit inorganic acids such as boric acid. These

- materials have been further evaluated by material selection expert C.P. Dillon i -l-,,,a, , , , , , , , , , , , , , , , 1 - -

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. who was subcontracted by Nickel Laboratories. His evaluation concludes "the development of intermediate concentrations of boric acid solution in the flange area (due to minor leaks and evaporation of the water) would not attack the bolting significantly and would be a marked improvement over low-alloy steel assemblies." To ensure that degradation mechanisms in these metals are mitigated, Union Electric maintains a program at the Callaway Plant that controls materials (insulation, thread lubricant, boron, etc.) that may come in contact with safety related components, including bolting. This program ensures that impurities are not present in concentrations that would promote development of stress corrosion cracking in stainless steel bolted connections. The only carbon steel bolted connections at the Callaway Plant on systems borated for the purpose of controlling reactivity inside the bioshield are Steam Generators manways, Reactor Coolant Pump bolting and Pressurizer manways. These areas will be inspected with the insulation removed in accordance with Code Case N533.

4) During Refueling Outage 8, Callaway verified the integrity of all Class 1 bolted connections during cold shutdown with the insulaticq removed and during the normal VT-2 with insulation installed in accordance with Code Case N533 and no evidence of degradation was discovered after 12 years of service. Based on the material properties of these bolted connections, degradation is not anticipated during the subsequent 18 months.

u The proposed attemative examination is requested for one-time use at Callaway during Refueling Outage 9. This alternative is not a request for use of Code Case N533 as its use has already been approved for Callaway by the NRC.

Licensee's Proposed Alternative Examination (As stated)

Bolted connections fabricated of materials resistant to boric acid corrosion in systems borated for the purpose of controlling reactivity shall receive a visual VT-2 examination during the system pressure tests of IWB-5000 and IWC-5000 with the insulation installed. If evidence of leakage is detected, either by discovery of active leakage or evidence of boric acid crystals, the insulation shall be removed and the bolted connection shall be re-examined and, if necessary, evaluated in accordance with the corrective measures of Subarticle IWA 5250.

Carbon steel bolted connections within the Inservice Inspection boundaries will receive an inspection for boric acid residue with the insulation removed. In addition, a VT-2 inspection will be performed in accordance with ASME Section XI requirements with the insulation installed at normal operating pressure and temperature.

If insulation is removed for planned maintenance, repair, or other inspection at a bolted connection in a system borated for the purpose of controlling reactivity, a visual examination shall be performed on the bolted connection prior to disassembly and, if evidence of leakage is discovered, evaluated in accordance with the corrective measures of Subarticle IWA-5250.-

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• 3.0 EVALUATION:

The licensee states that due to axial offset anomaly and fuel defects in the reactor core during the current fuel cycle, the reactor coolant activity will be higher than normal during the ninth

- refueling outage of Callaway Plant. Therefore, the radiation dose to personnel performing the

' Code visual VT-2 examination of bolted connections for components inside the bioshield, is expected to be high and is estimated to exceed 7 man-rem. For Refueling Outage 9, the staff has determined that removal of insulation at bolted connection to perform VT-2 visual examination for components listed in Table 1 of the licensee's letter of December 19,1997,

- would result in hardship without a compensating increase in the level of quality and safety. The staff has evaluated the effect of potential degradation mechanism on bolting material.and has concluded that the subject bolts being made of 410 stainless steel, are resistant to boric acid -

corrosion. Furthermore, the VT-2 visual examination of the bolts with the insulation removed during the previous outage had no evidence of degradation. Therefore, it is unlikely that a degradation mechanism would initiate during the next fuel cycle to make it susceptible to an Inservice failure. In the unlikely event that a flaw has initiated in a bolt during the past fuel

cycle, it is not anticipated that the flaw would grow to a critical size during one fuel cycle since the botting material is known to have an acceptable crack growth rate with adequate fiacture toughness. The licensee, however, will perform the Code-required examinations of the botting during the subsequent refueling outage. Nevertheless, during the upcoming Refueling Outage

- 9,~ the licensee has proposed to inspect the bolted connections with insulation in place during the system pressure test to detect any evidence of leakage either in the form of an active leakage or as presence of boric acid crystals and implement necessary corrective measures in accordance with the Code if any leakage is detected. Therefore, the licensee's proposed altemative provides a reasonable assurance of structural integrity during the coming fuel cycle.

Based on the above, the staff approves the licensee's proposed altemate examination for only a one-time use at the Callaway Plant during Refueling Outage 9.

4.0 CONCLUSION

The staff has determined that the reactor coolant system activity during the Refueling Outage 9 is expected to be higher than normal due to the axial offset anomaly and defective fuel pins in the reactor core during the current fuel cycle. Hence, the radiation levels inside the bioshield  !

I and consequent dose to personnel involved in the visual VT-2 examination of bolted connections for components inside the bioshield, are expected to be higher than normal during this outage. The licensee has proposed an attemative to the requirement of removal of insulation for visual VT-2 examination of bolted connections during system pressure test of components identified in Table 1 of their December 19,1997, submittal. Based on an evaluation of the bolting material, the results of previous examinations, the hardship involved in meeting the Code, and the assurance of structural integrity provided by the altemative, the staff has determined that compliance to the applicable Code would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Therefore, the proposed altamative is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for a one-time use at the L Callaway Plant, Unit i during Refueling Outage 9.

Principal Contributor: P. Patniak(

w Date: - March 24,1998 4

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