ML20210H653
| ML20210H653 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 07/30/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20210H642 | List: |
| References | |
| NUDOCS 9908040066 | |
| Download: ML20210H653 (7) | |
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NUCLEAR REGULATORY COMMISSION wAsHWGToN, D.C. 30006 4 001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUESTTO THE SECOND TEN YEAR INSERVICE INSPECTION PLAN UNION ELECTRIC COMPANY CAI I AWAY PLANT. UNIT 1 DOCKET NO, 50-483
1.0 INTRODUCTION
The Technical Specifications for the Callaway Plant, Unit 1 (Callaway) 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
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written relief has been granted by the Commission pursuant to Section 50.55a(g)(6)(i). Section 50.55a(a)(3) states that attematives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives 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.
1 Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2 and 3 components (including j supports) shall meet the requirements, except the design and access provisions and the j 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 examination 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 inspection interval, subject to the limitations and modifications listed therein. The applicable ASME Code,Section XI, for Callaway Plant, Unit 1, second ten-year inservice inspection (IS) interval is the 1989 Edition. The components (including supporis) 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 modifications 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 Section 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, 9908040066 990730 PDR ADOCK 05000483 P PDR I
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pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose I 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 1 due consideration to the burden upon the licensee that could result if the requirements were imposed.
In letters dated March 19 and June 18,1999, Union Electric Company (the licensee) submitted a relief request for approval of Altemate Examination ISI-12A in accordance with 10 CFR 50.55a(a)(3) for the 1989 Edition of ASME Section IX, IWA-5242(a). The relief request is an {
altamative to the ASME Code required examination for Class 1 bolted connections inside the bioshield at Callaway for the remainder of the current 10-year inspection interval (Interval 2) that ends December 19,2004. The scope of the request was limited to components inside the bioshield. The letters provided the hardship and unusual difficulty due to unnecessary man-rem exposure that would be incurred by removing insulation inside the bioshield on systems borated for the purpose of controlling reactivity. The relief request for an attemate examination was evaluated pursuant to 10 CFR 50.55a(s)(3)(ii). It was approved previously for the licensee's refueling outage 9 for Callaway in the staff's letter of March 24,1998.
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:
Altemate 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 attachment to the licensee's letter of March 19,1999 Code Requirements ,
i ASME Section XI,1989 Edition, Paragraph IWA-5242(a) states, "For systems borated for the l
. purpose of controlling reactivity, insulation shall be removed from pressure retaining bolted connections for visual examination VT-2." l l
Licensee's Basis for Proposed Alternative (As stated) !
l The licensee stated that authorization was requested for a proposed attemative from the !
requirement to remove insulation for visual VT-2 examination of bolted connections during a j system pressure te6t on systems borated for the purpose of controlling reactivity. This request is for an attemate examination from the code requirements of IWA-5242(a) for the Callaway i Class 1 bolted connections inside the bioshield for the remainder of the current 10-year l inspection interval (Interval 2). The licensee stated that the removal of insulation at bolted l connections of the components inside the bioshield for the sole purpose of visual examination is
impractical and will result in hardship and unusual difficulty. The reasons provided by the licensee are listed below:
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- 1) The visunt VT-2 examination of the Reactor Coolant System (RCS) is performed following the majority of outage maintenance activities and just prior to reactor 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 [ attached to the licensee's letter of March 19,199g,] were inspected without insulation in accordance with Code Case N533 during Refuel 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 corrosion or gross degradation due to intergranular stress corrosion cracking (IGSCC) was evident on the bolting material. Exposure for all examinations performed in accordance with Code Case N533 from Callaway Refuel 8 totaled 9.2 Person-Rom, with no evidence of degradation discovered. The projected dose rates for the nine components listed in Table 1 for Refuel 10 is expected to exceed 5.8 Person-Rem. This is considered an excessive amount of dose re!ative to the anticipated inspection results.
- 3) 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 of leaking.
- 4) Code Class i 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 will increase outage costs. Refuel 8 craft support of these inspections incurred $43,000. ,
These costs were incurred 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.
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- 5) VT-2 exams on the listed components [in Table 1] were performed with the insulation i installed in accordance with Altemative Examination ISl-12 during Callaway Refuel 9
[(relief request approved in staff letter dated March 24,1998)]. The inspections identified no leaking connections at any of the listed components. j
The licenses further stated that the established Callaway programs in addition to the attemative exarnination proposed below, provide an acceptable level of safety and quality for bolted connections in systems borated for the purpose of controlling reactivity in accordance with 10 CFR 50.55a(a)(3)(ii). The licensee described the programs as follows:
- 1) In response to NRC Generic Letter 88-05, [the licensee) 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, is 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 this 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, [the licensee] has committed to the botting 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 j total of 22 Reactor Coolant System isolation valves that are greater than 6" NPS. As a minimum, two nondestructive examination techniques are used whenever the bolted connection of one of the subject components is disassembled for maintenance or other inspection. These additional examinaSons 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 i 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 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 corrosion 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 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
o 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, (the licensee) 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 botting. 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 botting and Pressurizer manways. These areas will be inspected with the
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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 insulation 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.
The licensee has requested use of the proposed attemative examination for the remainder of the current inspection interval (Interval 2) which includes the upcoming Refueling Outage 10.
This is not a request for use of Code Case N533 as its use has already been approved for Callaway by the staff.
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. I If insulation is removed for planned . maintenance, repair, or other inspection at a bolted j 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. l I
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3.0 EVALUATION The licensee stated that the projected dose from the radiation levels inside the bioshield to the personnel that would be involved in the visual VT-2 examination of bolted connections for I
components inside the bioshield is more than 5.8 person-rem which the licensee considered excessive relative to the small inspection effort in that the exposure for all examinations performed in accordance with Code Case N533 from Callaway Refueling Outage 8 totaled 9.2 person-rom. The staff concludes that the licensee's compliance to the applicable ASME Code would result in hardship or unusual difficulty.
The staff has evaluated the effect of potential degradation mechanism on bolting materi'al 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 Refueling Outage 8 had no evidence of degradation Also, during Refueling Outage 9, the licensee inspected the bolted conner.tions with insulation in place during the ,
system pressure test to detect any evidence of leakage either in the form of an active leakage I or as presence of boric acid cystals and implemented necessary corrective measures in accordance with the ASME Code if any leakage is detected. The inspections identified no I leaking connections at any of the listed components. Therefore, the staff concludes that it is unlikely that a degradation mechanism would initiate during the remainder of the current '
inspection interval to make it susceptible to an inservice failure, in the unlikely event that a flow has initiated in a bolt during the past fuel cycle, it is not anticipated that the flaw would grow to a l critical size during one fuel cycle since the bolting material is known to have an acceptable crack growth rate with adequate fracture toughness. Nevertheless, during the remaining refueling outages of the current interval, 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. Therefora, the licensee's proposed altemative provides a reasc,nable assurance of structural integrity during the coming fuel cycle. Also, performing the ASME Code inspection without the insulation at the RCS temperature, can cause thermal stresses in the bolting to increase the probability of leakage. Therefore, the staff has also determined that removal of insulation at bolted connections to perform VT-2 visual examination for components listed in Table 1 would not result in a compensating increase in the level of quality and safety.
Based on the above, the staff concludes that the licensee's proposed attemate examination for use at the Callaway Plant during the remainder of Interval 2 meets the conditions of 10 CFR 50.55a(3)(ii) in that the licensee's compliance to the applicable ASME Code would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
4.0 CONCLUSION
The staff has determined that the radiation levels inside the bioshield and consequent dose to personnel involved in the visual VT-2 examination of bolted connections for components inside the bioshield, are expected to cause an excessive dose relative to the anticipated inspection results. 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 March ig,1999, submittal. Based on an evaluation of the botting material, the results of previous examinations, the hardship involved in meeting the ASME
Code, and the assurance of structuralintegrity provided by the attemative, the staff has determined that compliance to the applicable ASME 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 the remainder of the current inspection interval (Interval 2) at the Callaway Plant.
Principal Contributor: J.Donohew Date: July 30, 1999 l
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