ML20235V635
| ML20235V635 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 10/06/1987 |
| From: | William Orders, Peebles T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML20235V633 | List: |
| References | |
| 50-369-87-35, 50-370-87-35, NUDOCS 8710150248 | |
| Download: ML20235V635 (7) | |
See also: IR 05000369/1987035
Text
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- u a UNITED STATES ' ' p, Mq .- ' ' .. NUCLEAR REGULATORY COMMISSION = ..i a3-' REGION 88.. O.' d [ 3:,Ha .
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. ot M 10f fdARIETTA STREET,N.W; . .1 ' N L. ' . , ,,,;v j,. c;f' ' ATLANTA, GEORGI A 30323' ' ' , ' I - ' f ' - ,,
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'%.. /' ' - u .... . x l ' . l '. ' p l " % (Report Nos.: l50-369/87-35and'50-370/87-35 .i .c,
- 1.icenseei LDuke Power Company _
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- 422 South Church Street-
, < > pi : + Charlotte',.NC, 28242- , ' , ! - E ocket.Nos',': l50-369 and 50-370-
- , License Nos
- NPF-9 and NPF-17
' ' D ' 4 Facility Name: McGuire 1 andl2: ! 1 .
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. . > ' Inspection Conducted: ~ August 24-- September.4, 1987. - Inspector: 282N =/8 7 1.-Ordets,-Senior Res ent Inspector Date J'igned h 4[T2-
4 Approved'by: ' ' j . .-T.:A..Peebles, 56ction; Chief Date Signed- ' ' > Division'of Reactor Projects , ';G : i c % ' , 1 1, l, k ' ?! ' 't , ?l .a_ ,; .(f % I' ' 7 U j 1 ' SUMMARY ' ,
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, ,. ., ' w..- < . .y - Scope': 'This special,yyt unannounced ins'pection was conducted 'to evaluate the -, . 4 safety implications of " inoperable. containment divider barriers 'on McGuire ' ' Unit 2 ' ' > , f ,- 'l- .. , i Of! the areas inspected, 'one viola l tion was identified: Inoperable Results:5 . containment-divider barrier.y ' ' - ... i 1 + , . , y , ! ! n. ,, ,
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-. -__ _ 'I . .. iD l REPORT DETAILS ! ! 1. Persons Contacted ) Licensee Employees
T. McConnell, Plant Manager . B. Travis, St:; <.rintendent of Operations
- D. Rains, Superintendent of Maintenance
B. Hamilton, Superintendent of Technical Services 1 N. McCraw, Compliance Engineer i M. Sample, Superintendent of Integrated Scheduling '
- N. Atherton, Compliance
J. Snyder, Performance Engineer M. Robson, Design Engineer Other licensee employees contacted included construction craftsmen, techr.icians, operators, mechanics, security force members, and office . personnel.
- Attended exit interview
, 2. Exit Interview The inspection scope and finoings were summarized on September 4,1987, with those persons indicated in paragraph 1 above. The inspector described the areas inspected and discussed in detail the inspection findings. No dissenting comments were received from the licensee. The licensee did not identify as proprietary any of the materials provided to or reviewed by the inspector during this inspection. The following violation was discussed: Violation 370/87-35-01: Inoperable containment divider barrier I (par.agraph7). 3. Licensee Action on Previous Enforcement Matters An unresolved item (UNR) is a matter about which more information is required to determine whether it is acceptable or may involve a violation or deviation. No new unresolved items were identified in this report. f _ _ _ _ - - - - - - - J
_ . . . ! 2 ! '4. Event Analysis On L August 13, 1987, licensee personnel were preparing a contaminated , i storage area for an upcoming Unit I refueling outage when five large unidentified bolts were found. It was later determined that the bolts. were control rod drive mechanism (CRDM) missile shield hold-down bolts. l The missile shields'on each unit consist of five concrete and steel blocks with approximate dimensions of 28 feet x 6 feet x 3 feet each. When in place these blocks serve as a missile shield structure over the control rod drive mechanisms and as part of the divider barrier between upper and lower containment compartments. The barrier ensures that minimum bypass
steam flow will occur from the lower to the upper containment during a j LOCA.. This in turn ensures a diversion of the steam through the ice
condenser bays consistent with the LOCA analyses.
1 The shield blocks are designed such that blocks 1, 3 and 5 hold blocks 2 and 4 in place through physical overlap. Blocks 1, 3 and 5 employ hold-down bolts to maintain the components in place during an accident, whereas 2 and 4 do not. Block i employs 2 bolts, one at each end, blocks 3 and 5 have two bolts at each end. , On August 14, containment entries were made to determine actual shield / barrier status on both units, which was as follows: , Unit 1: Three hold-down bolts (out of a total of 10) were not installed The , ' missing bolt locations were the interior bolts on each end of block 3, and tSe inside bolt on one end of block number 5. The remaining bolts were considered adequate to carry the design loads. Unit 2:
Three hold-down bolts (out of a total of 10) were not installed. The ! missing bolt locations were the two interior bolts on each end of block number 5, and the bolt on one end of block number 1. The remaining bolts i of block number 5 were considered adequate to carry the design loads. The i remaining bolt in block number 1 could not be qualified to resist the j design loads at that panel. A review of available documentation indicates that the bolt missing from block 1 may have never been installed. i A review of the operating logs indicates that the Unit 2 operations staff became aware of the problem at 10:06 a.m. on August 14, and logged the shields inoperable pursuant to TS 3.6.S.5, Containment Systems. At 11:45 j a.m., it was erroneously concluded that the bolt missing from block I had been intentionally deleted since the bolt hole was filled with grout. Accordingly the shield blocks were declared operable. At 5:30 p.m. on August 14 the operations staff was notified by design engineering personnel that the single remaining bolt in block 1 was inadequate. The missile shield was again declared inoperable and the unit was subsequently - - - - _ _ _. _
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- shutdown pursuant to thel action -statement. of TS 3.6.5.5 beginning at
8:00 p.m.- , Ultimately; all bolts were installed on both units with the exception of one nut on Unit.1. The missing nut is in a "two- bolt" location, only one is required and'is in place. i Unit;2 was. restarted on the morning of August'16. LS. Safety Evaluation / Containment Functional Design , As mentioned l earlier thA blocks- are desig'ned to serve as a missile shield . ' structure.over the.. control rod ~ drive mechanisms, and as a divider barrier " between . upper and lower containment. Design engineering calculations indicate that there was not an operability concern relative to Unit:1, thus the prime concern is focused on the , . safety significance _of_the missing bolt on Unit 2. The- overriding safety ' issue in this case involves the displacement of block 1 during a. LOCA _ Design engineering calculations reveal that' the missile shield =would see a net uplift pressure- of 5.71 psi. The force. ' would be= sufficient to displace. the block and result in increased bypass - flow. from'the lower 'to the upper containment, flow'that would bypass the ' ' ' ice condenser. This in turn would apparently result in an increase in the post LOCA peak containment pressure as discussed below. ' U1'timately, the containment is designed to ensure that an acceptable upper '
limiti of leakage of radioactive material is not exceeded under design j accident conditions. .j The ice condenser .is designed to limit the containment pressure below the < design. pressure for all reactor coolant pipe break sizes up to and
including a double-ended severance, q I .s' The containment consists of a containment vessel and a separate reactor
' building enclosing an annulus. The containment vessel is a freestanding j welded steel-structure with a vertical cylinder, hemispherical dome, and a .. flat circular base. The reactor building is a reinforced concrete structure similar in' shape to the containment vessel. The design internal pressure for the containment is 15 psig, and the --design temperature;is 250'F. Design Evaluation - Loss of Coolant Accident During the first few seconds of the blowdown period of the Reactor Coolant j System following a LOCA,. containment conditions are characterized by rapid j pressure and temperature transients. It is during this period that the peak transient pressures, differential pressures, temperature and blowdown j ' loads occur. r ' i
. . P 4 As blowdown continues following the initial pressure peak from a double i ended cold leg break, the pressure in the lower compartment again
increases, reaching a peak at or before the end of blowdown. The pressure 4 in the upper compartment continues to rise from beginning of blowdown and i reaches a peak which is. slightly lower than the lower compartment [ pressure. After blowdown is complete, the steam in the lower compartment l ' continues to flow through the doors into the ice bed compartment and
condensed. The primary factor in producing the upper compartment pressure peak and in determining the containment design pressure is the displacement of air from the lower compartment into the upper compartment. The ice condenser effectively performs its function of condensing the steam that enters the ice . beds. Under assumed design conditions, the only source of steam q entering the uppsr containment is from leakage through the drain holes and , other leakage around crack openings in hatches in the operating deck j separating the lower and upper portions of the containment building. { Herein lies perhaps tha major area of concern. The volumes of the various j containment compartments determine directly the air volume compression ratio. This is basically the ratio of the total active containment air ( volume to the compressed air volume during blowdown. During blowdown, air 1 is displaced from the lower compartment and compressed into the ice , condenser beds and into the upper containment above the operating deck. .l It_is this air compression process wh1ch primarily determines the peak in
containment pressure, following the initial blowdown release. ' The equation which represents the compression peak pressure in the upper compartment for containment design is given by f r)" + W P P3=P0 deck where P = Compression peak pressure (psia) 3 C" = Volume compression ratio , P = Initial containment pressure, 15.0 psia ) g n = Polytropic exponent j WP = Pressure increase caused by deck leakage (psi) ) } deck This equation is detailed on page 6.2-6 of the FSAR. The point here, as can be seen in the equation, peak pressure appears to increase linearly 1 with deck leakage, a The divider barrier, including the enclosures over the pressurizer, steam j generators and reactor vessel, is designed to provide a reasonably tight seal against leakage. Potential leakage paths exist at all the joints between the operating deck and the pump access hatches and reactor vessel enclosure slabs. The total of all deck leakage flow areas is assumed to be approximately five square feet. _ _ _ - _ _ _ _ - -
- -__ U - . 5 t The metkod..of analysis used to obtain the maximum allowable deck leakage capacity as a function.of the primary system break size is detailed in the FSAR, page 6.2-10. l The allowable leakage area was determined for a numbe' of RCS break sizes and is detailed in-FSAR Section 6.2. Analysis reveiled that breaks of. , six or eight inches were the most limiting cases. Table 6.2.1-18 of the FSAR " Allowable Leakage Area for Various R^ actor Coolant System Break Sizes" indicates in part the following: L Break Size 5 ft2 Deck Leak Deck Leakage Resultant Peak Air Compression Area (fte) Containment - Peak (psig) Pressure (ps_id i: Double ended . 7.7 50 11.9 0.6 Double-ended 6.6 50 12.5 3 ft: 6.25 50 12.2 i 30.5 fte 5.75 50 14.5 8 inch diameter 5.5 40 14.9 6 inch diameter 5.0 40 14.7 As can be seen from the te,ble, peak containment pressure for the eight ! inch and six inch breab sppear to be the most limiting. From the previous equation it is seen that containment peak pressure is linearly dependent on deck leakage. , Conclusion: 1. Shield block 1 on Unit 2 would have displaced had a LOCA occurred. This would have resulted in additional leakage from lower to upper
- ontainment.
2: Containment peak pressure is directly proportional to leakage from lower to upper containment, j 3. A primary break of six or eight inches during the period when the bolt was missing from the number 1 shield block may have caused peak containment pressure to exceed the design pressure of 15 psi. 6. Administrative Controls A review revealed that there appears to be only one procedure applicable to the reinsta11ation of the control rod drive mechanism missile shield blocks. That procedure PT-0-A-4200-04, Divider Barrier Hatch Seal Inspection, is inadequate to assure that the barriers are appropriately installed and secured. The sections which either directly or indirectly deal with the blocks in question are sections 9.1 and Enclosure 13.2 page 5 of 10. Section 9.1, I - _ _ - . -
- - - _ 3 = , 6 ! . Test Method, simply . requires that "the hatch (blocks) will be reset and secured.....". Enclosure 13.2, simply requires that the " blocks are installed and secured." In neither case does the procedure discuss how to secure the blocks, number of bolts, torque to be applied, or sihilar pertinent ' information. Discussions with the licensee indicate that procedure changes will be implemented'during the upcoming Unit 1 outage, the intent of which is to prevent the recurrence of similar events. l The lack of adequate administrative control of the shield bolts appears to be the root cause of this event. .7. Enforcement Evaluation Technical Specification (TS) 3.6.5.5 requires in Modes 1, 2, 3 and 4 that the personnel access doors and equipment hatches between the containment's upper and lower compartments shall be OPERABLE and closed. With a personnel access door or equipment hatch inoperable or open except for- personnel transit entry, the door or hatch must 'be returned to OPERABLE status or to its closed position (as applicable) within one hour - or the unit must be in at least HOT STANDBY within the next six hours and in COLD ShdTDOWN within the following 30 h'mrs. Contrary to that requirement, the CRDM missile shield was not operable when the plant operated in Modes 1-4, from March 1983 until April 14, 1987. Technical Specification 6.8.1 requires that written procedures be established, implemented and maintained to cover the maintenance of safety-related structures, systems and components. Implicit in that requirement is the requisite that the procedure be written in the detail necessary to ensure the successful completion of the task. Contrary to that requirement procedure PT-0-A-4200-04, Divider Barrier Hatch Seal Inspection did not entail adequate instruction to assure proper installation of the control rod drive mechanism shield blocks. The example of failure to meet the Technical Specification Action statement and establish or implement an adequate procedure to control the installation of the shield blocks is an apparent violation (370/87-35-01). }}