ML20059A604
| ML20059A604 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 07/01/1985 |
| From: | Cutter A CAROLINA POWER & LIGHT CO. |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| IEB-84-03, IEB-84-3, NLS-85-215, NUDOCS 9008230128 | |
| Download: ML20059A604 (9) | |
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- JUL 011985 SERIAL: NLS-85-215 Dr. J. Nelson Grace, Regional AdminiktrStor'. o } 'Z ~[
United States Nuclear Regulatory' C6mmission Suite 2900 101.Marietta Street, NW Atlanta, GA --30303 SHEARON HARRIS NUCLEAR POWER PLANT UNIT NO.1 - DOCKET NOJ 50-400 f~- FINAL RESPONSE TO IEB 84103-REACTOR CAVITY SEAL FAILURE.
Dear Dr. Grace:
Carolina Power & Light Company (CP&L) hereby submits its final response to IEB 84-03 for the Shearon Harris Nuclear Power Plant (SHNPP). By letter dated November 26,1984 CP&L notified you that we were conducting a detailed evaluation and design mod,fication of the SHNPP refueling cavity water seal t design and would submit the results of our investigation by July 1,1985. Attached is the Company's evaluation of the potential ior and consequences of a refueling cavity water seal failure, specifically addressing each consideration enumerated in the Bulletin.. Although our investig"ation concluded that the type of accident described in IEB 84-03 is " highly unlikely to occur at SHNPP the consequences ' design,pid loss of refueling water raised sufficient concern to modify tbe cavit of a ra further reducing the chances of such an accident. The design modifications, as well as abnormal operating procedures that address fuel in transit, will be completed prior to fuelload. m i We conclude that the seal failure described in IEB 84-03 is not a credible concern at -SHNPP and we have met the requirements of this Bulletin. If you have any questions concerning this matter, please call Ms. Carol Love at (919) 836-8166. l You very tr 17 N h Na /, / l A. B. Cutter - Vice sident b Nuclear Engineering Licensing L CGL/ccc (1623CGL). 1 . Attachment L cc: Mr. B. C. Buckley (NRC) Mr. Wells Eddl man L Mr. G. F. Maxwell (NRC-SHNPP) Mr. John D. Runkle Mr. Daniel F.yne (KUDZU) Mr. Travis Pa Dr. Richard D. Wilson Read (CHANGE /ELP) Mr. G. O. Bright (ASLB) i . Wake County Public Library Dr. J. H. Carpenter (ASLB) Mr. J. L. Kelley (ASLB) A. B. Cutter, having been first duly sworn, did depose and say that the information contained herein is true and correct to the best of his information, knowledge and belief; .and the sources of his information are officers, employees, contractors, and agents of . Carolina Power & Light Company. g fYw k Ntou )./'??"* %lfI My commistion4*pires: ///.27/ff W Notary %460 ! p,/..........' c%,g gg 1 f NOTARY \\ g 9008230128 85070t hDR ADOCK 0t40 o ','. vHie street
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%,[ 4 71 ~ 0 i i E 77tichm:nt to'- ( (f - - v !S.g3 215 g, t., z. ATTACHMENT TO FINAL RESPONSE TO IEB 84-03 E EVALUATION OF A REACTOR CAVITY SEAL FAILURE AT SHNPP A." Potential for a Refueling Cavity Water Seal Failure 3 CP&L evaluated the SHNPP cavity seal design in regard to IEB 84-03 and the Haddam Neck incident. We have concluded that a gross failure such as that U experienced at Haddam Neck is not a credible event at SHNPP based on its design - and proper installation, as discussed below. O 1. Design and Installation The cavity seal ring girder spans the open area between the reactor vessel . refueling flange and the refueling cavity liner (Figure 1). The cavity seal consists of two inflatable seals positioned on either side of the ring girder which is a circular' metal plate structure yesting on support beams. This - l structure is designed seismic Category I. 'a. Ring Girder l The ring girder is segmented into three equidistant sections for handling purposes! _when bolted together, these segments interlock to form a complete ring. A rubber seal used between the segments prevents leakage at each joint. When installed, the ring girder spans the majority of the 3' 11.5" opening, but leaves two inch gaps (nominal) on both sides for the intlatable seals. ~t To ensure the ring girder is installed in the proper position on the support a
- beams, guide plates are welded to the bottom of the ring girder, and shims and guide plates are welded to the support beam. When installed, the ring l
girder guide plates straddle the support beams. These design features assure that the cavity seal gap dimensions are established and remain constant for each refueling outage. The ring girder also has sides which extend further down into the cavity i-than the length of the seats. These provide additional surface area for the - seals to press against and help to form a water-tight seal'when the seals i are inflated. While it is " highly unlikely" that the SHNPP inflatable seal would push through the cavity gap, the consequences of a rapid gross loss of refueling r water without adequate makeup capacity caused sufficient concern to revise the ring girder design. To further, reduce the possibility of a seal failure incident, the design has been modified as follows: Metal plates welded around the side of the ring girder below the location of the inflatable seals (Figure l) will act as " bottom stops" ly for the seals to prevent slippage down through the gap. b ?- (1623CGL/ccc )
7 A ,gx f_5 shm:nt to + 4 L t -(,) i 15-85-215 < v -- i A circular metal ring welded to support bars which are attached to-
- the cavity seal support beam provides additional surface (parallel to' r
the edge of the reactor vessel refueling ledge) for the inflatable seal U to press'against. This essentially prevents the seal from extruding, or; . ballooning," to the side. h . The bottom stops and metal support ring enhance the design's ability to: prevent the inflatable seal from pushing through the cavity gap, and thus, i prohibit a gross leakage of refueling water incident such as occurred at Haddam Neck.
- b. L Inflatable Seals An inflatable seal is installed in the two inch gaps on either side of the.
ring girder. While each inflatable seal is manufactured as a single component, it is not continuous like an O-ring. When a seal is positioned-in the gap opening, the ends of the seal interlock together!to form a-water-tight barrier when inflated. j The angular portion of the seals (Figure 2) rest on either side of the gap, j preventing the seal from falling through the opening. The. seals 'are wide - enough in the cross sectional plane to handle variations in nominal gap j --width. When inflated, the lower portions of the seals expand to press < tightly against the reactor vessel refueling ledge and ring girder on one ' d side, and refue!!ng cavity liner and ring girder on the other side to form a I water-tight seal (Figure 1). 'l The SHNPP seal design is significantly different from the Haddam Neck - seal in.two critical areast. the width of the upper. seal (flange) and the j ' haraness of the rubber material. The width of the SHNPP upper seal (flange)is 4 inches; the Haddam Neck seal was 3.5 inches. - The durometer l(material hardness) value of the rubber in.the SHNPP inflatable seals is .j 65 the Haddam Neck seal was only 30. This means that the SHNPP seats are less' flexible in the upper regions, increasing the resistance to " push : y through" the opening, such as what occurred at Haddam Neck. 1 ~ 2. Seal Testing The potential for seal failure due to varying seat gap width conditions and r equivalent water head pressures was both tested using a segment of spare H. B. Robinson Unit 2 inflatable seal which is similar in cross-sectional dimension and material properties to that used at SHNPP. With simulated gap epenings ,4 of 2 and 2.25 inches; the seal withstood a pressure' equivalent to four_ times the normal SHNPP refueling water head. Even with a 2.5 inch gap, the seal withstood a pressure equivalent to 3.8 times the normal SHNPP refueling '1 water head before the top of the seal began to bend excessively. 3. Installation Procedure Installation of the seal structure is controlled by a corrective maintenance installation procedure. This procedure inc!udes inspections to assure the seal 3 is properly in place. (1 L k (1623CGL/ccc ) t 2 --l-w
p [L ,"'tcchment to.- 4 L -( JS-85-215= p-in. -p. v. s - M' ' In conclusion, the potential for.a refueling cavity seal failure is not a credible-- concern due to the design features of the seal structure and mechanisms to assure proper installation. j B.- - Scenarlo for Gross Seal Failure. Although a gross seal failure is not a credible event at SHNPP, a " worst case" scenario was postulated in which all of the considerations enumerated in IEB 84 - are included (i.e., leak rate, make-up capacity, time to cladding failure,'effect on, ,i l stored fuel and fuel in transfer, and emergency operating procedure).' - r The following assumptions were used in this scenarios i The seal structure design modifications (described above) are not pr'esent.- The refueling water is initially at normal refueling water level (El. 284.5'). The refueling cavity, fuel transfer canal, and spent fuel pool are
- interconnected.
The transfer tube remains open throughout the scenario. -- A quarter section of each seal ring falls through the cavity opening. 1.' No operator action is taken. j l. Maximum Leak Rate The maximum leak rate for the above scenario would be approximately 34,000 gpm un. der the full water head. Approximately 512,000 gations of refueling water would flood past the seal into the bottom of containment. 3 v 2.- Makeup Capacity Makeup water from the following sources would be available to replace the water lost in the gross seal failure scenarios: y
- a.
Refueling Water Storage Tank (RWST) The RWST could supply water to the Fuel Transfer System using the fuel l pool cooling pumps or the fuel pool clean-up pumps. Two of each are available, having pump capacit;es of 4560 and 325 gpm, respectively. The RWST is designed to hold 470,000 gallons of water; however, only a + c' minimal water supply may be available af ter initially supplying the water needed for refueling. ? b. Emergency Service Water System (ESWS) The ESWS could supply water via the Fuel Pool Cooling System by using L emergency connections. This system has an almost unlimited water supply l' from eithe the Auxiliary or Main Reservoirs. (1623CGL/ccc) l ,i
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v s .c. - Reactor Makeup Water Storage Tank (RMWST) l KThis system could supply water to the Fuel Transfer System using one of s the Reacto' Makeup Water Pumps and utilizing the Chemical and Volume ~ 4 r Control System. The RMWST is designed to hold 85,000 gallons. l d. -Demineralized Water System jl i 'This system could supply water to either the RWST or the RMWST using 7 .two pumps that can supply up to 600 gpm each. - The demineralized water. l storage tank is designed.to hold 500,000 gallons of water. Complete descriptions of these systems can be found in the SHNPP FSAR. '3. Time to Cladding Damage Without Operator Action. l I The only condition under which cladding damage could occur is if a fuel: . assembly in transit was in the manipulator crane. Calculations were developed - to determine the time to fuel failure af ter being uncovered with water using' 4 the following assumptions: { Fuel had 48 hour cooling per!od prior to refueling.- .J .The fuel' assembly modeled was the peak assembly for three consecutive cycles. A peaking factor of 1.34 was used; the pe:'. king factor times the core - s average assembly power equals the modeled assembly power. - j ---. Reactor power is 100 percent during the assembly afe in core. The assembly;was irradiated at the full power level for;930 effective full-j power days, with no credit taken for shutdowns. The fuel rod heatup is totally adiabatic; all' heat generated in a rod stays in the rod. Cladding failure is at 1300*F due to burst rupture (NUREG-0630, Cladding - - Swelling and Rupture Models for LOCA Analysis (Draf t), November 1978). l 1 The coolant: temperature and the cla' ding temperature are equal just prior d
- to fuel uncovering.
F The operator takes no action. The time to fuel failure af ter uncovering would be approximately 17 minutes for. 48 hour cooled fuel. 4. Effect on Stored Fuel and Fuel in Transit A gross seal failure resulting in a loss of refueling water down to the elevation H ~J of the reactor vessel refueling ledge and cavity seal ledge (El. 260.2) has been evaluated for the effect on stored fuel and fuel in transit. The top of active (1623CGL/ccc )
r-- y-3 -; 3.s.:. / 1 ['it: chm:nt to- -(f .(s,.LS-85215 ? M,'. r 3 4 T fuel in the fuel upender, RCC change mechanism and spent fuel storage racks would remain covered with water, as shown in Figure 3. ' As long as the fuel 1 remains covered with water, it is not expected to fail. + Only a single fuel element in transit in the manipulator crane would have the . potential of being uncovered with water.- 5. Emergency Operating Procedures i I '(_ 'l v While CP&L considers separate emergency operating procedures for a gross. i loss of refueling water event unnecessary because the potential for a refueling. j 'I ' ~ cavity seal failure is not a credible concern, fuel in transit will be addressed in plant abnormal operating procedures, to be prepared prior to fuel load.- -w.:n; , l." f ;, I' g -,. 1) i /. -{ -' > 11 lh.; ' \\ I b l f: 'l i k t '. I; y; 4 l l I (1623CGL/ccc ) 1;s s-
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