ML19242A200
| ML19242A200 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 06/06/1979 |
| From: | Hendrie J NRC COMMISSION (OCM) |
| To: | Trible P HOUSE OF REP. |
| References | |
| NUDOCS 7907310585 | |
| Download: ML19242A200 (1) | |
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NUCLEAR REGULATORY COMMISSION
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y June 6, 1579 OFFICE OF THE CHAIRMAN The Honorable Paul Trible United States House of Repre,entatives Washington, D.C. 20515
Dear Congressman Trible:
I have received your letter of March 22, 1979 regarding the shutting down of the two unit Surry Power Station due to concerns regarding the level of protection provided against postulated earthquakes. A Federal Register notice summarizing the information which led to the Nuclear Regulatory Commission staff decision of March 13, 1979 to shut down these and the other thr,ee nuclear plants is enclosed.
Following the Nuclear Regulatory Commission order of March 13, 1979 to shut down the five nuclear power plants, including the two-unit Surry Power Station, independent review teams for each affected power plant were established within the staff of the Office of Nuclear Reactor Regulation.
In particular, the staff review team for the Surry facility is dedicated to prompt review and analysis of submittals by the Virginia Electric and Power Company (VEPCO) in support of lifting the Surry shutdown order. The Surry review team has met with the licensee at the site of the Surry facility and has travelled to the Stone and Webster offices in Boston to review the preliminary reanalysis results.
The Surry review team shares no members with review teams for the other affected power plants and remains ready to promptly review VEPCO's reanalyses.
Currently, VEPC0 is reanalyzing the affected piping systeins of Surry Unit No.1 only.
Surry Unit No. 2 had been previously shut down for stean generator replacement which is scheduled for completion by this Fall.
Accordingly, VEPC0 has indicated that a stress analyses of the Unit No. 2 piping systems will be performed subsequent to the current reanalysis effort for Unit No.1. The staff review team for the Surry Power Station will remain available for prompt review of the VEPC0 submittals for both Unit No. I and Unit No.'2.
One important characteristic of the Surry site is that the facility rests on about 1300 feet of sediments which overlay rock.
This condition, including the characteristics of overburden damping and amplification of vibrations from bedrock to the surface, was considered in establishing the seismic design basis for the facility.
- However, 5900C2 7907s10 5B5'
Honorable Paul Trible the 1300 feet of overburden at the Surry site masks the basement rock so that faulting cannot be identified in the area.
This is true for most of the eastern United States.
Since the tectonic structures which give rise to earthquakes cannot be identified and localized, our fract.ce is to assume that earthquakes at least as severe as any previously recorded in the region could occur anywhere in the region.
In addition, in establishing the seismic design bases for a nuclear power plant, we take into account the impacts on that plant of more distant earthquakes. For exaniple, the Charleston, South Carolina earthquake of 1886 was felt in the region of the Surry site.
To detennine Surry Plant response motion to seismic event VEPCO is considering using an advanced analysis method which takes into account soil-structJre interactions.
This refined analysis could lead to use of a reduced r,eismic forcing function in the Surry pipe stress reanalysis.
This methed was used by VEPC0 for the design of the now-cancelled Surry Unit Nos. 3 and 4.
However, it was not used in the or'ginal design analysis for Surry Unit Nos. 1 and 2.
We have maintained a dialogue with VETC0 regarding the use of this technique for Unit Nos.1 and 2, and VEf;0 is eware of our requirements in this matter.
While we continue to meet with VEPC0 and Stone and Webster representatives to discuss preliminary results of their reanalyses, we are at this time awaiting formal submittal of these results by VEPC0 for staff evaluation.
Following the staff evaluation of the VEPC0 submittals for each reactor unit, we will be in a position to reconsider whether continued suspension of operations at that unit remains necessary or appropriate.
The staff's recommendation concerning possible resumption of opert vion will be con.sidered by the Comission before a final decision is made.
' Sincerely,f-
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'90seph M. Hendrie Chairman
Enclosure:
As Stated 59CCr3
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NUCLEAR REGULATORY COMMISSION ABNCR1ML OCCURRENCE EVEr1T DEFICIEt;CIES IN PIPIT;G DESIGN Section 203 of the Energy Reorganization Act of 1974, as amended, requires the NRC to disseminate information on abnomal occurrences (i.e., unscheduled incidents or events which the Co=nission detemines are significant from the standpoint of public health and safety).
The following incident was detennined to be an abnormal occurrence using the eriteria published in 'h' FEDERAL REGISTER on February 24,1977 (42 FR 10950). Appendix A (Example I.D.2) of the Policy Statement notes that a major deficiency in design, construction or operation having safety implications (a'ffecting five plants in this case) requiring imediate remedial action can be considered an abnormal occurrence.
The following description of the event also contains 'the remedi.al actions taken.
Date and Place - During design and construction, an incorrect stmaation cf earthquake loads affected the design of safety related piping systems and associated pipe supports at five nuclear power plants.
On December 6, 1978, a Licensee Event Report from Duquesne Light Company mentioned differences between computer codes used in analyses of force summations, but did not elaborate on them.
Then, the NRC learned of an incorrect sur.ning cf loads in one of the codes on March 8,1979, at a meeting in Bethesda, Maryland with Stone and Webster, an architect engineering fim and the Du:;uesne Licht Company (DLC)., the licensee for Beaver Valley Unit 1, 59CCC4
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( a pressurized water nuclear plant located in Beaver County, Pennsylvania.
On March 9, NRC learned that the incorrect summation technique affected four other plants:
Plant Location FitzPatrick Oswego County, New York Maine Yankee Lincoln County, Maine Surry 1 & 2 Surry County, Virginia Nature and Probable Consbauences - In October 1978, uuquesne Light Company, the licensee of the Beaver Valley plant, was informed by Stone anc. Webster that for loading conditions associated with postulated earthquak.s, pipe supports associated with Safety Injection System piping would be overstressed.
Stone and Webster (S&W) was reanalyzing stresses in connection with a syste:n modification required by the NRC staff to correct a design deficiency not related to protection against postulated earthquakes.
During this reanalysis effort, the S&W engineers also came ar.ross inforination that had been provided to them by Westinghouse in M?y 1978 that showed some check valves in these lines were actually heavier than assumed iTi the earlier analysis.
Sometime during this reanalysis, either in connection with the planned modification or in reexamining the effect of the increased valve weights, S&W discovered a cisapplication of a hand calculation method.
In correcting this misapplication, S&W found some instances of local overstress.
The 590C05
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correction consisted of adding a snubber and modifying one support.
In doing the analysis related to making this correction, S&n'.: sed two computer
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programs.
A new one, fiUPIPE, predicted much higher stresses than the one, PIPESTRESS, used dur:ng a 1974 as-built check of these lines.
On October 26, 1978, the licensee orally notified the flRC Office of Inspection and Enforcement about the design error (hand calculations method misapplication) which required correction.
No explanation was provided for the differences in stresses predicted by the two codes at that time.
Repeated fiRC contacts with the licensee and S&W to identify the reason for the differences were not effective, since without the actual computer runs t6 look at there was a commt;nications proble.
During a meeting held on March 8,1979 to discuss these matters, ti.e Seaver Valley licensee informed the NRC staff that the differences in predicte' niping stresses between the two computer codes were attributable to the fact that the SHOCV2 subreutine of the PIPESTRESS code uses an algebraic su= ration of the loads calculated separately for the horizontal and the vertical component of earthquake motion.
The use of algebraic suanation is only acceptable if the time phasing of these loads is known.
The algebraic technique as used in SHOCK 2 is not conservative for response spectrum modal analysis because, in such analyses, time phasing is not considered.
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The analytical treatment of load combinations becomes significant because horizontal earthquake cotions can produce piping covement in both the horizontal and ve'. tical direction and the vertical earthquake motions can also produce piping movement in both horizontal and vertical directions.
For some designs the calculated piping stresses may differ significantly depending on the load summation techniques used in each mode of response.
Based on the three piping systems that had been reanalyzed by +.he newer code on Beaver Valley at the time of the March 8,1979 meeting, stresses over allowable values were expected to be found primarily in piping supports although significant increases in piping stresses had been observed.
NRC staff reviewers were sent to S&W's Boston office to determine the extent of this problem on Beaver Valley 1 and other potentially affected plants.
In following the course of the reanalysis at the S&W offices over the weekend of March 10,11 and 12, based on the information then available, it becane apparent that, when the NUPIPE code was used, a number of piping systems had calculated stresses over the allowable value for the design basis earthquake.
Also, for a few of these systems the core probable operating basis earthquake resulted in stresses above the allowable value.
In addition, the structural integrite and performance of pumps, valves and other essential equipment could be 59CCC7
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degraded.
Although results were still incomplete en March 12, information available at that time indicated that high stresses were calculated in a number of systems important to safety.
Because the overstressing of piping and supports was predicted even for earthquakes which might occur during the lifetimes of these facilities, the problem took on considerable safety significance.
Some of the systems identified at that time as having overstressed conditions under earthquake loadings were part of th,e reactor coolant pressure boundary, whose failure could cause a loss of coolant accident.
In addition, systems which would be needed to shut the plant down safely in the event of a loss of coolant accident were diso affected.
Thus an earthquake, of not extremely low likelihood, would have the potential both for causing an accident and for preventing safety systems, designed to cope with that accident, from operatir 9 A secondary concern was whether or not systems needed to provide adequate long tern cooling for the plant in the event of an earthquake without a LOCA could be assured.
Concurrent with the NRC Beaver Valley review, NRC staff records were reviewed to detemine whether or not oth3r facilities had used these same analysis techniques.
Based on the review of these records and information provided by S&W, the NRC staff concluded that four other facilities used the same techniques.
The four facilities are Maine Yankee, Fit: Patrick and Surry Units 1 and 2.
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. The t'RC staff concluded the potential for serious acverse effects in tne event of an eartnquake was sufficiently widespread that the basic defense in depth provided by redundant safety syste=s may be compromised.
The NRC ni. actor for Nuclear Reactor Regulation concluded that the public health and safety required that the affected facilities be placed in a cold shutdown condition pending further onier of the Cormiission.
Orders to this effect were issued to the licensees of the above reactors.
The Orders provide that within 20 days each licensee =.rst respond with respect to:
(1) why the licensee shot'd not reanalyze the facility piping systems for seismic loads on the piping system and any other affected safety systems us i:ig an appropriate piping analysis computer code which doas not combine loads algebraically, (2) why the licensee should not make any modifications to the facility piping systems indicated by the reanalysis, and (3) why facility operacion should not continue to be suspended until completion of the reanalysis and any required codifications.
All of the plants are now in a cold shutdown condition.
(Surry Unit 2 was already in an extended outage for steam generator re:laceraent.)
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Cause or Causes - The uncertainty in the calculated oiping stresses and support loadings in safety-related piping systems a: the five plants is attributable to the incorrect application of the algebraic sur.: nation technique in the SHOCK 2 ubroutine of the PIPESTRESS computer code, proprietary to Stone and Webster.
Actions Taken to Prevent Recurrence Licensee / Architect Encineer - Identification of all safety related systems that have been analyzed wi'n a piping computer code involving a program deficiency is underway.
Computer inputs are being checked to assure that all reanalyzed piping will reflect the as-built condition at each plant.
Piping analyses' are being verun'and piping and supports exceeding allowable stresses will be identified.
Modifications will be made as necessary.
NRC - The fMC ordered each of the utilities of the five :dentified nuclear power plants to shut down their plants within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.
The utilities are to remain shu'cdown pending further order of the CocInission.
The f;RC is in contact with the licensees and the architect engineer on actions being taken.
Piping stress computer codes to be used for reanalysis of the piping will be tested with NRC established benchmark problems.
Also, an independent audit of selected piping runs will be conducted by HRC consultants to verify the piping stress reanalysis.
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- RC is reviewing any generic implications at other facilities.
The fiRC's Office of Inspection and Enforcement issued Information Notice (IN) fio. 79-06, which described the event, on March 23, 1979, to all holders of reactor operating licenses and construction permits.
On April 14, 1979, the NRC's Office of Inspection and Enforcement issued Bulletin No. 79-07 to applicable licensees which identified actions to be taken.
This includes identification of the methods of analyses used, how they wera verified, safety systems affected, and a plan of action to assure plant safety.
As of liay 9,1979, the fiRC has received responses to Bulletin No. 7S-07 from all licens.ees of operating. reactors except for Three Mile Island Units 1 and 2 which are shut down.
The NRC staff is reviewing these responses on a high priority basis.
Additional actions will be taken as appropri ate.
For tha Nuclaar Regulatory Co=nission amueT J. Ch k
Secretary f the Commission Dated at Washington, D. C. this /
ay of May 1979.
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- .iM9 March 22, 1979 Mr. Joseph M.
Hendrie Chairman, Nuclear Regulatory Commission 1717 H Street, N. W.
Washington, D.
C.
20555
Dear 51r. Chairman:
Several of my constituents have contacted me regarding their concern over the shutdown of nuclear generating plants in Virginia because of possible earthquakes.
I would appreciate your reviewing this matter and offering me your advise.
\\
Paul Trible mob t..
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