ML19281B662
| ML19281B662 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 05/02/1979 |
| From: | Hendrie J NRC COMMISSION (OCM) |
| To: | Brennan J MAINE, STATE OF |
| Shared Package | |
| ML19281B663 | List: |
| References | |
| NUDOCS 7905300568 | |
| Download: ML19281B662 (7) | |
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4 UNITED STATES
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NUCLEAR REGULATORY COMMISSION W ASHINGTON. D. C. 20555 4lR.
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%, *....f May 2, 1979 CH AI RM AN The Honorable Joseph E. Brennan Governor of Maine Augusta, Maine 04333
Dear Governor Brennan:
I have received your TWX of March 23, 1979 regarding the shutting down of the Maine Yankee Atomic Power Station. A summary of the information which led to the Office of Nuclear Reactor Regulation's March 13, 1979 Crcer to shut down this and the other four nuclear plants is enclosed.
We are aware of the critical energy situation which now exists in Maine anc share your concern regarding the prompt resolution of this matter.
To expedite review, the NRC staff has established a team which is cedicated to the review of the analysis of the Maine Yankee plant.
This team visited the plant site at Wiscasset, Maine, on Tuesday, March 27, 1979.
At that time the NRC staff met with representatives of the utility and toured the facility.
At this meeting, the staffs discussed the safety-related piping reanalyses performed by Stone and Weo:ter.
In addition a member of the NRC review team met with Stone and Webster in Boston on March 29 and 30, 1979 to review some details of the reanalysis prior to its formal submittal.
Other meetings between the utility and the NRC staff were held on April 20 and May 1,1979 in Bethesda.
On April 2, 1979, the utility submitted their answer to the March 13, 1979 Order to Shcw Cause.
They stated that the results of the reanalysis snowed that no mcdifications to the facility piping systems are necessary.
In support of this, they also submitted an Interim Report by Stone and Webster dated April 1, 1979.
In response to the staff's request, the utility also submitted additional information by letters dated April 3, 12,13,19, and 27,1979. The NRC staff is currently reviewing this information.
As a result of our May 1,1979 meeting, the utility is expected to submit more information on May 2,1979.
The utility believes that this will be the final submittal and will resolve the matter of concern.
?S0530cGog
9 The Honorable voseph E. Brennan Af ter this information has been evaluated by the staff, they will be in a position to reconsider whether continued suspension of operations at Maine Yankee remains necessary.
lhe decision about possible resumption of operations will be made with the concurrence of the Commission.
We will keep your office informed regarding our progress in this matter.
If you have any additional questions, please contact my office.
h\\ \\ Sincerely,,
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' ' Anh2M Y ose h M. Hendrie
Enclosure:
Summary f
ys FACTS RELATED TO THE SHUTDOWN OF FIVE PLANTS To place the nature of the decision in perspective, a brief summary of the background leading up to the decision may be useful.
In October 1978, Duquesne Light Company, the licensee of the Beaver Valley p' ant, was informed by Stone and Webster that there were overstresses in pipe supports associated with Safety Injection System piping.
At the time Beaver Valley was shut do'.in because of main transformer difficulties.
Stone and Webster was reanalyzing stresses in connection with a system modification required by the NRC staff.
During this reanalysis, Stone and Webster found some instances of over-stresses in two lines.
In doing the analysis of the modifications needed to correct the overstress conditions, Stone and Webster used at least two computer programs. A new one called NUPIPE predicted much higher stresses than the cne used during a 1974 as-built check of these lines.
That older code is called PIPESTRESS.
On October 26, 1978 the licensee orally notified NRC's Office of Inspection and Enforcement about the design error which required correction.
The Office of Inspection and Enforcement became concerned about these large differences in results between the NUPIPE and PIPESTRESS codes even though both codes showed the original design error would be corrected with the modification to be made by the licensee.
On December 6,1978 the licensee submitted additional information in a Licensee Event Report.
- 2 In February, the Office of fiuclear Reactor Regulation initiated a tech-nical effort to assist Inspection and Enforcement in resolving the mat-
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ter.
At this time it did not appear to be a concern other than an error in application of the codes.
During a meeting held on March 8,1979 to discuss these matters, the Beaver Valley licensee infor ed the staff that the difference in pre-dicted piping stresses between the two computer codes was attributable to the fact that the PIPESTRESS code uses an algebraic sumnation of the loads.
The algebraic technique for combining seismic induced loads can result in an underestimate of the pipe stresses.
Based on the three systems that had been reanalyzed by the newer code on Beaver Valley at the time of the March 8,1979 meeting, stresses over allowable values were found primarily in piping supports although significant increases in piping stresses had been observed.
Based on the information received on March 8 and 9,1979, flRC reviewers were sent to Stone and k'ebster'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 Stone and Webster of-fices over the weekend of March 10,11, and 12, it became apparent that a number of piping systems had calculated stresses over the allowable
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, value for the design basis earthquake.
Also, for a few of these sys-tems the more probable operating basis eartheuake resulted in stresses above the allowable value.
In addition, the structural integrity and functionability of pumps, valves and other essential equipment could be affected.
The eastern United States is generally believed to be a region of low seismicity, when it is compared to the western part cf the country.
It is not, however, without significant historical seismic activity.
The recurrence interval of the operating basis earthquake for these facilities is on the order of 200-400 years.
Although results were still incomplete by Monday morning, March 12, 1979 arealyses of a significant fraction of the affected piping system in-dicated that high stresses were calculated in a number of systems irportant to safety.
Because the overstressing of piping and supports was predicted even for earthquakes which could reasonably be expected to occur during the lifetimes of these facilities, the problem took on considerable safety signi ficance.
Some of the systems identified as having overstressed conditions under earthquake loadings were part of the 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 also affected.
Thus, an earthquake, of not extremely low likelihood, would have the
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_ 4 potential both for causing an accident and for preventing safety sys-tems designed to cope with that accident from operating.
Concurrent with our Beaver Valley review,11RC records were reviewed to determine whether or not other facilities had used these same analysis techniques.
Eased on the review of the records and informa-tion pecvided by Stone and Webster it was concluded that four other facilities used the same techniques.
The four facilities are l'.aine Ycnkee, FitzPatrick and Surry Units 1 and 2.
The systems which were analyzed using these techniques performed sub-stantially the same safety functions as those in question at Beaver Valley.
The staff concluded the potential for serious adverse ef-fects in the event of an earthquake was sufficiently widespread that the basic defense-in-depth provided by redundant safety systems may be compromised.
In short, it was found that a computer code that had been utilized by the Stone and Webster Engineering Corporation in the seismic design of safety-relat -d piping for these five reactors produced results sig-nificantly different from results recently calculated with their current code.
On determining that the capability to shut down the plants safely in the event of an earthquake could not be assured on the basis of the results of a partial reanalysis of the Beaver Valley Power Station,
5 and having no reason to expect that the other four units would turn out any differently, it was recommended that operation of the af-fected plants be suspended ~and a shutdown order was issued.
To assure that the NRC review of the reanalysis of the affected safety systems of the five shutdown plants preceeds expeditiously, the Office of Nuclear Reactor Regulation has established a review organization of dedicated reviewers. This staff is presently involved in a series of independent actions to assure that the reanalysis of piping systems is conducted in an acceptable manner.
These actions are as follows:
Piping stress computer codes to be used for reanalysis of the piping will be run with NRC established benchmark problems.
An independent audit of selected piping runs will be conducted by NRC staff consultants to verify the piping stress reanalysis.
Our objective is to review the reanalysis of the piping systems o, the affected facilities in an expedited and disciplined manner such that these facilities can be returned to operation with the assurance that their operation does not constitute a threat to the public health and safety.