ML20203L708

Provides Basis for ASLAP Concerns Re 860131 Earthquake,To Aid Commission in Pursuing Matters Raised in ASLAP 860320 Order Concerning Event Safety Significance.Earthquake Caused Stress Values in Excess of Expected Magnitude

ML20203L708
Person / Time
Site:	Perry
Issue date:	07/29/1986
From:	Johnson W NRC ATOMIC SAFETY & LICENSING APPEAL PANEL (ASLAP)
To:	Zech L NRC COMMISSION (OCM)
Shared Package
ML20203L711	List: ML20203L708 ML20203M007
References
OL, NUDOCS 8608290096
Download: ML20203L708 (4)

Text

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't o,, UNITED STATES

[ Te( o NUCLEAR REGULATORY COMMIMitON l 5* 9f ATOMIC SAFETY AND LICENSING APPEAL PANEL W ASHINGTON, D.C. 20565 y -

July 29, 1986 r

Honorable Lando W. Zech, Jr.

Chairman U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Zech:

The Commission, in its Memorandum and Order of April 18, 1986 (CLI-86-07), denied a motion by intervenor OCRE to -

reopen the evidentiary record in the Perry Nuclear Power Plant proceeding to hear a contention regarding an earthquake that occurred on January 31, 1986, near the Perry site. The Commission also vacated an Appeal Board order of March 20, 1986 scheduling a hearing to explore the safety significance of that event. The Commission did indicate, however, that it would pursue with the NRC staff certain matters raised by the Appeal Board. In the hope that it may aid the Commission in this regard, I am writing to provide you, in some more detail, the basis for the Board's concerns regarding the earthquake.

The 1986 Ohio earthquake had a magnitude of 5.0. The Perry design basis Safe Shutdown Earthquake (SSE) is described as a magnitude 5.3 event. If one accepts the logarithmic nature of the earthquake magnitude scale, the 1986 Ohio was about a factor of two less energetic than the SSE.

Five seismic instruments recorded the motion of the event at the basemat or foundation level at Perry ,- three in the auxiliary building and two in the reactor building.

In the staff's response to the motion to reopen, affiant Arnold Lee suggested that the motion recorded at these foundation stations would be similar to free field ground motion. Despite the lower magnitude of the earthquake, 10 of the 14 values of peak ground acceleretion obtained from these instruments exceeded the acceleration value used as the anchor point for the Perry SSE spectrum, 0.15g.

Recordings of these five instruments yielded the following i'

average peak accelerations in the horizontal directions:

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i Honorable Lando W. Zech, Jr.

July 29, 1986 Page,2., .

{ North / South, 0.46g; East / West, 0.20g. The averag j acceleration in the vertical direction was 0.18g.g peak l It is accepted that a response spectrum derived from

, the entire time-history-of-motion of an earthquake represents a more definitive measure of the event's ability

, to affect structures and mechanical systems than do values of peak acceleration. In the case of the 1986 Ohio event there were twelve response spectra derived from four instruments located at foundation levels (3 PSR-1200s mentioned in footnote 1 and a Kinemetrics accelerograph D51-N101). As noted in the March 20 order, nine of these .

spectra exceeded the SSE spectrum throughout the frequency i range above about 15 Hz.

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4 The most direct way to measure an earthquake's effect would be to determine stresses developed in structures and

equipment due to its motion. Such stresses can be calculated for a particular event if a response spectrum or time-history-of-motion for the event exists. The staff's i safety evaluation report, SSER-9, states at page 3-10 that I stresses have been calculated using the 1986 Ohio event as input for certain pumps located at the auxiliary building

' I The recorders registering the highest values of peak i ground acceleration were Engdahl Peak Shock Recorders (Model i PSR-1200). The applicants, in Table 2 of Attachment 5 of their answer to OCRE's motion to reopen, did not include the j data from PSR-1200 units at the auxiliary building foundation (D51-R180 and D51-R190) or one at the reactor

! building foundation (D51-R160). They did, however, give the i

data for a PSR-1200 at the 630' elevation in the reactor building (D51-R170). To obtain a peak acceleration from this instrument (the PSR-1200 records response spectrum

! values directly and not a time-history-of-motion), the I applicants selected the acceleration value recorded at the i highest frequency, 25.4 Hz, and I have done the same for the comparison above. Although there were no reservations i stated by the applicants for using the PSR-1200 data this way -- and they did it themselves -- there may be some reason why data from this type of recorder do not accurately

)

reflect peak accelerations, thus explaining why this

information was not included in Table 2 and changing the i average values given above.

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1 i

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i Hongrable Lando W. Zech, Jr.

t July.29, 1986 4

Page 3~- ,

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, foundation level. The resulting stresses were within allowable limits, but they might exceed " original" calculated values. The Appeal Board was not told the basis

! for the " original" calculations, but assumed that it would be earthquake motion equivalent to the SSE. If this 1 assumption is valid, then the excitations (i.e., stresses) due to the 1986 Ohio earthquake exceed those for the SSE for l these items. The equipment in the auxiliary building to which these results apply was not identified in SSER-9, but we believe the pumps involved were in the the Low Pressure Core Spray (LPCS), the Residual Heag Removal (RHR), and High j Pressure Core Spray (HPCS) systems -

4 Thus, the information that was supplied or referred to j regarding the 1986 Ohio earthquake indicates that this d

earthquake, a factor of two less energetic than the SSE for Perry, has exceeded the SSE in peak acceleration and in the high frequency portion of the response spectra.

Calculations using the motion of this event as input have apparently led to stress levels in certain safety-related '

items that exceed those that would be calculated for the

SSE. Presumably an earthquake of similar spectral i characteristics but having the 5.3 magnitude of the SSE j would cause even greater stresses.

It is well documented that the 1986 Ohio earthquake was of short duration, and that its principal motions were in

the high frequency range. Response spectra derived from i

these motions have an odd shape, with a broad peak in the range of about 20 Hz. Very little was presented to us regarding the unusual character of this earthquake, its origins, or whether future earthquakes that might be experienced at the Perry site could be expected to have similar characteristics. Given that the peculiar motion frequency characteristics of this event have apparently

\

2 Appendix A of SSER-9 refers to a letter of February -

1 28, 1986, from the applicants to the staff.. Attachment 3,Section III 3 of this letter apparently provides some of the l bases for the staff testimony on stresses in pumps. Table 2

• of Attachment 3 illustrates that, for the LPCS, RHR, and HPCS systems, the "new" stress ratios are generally higher

, than the previously calculated values (presumably using the SSE as the exciting event).

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Honorable Lando W. Zech, Jr. ,

July 29, 1986 Page ,4_3 caused calculated stress values in excess of what might be expected for an earthquake of its magnitude, it would appear that more information should be developed regarding the nature of this event and the possibility of the recurrence of this type of high frequency motion at Perry and possibly other sites. .

The Appeal Boards concern about this earthquake seems to be shared by ACRS geology consultant, Dr. Paul W.

Pomeroy. In response to OCRE correspondence to the ACRS, ,

Dr. Pomeroy concluded (in a letter that was included in the NRC's April 8, 1986 presentation to the House Committee on .

Interior and Insular Affairs):

The large high frequency content of earthquake signals is a generic problem of significance to the successful operation of these plants. At frequencies greater than 14 Hz, the SSE for Perry was significantly exceeded. No significant failures in systems operating at the time of the earthquake have been reported. Nonetheless, at somewhat higher magnitude levels, these high frequency signals will be of importance and a

. generic study should be undertaken with the goal of modifying required response spectra and to insure the continuing safe operation of relays,

- valves and other devices that can potentially be affected by these frequencies.

I hope that the bases for our concern have been made clear and they will be of assistance in your consideration

of the Perry earthquake.

j sincerely,

?

W. Reed J nson l Member i Atomic Safety and Licensing Appeal Board i

_ . _ , _ _ _ _ _ _ , . _ . _ _ _ . _ . _ . , . . . _ . _ _ _ - . _ _ _ _ _ . . . _ , _ _ _ _ _ _ _ _ _ . _ . _ _ _ _ -