ML20112E392
| ML20112E392 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/31/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20112E390 | List: |
| References | |
| NUDOCS 9606060034 | |
| Download: ML20112E392 (9) | |
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4 UNITED STATES s
j NUCLEAR RESULATORY COMMISSION WASHINGTON, D.C. 20066-0001 k...
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
RELATED TO AMENDMENT NO. 144 TO FACILITY OPERATING LICENSE NO. DPR-25 COMMONWEALTH EDISON COMPANY DRESDEN NUCLEAR POWER STATION. UNIT 3 DOCKET NO. 50-249
1.0 INTRODUCTION
By letter dated May 22, 1996, as supplemented May 30, 1996, Commonwealth Edison Company (Comed, the licensee) submitted an amendment requesting NRC review and approval, on a one-time temporary basis, for operation of the Dresden Nuclear Power Station, Unit 3, with the structural steel members in the Low Pressure Coolant Injection (LPCI) corner rooms outside the Updated Final Safety Analysis Report (UFSAR) design parameters, but capable of performing their intended safety function. An unreviewed safety question was discovered by Comed following a 10 CFR 50.59 safety evaluation. (SE) of LPCI corner rooms steel structural members.
Following a reactor scram on May 15, 1996, the licensee performed an SE in accordance with the requirements of 10 CFR 50.59 to determine if the current 4
configuration of the corner room structural steel members had reduced the margin of safety as described'in the UFSAR. The SE determined that the configuration does not reduce the margin of safety with respect to the stress allowables for the structural steel if subjected to a Safe Shutdown Earthquake (SSE) which would result in the finding of an unreviewed safety question. An unreviewed safety question was determined to exist because stress allowables for the structural steel subjected to an Operating Basis Earthquake (OBE) were found outside the UFSAR requirements; however, the current configuration of the corner room structural steel members has not significantly reduced the margin of safety as described in the UFSAR.
In accordance with 10 CFR 50.59 and pursuant to 10 CFR 50.90, the licensee requested a license amendment requesting NRC review and approval to restart and operate Dresden, Unit 3, until the next scheduled refueling outage with the degraded corner structural steel. The licensee has committed to modify the LPCI corner room structural steel during the next scheduled refueling outage (September 1996) to return all original UFSAR design margins to the steel.
2.0 EVALUATION Following the Dresden, Unit 3, reactor scram on May 15, 1996, the licensee recognized the need to evaluate the operability of the structural steel members installed in the LPCI corner rooms.
Prior to the reactor scram, the licensee had identified that the LPCI corner room structural steel did not meet all of the design parameters listed in the UFSAR. The licensee failed to 9606060034 960531 P
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take timely corrective actions to restore the design margins of the structural steel. As a result, this condition constituted a change to the facility and as such, the change needed to be evaluated in accordance with 10 CFR 50.59 to determine if the change resulted in an unreviewed safety question.
The licensee performed a 10 CFR 50.59 evaluation and determined that the degraded condition of corner room structural steel had reduced the margin of safety as described in the UFSAR; however, the reduction in the margin of safety was not significant and the licensee determined that the structural steel would perform its intended safety function following a design basis seismic event. Therefore, the degraded condition created by the LPCI corner room structural steel constituted an unreviewed safety question.
In accordance with 10 CFR 50.59 the licensee requested a license amendment pursuant to 10 CFR 50.90 to justify restart and continued operation of Dresden, Unit 3, with the degraded LPCI corner room structural steel until the next refueling outage.
The licensee's May 22, 1996, application provided a safety evaluation to justify restart and continued operation of Dresden, Unit 3, with the degraded LPCI corner room structural steel. The licensee's justification presented in the evaluation was based on an existing evaluation of the LPCI corner room structure steel for Unit 2.
The structural steel in the LPCI corner rooms in Unit 2 has been modified to return the structural steel to the UFSAR design margins. The analysis justified that the Unit 2 Corner room structural steel evaluation bounded the Unit 3 LPCI corner structural steel configuration.
In the May 22, 1996 application, the licensee also committed to perform calculations for all the Unit 3 structural members in the most critical LPCI corner room and have the calculations at the Dresden Station for NRC staff for review by May 31, 1996.
On May 23, 1996, the licensee meet with the NRC to discuss the technical basis of the license amendment and the operability evaluation. During the meeting, the licensee provided additional information to clarify the operability evaluation. The additional information presented to the staff in the May 23, 1996 meeting was docketed by letter dated May 30, 1996.
Also, in the May 30, 1996, letter the licensee stated that all Unit 3 specific LPCI corner room structural steel calculations had been completed and would be at the site for inspection.
The licensee stated that the calculations confirmed that all the structural steel members in the 'LPCI corner rooms meet the operability criteria (OC) established for the corner room structural steel members in the May 22, 1996, application.
The operability evaluation performed by the licensee demonstrated that the LPCI corner room steel framing will remain capable of supporting the LPCI heat exchanger and other safe shutdown and safety related piping attached to the steel framing following a design basis seismic event.
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Each of the two units'at Dresden has.two corner areas in the reactor building.
' The steel framing in each corner area supports the [LPCI] system piping and a heat exchanger which, in turn, transmits the loads to three feet thick
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reinforced concrete walls and steel columns. Although, a general layout of the corner area framing is quite similar in both the. units, the main steel i
beams, auxiliary steel members, and pipe support and hanger locations are different. The staff reviewed the OC used by the licensee to compute the loads from the pipe-supports and heat exchangers on the steel framings, and s
j the OC used to compute the adequacy of the framings. The specific details of i
the licensee's operability evaluation are evaluated below.
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2.1 Pinina and Pine Suonort Evaluation I
The licensee evaluated the Dresden, Unit 2, southwest corner rcom structural steel as a bounding configuration ~for use in the Dresden, Unit 3, corner room structural steel operability evaluation.
In the May 22, 1996 application, the licensee described the analysis method used to obtain the piping and heat 4
i exchanger loads used in the operability evaluation of the corner room structural steel. The licensee developed a computer model of the LPCI corner l
room heat exchanger and four main piping subsystems that attach to the heat exchanger. The model included the stiffness of the corner room structural i
steel. The model was used to obtain the SSE loads at the heat exchanger j
attachment points for the operability evaluation of the corner room structural i
steel. The analysis was based on a damping value of 7 percent for the SSE.
l The value of 7 percent damping is recommended for the SSE in Regulatory Guide (RG) 1.61 for bolted structural steel members.
The licensee presented its j
argument for using the bolted steel structure damping in the analysis in a May-23,'1996, meeting with the staff. The licensee's argument is that the majority of the -load transmitted to the structural steel frame is due to the i
j interaction of heat exchanger mass and structural steel stiffness. Therefore, the licensee concluded that the damping associated with the bolted structural corner room steel would be appropriate for this operability evaluation to i
develop the loads applied to the structural steel.
The staff considers this argument reasonable and the licensee's use of the damping for this operability 4
evaluation acceptable. The licensee combined the loads from this operability I
evaluation with the piping loads from the UFSAR analysis and added the deadweight of the heat exchanger to evaluate the corner room structural steel.
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i The licensee also analyzed the model of heat exchanger and four attached i
piping subsystems using a damping value recommended for the SSE condition in RG 1.61 for piping systems of diameter less than or equal to-12 inches.
The licensee used the loads from this analysis to evaluate the piping.
In the May 22, 1996 application, the licensee has proposed using the OC for the piping and pipe supports that had previously been submitted by the licensee and reviewed by the staff. The staff's review of the criteria is documented in a September 27, 1991, letter to Comed.
The use of the criteria, previously accepted by the staff as documented in the September 27, 1991, letter, is also acceptable for this operability evaluation. The staff
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l previously accepted the damping contained in RG 1.61 for the evaluation of the i
l piping for the SSE load for interim operability evaluations.
2.2 Evaluation of Structural Steel Framinas Recognizing the problem that the existing structural steel can not meet the stipulated acceptance criteria for loadings consisting of normal operational, postulated accident and seismic loads, the licensee proposed the following OC:
1.
The postulate scismic loading to be considered for evaluating the steel framings and their connections will be that associated with the SSE.
The loading combinations incorporating the OBE will not be evaluated.
2.
Instead of using the licensing basis damping values, the licensee will utilize the damping values recommended in RG 1.61.
3.
For the evaluation of certain connection plates (e.g., check plates, attachment plates, seat angles), the maximum strain in the plates due to bending shall not exceed ten times the yield strain of the material.
4.
A factor of Safety of 2 (instead of 4) will be utilized for qualifying the wedge expansion bolts.
The following is the staff evaluation of 0C1, 0C2, 0C3, and 0C4.
OC1:
Incorporation of OBE in the load combinations ensures that the structural members and their connections will have low enough stresses and deformations that all supported and protected equipment and components could keep on functioning during an OBE.
It was not meant to control the design. As the OBE for both units are one-half of the SSE, i
the applied stresses and deformations during an OBE are generally higher j
than one-half of those during an SSE because of the lower damping of the structures expected during an OBE.
In case of Dresden, Unit 3, when OC2 and OC3 are implemented for SSE, though the stresses and deformations during an OBE will be higher than the corresponding allowables, they will be well within the UFSAR allowables for SSE. Moreover, the license has been conditioned to require Dresden, Unit 3 to shut-down and inspect the U.a.it, when the actual earthquake event is determined to exceed the OBE.
Thus, the staff considers the operability criterion acceptable.
002. The staff, in general, associates the RG 1.61 damping values with the use of RG 1.60 response spectra or with conservatively developed site specific spectra. The staff considers the use of RG 1.61 damping values with the Housner shaped spectra (relatively non-conservative) as inappropriate. The design response spectra for Dresden, Unit 3, as described in the UFSAR is based on Housner spectra. However, in the May 22, 1996 application, the licensee emphasized that the response calculations for the steel framings, and the LPCI piping and heat-exchanger is based on the floor spectra developed from the normalized l
4 time record of the N-S component of the El-Centro earthquake. The broad-band floor response spectrum developed from this time record was used in calculating the SSE loads on steel framings. Also, the floor spectrum, developed at the floor level about eight feet higher than the framing floor, was utilized in the SSE load computations. Thus, the staff finds the use of the RG 1.61 damping value acceptable for the operability evaluation of the steel framings.
OC3: The staff has previously accepted this OC for the evaluation of degraded embedment plates caused by large spacing of the anchor straps.
For i
Dresden Unit 3 connection plates, this 0C has been used only where the stresses / strains are predominantly due to bending, and the maximum strain (10 times the yield strain) is calculated in the plate elements using yield line theory.
In the yield line analysis, various plastic i
yield line patterns have been assumed and the collapse load (limited by the 0C3 strain criterion) calculated for each.
The optimum yield line pattern corresponding to the smallest capacity has been determined as the controlling yield line pattern capacity. The allowable moment capacity is limited by the product 0.95*F *Z, where F is the minimum y
y j
specified yield stress, and Z the plastic modulus of the section.
During the discussion of this 0C in the teleconference of May 29, 1996, the licensee stated that only three connections were affected by this 0C, and the deformations of the corresponding members were computed considering the plastic deformations of the plates or angles.
The maximum deformations (horizontal and vertical) of the heavily loaded beam were found to be less than 0.13 inches. This information was confirmed in the licensee's May 30, 1996 letter. The staff finds this criterion acceptable for interim operation of Dresden Unit 3.
j OC4: During the resolution of concerns related to the pipe support plates and i
expansion anchors in IE Bulletin 79-02, the staff had accepted the use of the lower safety factor as an operability criterion for a number of 4
plants, including Dresden and Quad Cities.
The expansion bolts are 2
subjected to combined tension and shear forces.
The licensee proposes to use linear interaction curve for combining these load effects which have been shown to be conservative. Thus, considering the prior precedence and conservative usage, the staff finds the criterion acceptable in the interim period.
2.3 CONCLUSION
Based on the review of the operating criteria and the method of implementing them for the structural steel framings, inspection of the framings and associated loadings at the Dresden site and discussions with the licensee, the staff concludes that the subject structural steel framings are able to withstand the postulated loadings without loss of function.
By letter dated l
May 30, 1996, the licensee stated that all specific calculations for Dresden, Unit 3, had been completed and the calculations confirmed that all structural steel members in the LPCI corner room were bounded by the OC established in
the May 22, 1996, application. Therefore,'the staff finds that for the interim period until the next scheduled refueling outage, Dresden, Unit 3, can restart and operate with the LPCI. corner structural steel members outside the UFSAR design margins.
3.0 EXIGENT CIRCUMSTANCES
Pursuant to 10 CFR 50.91(a)(5), Comed requested that the proposed license amendment be granted on an emergency basis, because failure of the Comission to act in a timely manor would result in the prevention of Dresden, Unit 3, of resumption of power operation.
Following the Unit 3 scram on May 15, 1996, the licensee was ready to resume power operation on May 24, 1996.
The Comission determined to issue this on an exigent rather than an emergency basis to afford the public an opportunity to comment. The proposed license amendment would not afford the normal 30-day public coment period.
10 CFR 50.91(a)(6) specifies that the Comission may, where exigent circumstances exist, allow less than 30 days for public comment. The Comission finds that exigent circumstances do exist in that Comed used its best effort to make a timely application following the reactor trip on May 15, 1996, and the discovery of an unreviewed safety question was not the result of any intentional delay on the part of the licensee.
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Accordingly, an announcement of the proposed license change and a discussion of a proposed finding of no significant hazards consideration was published in the Joliet Herald News on May 25, 1996, and in the Morris Daily Herald on May 29, 1996.
These announcements were in accordance with NRC procedures for exigent circumstances.
Tht. staff concludes that the licensee has justified the need for expedited action.
4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Comission's regulations in 10 CFR 50.92 state that the Comission may make a final determination that a license amendment involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not (1) involve a significant increase in the probability or consequences of an accident previously evaluated: or (2) create the possibility of a new or different kind of accident from any accident 4
previously evaluated; or (3) involve a significant reduction in a margin of safety. The staff has evaluated the licensee's proposed no significant hazards consideration against the three factors as part of the determination:
1.
The proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.
The current configuration of the corner room standard steel members will not increase the probability or consequences of the design basis seismic event.
The structural steel in the corners have adequate structural margin to withstand a SSE. All equipment attached to the structural steel and equipment
in the LPCI corner rooms will remain functional'and be able to perform their intended function following a design bisis seismic event. Therefore, the current configu)ation of the corner room structural steel being outside the UFSAR design parameters will not significantly increase the probability or consequences of the UFSAR design basis seismic event.
2.
The proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.
The proposed license amendment change will not create the possibility of a new or different kind of accident from any accident previously evaluated. The corner room structural steel will perform its intended safety function following all UFSAR design basis seismic events.
Because the structural steel members will remain intact following a seismic event, all safe shutdown and safety related equipment in the LPCI corner rooms will be able to perform their intended safety function following a design basis UFSAR seismic event.
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The proposed change does not involve a significant reduction in a margin of safety.
The basis for seismic design of the corner room structural steel framing and seismic analysis of piping is included in UFSAR Sections 3.7, 3.8.4, and 3.9.
Using the seismic methodology and acceptance criteria defined in those sections, the stress levels in the structural steel exceed those permitted in the UFSAR for an OBE which would constitute an unreviewed safety question by the requirements of 10 CFR 50.59. However, the margin of safety against failure is determined by the loading due to the design basis accident SSE, not the OBE. The corner room structural steel members will still remain functional following a design. basis UFSAR seismic event. This will ensure i
that'all safe shutdown and safety related equipment in the LPCI corner rooms will remain functional. The plant will operate in this condition for only a short period of time, approximately 5 months, until the next scheduled refueling outage; at which time the licensee intends to modify the corner structural steel and restore all original UFSAR design margins.
In the interim, the licensee will institute compensatory measures on Dresden, Unit 3, to treat the UFSAR OBE as a limiting condition of operation. Should vibratory ground motion exceed the current OBE ground motion the licensee will shut down the unit and not restart the unit until it receives approval from the NRC.
Based upon the above considerations, the staff concludes the amendment involves no significant hazards consideration.
5.0 PUBLIC COMMENTS i
Telephone connents were received on May 29, 1996, concerning the proposed license amendment. The comments received did not address the no significant hazards consideration determination that was published in two local j
newspapers. The comments concerned the licensee's timeliness and decision-making in restoring the UFSAR design margin to the structural steel members 4
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i installed the LPCI corner rooms at Dresden Unit 3.
A sumation of the comments is'11sted below:
Comment 1 Dresden has been on the NRC Watch List for 6 of the last 8 years.- Poor plant material condition has been identified as one of the leading contributors as to why Dresden was placed, and remains, on the NRC watch list. Allowing Dresden, Unit 3, to restart and operate until September 1996 without repairing the LPCI corner room structural steel will add to the poor material condition of the plant.
Comment 2 Waiting until the next scheduled refueling outage to make the modifications to the LPCI corner room structural steel members is an example of non-conservative decision-making.
Comment 3 The licensee has been aware since 1992 that the LPCI corner room structural steel members did not meet all UFSAR design parameters. Dresden, Unit 3, was shutdown for a long period of time in 1995. Not making the modifications to the LPCI corner room steel structural members in 1995 is an example of poor management at Dresden Station.
Response
As stated in the proposed no significant hazards consideration determination, the staff concluded that the interim operation of Dresden, Unit 3, with the current configuration of the corner room structural steel members does not significantly reduce the margin of safety.
Further as stated in the no significant hazards consideration determination, all safety related and safe shutdown equipment will remain functional following any UFSAR design basis seismic event which will assure that the plant can safely shutdown:following a design basis seismic event.
j In other related actions, the NRC has considered the timeliness of corrective actions, management decision-making processes and the plant material condition as it relates to the LPCI corner room structural steel members being outside the UFSAR design parameters. NRC Inspection Report Nos. 50-237/96005 and 50-249/96005 fully covers each of the above comments. The inspection report is available at the local public document room located at the Morris Area Public Library, 604 Liberty Street, Morris, Illinois or at the NRC's Resident Inspectors Office located at.the Dresden site. Based on the results of this inspection, the NRC noted apparent violations. involving inadequate design controls that resulted in the LPCI corner room structural steel not meeting applicable design margins and concerns over failure by the licensee to take timely corrective actions following the identification of the nonconforming conditions. On April 24, 1996, a predecisional enforcement conference was
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l L 4 held with the licensee concerning the issue of.LPCI corner room structural i
steel. At the enforcement conference, the NRC management expressed concerns-i to Comed over the length of time it has taken for the management team at Dresden to put adequate corrective actions into place to resolve the concerns 4
with the LPCI corner roon structural steel. The NRC is currently considering enforcement action concerning the corner structural steel in the LPCI corner i
room at Dresden.
6.0 STATE CONSHLTAI_ ION i
In accordance with the Commission's regulations, the Illinois State official
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was notified of the proposed issuance of the amerdment. The State official j
had no comments.
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7.0 ENVIRONMENTAL CONSIDERATION
i The amendment changes a requirement with respect to the installation or use of l
a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no i
significant increase in the amounts, and no significant change in the types, 4
of any effluents that may be released offsite, and that there is no, j
significant increase in individual or cumulative occupational radiation
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exposure. The Commission has previously issued an announcement of the proposed license change and a discussion of a proposed finding of no significant hazards consideration was published in the Joliet Herald News on 4
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May 25, 1996, and the Morris Daily Herald on May 29, 1996, and there has been j
no public comment on such finding. Accordingly, the amendment meets the I
eligibility criteria for categorical exclusion set forth in 10 CFR l
51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance j
of the amendment.
I 8.0 [0NCLUSION
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The Commission has concluded, based on the considerations discussed above, i
that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such i
activities will be conducted in compliance with the Commission's regulations, i
and (3) the issuance of the amendment will not be inimical to the common i
defense and security or to the health and safety of the public.
Principal Contributors: H. Asher J. Fair J. Stang Date: May 31, 1996
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