ML18057A485
| ML18057A485 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 09/20/1990 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9010020287 | |
| Download: ML18057A485 (8) | |
Text
September 20, 1990 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT -
RESPONSE TO INSPECTION REPORT 90017 OPEN ITEMS David P Hoffman Vice President Nuclear Operations Nuclear Regulatory Commission (NRC) Inspection Report 255/90017, dated August 31, 1990, documented the results of an examination of evaluations performed pursuant to 10CFR Part 50, Section 59 with primary focus on the Steam Generator Replacement Project (SGRP) at Palisades Plant.
While no violations were identified during this inspection, NRC requested a response within 30 days to the open items contained in the report.
The attachment to this letter provides that response.
Your cover letter noted that further NRC assessment of the temporary containment opening would be provided in future correspondence.
Due to the schedule for SGRP, we would appreciate clarification of any outstanding issues at the earliest date possible.
The attached response to open item 90017-02 provides further discussion on this topic.
Any referenced material can be provided to NRC promptly, or we will be glad to meet with you as needed.
Vice President CC Administrator, Region III, USNRC NRC Resident Inspector - Palisades Attachment
('{ _.,'
ATTACHMENT Consumers Power Company Palisades Plant Docket 50-255 RESPONSE TO IR 90-017 Open Items September 20, 1990 6 Pages
Response to IR 90017 Open Items Open Item 90017-01:
Facility Change (FC)-915, Component Cooling *water (CCW) Surge Tank Room Modifications, provides for an opening of approximately 48" by 21" in the ceiling of th~ CCW surge tank room and drilling a 2".hole in the floor of the room.
The room would be returned to its original configuration after the SGRP is completed.
The openings are required to provide equipment access to the containment post-tensioning system tendons located on the west side of containment buttress B.
The inspector reviewed the FC package, the SE, and toured the affected area.
Several concerns were identified with the SE.
o The Safety Evaluation (SE) did not address the potential for the release of airborne radioactivity through these openings.
o Some potential for damage to the CCW surge tank and other components in this area exists while the de-tensioning proc~ss is in progress.
The heat load on the CCW system during this period were not addressed in the SE.
The-SE noted that the surge tink was requir~d. only for "long term" CCW operation.
The duration of "long term" or heat loads during that period were not addressed.
Further, no contingency actions were identified if damage to the CCW system should occur.
Response - Both of the noted items have been addressed.in a later revi~ion of
- the* safety evaluation for FC-915.
Any potential for airborne release resulting from FC-915 involves two small holes (2 inch diameter) for passage of cables to be used with lift rigs during the SGRP Outage.
The hole in the floor of the CCW tank room enters a resin tank room below, which is not a high radiation source area and is vented through the Auxiliary Building HVAC to the plant discharge stack. Airflow in either direction through this small hole will not be a safety concern.
A second hole, in the roof of the fuel pool building (scope addition since IR
- 90-17 site visit), does communicate with outside air. Negative pressure inside the fuel pool area will assure no out-leakage through this small hole.
The area around the cable will be filled to the.extent possible tp further reduce air/rain passage through the hole.
The square access opening in the CCW tank room ceiling is within the fuel pool building ventilation boundary and opens no new pathways.
Regarding the second item, the SE approach continues to be that sufficient caution will be taken to prevent damage to the CCW surge tank.
In this regard, further protection measures have been incorporated - removal of a sight glass, piping protection, and a protective ~tructure over the tank.
In the very unlikely event of total loss of tank function, the loss of CCW off normal plant procedure referenced in the SE is based on CCW heat loads over*
various periods and the relative safety importance of those loads.
The only other practical contingency which was considered already exists in the form of 1
a water makeup hose in the area. Operators would have over an hour to utilize this backup souree to the CCW tank.discharge pipe at existing system leakage rates. A final note is that the CCW tank automatic makeup enters directly intp the tank discharge pipe, such that complete destruction of the tank itself would not starve the system.
Open Item 90017-02 Following are the concerns identified and responses to the ten items regarding FC-914, Containment Construction Opening.
- 1.
There was a large discrepancy between.the stress levels calculated at the containment foundation by two different analyses.. This discrepancy should be reconciled or the larger values should be used to determine if the stress levels are acceptable.
Response - The differences between the stress levels calculated by the analyses (i.e., the present analytical model versus the original analytical model) have been discussed and documented in Bechtel calculation 20557-C-053, Rev. 2 entitled **comparison of the Analysis Results Between the Original and Present Models."
The present finite element analysis of the containment shell uses three dimensional thin plate or shell element theory and the containment shell is assumed fixed at the basemat.
The original finite element of the containment shell used plane strain elements and considered basemat flexibility. The larger values of the stress levels derived from the present analysis have been used to verify the structural integrity of the containment structure.
It h~s been documented in Bechtel Calculation 20557-C-064, Rev~ 0, t~at the containment structure can withstand the maximum design loads per FSAR requirements during and after the modification.
This issue also has been addressed in NRC Inspection Report No. 50-255/90063 (DRS), Items 3 and 4.
- 2.
The finite element stress analysis of the containment averaged stresses in adjacent elements (i.e., an overstress iri one element was averaged with understresses in adjacent elements).* The basis for the acceptability of this technique should be provided.
Response - The basis for the acceptability of the stress averaging is documented in Bechtel Calculation 20557-C-071, Rev. O, entitled "Basis for Averaging the Stresses of Over-Stressed and Under-Stressed Elements." The basis for the acceptance is as follows:
(1), The over-stressed conditions are localized.
(2)
For each 16calized over-stressed condition, the size of the region which represents the area to be averaged is small.
Namely, {a) its dimension in either the vertical or hoop direction is less than 4-1/2 times the minimum thickness of the containment shell;
{b) its dimension in the vertical direction is less than one tenth of the height of the cylindrical portion of the containment shell; 2
- 3.
(3) and (c) its dimension in the hoop direction is less than one twentieth of the mean circumference of any horizontal section of the containment shell.
It is realized that a reinforced concrete structural component is typically designed based on assumption that the concrete cracks under tensile stress. The strength of a reinforced concrete.
structural component (such as beam, slab, etc.) is not based on a specific section or point in the component because once a section in the component begins to crack, its sectional stiffness is reduced. This leads to reproportioning of load within the immediate neighborhood of the cracked section in such a way that the cracked section carries proportionally lower load than its immediate uncracked region and in turn creates more cracked sections. With further load increase, such process continues and the cracked region expands until the regional capacity is reached.
For example, in a simply supported beam subjected to mid-span concentrated load, the size of its. cracked region is much larger than one tenth of the beam span (based on Figure 3.4 in Ferguson, P.M., Reinforced Concrete Fundamentals, 2nd Ed., John Wiley &
Sons, Inc.). Therefore, in reality the strength of a reinforced concrete structural component is intrinsically based on the averaged strength over a representative region.
However, by nature of the analytical structural analysis, point stresses or sectional forces are produced instead of the averaged stresses or forces over specific regions in the structure.
For the present finite element analysis of the Palisades containment, the.
sectional forces are produced at each element centroid.
To utilize the analytical results consistently with the actual reinforced concrete structural behavior, common design practice for designing structural region subjected to localized stress distribution is to develop reinforced concrete section capacities based on averaged analytical stresses over a representative regi~n. Therefore, th~ stress averaging procedure used in the Palisades containment evaluation is in accordance with accepted common practice and accounts for the behavior of reinforced concrete.
The results of the tests performed by the licensee on the concrete mix to be used to close the containment opening should be provided to support the creep and shrinkage values used in the analysis of the reconstructed portion of the containment.
Response - The concrete creep tests are being performed by the University of Illinois at Urbana - Champaign in accordance with Bechtel Specification 20557-C-6A(Q).
Extensive effort has been made to locate and qualify concrete constituents to satisfy the need of the containment construction opening, namely, ;o maximize concrete strength while minimizing creep and shrinkage.
The concrete mix designs* performed under Specification 20557-C-6A(Q) have yielded a concrete mix with high compressive strength (5000 psi at 7 days) and an acceptable low level of creep characteristics.
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Ba~ed on the available results of the creep tests, it can be concluded that the creep and shrinkage values used in the analysis are conservative.
(It will be documented in a calculation to confirm the fact when final creep test results become available).
- 4.
The containment liner will be cut as a part of the process for providing the containment opening.
The section removed will be welded back in place.
An analysis should be performed to demonstrate the structural integrity of the repaired lining.
Response - The containment liner section removed will be replaced with new liner plate sections in accordance with Bechtel Specifications 20557-C-50A(Q) and 20557-C-52A(Q).
Full penetration welds will be used in the restoration of the liner plate and non-destructive examinations will be performed to ensure that the liner plate is re-installed properly to meet the original design condition.. Bechtel calculation 20557-C-069, Rev. 0, addresses the adequacy of the steel liner plate in the containment opening after the.restoration. *It has been demonstrated that the structural ~ntegrity of the liner plate is maintained.
- 5.
The reinforcing steel used in the reconstructed area was to be spliced to existing reinforcing steel via Cadweld splicing. Assurance should be provided that the relative location of these splices in adjacent bars does not jeopardize the structural integrity of the containment.
Response.- The Palisades containment is a post tensioning, prestres~ed
- concrete structure of which the strength of the containment structure depends primarily on the prestressed tendons.
The reinforcing steel provided along the outside face of the containment wall is mainly to minimize the shrinkage crack.
The Cadweld rebar splices will be performed in ac~ordance with Specification 20557-C-303A(Q) and sister splice tests will be conducted to ensure that the structural integrity of the reinforcing steel is maintained.
As in the case of the original construction opening when the containment was built (reference drawing 5935-C-259), the relative location of these splices in adjacent bars (i.e., non-staggering pattern) does not jeopardize the structural integrity of the containment.
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It would be necessary to remove the containment prestressing tendons which would cross the containment opening.
These tendons will be inspected.and the undamaged ones reused.
An analysis should be performed to show that the creep and relaxation that has occurred in these tendons will not result in an increase in prestress loss after reinstallation and tensioning.
Response - The effect of concrete creep and tendon relaxation that could have occurred to the reinstalled tendons has been accounted for in the calculation of the required retensioning forces.
The calculated retensioning forces as shown on Bechtel Drawing 20557-C-3026, Rev. 3, will ensure that sufficient pre-stresses are maintained throughout the Plant life. The analysis for the required retensioning forces and expected elongation of the tendons is documented in Bechtel Calculation 4
20557-C-074, Rev. 0.
In addition per Bechtel Specification 20557-C-51B(Q), three wires, one from each work group (i.e., vertical, EB & FA),
will be pulled from the removed tendons for inspection. Samples of the wire will be tested in the laboratory to. support the engineering analysis.
- 7.
The prestressing tendons are contained in a sheathing which is filled with grease for corrosion protection of the tendons.
The sheathing crossing the containment opening will be removed and discarded.
New sheathing will be installed in this area when the opening is closed.
The details of connecting the new sheathing to the existing sheathing should be provided.
Response - The details *ot connecting the new sheathing to the existing sheathing are shown on bechtel Drawing 20557-C-3007.
A one-foot long coupling will be install~d at the joint with six inches overlapping to
- the new and existing sheathings.
The joint will then be "sealed with epoxy or caulk and taped to provide a leak tight seal.
- 8.
It wi 11 be necessary to withdraw some tendons from their sheathing and then reinsert it. The potential of damaging this sheathing should. be addressed.
- 9.
Response - The installation of the tendon sheathing is similar to the original design requirements.
Further, the tendon sheathing has been previously filled with greases so that the frictional force between the tendon and the sheathing is reduced.
Iri addition, the replaced tendons will be coated with Visconorust 1601, and tendon tips will be taped to eliminate any sharp edges.-
On this basis the potential for damage is no greater, and expected to be lower than that of the original installation. Nevertheless, damage associated with the tendon sheathing during tendon removal and reinstallation does not create a safety concern~ In the r~mote chance that damage should occur, the grease will contact the concrete. Since the grease contains a corrosion inhibitor to prevent corrosion of tendons, it will not cause any adverse effect on the reinforcing steel or on the concrete. Therefore, the.structural integrity of the containment will not be affected.
Extreme care will be taken during the tendon removal and.re-installation operation to minimize potential damage to the tendons and sheathings.*
The integrity of the Cadweld splices of the reinforcing bars is very important.
Mockup training on the installation of these splices should be provided.
- Response - The mockup training on the Cadweld splices of tha reinforcing bars will be conducted in the field to qualify the personnel to perform the work.
Paragraph 3.3 of Bechtel Specification 20557-C-303A(Q) addresses the operator qualification. Prior to starting production splicing for a splice position (horizontal or vertical), each member of the splicing crew (or each crew if the members work as a unit) shall prepare two qualification splices for the splice positions to be used.
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- 10.
The licensee plans to perform a structural integrity test (SIT) at 115%
of containment design pressure after repairing the containment.
The effect of this test on containment integrity considering the loss of prestress in the undisturbed tendons (which will not be retensioned) should be evaluated.
Response - The containment structure has been evaluated with load combination applying 115% of containment design pressure and considering all potential prestress losses to derive the available prestresses at the end of the 40-year life span of the Palisades Plant.
Bechtel calculations 20557-C-026, "Load C6mbinati~ns for the Containment Shell" (Load Combination No. 11), and 20557-C-038, "Adequacy Evaluation for the Containment Shell after the Construction Openirig Repair" documented the evaluation and concluded that the containment can withstand 115% of the containment design pressure at the end of the licensed life span of the Palisades Plant.
Open Item 90017-03 FC-904, Auxiliary Building Modification for Containment Access, provides for a 6'-6" by 7'-2" personnel and equipment access opening in the Auxiliary Building east wall.
The wall will be returned to its original configuration upon compl*etion of the SGRP.
The inspectors reviewed the FC package and SE.
One.concern was identified. The SE failed to address the potential release of airborne radioactivity via the access opening.
Response - The FC-904 safety evaluation has been revised to expand the section on ventilation aspects and add further detail regarding potential release of airborne radioactivity.
The attached access facility will have no windows or ventilation path to the outside, and doors will exist between it and the stairwell heading up to the new entry into the fuel pool deck area. This provides two stagnant air volumes between outside atmosphere and the proposed fuel building entry doors.
The entry doors to. the auxiliary building are a security boundary and thus alarmed if left ajar.
The fuel building is under a negative pressure to assure any airflow is inward.* This will be verified following constructiori and every shift during periods when the fuel building ventilation/charcoal filter system is required to be operable.
Open Item 90017-04 The licensee agreed to submit the six Technical Specifications change requests commensurate with the required dates. The revision of th2 SE for FC-909 to refl~ct the required schedule for TS changes will be tracked as an open item.
Response - The FC-909 safety evaluation has been revised to reflect the schedule for Technical.Specification changes. Three change submittals have already been sent to NRR and we plan to send the last three by October 15, 1990.
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