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An unresolved item was identified when sev … An unresolved item was identified when several operability determinations, from January 22 through March 26, 2008, associated with the already installed containment recirculation sump strainer modification, were required to ensure new design discoveries did not create unacceptable reductions in margin to net positive suction head requirements for essential core cooling components. 10 CFR Part 50, Appendix B, Criterion III, requires, in part, that measures be established to assure that applicable regulatory requirements and design basis be correctly translated into specifications, drawings, procedures and instructions. Technical Specifications 3.5.2 and 3.6.6 require that residual heat removal and containment spray system components remain operable. Contrary to this, measures were not adequate to assure the design basis calculation of strainer head loss for the modification to the containment recirculation sump was correct. Several operability determination reviews failed to uncover additional design issues that were later discovered. AmerenUE identified that associated vendor calculation, TDI-6002-05, for clean strainer head loss omitted the head loss component associated with the orifices located in the strainer support plate. The size of the orifice beneath each strainer was not large enough to prevent head loss in excess of the net positive suction head required per the design conditions defined in the purchase specification supplied to the strainer vendor. The additional head loss due to the calculation error was 2.28 feet. This resulted in net positive suction head required being less than net positive suction head available. AmerenUE performed three separate operability determination reviews to demonstrate that the head loss margin could be recovered. The initial operability determination, on January 22, 2008, addressed the smaller support plate orifice holes by using a separate vendor\'s flow analysis of the residual heat removal and containment spray piping systems to demonstrate lower flow and head losses than described in the FSAR. This operability determination determined the limiting case flow path was the hot leg recirculation flow path. Another operability review, on March 12, 2008, addressed a nonconservative temperature correction through the orifices. Subsequent to this, the licensee informed the NRC that additional nonconservative inputs were used in the January 22, 2008, flow analysis of the residual heat removal system. Additional analyses were performed to regain margin. This resulted in the limiting case flow path changing from hot leg recirculation to cold leg recirculation. At the completion of the inspection period, there were still unresolved questions about the assumptions and results associated with the software used for regaining net positive suction head margin. Initial reviews have determined that adequate margin still exists. However, these require additional inspection and, when completed, the inspection results will require significance determination. This issue is considered unresolved pending additional NRC review of AmerenUE operability determination calculations, Unresolved Item 05000483/2008002-01, Containment Recirculation Sump OperabilityContainment Recirculation Sump Operability

Discovered date

23:59:59, 31 March 2008 +

Docket

05000483 +

Event date

23:59:59, 31 March 2008 +

Finding

05000483/FIN-2008002-01 +

Finding integer

1 +

Finding type

URI +

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Identified by

NRC identified +

Inspection procedure

IP 71111.15, Operability Determinations and Functionality Assessments +

Inspection report

IR 05000483/2008002 +

Inspector

Vincent Gaddy +, David Dumbacher +, Paul Elkmann +, Jeremy Groom +, J Groomg + and Guerrad Dumbacher +

Modification date"Modification date" is a predefined property that corresponds to the date of the last modification of a subject and is provided by <a rel="nofollow" class="external text" href="https://www.semantic-mediawiki.org/wiki/Help:Special_properties">Semantic MediaWiki</a>.

00:32:55, 21 February 2018 +

Person