NUREG-0824, SER Supporting Integrated Plant Safety Assessment Rept NUREG-0824 Sections,Including Flooding Elevation & Roofs, Provided Fire Pump House Blockwalls Adequate to Resist Flood Loads

SER Supporting Integrated Plant Safety Assessment Rept NUREG-0824 Sections,Including Flooding Elevation & Roofs, Provided Fire Pump House Blockwalls Adequate to Resist Flood Loads

ML20138A784
Person / Time
Site:	Millstone
Issue date:	10/07/1985
From:	NRC
To:
Shared Package
ML20138A777	List:
References
RTR-NUREG-0824, RTR-NUREG-824 NUDOCS 8510110086
Download: ML20138A784 (4)

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SAFETY EVALUATION REPORT IPSAR SECTIONS 4.1.1, FLOODING ELEVATION; 4.1.7, ROOFS 4.5.1, FLOOD ELEVATION; 4.5.2, GROUNDWATER; 4.6.1, DEFICIENCIES NOTED DURING SITE VISIT MILLSTONE UNIT I I

] 1. INTRODUCTION The Integrated Plant Safety Assessment Report (IPSAR) for Millstone 1 (NUPEG-0824) identified areas related to new design basis flood levels, gra water and probable maximum precipitation where Millstone 1 did not c .rm to present requirements. As described in the referenced

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cions of NUREG-0824, the licensee agreed to review the issues

( icentified and determine the appropriate corrective actions, if any.

_3 The licensee addressed each of the issues in submittals dated February 2, 1984 and March 16, 1984.

The issues identified in the IPSAR are as follows:

L Section 4.1.1,. Flooding Elevation - Probable Maximum Hurricane (PMH) g flood levels including wave effects resulted in a water level of .

3 22.3 ft ms1 (18.11 ft msl stillwater level plus wave action). Safety-related structures are protected to elevation 19.0 msl by concrete floodwalls. The licensee agreed to address the effects of water inleakage from waves overtopping the flood walls in this section and to address structural effects in Section 4.5.1.

Section 4.1.7, Roofs - The IPSAR concluded that roofs with parapets may be overstressed as a result of a local probable maximum precipitation (PMP).

Section 4.5.1, Flood Elevation - The issue identified in this section is identical to that identified in Section 4.1.1; however, the licensee has addressed the structural effects of the increased water level in this section and the inleakage from wave action overtopping

. the floodwalls in Section 4.1.1.

Section 4.5.2, Groundwater - The licensee has stated that plant structures were designed to resist hydrostatic and uplift forces resulting from groundwater rising to grade. The IPSAR requested the licensee to determine whether these loads were considered in the proper load combination.

Section 4.6.1, Deficiencies Noted During Site Visit - During a site visit, the staff noted that two of four roof drains on the turbine building were inoperable. The licensee addressed this issue as part of the roof analysis conducted for Section 4.1.7.

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II. EVALUATION Section 4.1.1, Flooding Elevation; 4.5.1, Flood Elevation The licensee has addressed both water inleakage from vave overtopping and structural effects from increased flood levels by relying on the isolation condenser as the primary method to achieve safe shutdown for flooding events. This method is described in detail in the licensee's letter dated December 2, 1983.

The isolation condenser is located in the upper levels of the reactor butidirg and can be operated independent of AC power. The licensee has proposed to use water from the firewater system to provide make-up

, to the shell side of the isolation condenser. Either one of two motor driven fire pumps or one diesel driven fire pump located in the fire pump house will be used to pump the water to the isolation condenser. One of the rotor driven pumps receives emergency AC power from Millstone 1 and the other from Hillstone 2. To protect s these pumps, the licensee has proposed to extend the east flood gate on the cump house to elevation 21.75 msl and seal it at the top of the door opening.

.An alternate source of make up would be available as part of the nodifications proposed to satisfy tornado missile concerns. The

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licensee has proposed to tie into the city water system and supply a portable enoine driven pump to be stored in the reactor building along with necessary hoses. This pump would be used to punp make-up water

~, from a connection in the city water system to the isolation condenser.

The staff concludes that in the event of a PMH, sufficient netbeds exist to safely shutdown Hillstone I with the modifications proposed by the licensee. Even if emergency AC power is lost, either one of twe diesel driven pumps would still be available to provide make-up from different sources to the isolation condenser. As noted in Section 4.1.5 of the IPSAP, the oil storage capacity for the diesel-driven firewater pump a11nws pump operation for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> before oil makeup from other sources would be necessary.

The staff finds this approach acceptable; however, the ifcensee should assure that the blockwalls of the fire pump house can resist the floodwater, including wave effects. In addition, as part of the ifcensee's implenentation of the plant modifications described above, the staff will require that the licensee make any necessary changes to the clant's energency procedures to reflect the safe shutdown capability for flooding events.

a Section 4.1.7, Roofs; 4.6.1, Deficiencies Noted During Site Visit The licensee analyzed the roofs of safety-related structures, where the roof was surrounded by a parapet, in order to determine whether the roof was capable of withstanding the load imparted by a water level equal to the parapet height. The evaluation was done by calculating the water level that would impart a load equal to the original design live load and then comparf ag this water level to the parapet height.

The analysis took no credit for roof drains.

The licensee concluded that the radwaste disposal building, the intake structure, the radwaste/ control building, the southwest corner of the reactor building and the gas turbine building roofs can support the loads imparted by a local Probable Maximum Precipitation (PMP) resulting in water to the top of the parapet. However, the licensee ccncluded that the turbine building, the reactor building, warehouse, and HVAC area roofs cannot withstand the PMP loads. For t'hese buildings, the ,

licensee proposes to install scuppers at a height which will limit the maximum water depth to a level which maintains the load below the original design live load.

The staff concludes that properly installed scuppers will adequately limit roof ponding loads and, therefore, finds the licensee's proposal acceptable.

Section 4.5.2, Groundwater To address this issue, the licensee analyzed the reactor building for uplift forces and horizontal forces from soil, groundwater and earthquake loadings. The load combinations chosen were nomal dead and live loads including lateral earth pressure with the associated load factors and the extreme environmental loading which includes earthquake forces.

The structure was found to be adequate for uplift as well as for horizontal forces.

After reviewing the analysis, the staff notes that only inertial forces from the buoyant weight of the soil were included and that inertial forces from the groundwater were not. These forces would tend to increase the load on the wall where the factor of safety in the vertical direction has been calculated to be 1.04. Additionally, while selecting the reactor building for investigation because of its large embedment was prudent, it is also the most substantial structure on the site. Demonstrating adequacy for the reactor building does not necessarily demonstrate adequacy for all structures.

The reference 9 (ASCE-Manuals and Reports on Engineering Practice -

No. 58, " Structural Analysis and Design of Nuclear Power Plant Facilities) cited in the licensee's analysis report (02-0240-1141) concludes that the solution of soil-structure interaction problems to obtain dynamic earth pressure is warranted for Category 1 structures.

For less important structures and for a preliminary estimate of the

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dynamic earth pressure on Category I structures, the Mononobe-Okabe method and methods based on elastic theory can be 'ased. Thus, the simplified methods in Reference 9 should demonstrate ample margins to cover possible uncertainties introduced by using a simplified method; if ample margins do not exist, a more refined method should be used.

In view of the minimal margin of safety calculated for the reactor building and the lack of groundwater inertial forces, the staff believes that a more refined analysis should be performed to confirm an adequate margin of safety with respect to the ability of the reactor building to resist groundwater loads. In addition, the staff believes that additional simplified analyses should similarly be conducted to demonstrate the adequacy of other Category I structures.

The issue of groundwater loads in combination with other loads (e.g.,

seismic) will be addressed in the staff's evaluation of the licensee's Integrated Structural Assessment Program under ISAP Topic 1.19 and IPSAR Section 4.12. For that evaluation, assuming the groundwater level at grade would be ultimately conservative; a more appropriate level can be established from site measurements.

III. CONCLUSIONS The staff finds the licensee's comitment to modify the fire pump house to assure a source of make-up water to the isolation condenser acceptable as a method of shutting down the facility in the event of flooding conditions. However, to assure that the fire pump house will remain water tight, the licensee should analyze the blockwalls of the fire pump house for floodwater, including wave effects. In addition, the licensee should modify the emergency procedures, as necessary, to reflect these shutdown provisions.

The staff finds the proposal to instal,1 scuppers on the roofs of the turbine building, reactor building, warehouse, and HVAC area to be an acceptable way of limiting roof loads, imposed by standing water from the PMP.

The staff recomends that the licensee perform additional analyses to confirm a margin of safety for groundwater loads in Category I structures.

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