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13 3.1 Local Intense LIP Analysis (Reference 8 and Reference | 13 3.1 Local Intense LIP Analysis (Reference 8 and Reference | ||
: 10) ............................................... 14 3.1.1 Basis of l nputs ........................................... | : 10) ............................................... 14 3.1.1 Basis of l nputs ........................................... | ||
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17 3.2 Flood ing in Streams and R ivers (Reference 4 , Reference 5, and Reference | 17 3.2 Flood ing in Streams and R ivers (Reference 4 , Reference 5, and Reference | ||
: 9) ................... 24 3.2.1 Basis of I nputs .................. | : 9) ................... 24 3.2.1 Basis of I nputs .................. | ||
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27 3.2.2 Computer Softwa r e Programs .................................................................................. 29 3.2.3 Methodology | 27 3.2.2 Computer Softwa r e Programs .................................................................................. 29 3.2.3 Methodology | ||
............................................................................................................. 29 3.2.4 Resul t s ..................................................................................................................... | ............................................................................................................. 29 3.2.4 Resul t s ..................................................................................................................... | ||
40 3.3 Dam Brea ches and Failures (Reference | 40 3.3 Dam Brea ches and Failures (Reference | ||
: 25) ............................................... | : 25) ............................................... | ||
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............................................................................................................. 4 5 3.7.4 Re su lts ..................................................................................................................... 47 3.8 Channel Mig ration or Diversion (Re fe r ence 6) .................................... | ............................................................................................................. 4 5 3.7.4 Re su lts ..................................................................................................................... 47 3.8 Channel Mig ration or Diversion (Re fe r ence 6) .................................... | ||
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.47 3.9 Co mb ine d Effect Flood (Inc lud i ng Wi n d Generate d W aves, Reference | .47 3.9 Co mb ine d Effect Flood (Inc lud i ng Wi n d Generate d W aves, Reference | ||
: 7) .......................... .47 3.9.1 Basis of I nputs ......................................................................................................... .48 3.9.2 Computer So f tware Programs ................... | : 7) .......................... .47 3.9.1 Basis of I nputs ......................................................................................................... .48 3.9.2 Computer So f tware Programs ................... | ||
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........................................................................... 23 Table 3. Summary of Cu r rent Design Basis and Reeva l uated F l ood Hazard Elevations | ........................................................................... 23 Table 3. Summary of Cu r rent Design Basis and Reeva l uated F l ood Hazard Elevations | ||
............... 52 COLUMB I A GENERA TI NG STA T ION Pag e 4 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | ............... 52 COLUMB I A GENERA TI NG STA T ION Pag e 4 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | ||
): t-1ooaing Energy Northwest Columbia Generating Station 1. PURPOSE 1.1 Background September 27, 2016 Revision 0 I n response to the nuclear fuel damage at the Fukushima-Daiichi power p lant due to the March 11 , 2011, earthquake and s ubsequ en t t sunami, the United States Nuclear Regulatory Commission (N R C) establis h ed the Near T erm T ask Force (NTTF) to conduct a systematic rev i ew of NR C processes and regulations, and to make recommendations to the NRC fo r its policy direction. Th e N TTF reported a set of recommendations that were intended to clarify and strengthen t he regulatory framework for protection against n atura l phenomena. On March 12, 2012, the NR C issued an information request pursuant to T i tle 1 O of the Code of Federal Regulation s, Sect i on 50.54(f) (10 CFR 50.54(f) or 50.54(f) letter) (Reference | ): t-1ooaing Energy Northwest Columbia Generating Station 1. PURPOSE 1.1 Background September 27, 2016 Revision 0 I n response to the nuclear fuel damage at the Fukushima-Daiichi power p lant due to the March 11 , 2011, earthquake and s ubsequ en t t sunami, the United States Nuclear Regulatory Commission (N R C) establis h ed the Near T erm T ask Force (NTTF) to conduct a systematic rev i ew of NR C processes and regulations, and to make recommendations to the NRC fo r its policy direction. Th e N TTF reported a set of recommendations that were intended to clarify and strengthen t he regulatory framework for protection against n atura l phenomena. On March 12, 2012, the NR C issued an information request pursuant to T i tle 1 O of the Code of Federal Regulation s, Sect i on 50.54(f) (10 CFR 50.54(f) or 50.54(f) letter) (Reference | ||
: 24) which included six (6) enclosures: | : 24) which included six (6) enclosures: | ||
: 1. [N TTF] Recommendation 2.1: Seismic 2. [N TTF] Recommendation 2.1: Flooding 3. [NTTF] Recommendation 2.3: Seismic 4. [NTTF] Recommendation 2.3: Flooding 5. [NTTF] Recommendation 9.3: EP 6. Licensees and H olders of Construction Permits I n Enclosure 2 of informa t ion reques t (Reference 24), the NRC requested that licensees reevaluate the flooding hazards at their sites against present-day reg u lato ry gu i dance and methodologies being used fo r early site permits (ES P) and combined operating li cense (COL) reviews. On behalf of Energy Northwest Company , LLC , for the Co l umbia Nuclear Generating Station (CGS), this Fl ood H azard Reeva l u ation R epo r t (R eport) provides the information requested i n the March 2012 , 50.54(f) letter; specifically , the in formation listed under the "Requested In forma t ion" section o f Enclosure 2, paragraph 1 ("a" t hr ough "e"). Th e " R eq u ested I nformation" section of Enclosure 2, paragraph 2 ("a" through "d"), I ntegra t ed Assessment Report, will be addressed separately if the current design basis floods do not bound the reevaluated hazard for all flood-ca us i ng mechani sms. 1.2 Requested Actions Per Enclosure 2 of the NRC issued information request, 50.54(f) letter, CGS i s requested to perform a reevaluation of all appropriate externa l flooding sources at CGS, includ ing th e effects of l oca l intense precipitation (LIP) on the site, probable maximum f l ood (PMF) on streams and rivers , storm surges, seiches, tsunamis, and dam fai l ures (as applicable). It is requested that the r eevalua ti on apply present-day regu l atory guidance and methodologies being used for ESPs and ca l culation reviews, inc l uding current techniques, software, and methods used in present-day standard engineering practice to eval l uate the flood hazard. T he reque ste d infor mation wi l l be gathered in Phase 1 of the NRC staff's two-phase process to im p leme nt R ecommendation 2.1 , and will be used to identify potential | : 1. [N TTF] Recommendation 2.1: Seismic 2. [N TTF] Recommendation 2.1: Flooding 3. [NTTF] Recommendation 2.3: Seismic 4. [NTTF] Recommendation 2.3: Flooding 5. [NTTF] Recommendation 9.3: EP 6. Licensees and H olders of Construction Permits I n Enclosure 2 of informa t ion reques t (Reference 24), the NRC requested that licensees reevaluate the flooding hazards at their sites against present-day reg u lato ry gu i dance and methodologies being used fo r early site permits (ES P) and combined operating li cense (COL) reviews. On behalf of Energy Northwest Company , LLC , for the Co l umbia Nuclear Generating Station (CGS), this Fl ood H azard Reeva l u ation R epo r t (R eport) provides the information requested i n the March 2012 , 50.54(f) letter; specifically , the in formation listed under the "Requested In forma t ion" section o f Enclosure 2, paragraph 1 ("a" t hr ough "e"). Th e " R eq u ested I nformation" section of Enclosure 2, paragraph 2 ("a" through "d"), I ntegra t ed Assessment Report, will be addressed separately if the current design basis floods do not bound the reevaluated hazard for all flood-ca us i ng mechani sms. 1.2 Requested Actions Per Enclosure 2 of the NRC issued information request, 50.54(f) letter, CGS i s requested to perform a reevaluation of all appropriate externa l flooding sources at CGS, includ ing th e effects of l oca l intense precipitation (LIP) on the site, probable maximum f l ood (PMF) on streams and rivers , storm surges, seiches, tsunamis, and dam fai l ures (as applicable). It is requested that the r eevalua ti on apply present-day regu l atory guidance and methodologies being used for ESPs and ca l culation reviews, inc l uding current techniques, software, and methods used in present-day standard engineering practice to eval l uate the flood hazard. T he reque ste d infor mation wi l l be gathered in Phase 1 of the NRC staff's two-phase process to im p leme nt R ecommendation 2.1 , and will be used to identify potential | ||
" vu l nerabilit i es." (See defin it io n be l ow.) COLUMB I A GENERA TI NG S T A T ION Page 5 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | " vu l nerabilit i es." (See defin it io n be l ow.) COLUMB I A GENERA TI NG S T A T ION Page 5 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | ||
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I n the event that the roof drains are completely blocked during the precipitation event, overflow scuppers limit the depth of water to within the design load carry i i ng capabil it y of the roofs. Those safety-related structures that do not have this relief capability are structurally able to carry the entire precipitation accumulations (Reference 2). 2.1.2 Flooding in Streams and Rivers Analyses of the PMF are consisten t with t h e requirements of Regulatory Guide 1.59, Revision 2. The FSAR indicates an unregulated PMF flow rate of 1,600 , 000 cubic f t per second (cfs) in th e Columbia River at CGS (Reference 2). Adjustment of the flood profiles for the Hanford region r esults in a regulated PMF of 1,440 , 000 cfs and a water level of 390 ft-MSL at the Seismic Category II makeup water structure. | I n the event that the roof drains are completely blocked during the precipitation event, overflow scuppers limit the depth of water to within the design load carry i i ng capabil it y of the roofs. Those safety-related structures that do not have this relief capability are structurally able to carry the entire precipitation accumulations (Reference 2). 2.1.2 Flooding in Streams and Rivers Analyses of the PMF are consisten t with t h e requirements of Regulatory Guide 1.59, Revision 2. The FSAR indicates an unregulated PMF flow rate of 1,600 , 000 cubic f t per second (cfs) in th e Columbia River at CGS (Reference 2). Adjustment of the flood profiles for the Hanford region r esults in a regulated PMF of 1,440 , 000 cfs and a water level of 390 ft-MSL at the Seismic Category II makeup water structure. | ||
As indicated in the FSAR (Reference 2), the des i gn basis flood for CGS area resu l ts from the PMP event on the adjacent drainage basin and not from f l ooding of the Co l umb i a River. Th e methodology for p r edicting the t otal amount of precipitation requires add in g together the convergence PMP and the orographic PMP to obtain a single precipitation for a general storm. The U.S. Army Corps of Engineers (USAGE) Hydrologic Eng i neering Center (HEC) standard-step procedure for seven (7) cross sections was utilized to determine t h e WSE from the PMF event on the adjacent drainage basin , which was determined to be 431.1 ft-MSL (Reference 2). 2.1.3 Dam Breaches and Failures There are seven dams upstream and four dams downs t ream of CGS on the ma i n stream of the Columbia River within the U.S. The current license basis dam failure considered a flood from a breaching of Grand Coulee Dam in l ie u of a seismically induced flood. A massive hyd r aul i c failure of the Grand Coulee Dam with a release of 8 , 800 , 000 cfs was considered for analyses of floods resul t ing from potential dam failures. Following the assumed failure of the Grand Coulee Dam , all downstream dams between Grand Coulee Dam and CGS suffer some degree of failure and release their storage reservoirs to t he f l ood. The effect of potential dam failu r e on the water levels at CGS wa s determined using the assumption that the Columbia R iv er i s at flood stage w i th a standard COLUMB I A GENERA TI NG STA T ION Page 9 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | As indicated in the FSAR (Reference 2), the des i gn basis flood for CGS area resu l ts from the PMP event on the adjacent drainage basin and not from f l ooding of the Co l umb i a River. Th e methodology for p r edicting the t otal amount of precipitation requires add in g together the convergence PMP and the orographic PMP to obtain a single precipitation for a general storm. The U.S. Army Corps of Engineers (USAGE) Hydrologic Eng i neering Center (HEC) standard-step procedure for seven (7) cross sections was utilized to determine t h e WSE from the PMF event on the adjacent drainage basin , which was determined to be 431.1 ft-MSL (Reference 2). 2.1.3 Dam Breaches and Failures There are seven dams upstream and four dams downs t ream of CGS on the ma i n stream of the Columbia River within the U.S. The current license basis dam failure considered a flood from a breaching of Grand Coulee Dam in l ie u of a seismically induced flood. A massive hyd r aul i c failure of the Grand Coulee Dam with a release of 8 , 800 , 000 cfs was considered for analyses of floods resul t ing from potential dam failures. Following the assumed failure of the Grand Coulee Dam , all downstream dams between Grand Coulee Dam and CGS suffer some degree of failure and release their storage reservoirs to t he f l ood. The effect of potential dam failu r e on the water levels at CGS wa s determined using the assumption that the Columbia R iv er i s at flood stage w i th a standard COLUMB I A GENERA TI NG STA T ION Page 9 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | ||
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 project flood (SPF) of 570,000 cfs. A base flow of 50 , 000 cfs was assumed above the mouth of the Snake River for the dam failure flood (Reference 2). The failure of Arrow and/or Mica Dams in Canada could result i n greater re l eases of storage in terms of volume than t hat from t he Grand Coulee Dam , but the effects of such postulated releases are mitigated by a combination of valley storage and cri t ical (f l ow limiting) valley cross sec t ions. The river channel restrictions at Tra i l , British Columb i a, would restrict river flow to about 3,100 , 000 cfs, regardless of the postulated dam failure. A major failure ups t ream wou l d result in this maximum flow for many days, causing overtopping of Grand Cou l ee Dam. An analysis by the U.S. Bureau o f Reclamation concluded that overtopping which might resu l t from the failure of upstream dams will not cause failure of either the Grand Coulee Dam or the Forebay Dam (Reference 2). The failure of the Grand Coulee Dam represents an upper limit to seismical l y induced fai l ures. This failure would initiate a catastrophic flood , which would be augmented by the failure of the earthen portions of downstream dams and subsequent release of the storage pools behind them. T his flood wou l d have an outfall peak of 8,800,000 cfs at Grand Coulee Dam at the moment of breac h ing , and a pea k discharge at River M i le (RM) 338 (Richland) of 4 , 800,000 cfs. The resulting dam breach elevation a t RM 350 is 422 ft-MS L. An addi t io n al 2-ft allowance was included for wind and wave action , and adequate margin exists between the resultant flood elevation and the plant elevation of 441 ft-MSL (Reference 2). 2.1.4 Storm Surge The FSAR (Reference | Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 project flood (SPF) of 570,000 cfs. A base flow of 50 , 000 cfs was assumed above the mouth of the Snake River for the dam failure flood (Reference 2). The failure of Arrow and/or Mica Dams in Canada could result i n greater re l eases of storage in terms of volume than t hat from t he Grand Coulee Dam , but the effects of such postulated releases are mitigated by a combination of valley storage and cri t ical (f l ow limiting) valley cross sec t ions. The river channel restrictions at Tra i l , British Columb i a, would restrict river flow to about 3,100 , 000 cfs, regardless of the postulated dam failure. A major failure ups t ream wou l d result in this maximum flow for many days, causing overtopping of Grand Cou l ee Dam. An analysis by the U.S. Bureau o f Reclamation concluded that overtopping which might resu l t from the failure of upstream dams will not cause failure of either the Grand Coulee Dam or the Forebay Dam (Reference 2). The failure of the Grand Coulee Dam represents an upper limit to seismical l y induced fai l ures. This failure would initiate a catastrophic flood , which would be augmented by the failure of the earthen portions of downstream dams and subsequent release of the storage pools behind them. T his flood wou l d have an outfall peak of 8,800,000 cfs at Grand Coulee Dam at the moment of breac h ing , and a pea k discharge at River M i le (RM) 338 (Richland) of 4 , 800,000 cfs. The resulting dam breach elevation a t RM 350 is 422 ft-MS L. An addi t io n al 2-ft allowance was included for wind and wave action , and adequate margin exists between the resultant flood elevation and the plant elevation of 441 ft-MSL (Reference 2). 2.1.4 Storm Surge The FSAR (Reference | ||
: 2) indicates f l ooding due to surges is not applicable. | : 2) indicates f l ooding due to surges is not applicable. | ||
CGS has an inland location and does not connect d i rectly with any of the water bodies cons i dered for meteorological even t s associated with a storm surge. F l ooding due to a surge is not p l ausible at CGS. 2.1.5 Se i c h e T he FSAR (Reference | CGS has an inland location and does not connect d i rectly with any of the water bodies cons i dered for meteorological even t s associated with a storm surge. F l ooding due to a surge is not p l ausible at CGS. 2.1.5 Se i c h e T he FSAR (Reference | ||
: 2) indicates flooding due to seiche is not applicab l e. CGS has an inland location and does not connect directly wi t h any of the water bodies cons i dered for meteorologica l even t s associated with a seiche. F l ood i ng due to a seiche is not plausible at CGS. 2.1.6 Ts unam i The FSAR (Reference | : 2) indicates flooding due to seiche is not applicab l e. CGS has an inland location and does not connect directly wi t h any of the water bodies cons i dered for meteorologica l even t s associated with a seiche. F l ood i ng due to a seiche is not plausible at CGS. 2.1.6 Ts unam i The FSAR (Reference | ||
: 2) ind i cates flooding due to tsunamis i s not applicable. | : 2) ind i cates flooding due to tsunamis i s not applicable. | ||
CGS is not adjace n t to any coastal area; furthermore , it has an i nland location and does not connect di r ec tl y with any of the water bodies considered for tsunami events. F l ooding due to a tsunami is not a plausible at CGS. 2.1.7 Ic e-Indu ce d Flooding Historically, the Col u mbia River has never exper i enced complete flow stoppage or significant flooding due to ice b l ockage, so no instances of comple t e stoppage have occurred. Periodic ice blocking has caused reduced flows and limited flooding for only relat i vely s hort periods of time. Therefore , it was concluded that ice jam f l ooding potentia l is insignificant for CGS (Reference 2). COLUMB I A GENERA TI NG STA T ION Pa g e 10 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | CGS is not adjace n t to any coastal area; furthermore , it has an i nland location and does not connect di r ec tl y with any of the water bodies considered for tsunami events. F l ooding due to a tsunami is not a plausible at CGS. 2.1.7 Ic e-Indu ce d Flooding Historically, the Col u mbia River has never exper i enced complete flow stoppage or significant flooding due to ice b l ockage, so no instances of comple t e stoppage have occurred. Periodic ice blocking has caused reduced flows and limited flooding for only relat i vely s hort periods of time. Therefore , it was concluded that ice jam f l ooding potentia l is insignificant for CGS (Reference 2). COLUMB I A GENERA TI NG STA T ION Pa g e 10 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | ||
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==SUMMARY== | ==SUMMARY== | ||
OF FLOOD HAZARD REEVALUATION September 27, 2016 Revision 0 NUREG/CR-7046 Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (Reference 23), which references guidance from the American Nuclear Society (ANS), states that a single flood-causing event is inadequate as a design basis for power reactors and recommends that combinations should be evaluated to determine the highest flood water elevation at CGS. For CGS , the combination that produces the h i ghest flood water elevation is the effects of LIP. Energy Northwest Calculation No. CE-02-13-22 (Reference | OF FLOOD HAZARD REEVALUATION September 27, 2016 Revision 0 NUREG/CR-7046 Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (Reference 23), which references guidance from the American Nuclear Society (ANS), states that a single flood-causing event is inadequate as a design basis for power reactors and recommends that combinations should be evaluated to determine the highest flood water elevation at CGS. For CGS , the combination that produces the h i ghest flood water elevation is the effects of LIP. Energy Northwest Calculation No. CE-02-13-22 (Reference | ||
: 8) evaluated the effects of LIP. The CGS FSAR Section 2.4 (Reference | : 8) evaluated the effects of LIP. The CGS FSAR Section 2.4 (Reference | ||
: 2) provides eleva t ions in MSL datum. The CGS flood hazard reevaluation calculations provide e l evation results based on the NAVO 88 and NGVD 29. P r ior to 1973, NGVD 29 was named the Mean Sea Level Datum of 1929. Elevations in the CGS flood hazard reevaluation calculations re f erring to NGVD 29 are equ i valent to MS L and directly compared to the elevations referenced in the CGS FSAR (Reference | : 2) provides eleva t ions in MSL datum. The CGS flood hazard reevaluation calculations provide e l evation results based on the NAVO 88 and NGVD 29. P r ior to 1973, NGVD 29 was named the Mean Sea Level Datum of 1929. Elevations in the CGS flood hazard reevaluation calculations re f erring to NGVD 29 are equ i valent to MS L and directly compared to the elevations referenced in the CGS FSAR (Reference | ||
: 2) that use MSL. The methodology used in the f l ooding reevaluation for CGS is consistent with the following standards and guidance documents: | : 2) that use MSL. The methodology used in the f l ooding reevaluation for CGS is consistent with the following standards and guidance documents: | ||
* NRC Standard Rev i ew Plan , NUREG-0800 , revised March 2007 (Reference 22). | * NRC Standard Rev i ew Plan , NUREG-0800 , revised March 2007 (Reference 22). | ||
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* NRC RG 1.59 , Design Basis Floods for Nuclear Power Plants , Revision 2 , dated August 1 977 (Reference 21 ). | * NRC RG 1.59 , Design Basis Floods for Nuclear Power Plants , Revision 2 , dated August 1 977 (Reference 21 ). | ||
* NUREG/CR-7046, "Design-Basis Flood Estimat i on for Site Characterization at Nuclear Power Plants in the United States of America," dated November 2011 (Reference 23). | * NUREG/CR-7046, "Design-Basis Flood Estimat i on for Site Characterization at Nuclear Power Plants in the United States of America," dated November 2011 (Reference 23). | ||
* American National Standard for Determining Design Basis Flooding at Power Reactor Sites (ANS I/ANS 2.8-1992), dated July 28 , 1992 (Reference | * American National Standard for Determining Design Basis Flooding at Power Reactor Sites (ANS I/ANS 2.8-1992), dated July 28 , 1992 (Reference | ||
: 1) | : 1) | ||
* NEI Report 12-08 , Overview of External Flooding Reevaluations (Re f erence 13). T he following provides the flood-causing mechanisms and their associated WSEs that are considered in the CGS flood hazard reevaluation. | * NEI Report 12-08 , Overview of External Flooding Reevaluations (Re f erence 13). T he following provides the flood-causing mechanisms and their associated WSEs that are considered in the CGS flood hazard reevaluation. | ||
COLUMBIA GENERAT I NG STA T ION Pa g e 13 of 55 NTT F Recommendation 2.1 (Hazard R eevaluations): | COLUMBIA GENERAT I NG STA T ION Pa g e 13 of 55 NTT F Recommendation 2.1 (Hazard R eevaluations): | ||
F looding Energy Northwest Columb i a Generating Station September 27, 2016 Revision 0 3.1 Local Intense LIP Analysis (Ref e rence 8 and Reference | F looding Energy Northwest Columb i a Generating Station September 27, 2016 Revision 0 3.1 Local Intense LIP Analysis (Ref e rence 8 and Reference | ||
: 10) Calculation N o. CE-02-14-1 O (Re f ere n ce 10) evaluates site-spec ifi c PMP depths used as inp ut to the LIP analysis. | : 10) Calculation N o. CE-02-14-1 O (Re f ere n ce 10) evaluates site-spec ifi c PMP depths used as inp ut to the LIP analysis. | ||
Calculation No. CE-02-13-22 (Reference | Calculation No. CE-02-13-22 (Reference | ||
: 8) evaluates th e r unoff an d the r esulting WSE due to a LIP event at CGS. 3.1.1 Basis of Inputs The i nputs used in t he LIP analysis are based on the following: | : 8) evaluates th e r unoff an d the r esulting WSE due to a LIP event at CGS. 3.1.1 Basis of Inputs The i nputs used in t he LIP analysis are based on the following: | ||
* A site-specific storm-based a pproach PM P a na lysis based on CGS elevation and location was performed to define the PMP depths. Th e s i te-spec if ic PMP a n alysis ut i lized actual data fr om ext r eme r ain f all events within a P acific N orthwes t watershed domain that in c lud ed port ions o f W ash ingt on , Oregon , California, N eva da , Ut ah, a nd I daho. | * A site-specific storm-based a pproach PM P a na lysis based on CGS elevation and location was performed to define the PMP depths. Th e s i te-spec if ic PMP a n alysis ut i lized actual data fr om ext r eme r ain f all events within a P acific N orthwes t watershed domain that in c lud ed port ions o f W ash ingt on , Oregon , California, N eva da , Ut ah, a nd I daho. | ||
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* FL0-2D P ro B uil d 1 4.08.09 | * FL0-2D P ro B uil d 1 4.08.09 | ||
* SP A S Version 9.5 COLUMB I A GENERA TI NG STA T ION Pa ge 14 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | * SP A S Version 9.5 COLUMB I A GENERA TI NG STA T ION Pa ge 14 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | ||
Flooding Energy Northwest Columbia Generating Station 3.1.3 Methodology Site-Specific PMP September 27, 2016 Revision 0 The steps for the CGS site-specific PMP analysis using a storm-based approach in accordance with the most recent NWS H ydrometeoro l ogical Report No. 57, HMR-57 (Reference | Flooding Energy Northwest Columbia Generating Station 3.1.3 Methodology Site-Specific PMP September 27, 2016 Revision 0 The steps for the CGS site-specific PMP analysis using a storm-based approach in accordance with the most recent NWS H ydrometeoro l ogical Report No. 57, HMR-57 (Reference | ||
: 14) and the Wor l d Meteorologica l Orga n ization (WMO) Manual for PMP determinat i on (Reference 26 and Reference | : 14) and the Wor l d Meteorologica l Orga n ization (WMO) Manual for PMP determinat i on (Reference 26 and Reference | ||
: 27) are as fa ll ows: | : 27) are as fa ll ows: | ||
* Identify a set of storms , wh i ch represent ra i nfall even t s that are LIP-type events. This includes storms where extreme heavy rainfall accumulates over short duratio n s at a given location. | * Identify a set of storms , wh i ch represent ra i nfall even t s that are LIP-type events. This includes storms where extreme heavy rainfall accumulates over short duratio n s at a given location. | ||
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* The gro u nd elevation of each CGS-protected area survey po i nt of interest (PO I) is then compared with the calculated WSE to determine the water depth. Following the guidance outlined in N U REG/C R-7046 the runoff losses are ignored. The roof rain f all is assumed to be contributing to the overland runoff. The drainage system at CGS is assumed to be non-functional at t he time of the LIP event. The steps for CGS LI P analysis associated effects are as follows: | * The gro u nd elevation of each CGS-protected area survey po i nt of interest (PO I) is then compared with the calculated WSE to determine the water depth. Following the guidance outlined in N U REG/C R-7046 the runoff losses are ignored. The roof rain f all is assumed to be contributing to the overland runoff. The drainage system at CGS is assumed to be non-functional at t he time of the LIP event. The steps for CGS LI P analysis associated effects are as follows: | ||
* Obtain depth and velocity output from the FL0-20 modeling. | * Obtain depth and velocity output from the FL0-20 modeling. | ||
* FEMA guidance (Reference | * FEMA guidance (Reference | ||
: 11) is u tilized for ca l culating hy drostatic and hydrodynamic pressure. | : 11) is u tilized for ca l culating hy drostatic and hydrodynamic pressure. | ||
* Other associated effects are discussed qualitatively and determined to be insignificant based on the shallow depths and low velocit ies. COLUMB I A GENERA TI NG STA T ION Pa ge 1 6 of 55 NTIF Recommendation 2.1 (Hazard Reevaluations) | * Other associated effects are discussed qualitatively and determined to be insignificant based on the shallow depths and low velocit ies. COLUMB I A GENERA TI NG STA T ION Pa ge 1 6 of 55 NTIF Recommendation 2.1 (Hazard Reevaluations) | ||
: Flood in g Energy Northwest Co l umbia Generating Station 3.1.4 Results September 27 , 2016 Revision 0 The site-specific PMP analysis resulted in input LIP values that have a cumulative depth of 8.21 in ches for the total 6-hour durat i on. The 1-hour depth is 6.29 inches and the 15-minute depth is 3.15 in ches. Follow i ng the guidance of NUREG/CR-7046 , Appendix B , a front-peak i ng tempora l distribution was ut ili zed in the FL0-2D mode l to calculate LIP water surface elevation at CGS. Calculat i on No. CE-02-13-22 (Reference | : Flood in g Energy Northwest Co l umbia Generating Station 3.1.4 Results September 27 , 2016 Revision 0 The site-specific PMP analysis resulted in input LIP values that have a cumulative depth of 8.21 in ches for the total 6-hour durat i on. The 1-hour depth is 6.29 inches and the 15-minute depth is 3.15 in ches. Follow i ng the guidance of NUREG/CR-7046 , Appendix B , a front-peak i ng tempora l distribution was ut ili zed in the FL0-2D mode l to calculate LIP water surface elevation at CGS. Calculat i on No. CE-02-13-22 (Reference | ||
: 8) evaluates a total of 23 POis at CGS , which includes both safety and nonsafety related structures. | : 8) evaluates a total of 23 POis at CGS , which includes both safety and nonsafety related structures. | ||
The power b l ock buildings and the location of the doors that could potentially prov i de a pathway for the floodwaters are identified as Protected Area Survey Poi n ts (PASP), as shown in Figure 2. COLUMBIA GENERAT I NG STATION Page 17 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations): | The power b l ock buildings and the location of the doors that could potentially prov i de a pathway for the floodwaters are identified as Protected Area Survey Poi n ts (PASP), as shown in Figure 2. COLUMBIA GENERAT I NG STATION Page 17 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations): | ||
| Line 242: | Line 242: | ||
,.,....,....,.. | ,.,....,....,.. | ||
,..,, e T"ll""I.....,..,...... | ,..,, e T"ll""I.....,..,...... | ||
~~~~~---' | ~~~~~---' | ||
: 11. Benchmark in by NW remote air intake (no data on marker) 12. Benchmark in front of GSB ent r ance (N ll900, EllOO, el 440.12) 13. Benchmark in front of Bldg. 88 (couldn't ge t ca p off t o r e a d marker) Figure 2. CGS Protected Area Survey Points (PASP) The LIP resu l ts, in cludi ng the depth and duration of flooding at each designated point , are provided in Table 1. The LIP maximum water s urface e l evations at CGS varies between 435.14 ft-NGVD 29 and 443.27 ft-NGVD 29. The calculated maximum water depths vary between 0.03 ft and 0.79 ft. T he min i mum ponding depth of 0.025 f t (surface detentio n) i s u sed to in itiate flow rout in g in the FL 0-2D model. This flow depth is a reasonable minimum value to adapt as a starting depth for duration analysis based on F L 0-2D Data I nput M anua l recommendat i ons and guidelines. | : 11. Benchmark in by NW remote air intake (no data on marker) 12. Benchmark in front of GSB ent r ance (N ll900, EllOO, el 440.12) 13. Benchmark in front of Bldg. 88 (couldn't ge t ca p off t o r e a d marker) Figure 2. CGS Protected Area Survey Points (PASP) The LIP resu l ts, in cludi ng the depth and duration of flooding at each designated point , are provided in Table 1. The LIP maximum water s urface e l evations at CGS varies between 435.14 ft-NGVD 29 and 443.27 ft-NGVD 29. The calculated maximum water depths vary between 0.03 ft and 0.79 ft. T he min i mum ponding depth of 0.025 f t (surface detentio n) i s u sed to in itiate flow rout in g in the FL 0-2D model. This flow depth is a reasonable minimum value to adapt as a starting depth for duration analysis based on F L 0-2D Data I nput M anua l recommendat i ons and guidelines. | ||
Th e depth-COLUMB I A GENE RATIN G S TATI ON Pa ge 1 8 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations): | Th e depth-COLUMB I A GENE RATIN G S TATI ON Pa ge 1 8 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations): | ||
| Line 280: | Line 280: | ||
* Yakima Rive r -The Yakima River has its con fl uence with the Columb i a River approximately 18 miles downstream of CGS. PMF flows from the Yakima River create backwater effects on t h e Columbia River at CGS. Peak PMF discharge values on the Columbia, Yakima , and Snake Rivers due to PMP events occurring in respective watersheds were deve l oped to determine PMF WSEs on the Columbia River at CGS. I n addition , peak PMF discharge due to PMP events occur r ing on an adjacent local drainage basin was developed to determine the PMF WSE for the adjacent a r ea. COLUMB I A GENERA TI NG STA T ION Pa g e 25 of 55 NTI F Recommendation 2.1 (Hazard Reevaluations | * Yakima Rive r -The Yakima River has its con fl uence with the Columb i a River approximately 18 miles downstream of CGS. PMF flows from the Yakima River create backwater effects on t h e Columbia River at CGS. Peak PMF discharge values on the Columbia, Yakima , and Snake Rivers due to PMP events occurring in respective watersheds were deve l oped to determine PMF WSEs on the Columbia River at CGS. I n addition , peak PMF discharge due to PMP events occur r ing on an adjacent local drainage basin was developed to determine the PMF WSE for the adjacent a r ea. COLUMB I A GENERA TI NG STA T ION Pa g e 25 of 55 NTI F Recommendation 2.1 (Hazard Reevaluations | ||
): F looding Energy Northwest Columb i a Generating Station Figure 4. CGS Location Map COLUMB I A GENERA TI NG S T A T ION September 27, 2016 Revision 0 Page 26 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | ): F looding Energy Northwest Columb i a Generating Station Figure 4. CGS Location Map COLUMB I A GENERA TI NG S T A T ION September 27, 2016 Revision 0 Page 26 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | ||
): Flooding Energy Northwest Columbia Generating Station 3.2.1 Basis of Inputs 3.2.1.1 PMP and Snowmelt (Reference 4 and Reference | ): Flooding Energy Northwest Columbia Generating Station 3.2.1 Basis of Inputs 3.2.1.1 PMP and Snowmelt (Reference 4 and Reference | ||
: 5) September 27, 2016 Revision 0 | : 5) September 27, 2016 Revision 0 | ||
* Procedures in NUREG/CR-7046 (Reference 23), NU REG-0800 (Refe ren ce 22), and ANSI/ANS 2.8 (R eference 1) for determining PMP and LIP. | * Procedures in NUREG/CR-7046 (Reference 23), NU REG-0800 (Refe ren ce 22), and ANSI/ANS 2.8 (R eference 1) for determining PMP and LIP. | ||
| Line 298: | Line 298: | ||
* Mann ing's Roughness Coefficients (Manning's n-val u e), based on visual assessme nt of aerial photography and values recommended in published lit era t ure. | * Mann ing's Roughness Coefficients (Manning's n-val u e), based on visual assessme nt of aerial photography and values recommended in published lit era t ure. | ||
* R iverine and floodpl ain geometry from U SGS topographic maps. COLUMB I A GENERA TI NG STA T ION Page 27 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations | * R iverine and floodpl ain geometry from U SGS topographic maps. COLUMB I A GENERA TI NG STA T ION Page 27 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations | ||
): Flooding Energy Northwest Columbia Generating Station 3.2.1.3 Local Drain age Basin PMF (Reference | ): Flooding Energy Northwest Columbia Generating Station 3.2.1.3 Local Drain age Basin PMF (Reference | ||
: 9) September 27, 2016 Revision 0 | : 9) September 27, 2016 Revision 0 | ||
* Basin Topography | * Basin Topography | ||
-The 10-meter Digital Elevation Model (DEM) from the USGS National Elevation Dataset (Reference 19'), and used as in put to develop drainage basin delineation , basin parameters, elevation versus storage relationship, and PMF inundation mapping. The 10-meter DEM references the State Plane Washington South horizontal coordinate sys tem, NAD 83 and the NAVD 88. | -The 10-meter Digital Elevation Model (DEM) from the USGS National Elevation Dataset (Reference 19'), and used as in put to develop drainage basin delineation , basin parameters, elevation versus storage relationship, and PMF inundation mapping. The 10-meter DEM references the State Plane Washington South horizontal coordinate sys tem, NAD 83 and the NAVD 88. | ||
* Aerial Photogr aphy -National Agricultural Imag ery Progra m (NAIP) aer ial photography obtained from the USDA Geospatial Data Gateway was used for inundation mapping. | * Aerial Photogr aphy -National Agricultural Imag ery Progra m (NAIP) aer ial photography obtained from the USDA Geospatial Data Gateway was used for inundation mapping. | ||
* Snowpack Data -The month in which snowpack is maximized in the Columbia watershed, as well as 100-year snowpack data developed from a statistical analysis of snow gage data, were obtained from Calculation No. CE-02-13-17 ( Reference | * Snowpack Data -The month in which snowpack is maximized in the Columbia watershed, as well as 100-year snowpack data developed from a statistical analysis of snow gage data, were obtained from Calculation No. CE-02-13-17 ( Reference | ||
: 4) and used as input to snowmelt computations. | : 4) and used as input to snowmelt computations. | ||
* Snow Dens i ty -The historical snow depth and snow density data was obtained from the NOAA interactive snow website (Reference 4), which was used as an input to snowmelt computations. | * Snow Dens i ty -The historical snow depth and snow density data was obtained from the NOAA interactive snow website (Reference 4), which was used as an input to snowmelt computations. | ||
* Land Cover -Land cover information was obtained from Calculation No. CE-02-13-17 (Reference 4). | * Land Cover -Land cover information was obtained from Calculation No. CE-02-13-17 (Reference 4). | ||
* Four precip i tation alternatives calculated in Calculation No. CE-02-13-27 (Reference | * Four precip i tation alternatives calculated in Calculation No. CE-02-13-27 (Reference | ||
: 9) were distributed into five different temporal distributions for calculation of the loca l drainage basin PMF analysis using the HEC-HMS model. All simulations were executed at a 15-minute time step. The four precipitation alternatives input into the model were the general storm PMP, 100-yea r rainfall on probable maximum snowpack, the cool-season PMP on 100-year s nowpack , a nd the loca l s torm PMP. | : 9) were distributed into five different temporal distributions for calculation of the loca l drainage basin PMF analysis using the HEC-HMS model. All simulations were executed at a 15-minute time step. The four precipitation alternatives input into the model were the general storm PMP, 100-yea r rainfall on probable maximum snowpack, the cool-season PMP on 100-year s nowpack , a nd the loca l s torm PMP. | ||
* A hydro l ogic model of the local drainage basin was developed using the USACE's HEC-HMS compute r software. | * A hydro l ogic model of the local drainage basin was developed using the USACE's HEC-HMS compute r software. | ||
| Line 322: | Line 322: | ||
Drainage area , centroid coordinates, and elevation were computed using ArcG I S and are discussed in Calculation N o. CE-02-13-1 7 (Reference 4). Snowmelt computations require definition of the land cover , specifically the percent forested area, of each sub-basin. | Drainage area , centroid coordinates, and elevation were computed using ArcG I S and are discussed in Calculation N o. CE-02-13-1 7 (Reference 4). Snowmelt computations require definition of the land cover , specifically the percent forested area, of each sub-basin. | ||
The percent forested area of each sub-basin was computed using land cover in f ormation obtained i n a G I S format from the US D A Data Gateway and the Canadian Counci l on Geomatics Geo-Base website. The Co l umbia River waters h ed above CGS, the Yakima River watershed, and the Snake River watershed are located within the Co l umbia River Region HUC 017. The HUC system is a consisten t hierarchica l dataset that contains drainage bas i n boundaries on four p r imary leve l s , i ncluding reg i ons, sub-regions , accounting units , and cataloging units. The Columbia Ri ver watershed above CGS is divided i nto two HUC sub-regions , including t he U pper Columb i a (HUC 1702) and the Koo t enai-Pend Orei ll e-Spokane (HUG 1701 ). An additional sub-region contributing to the Columbia watershed located entirely in Canada was identif i ed as the Headwaters Columbia, but is not included in the HUC data set. The H eadwaters Co l umbia sub-region boundary i s defined by the Ca n adian Na t ional H ydro Network (NHN). The Snake River watershed is divided into three sub-regions including the Upper Snake (HUC 1704), the Middle Snake (H UC 1705), and the Lower Snake (HUC COLUMB I A GENERA TI NG STA T ION Pa g e 29 of 55 NTT F Recommendation 2.1 (Haza rd Reevaluations): | The percent forested area of each sub-basin was computed using land cover in f ormation obtained i n a G I S format from the US D A Data Gateway and the Canadian Counci l on Geomatics Geo-Base website. The Co l umbia River waters h ed above CGS, the Yakima River watershed, and the Snake River watershed are located within the Co l umbia River Region HUC 017. The HUC system is a consisten t hierarchica l dataset that contains drainage bas i n boundaries on four p r imary leve l s , i ncluding reg i ons, sub-regions , accounting units , and cataloging units. The Columbia Ri ver watershed above CGS is divided i nto two HUC sub-regions , including t he U pper Columb i a (HUC 1702) and the Koo t enai-Pend Orei ll e-Spokane (HUG 1701 ). An additional sub-region contributing to the Columbia watershed located entirely in Canada was identif i ed as the Headwaters Columbia, but is not included in the HUC data set. The H eadwaters Co l umbia sub-region boundary i s defined by the Ca n adian Na t ional H ydro Network (NHN). The Snake River watershed is divided into three sub-regions including the Upper Snake (HUC 1704), the Middle Snake (H UC 1705), and the Lower Snake (HUC COLUMB I A GENERA TI NG STA T ION Pa g e 29 of 55 NTT F Recommendation 2.1 (Haza rd Reevaluations): | ||
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 1 706). The Yakima R i ver watershed is one sub-region (HUC 1703). All the rivers HUCs and watershed boundaries are shown in F i gure 5. HUC sub-region and cataloging unit boundaries were downloaded in G I S format from the USDA Geospatial Data Ga t eway (Reference | Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 1 706). The Yakima R i ver watershed is one sub-region (HUC 1703). All the rivers HUCs and watershed boundaries are shown in F i gure 5. HUC sub-region and cataloging unit boundaries were downloaded in G I S format from the USDA Geospatial Data Ga t eway (Reference | ||
: 18) and imported for u se into ArcGIS. H UC boundary data are in the U niversal Transverse Mercator (UTM) Zone 11 N coordinate system, and refe r ence the hor i zontal North American Datum of 1983 (NAO 83). Bou n daries f or the Headwaters Columbia subreg i on and sub-sub-drainage (the equivalent of a cata l og i ng unit i n the HU G system) located in Canada were obtained i n ArcG I S format fro m the NH N as provided by the Nat io nal R esou r ces Canada Earth Sciences Sector Center fo r Topographic I nformation Geo-Base website. Sub-basins i n each s u b-reg i on were defined by first using and reviewing the HUC cata l oging un i ts and N H N sub-sub-drainages. | : 18) and imported for u se into ArcGIS. H UC boundary data are in the U niversal Transverse Mercator (UTM) Zone 11 N coordinate system, and refe r ence the hor i zontal North American Datum of 1983 (NAO 83). Bou n daries f or the Headwaters Columbia subreg i on and sub-sub-drainage (the equivalent of a cata l og i ng unit i n the HU G system) located in Canada were obtained i n ArcG I S format fro m the NH N as provided by the Nat io nal R esou r ces Canada Earth Sciences Sector Center fo r Topographic I nformation Geo-Base website. Sub-basins i n each s u b-reg i on were defined by first using and reviewing the HUC cata l oging un i ts and N H N sub-sub-drainages. | ||
Based upon drainage area or the l ocation of major dams some cataloging units/s ub-sub-drainages were either combined or subdivided. USGS topographic maps for t he U nited States we r e accessed through the ArcG I S USA Topo Maps Map Server and used to sub-divide and ref i ne HU C cata l oging unit areas using ArcGIS. Subdivision of Canadian dra i nages was conducted using the National Topographic Database available from the Canadian data server GeoGratis. | Based upon drainage area or the l ocation of major dams some cataloging units/s ub-sub-drainages were either combined or subdivided. USGS topographic maps for t he U nited States we r e accessed through the ArcG I S USA Topo Maps Map Server and used to sub-divide and ref i ne HU C cata l oging unit areas using ArcGIS. Subdivision of Canadian dra i nages was conducted using the National Topographic Database available from the Canadian data server GeoGratis. | ||
| Line 338: | Line 338: | ||
F or sub-watersheds , with total drainage area of approximately 10 , 000 squa r e mi l es, PMP storms were conservat i vely placed over the most downstream sub-watershed. I f a sub-region has a total drainage area less than 10 , 000 square miles , the PMP was applied to the entire sub-regional area. The purpose was to calculate PMP values applicable to the entire contributing watershed of the Columbia River upstream of CGS. This included an all-season and cool-season (rain-on-snow) PMP analysis. 3.2.3.2 1 00-year Snowpack and Snowmelt T he 100-year snowpack for the watershed is calculated from h i s t oric snow depth data from 3 11 weather gages located throughout the watershed with pe r iods of record greater than 25 years, ca l culated on a sub-watershed level. The 100-year snowpack is ca l culated by applying the F i sherTippett Type I (F T-I), or more commonly named Gumbel distr i bu t ion , to the snow depth data at each gage. T his is judged to be a conservative approach fo r the large watershed, as the actua l recurrence interval for each gage to have a coincident 100-year snowpack for the entire area of the watershed is likely to be greater than one in one hundred years. T he coo l-season PMP is considered to be an April event. T he T hiessen polygon method is used to calculate the 1 00-year snowpack for each sub-watershed by using an area-weighted average of the 100-year snow depth from t h e stations. Snowme l t is included in t wo o f the a l ternatives , and is determined using the USAGE energy budge t method. The energy budget method acco u nts for six (6) external sources of heat energy t ha t contribute to snowmelt. | F or sub-watersheds , with total drainage area of approximately 10 , 000 squa r e mi l es, PMP storms were conservat i vely placed over the most downstream sub-watershed. I f a sub-region has a total drainage area less than 10 , 000 square miles , the PMP was applied to the entire sub-regional area. The purpose was to calculate PMP values applicable to the entire contributing watershed of the Columbia River upstream of CGS. This included an all-season and cool-season (rain-on-snow) PMP analysis. 3.2.3.2 1 00-year Snowpack and Snowmelt T he 100-year snowpack for the watershed is calculated from h i s t oric snow depth data from 3 11 weather gages located throughout the watershed with pe r iods of record greater than 25 years, ca l culated on a sub-watershed level. The 100-year snowpack is ca l culated by applying the F i sherTippett Type I (F T-I), or more commonly named Gumbel distr i bu t ion , to the snow depth data at each gage. T his is judged to be a conservative approach fo r the large watershed, as the actua l recurrence interval for each gage to have a coincident 100-year snowpack for the entire area of the watershed is likely to be greater than one in one hundred years. T he coo l-season PMP is considered to be an April event. T he T hiessen polygon method is used to calculate the 1 00-year snowpack for each sub-watershed by using an area-weighted average of the 100-year snow depth from t h e stations. Snowme l t is included in t wo o f the a l ternatives , and is determined using the USAGE energy budge t method. The energy budget method acco u nts for six (6) external sources of heat energy t ha t contribute to snowmelt. | ||
The energy budget method yields a set of six e quation s; the selection of the appropriate equa t ion is dependent upon a rain-on-snow or rain-f ree me l t period and the percent forest cove r w i thin the d r a i nage area. The available water in the snowpack is calculated based on Federa l Energy Regu l atory Commission (FERC) guide l ines , which st i p ul ate: Water equivalence data are rarely recorded. | The energy budget method yields a set of six e quation s; the selection of the appropriate equa t ion is dependent upon a rain-on-snow or rain-f ree me l t period and the percent forest cove r w i thin the d r a i nage area. The available water in the snowpack is calculated based on Federa l Energy Regu l atory Commission (FERC) guide l ines , which st i p ul ate: Water equivalence data are rarely recorded. | ||
If total snowpack depth is available , assume a 100-year snowpack for the month of the cool-season Probable Maximum Storm and a starting water equivalence of 30 percent. 3.2.3.3 PMF Analysis (Reference | If total snowpack depth is available , assume a 100-year snowpack for the month of the cool-season Probable Maximum Storm and a starting water equivalence of 30 percent. 3.2.3.3 PMF Analysis (Reference | ||
: 5) Altern a t i ve 1 -All-Season PMP (General Storm PMP (7 2-hr Storm)) The all-season PMF resulte d i n a flow of 2 , 897,000 cfs on Columbia River downstream of Snake Confluence based on scena r io No. 3 -Headwater Columb i a. COLUMB I A GENERA TI NG STA T ION Pa g e 32 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | : 5) Altern a t i ve 1 -All-Season PMP (General Storm PMP (7 2-hr Storm)) The all-season PMF resulte d i n a flow of 2 , 897,000 cfs on Columbia River downstream of Snake Confluence based on scena r io No. 3 -Headwater Columb i a. COLUMB I A GENERA TI NG STA T ION Pa g e 32 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | ||
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 An antecedent storm equivalent to 40 percent of the all-season PMP is app li ed to the HEC-HMS model with a 72-hour dry period between the antecedent stor m and the PMP event. The all-season PMP as described above is applied to the HEC-HMS model to determine flow hydrographs at key points in the model. T he all-season PMF is determined not to be the contro ll ing PMF scena r io and addit i onal combined event analysis is not performed. | Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 An antecedent storm equivalent to 40 percent of the all-season PMP is app li ed to the HEC-HMS model with a 72-hour dry period between the antecedent stor m and the PMP event. The all-season PMP as described above is applied to the HEC-HMS model to determine flow hydrographs at key points in the model. T he all-season PMF is determined not to be the contro ll ing PMF scena r io and addit i onal combined event analysis is not performed. | ||
Alternative 2 -Probable Maximum Snowpack (24-hr storm) and 100-Year Cool-Season Rainfall The 100-year rainfall wou ld be significant l y less rainfall t han the PMP , resulting in the majority of the snowmelt occurring as r ain-free. The rain-free snowmelt rates are typically close to or lower than the verif i ed constant losses for each sub-watershed; therefore , most of the snowmelt would be lost through the constant losses and would not be ava i lable for runoff. For similar reasons , given the large size of the CGS watershed (approx i mately 212, 1 56 square miles), calculating the probab l e maximum snowpack covering the entire watershed from the cool-season PMP precipita t ing as snow would result in comparable snow-water equivalent available for melt i ng as the snow-water equivalent to be used i n Alternative | Alternative 2 -Probable Maximum Snowpack (24-hr storm) and 100-Year Cool-Season Rainfall The 100-year rainfall wou ld be significant l y less rainfall t han the PMP , resulting in the majority of the snowmelt occurring as r ain-free. The rain-free snowmelt rates are typically close to or lower than the verif i ed constant losses for each sub-watershed; therefore , most of the snowmelt would be lost through the constant losses and would not be ava i lable for runoff. For similar reasons , given the large size of the CGS watershed (approx i mately 212, 1 56 square miles), calculating the probab l e maximum snowpack covering the entire watershed from the cool-season PMP precipita t ing as snow would result in comparable snow-water equivalent available for melt i ng as the snow-water equivalent to be used i n Alternative | ||
: 3. Thus, t his alternative is not the controll i ng fl ooding scenario at CGS. Alternative 3-100-Year Snowpack and Cool-Season PMP Two different time periods, includ in g the months of November th r ough February and the month of March, are utilized per the PMP data. Both data se t s were evaluated by sub-basin. | : 3. Thus, t his alternative is not the controll i ng fl ooding scenario at CGS. Alternative 3-100-Year Snowpack and Cool-Season PMP Two different time periods, includ in g the months of November th r ough February and the month of March, are utilized per the PMP data. Both data se t s were evaluated by sub-basin. | ||
The time period with the highest coo l season PMP on 100-year snowpack was selected for use in the HEC-HMS modeling. | The time period with the highest coo l season PMP on 100-year snowpack was selected for use in the HEC-HMS modeling. | ||
| Line 350: | Line 350: | ||
The HEC-HMS modeling conservatively assumes no precipitation losses , no accounting for reservoir storage, and coincidental flooding occurring on adjacent rivers contributing to the Columbia River. The PMF runoff hydrographs computed in HEC-HMS due to PMP were combined with a constant inflow of lesser flood events occurring in adjacent drainages to develop the most conservative WSEs on the Columbia River at CGS. Resulting WSEs due to the PMF on the Columbia River were then compared with the lowest elevation of critical facilities at CGS. 3.2.3.5 Hydraulic Model (HEC-RAS) The HEC-RAS hydraulic model requires: | The HEC-HMS modeling conservatively assumes no precipitation losses , no accounting for reservoir storage, and coincidental flooding occurring on adjacent rivers contributing to the Columbia River. The PMF runoff hydrographs computed in HEC-HMS due to PMP were combined with a constant inflow of lesser flood events occurring in adjacent drainages to develop the most conservative WSEs on the Columbia River at CGS. Resulting WSEs due to the PMF on the Columbia River were then compared with the lowest elevation of critical facilities at CGS. 3.2.3.5 Hydraulic Model (HEC-RAS) The HEC-RAS hydraulic model requires: | ||
* Columbia River Topography | * Columbia River Topography | ||
-The DEM from the USGS National Elevation Dataset (Reference | -The DEM from the USGS National Elevation Dataset (Reference | ||
: 19) and used to develop model geometry. | : 19) and used to develop model geometry. | ||
* Aerial Photography | * Aerial Photography | ||
| Line 370: | Line 370: | ||
-Channe l Thalweg -CGS Site Loca ti on , Critica l Elev 4 44.4 | -Channe l Thalweg -CGS Site Loca ti on , Critica l Elev 4 44.4 | ||
* Overtoping Point #1, E l ev 437.9 o Overto pp ing Poin t 11 2 , E l ev 44 1 | * Overtoping Point #1, E l ev 437.9 o Overto pp ing Poin t 11 2 , E l ev 44 1 | ||
* Ove rt opplng Po in t#3, E l ev 46 4.8 o Overtopping Po i n t 114 , E l ev 4 74.4 3.2.3.6 Figure 7. Columbia River PMF Water Surface Profiles Local Drainage Basin PMF (Reference | * Ove rt opplng Po in t#3, E l ev 46 4.8 o Overtopping Po i n t 114 , E l ev 4 74.4 3.2.3.6 Figure 7. Columbia River PMF Water Surface Profiles Local Drainage Basin PMF (Reference | ||
: 9) PMF due to PMP was analyzed for the 40.5-square-mile local drainage basin at CGS. Review o f topography and aerial photographs indicate that the loca l basin is topographically closed and does not have a defined waterway, creek , or river running through it. El evations in the basin range from a minimum of 409.3 ft-NAVD88 up to a maximum of 594 ft-NAVD88 , with an out l et elevation o f 437.9 ft-NA VD88. CGS is located in a depression that will fill up and store water before water spills out of the basin. Topographic data indicate that the basin i s capab l e of storing approximately 31,000 acreft of water with a maximum depth of 28.6 ft befo r e flow reaches the basin outlet and spills towards the Co l umbia River. The PMP calculat i ons for the local drainage basin were conducted u sing the current applicable guidance contai n ed in HMR-57. F our alternat iv e PMP storms were developed for input to hydrologic modeling per ANS guidance provided in NUREG CR-7046. T he stepw i se procedure used to calcu l ate the l ocal storm PMP can be found in Section 15.4 of HMR-57. Loca l storm PMP estimates can be determined for durations between 1 5 minutes and 6 hours applicable to storm areas of 1 to 500 square miles. The local storm PMP was computed for the CGS local basin and used as input to precipitation computations as part of the PMF analysis. | : 9) PMF due to PMP was analyzed for the 40.5-square-mile local drainage basin at CGS. Review o f topography and aerial photographs indicate that the loca l basin is topographically closed and does not have a defined waterway, creek , or river running through it. El evations in the basin range from a minimum of 409.3 ft-NAVD88 up to a maximum of 594 ft-NAVD88 , with an out l et elevation o f 437.9 ft-NA VD88. CGS is located in a depression that will fill up and store water before water spills out of the basin. Topographic data indicate that the basin i s capab l e of storing approximately 31,000 acreft of water with a maximum depth of 28.6 ft befo r e flow reaches the basin outlet and spills towards the Co l umbia River. The PMP calculat i ons for the local drainage basin were conducted u sing the current applicable guidance contai n ed in HMR-57. F our alternat iv e PMP storms were developed for input to hydrologic modeling per ANS guidance provided in NUREG CR-7046. T he stepw i se procedure used to calcu l ate the l ocal storm PMP can be found in Section 15.4 of HMR-57. Loca l storm PMP estimates can be determined for durations between 1 5 minutes and 6 hours applicable to storm areas of 1 to 500 square miles. The local storm PMP was computed for the CGS local basin and used as input to precipitation computations as part of the PMF analysis. | ||
L ocal storm PMP va l ues were computed in 1 5-minute increments for a 6-h our storm durat i on. Five different temporal distributions of th e 15-minute COLUMB I A GENERA TI NG STA TI ON Pa g e 37 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations): | L ocal storm PMP va l ues were computed in 1 5-minute increments for a 6-h our storm durat i on. Five different temporal distributions of th e 15-minute COLUMB I A GENERA TI NG STA TI ON Pa g e 37 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations): | ||
| Line 393: | Line 393: | ||
): F looding Energy Northwest Columbia Generating Station Legend | ): F looding Energy Northwest Columbia Generating Station Legend | ||
* Columbia Genera t ing Stat i on -L oca l PMF I nundat i on Area t::J L oca l Drainage Basin 0.75 1.5 Mi l es Figure 10. Local Drainage Basin PMF Inundation Map COLUMB I A GENE RATIN G STATION September 27, 2016 Revision 0 Pa ge 43 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | * Columbia Genera t ing Stat i on -L oca l PMF I nundat i on Area t::J L oca l Drainage Basin 0.75 1.5 Mi l es Figure 10. Local Drainage Basin PMF Inundation Map COLUMB I A GENE RATIN G STATION September 27, 2016 Revision 0 Pa ge 43 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | ||
): Flooding Energy Northwest Columbia Generating Station 3.3 Dam Breach es and Failures (Reference | ): Flooding Energy Northwest Columbia Generating Station 3.3 Dam Breach es and Failures (Reference | ||
: 25) September 27, 2016 Revision 0 The dam failure analysis for the Columbia Riv e r watershed was performed by the USAGE under For Official Use Only (FOUO) r estrictions (Reference 25). T h ere f ore, deta ils of the ana l ysis are no t provided. Ons it e impoundments are located southeast and northeast of the power block. The power block is located at a higher elevation than the ponds. The t opography slopes away from the power block to the east. T herefor e, potentia l failure of the onsite impoundments would release impounded water away from the power block into the adjacent depression of the local drainage basin discussed in Section 3.2. 3.3.1 Results (b)(3) 16 U.S C § 824o-1(d),(b)(4),(b)(7)(F) | : 25) September 27, 2016 Revision 0 The dam failure analysis for the Columbia Riv e r watershed was performed by the USAGE under For Official Use Only (FOUO) r estrictions (Reference 25). T h ere f ore, deta ils of the ana l ysis are no t provided. Ons it e impoundments are located southeast and northeast of the power block. The power block is located at a higher elevation than the ponds. The t opography slopes away from the power block to the east. T herefor e, potentia l failure of the onsite impoundments would release impounded water away from the power block into the adjacent depression of the local drainage basin discussed in Section 3.2. 3.3.1 Results (b)(3) 16 U.S C § 824o-1(d),(b)(4),(b)(7)(F) | ||
| Line 418: | Line 418: | ||
Flooding Energy Northwest Columbia Generating Station 3.9.1 B as i s of Inpu ts September 27, 2016 Revision 0 | Flooding Energy Northwest Columbia Generating Station 3.9.1 B as i s of Inpu ts September 27, 2016 Revision 0 | ||
* Aerial Photography | * Aerial Photography | ||
-National Agricultural Imagery Program (NA I P) aeria l photography obtained from the U.S. Department of Agricu l ture (USDA) Geospa t i a l Data Gateway (Reference | -National Agricultural Imagery Program (NA I P) aeria l photography obtained from the U.S. Department of Agricu l ture (USDA) Geospa t i a l Data Gateway (Reference | ||
: 18) was used for i nundation mapping (Reference 7). | : 18) was used for i nundation mapping (Reference 7). | ||
* Basin Topography meter DEM used in t he de t ermination of Columbia River PMF WSE was used (Reference 5). The 10-meter DEM references the State Plane Washington South horizontal coordinate system and NAO 83 and N AVO 88. | * Basin Topography meter DEM used in t he de t ermination of Columbia River PMF WSE was used (Reference 5). The 10-meter DEM references the State Plane Washington South horizontal coordinate system and NAO 83 and N AVO 88. | ||
* CGS Structu r es -CGS structures such as buildings , VBS , and other related faci l ities were obtained from the effects o f Local I ntense Precip i tation Calculation CE-02-1 3-22 (Reference 8). | * CGS Structu r es -CGS structures such as buildings , VBS , and other related faci l ities were obtained from the effects o f Local I ntense Precip i tation Calculation CE-02-1 3-22 (Reference 8). | ||
* The L oca l Drainage Basin PMF was determined i n calcu l ation CE-02-1 3-27 , L oca l Drainage Basin PMF Analysis for CGS (Reference 9). | * The L oca l Drainage Basin PMF was determined i n calcu l ation CE-02-1 3-27 , L oca l Drainage Basin PMF Analysis for CGS (Reference 9). | ||
* The controlling dam failure WSE for Colu m bia River was determined by the USACE under FOUO restrictions (Reference 25). 3.9.2 Comput e r Softw a re Prog r am s ArcG I S 10.1 3.9.3 Methodology Coincident Wind-Wave Activity The simplified method for wave forecast i ng as outlined in the USACE Coastal Eng i neering Manua l (Reference | * The controlling dam failure WSE for Colu m bia River was determined by the USACE under FOUO restrictions (Reference 25). 3.9.2 Comput e r Softw a re Prog r am s ArcG I S 10.1 3.9.3 Methodology Coincident Wind-Wave Activity The simplified method for wave forecast i ng as outlined in the USACE Coastal Eng i neering Manua l (Reference | ||
: 17) is used to determ i ne the inputs (significant wave height , wave period , wind speed , and wave le ngth) for calcu l ating the wave runup at CGS (Reference 7). The wave se t up is the elevat i on of the water surface due to wave action , i n particular , wave breaking. | : 17) is used to determ i ne the inputs (significant wave height , wave period , wind speed , and wave le ngth) for calcu l ating the wave runup at CGS (Reference 7). The wave se t up is the elevat i on of the water surface due to wave action , i n particular , wave breaking. | ||
Wind set u p i s the effect of the horizontal stress of the wind on the water , driving it i n the direction of the wind. Based on the maximum water surface elevation from the flooding analysis , the l ongest critical st r aight line fetch is dete r mined. T he 2-year wind speed is appl i ed to the straight l i n e fetch to develop the wind-wave characteristics. I n accordance with N U REG/CR-7046 (Reference 23), different external f looding mechanisms are combined to calculate the maxim u m WSE including coincident wind-wave activity at CGS. The results of the combined events analysis (Reference | Wind set u p i s the effect of the horizontal stress of the wind on the water , driving it i n the direction of the wind. Based on the maximum water surface elevation from the flooding analysis , the l ongest critical st r aight line fetch is dete r mined. T he 2-year wind speed is appl i ed to the straight l i n e fetch to develop the wind-wave characteristics. I n accordance with N U REG/CR-7046 (Reference 23), different external f looding mechanisms are combined to calculate the maxim u m WSE including coincident wind-wave activity at CGS. The results of the combined events analysis (Reference | ||
: 7) yielded that floods caused by precipitation events ba se d on th e following combination of mechani s m resulted the h ig he st water l evel: * (b)(3) 16 USC § 824o-1(d),(b)(4),(b)(7)(F) | : 7) yielded that floods caused by precipitation events ba se d on th e following combination of mechani s m resulted the h ig he st water l evel: * (b)(3) 16 USC § 824o-1(d),(b)(4),(b)(7)(F) | ||
* L ocal D rainage Basin P M F coincident with wave induced by 2-year wind speed applied a l ong the cr i tica l fetch d i rection. T his corresponds to the local drainage Basin PMF WSE of 435.4 ft-NAVO 88 (Reference 7). COLUMB I A GENERA TI NG STA T ION Pa ge 48 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations | * L ocal D rainage Basin P M F coincident with wave induced by 2-year wind speed applied a l ong the cr i tica l fetch d i rection. T his corresponds to the local drainage Basin PMF WSE of 435.4 ft-NAVO 88 (Reference 7). COLUMB I A GENERA TI NG STA T ION Pa ge 48 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations | ||
): Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 3.9.4 Results The following summarizes the resu l ts of the combined events analysis (Ref erence 7) for CGS: Wind-Wave Activity | ): Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 3.9.4 Results The following summarizes the resu l ts of the combined events analysis (Ref erence 7) for CGS: Wind-Wave Activity | ||
* Th e maxim um combined eve nt s WSE for the CGS is determined by addi ng th e wind setup and w i nd-wave run-up , including wave setup , to the local drainage PMF WSE and Dam Failure Maximum WSE (PMF WSE + wind setup + runu t at C~S. The maximum dam failure WSE including coincident wind-wave activity i * . t.NG~;J:~(~),~b~ | * Th e maxim um combined eve nt s WSE for the CGS is determined by addi ng th e wind setup and w i nd-wave run-up , including wave setup , to the local drainage PMF WSE and Dam Failure Maximum WSE (PMF WSE + wind setup + runu t at C~S. The maximum dam failure WSE including coincident wind-wave activity i * . t.NG~;J:~(~),~b~ | ||
: 29. (4),(b)(?)(F) | : 29. (4),(b)(?)(F) | ||
* The maximum combined events WSE for the local drainage basin PMF i s determined by adding the wind setup and wind-wave run-up , including wave setup , calculated for the local drainage basin PMF to the resulting WSE due to local drainage basin PMF. The maximum WSE of the local drainage basin PMF including co i ncident wind-wave act ivity i s 433.3 ft-NGVD 29. (b)(3) 16 us c. Th erefor o ntrolling maximum WSE i s the dam failure scenar io coincident wi t h wind-wave Mr:i.1o-~{_altt activityts | * The maximum combined events WSE for the local drainage basin PMF i s determined by adding the wind setup and wind-wave run-up , including wave setup , calculated for the local drainage basin PMF to the resulting WSE due to local drainage basin PMF. The maximum WSE of the local drainage basin PMF including co i ncident wind-wave act ivity i s 433.3 ft-NGVD 29. (b)(3) 16 us c. Th erefor o ntrolling maximum WSE i s the dam failure scenar io coincident wi t h wind-wave Mr:i.1o-~{_altt activityts | ||
| Line 442: | Line 442: | ||
Q (4),(b)(?)(F) associated wind-wave activity. | Q (4),(b)(?)(F) associated wind-wave activity. | ||
The reevaluate , including coincident wind-wave activity is below the critical fa cility elevation of 441 ft-MSL. COLUMBIA GENERAT I NG STATION Pa ge 49 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | The reevaluate , including coincident wind-wave activity is below the critical fa cility elevation of 441 ft-MSL. COLUMBIA GENERAT I NG STATION Pa ge 49 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations): | ||
Flooding Energy Northwest Columbia Generating Station 5. COMPARISON WITH CURRENT DESIGN BASIS September 27, 2016 Revision 0 The reevaluated maximum water surface elevations due to the Columb i a River PMF, the Adjacent Drainage B asin P M F , dam failure, and the combined effect flood for dam failure w i th coinc i dent wave activity exceed the design basis. For each flood-causing mechanism that exceeds the design basis , the maximum water surface elevation is still be l ow the 441 ft-MS L crit i cal elevation at CGS. The reevalua t ed maximum water surface elevations due to ice-induced flooding are bounded by other flood-causing mechanisms and are below the 441 ft-MSL critical e l evation at CGS. The reevaluated maximum water surface elevations due to the LIP va r y between 435.14 ft-NGVD 29 and 443.27 f t-NG VD 29 at the designated protected area survey points. The reevaluated maximum water surface elevations at six of t he survey points slightly exceed the 441 f t-MSL critica l elevation at CGS. However , the six survey points are either not adjacent to safety-r elated SSCs , or based on specific configuration at the survey point l ocation, the results are inconsequential and do not compromise safety-related SSCs, as discussed in Section 3.1.4. During the flooding walkdowns conducted for Recommendation 2.3 , the fo ll owing was reported on November 12, 2012 i n l etter G02-12-164 (Reference 3): 1. T he safety-re l ated SSCs are bui l t within t h e Protected Area and at the Standby Se r vice Water Pumphouses at the finished floor slab of el. 441 ft-MSL. Be l ow-grade areas in the R eactor Bui l ding are a t slab el. 422 ft-3 inches MSL, and below-grade areas in the Pumphouses are at 43 1 ft-MSL. Penetrations in the Reactor Bui l ding's below-grade concrete walls were visually observed as sea l ed, and design-bas i s groundwa t er (420 ft-MSL) is below this level so n o hydrostatic loading is applied to t hese seals. Penet r ations in the Standby Service Water Pumphouses exposed to the design basis flood elevation of 433.3 ft-MS L were noted as sealed. Penetra t ions located below grade el. 441 ft-MSL a t exterior walls are above the groundwater el. of 420 ft-MSL. I n the safety-related structures, exterior concrete wa ll s showed no cracking equal or greate r than 0.04 i n ches that challenged the ability to wi th stand water infiltration. | Flooding Energy Northwest Columbia Generating Station 5. COMPARISON WITH CURRENT DESIGN BASIS September 27, 2016 Revision 0 The reevaluated maximum water surface elevations due to the Columb i a River PMF, the Adjacent Drainage B asin P M F , dam failure, and the combined effect flood for dam failure w i th coinc i dent wave activity exceed the design basis. For each flood-causing mechanism that exceeds the design basis , the maximum water surface elevation is still be l ow the 441 ft-MS L crit i cal elevation at CGS. The reevalua t ed maximum water surface elevations due to ice-induced flooding are bounded by other flood-causing mechanisms and are below the 441 ft-MSL critical e l evation at CGS. The reevaluated maximum water surface elevations due to the LIP va r y between 435.14 ft-NGVD 29 and 443.27 f t-NG VD 29 at the designated protected area survey points. The reevaluated maximum water surface elevations at six of t he survey points slightly exceed the 441 f t-MSL critica l elevation at CGS. However , the six survey points are either not adjacent to safety-r elated SSCs , or based on specific configuration at the survey point l ocation, the results are inconsequential and do not compromise safety-related SSCs, as discussed in Section 3.1.4. During the flooding walkdowns conducted for Recommendation 2.3 , the fo ll owing was reported on November 12, 2012 i n l etter G02-12-164 (Reference 3): 1. T he safety-re l ated SSCs are bui l t within t h e Protected Area and at the Standby Se r vice Water Pumphouses at the finished floor slab of el. 441 ft-MSL. Be l ow-grade areas in the R eactor Bui l ding are a t slab el. 422 ft-3 inches MSL, and below-grade areas in the Pumphouses are at 43 1 ft-MSL. Penetrations in the Reactor Bui l ding's below-grade concrete walls were visually observed as sea l ed, and design-bas i s groundwa t er (420 ft-MSL) is below this level so n o hydrostatic loading is applied to t hese seals. Penet r ations in the Standby Service Water Pumphouses exposed to the design basis flood elevation of 433.3 ft-MS L were noted as sealed. Penetra t ions located below grade el. 441 ft-MSL a t exterior walls are above the groundwater el. of 420 ft-MSL. I n the safety-related structures, exterior concrete wa ll s showed no cracking equal or greate r than 0.04 i n ches that challenged the ability to wi th stand water infiltration. | ||
: 2. No flood protection features were exc l uded from t he walkdowns. | : 2. No flood protection features were exc l uded from t he walkdowns. | ||
N o degraded, conforming, or unanalyzed conditions credited for f lood protect i on were identified by the walkdown visua l i nspection. | N o degraded, conforming, or unanalyzed conditions credited for f lood protect i on were identified by the walkdown visua l i nspection. | ||
| Line 451: | Line 451: | ||
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 5. Energy Northwest chose to visually inspect accessible below grade penetrations , walls, and f l oors in the Reactor Building and the Standby Service Water Pumphouses , wh i ch house the SSCs important to safety. Below grade walls, floors , and penetration seals that were visually inspected were found to be in good cond i tion , with two exceptions. | Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 5. Energy Northwest chose to visually inspect accessible below grade penetrations , walls, and f l oors in the Reactor Building and the Standby Service Water Pumphouses , wh i ch house the SSCs important to safety. Below grade walls, floors , and penetration seals that were visually inspected were found to be in good cond i tion , with two exceptions. | ||
There were two conduits in one of the Standby Service Water Pumphouses that did not have a visible seal viewed from the building side; the other side was in a buried duct bank and was not accessible. | There were two conduits in one of the Standby Service Water Pumphouses that did not have a visible seal viewed from the building side; the other side was in a buried duct bank and was not accessible. | ||
The interiors of the conduits were clean and there was no dirt , corrosion, debris, o r evidence of water or i nsect intrusion from the outside. These exceptions are not deficiencies as defined in NEI 12-07 (Reference | The interiors of the conduits were clean and there was no dirt , corrosion, debris, o r evidence of water or i nsect intrusion from the outside. These exceptions are not deficiencies as defined in NEI 12-07 (Reference | ||
: 12) because the conduit seals are not credited to perform an intended flood protection function. These two conduits are located above the design-basis groundwater elevation. In summary , the reevaluated maximum water surface elevations validate the current flood mitigation strategy of the current license basis, which states that CGS can be maintained in a safe condition for water levels up to 441 ft-MSL. Therefore , no interim actions are identified. | : 12) because the conduit seals are not credited to perform an intended flood protection function. These two conduits are located above the design-basis groundwater elevation. In summary , the reevaluated maximum water surface elevations validate the current flood mitigation strategy of the current license basis, which states that CGS can be maintained in a safe condition for water levels up to 441 ft-MSL. Therefore , no interim actions are identified. | ||
No additional actions are planned to address flooding hazards as the reevaluated maximum water surface elevations do not impact any safety-related structures. | No additional actions are planned to address flooding hazards as the reevaluated maximum water surface elevations do not impact any safety-related structures. | ||
| Line 461: | Line 461: | ||
* NGVD 29. (b)(3) 16 L. The reeva u a ed WSE, i~ci J , R~;";l\<) SC ,(b) ) coincident w i nd-wave activity is below the crit i cal facil i ty eleva t io n of 441 ft-M SL. | * NGVD 29. (b)(3) 16 L. The reeva u a ed WSE, i~ci J , R~;";l\<) SC ,(b) ) coincident w i nd-wave activity is below the crit i cal facil i ty eleva t io n of 441 ft-M SL. | ||
* Since these mechanisms were screened ou t as part of flood hazard r evaluation , they were also cons i dered bo u n d ed by th e curr e nt d e sign b as is. COLUMB I A GENERA TI NG STA T ION P a g e 53 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | * Since these mechanisms were screened ou t as part of flood hazard r evaluation , they were also cons i dered bo u n d ed by th e curr e nt d e sign b as is. COLUMB I A GENERA TI NG STA T ION P a g e 53 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations | ||
): Flooding Energy Northwest Columbia Generating Station 6. REFERENCES September 27, 2016 Revision 0 1. American Nuclear Society, ANS I/A N S-2.8-1992, American National Standard for Determining Design Basis Flooding at Power Reactor Sites, prepared by the American Nuclear Society Standards Com mi ttee Wo r king Group ANS-2.8, L a Grange Park , Illinois. | ): Flooding Energy Northwest Columbia Generating Station 6. REFERENCES September 27, 2016 Revision 0 1. American Nuclear Society, ANS I/A N S-2.8-1992, American National Standard for Determining Design Basis Flooding at Power Reactor Sites, prepared by the American Nuclear Society Standards Com mi ttee Wo r king Group ANS-2.8, L a Grange Park , Illinois. | ||
: 2. Northwest Columbia Generating Station Final Safety Analysis Report, Amendment 63, December 2015. 3. Energy Northwest, Columbia Flooding Walkdown Report , L etter 802-12-164, dated November 12 , 2012 , NRC Docket No. 50-397. 4. Energy Northwest Calculation No. CE-02-13-17 , Probable Maximum Precipitation (PMP) Analysis for Columbia Generating Station, Revision 0. 5. Energy Northwest Calculation No. CE-02-1 3-1 8, Prob able Maximum Flood (PMF) An alysis for Columbia Generating Station , Revision 0. 6. Energy N orthwest Calculation No. CE-02-13-20, Ice Effects and Channel Migration Assessment for Columbia Generating Station , Revision 0. 7. Energy N orthwest Calculation No. CE-02-1 3-2 1, Combined Flood Events Analysis for Columbia Generating Station , Revision 0. 8. Energy N orthwest Calculat i on No. CE-02-13-22, Effects of Local Intense Probable Maximum Precipitation An alysis for Columbia Generating Station (CGS), Rev ision 0. 9. Energy Northw est Calculation No. CE-02-13-27, Local Drainage Basin Probable Maximum Flood (PMF) Analysis for Columbia Generating Station, Revision 0. 10. (Energy Northwest , 2016g) Energy N orthwest Calculat i on No. CE-02-14-10 , Site-Specific Local Intense PrecipHation (LIP) Determination for Columbia Generating Station, Revision 0. 11. Federal Emergency Management Agency, FE MA P-259 , Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures, January 2012. 12. Nuclear Energy I nstitute (NEI), NEI 1 2-07 , Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features, Rev is ion 0 , May 2012. 13. Nuclear Energy I nstitute (NE I), NEl-1 2-08, Overview of External Flooding Reevaluations, August 2012. 14. National Oceanic and Atmospheric Administration, National Weather Service , U.S. Department of Commerce, Hydrometeorological Report No. 57 , Probable Maximum Precipitation | : 2. Northwest Columbia Generating Station Final Safety Analysis Report, Amendment 63, December 2015. 3. Energy Northwest, Columbia Flooding Walkdown Report , L etter 802-12-164, dated November 12 , 2012 , NRC Docket No. 50-397. 4. Energy Northwest Calculation No. CE-02-13-17 , Probable Maximum Precipitation (PMP) Analysis for Columbia Generating Station, Revision 0. 5. Energy Northwest Calculation No. CE-02-1 3-1 8, Prob able Maximum Flood (PMF) An alysis for Columbia Generating Station , Revision 0. 6. Energy N orthwest Calculation No. CE-02-13-20, Ice Effects and Channel Migration Assessment for Columbia Generating Station , Revision 0. 7. Energy N orthwest Calculation No. CE-02-1 3-2 1, Combined Flood Events Analysis for Columbia Generating Station , Revision 0. 8. Energy N orthwest Calculat i on No. CE-02-13-22, Effects of Local Intense Probable Maximum Precipitation An alysis for Columbia Generating Station (CGS), Rev ision 0. 9. Energy Northw est Calculation No. CE-02-13-27, Local Drainage Basin Probable Maximum Flood (PMF) Analysis for Columbia Generating Station, Revision 0. 10. (Energy Northwest , 2016g) Energy N orthwest Calculat i on No. CE-02-14-10 , Site-Specific Local Intense PrecipHation (LIP) Determination for Columbia Generating Station, Revision 0. 11. Federal Emergency Management Agency, FE MA P-259 , Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures, January 2012. 12. Nuclear Energy I nstitute (NEI), NEI 1 2-07 , Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features, Rev is ion 0 , May 2012. 13. Nuclear Energy I nstitute (NE I), NEl-1 2-08, Overview of External Flooding Reevaluations, August 2012. 14. National Oceanic and Atmospheric Administration, National Weather Service , U.S. Department of Commerce, Hydrometeorological Report No. 57 , Probable Maximum Precipitation | ||
-Pacific Northwest States, Columbia River (including portions of Canada}, Snake River and Pacific Coastal Drainages , Silver Spring Maryla nd, 1994. 15. U.S. Army Corps of Engineers , EM 1110-2-1406, Engineering and Design , Runof f from Snowmelt , Washington , DC 20314-1000, March 31, 1998. 16. U.S. Army Corps of Engineers , EM 1110-1-1005 , Engineering and Design , Control and Topographic Surveying , Washington , DC 203 1 4-1000 , January 0 1 , 2007. COLUMB I A GENERA TI NG STA T ION P age 54 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations | -Pacific Northwest States, Columbia River (including portions of Canada}, Snake River and Pacific Coastal Drainages , Silver Spring Maryla nd, 1994. 15. U.S. Army Corps of Engineers , EM 1110-2-1406, Engineering and Design , Runof f from Snowmelt , Washington , DC 20314-1000, March 31, 1998. 16. U.S. Army Corps of Engineers , EM 1110-1-1005 , Engineering and Design , Control and Topographic Surveying , Washington , DC 203 1 4-1000 , January 0 1 , 2007. COLUMB I A GENERA TI NG STA T ION P age 54 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations | ||
Revision as of 18:55, 22 April 2019
| ML19009A327 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 01/08/2019 |
| From: | NRC/OCIO |
| To: | |
| Shared Package | |
| ML19009A324 | List: |
| References | |
| FOIA, NRC-2017-000688 | |
| Download: ML19009A327 (56) | |
Text
Withhold from Public Qiecloeure ifl Accorder1ce with 19 ci;;R 2,399 G02-1 6-1 43 Enclosure 2 COLUMBIA GENERATING STATION FLOODING HAZARD REEVALUATION REPORT Withhold from Public Qiecloeure ifl Acconler1ce 1tvith 19 ci;;R 2,399 Preparer: Verifier:
Approver: FLOOD HAZARD REEVALUATION REPORT IN RESPONSE TO THE 50.54(f) INFORMATION REQUEST REGARDING NEAR-TERM TASK FORCE RECOMMENDATION 2.1: FLOODING for the Columbia Generating Station ~ENERGY ~NORTHWEST People* Vision* Solutions Energy Northwest P.O. Box 968 Richland , Washington 99352-0968 Prepared by: F.;;t ENERCON Excellence-Every pro1ec1. Every day Enercon Services I nc. 1601 Northwest Expressway, Suite 1000 Oklahoma City, OK 73118 Revision 0 , Submitted Date: September 27, 2016 Printed Name Affiliation Signature Anubhav Gaur Enercon Freddy Dahmash Ene rcon Pat Brunette Enercon Date a.~ 121[:i~-\' I o'f) L:f [zz,I 9-27-16 NTT F Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station Table of Contents September 27, 2016 Revision 0 1. PURPOSE ..........................................
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5 1.1 B ackground
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........ 5 1.2 Requested Actions .................................................
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5 1.3 Requested ln formation
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6 2. SITE INFORMATION
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8 2.1 Current Design Basis Flood ....................................................................................................
9 2.1.1 LIP ....................................................
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................................................ 9 2.1.2 Flooding in S t reams and Rivers .....................................................
............................ 9 2.1.3 Dam Breaches and Failures ....................................................................................... 9 2.1.4 Storm Surge ..................
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............. 1 0 2.1.5 Seiche ................................
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.... 10 2.1.6 Tsunami ....................................................................................................................
10 2.1. 7 Ice-I nduced F lood ing ......................................................
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............. 1 O 2.1.8 Channel Migration or Diversion
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11 2.1.9 Combined Effect F lood (including Wind-Generated Waves) .................................... 11 2.2 Flood-Re late d Changes to the Licensing Basis ....................................
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1 1 2.2.1 F loo d-Re lated Changes to the Licensing Bas is since License I ssuance .................
11 2.2.2 Flood Protection Changes (I ncluding Mitigation) Since License Issuance ...............
11 2.3 Changes to the Watershed since License I ssuance ............................................................. 11 2.4 Current Licens ing Basis Flood Protection and Pertinent Flood Mitigation Features at CGS 11 3.
SUMMARY
OF FLOOD HAZARD REEVALUATION
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13 3.1 Local Intense LIP Analysis (Reference 8 and Reference
- 10) ............................................... 14 3.1.1 Basis of l nputs ...........................................
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................ 1 4 3.1 .2 Computer Software Programs .................................................................................. 1 4 3.1.3 Methodology
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15 3.1.4 Re su lts ..................................
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17 3.2 Flood ing in Streams and R ivers (Reference 4 , Reference 5, and Reference
- 9) ................... 24 3.2.1 Basis of I nputs ..................
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27 3.2.2 Computer Softwa r e Programs .................................................................................. 29 3.2.3 Methodology
............................................................................................................. 29 3.2.4 Resul t s .....................................................................................................................
40 3.3 Dam Brea ches and Failures (Reference
- 25) ...............................................
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..... .44 3.3.1 Results .........................................................
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............. 44 3.4 Storm Surge .............
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........ 44 3.5 Seiche 44 COLUMBIA GENERA TI NG STA T ION Page 2 of 55 NTT F Recommendation 2.1 (Haza rd R eevaluations):
F looding Energy Northwest Columb i a Generating Station September 27, 2016 Revision 0 3.6 T sunam i ................................................................................................................................
44 3.7 I ce I nduced Flo odi n g (R eference 6) ..................................................................................... .44 3.7.1 Basis of l nputs ...........................................
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44 3.7.2 Computer Software P rogra m s ...................
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.45 3.7.3 Methodology
............................................................................................................. 4 5 3.7.4 Re su lts ..................................................................................................................... 47 3.8 Channel Mig ration or Diversion (Re fe r ence 6) ....................................
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.47 3.9 Co mb ine d Effect Flood (Inc lud i ng Wi n d Generate d W aves, Reference
- 7) .......................... .47 3.9.1 Basis of I nputs ......................................................................................................... .48 3.9.2 Computer So f tware Programs ...................
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.48 3.9.3 Methodology
............................................................................................................ .48 3.9.4 Results ..................................................................................................
................... 49 4. CONCLUSION
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............................... 49 5. COMPARISON WITH CURRENT DESIGN BASIS ......................................................
50 6. REFERENCES
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...... 54 COLUMB I A GE NERATING S TATION Pag e 3 of 55 NTT F Recommendation 2.1 (Haza rd Reevaluations):
Flooding Energy Northwest Columbia Generating Station List of Figures September 27, 2016 Revision 0 Figure 1. CGS General Location Map ..............................
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8 F igure 2. CGS Protec t ed Area Survey Points (PASP) ....................................................................
1 8 Figure 3. CGS Map for LI P ..............................................
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21 Figure 4. CGS Location Map ..........................................................................................................
26 F igure 5. Co l umbia, Snake, and Yakima Sub-waters h ed !Map .......................................................
31 Figure 6. HEC-RAS Model Cross Section Locations
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36 Figure 7. Columbia River PMF Water Surface Profiles ...................................................................
37 F igure 9. Columbia R i ver near CGS I n unda t ion Map -Snake River PMF .............
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42 Figure 10. Local Drainage Basin PMF I nundation Map .................................................................
.43 Figure 11. Upstream and Downstream Br i dge Locations for Ice Jam ............................................
46 List of Tables T able 1. Summary of L I P Results .......................
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............... 22 T able 2. Summary of Associated Effects .............
........................................................................... 23 Table 3. Summary of Cu r rent Design Basis and Reeva l uated F l ood Hazard Elevations
............... 52 COLUMB I A GENERA TI NG STA T ION Pag e 4 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations
): t-1ooaing Energy Northwest Columbia Generating Station 1. PURPOSE 1.1 Background September 27, 2016 Revision 0 I n response to the nuclear fuel damage at the Fukushima-Daiichi power p lant due to the March 11 , 2011, earthquake and s ubsequ en t t sunami, the United States Nuclear Regulatory Commission (N R C) establis h ed the Near T erm T ask Force (NTTF) to conduct a systematic rev i ew of NR C processes and regulations, and to make recommendations to the NRC fo r its policy direction. Th e N TTF reported a set of recommendations that were intended to clarify and strengthen t he regulatory framework for protection against n atura l phenomena. On March 12, 2012, the NR C issued an information request pursuant to T i tle 1 O of the Code of Federal Regulation s, Sect i on 50.54(f) (10 CFR 50.54(f) or 50.54(f) letter) (Reference
- 24) which included six (6) enclosures:
- 1. [N TTF] Recommendation 2.1: Seismic 2. [N TTF] Recommendation 2.1: Flooding 3. [NTTF] Recommendation 2.3: Seismic 4. [NTTF] Recommendation 2.3: Flooding 5. [NTTF] Recommendation 9.3: EP 6. Licensees and H olders of Construction Permits I n Enclosure 2 of informa t ion reques t (Reference 24), the NRC requested that licensees reevaluate the flooding hazards at their sites against present-day reg u lato ry gu i dance and methodologies being used fo r early site permits (ES P) and combined operating li cense (COL) reviews. On behalf of Energy Northwest Company , LLC , for the Co l umbia Nuclear Generating Station (CGS), this Fl ood H azard Reeva l u ation R epo r t (R eport) provides the information requested i n the March 2012 , 50.54(f) letter; specifically , the in formation listed under the "Requested In forma t ion" section o f Enclosure 2, paragraph 1 ("a" t hr ough "e"). Th e " R eq u ested I nformation" section of Enclosure 2, paragraph 2 ("a" through "d"), I ntegra t ed Assessment Report, will be addressed separately if the current design basis floods do not bound the reevaluated hazard for all flood-ca us i ng mechani sms. 1.2 Requested Actions Per Enclosure 2 of the NRC issued information request, 50.54(f) letter, CGS i s requested to perform a reevaluation of all appropriate externa l flooding sources at CGS, includ ing th e effects of l oca l intense precipitation (LIP) on the site, probable maximum f l ood (PMF) on streams and rivers , storm surges, seiches, tsunamis, and dam fai l ures (as applicable). It is requested that the r eevalua ti on apply present-day regu l atory guidance and methodologies being used for ESPs and ca l culation reviews, inc l uding current techniques, software, and methods used in present-day standard engineering practice to eval l uate the flood hazard. T he reque ste d infor mation wi l l be gathered in Phase 1 of the NRC staff's two-phase process to im p leme nt R ecommendation 2.1 , and will be used to identify potential
" vu l nerabilit i es." (See defin it io n be l ow.) COLUMB I A GENERA TI NG S T A T ION Page 5 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 For the sites where the reeva luat ed flood exceeds the design basis , addressees are reque sted to submit the hazard evaluatio n along with an interim action plan that documents actions planned or taken to address the reevaluated haza r d. Subsequently, ad d ressees should perform an in tegrated assessment of the plant to iden tif y vulnerab il i ties and actions to address them. The scope of the i ntegrated assessment report w i ll include full power operations and other plant configurations that could be susceptible to f l ooding due to the sta t us of the f loo d protection featu res. The scope also i ncludes evaluating those features o f the ultima t e heat sin k s (UHS) that could be adverse l y affected by flood conditio n s and lead to degradation of the flood protection (the loss of UHS from non-f lood associated causes are no t included).
It is also r equested that the i ntegrated assessment address the entire duration of the flood conditions. A definition of vulnerability in the context of [Enclosure 2] is as follows: Plant-specific vulnerabilities are those features important to safety that when subject to an increased demand due to the newly calculated hazard evaluation have not been shown to be capable of performing their intended functions.
1.3 Requested
Informa t ion Per Enclosure 2 of the NRG-issued information reque st 50.54(f) letter, the Report should provide docume nt ed results , as well as pertinent CGS informatio n and detai le d ana l ysis to include the following:
a) Site information rela te d to the flood hazard. Relevant structures , systems and components (SSCs) important to sa f ety and the UHS are i ncluded in the scope of this reevaluation , and p ert inent data concerning these SSCs shou l d be included.
Other relevant site data inc lud e the following:
- Detailed site information (both designed and as-built), inc l uding present-day s it e layout , elevat i on of pertinent SSCs important to sa f ety , a n d site topograp h y, as well as pertinent spatial and temporal data sets;
- Current design basis f l ood elevations for a ll flood-causing mechanisms
- Flood-r elated changes to the licensing basis and any flood protection changes (incl udi ng mitigation) since license iss u ance;
- Changes to the watershed and local area since license issuance;
- Current licensing basis flood protection and pertinent flood mi ti ga tio n featu res a t the site;
- Additional site details, as necessary , to assess t he f l ood hazard (i.e., bathymetry , walkdown r esu l ts , etc.). b) Evaluation of the flood hazard for each flood-ca u s ing mechanism , based on present-day methodologies and regul atory guidance. Provide an ana ly sis of each fl ood-causing m echa ni sm that m ay impac t the s ite , including LI P an d site drai n age, flooding in streams and COLUMB I A GENERA TI NG STA T ION Page 6 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 rivers, dam breaches and failures, storm surge and seiche , tsunami, channe l! migration or diversion, and combined effects. Mechanisms that are not applicable at CGS may be screened out; however, a justification should be provided.
Provide a basis for inp uts and assumptions , methodologies and models used including input and output files, and other pertinent data. c) Comparison of current and reevaluated flood-caus i ng mechanisms at CGS. Provide an assessment of the current design basis flood elevation to the reevaluated flood elevation for each flood-causing mechanism.
Include how the findings from Enclosure 2 of the 50.54(f) letter (i.e., Recommendation 2.1, Flood Hazard Reevaluations) support this determinat i on. If the current design basis flood bounds the reevaluated hazard for all fl ood-causing mechanisms , inc lude how this f i nding was determ i ned. d) Interim evaluation and actions taken or planned to address any higher flooding hazards relative to the design basis , prior to completion of the integrated assessment described below, if necessary.
e) Additional actions beyond Requested I nformation It em 1.d taken or planned to address flooding hazards, if any. COLUMBIA GENERATING STATION Page 7 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
F looding Energy Northwest Columbia Generating Station 2. SITE INFORMATION September 27, 2016 Revision 0 CGS is located in the southeast area of the U.S. Department of Energy's (DOE) H anford Site in Ben t on County , Was h ington. CGS is approximate l y 3 miles wes t of the Co l u m bia R i ve r at R iver M il e 352, approx i mate l y 10 mi l es north o f North Rich l and , 45 miles downstream from Grant County Pub l ic Util i ty Di strict (P U D) Priest Rapids Dam , 18 mi l es northwest of P asco, and 21 m i les northwest of Kennewick.
CGS general l ocation i s presented in F i gure 1. F i gure 1. CGS General Location Map T opog r aphic re l ief at CGS is l ow and relative l y f l at, with a mean station reactor floor e l evation of 4 41 feet (ft) Mean Sea L evel (MS L), as reported in the CGS Final Safety Ana l ysis Repor t (FSAR) (Reference 2). E l evat i ons in this r eport refer to Nationa l Geodetic Vertica l D atum of 1929 (NGVD 29) and N orth American Vert i ca l D atum o f 1 988 (N AV O 88). All referenced ca l culations and computations were conducted in N AVO 88. T he FSAR identifies the c r itical elevation at CGS as 441 ft-M S L. T he NGV D 29 was originally named the Mean Sea L evel Datum of 1929 (Reference 16). Elevations referenced in the current FSAR that u se the MSL are equivalent to NGVD 29. The datum shift of -3.4 f t from N AVO 88 t o NGVD 29 was calculated us i ng the web-based program VERTCO N v2.1 developed by the Nationa l Geodetic Survey. ft-MS L = ft-N GVD 29 ft-N GVD 29 = f t-NAVO 88 -3.4 COLUMB I A GENERA TI NG S T A T ION Page 8 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station T he relevant flooding data for CGS include the following:
2.1 Current
Design Basis Flood September 27, 2016 Revision 0 The current design basis f lood elevation for CGS is 433.3 ft-MSL , which includes coincident wave activity.
This is less than the east spray pond overflow weir at elevation of 434.5 ft-MSL and the CGS reactor floor elevat i o n of 441 ft-MSL (Reference 2). The following is a list of flood causing mechanisms and the i r associated water surface elevations (WSEs) that are considered in the CGS cur r ent l i censing basis (CLB). 2.1.1 LIP Local thunderstorms can produce short duration rains, which have the potent i a l for causing serious flooding.
To provide adequate surface drainage during severe precipitation conditions , such as heavy rainfall and fast snowmelts, a system of catch basins and dry wells is constructed with inle t elevations lower than the finished floor elevat i on of the nearest building(s).
T he roofs of safety-related buildings are designed to handle LIP events w it h adequate drainage.
I n the event that the roof drains are completely blocked during the precipitation event, overflow scuppers limit the depth of water to within the design load carry i i ng capabil it y of the roofs. Those safety-related structures that do not have this relief capability are structurally able to carry the entire precipitation accumulations (Reference 2). 2.1.2 Flooding in Streams and Rivers Analyses of the PMF are consisten t with t h e requirements of Regulatory Guide 1.59, Revision 2. The FSAR indicates an unregulated PMF flow rate of 1,600 , 000 cubic f t per second (cfs) in th e Columbia River at CGS (Reference 2). Adjustment of the flood profiles for the Hanford region r esults in a regulated PMF of 1,440 , 000 cfs and a water level of 390 ft-MSL at the Seismic Category II makeup water structure.
As indicated in the FSAR (Reference 2), the des i gn basis flood for CGS area resu l ts from the PMP event on the adjacent drainage basin and not from f l ooding of the Co l umb i a River. Th e methodology for p r edicting the t otal amount of precipitation requires add in g together the convergence PMP and the orographic PMP to obtain a single precipitation for a general storm. The U.S. Army Corps of Engineers (USAGE) Hydrologic Eng i neering Center (HEC) standard-step procedure for seven (7) cross sections was utilized to determine t h e WSE from the PMF event on the adjacent drainage basin , which was determined to be 431.1 ft-MSL (Reference 2). 2.1.3 Dam Breaches and Failures There are seven dams upstream and four dams downs t ream of CGS on the ma i n stream of the Columbia River within the U.S. The current license basis dam failure considered a flood from a breaching of Grand Coulee Dam in l ie u of a seismically induced flood. A massive hyd r aul i c failure of the Grand Coulee Dam with a release of 8 , 800 , 000 cfs was considered for analyses of floods resul t ing from potential dam failures. Following the assumed failure of the Grand Coulee Dam , all downstream dams between Grand Coulee Dam and CGS suffer some degree of failure and release their storage reservoirs to t he f l ood. The effect of potential dam failu r e on the water levels at CGS wa s determined using the assumption that the Columbia R iv er i s at flood stage w i th a standard COLUMB I A GENERA TI NG STA T ION Page 9 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 project flood (SPF) of 570,000 cfs. A base flow of 50 , 000 cfs was assumed above the mouth of the Snake River for the dam failure flood (Reference 2). The failure of Arrow and/or Mica Dams in Canada could result i n greater re l eases of storage in terms of volume than t hat from t he Grand Coulee Dam , but the effects of such postulated releases are mitigated by a combination of valley storage and cri t ical (f l ow limiting) valley cross sec t ions. The river channel restrictions at Tra i l , British Columb i a, would restrict river flow to about 3,100 , 000 cfs, regardless of the postulated dam failure. A major failure ups t ream wou l d result in this maximum flow for many days, causing overtopping of Grand Cou l ee Dam. An analysis by the U.S. Bureau o f Reclamation concluded that overtopping which might resu l t from the failure of upstream dams will not cause failure of either the Grand Coulee Dam or the Forebay Dam (Reference 2). The failure of the Grand Coulee Dam represents an upper limit to seismical l y induced fai l ures. This failure would initiate a catastrophic flood , which would be augmented by the failure of the earthen portions of downstream dams and subsequent release of the storage pools behind them. T his flood wou l d have an outfall peak of 8,800,000 cfs at Grand Coulee Dam at the moment of breac h ing , and a pea k discharge at River M i le (RM) 338 (Richland) of 4 , 800,000 cfs. The resulting dam breach elevation a t RM 350 is 422 ft-MS L. An addi t io n al 2-ft allowance was included for wind and wave action , and adequate margin exists between the resultant flood elevation and the plant elevation of 441 ft-MSL (Reference 2). 2.1.4 Storm Surge The FSAR (Reference
- 2) indicates f l ooding due to surges is not applicable.
CGS has an inland location and does not connect d i rectly with any of the water bodies cons i dered for meteorological even t s associated with a storm surge. F l ooding due to a surge is not p l ausible at CGS. 2.1.5 Se i c h e T he FSAR (Reference
- 2) indicates flooding due to seiche is not applicab l e. CGS has an inland location and does not connect directly wi t h any of the water bodies cons i dered for meteorologica l even t s associated with a seiche. F l ood i ng due to a seiche is not plausible at CGS. 2.1.6 Ts unam i The FSAR (Reference
- 2) ind i cates flooding due to tsunamis i s not applicable.
CGS is not adjace n t to any coastal area; furthermore , it has an i nland location and does not connect di r ec tl y with any of the water bodies considered for tsunami events. F l ooding due to a tsunami is not a plausible at CGS. 2.1.7 Ic e-Indu ce d Flooding Historically, the Col u mbia River has never exper i enced complete flow stoppage or significant flooding due to ice b l ockage, so no instances of comple t e stoppage have occurred. Periodic ice blocking has caused reduced flows and limited flooding for only relat i vely s hort periods of time. Therefore , it was concluded that ice jam f l ooding potentia l is insignificant for CGS (Reference 2). COLUMB I A GENERA TI NG STA T ION Pa g e 10 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station 2.1.8 Ch a n ne l Migr a tion or Div e r s ion September 27, 2016 Revision 0 The Columbia River flow in the H anford reach is contro ll ed to a large extent by regulation of the upstream reservoir projects.
Columbia River flow is controlled by t he operation of upstream reservoirs by the USAGE. The riverbed in the vicinity of CGS is well defined. There f ore, it is very unlikely that it would be diverted from its present l ocation by natural causes. Any possible effect on water supply to the makeup water pump house from riverbed changes would come from ext r emely slow changes which can be corrected if and when they occur (Reference 2). 2.1.9 Combin e d Eff e ct Flood (including Wind-G e n era t e d W a v es) Procedures published by the USAG E were used to determine the wind-wave activity. T he maximum wave height was calculated to be 4.0 ft, the wind se t up was computed to be 0.3 ft , and the maximum wave runup 1.9 ft. The resulting design WSE including coincident wind-wave activity is 433.3 ft-MSL , which is l ess than the east spray pond overflow weir elevation of 434.5 ft-MSL (Reference 2). The allowance for sim ul taneous wind and wave action on t he Columbia River is 2 ft. The resulting WSE for the Columbia River including coincident wind-wave activity is 424 ft-MSL (Reference 2). 2.2 Flood-R e l a ted Ch a nges to the Licensing Ba s i s 2.2.1 Flood-Rel a ted Ch a nge s to th e Licensing Basi s s in ce Lic e nse Is s u a nc e T here have been no flood-re l ated changes to the CGS l i censing basis wi t h respec t to an externa l flooding event. 2.2.2 Flood Protection Ch a nge s (Including Mitigation)
Since Licen se Is s uance There have been no f l ood pro t ection changes made since l i cense i ssuance. No physica l modi f ications have been installed speci f ically i n support of t he external flooding response.
2.3 Ch a nge s to the Wat e rshed since License Issu a nce T he Columbia River drains an area of approx i mately 258,000 square miles, lying to the west of the Continental Divide in the northwes t ern part of the U.S. (85%) and southwestern part of Canada (15%) (Reference 2). The Columbia River watershed upstream of CGS has a tota l drainage area of approximately 98,000 sq. mi l es. The Yakima and Snake River watersheds , downstream of CGS and tributary to the Columbia River, have watershed drainage areas of 6, 1 56 sq. miles and 108,000 sq. mi l es , respec t ive l y (Reference 5). Based on a review of aerial images , the most significant change to the watershed is the expa n sion of urbanized areas. These areas comprise a very small fraction of the watershed area. Even i f watershed changes are anticipated in the Columbia River Bas i n, the impact of any changes will be insignificant due to the reg u la t ion effect of the large number of flow reg u latio n structures upstream of CGS. 2.4 Curre n t Licensi n g Basis Flood P r ot e ct i on and P e rti nen t Flood M i t i g a t i on F e atu re s at CGS All safety-related facilities are housed in Seismic Categoll'y I struc t ures protected from f l ooding and designed to withstand the static and dynamic forces of all postulated f l oods. CGS can be safely shut COLUMB I A GENERA TI NG STA T ION Pa g e 11 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 down in the event of any flood and maintained in a safe condition for flood levels up to 441 ft-MSL (Reference 2). The PMF elevation of the Columbia River is estimated to be 390 ft-MSL , so emergency flood protection procedures are not necessary for Columbia River PMF (Reference 2). For flood levels between 373 ft-MSL and 440 ft-MSL , any mode of operation is possible with no additional protective measures.
The plant is maintained in a safe condition and is safe for any shutdown condition (Reference 2). All non-safety-related facilities are above the limiting case flood (LCF) elevation , except for the makeup water pump house , which would not be affected by flooding , and thus would not affect any safety-related equipment and would not hinder the safe shutdown of the plant. The approximate finished grades at all Seismic Category I structures except the spray ponds are at elevation 440 ftMSL. The fin i shed grade of the spray ponds is 434 ft-MSL. The cur r ent design basis flood elevation for CGS is 433.3 ft-MSL , w h ich includes coincident wind-wave activity. This is less than the east spray pond overflow weir elevation of 434.5 ft-MSL and the CGS reactor building floor elevation of 441 ft-MSL (Reference 2). Se i smic Category I structures are designed to withstand the static and dynamic forces which could result from a flood due to a breach of Grand Coulee Dam. Since this represents the LCF , the structures are also considered secure against the forces due to the lower PMF. The access openings to all seismic Category I structures are located well above all flood water elevations, including those due to wind and wave action. The groundwater table elevation at CGS is approximately 380 ft-MSL. The groundwater design basis is 420 ft-MSL (Reference 2). Seism i c Category I structures house safety-related systems and components.
The lowest floor level of these structures, except the standby service water pump houses, is above the groundwater design basis. The standby serv i ce water pump houses are designed to resist the increased hydrostatic pressure from the groundwater des i gn basis elevation. Se i smic Category I piping and electric conduit penetrations that are below grade are above the design basis groundwater table , and sealing against groundwater pressure is therefore not required.
However , all pipes penetrat i ng exter i or wall s are waterproofed sealed by boots installed on both sides of the wall penetration; all electrical conduit penetrat i ons are through-wall waterproof sealed using silicon foam. COLUMBIA GENERATING STATION Pa g e 12 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station 3.
SUMMARY
OF FLOOD HAZARD REEVALUATION September 27, 2016 Revision 0 NUREG/CR-7046 Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (Reference 23), which references guidance from the American Nuclear Society (ANS), states that a single flood-causing event is inadequate as a design basis for power reactors and recommends that combinations should be evaluated to determine the highest flood water elevation at CGS. For CGS , the combination that produces the h i ghest flood water elevation is the effects of LIP. Energy Northwest Calculation No. CE-02-13-22 (Reference
- 2) provides eleva t ions in MSL datum. The CGS flood hazard reevaluation calculations provide e l evation results based on the NAVO 88 and NGVD 29. P r ior to 1973, NGVD 29 was named the Mean Sea Level Datum of 1929. Elevations in the CGS flood hazard reevaluation calculations re f erring to NGVD 29 are equ i valent to MS L and directly compared to the elevations referenced in the CGS FSAR (Reference
- 2) that use MSL. The methodology used in the f l ooding reevaluation for CGS is consistent with the following standards and guidance documents:
- NRC Standard Rev i ew Plan , NUREG-0800 , revised March 2007 (Reference 22).
- NRC Office of Standards Development , Regulatory Gu i des , RG 1.102 -Flood Protection for Nuclear Power Plants, Revision 1 , dated September 1976 (Reference 20).
- NRC RG 1.59 , Design Basis Floods for Nuclear Power Plants , Revision 2 , dated August 1 977 (Reference 21 ).
- NUREG/CR-7046, "Design-Basis Flood Estimat i on for Site Characterization at Nuclear Power Plants in the United States of America," dated November 2011 (Reference 23).
- American National Standard for Determining Design Basis Flooding at Power Reactor Sites (ANS I/ANS 2.8-1992), dated July 28 , 1992 (Reference
- 1)
- NEI Report 12-08 , Overview of External Flooding Reevaluations (Re f erence 13). T he following provides the flood-causing mechanisms and their associated WSEs that are considered in the CGS flood hazard reevaluation.
COLUMBIA GENERAT I NG STA T ION Pa g e 13 of 55 NTT F Recommendation 2.1 (Hazard R eevaluations):
F looding Energy Northwest Columb i a Generating Station September 27, 2016 Revision 0 3.1 Local Intense LIP Analysis (Ref e rence 8 and Reference
- 10) Calculation N o. CE-02-14-1 O (Re f ere n ce 10) evaluates site-spec ifi c PMP depths used as inp ut to the LIP analysis.
Calculation No. CE-02-13-22 (Reference
- 8) evaluates th e r unoff an d the r esulting WSE due to a LIP event at CGS. 3.1.1 Basis of Inputs The i nputs used in t he LIP analysis are based on the following:
- A site-specific storm-based a pproach PM P a na lysis based on CGS elevation and location was performed to define the PMP depths. Th e s i te-spec if ic PMP a n alysis ut i lized actual data fr om ext r eme r ain f all events within a P acific N orthwes t watershed domain that in c lud ed port ions o f W ash ingt on , Oregon , California, N eva da , Ut ah, a nd I daho.
- The Digital Terrain Model (DTM) was developed from an aerial survey pe rfo r med by the Sanbo rn M ap Com pany. The grid system fo r comp utatio n was developed bas ed on a se l ected ce ll size o f 1 O ft an d optimized t o provide the best possible combination of to po graphic da ta reso l ution an d acceptable model run time. Th e t opographic data w ere processed u sing ArcGIS 10.1.
- T he obstructions at CGS were ident if i ed using the aer ial im age for CGS and the AutoCAD survey file from San born Map Company. Two type s of obstructions were modeled: (1) buildings and st ru ct ur es that completely block the water passage regardless of ca l cu l ated WSE; a nd (2) vehicle an d secur ity b arriers that m ay be overtopped if the calculated WSE i s above the top of the barrier.
- F low velocities and depths in overland flow are affected by top ography and gr i d e l ement roughn ess. Th e l an d cover in formati o n w as obtained using aer ial imag es a n d the AutoCAD survey file from Sanborn Map Company.
- FL0-2 D , a two-dimensional physical process and vo l ume conse r vation model , was used to es t imate the maximum water surface and water depth at CGS.
- For sur f ace roughness coefficients the M anning's n-values are used in the analys i s. Th e roughness coefficients a r e se l ected based on the l and cover type id ent i fied using aerial topographical su rv ey infor mat io n and available aer i a l imagery. The Ma nn i ng's n-values are se l ected fo ll owing th e suggested range for th e ove rl and flow r un o ff provided in the FL0-2D Reference M anua l.
- Associated effects for hydrostatic and hydrodynamic l oads were determined using the FL0-2D ou tp u t depths and velocities.
3.1.2 Computer
Software Programs
- ArcG I S D es k top 10.1
- AutoCAD Civ i l 30 2012 Service Pack 1
- FL0-2D P ro B uil d 1 4.08.09
- SP A S Version 9.5 COLUMB I A GENERA TI NG STA T ION Pa ge 14 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station 3.1.3 Methodology Site-Specific PMP September 27, 2016 Revision 0 The steps for the CGS site-specific PMP analysis using a storm-based approach in accordance with the most recent NWS H ydrometeoro l ogical Report No. 57, HMR-57 (Reference
- 14) and the Wor l d Meteorologica l Orga n ization (WMO) Manual for PMP determinat i on (Reference 26 and Reference
- 27) are as fa ll ows:
- Identify a set of storms , wh i ch represent ra i nfall even t s that are LIP-type events. This includes storms where extreme heavy rainfall accumulates over short duratio n s at a given location.
- Each storm event was then maximized in-place to produce a scenario representing how much larger the rainfall could have been had all atmospheric processes been combined in ideal conditions.
- Each storm i s then transpositioned from its original locat i on to CGS. I n this transposition process , diffe r ences in moisture between the or i ginal l ocation and CGS are accounted for and quantified.
- The greatest depth of the tota l adjus t ed rainfall of all transpositionable storms becomes the LI P depth for CGS at hourly increments up to 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
- Sub-hourly increments were determ i ned using the ra t ios from H MR-57.
- Cumulative LIIP va l ues were plotted on a smooth curve , which was used to i nte r po l ate 15-minute increment values.
- Five tempora l distributions of the 1 5-minute incrementa l LI P va l ues were developed that inc l uded centering the highest 15-minute increment at the front , one-thi r d , center, two-thirds , and end position within t he 6-hour storm duration , whi l e placing the next highest va l ues on a l ternating sides of the highest 15-minute increment.
Effects of LIP The Effects of LI P analysis uses a two-dimensional (20) hydrodynamic model , the FL0-20 mode l (FL0-20). F L 0-20 is a volume conservation model. The F L 0-20 model simulates open channe l flow throug h a numerical approximation of the shallow water equations.
F lood wave p r og r ession over the flow domain is controlled by t opography and resistance to flow. Flood routing in two dimensions is accomplished through a numerical in t egration of the equations of motion and the conservation of fluid volume. A two-dimensional mode l is appropriate and better suitable model compared to a one-d i mens i onal model to simulate the overland flow conditions at CGS, which are sheet flow , shallow concentrated flow , and open channel flow. T he two-dimens i ona l mode l determ i nes the f l ow direct i on based on well-defined ground topog r aphy , where the one-dimensional mode l requires the f l ow direction to be assigned. The one-dimensional mode l s , s u ch as unsteady-state H EC-RAS mode l , are capable to ut i lize similar computational approaches as the FL0-20 model (equations of motion and volume conservation). However, because the flow direction is ini t ially assigned , the mode l forces water f l ows COLUMB I A GENERA TI NG STA T ION Pa g e 1 5 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 in the assigned general direction rather than determining the direction.
Additionally, the f l ow path in the one-dimensional model i s represented by cross sect i ons a l ong the assumed flow direct i on and the averaged cross sections are uti l ized for the computational processes. On the other hand , the two-dimensional model uses a grid to represent the ground surface. Each grid elemen t is treated as a compu t ational cell and the hydraulic relationships are determined for each cell depending on the hydrologic and hydraulic properties of the cell itself and the surrounding cells. The ground is closely represented in the two-dimensional model because each grid element is assigned a corresponding ground surface elevation, roughness coefficient, and , when applicable , reduction factor(s) to account for obstructions (buildings , walls, etc.). The steps for CGS LIP analysis using FL0-20 are as follows:
- Crea t e a grid system using ground surface topographical data.
- Assign properties
/details to the mode l such as computationa l boundary and outflow elements.
- Specify roughness coefficients (Manning's coefficients) corresponding to the site's land cover type (e.g., concrete , grass, etc.).
- Identify obstructions complete l y blocking water f l ow (i.e., build i ngs).
- Identify obstructions diverting water flow (i.e., vehicle barrier).
The model boundary of FL0-20 and the obs t ructions at CGS are shown i n Figure 3.
- Assign precipitation inflow to the mode l (the five temporal distributions of LIP).
- Perform the FL0-20 computation.
- Analyze the results produced by F L 0-20.
- The gro u nd elevation of each CGS-protected area survey po i nt of interest (PO I) is then compared with the calculated WSE to determine the water depth. Following the guidance outlined in N U REG/C R-7046 the runoff losses are ignored. The roof rain f all is assumed to be contributing to the overland runoff. The drainage system at CGS is assumed to be non-functional at t he time of the LIP event. The steps for CGS LI P analysis associated effects are as follows:
- Obtain depth and velocity output from the FL0-20 modeling.
- FEMA guidance (Reference
- 11) is u tilized for ca l culating hy drostatic and hydrodynamic pressure.
- Other associated effects are discussed qualitatively and determined to be insignificant based on the shallow depths and low velocit ies. COLUMB I A GENERA TI NG STA T ION Pa ge 1 6 of 55 NTIF Recommendation 2.1 (Hazard Reevaluations)
- Flood in g Energy Northwest Co l umbia Generating Station 3.1.4 Results September 27 , 2016 Revision 0 The site-specific PMP analysis resulted in input LIP values that have a cumulative depth of 8.21 in ches for the total 6-hour durat i on. The 1-hour depth is 6.29 inches and the 15-minute depth is 3.15 in ches. Follow i ng the guidance of NUREG/CR-7046 , Appendix B , a front-peak i ng tempora l distribution was ut ili zed in the FL0-2D mode l to calculate LIP water surface elevation at CGS. Calculat i on No. CE-02-13-22 (Reference
- 8) evaluates a total of 23 POis at CGS , which includes both safety and nonsafety related structures.
The power b l ock buildings and the location of the doors that could potentially prov i de a pathway for the floodwaters are identified as Protected Area Survey Poi n ts (PASP), as shown in Figure 2. COLUMBIA GENERAT I NG STATION Page 17 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
F looding Energy Northwest Columb i a Generating Station 1 ---I ' 1. High point near Radwaste Building t ruc k ra m p 2. DG building entrance doors (3) 3. Reactor Building crane bay door 4. Service Water A pumphouse personne l doo r 5. Service Water A spray pond wall (not scupper) 6. Service Water B pumphouse personne l door 9. September 27, 2016 Revision 0 10"". "'e""'n~c""'m""'a"" r.,..,"" n"" r""'on~o ...... .,...,, en""" t""'ra"" n""'ce ,.....,.......,..,...
,.,....,....,..
,..,, e T"ll""I.....,..,......
~~~~~---'
- 11. Benchmark in by NW remote air intake (no data on marker) 12. Benchmark in front of GSB ent r ance (N ll900, EllOO, el 440.12) 13. Benchmark in front of Bldg. 88 (couldn't ge t ca p off t o r e a d marker) Figure 2. CGS Protected Area Survey Points (PASP) The LIP resu l ts, in cludi ng the depth and duration of flooding at each designated point , are provided in Table 1. The LIP maximum water s urface e l evations at CGS varies between 435.14 ft-NGVD 29 and 443.27 ft-NGVD 29. The calculated maximum water depths vary between 0.03 ft and 0.79 ft. T he min i mum ponding depth of 0.025 f t (surface detentio n) i s u sed to in itiate flow rout in g in the FL 0-2D model. This flow depth is a reasonable minimum value to adapt as a starting depth for duration analysis based on F L 0-2D Data I nput M anua l recommendat i ons and guidelines.
Th e depth-COLUMB I A GENE RATIN G S TATI ON Pa ge 1 8 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 duration is the length of time in hours to which the flood of depth above 0.025 ft occurred on the surface. The water surface elevation results at PASP Nos. 1 , 3 , 4, 17 , 18, and 20 exceed the critical elevation of 441 ft-NG VD 29. However, these results do not indicate flooding of CGS safety-related SSCs. The topographic contours in the v i cinity of these reference points indicate positive runoff away from the reference point. The minimal depth of flooding at the short duration is due to the peak intensity rainfall directly on the modeled grid cell. The LIP results in a depth of 0.03 ft at the railroad bay door (PASP No. 3) for less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The railroad bay door would not l i kely be compromised by the short duration and limited depth of LIP flooding.
However , assuming small amount of floodwater entered through the railroad bay door, it will not impact any safety-related equipment.
No safety-related equipment located within the Reactor Bu i lding railroad bay would be adversely affected by a small amount of water on the floor. Additionally , the access doorway within the Reactor Building railroad bay has a threshold that will prevent the water from entering the rest of the Reactor Building.
The LIP results in a depth of 0.03 ft at the Diesel Generator Tank Access (PASP No. 20) for less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The Diesel Generator Tank Access is located at a high spot. The Diesel Generator Tank Access is capable of withstanding much higher water levels and is not compromised by the limited depth and duration of LIP flooding.
The LIP results in a depth of 0.03 ft at the Service Water B pump house personnel door (PASP No. 4) for less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The concrete pad in front of the personnel access door is about 25 sq. ft and it slopes away from the door. There is a drop off from the slab down to gravel (on three sides) of at least 2 inches. The door has a weather strip across the bottom. There is also a threshold across the bottom that is water proof and approximately one-inch high. Inside the doorway, the hallway concrete floor rises slightly for about six feet. However , assuming floodwater entered through the personne l door, i t would flow on the floor to grating, under which there is no safety-related equipment that will be impacted. The entry door would not likely be compromised by the short duration and minimal depth of flooding.
However , assuming floodwater entered through the Service Water B pump house personnel door, the effects are inconsequential.
The LIP results in a depth of 0.03 ft near the Radwaste Building truck ramp (PASP No. 1) for less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. If any runoff enters the building, it will be most likely intercepted by grates across the top and bottom of the ramp just outside the building rollup door. There are no safety-related equipment at floor elevation 437 ft-NGVD29 that would be adversely affected by limited runoff. The ISFSI Pad North (PASP No. 17), and the ISFSI Pad South (PASP No. 18) ar e not directly adjacent to safety-related SSCs. The associated effects of the LIP are provided in Table 2. The hydrostatic pressures at the designated locations vary between 1.87 lb/sq. and 49.30 lb/sq. ft. The hydrodynamic pressure at the designated locations vary between 0.11 lb/sq. and 12.18 lb/sq. ft. The hydrostatic and hydrodynamic loads associated w i th the LIP event are insignificant due to the shallow depth and low velocity resulting from the LIP event at CGS. The shallow flow depth and low velocity due to LIP also would COLUMBIA GENERATING STATION Pa g e 19 of 55 NTIF Recommendation 2.1 (Hazard Reevaluations)
- Flood in g Energy Northwest Co l umbia Generating Station September 27 , 2016 Revision 0 not be expected to cause debris impact loading , sediment deposition , or erosion at CGS. A local in tense precipitation event has no appreciable warn i ng time except those provided by a weather (precipitation) forecast.
The groundwater table elevation at CGS is approximately 380 ft-MSL. The groundwater design basis i s 420 ft-MSL. The LIP i s a short durat i on event and is not expected to result in changes to the groundwater level. However , all p i ping and e l ectric conduit penetrations that are below grade are waterproof sealed. COLUMBIA GENERAT I NG STATION Page 20 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
F looding Energy Northwest Columbia Generating Station I I I I I I I D : ~o cCJ ****** 0 -::::::11-==----====----Fe e t 0 125 250 500 750 1 ,000 Figure 3. CGS Map for LIP COLUMB I A GENERA TI NG STA T ION September 27, 2016 Revision 0 Legend -Veh i c l e Barrier -P o n d CJ Bu il di ng *1* * **1 F L 02D Model Area *** N A Pa ge 2 1 of 55 NTT F Recommendation 2.1 (Hazard R eevaluations):
F looding Energy Northwest Columb i a Generating Station Table 1. Summary of LIP Results POI El evatio n Maximum Water Surface El evation No. PASP NAVD 88 NGVD 29 NAVD 88 NGVD 29 (ft) (ft) (ft) (ft) 1 High point near Radwaste 444.65 441.21 444.68 441.24 Building truck ramp 2-1 DG Build i ng Exterior Door 444.26 440.82 444.30 440.86 (DG2) 2-2 DG Build i ng Exterior Door 444.29 440.85 444.34 440.90 (DG1) 2-3 DG Build i ng Exterior Door 444.27 440.83 4 44.32 440.88 (HPCS DG) 3 Reac t or Bui l ding 444.52 441.08 444.55 441.11 railroad bay door 4 Service Water B 444.42 440.98 444.45 441.01 pump house personnel door 5 Service Water B 438.55 435.11 438.62 435.18 spray pond w al l 6 Service W ater A 442.42 438.98 4 42.45 439.01 pump house personnel door 7 Service W ater A 438.47 435.03 4 38.58 435.14 spray pond wal l 8 Roof drain (storm sewer) 443.6 1 440.17 44 3.77 440.33 header manhole MH-S5 9 Vehicle Barrier System 444.17 440.73 4 41.46 438.02 high point 10 Benchmark 443.25 439.81 444.04 440.60 in front of TSC entrance 1 1 Benchmark 443.72 440.28 444.40 440.96 in by NW remote air intake 12 Benchmark 443.67 440.23 4 44.3 7 440.93 in front of GSB en trance 13 Benchmark 443.40 439.96 44 3.99 440.55 in front of Bui l ding 88 14 North Side of 443.85 440.41 4 44.02 440.58 FLEX Build i ng 82 15 North Side of 441.19 437.75 441.24 437.80 F LEX Building 600 16 South Side of 441.36 437.92 4 41.39 43 7.95 F L EX Building 600 17 ISFSI Pad (North) 446.66 443.22 44 6.71 443.27 18 I SFSI Pad (So uth) 446.66 443.22 4 46.69 443.25 19 F ac i li ti es Fue l Station 444.04 440.60 444.07 440.63 20 D i esel Generator Tank 445.52 442.08 44 5.55 442.11 Access 21 FLEX Gasoline Sto r age 443.54 440.10 444.1 9 440.75 Module September 27, 2016 Revision 0 Maximum Flooding Flow Depth Duration Over from P O I PASP El eva tion (ft) (hours) 0.03 0.73 0.04 2.25 0.05 2.76 0.05 3.08 0.03 0.89 0.03 0.68 0.07 1.22 0.03 0.82 0.11 1.70 0.16 2.55 N/A* N/A* 0.79 5.20 0.68 0.73 0.70 3.76 0.59 3.4 2 0.1 7 2.35 0.05 1.8 1 0.03 0.94 0.05 0.73 0.03 0.73 0.03 0.73 0.03 0.7 1 0.65 3.73
- N/A: N ot Applicab l e. The max i mum water surface elevation reported for the grid element 1s l ower than the VBS height. COLUMB I A GENERA TI NG STA T ION P age 22 of 55 NTT F Recommendation 2.1 (Hazard R eevaluations):
F looding Energy Northwest Columb i a Generating Station T bl 2 S a e fA . t d Eff t ummary o ssoc1a e ec s M aximum Maximum PASP Flow D e pth Flow Hydro-st a tic from Grid V e lo c it y Pr ess ur e Elevation at Grid No. N ame (ft) (ft/s) (lb/s q. ft) 1 H i gh point near Radwaste 0.03 1.13 1.87 Build i ng truck ramp 2-1 DG Bui l ding Exterior Door 0.04 1.29 2.50 (DG2) 2-2 DG Bui l ding Exterior Door 0.05 1.44 3.12 (DG 1) 2-3 DG Bui l ding Exterior Door 0.05 1.44 3.12 (HPCS DG) 3 Reactor Building 0.03 0.75 1.87 railroad bay door 4 Serv i ce Water B 0.03 2.26 1.87 pump house personnel door 5 Serv i ce Water B 0.07 0.95 4.37 spray pond wall 6 Serv i ce Water A 0.03 2.51 1.87 pump house personne l door 7 Serv i ce Water A 0.11 1.1 6 6.86 spr a y pond wall 8 Roof dra i n (storm sewer) 0.1 6 0.85 9.98 h eade r manhole MH-S5 9 V e hi c l e Barr i er System 0.43 1.82 26.83 h i gh point 10 Benchmark 0.79 1.21 49.30 in front of TSC entrance 11 Benchmark 0.03 0.81 1.87 i n by NW remote air i ntake 12 Benchmark 0.25 0.56 15.60 in front of GSB entrance 13 Benchmark 0.59 0.28 36.82 in front of Building 88 14 North S i de of 0.17 1.54 10.61 FLEX Building 82 15 N orth S id e of 0.05 1.22 3.12 FLEX Bui l ding 600 16 South Side of 0.03 0.67 1.87 FLEX Bu il ding 600 17 ISFSI Pad (North) 0.05 0.35 3.12 18 ISFSI Pad (South!) 0.03 0.24 1.87 19 Facil i ties Fuel Station 0.03 0.62 1.87 20 Dies e l Gene r ator Tank 0.03 1.71 1.87 Ac cess 21 FLEX Gasoline Storage 0.65 0.48 40.56 Module COLUMB I A GENERA TI NG STA T ION September 27, 2016 Revision 0 H ydro-dynamic Pr essu r e (lb/s q. ft) 2.49 3.24 4.02 4.04 1.08 9.90 1.74 12.18 2.6 1 1.41 6.42 2.84 1.29 0.61 0.15 4.60 2.8 9 0.87 0.24 0.11 0.74 5.65 0.45 Pa ge 23 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 3.2 Flooding in Streams and Rivers (Reference 4 1 Reference 5 1 and Refer e nce 9) The probable maximum flood is the hypoth etica l flood (peak disc h arge , volume and hydrograph shape) that is considered to be the most severe reasonably possible, based on comprehensive hydrometeo r ological app l ication of probable max i mum precip i tation and other hydrologic fac t ors favorable for maximum flood runoff such as sequential storms and snowme lt. As outlined in the guidance provided in ANSI/ANS-2.8-1992 and in NUREG/CR-7046, Appendix H , the design basis from flood hazards should include several flood-causing mechanisms a nd combinations of these mechanisms.
For the flood s caused by precipitation events , the following should be examined:
F looding in Rivers an d Streams Alternative 1 -Combination of:
- Mean monthly base flow
- Median soil moisture
- Antecedent of subsequent rain: the lesser of (1) rainfall equa l to 40 percent o f PMP , and (2) a 500-year rainfall
- The PMP
- Waves induced by 2-year wind speed applied along the critica l direction Alternative 2 -Combination of:
- Mean mont h ly base flow
- Probable maximum snowpack
- A 1 00-year s now-season rainfall
- Waves induced by 2-year wind speed applied along the critica l direction Alterna t ive 3 -Combination of:
- Mean monthly base flow
- A 1 00-year snowpack
- Snow-season PMP
- Waves induced by 2-year wind speed applied along the critica l direction CGS is located approximately 3 miles west of the Col u mbia River in Benton County , Wash ingt on , as sho wn on CGS location map provided in Figur e 4. CGS l ocation map also identifies the following landmarks which are import ant to the PMF analysis:
- McNary Dam -L ocated on the Col u mbia River 60 miles downstream of CGS. COLUMB I A GENERA TI NG STA T ION Page 24 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0
- Wallula Gap -A geological constriction of the Columbia River and f l oodplain located upstream of McNa ry Dam. Backwater effects from the natural constriction of PMF flows at the Wallula Gap heavily influence WSEs on the Columbia Rive r at CGS.
- Snake River -The Snake River has its confluence with the Columb i a River approximately 27 miles downstream of CGS. Snake River PMF flows cont r ibuting to the Columb i a River create backwater effects at CGS.
- Yakima Rive r -The Yakima River has its con fl uence with the Columb i a River approximately 18 miles downstream of CGS. PMF flows from the Yakima River create backwater effects on t h e Columbia River at CGS. Peak PMF discharge values on the Columbia, Yakima , and Snake Rivers due to PMP events occurring in respective watersheds were deve l oped to determine PMF WSEs on the Columbia River at CGS. I n addition , peak PMF discharge due to PMP events occur r ing on an adjacent local drainage basin was developed to determine the PMF WSE for the adjacent a r ea. COLUMB I A GENERA TI NG STA T ION Pa g e 25 of 55 NTI F Recommendation 2.1 (Hazard Reevaluations
): F looding Energy Northwest Columb i a Generating Station Figure 4. CGS Location Map COLUMB I A GENERA TI NG S T A T ION September 27, 2016 Revision 0 Page 26 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station 3.2.1 Basis of Inputs 3.2.1.1 PMP and Snowmelt (Reference 4 and Reference
- 5) September 27, 2016 Revision 0
- Procedures in NUREG/CR-7046 (Reference 23), NU REG-0800 (Refe ren ce 22), and ANSI/ANS 2.8 (R eference 1) for determining PMP and LIP.
- Historic rainfall and other meteo r ologica l da ta co ll ected by the N ational Weather Service (NWS) at numerous recording and cooperative climate stations and availab l e from the Nat ion al Climatic Data Center (NCDC), the National Oceanic and Atmospheric Administration (NOAA) Atlas 2 for the U.S. portions of the contributing drainage area, an d the Rainf a ll Frequency Atla s f or Canada fo r the Canadian portions of the contributing drainage area.
- H ydrologic Unit Code (HUC) sub-regions da ta are provided in GIS format from the U.S. Department of Agriculture
's (U SDA) on li ne Geospatial Data Gateway (Reference 18).
- NWS HMR-57 (Reference 14), standard isohyetal patterns , storm or i en t ation , percentage of 6-hour increment of PMP , and standard i sohyetal geometry information.
- Precipitation frequency maps.
- E s t imates of snow density for cool-season months were computed to calculate the Snow Water Equivalen t (SWE) needed for use in the snowmelt analysis.
- Other snowmelt parame t ers were determined using the calculation procedure provided in Sections 15.2 and 15.3 of HMR-57 (Reference 14).
- Snowme lt rate (ene r gy budget) equations a n d constan t s are based on USAGE Engineering Manual EM 1 110-2-1 406 (Reference 15). 3.2.1.2 PMF Hydrologic and Hydraulic Analysis (R e f erence 5)
- PMP and associated snowme lt hour all-season and cool-season (with coinc id ent snowmelt)
PMPs for the waters h ed area upstream and downstream of CGS.
- U nited States Geologic Survey (USGS) stream and flow gage data.
- Ho u rl y precip i tation data at all NW S cooperative stations throughout and adjacen t to the watershed in Washington, distributed by the NCDC.
- Soil types within the watershed, developed using Natura l Resources Conservation Service (NRCS , formerly Soil Conservat i on Service) soils data.
- Mann ing's Roughness Coefficients (Manning's n-val u e), based on visual assessme nt of aerial photography and values recommended in published lit era t ure.
- R iverine and floodpl ain geometry from U SGS topographic maps. COLUMB I A GENERA TI NG STA T ION Page 27 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station 3.2.1.3 Local Drain age Basin PMF (Reference
- 9) September 27, 2016 Revision 0
- Basin Topography
-The 10-meter Digital Elevation Model (DEM) from the USGS National Elevation Dataset (Reference 19'), and used as in put to develop drainage basin delineation , basin parameters, elevation versus storage relationship, and PMF inundation mapping. The 10-meter DEM references the State Plane Washington South horizontal coordinate sys tem, NAD 83 and the NAVD 88.
- Aerial Photogr aphy -National Agricultural Imag ery Progra m (NAIP) aer ial photography obtained from the USDA Geospatial Data Gateway was used for inundation mapping.
- Snowpack Data -The month in which snowpack is maximized in the Columbia watershed, as well as 100-year snowpack data developed from a statistical analysis of snow gage data, were obtained from Calculation No. CE-02-13-17 ( Reference
- 4) and used as input to snowmelt computations.
- Snow Dens i ty -The historical snow depth and snow density data was obtained from the NOAA interactive snow website (Reference 4), which was used as an input to snowmelt computations.
- Land Cover -Land cover information was obtained from Calculation No. CE-02-13-17 (Reference 4).
- Four precip i tation alternatives calculated in Calculation No. CE-02-13-27 (Reference
- 9) were distributed into five different temporal distributions for calculation of the loca l drainage basin PMF analysis using the HEC-HMS model. All simulations were executed at a 15-minute time step. The four precipitation alternatives input into the model were the general storm PMP, 100-yea r rainfall on probable maximum snowpack, the cool-season PMP on 100-year s nowpack , a nd the loca l s torm PMP.
- A hydro l ogic model of the local drainage basin was developed using the USACE's HEC-HMS compute r software.
In puts to the hydrologic modeling include identification of sub-basins , PMP , and an elevation versus storage curve.
- The watershed draining to the CGS is a 40.5-square-mile depression, with the CGS centrally locate d (north-south) and near the lowest point i n the basin. The basin was sub-divided into two sub-basins, with the boundary near CGS and the low point in th e basin. Sub-basin delineation was conducted to denote the direction of flow towards CGS. The upstream sub-basin (or northern sub-basin) drains to the south towards CGS. The downstream sub-basin (or southern sub-basin) drains to the north towards CGS until w ater reaches the elevation of the outlet, which is located at the south end of th e basin. I f water reaches the elevation of the outlet , at 437.9 ft-NA VD 88 , flow in the downstream sub-basin will reverse direction and will flow towards the sou th over the outlet, and then towards the Columbia River.
- An elevation versus storage relationship for input to the HEC-HMS model was developed using th e 10-meter DEM data and ArcGIS. The elevation versus storage COLUMBIA GENERAT I NG STATION Page 28 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 curve shows that approximately 3 1 , 1 30 acre-f t of storage is available below the outlet elevation of 437.9 ft. 3.2.2 C o mput e r Softw a r e P r og ra m s 3.2.2.1 PMP and Snowmelt Analysis
- ArcG I S Desktop 10.0 3.2.2.2 PMF and L ocal Dr ainage Basin PMF Analys i s (H ydrologic a n d Hydraulic A n a l ysis)
- ArcG I S D esktop 10.0
- H EC-H MS 3.5
- H EC-R AS 4.1 .0
- H EC-GeoRAS 10.1
- VERTCON 2.1 3.2.3 M e thodol o gy 3.2.3.1 PMP Ana l ysis CGS i s l ocated in Benton County , Washing t on , approximately 3 miles west of t he Co l u mbia River. PMP was developed for the Columbia River watershed upstream of CGS. The Yakima River and the Snake River merge with the Columbia River downstrea m of CGS and upstream of McNary Dam. Backwater effects from Mc N ary Dam on the Columbia River at CGS were also considered in the PMF analysis; therefore, PMP was also developed for the Yakima and Snake River watersheds. Sub-basin parame t ers for PMP computat i ons include drainage area , location of the sub-basin centroid , and elevation.
Drainage area , centroid coordinates, and elevation were computed using ArcG I S and are discussed in Calculation N o. CE-02-13-1 7 (Reference 4). Snowmelt computations require definition of the land cover , specifically the percent forested area, of each sub-basin.
The percent forested area of each sub-basin was computed using land cover in f ormation obtained i n a G I S format from the US D A Data Gateway and the Canadian Counci l on Geomatics Geo-Base website. The Co l umbia River waters h ed above CGS, the Yakima River watershed, and the Snake River watershed are located within the Co l umbia River Region HUC 017. The HUC system is a consisten t hierarchica l dataset that contains drainage bas i n boundaries on four p r imary leve l s , i ncluding reg i ons, sub-regions , accounting units , and cataloging units. The Columbia Ri ver watershed above CGS is divided i nto two HUC sub-regions , including t he U pper Columb i a (HUC 1702) and the Koo t enai-Pend Orei ll e-Spokane (HUG 1701 ). An additional sub-region contributing to the Columbia watershed located entirely in Canada was identif i ed as the Headwaters Columbia, but is not included in the HUC data set. The H eadwaters Co l umbia sub-region boundary i s defined by the Ca n adian Na t ional H ydro Network (NHN). The Snake River watershed is divided into three sub-regions including the Upper Snake (HUC 1704), the Middle Snake (H UC 1705), and the Lower Snake (HUC COLUMB I A GENERA TI NG STA T ION Pa g e 29 of 55 NTT F Recommendation 2.1 (Haza rd Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 1 706). The Yakima R i ver watershed is one sub-region (HUC 1703). All the rivers HUCs and watershed boundaries are shown in F i gure 5. HUC sub-region and cataloging unit boundaries were downloaded in G I S format from the USDA Geospatial Data Ga t eway (Reference
- 18) and imported for u se into ArcGIS. H UC boundary data are in the U niversal Transverse Mercator (UTM) Zone 11 N coordinate system, and refe r ence the hor i zontal North American Datum of 1983 (NAO 83). Bou n daries f or the Headwaters Columbia subreg i on and sub-sub-drainage (the equivalent of a cata l og i ng unit i n the HU G system) located in Canada were obtained i n ArcG I S format fro m the NH N as provided by the Nat io nal R esou r ces Canada Earth Sciences Sector Center fo r Topographic I nformation Geo-Base website. Sub-basins i n each s u b-reg i on were defined by first using and reviewing the HUC cata l oging un i ts and N H N sub-sub-drainages.
Based upon drainage area or the l ocation of major dams some cataloging units/s ub-sub-drainages were either combined or subdivided. USGS topographic maps for t he U nited States we r e accessed through the ArcG I S USA Topo Maps Map Server and used to sub-divide and ref i ne HU C cata l oging unit areas using ArcGIS. Subdivision of Canadian dra i nages was conducted using the National Topographic Database available from the Canadian data server GeoGratis.
A shape file containing a ll sub-basin boundaries was developed using ArcG I S for use in PMP calculations.
The s ub-basin G I S shape f ile references the UTM Zone 11 N coordinate system and the horizontal NAO 83. All sub-bas i ns with drainage areas less than 1 0 ,0 00 square mi l es were defined. The Co l umbia River wate r shed is divided into sub-basins, and these sub-basins are grouped into three (3) sub-wa t ersheds (Columbia , Yakima, and Snake River). The sub-watersheds were selected to have similar hydrometeorolog ic al characteristics , based on location of major tribu t aries to the Columbia River and location of U SGS stream gages located on the m a in stem of the Columbia River. The sub-wa t ersheds were divided i nto n i ne sub-regions. The location of the CGS watershed is within the domain of the H MR-57 guidan c e. Generally, the allseason P M P is determ i ned using genera l ized P M P estimates derived from HM R-57 gu i dance. H owever , the use of H M R-57 for developing PM P values is not app l icab l e due to its wate r shed area size limitation of 1 0 , 000 square mi l es (maximum). The watersheds analyzed in the PMP and PMF analysis are id e nt i fied in Figure 5 and are as follows:
- Columbia (98 , 000 sq. miles)
- Yakima (6, 1 56 sq. miles)
- Snake River (108 ,0 00 sq. m i les) COLUMB I A GENERA TI NG STA T ION Pa ge 30 of 55 NTT F Recommendation 2.1 (Hazard Reevalua tio ns): F looding Energy Northwest Columb i a Generating Station A *-==i***=====-*** M i les 0 25 50 100 150 200 September 27, 2016 Revision 0 Figure 5. Columbia , Snake , and Yakima Sub-watershed Map COLUMB I A GENERA TI NG STA T ION Page 3 1 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station T he method of analysis for determining the PMP included the following:
September 27, 2016 Revision 0
- Develop a method or strategy to calcu l ate PMP based on HMR-57 guidance and limitation of 10,000 square miles.
- Calculate site-specific depth-area-duration data for various PMP storm centers.
- Calculate 6-hour incremental 72-hour PMP values.
- Calculate 100-year snowpack and snowmelt rates for cool-season PMP. A 10,000-square-mile PMP storm was placed at different locations throughout each sub-watershed to determine which storm center produces the critical PMF. HEC-HMS hydrologic models were developed for each of the sub-regions identified in the above sub-watersheds.
F or sub-watersheds , with total drainage area of approximately 10 , 000 squa r e mi l es, PMP storms were conservat i vely placed over the most downstream sub-watershed. I f a sub-region has a total drainage area less than 10 , 000 square miles , the PMP was applied to the entire sub-regional area. The purpose was to calculate PMP values applicable to the entire contributing watershed of the Columbia River upstream of CGS. This included an all-season and cool-season (rain-on-snow) PMP analysis. 3.2.3.2 1 00-year Snowpack and Snowmelt T he 100-year snowpack for the watershed is calculated from h i s t oric snow depth data from 3 11 weather gages located throughout the watershed with pe r iods of record greater than 25 years, ca l culated on a sub-watershed level. The 100-year snowpack is ca l culated by applying the F i sherTippett Type I (F T-I), or more commonly named Gumbel distr i bu t ion , to the snow depth data at each gage. T his is judged to be a conservative approach fo r the large watershed, as the actua l recurrence interval for each gage to have a coincident 100-year snowpack for the entire area of the watershed is likely to be greater than one in one hundred years. T he coo l-season PMP is considered to be an April event. T he T hiessen polygon method is used to calculate the 1 00-year snowpack for each sub-watershed by using an area-weighted average of the 100-year snow depth from t h e stations. Snowme l t is included in t wo o f the a l ternatives , and is determined using the USAGE energy budge t method. The energy budget method acco u nts for six (6) external sources of heat energy t ha t contribute to snowmelt.
The energy budget method yields a set of six e quation s; the selection of the appropriate equa t ion is dependent upon a rain-on-snow or rain-f ree me l t period and the percent forest cove r w i thin the d r a i nage area. The available water in the snowpack is calculated based on Federa l Energy Regu l atory Commission (FERC) guide l ines , which st i p ul ate: Water equivalence data are rarely recorded.
If total snowpack depth is available , assume a 100-year snowpack for the month of the cool-season Probable Maximum Storm and a starting water equivalence of 30 percent. 3.2.3.3 PMF Analysis (Reference
- 5) Altern a t i ve 1 -All-Season PMP (General Storm PMP (7 2-hr Storm)) The all-season PMF resulte d i n a flow of 2 , 897,000 cfs on Columbia River downstream of Snake Confluence based on scena r io No. 3 -Headwater Columb i a. COLUMB I A GENERA TI NG STA T ION Pa g e 32 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 An antecedent storm equivalent to 40 percent of the all-season PMP is app li ed to the HEC-HMS model with a 72-hour dry period between the antecedent stor m and the PMP event. The all-season PMP as described above is applied to the HEC-HMS model to determine flow hydrographs at key points in the model. T he all-season PMF is determined not to be the contro ll ing PMF scena r io and addit i onal combined event analysis is not performed.
Alternative 2 -Probable Maximum Snowpack (24-hr storm) and 100-Year Cool-Season Rainfall The 100-year rainfall wou ld be significant l y less rainfall t han the PMP , resulting in the majority of the snowmelt occurring as r ain-free. The rain-free snowmelt rates are typically close to or lower than the verif i ed constant losses for each sub-watershed; therefore , most of the snowmelt would be lost through the constant losses and would not be ava i lable for runoff. For similar reasons , given the large size of the CGS watershed (approx i mately 212, 1 56 square miles), calculating the probab l e maximum snowpack covering the entire watershed from the cool-season PMP precipita t ing as snow would result in comparable snow-water equivalent available for melt i ng as the snow-water equivalent to be used i n Alternative
- 3. Thus, t his alternative is not the controll i ng fl ooding scenario at CGS. Alternative 3-100-Year Snowpack and Cool-Season PMP Two different time periods, includ in g the months of November th r ough February and the month of March, are utilized per the PMP data. Both data se t s were evaluated by sub-basin.
The time period with the highest coo l season PMP on 100-year snowpack was selected for use in the HEC-HMS modeling.
Five tempora l dist r ibutions of the hourly incremental precipitation data were utilized in the hydrologic model to determine the critical PMF. The 100-year snowpack and a cool-season PMP resulted in t he controlling PMF at CGS. 3.2.3.4 Hydroloqic Model (HEC-HMS) USAGE HE C-H MS hydrologic software is used to co n vert rain f all to runoff. Rainfall is appl i ed to each sub-watershed and transformed to runoff using the Clark unit hy drograph methodology.
The subwatershed parameters are c a librated and validated with his t oric extreme events for which sufficien t stream flow and rainfall data are available.
The H EC-HM S software is used to model and calibrate Clark unit hydrograph para m eters and Muskingum-Cunge reach routing parameters. Baseflow is obtained from gage data and monthly average base flow i s used in t he H EC-HMS model. Mean Monthly base flow for Co l umbia , Yakima , and Snake Rivers was determined using USGS gage data. Base flow was determined by calculating the average monthly d i scharge. The highest average mean monthly base flow was applied as a constant inflow within each HEC-HMS model. The unit hydrographs for each sub-watershed are then modified to account for the effects of nonlinear ba s in response in accordance with NUREG/CR-7046 (Reference 23). The peak of each unit hydrograph is increased by one-fifth (20%) and the time-to-peak is reduced by one-third (33%). The remaining hydrograph ordinates are adjusted to preserve the runoff vo l ume to a unit depth over the drainage area. In this case, hydrographs with nonlinear basin adjustment resulted in lower flows. COLUMB I A GENERA TI NG STA T ION Pa g e 33 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 Therefore, to be conservative , hydrographs without nonlinear adjustments are used in the PMF analysis.
The HEC-HMS modeling conservatively assumes no precipitation losses , no accounting for reservoir storage, and coincidental flooding occurring on adjacent rivers contributing to the Columbia River. The PMF runoff hydrographs computed in HEC-HMS due to PMP were combined with a constant inflow of lesser flood events occurring in adjacent drainages to develop the most conservative WSEs on the Columbia River at CGS. Resulting WSEs due to the PMF on the Columbia River were then compared with the lowest elevation of critical facilities at CGS. 3.2.3.5 Hydraulic Model (HEC-RAS) The HEC-RAS hydraulic model requires:
- Columbia River Topography
-The DEM from the USGS National Elevation Dataset (Reference
- 19) and used to develop model geometry.
- Aerial Photography
-Aerial photography obtained from the USDA Geospatial Data Gateway was used to get landmarks and verify Manning's n-values utilized in the model.
- Critical PMF peak discharge profiles and hydrographs were determined from HECHMS modeling results.
- Downstream boundary conditions
-Normal depth of flow was utilized for the downstream boundary condition in HEC-RAS. The controlling PMF scenario is determined to be from Alternative 3, a snow or cool-season PMP with a 100-year snowpack. The steady flow module within HEC-RAS model is used to perform steady state backwater computation for a sub-critical flow regime and to transform the resulting flow hydrographs from the controlling alternative into a WSE hydrograph under steady flow conditions.
The HEC-GeoRAS extension for ArcGIS was used to construct the hydraulic model geometry , based on including PMP events occurring in the Columbia watersheds of interest.
The scope of the RAS model is based on landmark locations and features influencing the PMF analysis, such as dams and main rivers, which provide natural breakpoints.
The hydraulic model includes 156 miles of the Columbia River starting about 50 miles downstream of McNary Dam , extending upstream to Priest Rapids Dam. Therefore , the downstream boundary condition location is approximately 100 miles downstream of CGS, so that the model accounts for backwater effects due to the Wallula Gap and the McNary Dam. F i gure 6 provides a map showing HEC-RAS cross sect i on locations between CGS and McNary Dam. Hydraulic modeling assumes that McNary Dam is inoperable and incapable of passing flow through its various outlets, spillways, and lock facilities.
The HEC-RAS model assumes that all Columbia River flows overtop McNary's main channel concrete crest and overbank earthen embankments.
In other words, the dam is conservat i vely assuming that that flow would overtop and not pass through at lower elevations.
This overtopping elevation is also conservative since COLUMBIA GENERATING STATION Pa g e 34 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 the flows from the three river sources are directly combined.
Th e model also assumes that McNary Dam remains i ntact and does not fail during the PMF event. The PMF flow hydrographs are entered into the HEC-RAS model at the upstream end of the mode l and at the intermediate points representing other tributary rivers/streams using the " Lateral Flow" tool in HEC-RAS. The HEC-RAS model is evaluated using steady-state flow for cool-season PMP (Alternative 3), which is the controlling scenario for CGS. Hydraulic modeling results were reviewed for PMF events occurring in each watershed individually.
Results in each watershed were then compared to determine which event produces the highest WSEs near CGS. To demonstrate impacts at CGS due to the PMF event, WSEs at Cross Section 302788 (or OT#2) and Cross Section 281758 (or OT#1) were compared with the overtopping elevation of the west bank (HEC-RAS right bank). Cross section locations and identification of OT#1 and OT#2 are provided in Figure 6 , and the Columbia R iver PMF water surface profile is shown in Figure 7. Cross section 302788 is adjacent to CGS at OT#2. WSEs at this cross section would have to be at or above an elevation of 441 ft-NAVO 88 (437.6 ft-NGVD 29) in order to spill water into CGS local basin , west of the Columbia R iver's west bank (HEC-RAS right bank). Cross sec tion 281758 i s loca te d ju s t downstream of CGS at OT#1. WSEs at this location would have to be at or higher than an elevation of 437.9 ft-NAVO 88 (434.5 ft-NGVD 29) in order to overtop the west bank (HEC-RAS right bank) and spill water in to CGS local basin. COLUMBIA GENERATING STATION Page 35 of 55 NTTF Recommendation 2.1 (Hazar d Reevalua t ions): F looding Energy Northwest Columb i a Generating Station Not e: All e l e vat io ns reference th e North American Vertical Datum of 1988 (NAVD88). OT#3 .... E l ev '!I. ..s*.s Figure 6. HEC-RAS Model Cross Section Locations COLUMB I A GENERA TIN G S TAT ION September 27, 20 1 6 Revision 0 Pa ge 36 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
F looding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 00 00 i 8 'ii > .. Ill 500 450 400 E 8 "' 350 -0 *a. "' cc ., *c: a. 300 ' ' ' ' ' ! I ' ' ' ' ' I ----: ' ' ' i ' . . -:-' ' ' ! ' ' ' ' __,_ ' ' ' -+----: ' y-... I I t t " ! ~L ! E: --------I I.. -a. J!l "" \.. a, (Q (J 1 , +-----1 t--~~=-; ----.,.,i-=-------< bi ,_ _:;;: > ' I---_;~ ! ! 250 0--------0-----+-----~----+-------o------f--------l 600,000 500,000 400,000 300,000 200,000 100,000 0 -100,000 Columb ia R i v er Stream Di sta nc e (f ee t) -Co l um bla PM F Water Surface ---Y akima PMFWaterSurface
--SnakeP M FWaterSurface
-Channe l Thalweg -CGS Site Loca ti on , Critica l Elev 4 44.4
- Overtoping Point #1, E l ev 437.9 o Overto pp ing Poin t 11 2 , E l ev 44 1
- Ove rt opplng Po in t#3, E l ev 46 4.8 o Overtopping Po i n t 114 , E l ev 4 74.4 3.2.3.6 Figure 7. Columbia River PMF Water Surface Profiles Local Drainage Basin PMF (Reference
- 9) PMF due to PMP was analyzed for the 40.5-square-mile local drainage basin at CGS. Review o f topography and aerial photographs indicate that the loca l basin is topographically closed and does not have a defined waterway, creek , or river running through it. El evations in the basin range from a minimum of 409.3 ft-NAVD88 up to a maximum of 594 ft-NAVD88 , with an out l et elevation o f 437.9 ft-NA VD88. CGS is located in a depression that will fill up and store water before water spills out of the basin. Topographic data indicate that the basin i s capab l e of storing approximately 31,000 acreft of water with a maximum depth of 28.6 ft befo r e flow reaches the basin outlet and spills towards the Co l umbia River. The PMP calculat i ons for the local drainage basin were conducted u sing the current applicable guidance contai n ed in HMR-57. F our alternat iv e PMP storms were developed for input to hydrologic modeling per ANS guidance provided in NUREG CR-7046. T he stepw i se procedure used to calcu l ate the l ocal storm PMP can be found in Section 15.4 of HMR-57. Loca l storm PMP estimates can be determined for durations between 1 5 minutes and 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> applicable to storm areas of 1 to 500 square miles. The local storm PMP was computed for the CGS local basin and used as input to precipitation computations as part of the PMF analysis.
L ocal storm PMP va l ues were computed in 1 5-minute increments for a 6-h our storm durat i on. Five different temporal distributions of th e 15-minute COLUMB I A GENERA TI NG STA TI ON Pa g e 37 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 incremental local storm PMP values were developed.
Distributions include centering the highest 15-minute incremental value at the front, one-third, center, two-thirds, and end position within the storm duration, while placing the next highest values on alternating sides of the highest 15-minute value. Hydrologic modeling of the local drainage basin was developed using the USACE's HEC-HMS computer software.
The hydrologic model computes direct runoff of PMP storms , assuming no losses, no infiltration, no rainfall-to-runoff transformation, and no routing. PMP storm volumes were found to be less than the volume of storage available in t he basin below the elevation of the basin outlet. This indicates that runoff due to PMP can be stored in the local basin without any outflow, eliminating the need to develop hydraulic computations.
The HEC-HMS model used an versus-storage relationship developed from basin topography to compute PMF WSEs as a result of direct runoff due to PMP. CGS local basin was split into two sub-basins, one upstream of CGS (or north of CGS with a drainage area of 26.7 sq. miles) and one downstream of CGS (or south of CGS with a drainage area of 13.8 sq. miles). The HEC-HMS model applies the PMP to both sub-basins.
Both sub-basins are connected to a reservoir storage element in the HEC-HMS model. The reservoir storage element applies an elevation-versus-storage relationship developed from basin topography to compute PMF WSEs as a result of direct runoff due to PMP. The elevation-versus-storage relationship was calculated using 10-meter DEM data in ArcGIS. The CGS local sub-basins are identified in Figure 8. Four PMP alternat i ves were run in the local drainage basin HEC-HMS model: 1. General storm PMP with antecedent storm equal to 40 percent of the PMP 2. 100-year rainfall on probable maximum snowpack 3. Cool season PMP on 100-year snowpack 4. Local storm PMP The PMP was input into the HEC-HMS hydrolog i c model in the form of incremental hyetographs.
All five temporal distributions of each alternative precipitation event were included in the HEC-HMS modeling, resulting in a total of 20 different precipitation simulations.
Multiple HEC-HMS runs of alternative precipitation with varying temporal distributions were included to determine which event results in the most critical PMF WSE. COLUMBIA GENERATING STATION Pa g e 38 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations
): Flood ing Energy Northwest Columbia Generating Station Legend
- Columbia Genera t ing Stat i on c:::::J L oca l Dra in age Basin 0.75 1.5 Mil .. Figure 8. CGS Loc a l Dr ai n age Basin COLUMB I A GENERA TI NG STA T ION September 27, 2016 Revision 0 Page 39 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station 3.2.4 Results September 27, 2016 Revision 0 Calculation of the Columbia River PMF considered PMP events occurring in various locations throughout the Columbia, Yakima, and Snake River watersheds.
- The Columbia River PMF is a combinat i on of runoff from PMP occurring in the Headwaters Columbia sub-region with a discharge of 2 , 560,000 cfs, a 500-year flood on the Yakima River with a discharge of 97,000 cfs, and a peak historic discharge of 312 , 000 cfs on the Snake River. The total discharge at the Wallula Gap constriction is 2 , 969 , 000 cfs. The PMF water surface elevations on the Columbia River near the CGS show a water surface elevation of 412.2 ft-NAVO 88 (408.8 ft-NG VD 29) at OT#1 (Cross Section 281758) and 415.2 ft-NAVO 88 (411.8 ft-NGVO 29) at OT#2 (Cross Section 302788 -adjacent to CGS). The water surface elevation at OT#1 is 25.7 ft below the overtopping elevation of 437.9 ft-NAVO 88 (434.5 ft-NGVD 29), which indicates that water will not spill into the local basin. Similarly , the water surface elevation at OT#2 is 25.8 ft below the overtopping elevation of 441 ft-NAVO 88 (437.6 ft-NGVO 29). Results indicate that there is a minimum of 25.7 ft of freeboard on the west bank (HEC-RAS right bank) of the Columbia River near CGS.
- The Yakima River PMF is a combination of runoff from PMP occurring in the Yakima watershed with a discharge of 1,056 , 000 cfs, the un-regulated standard project flood on the Columbia River of 740,000 cfs , and a peak historic discharge of 312,000 cfs on the Snake River. The total discharge at the Wallula Gap constriction is 2,108 , 000 cfs. PMF water surface elevations on the Columbia River near the CGS show a water surface elevation of 401.6 ft-NAVO 88 (398.2 ft-NGVO 29) at OT#1 (Cross Section 281758) and 402.2 ft-NAVO 88 (398.8 ft-NGVD 29) at OT#2 (Cross Section 302788 -adjacent to CGS). The water surface elevation at OT#1 is 36.3 ft below the overtopping elevation of 437.9 ft-NAVO 88 (434.5 ft-NGVO 29), which indicates that water will not spill into the local basin. Similarly, the water surface elevation at OT#2 is 38.8 ft below the overtopping elevation of 441 ft-NAVO 88 (437.6 ft-NGVD 29). Results indicate that there is a minimum of 36.3 ft of freeboard on the west bank (HEC-RAS right bank) of the Columbia River near CGS.
- The Snake River PMF is a combination of runoff from PMP occurring in the Upper Snake sub-region with a d i scharge of 2 , 860,000 cfs, the un-regulated standard project flood on the Columbia River of 740 , 000 cfs, and a 500-year flood on the Yakima River with a discharge of 97,000 cfs. The total discharge at the Wallula Gap constriction is 3,697 , 000 cfs. PMF water surface elevations on the Columbia River near the CGS show a water surface elevation of 415.2 ft NAVO 88 (411.8 ft-NGVO 29) at OT#1 (Cross Section 281758) and 415.4 ft-NAVO 88 (412.0 ft-NGVO 29) at OT#2 (Cross Section 302788 -adjacent to CGS). The water surface elevation at OT#1 is 22.7 ft below the overtopping elevation of 437.9 ft-NAVO 88 (434.5 ft-NGVD 29), which indicates that water will not spill into the local basin. Similarly, the water surface elevation at OT#2 is 25.6 ft below the overtopping elevation of 441 ft-NAVO 88 (437.6 ft-NGVO 29). Results indicate that there is a minimum of 22.7 ft of freeboard on the west bank (HEC-RAS right bank) of the Columbia River near CGS. COLUMBIA GENERATING STATION Pa g e 40 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 Comparison of results from each watershed PMF indicates that the Snake River PMF produces the highest water surface elevations on the Columbia River near CGS. Results are driven by the tota l discharge in the Columbia River at the Wallula Gap constriction, which creates backwater effects upstream past CGS. The time (based on the HEC-HMS simulation) for the discharge to peak on the Columbia River at the Wallu l a Gap constriction is 1 day , 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> , and 45 minutes. Water surface elevations from HEC-RAS modeling of the Snake River PMF were used to conduct inundation mapping on the Columbia River near CGS. Inundation mapping of the critical PMF water surface profile (from the Snake River PMF) was conducted using the 10-meter DEM in ArcGIS. Inundation mapping of the water surface elevations on the Columbia River near CGS associated with the Snake River PMF is shown in Figure 9. The inundation mapping shows that the west bank (HEC-RAS right bank) of the Columbia River near CGS is not overtopped , and CGS local basin remains dry during the PMF on the Columbia River. The flooding results for the PMF do not encroach on CGS. Therefore, no associated effects are determined.
Analysis of the PMF due to PMP occurring in CGS local basin is addressed in a separate calculation entitled Local Drainage Basin PMF Analysis for CGS, Calculation No. CE-02-13-27 (Reference 9). The critical PMF peak water surface elevation of 435.4 ft-NAVO 88 (432.0 ft-NGVD 29) was compared with CGS critical facilities elevation of 444.4 ft-NAVO 88 (441 ft-NGVD 29), indicating that there is approximately 9.0 ft of freeboard during the crit i cal PMF event. Inundation mapping of the cr i tical PMF WSE of 435.4 ft-NAVO 88 associated with Alternative 1 precipitation was conducted using the 10-meter DEM and ArcGIS. Critical PMF inundation mapping is provided in Figure 10. From the onset of the PMP storm , the maximum water surface elevation is reached in 69 hours7.986111e-4 days <br />0.0192 hours <br />1.140873e-4 weeks <br />2.62545e-5 months <br />. The flooding results for local basin do not encroach on CGS. Therefore, no associated effects are determined.
The groundwater table elevation at CGS is approximately 380 tt-MSL. The groundwater design basis is 420 ft-MSL. The peak effects of the PMP event occur over a relatively short duration.
Therefore , changes to the groundwater design basis level are not expected. However , all p i ping and electric conduit penetrations that are below grade are waterproof sealed. COLUMBIA GENERATING STATION Pa g e 41 of 55 NTTF Recommendation 2.1 (Ha zard Reevaluations
): Flooding Energy Northwest Columbia Generating Station {c CGS S it e Loca~on A Ove r topping Location .rv-Rive r Cross Sec t i ons PMF I n unda ti on Area 0 0.75 1.5 3 M*1 \ -,, 1 es . ~LJ. Note: A ll elevations reference the North 1 \ American Vertical Datum of 1988 (NAVD88). September 27, 2016 Revision 0 Figure 9. Columbia River near CGS Inundation Map -Snake River PMF COLUMB I A GENERA TI NG STA TI ON P age 42 of 55 NTTF Recommendation 2.1 (Ha zar d Reevaluations
): F looding Energy Northwest Columbia Generating Station Legend
- Columbia Genera t ing Stat i on -L oca l PMF I nundat i on Area t::J L oca l Drainage Basin 0.75 1.5 Mi l es Figure 10. Local Drainage Basin PMF Inundation Map COLUMB I A GENE RATIN G STATION September 27, 2016 Revision 0 Pa ge 43 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station 3.3 Dam Breach es and Failures (Reference
- 25) September 27, 2016 Revision 0 The dam failure analysis for the Columbia Riv e r watershed was performed by the USAGE under For Official Use Only (FOUO) r estrictions (Reference 25). T h ere f ore, deta ils of the ana l ysis are no t provided. Ons it e impoundments are located southeast and northeast of the power block. The power block is located at a higher elevation than the ponds. The t opography slopes away from the power block to the east. T herefor e, potentia l failure of the onsite impoundments would release impounded water away from the power block into the adjacent depression of the local drainage basin discussed in Section 3.2. 3.3.1 Results (b)(3) 16 U.S C § 824o-1(d),(b)(4),(b)(7)(F)
3.4 Storm
Surge CGS h as an in l and location and does not connect directly with any of the water bodies considered for meteorological events associated with storm surge. Therefore , flooding due to a storm surge is not applicable at CGS. 3.5 Seiche CGS has an inland location and does not connect directly with any of the water bodies considered for meteorologica l events associated with seiche. Therefore, flooding due to a seiche is not applicable at CGS. 3.6 Tsunami CGS has an in l and location and does not connect directly with any of the water bodies considered for T s unami events. Therefore, f l ooding du e to a tsunami is not app licabl e at CGS. 3.7 Ice Induced Flooding (R e ference 6) As identified by NUREG/CR-70 46 (Reference 23), ice jams and ice dams can form in rivers and streams adjacent to a site and may lead to flooding by two mechanisms
- Collapse of an ice jam or a dam upstream of the site can result in a dam breach-like flood wave that may propagate to the site and,
- An ice jam or a dam downstream of a site may impound water upstream of itself, thus causing a flood via backwater effects. 3.7.1 Basis of Inputs Calculation inputs include the following:
COLUMB I A GENERA TI NG STA T ION Page 44 of 55 NTT F Recommendation 2.1 (Haza rd Reevaluations):
Flooding Energy Northwest Columbia Generating Station
- U SAGE I ce Jam Database.
September 27, 2016 Revision 0
- Historica l ice j am information was obtained from the USAGE I ce Jam Database. 3.7.2 C om puter Softwar e P r o gra m s
- Arc G I S 10.1
- VERTCON 2.1 3.7.3 M e thodology I ce-induced flooding is assessed by reviewing the USAGE national ice jam database to determ i ne the most severe his t orical events that have occurred on the Columbia River , in the vicinity of CGS. As discussed in Calculat io n CE-02-13-20 (Reference 6), the period o f historical i ce jam reco rd i s available from 1919 through January 2011. The ice jam height was calcu l ated as a recorded gage height due to ice jam mi n us the base f l ow i n t he stream. T he maximum ice jam height was selected.
The peak eleva t ion of recorded ice jam flooding minus the normal surface water elevation at tha t location is assumed to represent the fu ll height of the ice jam at the recorded loca tion. The historic ice-induced flood is calculated to be the result from the February 2 , 2009 , ice jam occurring in T wisp , Washington, recorded on the Methow Rive r in Twisp. T he maximum ice jam is determined by selecting the histo r ic event that produced the maximum flood stage relative to the norma l WSE at that l ocation. R ega r dless of spec i fic cond i tions that produced the historic flood stage at a specific location, t he fu ll height is conservatively assumed to represent the ice jam. The maximum ice jam height occurring on the Methow River near Twisp is transposed to CGS. This approach is conservative as it maximizes the ice jam in the immediate v i cinity of CGS. An upstream ice jam can cause flooding by impounding water and then collapsing.
T he nearest probable location for an upstream ice jam is the Vernita Bridge on State H ighway 24, approximate l y 36.7 mi l es upstream of CGS. A downstream ice jam can cause flooding by impounding water and then creating backwater effects. The nearest applicable location for a downstream ice jam is the bridge on I nterstate 1 82 in Richland, Washington , approximate l y 1 6.1 miles downstream of CGS. T he locations of the upstream and downstream bridges are shown in F i gure 11. The results o f the ice jam e f fects are compared to the finished f l oor elevations of CGS and to t h e resulting flood elevations from the PMF and dam fa i lure analyses to demonstrate that ice jam flooding is bounded by these flooding mechanisms.
COLUMB I A GENERA TI NG STA T ION Pa ge 45 of 55 NTI F Recommendation 2.1 (Hazard Reevaluations
): F looding Energy Northwest Columb i a Generating Station September 27, 2016 Revision 0 Figure 11. Upstr ea m and Downstream Bridge Locations for Ic e Jam COLUMB I A GENERA TI NG S T A T ION Pa ge 4 6 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station 3.7.4 R es ult s September 27, 2016 Revision 0 The maximum WSE at CGS resulting from the upstream ice jam breaching was ca l culated to be 419.9 ft-NAVO 88 (416.5 ft-NGVD 29), which is more than 24 ft below CGS grade of 44 1 ft-MSL. The maximum WSE at CGS resul t ing from backwater from a downstream ice jam is 362.8 ft-NAVO 88 (359.4 ft-NGV D 29), which is more than 81 ft below CGS grade of 441 ft-MSL. The upstream and downstream ice jam l ocations are identified in Figure 12. The ice jam elevation near CGS was determined to be 365.5 ft-NAVO 88 (362.1 ft-NGVD 29), which is more than 78 ft below CGS grade of 441 ft-MSL. The resulting flood elevation from the PM F analysis (Refere n ce 5) is 4 1 5.4 ft-NA VD 88 ( 412 f t-NG VD 29). Note the upstream ice jam breaching resul t is bounded by the dam failure analysis performed by the USAGE under For Official Use Only (FOUO) restrictions.
By comparison , the ice jam effects are bounded by the P MF and Dam Failure f l ooding water surface e l evations and do not produce the flooding conditions for CGS. 3.8 Chann e l Migr a tion or Div e rsion (R e f e r e n ce 6) As ident i fied by NUREG/CR-7046 (Reference 23), Section 3.8 , there are no well-estab l ished predictive models for cha n nel divers i ons. Therefore , it is not possible to postulate a probable maximum channel diversion event. I nstead, h istorical records and hydro-geomorphologica l data should be used t o determine whether an adjacent channel , stream , or river has exhibited the tendency to meander towards CGS. Evidence of channel migration was examined using h i storical maps obta i ned from the USGS. Topographic map of 2011 was used as the basis for comparison as it reflects current conditions (at the time of development o f Calcu l ation CE-02-13-20).
H is t orica l topographic maps from the years o f 1917, 1951, 1978 , and 1992 are downloaded from the USGS store and compared to the current topographic map of 2011 (Reference 6). The historical map of 1917 , which is assumed to be based on a hand drawing , shows a small discrepancy in the boundaries of the river banks and islands with a maximum difference of 0.18 mile, w h en compared t o the topographic map of 2011. The othe r maps represent almost the same river bank and island boundaries when compared to the current map. Therefore , i t is concluded that there is no evidence of channel migration at CGS and its vicinity.
3.9 Comb i ned Eff e ct Flood (In c luding Wind Gen e rated Waves, R e ference 7) The criteria for combined events are provided in N UREG/CR-7046 (Reference 23). The combined even t s incorporate the flood causal mechanisms previously discussed for precipitation events and hydrologic or seismic dam fa i lures. Each combined event also incorporates waves induced by 2-year wind speed app l ied a l ong the critica l direction. Based on the resu l ting water surface e l evations previously discussed, basin topography is used to develop the fetch lengt h. The 2-year wind speed is determined us i ng the ANS I/ANS-2.8-1992 guidance (Reference 1 ). COLUMB I A GENERA TI NG STA T ION Pa g e 47 of 55 NTT F Recommendation 2.1 (Haza rd Reevaluations):
Flooding Energy Northwest Columbia Generating Station 3.9.1 B as i s of Inpu ts September 27, 2016 Revision 0
- Aerial Photography
-National Agricultural Imagery Program (NA I P) aeria l photography obtained from the U.S. Department of Agricu l ture (USDA) Geospa t i a l Data Gateway (Reference
- 18) was used for i nundation mapping (Reference 7).
- Basin Topography meter DEM used in t he de t ermination of Columbia River PMF WSE was used (Reference 5). The 10-meter DEM references the State Plane Washington South horizontal coordinate system and NAO 83 and N AVO 88.
- CGS Structu r es -CGS structures such as buildings , VBS , and other related faci l ities were obtained from the effects o f Local I ntense Precip i tation Calculation CE-02-1 3-22 (Reference 8).
- The L oca l Drainage Basin PMF was determined i n calcu l ation CE-02-1 3-27 , L oca l Drainage Basin PMF Analysis for CGS (Reference 9).
- The controlling dam failure WSE for Colu m bia River was determined by the USACE under FOUO restrictions (Reference 25). 3.9.2 Comput e r Softw a re Prog r am s ArcG I S 10.1 3.9.3 Methodology Coincident Wind-Wave Activity The simplified method for wave forecast i ng as outlined in the USACE Coastal Eng i neering Manua l (Reference
- 17) is used to determ i ne the inputs (significant wave height , wave period , wind speed , and wave le ngth) for calcu l ating the wave runup at CGS (Reference 7). The wave se t up is the elevat i on of the water surface due to wave action , i n particular , wave breaking.
Wind set u p i s the effect of the horizontal stress of the wind on the water , driving it i n the direction of the wind. Based on the maximum water surface elevation from the flooding analysis , the l ongest critical st r aight line fetch is dete r mined. T he 2-year wind speed is appl i ed to the straight l i n e fetch to develop the wind-wave characteristics. I n accordance with N U REG/CR-7046 (Reference 23), different external f looding mechanisms are combined to calculate the maxim u m WSE including coincident wind-wave activity at CGS. The results of the combined events analysis (Reference
- 7) yielded that floods caused by precipitation events ba se d on th e following combination of mechani s m resulted the h ig he st water l evel: * (b)(3) 16 USC § 824o-1(d),(b)(4),(b)(7)(F)
- L ocal D rainage Basin P M F coincident with wave induced by 2-year wind speed applied a l ong the cr i tica l fetch d i rection. T his corresponds to the local drainage Basin PMF WSE of 435.4 ft-NAVO 88 (Reference 7). COLUMB I A GENERA TI NG STA T ION Pa ge 48 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 3.9.4 Results The following summarizes the resu l ts of the combined events analysis (Ref erence 7) for CGS: Wind-Wave Activity
- Th e maxim um combined eve nt s WSE for the CGS is determined by addi ng th e wind setup and w i nd-wave run-up , including wave setup , to the local drainage PMF WSE and Dam Failure Maximum WSE (PMF WSE + wind setup + runu t at C~S. The maximum dam failure WSE including coincident wind-wave activity i * . t.NG~;J:~(~),~b~
- 29. (4),(b)(?)(F)
- The maximum combined events WSE for the local drainage basin PMF i s determined by adding the wind setup and wind-wave run-up , including wave setup , calculated for the local drainage basin PMF to the resulting WSE due to local drainage basin PMF. The maximum WSE of the local drainage basin PMF including co i ncident wind-wave act ivity i s 433.3 ft-NGVD 29. (b)(3) 16 us c. Th erefor o ntrolling maximum WSE i s the dam failure scenar io coincident wi t h wind-wave Mr:i.1o-~{_altt activityts
-NGVD 29. When compared ~elevation of 441 ft-MSL , the maximum WSE r:~~~i>~~l(o)------::~~h;i::
at--CG-~-~~:~~~:~~.a~t~~yi~wt~;:
---~~-u~~i~:~o~ ;~u i~:~r:f~::t:h~
-~~~:!!i if(;l\~?b~-
WSE. 4. CONCLUSION As discussed in Section 3.0, se vera l flood causing mechanisms were considered following the guidance provided in NUREG/CR-7046 (Reference 23). In summary , the reevaluated flood elevation is e ith er below th e critica l e l evation of 441 ft-NG VD 29 ( 444.4 ft-NA VD 88) or does not impact any safety-re lat ed equipment.
The maximum WSE du e to the LIP event at CGS var i es between 435.14 ft-NGVD 29 and 443.27 ftNGVD 29. Areas where ma ximum WSE results exceed 441 ft-NGVD 29 are either not adjacent to safety-re l ated SSCs , or based on specific configuration at the survey point location, the results are do not compromise any safety-related SSCs. §824o-1 (o);(b) ThemaximumWSEduetoriverinefloodingls
ft-NGVD 29 , which includes dam f ai lure a nd (b)(3)16U.SC.
Q (4),(b)(?)(F) associated wind-wave activity.
The reevaluate , including coincident wind-wave activity is below the critical fa cility elevation of 441 ft-MSL. COLUMBIA GENERAT I NG STATION Pa ge 49 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station 5. COMPARISON WITH CURRENT DESIGN BASIS September 27, 2016 Revision 0 The reevaluated maximum water surface elevations due to the Columb i a River PMF, the Adjacent Drainage B asin P M F , dam failure, and the combined effect flood for dam failure w i th coinc i dent wave activity exceed the design basis. For each flood-causing mechanism that exceeds the design basis , the maximum water surface elevation is still be l ow the 441 ft-MS L crit i cal elevation at CGS. The reevalua t ed maximum water surface elevations due to ice-induced flooding are bounded by other flood-causing mechanisms and are below the 441 ft-MSL critical e l evation at CGS. The reevaluated maximum water surface elevations due to the LIP va r y between 435.14 ft-NGVD 29 and 443.27 f t-NG VD 29 at the designated protected area survey points. The reevaluated maximum water surface elevations at six of t he survey points slightly exceed the 441 f t-MSL critica l elevation at CGS. However , the six survey points are either not adjacent to safety-r elated SSCs , or based on specific configuration at the survey point l ocation, the results are inconsequential and do not compromise safety-related SSCs, as discussed in Section 3.1.4. During the flooding walkdowns conducted for Recommendation 2.3 , the fo ll owing was reported on November 12, 2012 i n l etter G02-12-164 (Reference 3): 1. T he safety-re l ated SSCs are bui l t within t h e Protected Area and at the Standby Se r vice Water Pumphouses at the finished floor slab of el. 441 ft-MSL. Be l ow-grade areas in the R eactor Bui l ding are a t slab el. 422 ft-3 inches MSL, and below-grade areas in the Pumphouses are at 43 1 ft-MSL. Penetrations in the Reactor Bui l ding's below-grade concrete walls were visually observed as sea l ed, and design-bas i s groundwa t er (420 ft-MSL) is below this level so n o hydrostatic loading is applied to t hese seals. Penet r ations in the Standby Service Water Pumphouses exposed to the design basis flood elevation of 433.3 ft-MS L were noted as sealed. Penetra t ions located below grade el. 441 ft-MSL a t exterior walls are above the groundwater el. of 420 ft-MSL. I n the safety-related structures, exterior concrete wa ll s showed no cracking equal or greate r than 0.04 i n ches that challenged the ability to wi th stand water infiltration.
- 2. No flood protection features were exc l uded from t he walkdowns.
N o degraded, conforming, or unanalyzed conditions credited for f lood protect i on were identified by the walkdown visua l i nspection.
There were no f l ooding hazard findings or actions that required entry into the Corrective Action Program (CAP). T here are no exterior incorporated or t emporary flood barriers or advance preparations of emergency f l ood-related equipment credited in the C L B for CGS. 3. CGS Si t e topography was noted to main t ain overall na t ural drainage profiles of the origina l C L B. No washouts or significant areas of erosion were found. Concrete, aspha l t, and grave l paved areas are we ll mainta i ned and no degraded areas were observed.
The perimeter concrete security barrier is not a hazard or obstruct i on relative to f l ooding. 4. The walkdown visual inspections of CGS site modifications and building flood protection measures required per the N RG-endorsed f l ooding wal k down guidel i nes we r e satisfactorily accomplished.
There was no restricted access or inaccessib l e features concerning related inspections.
COLUMB I A GENERA TI NG STA T ION Pa ge 50 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations):
Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 5. Energy Northwest chose to visually inspect accessible below grade penetrations , walls, and f l oors in the Reactor Building and the Standby Service Water Pumphouses , wh i ch house the SSCs important to safety. Below grade walls, floors , and penetration seals that were visually inspected were found to be in good cond i tion , with two exceptions.
There were two conduits in one of the Standby Service Water Pumphouses that did not have a visible seal viewed from the building side; the other side was in a buried duct bank and was not accessible.
The interiors of the conduits were clean and there was no dirt , corrosion, debris, o r evidence of water or i nsect intrusion from the outside. These exceptions are not deficiencies as defined in NEI 12-07 (Reference
- 12) because the conduit seals are not credited to perform an intended flood protection function. These two conduits are located above the design-basis groundwater elevation. In summary , the reevaluated maximum water surface elevations validate the current flood mitigation strategy of the current license basis, which states that CGS can be maintained in a safe condition for water levels up to 441 ft-MSL. Therefore , no interim actions are identified.
No additional actions are planned to address flooding hazards as the reevaluated maximum water surface elevations do not impact any safety-related structures.
The comparisons of existing and reevaluated flood hazards are shown in Table 3. COLUMBIA GENERATING STATION Pa ge 51 of 55 NTT F Recommendation 2.1 (Hazard R eevaluations):
F looding Energy Northwest Columb i a Generating Station September 27, 2016 Revision 0 T a bl e 3. Summ a ry of Cu r rent D es ign B as i s a nd Reev a lu a t e d Flood H aza rd El e v a tions C urren t D es ig n B asis Flo o d-C a u s ing F lood i ng H aza rd M ec h a ni s m E l evation s LIP Description in FSAR is very general and does not provide a WSE due to LIP for CGS. Flooding in Columbia River PMF i s Streams and 390 ft-MSL (at the Rivers (PMF) Seism i c Category I I m akeup water structure).
Adjace nt Drai nage Bas i n PMF is 431.1 ft.-MSL. Dam Br eac h es The FSAR considers the and Fai lu res effect of up s tream dam failure (from breaching Grand Cou l ee Dam) in l ieu of a seismically i nduced flood. Dam Fai l ure coinciden t with the Standard Project Flood i s 422 ft-MSL. Storm Surge Not spec ifi cally addressed in the FSAR. Seiche Not specifically addressed in the FSAR. Tsunami Not specifically addressed in the FSAR. COLUMBIA GENERA TI NG STA T ION C omp a ri s on T he result i ng WSE from this f lood-causi n g mechanism i s not described in the F SAR. N ot Bounded, but available physica l margin exists. N ot Bo unded , but ava il able physica l margin exists. N ot Bounded, but a vailable physical margin exists. Bounded* Bounded* Bounded* Flood H a z a rd R ee v a lu a t io n El evati on T he maximum WSE at the protected area survey po i nts varies between 435.14 ft-N GVD 29 and 443.27 tt-NGVD 29. T he corresponding calcu l ated maximum water depths vary between 0.03 ft a nd 0.79 ft. Areas where maximum WSE resu l ts exceeding 441 ft-NGVD 29 are either not adjace n t to safety-related SSCs, or based on specific configuration at the survey point location, the results are inconsequential a nd do not compromise sa f ety-re l ated SSCs. T he Columbia River reeva l uated critical PMF WSE of 412.0 ft-N GVD 29 is below t he critica l facility elevation of 441 f t-MSL. T he l ocal drainage basin reeva l uated crit i ca l P MF WSE of 432.0 ft-NGVD 29 is below th e critical facility elevation of 441 f t-MSL. T he cont T llin q d\m fai lur e WSE re*;~; ~;~!Y£f i~J l) be l ow the critica l faci li ty elevatio n SC ,(b) ) of 441 ft-M SL. Screened Out. Screened Out. Screened Out. P age 52 of 55 NTT F Recommendation 2.1 (Hazard R eevaluations):
F looding Energy Northwest Columb i a Generating Station Curr en t D es ign B asis Flood-Cau s ing Flooding H a z a rd M ec h a n is m E leva tion s C om p a ri so n Ice-I nduced As ind i cated in the The result i ng WSE from Flooding FSAR, ice f l oo d ing is this f lood-causi n g considered insignificant mechanism is not at CGS and in any described in the FSAR. event , ice f l ooding will not affect the capab il ity to shut down the reactor in a safe and orderly manner. Channel Migration As ind i cated in the Bounded. or Diversion F SAR, t h e r i verbed i s well defined near CGS , and th erefore , unlikely to be diverted from its present location.
Combi ned Effect Lo ca l Drainage PMF + Bounded. Flood Coincident W ind-Wave (including wind = 433.3 ft-MSL generated w aves) D am Fai l ure + Not Bounded, but Coinciden t Wind-Wave ava i l ab le physica l = 424 ft-MS L margin exis t s. September 27, 2016 Revision 0 F lo od H a z a rd R ee v a lu a tion El e v atio n Upstream br i dge i ce jam elevation is 416.5 ft-NGVD 29 Downstream bridge i ce ja m e l evat i on i s 359 .4 ft-NG VD 29 Ice j am e l evat i on n ear CGS is 362.1 ft-NGV D 29. Ice Jam elevations are bounded by PMF and Dam Fa i lure mechanisms and are below the c rit ical fac i lity elevation o f 4 41 f t-MSL. N o evidence of channel migration near CGS. L oca l Dr ainage PMF + Co i ncide nt W i nd-W av e = 433.3 ft-N GVD 29. Dam F u oincident Wind* Wave ..................
- NGVD 29. (b)(3) 16 L. The reeva u a ed WSE, i~ci J , R~;";l\<) SC ,(b) ) coincident w i nd-wave activity is below the crit i cal facil i ty eleva t io n of 441 ft-M SL.
- Since these mechanisms were screened ou t as part of flood hazard r evaluation , they were also cons i dered bo u n d ed by th e curr e nt d e sign b as is. COLUMB I A GENERA TI NG STA T ION P a g e 53 of 55 NTT F Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station 6. REFERENCES September 27, 2016 Revision 0 1. American Nuclear Society, ANS I/A N S-2.8-1992, American National Standard for Determining Design Basis Flooding at Power Reactor Sites, prepared by the American Nuclear Society Standards Com mi ttee Wo r king Group ANS-2.8, L a Grange Park , Illinois.
- 2. Northwest Columbia Generating Station Final Safety Analysis Report, Amendment 63, December 2015. 3. Energy Northwest, Columbia Flooding Walkdown Report , L etter 802-12-164, dated November 12 , 2012 , NRC Docket No. 50-397. 4. Energy Northwest Calculation No. CE-02-13-17 , Probable Maximum Precipitation (PMP) Analysis for Columbia Generating Station, Revision 0. 5. Energy Northwest Calculation No. CE-02-1 3-1 8, Prob able Maximum Flood (PMF) An alysis for Columbia Generating Station , Revision 0. 6. Energy N orthwest Calculation No. CE-02-13-20, Ice Effects and Channel Migration Assessment for Columbia Generating Station , Revision 0. 7. Energy N orthwest Calculation No. CE-02-1 3-2 1, Combined Flood Events Analysis for Columbia Generating Station , Revision 0. 8. Energy N orthwest Calculat i on No. CE-02-13-22, Effects of Local Intense Probable Maximum Precipitation An alysis for Columbia Generating Station (CGS), Rev ision 0. 9. Energy Northw est Calculation No. CE-02-13-27, Local Drainage Basin Probable Maximum Flood (PMF) Analysis for Columbia Generating Station, Revision 0. 10. (Energy Northwest , 2016g) Energy N orthwest Calculat i on No. CE-02-14-10 , Site-Specific Local Intense PrecipHation (LIP) Determination for Columbia Generating Station, Revision 0. 11. Federal Emergency Management Agency, FE MA P-259 , Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures, January 2012. 12. Nuclear Energy I nstitute (NEI), NEI 1 2-07 , Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features, Rev is ion 0 , May 2012. 13. Nuclear Energy I nstitute (NE I), NEl-1 2-08, Overview of External Flooding Reevaluations, August 2012. 14. National Oceanic and Atmospheric Administration, National Weather Service , U.S. Department of Commerce, Hydrometeorological Report No. 57 , Probable Maximum Precipitation
-Pacific Northwest States, Columbia River (including portions of Canada}, Snake River and Pacific Coastal Drainages , Silver Spring Maryla nd, 1994. 15. U.S. Army Corps of Engineers , EM 1110-2-1406, Engineering and Design , Runof f from Snowmelt , Washington , DC 20314-1000, March 31, 1998. 16. U.S. Army Corps of Engineers , EM 1110-1-1005 , Engineering and Design , Control and Topographic Surveying , Washington , DC 203 1 4-1000 , January 0 1 , 2007. COLUMB I A GENERA TI NG STA T ION P age 54 of 55 NTTF Recommendation 2.1 (Hazard Reevaluations
): Flooding Energy Northwest Columbia Generating Station September 27, 2016 Revision 0 17. U.S. Army Corps of Engineers, EM 1110-2-1100 (Part II), Coastal Engineering Manual , August 1 , 2008 (Change 2). 18. U.S. Geologica l Survey (USDA), Geospatial Data Gateway Website, available at https://datagateway.nrcs.usda.gov
/gatewayhome
.html, Accessed:
February, 2014. 19. U.S. Geological Survey (USGS), National Elevation Dataset , available at http://viewer.nationa l map.gov/viewer/, Accessed:
February , 2014. 20. U.S. Nuclear Regulatory Commission (USN RC), Regulatory Guide 1.102, Flood Protection for Nucle ar Power Plants , Revision 1 , Washington, D.C. 21. U.S. Nuclear R egulatory Commission (USNRC), R eg ulatory Guide 1.59 , Design Basis Flood for Nuclear Power Plants , Revision 2 , Washington , D.C. 22. U.S. Nuclear Regul a tory Commission (USNRC), NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: L WR Edition -Site Characteristics and Site Parameters (Chapter 2), ML070400364 , March 2007. 23. U.S. Nuclear Regulatory Commission (USNRC), NUREG/CR-7046 , PNNL-20091, Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America , ML 11321 A 195 , November 2011. 24. U.S. Nuclear Regu la tory Commission (USNRC), Letter to Licensees (NRC 50.54 (f) Letter). Request for I nformation Pursuant to Title 1 O of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the Near Term Task Force Review of In s ights from the Fukushima Dai-ichi Accident, March 12 , 2012. 25. U.S. Nu clea r R eg ulatory Commission (USNRC), Letter to Energy Northw est, Columbia Generating Station -Transm i ttal of U.S. Army Corps of Engineers Flood H azard Reevaluat ion I nformation (CAC No. MF3039), ML 16202A414, August 11, 2016. 26. World Meteorological Organiza t ion (WMO), WMO No. 332, Manual for Estimation of Probable Maximum Precipitation, Operational H ydrology Report 1, 1986. 27. World Meteorological Organization (WMO), WMO No. 1045, Manual for Estimation of Probable Maximum Precip itation, Operational Hydrology Report 1, 2009. COLUMBIA GENERAT I NG STATION Page 55 of 55