ML12306A393

Request for a Written Response to NRC Observations and Concerns Regarding Dresden Station Response Plan for External Flooding Events

ML12306A393
Person / Time
Site:	Dresden
Issue date:	11/01/2012
From:	Cameron J L NRC/RGN-III/DRP/B6
To:	Pacilio J M Exelon Generation Co, Exelon Nuclear
References
Download: ML12306A393 (96)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION REGION III 2443 WARRENVILLE ROAD, SUITE 210 LISLE, IL 60532

-4352 November 1, 2012 Mr. Michael J. Pacilio Senior Vice President, Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO), Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

REQUEST FOR A WRITTEN RESPONSE TO NRC OBSERVATIONS AND CONCERNS REGARDING DRESDEN STATION RESPONSE PLAN FOR EXTERNAL FLOODING EVENTS

Dear Mr. Pacilio:

This letter is in response to the results of recent site walkdowns conducted by NRC inspectors and technical experts to address NRC Temporary Instruction (TI) 2515/187 (ML12129A108) in response to the "Near-Term Task Force Review of Insights from the Fukushima Dai

-ichi Accident ," and confirm s discussions between Mr. David Czufin, Site Vice President of Dresden Station , and myself and other member s of the NRC regarding our observations and concerns about Dresden Station's response plan associated with external flooding event

s. Dresden Station

, Unit 2, as originally licensed, did not consider external flooding events above the height of the principle structure of 517 feet above mean sea level (MSL). The design basis for the construction license

, in accordance with the design criteria in effect at the time , concluded that the location of Unit 2 structures 10 feet above historic flood levels was adequate.

However, in 1982 following the original licensing , construction, and initial operation of Unit 2, the NRC began the Systematic Evaluation Program (SEP)

, which reevaluated hazards for facilities licensed prior to the incorporation of the General Design Criteria in 10 CFR Part 50, Appendix A. As part of SEP, the NRC performed additional hydrology evaluations for Dresden Station, Unit 2, and revised the site's design requirements, which were then incorporated into a new flooding design basis. The se new design requirement s incorporated a concept termed "probable maximum flood

" as defined in NUREG

-0800, Section 2.4.3 (ADAMS Accession Number ML070730405), which provided an upper bound for possible flood levels for a given area determined by extreme precipitation or river flow values. As a result of that re

-evaluation under SEP, the probable maximum flood value of 528 feet MSL became Dresden Station's new design basis for flooding

. It is important to note that historical floods at th e 528 feet level have not been previously observed in the vicinity of the Station and are considered to be improbable. Records of all previous floods in the area indicate that they have been below the grade level at the site. For this reason, we do not consider these issues to be an immediate safety issue. Nevertheless, licensees are expected to demonstrate that they can protect against design basis external events

.

M. Pacilio To address the disparity between the original and revised design basis for flooding, Dresden Station developed a response procedure and strategy that permitted flooding of plant structures and provided supplemental equipment and actions to quickly shut down the plant in advance of a predicted flood and maintain the reactors in a safe condition. During NRC's review of that response procedure and strategy, as part of the 1982 SEP reevaluation , the staff identified a number of observations and concerns regarding the viability of elements of the procedure as written. Those observations and concerns were documented in the Technical Evaluation Report

- "Hydrological Considerations Dresden Unit 2," prepared by the Franklin Research Center, on behalf of the NRC, on May 7, 1982 (ADAMS Accession Number ML12300A305), beginning on page 51, and are included as Enclosure 1. As a result of our recent site walkdown for NRC Temporary Instruction (TI) 2515/187

, NR C inspectors and technical experts again question ed the adequacy of elements of Dresden's current flood response procedures and strategy in the event of a design basis flood to execute a timely shutdown of the reactors and to maintain cooling of the reactors. Those current observations and concerns were verbally communicated to Station personnel at the end of the walkdowns, and are included in Enclosure 2 to this letter. Following those recent walkdowns, NRC staff raised additional questions regarding the viability of the current flood response plan at Dresden. Those additional questions are included in Enclosure 3. The NRC staff recognize s that Exelon Nuclear is currently preparing its response to our March 12, 2012, Request for Information Pursuant to 10 CFR 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the "Near Term Task Force Review of Insights From the Fukushima Dai

-ichi Accident," and that response may address some of our current and past observations regarding Dresden's response plan and strategy. However, since many of the observations we conveyed to you following our 1982 assessment of your flooding response plan and strategy continue to be identified during our most recent flooding walkdowns, for completeness we request a specific written response to each issue in Enclosures 2 and 3 to ensure that those current and past concerns are adequately addressed.

Although our observations and concerns do not constitute an immediate safety issue, we request that Exelon Nuclear, by written response within 30 days of this letter, address those specific observations and concerns contained in the enclosures to this letter

. Ultimately you should be able to demonstrate that your existing procedures and strategies would be successful in response to postulated external flooding events, up to and including those involving a probable maximum flood. In your response, you should also provide a listing of actions and a schedule for those actions necessary to update or revise the current response plans and strategies

, or provide acceptable alternatives to the current plan.

If you believe that additional technical evaluations and assessments are necessary to fully address our observations and concerns within 30 days , please describe the specific actions that you have taken, or plan to take, and a schedule for completion of those actions. If you propose alternative solutions vice your current response plan, please provide details for your formulation of solutions and a schedule for implementation

.

M. Pacilio Following the receipt and review of your response s , we will contact you to arrange for a meeting to discuss your response s to our observations and concerns. The public will be invited to observe this meeting and will have opportunities to communicate with the U.S. NRC after the business portion, but before the meeting is adjourned

.

If you have any questions regarding this request, please contact me at (630) 829

-9 833.

Sincerely, /RA/

Jamnes L. Cameron, Chief Branch 6 Division of Reactor Projects Docket Nos. 50

-237/249 and 72-037 License No. DPR

-19 and DPR-25 Enclosures

1. Technical Evaluation Report

- "Hydrological Considerations Dresden Unit 2," May 7, 1982 2. NRC Temporary Instruction (TI) 2515/187

- NRC Staff Flooding Walkdown Observations for Dresden 3. Additional NRC Observations following Staff Flooding Walkdowns for Dresden cc w/encls:

Distribution via ListServ TM

Enclosure 2 Summary of External Flooding Hazard Recommendation 2.3 Walkdown Observations August 13-16, 2012 Dresden Unit 2 and 3 During the week of August 13

-16, 2012, Region III and NRR staff observed licensee activities associated with the Fukushima Near Term Task Force Recommendation 2.3.

The licensee was briefed on the following observations described below.

Licensee staff stated they are generating an Issue Report on Dresden Operating Abnormal (DOA)

Procedure 0010

-04 (the primary flood protection procedure).

It is noted that many of the observations from the August 2012 walkdown were previously observed and documented in Technical Evaluation Report, "Hydrological Considerations," for Dresden Unit 2, by Franklin Research Center, May 7, 1 982. Observations of procedural weakness of the external flooding plan are as follows:

1. The procedures were not sufficiently detailed with respect to the actions to be performed and relied heavily on an individual's knowledge of plant system.

Please describe your basis for relying on knowledge-based actions and decisions and how that approach would be sufficient to ensure all required actions are accomplished.

2. Discuss how plant notification and/or measurement of flood water levels above elevation 510' (when the gage at the US Army Corps of Engineers (USACE) Navigation Lock and Dam is submerged) is performed. Explain how river level would be determined once flood waters exceed 510 feet, especially at critical flood levels where operator actions are specified in your procedure.

3. The procedure makes general statements like "deenergize all transformers at EL XX" without providing a list of the equipment.

This produced confusion and uncertainty during the walkdown simulation regarding which equipment was located at what elevation.

Please describe your basis for relying on knowledge

-based actions and decisions and how that approach would be sufficient to ensure all required actions are accomplished.

4. The procedure appears to initiate actions when they should already have been completed to protect station staff.

For example, the procedure states, "If the water reaches EL 517', deenergize down all transformers and motor control centers (MCCs) on El 517' (DOA-0010-04, D.14.a).

Although there are small (~4 inch) s ill barriers on the doors, this would likely be a situation where Aux Operators were performing activities in flooded areas of the plant with the potential for local energized equipment.

NRC Staff noted that, at some locations in your facility, sill barriers were not completely intact.

Please clarify what activities, following existing flood response procedures as written, could require operators to perform activities in the presence of environmental hazards. Explain how those activities can be performed safely.

5. The procedure makes statements like

, "check level in below

-ground storage tanks and fill ," without stating which tanks

. Please describe your basis for relying on knowledge

-based actions and decisions and how that approach would be sufficient to ensure all required actions are accomplished.

6. The procedure provides direction to "obtain boats," however, the details of such an activity are not included (e.g., from onsite storage, offsite entity with a durable agreement, etc).

Explain the actual arrangements for obtaining needed boats (number, type, purpose, and source)

. 7. The procedure directs activities from a starting condition of normal plant operations.

No apparent consideration for starting these activities from an abnormal condition where the plant may be in a different configuration. Explain the strategy for entering the flooding procedure from a starting condition of other than normal operations. Clarify where and how that strategy has been provided to operating crews.

8. The procedure does not appear to consider that the electrical bus for the emergency diesel generators (EDGs) is at the 517' elevation and the potential to create a personnel hazard if the bus were automatically energized.

Explain provisions for addressing normal automatic plant responses, such as automatic start of diesel generators and energization of an electrical bus, in situations where personnel hazards could be created because of flooding. Explain where those provisions are provided to operating crews.

Observations of design weakness of the external flooding plan are as follows:

1. Visual observation of the connection points for the diesel

-driven pump used to provide water to the isolation condensers showed that fire

-water system piping could interfere with connection of the spool piece.

It was initially unclear that the procedures accounted for physical impediments to connections to the fire header. It was unclear if the connection had ever been installed or tested while installed.

After questioning the licensee identified that there were additional pipe fittings staged for dealing with pipe interface conflicts.

This equipment, however, was not tagged for association with DOA-0010-04 and this was why it was not initially utilized.

The licensee entered this issue into the Corrective Action Program (CAP). Provide how this issue was addressed and the current status of the resolution and the schedule for completing any open items.

2. The licensee's procedures called for local control of both the Isolation Condenser inlet valves and the hoist height of the diesel

-driven pump.

It was not clear that the licensee had accounted for the battery life of the communication pathway (walkie

-talkie) to support this activity.

Additionally, communication with both operators in the control room is critical since the Isolation Condenser controls for Unit 2 and Unit 3 are on opposite sides of the control room.

Explain arrangements for ensuring that adequate communications would be available for the duration of a probable maximum flood event.

3. The sand bagging effort associated with protection of the normal Isolation Condenser make-up pump building appears to be labor intensive without a commensurate benefit.

The building is protected to 517' and the sand bagging stated purpose is to provide additional protection between 517' and 519.5'.

Since the building contains multiple penetrations, including louvers to vent the exhaust, and since the current design basis probable maximum flood (PMF) is at 528'

, it appears that a significant amount of site resources may be devoted to an activity that may ultimately not protect the subject equipment.

Provide current plans for sandbagging, the expected benefits, and explain any impacts this would have on resources needed for other flooding preparation activities.

4. The optional procedure to enter the Crib House (intake structure house) and remove two of the Service Water Pump Motors for later plant recover y appears to be labor intensive without a commensurate benefit.

These motors weigh approximately 8000 pounds. The procedure states the motors should be removed from the Crib House and relocated to the turbine deck.

Since the rotating trash

-rack screens would allow water to enter the Crib House at approximately elevation 509', these pump motors would be wetted just before the site floods.

It appears that a significant amount of site resources may be devoted to an activity that may ultimately not protect the station.

Provide current plans for motor removal, the expected benefits, and explain impacts this would have on resources needed for other flooding preparation activities.

5. There is uncertainty regarding the ability of the licensee to monitor rapidly rising water levels above elevation 509' (eight feet below site grade and up).

Although not all procedures were reviewed, the licensee and its contractors stated the primary source of water level information was the USACE via contact with the Lock Master at Dresden Lock and Dam.

Staff visited the Lock and Dam, and toured the facility with USACE staff. NRC staff located the automatic, telemetered, water-level gage.

Data from the water level gage is automatically sent to the Rock Island District office.

In addition, a second staff gage located nearby can be visually read.

However, both gages will be unusable at approximately elevation 510 ft (the visual staff gage ends at 508' and the electronic unit will flood).

The Systematic Evaluation Program (SEP) Technical Evaluation Report (TER) TER-C5257-421 states that the top of the dam is elevation 506.5'. Therefore, it is unclear to NRC staff how the water level at the site will be estimated once the USACE Dam is submerged and the gages are not available.

In addition, because the USACE Dam is downstream, water level estimates during a large storm would likely be lower than at the upstream Dresden site. Explain how river level would be determined or why measurements of site flood levels would not be required once existing gages become unavailable.

Enclosure 3 Subsequent NRC Staff Observations Re: Design Flooding Plan Dresden Unit 2 and 3 Additional NRC Staff Identified Issues with the External Flooding Design Plan:

1. The licensee's plan calls for using flood waters, pumped through the elevated diesel pump, as a cooling source for the Isolation Condenser. Explain how the clogging of pump intake hose(s) by flood debris will be prevented.

2. The Updated Final Safety Analysis Report (UFSAR), Section 3.4, discusses using an "emergency flood pump" to pump water to both units' isolation condensers. Dresden's Dresden Operating Abnormal (DOA) procedure 0010

-04 states: "Rig the reactor building crane or jib crane at elevation 545 foot with a 2 ton capacity chain fall to allow lifting the diesel-driven emergency make

-up pump to a height of a least 15 feet above the floor." Please describe the logistics of operating a diesel pump while suspended from a chain fall and explain the reliability of this approach.

3. The use of flood waters as a cooling source for the Isolation Condenser will likely lead to silt and mud fouling of isolation condenser. Condenser fouling could lead to tube failure, and subsequently provide a direct pathway for release from the reactor. Please address the potential for Isolation Condenser fouling due to mud and silt, and explain how this will be prevented. 4. The flood response plan does not call for removal of the reactor head. With the head intact, and all ECCS systems unavailable due to internal plant flooding, explain how cooling water inventory would be added to the reactor cooling system, if needed, during a flooding event. 5. The flood response plan calls for use of flood waters as a cooling source for the Isolation Condenser. When flood waters recede below the plant grade of 517 feet, please identify what water source will be used to continue cooling of the Isolation Condenser.

6. In the event of a flood at the level up to the probable maximum flood (528 feet), explain how relief crews will gain access to the site, considering the nearest dry land will likely be several miles away. Furthermore, explain how they will gain entry to, and existing crews will evacuate from, site buildings, since all normal entry/egress points will be under water. For those crews on site during such a flooding event, please describe the environmental conditions they may have to contend with in order to implement your flood response plan and strategy.

7. In the event of a flood at the level up to the probable maximum flood (528 feet), please describe the potential impact of flood waters on radiological conditions on site (for example, flooded contaminated areas and rooms containing tanks of radioactive materials/waste). Please discuss the radiological conditions that operators onsite would have to contend with while performing required actions.

8. Considering the extreme hardship potentially posed to crews tasked with implementing your flood response plan, please address human reliability of executing all aspects of the flooding plan procedure.

9. The 500-year flood level for Dresden is estimated to be between 511.5 feet and 514.9 feet based on analyses performed in various reports (e.g., U.S. Army Corps of Engineers, Franklin Research Center, Independent Spent Fuel Storage Installation Operability Evaluation, etc.). Please provide a best estimate of the frequency and uncertainty of a flooding event reaching the plant grade of 517 feet. Also, please explain what assumptions were used in making this estimation and justify why these assumptions are appropriate.

M. Pacilio Following the receipt and review of your response s, we will contact you to arrange for a meeting to discuss your responses to our observations and concerns. The public will be invited to observe this meeting and will have opportunities to communicate with the U.S. NRC after the business portion, but before the meeting is adjourned.

If you have any questions regarding this request, please contact me at (630) 829

-9833.

Sincerely, /RA/

Jamnes L. Cameron, Chief Branch 6 Division of Reactor Projects Docket Nos. 50

-237/249 and 72

-037 License No. DPR

-19 and DPR

-25 Enclosures

1. Technical Evaluation Report

- "Hydrological Considerations Dresden Unit 2," May 7, 1982 2. NRC Temporary Instruction (TI) 2515/187

- NRC Staff Flooding Walkdown Observations for Dresden 3. Additional NRC Observations following Staff Flooding Walkdowns for Dresden cc w/encls:

Distribution via ListServ TM

DOCUMENT NAME:

G:\DRPIII\Dres\Dresden Flooding Ltr 2 Licensee for Responses.docx Publicly Available Non-Publicly Available Sensitive Non-Sensitive To receive a copy of this document, indicate in the concurrence box "C" = Copy without attach/encl "E" = Copy with attach/encl "N" = No copy OFFICE RIII RIII NAME JRutkowski:dtp JCameron DATE 11/01/12 11/01/12 OFFICIAL RECORD COPY

Letter to M. Pacilio from J. Cameron dated November 1, 2012.

SUBJECT:

REQUEST FOR A WRITTEN RESPONSE TO NRC OBSERVATIONS AND CONCERNS REGARDING DRESDEN STATION RESPONSE PLAN FOR EXTERNAL FLOODING EVENTS

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