ML20248M288
| ML20248M288 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 06/12/1998 |
| From: | Larry Wheeler NRC (Affiliation Not Assigned) |
| To: | NRC |
| References | |
| TAC-MA2057, NUDOCS 9806150256 | |
| Download: ML20248M288 (22) | |
Text
- - _ _ _ _ _ _ _ _ _ _ - _ - _ _ _ _ _
9k 4
e NOTE TO:
File d., ((/
6 /2 Yf FROM:
Louis L. Wheeler Project Manager fo'r Humboldt Bay Power Plant PDND,DRPM,NRR
SUBJECT:
OPENING OF TAC NO. MA2007 (HUMBOLDT BAY VENT STACK REMOVAL)
The purpose of this Note is to provide a document that can be referenced as the basis for opening TAC No. MA2057 - Humboldt Bay Vent Stack Removal.
On June 11,1998, the NRC staff received an information copy of the enclosed 10 CFR 50.59 safety evaluation prepared by Pacific Gas and Electric Company (PG&E) for the addition of a new vent stack and the removal of the existing vent stack at the Humboldt Bay Power Plant.
TAC MA2057 was opened because it became apparent that staff resources should be used to review of the safety evaluation to determine if an unresolved safety question exists.
By distribution copy of this Note with its enclosure, the PG&E safety evaluation sent to the NRC staff is being placed in the Humboldt Bay docket file.
Enclosure:
As stated DISTRIBUTION:
PDND reading file Docket File (50-133)
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SUMM ARY OF SAFETY EVALUATION FOR HBPP UNIT 3 VENTILATION STACK REPLACEMENT DESCRIPTION OF CHANGE:
This modification consists of removal of the two main exhaust fans, fan discharge ductwork that is attached to the existing exhaust stack, and plenum No. 2. Subsequently, a single exhaust fan, a High Efficiency Particulate Air (HEPA) filter unit and a 48" diameter,50 fl stack, including instrumentation and controls will be installed.
The purpose of the existing plenum No. 2 and the fans is to draw ventilation exhaust air from different areas of the plant and deliver it to the stack for monitoring and release to the atmosphere. The fans l
maintain plenum No. 2 at a negative pressure of approximately 2.0 inches w. g. The above equipment is being replaced, as a new stack is required for a single point monitoring and discharge path for plant effluents which will allow removal of the existing ventilation exhaust stack. A HEPA filter unit is required to capture potential airborne contamination prior to its release to the atmosphere during the plant stack removal and future decommissioning activities. A fan with high differentialiressure capacity is required to provide adequate airflow and static pressure to treat the exhaust air through HEPA filters, maintam airflow direction from areas oflow potential to high potential of radioactivity, and maintain a negative pressure in the exhaust ducts.
ISSUES:
The difference between the new and the existing stack heights (250' vs. 50') with respect to the e.
discharge air dispersion has been evaluated and found to be acceptable (see calculation no. N-238 and the attached TES evaluation dated June 20,1997). The fuel handling and heavy load drop accidents that were previously analyzed in the SAFSTOR Decommissioning Plan (SDP) used the 250' stack and the 1984 Kr-85 inventory in the spent fuel. The current analysis for the consequences of these accidents with a 50' stack height uses the current-day Kr-85 inventory in the fuel. The fuel handling accident consequences for either scenario is 0.13 mrem dose at the site boundary. The heavy load drop consequences for the 250' stack and the 1984 Kr-85 inventory is 5.1 mrem dose at the site boundary, while the consequences using the 50' stack and the current-day Kr-85 inventory is 5.08 mrem. The ability to have no increase in consequences of an accident previously analyzed in the SAFSTOR Decommissioning Plan relies on taking credit for the decay of the Kr-85 inventory in the spent fuel during the period from 1984 to the present. This does not change any input assumptions in the accident analyses, as the same spent fuel is analyzed. He NRC SER for the SDP calculated consequences of 20 mrem assuming a ground level release. Hey concluded that these consequences are very small fractions of and, therefore, are well within the guideline values of 10 CFR Part 100 (25 Rem to the whole body and 300 Rem to the thyroid).
During a portion of the modification, the stack gas monitor will be inoperable. The Technical e.
Specification requires that the gas monitoring system be operable whenever the ventilation system is running. Since the ventilation system will be shutdown during the modification, the stack gas monitor is not required to operate because there are no radioactive releases to the environment through the stack to warrant the need for radiation monitors or alarm.
CONCLUSION:
There are no safety concerns that will affect design features or SAFSTOR Licensing requirements. The new stack height impact has been evaluated and found to be adequate. Also, the ventilation system need not be in operation since no fuel handling operations will be conducted and no work will be performed that i
l could potentially damage the stored fuel during this modification. The proposed DCN does not violate the i
l design bases for the refueling building exhaust as defined in Technical Specifkation and the SAFSTOR Decommissioning Plan (SDP),
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___._m._
SUMMARY
OF SAFETY EVALUATION FOR HBPP UNIT 3 VENTILATION STACK REMOVAL i
DESCRIPTION OF CHANGE:
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ne 250-foot ventilation stack for llBPP Unit 3 exhausts gaseous effluents from various Unit 3 buildings, including the Refueling Building. Due to its proximity and height, the stack poses the greatest potential
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risk to site personnel and fuel stored in the Spent Fuel Storage Pool during an earthquake exceeding the j
seismic capability of the stack. To eliminate this risk, the existing stack will be removed and replaced with j
a 50-foo' steel stack that serves the same function. Installation of the new stack is covered by Design i
Change Package M-00429 which has a separate safety evaluation.
Removal of the existing stack will be performed using a 300-foot, track-mounted, counterweight-equipped crawler crane. Beginning at the top, the stack will be cut in sections of approximately 40 feet or less, and lowered to the ground. Once the sections are on the ground and detached from the crane, disposition of the stack sections will be controlled by procedures outside the scope of this safety evaluation.
ISSUEF:
The main issue associated with this safety evaluation is the potential for dropping a stack section caused by failure of the crane system. This heavy load drop could impact nearby targets such as the Spent Fuel Storage Pool, the Liquid Radwaste Treatment Facility, and a natural gas pipeline. This issue has the potential to increase the probability and consequences of accidents previcusly evaluated in the HBPP SAFSTOR Decommissioning Plan (HBPP's equivalent FSAR).
In order to prevent this safety evaluation from constituting an Unreviewed Safety Question, HBPP proposes to provide administratively controlled compensatory measures to preclude the possibility of a heavy load drop.
INCREASE IN PROBABILITY OF OCCURRENCE:
The heavy load drop accident previously analyzed in the SDP considered a non-mechanistic load drop inside the Refeuling Building onto the Spent Fuel Storage Pool. The accident did not consider a load drop from outside the Refueling Building. Therefore, a heavy load drop of a section of the ventilation stack could be considered an increase in probability of occurrence. However, consistent with NRC guidance, a project-specific evaluation is included in the safety evaluation to demonstrate the acceptability of offsetting the potential increase of probability of occurrence with compensatory measures. Compensatory measures are employed to assure crane reliability and safe load paths to prevent heavy load drop onto a seuitive target. Since the relevant issues of the safety evaluation are tied to the potential for a heavy load drop onto a sensitive target, using compensatory measures is vital to the determination that there will not be an increase in probability of occurrence of an accident previously evaluated.
INCREASE IN CONSEQUENCES:
As stated above, the safety evaluation relies on the compensatory measures to prevent a ventilation stack heavy load drop accident from occurring, thereby preventing an mcrease in consequences of the accident.
ne accident analyses in the SDP assumed that Kr-85 in the spent fuel would be released through the 250-foot stack as a result of an accicient associated with the spent fuel. A heavy load drop from the stack would cause a Kr-85 release through a hole ir, the roof of the Refueling Building, approximately 40 feet above ground. A release at this lower elevation would result in an increase in the dose consequences at the site boundary. However, this increase in dose (calculated to be 28.6 mrem) is well below the 2500 mrem,10 CFR 100 acceptance limit.
l 1
ItBAP C-19 Attichment 8.2 Rev. 7 Pagei 10CFR50.59 WRITTEN SAFETY EVALUATION (SE)
(Unreviewed Safety Question Determination)
REFERENCE DOCUMENT No.
DCP M-00431 Doc. Rev. No.
0 (i.e., indicate the procedure number, DCP/DCN number, or other reference document for which the screen is performed, including the document revision number or date).
Reference Document -
Title UNIT 3 VENTILATION STACK REMOVAL Sponsoring Organization Design Engineering Services and HBPP - Engineering Preparer Peter G. Rasmussen (Print)
DESCRIPTION OF CIIANGE:
He proposed modification is to remove the existing 250-foot reinforced concrete Ventilation Stack down to approximately the 34'5" elevation, leaving the basement and the two existing, above-ground levels of equipment in place. The stack will be replaced with a shorter, carbon steel stack, the installation of which is covered by Design Change Package M 00429. The new st.ck will be placed into service prior to removal of the existing stack. The purpose of removing the stack is to reduce the seismic hazard to the stored spent fuel, plant personnel, and other structures within the radius of the 250' stack.
The current stack is a concrete and steel reinforced structure located within 5' of the north (all directions refer to
" plant" compass headings, which do not correspond to true or magnetic compass headings) wall of the Refueling Building. The stack is located on the north - south centerline of the reactor vessel. The entire structure rests on a concrete cantilevered pH that is integral to the Reactor Caisson. He stack provides the monitored discharge point for all gaseous effluents tnat originate within the Refueling and Turbine Buildings. The removal of the stack will take place after the new replacement stack, HEPA Filter and ancillary equipment are installed and declared operational. The new system will perform the same function as the current system. The stack also acts as an aircraft and boat navigation point and key landmark. The California Coastal Commission, the Coast Guard and the FAA have been notifica of the change.
The stack will be removed section-by section, using a track-mounted, counterweight-equipped crawler crane with a boom approximately 300' in length and a mast approxinmdy 160' in leng h. The crane will be located north of the Refueling Building and the Liquid P.adwaste Treatment Facility, and within approximately 150' of the stack. The boom will clear the 250' height of the stack. To assure a stable working platfona for the crane and its intended load, a platform will be constructed for the crane to operate upon. The platform will consist of multiple crane pads that are constructed from five l' by l' by 20' long Douglas Fir beams bolted together on a leveled grave' base. The crane pads will form a platform area of approximately 4900 square feet.
The basis for selecting the crane location was two factors: safety of the spent fuel, and soil bearing capacity. An alternate location near the northeast corner of the Refueling Building was proposed to avoid the possibility of the crane boom falling uncdrollably on the Refueling Building roof. Upon further review, however, it was determined that the boom could fail mechanically in an unknown configuration. Since boom failure,1 owever remote a possibility, could occur in any direction, the pctential protection of the spent fuei from placing the crane parallel to the Refueling Building would not be realized. More importantly, the soit loading capabilities in this area are substantially less.han the area north of the Liquid Radwaste Treatment Facility.
l The purpose of the platform is to provide a stable base for the crane and to reduce the bearing stresses on the soil.
The crane will be used for removing each stack section as it is cut from the mr.in stack. The crane will lower the l
section and transport the section to a predefined location for disposition. To gain access to the top of the stack and l
J
IIBAP C-19 l
!.2 Rev.7 Page 2 provide a working area, an Aliclimber mast and platform will be used. The Aliclimber platform is basically an elevator that surrounds the circumference of the stack. 't he rails for the Aliclimber are attached to the stack walls by means of anchor bolts embedded into the concrete. With the Aliclimber in place, workers, the diamond saw cutting tools, and other support equipment are transported to the location of the intended cut. The Alictimber platform, l
l equipment, and personnel weigh approximately 10,000 lb.
Stack cutting will take place once the weight of the intended section is verified to be within the designated capacity cf the crane. The lining rigging will be attached above the section center of gravity. The crane will exert an initial vertical tension on the stack of approximately 10% of the stack section weight. As the cut progresses towards the stack's inside diameter, the crane will increase the vertical tension on the stack section. Cutting will be terminated when the remaining concrete thickness is approximately % of an inch. By this time, the crane will have exerted a tension on the section of stack equal to the section's weight. The section will then be hydraulically separated from the remainder of the stack. To assure proper vertical alignment between the stack and crane, guide blocks will be attached to the stack, and extend past the area of the cut. In the event of misalignment of the crane and cut section, the guide blocks will prevent the load from swinging. This will allow the operator to reposition the boom, thereby producing a clean lift. Once lifted, the section will then be transported to the ground for disposition and additional size reduction. Engineering controls will be in place to prevent the spread of radioactive contamination.
Safety Evaluation " Probability of Occurrence" Risk Assessment Methodology, Use of Compensatory Measures and Probabilistic Risk Assessment (PRA):
Intmduction An evaluation has been performed regarding the removal of the ventilation stack at HBPP Unit 3. The evaluation demonstrated that the propot i change did not result in an increase in the probability of an accident previously evaluated in the SAFSTOR Decommissioning Plan (SDP). This conclusion was based on the compensatory measures to be implemented and the guidance provided in the following documents:
NRC Inspection Manual, Part 9900,10 CFR Guidance,4/9/96 e
NSAC 125 SECY 97-035 (Ill.M.4,Ill.P.4) e e
NEl 96-07 Letter from Samuel L Collins to NEl dated January 9,1998 e
'Ihis evaluation provides the basis fot the acceptability of crediting compensatory measures in reducing the probability of an accident as a valid method to use in 10 CFR 50.59 safety evaluations.
Evaluation The existing accidents analyzed in the SDP that could be impacted by removal of the stack due to dropping a portion of the stack or the crane falling are:
Spent Fuel Storage Pool rupture, Heavy load drop into the Spent Fuel Storage Pool, e
Uncontrolled release of radioactive liquid radwaste to the environment, and e
Explosions, delayed ignition of Gammable vapor clouds, release of toxic chemicals, or fire.
e Although the SDP assumes that a load drop occu.s that results in damage to the fuel or the spent fuel pool, the analysis is non-mechanistic in that a particular loaa is not identified. As such, the introduction of potential new heavy lands (such as pieces of the stack as they are removed) that could cause the damage described in the SDP could be potentially considered an increase in the probability of an accident.
SECY 97-035 states that "Section 50.59 uses the term 'may be increased,' and therefc,re, any increase, however slight, will trigger an unreviewed safety question (USQ) and thus require staff review. Accordmgly, the staft's position is that the language of 10 CFR 50.59 (probability may be increased) indicates that any uncertainty or doubt about whether an increase, even a negligible one, has occurred should lead to the conclusion that a USQ is involved.
~
HBAP C-19 Attichment 8.2 Rev.7 Page 3 l
llowever, removal of the stack is being performed such that the sections of the stack being removed could net be dropped, and if they were, they would not impact the Liquid Radwaste tanks or the Refueling Building since load paths have been established to avoid movement ofloads over the buildings. The standard corapensatory measures that would normally be employed by a prudent heavy lift contracte include:
Crane Design meets the requirements of ANSI B30.5 for Mobile Rigs Crane Operator Training meets ANSI B30.5 and crane operators shall be ofjourneyman status Below the Hook Lifting Devices meets ANSI B30.20 requirements e
Slings meets ANSI B30.9 (No chain slings will be used) e Riggers will be ofjourneyrnan status and will be instructed in the requirements of ANSI B30.9.
e Crane Inspection and Maintenance meets ANSI B30.5 requirements, California and Federal OSHA Standards, and is California Certified Crane placement will be evaluated to maximize stability Load will be moved to the safest configuration as soon as possible e
Load guides for the stack sections will be installed to help control the load Beyond the above good industry practices, the following additional compensatory measures will be employed:
Special Lifting Devices are designed to meet ANSI N45.2.15 (Attachment to the Stack)
Dead Load testing in accordance with ANSI B30.20 e
Load Paths and Exclusion Areas will be established.
e Independent verification of crane certification and lifting equipment qualifications.
A verification lift, at a low load, will be performed to evaluated the equipment and the process.
Crane Load Capacity will be reduced to increase the margin of safety.
Weather limitations will be established.
Adequate Crane Operator coverage during all required crane evolutions
=
PG&E Oversight during all load picks with stop work authority.
e I
Critical Lifl and Load Handling procedures will be established.
e Use of compensatory measures to compensate for increased risk due to a particular change is allowed by the NRC.
Specifically, NRC Inspection Manual Part 9900,10 CFR Guidance, states,"In considering the acceptability of a licensee's 10 CFR 50.59 evaluation, the staff has found compensating effects such as administrative controls
(
acceptable in offsetting uncertainties and increases in the probability of occurrence...of an accident previously evaluated.. " NSAC 125 endorses this same guidance regarding the.nse of compensatory measures to offset potential increases in probability of occurrence of an accident.
l l
The administrative controls established, as discussed above, including meeting crane operation and maintenance standards, operator and rigger training, and the establishment of exclusion area s and load paths are administrative i
controls designed to compensate for the efrect of moving the stack and having a large crane on site in the vicinity of
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the Refueling Building.
The purpose of the 10 CFR 50.59 evaluation is to determine whether a particular change is within the licensing basis of the plant. SEC (97-035 states,"Section 50.59 is a regulatory test of whether a change falls within the licensing envelope reviewed and approved by the staff, not a test of its safety or risk significance. The reference point for evaluation of a change is the FSAR [or in the case of HBPP, the SDP]. The FSAR analyses are typically deterministic and are based on a set of postulated design basis events and the single failure criterion." Given this guidanee, a probabilistic assessment in and of itself cannot provide a decision regarding an unreviewed safety question. An increase in probability as indicated by a PRA evaluation does not necessarily represent a USQ. This is stated in SECY 97-035,"Thus, in general, the staff concludes that PRA is not suitable as a decision making tool for 10 CFR 50.59 evaluations." Although a PRA might indicate some small risk increase due to removal of the stack, the PRA did not serve as the licensing basis for HBPP. Additionally, although not specifically credited as part of this evaluation, continued operation with the stack in place poses a risk ts a result of the seismic activity in the vicinity of the plant site. The risk of the stack collapsing and becoming a heavy !nd ifit remains in place may be greater than the risk of removing the stack. SECY 97-035 indicates the following iegarding the use of PRA in conjunction with
3 IIBAP C-19.2 Rev.7 Page 4 USQ determinations: "With respect to more traditional topic where PRA was not used in the licensing basis, PRA results and risk insights would play no direct role in the evaluation of potential unreviewed safety questions."
Since HBPP was not licensed using PRA techniques, risk increases must be evaluated from a deterministic viewpoint, in which case compensatory measures can be credited for compensating for any increase in risk that ma exist from using a crane to remove the stack. Engineeringjudgment regarding the adr.1inistrative controls indicates that the removal of the stack under the above described administratively controlled compensatory measures cannot result in a load being dropped such that it would damage the fuel or radwaste processing equipment. Therefore, the probability of a previously evaluated accident is not increased.
NEl 96-07 and the Samuel Collins memo dated January 9,1998 were also reviewed for applicability and determined ta provide no additional information relevant to this evaluation.
Conclusions In summary, administrative controls have been established that act as compensatory measures to offset any increase in probability of occurrence of a load drop that could damage fuel. This is allowed by NRC documents and is an acceptable means by which to perform a 10 CFR 50.59 evaluation and evaluate a potential unreviewed safety question. As such, the proposed removal of the HBPP Unit 3 t i ntilation stack does not result in an increase in the probability of occurrence of an accident previously evaluated in the SOP.
Potential Safety Evaluation Issues:
Issue No. I:
The crane, or a component of the crane, could fail, cauaing the load or the crane to fall, impacting one or more of many potential targets. These targets include:
The Refueling Building. He Refueling Building and the Spent Fuel Store s fool could be impacted, creating a hole in the Refueling Building roof, crushing the spent fuel, and releasing. me or all of the 10-85 inventory in the spent fuel assemblies to the environment. The hole in the roof would provide a different pathway for the dispersion of the gaseous effluent than the normal plant exhaust.
The Liquid Radwaste Treatment Facility. The three waste receiver tanks, the two waste hold tanks or the Resin Disposal Tank could be damaged, leading to a release ofliquid radwaste to the environment.
The Cordensate Storage / Demineralized Water Tank. Damage to the tank could mix the demineralized water with the radioactive contamination in the empty Condentate Storage Tank, leading to a liquid radwaste release.
The Natural Gas Pipeline. This pipeline runs underground, adjacent to the east boundary of the Restricted Area, then crosses through the Restricted Area between the north side of the Liquid Radwaste Enclosure and the High Level Radwaste Storage Vault. The pipeline exits the Restricted Area, then splits and each branch turns south toward the two boilers, running above ground in overhead pipe racks. The pipeline could be severed, causing an explosion and/or fire.
Issue No.1 Resolution:
The crane used to dismantle the stack will lift sections of the stack and transport them to the ground to be prepared for decontamination and/or shipment offsite. Controls and inspecti ms will be in place to assure that the crane load l
will not be dropped or the crane will not tip over or break. The crane that will be used will meet the following
)
industry standards and operational criteria to assure that the crane and the load will be positively controlled at all times:
Crane Design meets the requirements of ANSI B30.5 for Mobile Rigs Crane Operator Training meets ANSI B30.5 and crane operators shall be ofjourneyman status e
Below the Hook Lifting Devices meets ANSI B30.20 requirements e
Slings meets ANSI B30.9 (No chain slings will be used) e
IIBAP C-19.2 Rev.7 Page 5 Riggers will be ofjourneyman status and will be instructed in the requirements of ANSI B30.9.
e Crane Inspection and Maintenance meets ANSI B30.5 requirements, California and Federal OSHA Standards, and is California Certified Crane placement will be evaluated to maximize stability e
Load will be moved to the safest configuration as soon as possible e
Load guides for the stack sections will be installed to help control the load Beyond the above good industry practices, the following additional compensatory measur:s will be employed:
Special Lilling Devices are designed to meet ANSI N45.2.15 (Attachment to the Stack)
Dead Load testing in accordance with ANSI B30.20 e
Load Paths and Exclusion Areas will be established.
e Independent verification of crane certification and lifting equipment qualifications.
A verification lifl, at a low load, will be performed to evaluated the equipment and the process.
Crane Load Capacity will be reduced to increase the margin of safety.
Weather limitations will be established.
Adequate Crane Operator coverage during all required cranc evolutions PG&E Oversight during all load picks with stop work authority.
e Critical Lift and Load Handling procedures will be established.
Notwithstanding all of the above activities to preclude any heavy load urop on a plant target, the following mitigation measures will be put in place to limit panicular consequences.
Operator will be stationed at the Primary Gas Regulator Station shut off valve The combined contents of the Waste Receiver and Waste Hold tanks will be limited to a total activity of 0.010 e
Curies Compensatory Measures The brake design for this crane is considered to be fait safe. The main hoist drum assembly and auxilian hoist drum assembly contrc,1 the movement and translation of the load. To change the elevation of the load, the air supply releases the brake allowing the drum to rotate and spool the cable. A sudden loss of air results in the spring set engaging the brake mechanism preventing the load from changing elevation. Under normal opeiation the operator must engage the air system to release the brake to effect load elevation changes. The brake system is capable of maintaining rated load without operator intervention indefinitely.
To assure that operator error does not result in improper crane operation that could cause a load to fall, only qualified operators will be allowed to operate or be in the cab of the crane. There will be no on-the-job training of apprentices.
OverloadLg the crane can happen through the negligence of the crane operator or indication problems with the load cell. This would require the operator to be unaware of the load cell problems or that the load cell readout in the cab is exceeding designated limits. The indication ofincreasing load would first be indicated in the trailing counterweight l
which would lift further off the platform, followed by the un-weighting of the track rollers. This problem would be readily apparent to experienced crane support personnel and PG&E oversight in contact with the crane operator.
This will be avoided by having a qualified, experienced operator at the controls, procedural guidance and good communications during all phases of the pick.
During stack removal, as soon as the cut section of stack is lifted and cleared from the parent stack, the section will be lowered to a height that is close to the ground. Once in this position, the stack section cannot damage any of the potential load drop targets.
To compensate for boom position prior to stack sectLa separation, load guides will be installed. The Nd guides will help the operator control the load after separation and allow boom adjustments to a plumb position before the load is allowed to swing free.
IIBAP C-19.2 Rev.7 Page 6 Dead load testing will be performed with the crane in position in accordance with ANSI B30.20. The dead load test will be accomplished using a calibrated load indicating device and the crane will be rotated to minimize any interaction with the Refueling Building or potential twets during the testing.
During stack removal, actions will be taken to assure that the load does not cms over the Refueling Building or other targets like the Liquid Radwaste tanks. These measures include establishing load paths and exclusion areas for the stack sections as they are being lowered to the ground. The load paths will identify those areas in which heavy loads shall be transported. He load paths will maximize the distance between the loads and the identified targets.
PG&E will verify that all required certifications for the crane and all lifting equipment are in compliance with required standards.
A verification lift will be penormed. The purpose of the verification lift is to cut and remove a much smaller section of the stack. This will allow the entire crane system to perform a lift at a reduced capacity to assure all procedures are adequate, and the crane configuration is safe. The verification lift will employ a stack section that is 50% (or less) of the crane's capacity. After the successful verification lift, the capacity will be increased.
Subsequent loads, including all rigging and stack sections will be limited to 70% of the crane capac4y during critical crane positions. This factor is 30% below the crane manufacturer's recommended capacity and 55% below the actual design capacity. The 70% limit shall always be in efrect during any critical crane position. If a greater apacity is needed, above the 70% limit, an evah.ation of potential targets will be performed by PG&E, but under no circumstance will the limit be increased above 85% of the manufacturer's recommended capacity.
PG&E and the Contractor will establish guidelines for crane operation during periods of adverse wind or weather conditions. This will include the installation of an anemometer and periodic monitoring of weather reports. The crane that will be used for the stack removal project can safely operate in steady wind conditions of 25-35 miles per hour, even with periodic gusting. If wind conditions maintain a steady wind speed exceeding 25 mph or if gusts exceed 35 mph, crane operation will be suspended.
The crane will be staffed to allow continuous coverage during the critical evolution of stack cutting and load handling.
Along with the crane operator, a designated PG&E employee will be authorized to halt work if conditions are decued unsafe in any manner. In these cases, the operation will be halted and the crane parked in a safe conDguration until work can resume. PG&E m:nagement will provide direct oversight of the removal of the stack to assure that all the other compensatory measures specified in this evaluation are satisfied. The actions of the vendor will be controlled in accordance with the llBPP QA plan and procedures reviewed by the liBPP PSRC and approved by the ilBPP Plant Manager.
Prior to the initial section of the stack being lifted a " Critical Lift Procedure" will be developed to verify all required parameters and precautions are in place. For example, the weight of the cut section will be determined and compared to the established limited capacity for the given boom angle. A pre-lift meeting will be conducted to ensure that all parties understand the procedure and that all requirements have been met. Once the procedure is complete a " Lift Permit" will be issued.
Mitigation Measures To preunt a major fire due to the natural gas line being severed in the unlikely event of a load or boom drop onto the gas line, whenever a crane load is being transported, an operator will be stationed at the Primary Gas Regulator Station shut off valve to stop the flow of gas in case of a load or boom drop onto the gas pipeline.
As a mitigation measure, while the crane is under load, the combined contents of the waste receiver and waste hold tanks will be limited to a total activity of 0.010 Curies, which is less than 5% of the basis for the existing SDP accident analysis of a release ofliquid radwaste to the environment. Based on engineeringjudgment, the Resin Disposal Tank is not vulnerable to a crane failure, as it is inside a stout concrete vault that, although primarily designed as radiation shielding, will protect the tank from impact damage.
IIBAP C-19
..2 Rev. 7 Page 7 j
Crane Placement There were two objectives considered in placement of the crane. These were to minimize any interactions crane components might have with sensitive plant targets in the event of crane failure and to provide the most stable work platform possible for the crane to operate from.
Relative to these criteria, there were two placement alternatives: the first is just north of the Liquid Radwaste Building (LRW site), the second is northeast of the Refueling Building (RFB site).
From the LRW site. the crane boom would extend over the Liquid Radwaste Building tojust above the stack. While never traveling over the Refueling Building, the boom would be in close proximity and pointed at it for much of the pick. This crane placement location is 20 feet above grade on a cut bluff. Based on preliminary soil data taken in the vicinity of the crane location, soil loading capabilities were considered to be excellent.
rhe RFB site alternative is a location from which the crane boom would not cross over nor at any time be pointed in tne direction of the Refueling Building. However, it would often point at the Liquid Radwaste Building and at a gas pipeline serving the fossil boilers of Units I and 2. This location is at plant grade and has relatively marginal soil loading capabilities.
To determine whether either location provided a smaller chance of target interaction if there were a crane failure, it was necessary to obtain information on crane failure modes. Failure modes and frequencies were discussed with the crane manufacturer; American Crane Corporation, the rigging company; Bigge Crane and Rigging Corrpany, and a national crane certification compar.y. In the course of these discussions we were advised that because of good performance there is little or no historical reliability information available on this crane. The engineering judgment of the operator and manufacturer, however, was that in the event of structural failure, most directions would be equally likely for the fallout of failed crane components. This is crimarily because the major structural components of the crane consist of a lattice assembly of smaller members, the fanure of any one of which could result in the boom or other large components failing in almost any direction. Given the unknown direction major crane components could travel should it fail, there was no tangible benefit in locating the crane in the RFB alternative location, since this location would not produce any increase in safety.
On the other hand, the operator identified that in their opinion, the stability of the pad from which the crane operated was one of the most important factors in crane safety. The RFB alternative site clearly had poorer soit loading capabilities and while this may have been mitigated, our engineeringjudgment is that the LRW site provides the safest placement for the crane.
It should be noted' that crane tipping would result in crane failure in the direction in which the boom and load were pointing. Tipping, however, as opposed to structural failure, is a transient which has much less uncertainty in terms of when and how it will occur and therefore does not require the large safety factors needed in structural design. With the LRW location soil stability, controls on loading and the initial pick precautions, the likelihood of tipping is extremely remote and not considered a credible failure mode. A soil report for the crane location will be obtained to assure that the soil loading capability is at least a factor of 2 times that required by the crane in the highc:t soit loading configuration anticipated during the stack removal process.
Issue No. I Conclusion With crane reliability, in standard application, being very high (Iow probability of failure) it is our engineering judgment that with the additional admimstrative controls in place (increased safety margin, operaticaal restrictions, and accident mitigation efforts), the effort to remove the stack will not increase the probability of an accident l
previously evaluated in the SDP.
Issue No. 2:
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(
IIBAP C-19 l.2 Rev. 7
)
Page 8 f
The working platform attached to the stack could fall through the roof of the Refueling Building, crushing the fu the pool and releasing some or all of the Kr-85 inventory in the fuel. The hole in the roof would provide a different pathway for the dispersion of the gaseous effluent than the normal plant exhaust.
Issue No. 2 Resolution:
The platform and attendant track is an engineered device, designed for this type of service. It will be attached to the stack with anchor bolts. The platfonn is essentially an elevator that surrounds the stack circumference. The platfor and the anchor points will be evaluated and designed to assure adequate holding strength, and not result in degradation to the stack which could result in the platform slipping, or pulling away from the stack and impacting the Refueling Building.
Issue No. 3:
He additional weight of the work platform near the top of the stack will create additional static loading on the stack and change the response of the stack to seismic and wind loads. This could cause the stack to fail and a portion of the stack fall through the roof of the Refueling Building, crushing the fuel in the pool and releasing some or all of the Kr-85 inventory in the fuel. The hole in 5 : roof would provide a different pathway for the dispersion of the gaseous effluent than the normal plant exhaust.
Issue No. 3 Resolution:
De stack has been reviewed to assure that the addition of the work platform and track does not turn the stack into an unstable structure either statically or with structural resonant frequencies capable of being excited by natural high l
frequency drivers such as wind and/or minor seismic events. The work platform weighs approximately 5 tons, which is equivalent to an additional 8 feet ofstack height. Based on engineeringjudgment, an additional 8 feet of height on a 250' stack would not create a structural instability of the stack.
Issue No. 4:
During the concrete cutting operation, including the final separation of the stack section using wedges or hydraulics, radioactive contamination in the concrete dust could be released offsite.
Issue No. 4 Resolution:
l Engineering measures will be taken to mitigate dust and debris generated during stack removal. A water and slurry l
collection system will be attached to the stack directly below the cutting area to collect the concrete slurry. The area of the cut will be contained with respect to airborne contamination, and adequate engineering controls will be employed to capture any contamir.ated debris generated during any stack removal activity that has the potential to generate airborne radioactive contamination. Monitoring for airborne radioactive contamination will be performed during cutting and removal operations.
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A written response must beprovidedfor each ofthe qrtions asked This response must provide a basisfor the Yes/No answer.. An equivalent to thisform may be usedfor the written safety evaluation. as additionalspace may be required to adequatelyjustify the response to one or more ofthe questions posed Ifan equivalent to thisform is used. it shall include, but not be limited to. all ofthe information in thisform.
1.
May the probability of occurrence of an accident previously evaluated in the SAFSTOR Decommissioning Plan be increased?
YES
[]
NO g
BASIS:
HBAP C-19 A ttachment 8.2 Rev. 7 Page 9 The accidents listed below are identified and evaluated in Appendix I of the SDP. There is no increase in the probability of occurrence of any of these accidents as a result of this modification, as noted:
Spent fuel handline accident: No handling of spent fuel will be performed during the removal of the stack, Spent Fuel Storace Pool rupture: If not carefully controlled, mishandling of the cut pieces of the e
stack or other large equipment has the remote potential to cause a dropped piece of stack to rupture the Spent Fuel Storage Pool. The stack removal will be administratively controlled as described in the resolution ofIssue No. I above, in order to preclude the possibility of mishandling that could cause the rupture of the Spent Fuel Storage Pool.
Heavy load dron into the Spent Fuel Storace Pool: If not carefully controlled, mishandling of the cut pieces of the stack or other large equipment has the remote potential to cause a dropped piece of stack to cause a heavy load drop into the Spent Fuel Storage Pool. The stack removal will be administratively controlled as described in the resolution of issue No. I above, in order to preclude the possibility of mishandling that could result in a heavy load drop into the Spent Fuel Storage Pool.
Uncontrolled release of radioactive liauid radwaste to the environment: If not carefully controlled, mishandling of the cut pieces of the stack or other large equipment has the remote potential to cause a dropped piece of stack to cause an uncontrolled release ofliquid radwaste to the environment from the waste receiver or hold tanks, the Resin Disposal Tank or the Condensate Stcrage/ Demineralized Water Tank. The stack removal will be administratively controlled as described in the resolution ofIssue No. I above, in order to preclude the possibility of mishandling that could result in the uncontrolled release ofliquid radwaste to the environment.
Explosions. delayed ienition of flammable vanor clouds, release of toxic chemicals. or fire: If not carefully controlled, mishandlitig of the cut pieces of the stack or other large equipment has the remote potential to cause a dropped piece of stack to sever the natural gas pipeline that provides fuel to the fossil boile s of Units I and 2, causing an explosion, delayed ignition of the f ammable natural gas, release of toxic chemicals in the natural gas, or fire. The stack removal will be administratively controlled as described in the resolution of tssue No. I above, in order to preclude the possibility of mishandling that could result in an explosion, delayed ignition of the flammable natural gas, release of toxic chemicals in the natural gas, or fire.
The use of cranes will also introduce additional diesel fuel, hydraulic fluid and wood into the
- estricted area. The risk of explosions, release of toxic chemicals or fire, however, is not increased, as all combustible and flammable material introduced into the restricted area will be evaluated in accordance with the current Fire Hazard Analysis, and compensatory measures taken in order to preclude an increased risk.
Based ca the crane reliability and associated administrative controls, the training of the operators and riggers, and the administrative controls to control the load paths and exclusion zones, the work effort to remove the stack will not increase the probability of an accident previously evaluated in the SDP.
1 2.
May the consequences of an accident previously evaluated in the SAFSTOR Decommissioning Plan be increased?
YES O
NO e
BASIS:
ilBAP C-19.2 Rev.7 Page 10 Spent fuel handline accident; A fuel handling accident has the potential for release of fission products into the Refueling Building atmosphere. Prior to beginning the removal of the 250' Main Ventilation Exhaust Scack, a new stack will be in place, and has been designed so that the consequences of a spent fuel handling accident will not exceed the 0.13 mrem dose to the maximally exposed person at the site boundary that is the resulting consequence of the spent fuel handling accident previously evaluated in the SDP. There will be separate Written Safety Evaluation performed for this modification. As a result, this modification does not chang-the consequences of the spent fuel handling accident previously evaluated in the SDP.
Snent Fuel Storace Pool runture: This SDP accident evaluation assumed direct radistion from the spent fuel due to uncovering the fuel. For the stack removal process, none of the input assumptions that were used in che analysis of the Spent Fuel Storage Pool rupture accident described in the SDP changed. As a result, there is no increase in the consequences of the Spent Fuel Storage Pool rupture accident previously evaluated in the SDP.
Heavy loat drop into the Spent Fuel Storace Pool: As previously discussed, the stack removal will be administratively controlled in order to preclude the possibility of mishandling that could result in a heavy load drop into the Spent Fuel Storage Pool. Therefore there will be no increase in dose consequences beyond those previously analyzed for a heavy load drop into the Spent Fuel Storage Pool, as described in the SDP.
Nevertheless, PG&E personnel performed a calculation to determine dose consequences if a portion of the stack would drop through the roof of the Refueling Building, fall into the Spent Fuel Storage Pool and damage all 390 fuel assemblies. Under this scenario, with a release of 100% of the current-day Kr-85 inventory out through the hole in the Refueling Building roof, the calculated dose at the site boundary would be approximately 30 mrem. In the Safety Evaluation Report for the SDP, the NRC staff estimated that the consequences using the same release mechanism and 1984 Kr-85 inventory, were 20 mrem to the whole body. The NRC staff concluded in the heavy load drop accident analysis that these consequences are very small fractions of and, therefore, are well within the guideline values of 10 CFR Part 100 (25 Rem to the whole body and 300 Rem to the thyroid), We believe that the whole body dose of s approximately 30 mrem continues to meet the NRC acceptance of being well within the 10 CFR Part 100 guideline values of 25 Rem to the whole body and 300 Rem to the thyroid.
Uncontrolled release of radioactive liauid radwaste to the environment: The liquid wastes that will be generated during removal of the stack will be of both minimal volume and radioactivity.
These wastes will not appreciably add to the liquid radioactive waste inventory, and will certainly be less total activity than a small percentage of the two concentrated waste tanks that were postulated to be released to the environment in the same accident previously evaluated in the SDP. Therefore, there is no increase in the consequences of the uncontrolled liquid radwaste release accident previously evaluated in the SDP.
Explosions. delayed ignition of Hammable vapor clouds, release of toxic chemicals. or fire: The quantity of combustibles and flammables that will be introduced during the removal of the stack f
are only a very small percentage of s e fire loading of the fuel oil tank explosion previously i
evaluated in the SDP. This increased fire loading will not cause any detectable change in the
{
amount of damage postulated. Therefore, this modification does not result in any increase in the l
consequences of these types of accidents previoucly evaluated in the SDP.
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In summary, the consequences are not increased since the administrative control measures taken will 1
prevent a section of the stack from being dropped into the fuel storage building. Ilowever, even if the f
control measures did not exist and a section of the stack was dropped into the Spent fuel Storage Pool, i
the resulting dose would not exceed the acceptance limit used for approval of the SDP as defined in the Safety Evaluation Report for the SDP. Therefore, the proposed change does not result in an increase in the consequences of an accident previously evaluated in the SDP.
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a IIBAP C-19.2 Rev.7 Page 11 3.
May the probability of occurrence of a malfunction of equipment important to safety previously evaluated in the SAFSTOR Decommissioning Plan be increased?
YES O
NO g
BASIS:
In the SAFSTOR condition, ti.e only equipment classified as important to safety are the Boral Cans that tct as the neutron absorbing contamers for the spent fuel. The Boral Cans are passive devices that can still perform their intended function in any physical configuration, even if flattened by a heavy load dropped into the Spent Fuel Pool. Therefore, removing the stack does not increase the probability of occurrence of a malfunction of any equipment classified as important to safety.
l l
l 4.
May the consequences of a malfunction of equipment important to safety previo, ay evaluated in the SAFSTOR Decommissioning Plan be increased?
YES O
NO BASIS:
In the SAFSTOR condition, the only equipment classified as important to safety are the Boral Cans that act as the neutron absorbing containers for the spent fuel. The Boral Cans are passive devices that can still perform their intended function in any physical configuration, even if flattened by a heavy load dropped into the Spent Fuel Pool. Since the Boral Cans cannot malfunction, there are no consequences to increase. Therefore, the stack removal project does not increase the consequences of a malfunction of any equipment classified as important to safety.
i May the possibility of an accident of a different type than any previously evaluated in the SAFSTOR Decommissioning Plan be created?
YES O
NO g
BASIS:
l The types of accidents that are associated with the elevated transportation oflarge heavy objects and equipment that could have the potential to occur during the stack removal if the process is not carefully controlled have been previously analyzed in the SDP. Therefore, the stack removal project does riot creste the possibility of a different type of accident than any previously evaluated in the SDP.
6.
May the possibility of a malfunction of equipment important to safety of a different type than any previously evaluated in the SAFSTOR Decommissioning Plan be created?
YES O NO @
BASIS:
1 j
in the SAFSTOR condition, the only equipment classified as important to safety are the Boral Cans that act as the neutron absorbing containers for the spent fuel. The Boral Cans are passive devices that can still perform their intended function in any physical configuration, even if flattened by a heavy load dropped into the Spent Fuel Pool. Therefore, removing the stack does not create the possibility of a malfunction of any equipment classified as important to safety of a different type than any previously evaluated in the SDP.
1
IIBAP C-19.2 Rev.7 Page 12 7.
Is the n.. rgin of safety, as defined in the basis for any Technical Specification, reduced?
YES O
NO
_E BASIS:
Technical Specification IV.A.1, Refueling Building Ventilation System Design Features requires that the ventilation system provide normal ventilation to the Refueling Building, exhaust to the main ventilation stack, and that isolation valves be provided to permit isolation of the Refueling Building. Technical Specincation IV.B.1, Refueling Bui' ding Ventilation System Operating Limits and Requirements requires that the ventilation system be operated to maintain a negative pressure of at least % inch of water whenever spent fuel is being moved or whenever work is in progress that might potentially damage the sper.t fuel.
Prior to removal of the 250' stack, an alternate ventilation exhaust stack will be constructed and placed into service. Therefore, there is no reduction in the margin of safety as defined in the basis for any Technical Specification. Also, the stack removal will employ administratively controlled compensatory measures as described in the resolution ofIssue No. I to maintain the integrity of the Refueling Building.
If the answer to any of the above is "Yes", then the proposal involves an unreviewed safety question and require PSR*-' and NSOC ieview and approval by the NRC before the change can be made.
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Prepared By Date Reviewed by Plant Engineer Date PSRC Review
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Meeting Number Date
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