05000458/LER-1998-001, :on 980417,flow Rate Through SGTS Filter Assembly Units Were Found to Be Higher than Design Flow Rate.Caused by Personnel Error.Reviewed & Updated Design & Licensing Basis Documents
| ML20236J006 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 06/30/1998 |
| From: | Lorfing D ENTERGY OPERATIONS, INC. |
| To: | |
| Shared Package | |
| ML20236J001 | List:
|
| References | |
| LER-98-001, LER-98-1, NUDOCS 9807070447 | |
| Download: ML20236J006 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4581998001R00 - NRC Website | |
text
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 (4-95)
EXPIRES 04/30/98 f##1'Ba"W/c'"Me"UMJ a"s%"ain'o%rWM=
LICENSEE EVENT REPORT (LER)
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IN FAGIUTY NAME (1)
DOGKE1 Numptn (2) g FAGE {3)
River Bend Station 05000-458 l
1 of 7 m u H3 Flow Rate Through tne Standby Gas Treatment System Filter Assembly Units Found to be Higher Than the Design Flow Rate EVENT DATE (5)
LER NumptM (5) l MtPORT DATE (7) l OTHER FACILilits INVOLVED (6p l
MUNIH DAT TLAM YLAR bL U NIiAL R
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20.2203(a)(1) 20.2203(a)(3)0) 50.73(a)(2)(W) 50.73(a)(2)(x) 20.2203(a)(Zl(i) 20.2203(aX3)(si) 50.73(a)(2)(m) 73.71 20.2203(a)(2)(n) 20.2203(a)(4) 50.73(a)(2)(iv)
X OTHER 20.2203(a)(2Xm) 50.36(c)(1) 50.73(a)(2)(v) sg act below 20.2203(ax2Xiv) 50.36(cK2) 50.73(aX2)(vii)
Voluntary Report LIGEN5EE GONTACT FOR THIS LER (12)
NAML ILLLPHUNL NUMBLR (include Arte Gmie)
D. N. Lorfing, Supervisor - Licensing 504-381 4157 COMPLtit ONE LINE FOR EACH COMPONENT FAILURE DEUGRIBLD IN THIS MtrvMi (13)
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NO Of yes. complete EXPECTED T'J3 MISSION DATE).
IUSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)
On April 17,1998, with the plant in Mode 4 (Cold Shutdown), flow rate through Standby Gas Treatment (GTS) system filter assembly unit "B" was determined to be higher than its design flow rate. Subsequently, filter unit "A" was also determined to have an elevated flow rate. The nominal design flow rate of the filter unit is 12,500 cubic feet per minute (CFM). An evaluation found that the GTS system was operable in the as-found condition, with elevated flow rates through the filter assembly units..his report is submitted as a voluntary report.
Resolution of the condition was achieved by rebalancing el the system. Filter unit flow rate was established within 12,500 CFM, plus or minus 10 percent. The primary root cause was River Bend Station personnel did not exhibit a comprehensive level of sensitivity to the complex design and licensing requirements for the GTS system. Corrective actions include review and update of design and licensing basis documents. A detailed evaluation of the system's ability to perform its safety function at the elevated filter unit flow rates was performed. The conclusion of this evaluation was that the GTS system was capable of performing its safety function at the elevated filter unit flow rates.
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9807070447 980630 PDR ADOCK 05000458 S
.U.S. NUCLEAR REGULATORY COMMISSION (4:5)
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Reported Condit.fon On April 17,1998, with the plant in Mode 4 (Cold Shutdown), flow rate through Standby Gas Treatment System (OTSi filter (*FLT*) assembly unit "B" was determined to be higher than its design flow rate. The l
design flov. : ate of the filter unit is 12,500 cubic feet per minute (CFM). The actual flow rate with filter train "B"in its post-accident configuration was found to be 15,360 CFM. Subsequently, the actual flow rate through the "A" filter assembly unit was found to be 14,679 CFM. Note that actual flow rate is dependent on system damper configuration and balancing, as well as the condition of the building and filter unit.
Operability / Deportability Evaluation An evaluation of the impact of the condition on operability of the GTS system was performed to support a determination ofreportability. This evaluation found that the GTS system was operable in the as-found condition, with elevated flow rates through the filter assembly units. The evaluation included a detailed review of system safety function, focusing on the ability of each subcomponent of the GTS filter units to perform their required function. The conclusion of this evaluation was that each filter unit could perform its safety function.
Thus, there was no loss of safety function due to the condition.
The operability evaluation also included a review of Technical Specification requirements for GTS. Technical Specification (TS) 3.6.4.3, " Standby Gas Treatment (SGT) System," and TS 5.5.7, " Ventilation Filter Testing Program" were reviewed. As part of the testing program for the filter units, TS 5.5.7 specifies tests be performed at a design nominal flow rate of 12.500 CFM, plus or minus 10 percent. The last performance of the tests specified in TS 5.5.7 were performed within this flow rate range. This surveillance demonstrated the performance capabilities of the filter units and the quality of the subcomponents at the flow rate specified in the Technical Specifications. The results of the last performance of these tests were used to correlate performance of the units at the elevated flow rate. For this evaluation, a flow rate of 15,400 CFM was used as a bounding value for both filter units. This evaluation found that the filter units were capable ofmeeting the surveillance acceptance criteria at the elevated flow rate. Thus, the conclusion of this evaluation was that TS surveillance requirements were met, and that operation at the higher flow rate remained within the TS acceptance criteria for the filter units.
In summary, it was concluded that the requirements for operability were met in the as-found condition. This condition did not result in " operation prohibited by Technical Specifications" nor did it result in any loss of safety function. The condition was determined to be not reportable. This report is submitted as a voluntary report for industry review of generic applicability.
i B:ckground Information The function of the G!S system is to ensure that radioactive materials that leak from the primary containment into the secondary containment following a postulated Design Basis Accident (DBA) are filtered and adsorbed prior to exhausting air to the environment. The GTS system consists of two fully redundant subsystems, each
.U.S. NUCLEAR REGULATORY CoMMISSloN (4-95)
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River Bend Station 05000 458
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98 001 with its own set of ductwork, dampers, charcoal filter unit, and controls. Each charcoal filter unit consists of l
(components listed in order of the direction of the air flow):
a moisture separator; an electric heater; a l
prefilter; a high efficiency particulate air (HEPA) filter; a charcoal adsorber; a second HEPA filter; and a centrifugal fan.
The GTS system is designed to maintain a negative pressure in the annulus (area between the containment structure and the shield building) and in the Auxiliary Building during post-accident conditions. Filter train subcomponents perform the following functions. The moisture separator is provided to remove entrained water in the air, while the electric heater reduces the relative humidity of the airstream. The prefilter removes large particulate matter, while the HEPA filter is provided to remove fine particulate matter and protect the charcoal from fouling. The charcoal adsorber removes gaseous elemental iodine and organic iodides, and the final HEPA filter is provided to collect any carbon fines exhausted from the charcoal adsorber.
A simplified drawing of the system in its post accident configuration is attached.
Event Description
During review of an engineering modification to the GTS system, a concern was identified related to flow rates through the GTS filter units with the system in its post accident configuration. The post accident configuration for the system was with damper (DMP) 5 A/B, in the filter train recirculation ductwork, throttled approximately 20 percent open. The concern was that flow rate through the filter units was not directly measured. Actual flow rates, with the recirculation path open, were not known. Upon identification of this concem, River Bend personnel installed test instrumentation to directly measure filter unit flow rate, and flow rate measurements were taken with the system in the post accident configuration (point 2 in the attached figure). Previously, flow rate was measured at point 1 in the attached figure. Actual flow rates were determined to be higher than the nominal design flow rate of 12,500 CFM. In addition, the flow rates were higher than the test parameter flow rate given in Technical Specification 5.5.7, " Ventilation Filter Testing Program" (12,500 CFM, plus or minus 10 percent).
Investigation and Immediate Actions Upon identification of the elevated flow rates, an initial investigation was conducted and alternative solutions for the condition were identified and pursued. The operability evaluation, discussed above, was performed to determine operability in the as-found condition. Resolution of the condition was achieved by rebalancing the system filter unit flow rate to within 12,500 CFM, plus or minus 10 percent. Based on rebalanced system flow rates, the post LOCA (loss of coolant accident) positive pressure period was determined to be longer than previously calculated. An operability calculation of post LOCA off site doses, assuming the longer positive pressure period, was performed. This operability calculation determined that post LOCA off site and control room doses were within the doses stated in the USAR. In addition, an engineering evaluation and visual 3
inspection of the filter units were performed which determined there was no adverse affects caused by the elevated flow rates through the GTS filter units.
k NRC FGiWu 308A U.S. NUCLEAR REGULATORY masameerw (4-96)
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'4 of. 7 98 001 Based on rebalancing of the system to within the nominal design flow rate, confirmation of the ability of the system to perform its safety function to limit post LOCA off site doses to within regulatory limits, and engineering evaluation of the impact of the condition on the system, the system was retumed to service.
Root Cause(s)
A root cause analysis for this condition and other related issues involving the GTS system and Auxiliary Building negative pressure was performed. The primary root cause was River Bend Station personnel did not exhibit a comprehensive level of sensitivity to the complex design and licensing requirements for the GTS system.
System and Design engineers were constrained by their assumption that the original design of the GTS system was capable of meeting the diverse requirements placed on it. In fact, later review and balancing attempted during Forced Outage 98-01 demonstrated that the design configuration simplicity of the
__ system will not allow it to meet all system requirements, such as: drawdown requirements, maintain a flow rate of 12,500 CFM in both the containment purge and the Loss of Coolant Accident mode, and result in long term Auxiliary Building negative pressures between 1/4 in. Water Gauge (W.G.) and 1/2 in. W.G.
River Bend Station personnel were focused on the safety functions of the Secondary Containment and the GTS system to contain, dilute, and hold up fission products that may leak from the primary containment following a Loss of Coolant Accident. It was understood the GTS system must meet the Technical Specification drawdown times to assure the performance is within the assumptions of the offsite dose calculations. Personnel developed the assumption that a higher long term negative pressure would only help to assure that air exhausted from the Annulus and Auxiliary Building was filtered and adsorbed by the GTS system. Although Specification 216.300, " Air Conditioning and Ventilation Systems - Hydronic Balancing", was referred to in the condition investigation, it was believed the pressure criteria contained in the specification applied only to initial system balancing done at startup
. and did not constitute design requirements for the system. River Bend Station should have recognized the need to reconcile the nonconformances with design and licensing bases documentation at this time.
Additionally, the relationship between recirculation line alignment, Auxiliary Building pressure, and
- - filter train flow requirements was not recognized, although the individual requirements were known.
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Cctributing Factors:
The root cause analysis identified contributing factors related to the reported condition and other related issues. The contributing factor specifically related to the reported condition is given below. Other contributing factors are being addressed within the River Bend Station corrective action program, The balancing instructions contained in Specification 216.300 lead to a system alignment where o
filterflow may exceedsystem designflow rate of12,500 CFM.
The specification states, "The (SGTS) bypass loop dampers, IGTS*AOD 22A,22B, must be closed." The inlet damper is then adjusted for a flow rate of 12,500 CFM arid suction paths established to the GTS system from the Auxiliary Building and Annulus via Annulus Mixing.
Then, the specification directs the user to,"Open (SGTS) filter train bypass loop damper IGTS*AOD22A or 22B, and adjust and set the pressure for the Auxiliary Building with manual dampers 1GTS*DMP5A or 5B." This results in filter train flows substantially different from, and higher than, the 12,500 CFM obtained during the prerequisite balancing.
j Ccrrective Actions Immediate actions taken upon discovery of the condition are described above. Actions to address the results of the root cause analysis as related to the reported condition are given below.
River Bend will perform a review of the design and licensing bases of the Standby Gas Treatment system o
and secondary containment prior to plant startup following Refueling Outage 8.
Complete the System Design Criteria review for Standby Gas Treatment and update licensing bases l
o documentation prior to plant startup following Refueling Outage 8.
Update Specification 216300 and clarify Environmental Design Criteria 215.150 to reflect maximum o
negative pressures and correct the inaccuracies in the balancing instructions that contributed to the high flow situation prior to plant startup following Refueling Outage 8.
Brief Engineering Department personnel on the specific lessons learned from this issue including o
recognizing the importance of both high and low limits for design ranges; and the proper use of configuration control change mechanisms.
S:fety Significance A detailed evaluation of the system's ability to perform its safety function at the elevated filter unit flow rates was performed. Each subcomponent of the GTS filter units was evaluated to determine impact of elevated flow
- U.S. NUCLEAR REGULATORY COMMIS$10N (G95)
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River Bond Station 05000-458
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98 001 rate on the subcomponents ability to perform its intended function. This evaluation concluded that each subcomponent was capable of performing its required function at the elevated flow rate. Evaluation of other system components, such as the exhaust fans, dampers, ductwork, and the filter housing, concluded that the elevated flow rates did not impact the ability of the system to perform its function. Dose analysis was also reviewed to ensure no impact due to the elevated flow rates. The conclusion of this evaluation was that safety function was not impacted at the elevated filter unit flow rates.
Note: Energy Industry Identification codes are identified in the text as (*XX*)
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NRC FORM 344A U.S. NUCLEAR REGULATORY COMMISSION (4-95)
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River Bend. Station 05000 458
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COMMITMENT
ONE-TIME CONTINUING ACTION COMPLIANCE Review the design and licensing bases of the Standby Gas Treatment X
System and Secondary Containment. Additionally, RBS will complete the Standby Gas Treatment System Design Criteria review and update the Licensing and Design Bases documentation.
Brief Design and System Engineering personnel on the specific lessons X
leamed from this issue including recognizing the importance of both 3
high and low limits for design ranges and the proper use of I
configuration control change mechanisms.
Update Specification 216.300, " Air Conditioning and Ventilation X
Systems - Hydronic Balancing" and clarify Environmental Design Criteria 215.150 to reflect maximum negative pressures and correct the inaccuracies in the balancing instructions that contributed to the high flow situation.
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