ML20245B664
| ML20245B664 | |
| Person / Time | |
|---|---|
| Issue date: | 11/06/1987 |
| From: | Chiramal M NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20235Z171 | List: |
| References | |
| REF-GTECI-050, REF-GTECI-A-44, REF-GTECI-EL, REF-GTECI-NI, TASK-050, TASK-50, TASK-A-44, TASK-AE, TASK-OR, TASK-T710 AEOD-C605, AEOD-C701, AEOD-T701, AEOD-T710, NUDOCS 8904260206 | |
| Download: ML20245B664 (4) | |
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AE0D TECHNICAL REVIEW REPORT UNIT: Multiple TR REPORT: AE0D/T710 DOCKET No.: Multiple DATE: November 6, 1987 LICENSEE: Pultiple EVALUATOR / CONTACT: M. Chiramal NSSS/AE: Multiple
SUBJECT:
HEATING, VENTILATING AND AIR CONDITIONING SYSTEM PROBLEMS INTRODUCTION In the October 15, 1987 ACRS memo to the EDO, ACRS recommended that NRC staff examine the generic extent of the problems experienced by nuclear plant heating, ventilating and air condition (HVAC) systems, and take any necessary corrective actions. As a followup to this memo, Ed Jordan requested an evaluation of the the generic dimensions of this problem. This report is in response to that request.
The report documents the review of operating experience involving HVAC system problems at operating nuclear plants from 1981 to mid-1987. The review considered the root causes of the problems, the safety-related systems affected by the problems, and the actions taken in response to the problems.
Based on the safety consequences of the problems and the adecuacy of corrective actions taken, the intent of the report is to look at future actions that may be needed to fully address the problems.
REVIEW PROCESS The Sequence Coding and Search Sytem (SCSS) data base was searched for licensee event reports involving HVAC system problems causing high ambient temperatures, HVAC system problems caused by high temperatures, and HVAC system problems adversely affecting other safety-related systems or equipment.
The search identified 183 such LER's for the period extending from 1980 to mid-1987.(Itshouldbenotedthatbecauseofthesearchstrategyusedonlya subset of events involving HVAC problems were obtained. However, for the purpose of the intended review this samplim ' onsidered sufficient.) The l abstracts of the 183 LER's were reviewed for . cot cause of failures and systems affected..
Generic actions, and communications such as information notices and bulletins, taken by the NRC in the area of HVAC related problems were also reviewed.
FINDINGS !
The root cause of the problems fell into three broad categories:
(1) design deficiency, (2) equipment or component failure, and l (3) personnel or procedural error.
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6904260204 871116 PDR l
ORG NEXD PDC
The following table shows the division of the 183 LER's in each of these categories.
l Table 1 1 Catetory Number of LER's
- 1. Design Deficiency 55 l
- 2. Equipment / Component failure 84 1
- 3. Persornel/ Procedural Error 44 The safety-related systems affected by the HVAC system problems are found to be readily identified by the location of the equipment or components of the affected systems. The 183 LER's are divided among the various system and associated areas as follows.
Table 2 Area /Systemn Number of LER's Control Room 25 BWR Containment (Drywell) 23 38 PWRECCS BWR Containment Rooms (HPCI,(Reactor RCIC, RHR,Building)
CS ) 38 PWR ECCS Rooms 17 Reactor Water Clean-Up System Room 13
' Diesel Generator Poom 9 Switchgear Room (including Battery / Inverter area) 9 Aux. Feedwater System Room 3 Miscellaneous Areas 8 Review of NRC generic communication data (bulletins, circulars and information notices) showed that many of the FVAC problems related to design deficiency have been the subject of followup and feedback actions. A total of approximately 20 bulletins, circulars and IN's dealing with environmental qualification of equipment (both inside and outside the containment), diesel generator ventilation systems, control room elevated temperatures, inverter problem temperature effects on level measurements, freezing weather, and electrical cable aging, have been issued. For example: Bulletins 79-01,79-01A, 79-01B and its supplements 1, 2, and 3 fiealt with environmental qualification of Class IE equipment, Bulletin 79-21 was on Temperature Effects on Level Measurements, Bulletin 79-24 was on Frozen Lines, Bulletin 79-28 was on Possible Malfunction of NAMCO Limit Switches at Elevated Temperatures, IN 84-21 dealt with Service Life of Relays in Safety-Related systems, IN 84-90 was on Main Steam Line Break Effects on Environmental Qualification of Equipment, In 85-89 was on Potential Loss of Solid-State Instrumentation Following Failure of control room Cooling, IN 86-49 was on Age / Environment Induced Electrical Cable Failures, IN 86-76 was on Problems Noted in Control l
J Room Emergency Ventilation. Systems, IN 87-09 dealt with Emergency Diesel '
Generator Poom Cooling Design Deficiency, and IN 87-24 was on losses of Electrical Inverters.
Some of the design deficiency problems are already covered by plant technical specifications--containment temperatures, ECCS room temperatures, control room ,
temperatures, steamline tunnel area temperatures.
Studies completed by AE00 on the effects of elevated ambient temperatures on electronic components, inverter failures and plant instrument air system problems (AE00/0604, AE0D/C605 and AE00/C701), also deal with some of the J generic design and common mode failure aspects of the plant ventilation and f cooling system. The ongoing AE0D study of service water :;ystems will be acdressing some of the HVAC auxiliary system design and operational problems, too.
Genric issues, such as, A-44--Station Blackout, and GI 50--BWR vessel level instrumentation, also deal with some of the generic design, installation and operational problems associated with ventilation systems.
DISCUSSION AND CONCLUSIONS Plant HVAC systems are designed and operated to provide controlled environments:
(1) for the safety and comfort of planc personnel, (2) to assure operabilty of c.umponents and equipment during normal operation, anticipated operational transients, and design basis accidents, and (3) to control and confine airborne radioactivity to particular areas.
All the events described in the 183 LER's reviewed for this study involved problems involving item 2 above (although, peripherally some of the events would involve items 1 or 3 as well).
Table 1 in the above section shows that equipment and component failures is the predominant root cause of the problems of HVAC systems. A review of the generic actions taken show that very little emphasis has been given to correcting this root cause. This suggests the need to analyse these types of failures and to identify and initiate corrective actions to address them.
The next major root cause of HVAC related problems, as shown in Table 1, is design deficiency. This is an area that has received followup actions and is likely to continue to get them. Actions relative to the ongoing generic issues on station blackout and level instrumentation, the recently issued AE00 case studies on inverters, instrument air systems and elevated ambient temperatures, the ongoing study on service water systems, and the many bulletins, generic letters and information notices, are evidence of this.
4 The final root cause in Table 1 is personnel and procedure problems. The review of the events in this category show that although the root cause is generally corrected at the plant that had these errors and problems, the experience and lessons learned are not effectively fedback to other nuclear plants. This is not surprising, for individually most such problems are not
-serious enough to warrant industry wide attention. However, collectively they show a need for licensees to pay more attention to the routine operational and maintenance needs of auxiliary systems, such as the HVAC system.
The data in Table 2 show that the problems identified are predominantly in areas that are governed by plant technical specification requirements. Areas such as control rooms, containments, ECCS rooms and RWCll system rooms are required by technical specifications to be operated within certain temperature t limits. The basis for these limits is analogous to the design basis of the area ventilating and cooling systems, and hence temperature problems should not be impacting operability of equipment in these areas. However, the LER data shows otherwise. This discrepancy implies that the area bulk average temperature, used for meeting the technical specification requirements, is not reflecting the local temperatures to which equipment and components are
. exposed to. The problem and effects of area temperature, the HVAC systems and operability of equipment are covered by past studies by AE0D and the ongoing station blackout issue. Ongoing efforts within the NRC and by some licensees are addressing the recommendations of these studies. Individual plants experiencing repeated elevated temperature problems, once identified as such, are taking corrective actions. Based on these efforts, no additional action is needed on this aspect of the HVAC system problem.
i RECOMMENDATIONS Based on the findings and conclusions, the following recommendation is provided:
AE0D should initiate a comprehensive study to analyze and evaluate operating experience involving plant HVAC systems. The focus of the study should be on those events involving component or equipment failure (or degradation) as the root cause of the problem. The study should identify and initiate comprehensive corrective actions to address the root cause. The study would also identify HVAC system problems involving design deficiencies and determine the adequacy of ongoing efforts in correcting such problems.
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