ML20212N616
| ML20212N616 | |
| Person / Time | |
|---|---|
| Issue date: | 08/08/1986 |
| From: | Lam P NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Rubin S NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| Shared Package | |
| ML20212N620 | List: |
| References | |
| NUDOCS 8608290037 | |
| Download: ML20212N616 (2) | |
Text
,
y ; 8- [M August 8, 1986 b
MEMORANDUM FOR: Stuart D. Rubin, Chief AE0D/E609 Reactor Operations Analysis Branch Office for Analysis and Evaluation of Operational Data FROM: Peter Lam, Chief
' Reactor Systems Section 2 Reactor Operations Analysis Branch i Office for Analysis and Evaluation '
of Operational Data
SUBJECT:
INADVERTENT DRAINING 0F REACTOR VESSEL DURING SHUTDOWN COOLING OPERATION Enclosed is an engineering evaluation report on operational events involving inadvertent draining of the reactor vessel in boiling water reactors (BWRs) during shutdown cooling operation. Eleven operational events which occurred at nine differeat plants in the past four years were analyzed and evaluated in detail. These operational events were primarily caused by human errors associated with the operation of the residual heat removal (RHR) system in the t
. shutdown cooling mode. The cause of these human errors can be traced to deficient procedures, improper or inadvertent actions, lack of knowledge or training, man / machine interface problems, cognitive errors, or maintenance errors.
The need for manual operation of the RHR shutdown cooling valves, the elevational differences and interconnections between the RHR subsystems, and the absence of comprehensive valve interlocks also contributed to the occur-rence of these operational events.
Four principal competing-factors significantly impact the safety significance of these operational events. The relatively low heat production rate during shutdown and the fact that for modern BWRs the reactor vessel can only be drained to_ expose the top one third core are two factors that tend to limit the ,
reactor accident risks associated with inadvertent draining of the reactor vessel. On the other hand, the reduced requirements for emergency core cooling ,
systems operability during plant shutdown and the lack of reactor vessel and prin,ary containment integrity, which are in place during normal power operation, would tend to increase the probability of a significant accidental radioactive release.
The study concludes that these operational events marginally increase (about 5%)
the likelihood of accidental radioactive releases in the BWR-2 release category in which a core-melt accident is postulated to progress witnout the benefit of containment integrity. In view of the severity of the BWR-2 release category, a 5% increase in the release probability is considered to be of medium safety significance.
TD43 EacS A O &n b '1 cod B608290037 860808 PDR ORG NEXD
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- Stuart D. Rubin , Because of the relatively high frequency and the safety significance of these events, the study suggested that several relatively low cost measures be implemented to prevent their recurrence.
Peter Lam, Chief Rea.ctor Systems Section~ 2 Reactor Operations Analysis Branch Office for Analysis and Evaluation of Operational Data
Enclosure:
DISTRIBUTION:
As stated POR AE0D S/F cc w/ enclosure: ROAB C/F K. Black, AEOD Plam J. Jankovich, NRR SRubin L. Kintner, NRR KBlack J. Strosnider, RI WLanning
- M. Wegner, IE FHebdon M. Jordan, RIII CJHeltemes R. Butcher, RII MWilliams A. Toth, RV W. Ruland, RII P. Holmes _ Ray, RII ,
J. Berry, RI D. Chamberlain, RIV T. Johnson, RI 4
s OFC :ROAB :ROAB : : : : :
_____:-__.... y-._: ______ _
- NAME :Plam:n .
- SRubin : : : : :
, DATE :R/cli/86 ;P/4f /86 : : : : :
0FFICIAL RECORD COPY 9
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