ML17209A766
| ML17209A766 | |
| Person / Time | |
|---|---|
| Issue date: | 11/17/1980 |
| From: | Ahearne J NRC COMMISSION (OCM) |
| To: | Udall M HOUSE OF REP., INTERIOR & INSULAR AFFAIRS |
| Shared Package | |
| ML17209A767 | List: |
| References | |
| NUDOCS 8012110047 | |
| Download: ML17209A766 (6) | |
Text
gg 'h REC~
~ yC
~
fp
+
0
(
.~
I
~o g4 CHAIRMAN UNtTEO STATES NUCLEAR REGULATORY COMMiSSiON WASHINGTON D C. 20555 November 17, 1980 The Honorable Morris K. Udall, Chairman Subcommittee on Energy and the Environment ComIIittee on Interior and Insular Affairs United States House of Representatives Washington, D.
C.
20515 D ar Mr. Chairman:
This responds to your letter of June ll, 1980 in which you asked the Commission again to consider seriously control system ailures in.uclear power plants.
Since such failures may have severe consequences, the NRC staff has begun to be ter define their safety significance.
Enclosure 1 sumarizes these actions.
Recen operating experience, such as the Crystal River event of last February, and continuing evaluation of the control system failure"issue, has led the s
a f tb propose to the Commission tha the issue has sufficient safety sig-.
nificance to justify its being designated as an "Unresolved Safety Issue" (USI) and reported to the Congress under Section 210 of the Eneroy Reorgani-zation Ac. (See Enclosure 2).
That proposal is currently under consideration by che Comission.
Classification as 'an USI would assure priority for resources needed for timely and effective resolu ion of this issue.
At the presen time, the Commission is relying on the consensus engineering judgment o
senior staff that
.he risk associa ed with control system failures is not suf icient o require imm diate corrective ac.ions such as power dere.ing. This judg,. nt is no. based on any special analyses or calculations beyond ihose normally per ormed in.he course of s.a
, review of postulated transients and accidents.
We recoonize (as you noted in Mr. Denton's October 22, 1979 memorandum) that the analyses do not take into'ccount all events that can be pos ulated.
The program outlined in Enclosure 2 is intended to provide a better basis for judging the adequacy of plant protection features and operator actions co mitigate control system failures.
With respect to th differences you no ed between the wording of our May 14 response and tha. o the previous staff statement enclosed with that response, the wording in the May 1-': letcer does convey a greater sense of certainty abou. the adequacy of analyses per,ormed to evalua
.e
.he interac.ion between high energy 1 ines and con rol sys.ems
.han does the December 1S, 197S memorandum.
We regret any misunderstanding this may'ave caused.
I
The Honorable l',orris I;. Udall please be assured that th Co-,nission is evaluating the safety significance of control svst~ failures and, depending on our findings, will take whatever actions are necessary to continue to assuro adequate protection of the public h alth and safe"y.
Sincerely, Oz ig-nel "-<<gaee 3V Do~a Z ~ Ehea;55 John F. Ahearne
Enclosures:
As stated
QSURi UPDnT.:
QF IYFQ.-",!'>ETIO>i PRO>';D="D I>l>':-'A.Pl'~~fr"S P> "v Q " cDQJ'~
Q Li"" I l-Sicr>i
> ican. corrective measures which h>ave been or will be reouired'a's a
result o> control system malfunc.ion or >ailure analyses conducted to da.e include the followino:
1.
For hioh energy line breaks which may be exacerbated by consequential con.rol system failures, some licensees adop.ed new operator procedures as needed to assure that the postulated events would be adeouately m>itioated.
2.
Jn response to Bulletin 79-27, som licensees have taken corrective
~.t action includjng hardware
- chanoes, and revised proceoures
.o assure'hat sinole failures of power supplies will not simul.an ously cause transients and failu-.e o-instru entation required to mitigate
,hese transients.'.
Licensees with BGW plants h>ave been required to address changes-ln the Integrated Control Sys.em to enhance its reliabili.y.
Tne analyses upon which decisions concerning he foregoing corrective maasu es have been based are as folios; 1
~
~
Opera;or procedures to mi+ica+e high eneroy line breaks causi>no add>tional cortrol system ailu'es were baseo on an ass ssl ent G
requi ed Gperat on acions and small break L'OCR analyses.
Cori ec.
1 v6 ac. ions result in
- 0. I 0 I 1 BT
< n I -27 have not bee as c on calcuIa. ions bu. rathe on ceouc ion regarding
-.he sequence 0
even s
expected
=rom postulated con.rol system failures.
A limited amount of sting has been done a. Crys.al River o confirm som o-the conclusions.
3.
t'erasures to enhance BOW integrated Control System reliability were based'on failure modes and effects analysis and operating history review.
The Commission's prooram =or determining the extent to which unanticipated control system feilures could aogravate accident sequences currently con-side", ed in the NRC's reoula.ory reouil em n.s consists of the followin :
I Creation of a new branch to'cus on systems interactions.
2.
Con.inua.ion of integrated Reliability =valua.ion Program to establish the relative risks o
control svstem failures.
Id notification of failure modes o
safety related instrumentation con-cu'ent with cont1 ol system failt,re throuoh reviews of licensee replies to Bulletin 79-27.
4.
tutu e 'Inoep h
I eview 0
license appl ications aoains.
Bxis ing Standard Rev',ew Plan Sec.',On 7.7 accepta cB criteria, inclucino;ailure "IGGBs and Bffec.s analyses.
Partici patio wi 'h an T:".":- working group in Gev~lopme t 0 5
"- darQs
- or control and o
- her non-safe'y B
'pment.
> h-Co
. iiss io i sta is a! So Gnsice inc es. ab I i shi ic a
neh' l esclve I
safety issue, Safety implications of Control Systems."
P paper which presents
.his
- p. oposal is unoe",'onsioe ation by the Co~iiission.
~
~
~ I