ML19269E496
| ML19269E496 | |
| Person / Time | |
|---|---|
| Issue date: | 03/07/1979 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-1608, NUDOCS 7906290175 | |
| Download: ML19269E496 (20) | |
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muss e Tas mRS SUBCOt4ITTEE ON ECCS WASHINGTON, D.C.
I h@h JANUARY 16, 1979 PDt2 9 n The ECCS Subcommittee of the ACRS held a meeting on January 16, 1979, in Room 1046, at 171/ H Street, h../., Washington, D.C.
W e main purpose of the meeting was to discuss a number of issues related to DCCS systems (listed on Attachment C). tbtice of this meeting was published in the Federal Register on Friday, December 29, 1978. Copies of the meeting notice, meeting attendees and the schedule are included as Attachments A, B, amd C, respectively.
No requests for time to make oral statements were re.ceived from members of the p.2blic and no written statements were received.
We Designated Federal Employee for the meeting was Dr. Andrew Bates.
'NESDAY, JANUARY 16, 1979 Introductory Statement by Subcommittee Chairman Dr. plesset, Subcommittee Chairman, convened the meeting at 8:40 a.m.,
indicated the purgse of the meeting, and that the meeting was being conducted in accordance with the provision of the Federal Advisory Committee Act and the Government in the Sunshine Act.
NRC Audit of the Vendors Code QA Procrams Mr. B. Sheron, NRC Staff, reviewed the audits that were performed by the NRC on the CA programs of the Vendors Codes. Se Audit was initiated in response to concerns expressed by Commissioner Gilinsky follcwing the discovery of a number of code errors in the spring of 1978. S e intent of the audit was to review the procedures in use by GE, Exxcn, CF, B&W, and W for the developnent and maintenance of their safety related computer 2145'198
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ECCS January 16, 1979 codes to see if they were sufficient to preclude or minimize code errors.
The audit was performed by a group made up of personnel from the Region IV I&E office and the NRC Analysis Branch. Se audit team visited each of the reactor vendors and reviewed one or two codes to see how their proce-dures work in actual practice. S e Staff also held a meeting with each of the vendors prior to the visit so that they could review the m procedures. During the visit the St. ff reviewed the code files to see how the available documentation reflected the required procedures for code verification and review. Se CA procedures of each of the Vendors had previously been approved by the NRC. S e procedures are generally based on ANSI N45.2.ll and Regulatory Guide 1.64 (see Attachment D).
Typically a code begins in a low cJassification category such as "developnental" and as the work on the code Mvances and the mathematical models are checked out and verified the code classification progresses through several more stages until the highest category is reached. At this point the fully mature code has been reviewed aM verified and is used in various safety analyses. During the review of the Code CA procedures the Staff looked at the errors that had been found to me if there had been reasons for the errors and ways that they could have been avoided. Se Staff found that errors are generally found by code users who notice anomalous results or by internal au3its b/ the code orginators. Errors generally involve input errors, errors in code application, errors in models, and programming errors. We Stiff indicated that the M procedures do not and will not guarantee corS to be error free, that experimental' verification will not pick up small errors, that the impact of most errors has been snall (especi-ally since some vendors typically offset error penalties with model improve-ments or revisions), and that the present reporting requirements are stringent and do rot distinguish magnitude of error.
As a result of their Audit the Staff reached a number of General Con-clusions (Attachment E) and found areas where improvements should be made (Attachment F). Recommendations (Attachment G) are being developed and the Staff plans to report to the Commission this spring.
2145 199 s.
venuary 16, 1979 ECCS During discussions with the Staff Subecomittee consultants expressed concerns over vendor procedures for reprting errors to the Staff and the continued use of codes with known errors. n e Staff indicated that in general the strict reporting requirements apply to ECCS codes that must meet Appendix K requirements, other safety related codes do not have the same reporting requirements. Bere are reprting requirements in 10 CFR Part 21 but in that case "significant safety deficiences must be reprted and the Vendors may not consider the error discovered to be of significant safety concern. S e Staff also pointed out that the vendors generally do not do additional verifica-tion of their approved ECCS models.
In general they believe that the models are conservative and that additional verification work will only continue to show that'the codes have conservatisms, but will not identify errors unless they are very large. % e vendors do participate in the Standard Problem Program which can help to identify problen areas with codes; although this is generally applicable to BE models rather then Di models. Dr. Theofanous suggested that a set of problems might be set up with the intention of p2shing the code to certain limits that are intended to identify inconsistencies and errors.
Subcommittee members and consultants indicated that the methods used by the various vendors to verify a code and check it out vary consider-ably and that some appeared to be less than adequate. Mr. Sheron indicated that ANSI N45.2.ll allows different methods of verification and that the vendors have interpreted th'e requirements in different ways. Part of the NRC recommendation includes clarification of the applicability of the ANSI code to computer code CA programs.
Dr. Plesset indicated that the Subcommittee would report to the full Committee on the Staff Code audit.
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ECCS January 16, 1979 t
NRC Report on Notification of Licens'ng Boards in Reponse to Tests in Semiscale (S-07-6) and the Two-Loop Test Apparation TLTA Mr. B. Sheron reported on the results of the first integral blowdown-reflood test conducted in the new Semiscale Mod-3 system (S-07-6).
The reflood portion of the test results showed a number of periods of refill and captying of the downcomer and core, causing reflood to take over 500 seconds versus a predicted 140-150 seconds (Attachment H).
Due to the unexpected results the Staff notified licensing boards of the observed phenomena and the inability to correctly compute the results.
Analysis of the test results, along with the results of tm subsequent tests have shown that the observed phenomena are probably related to a number of things. tese include an excess heat transfer from the downcomer walls to the downcomer fluid), excess heat transfer from core structural materials to the core fluid, and oscillating core steam production which produces an oscillating intact loop steam flow and an oscillating ECC subcooling in the downcomer. It is felt that the excess heat transfer in the downcomer with the oscillating fluid sub. cooling produces an overall system oscillation which empties and refills tha downcomer and core. Subsequent computer calculations with REIAP tend to support this explanation; however, REIAP has some limitations in its models which prevent calculations of all of the postulated physical phenomena at the present time. IASL is in the process of doing a calculation with TAAC and it should be completed at the end of January 1979. W e Staff will review the results of the TRAC analysis.
If TRAC calculates the observed phenemina, a WR calculation will be preformed to see if the oscillations occur in large reactors. If oscillations are also predicated there, the vendors will be asked to revise their codes.
If 'IRAC cannot calculate the phenomena the Staff will have to consider other analysis tools.
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-o-sanuary 16, 1979 The Staff is also reviewing methods by which they can reduce the down-comer heat transfer in order to make the system more typical of a IMR.
Further results of the analysis of this test will be reported to the ACRS at the March 19-20, 1979 meeting.
Mr. W. Hodges reviewed the results of recent tests conducted in the GE
'No-Loop Test Apparatus. We tests were the first ever conducted with combined blowdown and ECC injection. me test results indicated a slower depressurization of the system with the ECC injection (Attachment I).
1;' had not been expected that the ECS injection would produce higher pressures; the ECC fluid was expected to condense steam and re-duce pressure. Ibwever, no pretest calculations were done, the expected results were based upon intuition. Subsequent hand calculations indicate that ECC condensation of system steam is more than offset by additional steam production in the reactor core. Calculations now show that the GE vaporization correlation under-predicts the amount of vapor produced.
Part of the problem appears to be the amount of water being held within the fuel bundle which was greater than expected. We correlation was based on tests where water did not collect in the test bundle.
me slower rate of system depressurization can have a negative effect on the effectiveness of the KCS through delay in the actuation of the low pressure core spray and injection systems. Ibwever a review of the temperature history of the tests with ECC injection shows that the in-creased core steam production is very effective in cooling the core with temperatures several hundred degrees lower during the EC injection tests. Se Staff and GE are reviewing the tests to judge their appli-ability to BWR's.
GE is looking at the flooding of the bundle to see if the steam velocities and flow areas at the bundle entrance are typical of reactor bundles (flooding in reactors is generally thought to occur at the upper tie plate rather then at the bundle lower entrance). GE is 2145 202 e
.auary 16, 1979 also doing additional EM calculations with the new vaporization data $
see if the PCT values are affected. Se increased vaporization rate and delay of low pressure injection may be counterbalanced by the increased heat transfer obtained.
EG&G at Idaho Falls has also done a RELAP calculation for the system. Se results show much better cooling than was observed in the test, however they believe that they have a problem with the slip flow model in the calculations and that the REIAP model can't handle the EWR problem.
The Subcommittee will be kept informed on the progress of the GE and Staff review efforts.
NRC Report on the Status of Low Pressure Injection System Diversion in BhR's Mr. T. Novak reported on the Staff review of GE's proposed diversion of LPIS water to containment spray systems. As a part of the GESSAR-238 review in 1975 the concept of diversion of LPIS water to wet well sprays was con-sidered for a variety of cases where steam leaked from the dry well to the wet well, bypassing the normal flow paths. We consideration is only im-portant for certain small breaks where blowdown is prolonged over a period of time. In a base case evaluation, the worst small break shows a ECT 2
value of 1200 F.
If a small steam bypass area is asstraed (1 ft ) then after 10 minutes action is needed to reduce the wet well air space pressure.
Diversion of two of the LPIS injection pump flows to sprays in the wet well reduces pressure. Se unavailability of the low pressure injection water on PCT values was evaluated. S e differences in PCT value is on the order of 50 to 75 F.
In 1977 GE and the Staff identified a number of input errors in the snall break calculations and the new calculations showed higher FCT values for both the base case and the case with diversion. A new PCT curve has now been generated (Attachment J).
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...Jary 16, 1979 The new PCT values for the %R 4/5 plant are calculated to be about 1650 F/1725 F with diversion of LPIS water (1250 F without).
his item will be reviewed on the Shoreham and Zimmer plants (BWR 4/5) and on the Black Fox and Allens Creek designs (BWR/6).
NRC Plan to Revise Accendix K to 10 CFR 50.46 Mr. B. Sheron reviewed the status of the NRC plans to revise Appendix K.
We changes will be made in tw steps; the first will be procedural items, the second will be technical. Se Staff (NRR) plans to ask Standards to indicate rulemaking on the procedural item this summer, the technical changes will be sent to Standards at the end of 1979 and rulemaking is expeted,to take 1 to 11/2 years.
%e procedural requirements involve five items:
(1) Recalculation requirements (2) Revision to allow less than 1"/see flood rate heat transfer data (3) Revision to the return to nucleate boiling require-ment (4) Revision to the transicion boiling reference (5) More definitive requiements for documentation of ECCS model changes.
The 1st item would eliminate the need to do repeated ECCS calculation between the CP and OL stages of plant review and would eliminate the need to re-do calculations when the PCT would be decreased when a code error is found or a change is made. We use of reflood heat transfer data at rates below 1"/second.would be allowd. his change tends to be more conservative than the present steam cooling requirements due to the method of treating entrained liquid in the steam. Return to nucleate boiling from transition boiling would be allowed if supported by the
EECS January 16, 1979 s
experimental data. Return to nucleate boiling from film boiling would not be' allowed. Se Appendix K reference to the transition boiling is being charged to correct an error in Appendix K which references a wrcng paper by the same authors. Finally the changes would include definitive requirements for notification of the hRC when model changes are made.
The Subcommittee and consultants expressed some concern over the wordirg of the changes allowing return to nucleate boiling. Rey indicated that it should be clear that it is a return to nirleate boiling from transition boiling, not a rewet or quench phenomena.
We Subcommittee indicated that they wauld like to see the final wording ~
of the proposed changes.
Se Staff will spend additional time in the future reviewing possible technical changes with the Subecmittee.
Dr. Rosztoczy reported on se.veral items. Se Staff have asked EG&G at INEL to conduct a small break test on semiscale. m is is to give the Staff some additional data for use in evaluating small break models that the vendors have. Se test should be completed in January 1979.
The BWR EM package at SRL is in its final checkout phase. Se ER
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model should be done at the end of the year. mis will give the NRC Staff the capability of doing independent EM calculations to atriit the vendors results.
Several minor errors were found in the TOOCEE code. S e NRC has notified the US users of the errors and-they are being corrected.
(The errors were found by a foreign user and the NRC was notified by them.)
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ECCS January 16, 1979 Dr. Plesset thanked the participants and adjourned the meeting at 3:50 p.m.
For those who want a more detailed description of the meeting, a complete transcript is available at the NRC Public Document Room,1717 H Street, N.W., Washington, D.C., or from Ace-Federal Reporters, 444 North Capital Street, N.W., Washington, D.C.
A complete copy of the slides used is on file with the record copy of the minutes.
s.
2L45 206
_ NOTICES
[7590-01-M]
The agenda for subject snecting shall be as follows:
ADvisotf COMMITTit ot4 RIACToa SApt.
Tuesday. January 16.1979. 8:30 a.m.
QUARDS $USCOMMITTit ON' f>AIRGENCY tenfff the concluJion of business.
Coat COCUNG SY511M1 (ICC3)
The Subcommittee may meet in Ex.
ecutive Session, with any of its consul-Meeks tants who may be present, to explore The ACRS Subcommittee on Emer-and exchange their preliminary opin-gency Core Cooling will hold an open lons regarding matters which should meeting on January 16.1979 in Room be considered during the meeting and 1046. 1717 H Street. N.W.. Washing-to formulate a report and recommen-ton D.C. 20555 to review NRC licens-dations to the full committee.
ing activ:tles related to the proposed At the conclusion of the Executive revision of Appendix K.10 CFR 50 Session. the Subcommittee will hear the NRC audit of Code Quality Assur-j presentations by and hold discussions i
ance Programs the Standard Problem with representatives of the NRC Staff, Program. a sem,iscale small break test, and their consultants, pertinent to the and other items of furrent interest.
above topics.
Notice of this meeting was announced Further information regarding December 20.1978 (43 FR 59447).
topics to be discussed. whether the In accordance with the procedures meeting has been cancelled or resched-outlined in the FrnrxA2. Rectsm on uled. the Chairman's ruling on re-October 4.1978 (43 FR 45926), oral or quests for the opportunity to present written statements may tre presented oral statements and the time allotted by members of the pub!!c. recordings therefor can be obtained by a prepaid will be permitted only during those telephone call to the Designated Fed-portions of the meeting when a tran*
eral Employee for this meeting / Dr.
script is being kept, and questions may Andrew L. Bates (telephone 202/634 '
t be asked only by members of the Sub.
3267) between 8:15 a.m. and 5:00 p.m committee. Its consultants, and Staff.
EST.
Persons desiring to make oral state.
Dated: December 22,1978.
ments should notify the Designated Federal Employee as far in advance as JOHN C. Mont.
Advisory Committee practicable so that appropriate ar.
rangements can be made to allow the
- Management O//icer.
necessary time during the meeting for (FR Doc. 78-38288 Filed 12-28-78. 8:45 aml 5
such statements.
5 FEDERAt REGISTER. VCt. 43, No. 231-n!0AY, O(CIM8Et 29.1978 ATTACHMENT A 2145 207
ACRS SUBCGNITTEE ON ECCS 1GSHINGION, D.C.
JANUARY 16, 1979 ATTENDANCE LIST ACRS h7,C FI Flesset, Meder C ornstein H. Etherington, Member W. Lanning I. Catton, Consultant W. Paulson K. Garlid, Consultant T. Gilray R. Shumway, Consultant W. Haass H. Sullivan, Censultant Z. Ros: toc:y T. Theofanous, Consultant H. Scott i
T. Wu, Consultant B. Sheron F. Zaloudek, Consultant W. Hodges Z. Zudans, Consultant R. Tedsco A. Bates, Staff
- G. Bennett T. Novak
- Designated Federal Frployee hTSTINGmUSE ELECTRIC MITSUBIGI HEAVY INDUSTRIES V. Esposito K. Yamauchi D. Paddleford K. Itahara DUKE POWER CO CDfBUSTION ENGINEERING P. Abraham C. Brirhan G. Menzel SCANDPCNER, INC J. Cicerchia B. Leyse 1
BAB00CK S WILOOX ACE - REPORTERS R. Borsum D. Hoffman I
H. Bailey I
ATTACHMENT B 2145 208
PROPOSED PRESENTATION SCiEDULE FOR JANUARY 16, 1979 ECCS SUBCOAtITTEE MEETING WASHINGTON, DC I.
OPENING COMMENTS 8:30 a - 8:45 a a) ACP.S - 11. Plesset b) NRC Staff - 2. Rosztoczy II. NRC AUDIT OF CODE QA PROGRAMS (B. Sheron) 8:45 a - 9:45 a III. NRC STAFF NOTIFICATION OF LICENSING BOARDS IN RECENT RESEARCH TEST RESULTS a) Semiscale S-07-6 (B. Sharon) 9:45 a - 10:45 a b) TLTA (W. Hodges) 10:45 a - 11:45 a DISCUSSION 11:45 a - 12:00 noon LUNCH 12:00 noon - 1:00 p IV. NRC STANDARD PROBLEM PROGRAM (L. Phillips) 1:00 p - 2:00 p V.
NRC REVISIONS TO APPENDIX X T010 CFR 50 (B. Sheron) 2:00 p - 3:00 p VI. LPIS DIVERSION IN BWRs (T. Novak) 3:00 p - 3:30 p VII. OTHER ITEMS (Z. Rosztoczy) 3:30 p - 3:50 p a) Semiscale Small Break Test b) WRAP Audit Code Package at SRL c) T000EE Code Error VIII. CLOSING COMMENTS AND DISCUSSION 3:50 p - 4:00 p ATTACHMt.4T C 2145 209
v vy v
v NRR/QAB APPROVES QA IE DETERMINES IF VENDOR l
VEND 0R DEVELOPMENT D RE A
QA PROGRAM DESCRIPTION OF y
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VENDOR (REVIEW OF QA AND STANDARDS l
TOPICAL)
VEND 0R PROCEDURES l
FOR CODE DEVELOPMENT A
' E DEVELOPMENT COM-l ENDORSES ANSI N45.2.11 IE DETERMINES IF VENDOR PLETED-CODE CLASSIFIED STANDARD TliRU REG.
PROCEDURES INCLUDE RE-
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" DEVELOPMENTAL", " CON-GUIPE 1.64 QUIREMENTS OF ANSI STANDARD l
DITIONAL", U C.
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i CODE TOPICAL REPORT
, PREPARED AND SUBMITTEL l
TO NRC FOR REVIEW NRR/ DSS REVIEWS TOPJCAL y
y REPORT - ON SAFETY CODE DESIGN FILE COMPLETE VERIFICATION ANALYSIS METHODS &
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MOVE CODE INTO HIGHEST A
IE ROUTINE INSPECTIONS CLASSIFICATION CATAGORY STAFF HAY PERFORM y
PROCEDURES ARE BEING AUDIT CALCULATION FOLLOWED CODE APPLIED TO SAFETY PROJECT 4
ANALYSES FILE
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GENERAL CONCLUSIONS F da n unc c.o 6 p o i-r e VENDOR PROCEDURES ARE REASONABLY UNIFORM IN CONTENT, SCOPE, AND APPLICABILITY.
VENDORS ARE REQUIRED TO REPORT (UNDER 10CFR21) ERRORS WHICH COULD RESULT IN SIGNIFICANT DEFICIENCIES IN PLANT DESIGN.
ONCE A FINDING IS MADE OF A POTENTIAL DEFICIENCY, TIMELY REPORTING IS REQUIRED.
HOWEVER, THERE IS NO TIME LIMIT TO THE EVALUATION PROCESS.
MANY VENDORS TYPICALLY KEEP SAFETY ANALYSIS CODES IN CLASSIFICATION OTHER THAN THE HIGHEST.
MAJORITY OF ECCS CODE ERRORS TO DATE HAVE BEEN PROGRAMING ERRORS AND HAVE HAD LITTLE IMPACT ON RESULTS, BASIC CAUSE IS NOT HAVING LINE-BY-LINE INDEPENDENT CHECKING.
COMPARISONS TO TESTS WILL NOT UNC0VER SMALL ERRORS, ONLY LARGE ERRORS.
VENDORS CONTINUALLY REVISE AND UPDATE PROCEDURES, WHICH IN GENERAL IMPROVE THEM.
IE INSPECTION PROCEDURES DO NOT ADDRESS SPECIFICALLY COMPl!TER CODE DEVELOPMENT AND USE, INSPECTORS DO NOT, HAVE SPECIFIC INSPECTION PROCEDURES TO PERFORM SAFETY ANALYSIS CODE INSPECTIONS.
AMONG THE CODES AUDITED, ECCS CODE FILES ARE GENERALLY BETTER ORGANIZED THAN NON-ECCS CODE FILES.
THERE IS REASONABLE ASSURANCE CODES DO NOT HAVE MAJOR ERRORS.
PERCENTAGE OF ERRORS THAT ARE FOUND AFTER CODE RELEASE IS SMALL COMPARED TO PERCENTAGE FOUND DURING CODE DEVELOPMENT AND CHECK 0UT.
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GENERAL CONCLUSIONS (CONT.)
6*
MOST ERRORS REPORTED TO DATE WERE INTRODUCED INTO CODES DURING DEVELOPMENT.
FOR ECCS CODES, MANY INTRODUCED DURING 1974 COMPLIANCE PERIOD.
EXTENT OF GOOD CODE DEVELOPMENT AND MAINTENANCE PRACTICES (IN ASSENCE OF DEFINITIVE PROCEDURES) CANNOT BE ADEQUATELY DETERMINED DUE TO LACK 0F DOCUMENTATION.
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CERTAIN IMPROVEMENTS IN QA/QC PROCEDURES WOULD DECREASE POTENTIAL I
FOR UNDETECTED ERRORS AND WOULD IMPROVE CODE DOCUMENTATION.
EXPERIENCE GAINED FROM CODE INSPECTIONS BENEFICIAL TO NRR, IE, AND INSPECTED ORGANIZATIONS.
MANY AREAS FOR IMPROVEMENT OF PROCEDURES ARE ALREADY REQUIRED BY ANSI N45.2.11.
THE APPLICABILITY OF THE ANSI STANDARD TO CODE DEVELOPMENT IS NOT CLEARLY DEFINED.
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,&F AEAS HRE IfHU/EfBES IN PROCEDURES SHOULO BE fME INCLUDE:
l SPECIFYItE HOW L0tB A COE CAN ret %IN IN A C0f0lTI0tE, DEVELOREEAL,...ETCSTATE i
TitELY ASESS!EE OF SAFETY C0tTRS Ak0 DOCLENTATION l
OF C0tEERf6 R1f0 t0T REPORTA%E j
DOCtfEITIt0 VERIFICATION RESULTS ASSURitG 01PLETION OF DEVELOPER AfD ItNPEf0EfE j
VERIFICATI0fl REVIE)6 0F DOClfe US (SAR'S,T0oICALS, ETO l
PRIOR TO SUBMITTAL TO NRC VERIFICATION OF CODES DEVELOPED EXTEPJ R TO T11E ORGANIZAT
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INDEXING 0F CODE FILES 1
ASSURING CONSISTANCY OF TOPICAL REPORT WITH COMPUTER
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CODE B
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RECOMMENDATIONS cAU*
1.
ESTABLISH REQUIREMENTS FOR TIMELY RESOLUTICN OF SAFETY CONCERNS UNC0VERED IN CODE DEVELOPMENT.
2.
ESTABLISH REQUIREMENTS FOR KEEPING SAFETY ANALYSIS CODES IN HIGHEST CLASSIFICATIONS.
3.
IE INSPECTION PROCEDURES SHOULD BE CONSIMD RR MPER CODE DEVELOPMENT AND USE.
4.
CLARIFY APPLICABILITY OF ANSI N45.2.11 TO COMPUTER CODE DEVELOPMENT.
5.
NRR STAFF ASSIST IE INSPECTORS MORE FREQUENTLY.
6.
INCORPORATE AREAS FOR IMPROVEMENT IN APPROPRIATE NRC DOCUMENTS (E.G., STANDARD REVIEW PLAN, BRANCH TECHNICAL POSITIONS).
2145 214
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