ML19211C824
| ML19211C824 | |
| Person / Time | |
|---|---|
| Issue date: | 11/16/1977 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19211C822 | List: |
| References | |
| REF-GTECI-A-09, REF-GTECI-SY, TASK-A-09, TASK-A-9, TASK-OR NUDOCS 8001150039 | |
| Download: ML19211C824 (9) | |
Text
.
IlylSilU 1
?
Title:
ATilS (A-9)
(TAC #4019)
Lead Responsibility: DSS Lead Assistant Director:
D. F. Ross, Jr., A/D for Reactor Safety Task Manager:
A. C. Thadani 1.
Problem Description The Technical Report on Anticipated Transients Without Scram for Water-Cooled Power Reactors, WASH-1270, discussed the probability of an ATWS event and an appropriate safety objective for these events.
After several years of discussions with the vendors and evaluation of vendor models and analyses, the staff published in late 1975 its status report on each vendor analysis including detailed guidelines on analysis models, and ATWS safety objectives.
The available information on consequences consists of vendor calculations based on essentially realistic models, but with some conservatism in the input data. The calculated consequences using the staff status report indicate design changes ranging from minor to significant are needed to meet the safety objective.
The industry has argued that the staff requirements in the status reports are excessive and that inadequate attention has been given to ATWS probabilities and consequences.
2.
Plan for Resolution:
The staff is presently rereviewing the whole ATWS program to reassess the impact of the status report requirements.
In this regard, a task force, chaired by Dr. Stephen Hanauer, has prepared a draft technical report which includes a review of recent vendor calculations, probability of an ATWS, discussion of various options, and a I
recommended course of action.
The following provides an estimate of the manpower effort needed to complete this generic review.
This estimate on manpower and schedule would have to be revised if one or more of the potential problems discussed in Section 8 materialize.
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i 1
I I.
TECHNICAL REPORT.
I The Hanauer task force has completed a draf t technical report I
which includes the following considerations.
1.
Safety Goal 1
Rationale for safety goal usino UASH-1270 WASH-1400 and conservative versus realistic risk calculations.,
2.
Frequency of ATWS Transients of concern and their recurrence frequency and the reliability of scram systems.
The data and methods use the information presented in WASH-1270, WASH-1400, I
EPRI reports and other publications. The scram system unreliability estimates include the consideration of the rods and drives.
3.
Course of ATWS Events The discussion covers evaluation of each vendor analysi:
assumptions, evaluation models and transient analyses.
This 1
evaluation also includes a discussion of system availability.
4 Conclusions Using the ATWS safety goal, estimates frequency of events and the 1
calculated consequences,and decides which design modifications are necessary.
5.
Criteria for Acceptable Fix Having defined the kinds of design changes indicated to meet the 1
ATUS goals, the staff criteria for acceptability of any required design modifications are provided.
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i i
II.
IflTERilAL REVIEW 0F THE DRAFT TECHfilCAL REPORT The staff has initiated an internal review of the draft technical I
report on ATWS.
The necessary steps in the conduct of this review are outlined in the plan in Section 7.
At the conclusion of this phase of review a revised draft ATWS report will be prepared, including the proposed requirements to mitigate, if necessary, the consequences of the postulated ATWS event. This report will form the basis for staf f recommendations to the ACRS and the RRRC.
111.
BWR POOL TEMPERATURE LIMIT Establishment of the suppression pool temperature limit is needed to completely identify the necessary design changes for Boiling Water Reactors.
The pool temperature limit is part of a Category A item (this activity number not yet assigned) and an interim acceptance limit is expected to be available in flovember 1977 and the final acceptance limit to be available in June 1978.
IV. COMPLET10ft 0F EVALUAT10f1 MODELS (See Item 3D)
V.
STAflDARD REVIEW PLAf1 Following completion of the technical report and selection of an alternative for cps and OLs, it would be necessary to develop a plan for review of individual license applications.
VI. OPERATlflG REACTORS A) Short Term Fix D0R has begun an effort to require implementation of a recircu-latio., pump trip on all operating BWRs.
This task involves development of criteria and implementation procedures.
B) long Term ATWS Fix Following selection of an option for satisfying ATWS requirements for cps and OLs, develop requirements for the operating reactors.
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.A.
VII.
REVIEW 0F FINAL VENDOR ATWS GENERIC ANALYSES In conformance with the selected option, the vendors will be required to provide ATWS analyses.
The analyses will be reviewed to insure that the assumed modifications satie.fy the ATWS limits.
3.
NRR Technical Organizations Involved: (Mai, power Estimates for FY 78 only)
A.
DSS / Reactor Systems Branch (1) Coordination of ATWS Program (2) This effort would involve coordination of internal reviews, meetings with veadors and consultants.
(3) Manpower Requirements:
4 Man Months B.
DSS /RSB/AB/CPB/CSB/ICSB, DOR, EDO, DSE, RES (RSB Estimates)
(1) Draft Technical Report Review (Task II) 1 (2) Technical Report Discussions with ACRS, other NRR Divisions, and Preparation of DSS Draf t ATWS Report.
(3) Manpower Requirements:
EDO: 5 Man Month ICSB:
1 Man Month RSB:
8 Man Months DOR:
2 Man Months AB:
1 Man Month DSE:
1 Man Month CPB:
2 Man Months RES:
2 Man Months CSB:
2 Man Months C.
DSS /AB/ICSB for GE Model (Task IV)
(1)
Evaluation Models (2)
Complete Review of B&W and GE Models (3) Manpower Requirements: AB:
2 Man Months ICSB:
9 Man Month D.
DSS /RSB/CPB/ICSB/CSB, DSE/AAB (Task V)
(1) Develop Standard Review Plans including consideration of value impact and obtain RRRC approval.
(2) RSB with support from other branches will develop review guidelines.
(3) Manpower Requirements:
RSB:
3 Man Months ICSB: 3 Man Months Other Branches:
3 Man Months 1744 289 E.
DSS /RSB/l&CSB/CSB/MEB/AB/CPB (Task VII)
(1) Generic vendor analyses for staff guidelines (2) The staff will review the vendor analyses to assure that the analyses are performed in accordance with the staff guidelines.
Design changes necessary to meet the limits would also be identified.
(3) Manpower Requirements:
1 1
1 4 MM MEB
's 3/4 1
2'3 MM AB 1
'4 3/4 MM 4
4 AAB 3
'3
's
!3 4 MM CPB 24
'4
'a
'4 1 MM CSB
'4 1/8 1/8 1/8 5/8 Mit I&CSB 1
1 1
1 4 MM F.
AAB/DSE Review vendor analyses and calculate radiological consequences.
Four fian lionths G.
DOR /PSB/RSB/0RB (Task VI A)
(1)
Short Term Fix on BWRs (2)
This effort involves development of criteria for recircula-tion pump trip and development of implementation procedures.
(3) Manpower Requirements:
Plant Systems Branch:
6 Itan Months Reactor Safety Branch:
6 Man Months Operating Reactors Branch: 6 Man Months 1744 294
-.? _ =
_ x.
=.
H.
DOR /PSB/RSB/ORD (Task VI B)
(1) long Term ATWS Program (2) Depending on DSS findings, develop criteria and implementa-tion procedures for required fixes on operating reactors.
(3) Based on presently available information, the projected required manpower is as follows:
Plant Systems Branch:
6 Man Months Reactor Safety Branch:12 Man Months Operating Reactors Branch:
6 Man Months I.
DOR /PSB/RSB/0RB (1) Contributions to other subtasks (2) Liason and review efforts that D0R will supply (3) Manpower Requirements:
Plant Systems Branch:
6 Man Months Reactor Safety Branch: 6 Man Months Operating Reactors Branch: 3 Man Months 4.
Technical Assistance Requirements:
A.
Bill:
Computer runs for D&U 177 FA plant to ob+.ain sensitivity values for changes in initial conditions.
This 1
task has been completed.
B.
Sandia:
Perform Monte Carlo calculations using vendors' and BNL calculations.
Support ATWS probability studies Management:
ED0 ED0/RSB Effort - Two Man Weeks Funding:
FY 78 Scope not yet estimated 1744 290
./
-l C.
Reactor Pressure Vessel Closure (TAC-3932)
Finite Element Analysis of B&W Vessel Report Completed and Reviewed 11/15 Management: Mechanical Engineering Branch MEB Effort - 2 Man Weeks Funding:
$ 3GK D.
Three-Dimensional Inelastic RPV Closure Analysis The decision to contract this analysis will be made following review of the two-dimensional analysis.
Funding:
$ 100K MEB Manpower - Five Man Weeks 5.
Interactions with Outside Organizations A.
EPRI The staff has been reviewing the EPRI probabilistic studies and intends to document its review in the technical report.
B.
KWU As noted in 8.E.
C.
Standard Development It is anticipated that an AT'd5 ANSI standard would be developed.
HRC and vendor participat: 30 in this task is anticipated.
The standard would be a useful tool in the implementation stages.
Therefore, a decision to participate in the standard development effort must be made.
6.
Ass _istance Req _uirements from other NRC Of fices:
Huclear Regulatory Research/Probabilistic Analysis Branch Support on ATWS statistical effort.
)]hh 5
A-
-b 7.
Schedule for Problem Resolution:
Technical Report (TR) Draf t #1 10/19/77 Comments on TR Draft #1 Received 11/03/77 TR Draft #2 Complete 12/13/77 ACRS, RRRC Information Meetings 12/20/77 Technical Report transmitted to ACRS and RRRC; Comission Briefing 01/15/70 1
ACRS Subcommittee, RRRC Decision 02/15/78 ACRS Committee 03/15/78 Commission Consideration of Policy Paper 04/15/78 Vendor Analyses Submittal 06/15/78 Standard Review Plans 07/30/78 GE - SER 10/30/78 il
- SER 12/30/78 CE - SER 01/39/79 B&W - SER 02/30/79 8.
Potential Problems A.
Rulemaking Hearings If rulemaking is eventually chosen as the method of generic resolution of this problem, hearings would likely be requested.
If so, it is difficult to assess the length of time and manpower the hearings would require.
B.
Plant Hearings Extensive effort is expected for hearings on some plants.
For example, the Black Fox hearing (possibly this fall), would require significant effort because of the type and the detaiis of contentions.
Three or more man months f rom RSB and two man months effort from other branches may be needed.
C.
Role of Hanauer Task Force if the completion of the technical report is delayed or if the reconinendation of the task force is to do additional studies, this action plan would have to be revised.
D.
Reactor Safety Study Possible differing conclusions between NRR and RES on ATWS contribution to the overall risk.
E.
Pressurizer Safety Valve Integrity and Water Relief Rate If the decision is made to obtain this information experimentally, the staff could continue ATWS generi review with an im
{
^
_q.
statement on safety valve integrity and water relief rate.
However, significant effort from the Reactor Systens Branch to coordinate this experimental program would be required.
F.
Long-Term Detailed Probabilistic Studies:
In the present simplified probabilistic study, a large number of assumptions, necessarily made to get some quick results, may cast a doubt on the study.
These concerns relate to inadequate selection of parameters, their distributions, nonlinear effects of parameters, interdependencies between parameters, etc., and the staff may recommend in the technical report to perform a more detailed study.
Management:
Reactor Systems Branch RSB:
Significant Efforts (Support from ASG) FY '78 and FY '79 Estimated Cost:
$ 2 '3 M G.
Standard Development If it is decided to participate in the ANSI ATWS standard development effort, approximately two man months of RSB effort would be anticipated and support from other brancnes my be necessary.
H.
Recent tests related to the GE evaluation model have resulted in a nossible need for a revision in the GF evaluation model.
1 The schedule for a modified model submittal and the staff review effort is being developed.
I.
If substantive comments on the Technical Report (TR) draf t #1 1
are received after 11/10/77, the schedule in item 7 would need a revision.
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