ML20056A711
| ML20056A711 | |
| Person / Time | |
|---|---|
| Issue date: | 08/30/1989 |
| From: | Baer R, Cherny F, Rachel Johnson NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| Shared Package | |
| ML20056A707 | List: |
| References | |
| REF-GTECI-015, REF-GTECI-NI, TASK-015, TASK-15, TASK-OR NUDOCS 9008090073 | |
| Download: ML20056A711 (19) | |
Text
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4 TASr, ACTION PLAN Revision 0
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August 3D, 1989 Generic Safety Issue 15 Radiation Effects on Reactor Vessel Supports Issue Type:
High/ Generic Safety Issue 1
Lead Organization:
Engineering Issues Branch Division of Safety Issue Resolution Office of Nuclear Regulatory Research Task Manager:
Richard E. Johnson Engineering Issues Branch Division of Safety Issue Resolution Office of Nuclear Regulatory Research Lead Supervisor:
Frank C. Cherny, Section Leader, Section B Engineering Issues Branch Division of Safety Issue Resolution Office of Nuclear Regulatory Research Contractors:
INEL Applicability:
All LWR Nuclear Power Plants Projected Completion Date:
DATE 11!M[M,TaskManager l
Approved le N N
RichardE.hJohnson 6
[ A /Jd6/
- ,u 4 1, Section Leader FrankC.Cherny-f pdf I, b'd '7
/// 22/7 Chief, EIB Robert L. Baer 7_ /
//, t, 9, Deputy Director, DSIR Thomas L. King
/z/
Director, DE
[awrenceC.Shao
/
N e[r,
'/C/
, Director, DSIR m
Warren Minners 0
9008090073 900116 PDR GTECI GNIO15 PDC
a.
J I.
Description of Problem.
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A, Statement of Issue Generic Safety. Issue 15.(GSI-15), " Radiation Effects on Reactor Vessel
~ Supports," will address the concern that low-temperature, low-flux
)
irradiation may embrittle reactor pressure vessel (RPV) supports more rapidly than expected.
A recent Department of Energy (00E)/0ak Ridge National Laboratory (ORNL) study of the High Flux' Isotope Reactor (HTIR) showed that the embrittlement of the HFIR RPV, exposed to 3
P low-temperature, low-flux radiation was more rapid than previously expected.
Responding to a question from the ACRS, the NRC asked ORNL
[-
to evaluate the potential for more rapid than expected embrittlement of RPV supports based on the results of the HFIR study.
Prelimina ry reviews of neutron radiation parameters and residual support strength.
s by the NRC failed to confirm a need for an immediate fix of the safety concern in this issue suggesting that GSI-15 might be treated in the context of long term aging effects, further investigation, therefore, is needed under GSI-15 to assess the short-term and long-term radia-tion effects on RPV supports exposed to low-temperature, low-flux radiation. 'The problem is further complicated by a number of other
- factors, for example, preliminary reviews showed that reactor
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structural support records are inadequate.
Inexact knowledge of the chemical composition, metallurgical condition and initial mechanical properties of support steels contributes to uncertainties in predicted irradiated properties and response to the high strain rates and loads from accident scenarios.
Resolution of the issue must~ address either more precise property determination or a conservative analysis using approximations..
B.
Background
GSI-15 addresses the potential problem of radiation embrittlement of RPV supports.. It was originally identified as a candidate Unresolved Safety Issue (USI) in NUREG-0705 (Ref. 1) where it was recommended for further study before a judgment was made on its designation as a USI.
In a prioritization of the issue in November 1983, it was concluded that the total occupational dose associated with resolving the issue outweighed the potential decrease in public risk.
As a result, the issue was assigned a LOW priority until additional data on the problem became available.
In June of 1987, the Advisory Committee on Reactor Safeguards ( ACRS) asked the NRC to consider the possibility of more rapid than expected s
embrittlement of RPV supports when exposed to low-temperature, i
low-flux irradiation.
The ACRS was reacting to information derived from a Department of Energy investigation into the embrittlement and fitness for continued service of the High Flux Isotope Reactor (HFIR) located at ORNL.
That investigation, described in ORNL/TM-10444 (Ref. 2), revealed significantly more embrittlement of the HFIR pressure vessel than would be expected based on traditional irradiation damage data.
At the end of the HFIR study, the researchers were left with the conclusion that the more rapid than 1
expected embrittlement was due to low-temperature (~120*F), low-flux (108 - 10' n/cm -sec E > 1MeV) irradiation.
This was called a r
" fluence-rate ef fect" wherein it was postulated that low flux irradiation produces more damage than high flux for a given fluence.
Since RPV supports operating temperatures are typically in the range of 100'F to 200*F and the cavity flux in the vicinity of the core mid plane is similar to that for the HFIR vessel wall, the ACRS questioned the potential for more rapid than expected embrittlement of these supports.
An initial scoping study by the ORNL researchers involved in the HFIR study indicated that there was a significant potential for these support structures to become embrittled.
Based on that conclusion, a reassessment of the priority of this issue was performed by the staf f in December,1988 resulting in a reclassifica-tion of the issue to a'HIGH priority ranking.
A more detailed, but still preliminary, study was undertaken by the ORNL researchers as a task under the Heavy Section Steel Technology (HSST) program.
The study focused on evaluating the structural integrity of specific plant support structures.
As part of the study, a survey of the various types of support structures was completed.
1 Five support types were identified--skirts, shield tanks, long column 4, short columns, and suspension studs.
The skirt type supports were not
. considered further because of the extremely low fluence the; receive.
Evaluations provided by the industry concluded that shield tank and long column supporte were acceptable, and ORNL did not undertake detailed reviews of them.
Suspension studs are used on only one SWR; apparently they operate at a relatively high temperature and were not considered further.
Thus the preliminary conclusion was that the short column type supports were of primary concern.
The short column support designs were reviewed and two plants (Trojan and Turkey Point Unit 3) were selected based on a review of the final Safety Analysis Report (FSAR) drawings.
Support structures at both plants had members that were in tension, that were exposed to neutron irradiat.on fluxes similar to those in the HFIR, and that operated at low temperatures.
Results of analyses of these two plants were reported in NUREG/CR-5320 (Ref. 3).
A number of assumptions were required to coniplete these analyses.
These included assumptions regarding the material-ano its mechanical properties, the size of flaws that could have resulted f rom the f abrication process, the loadings, the neutron flux and energy spectrum at the tension members in the supports, the attenuation of that flux due to the concrete biological shield wall, and the ef fects of lov;-temperature, low-flux irradiation, and the strain rate effect (due to accident loading) on the fracture of RPV supports.
The analyses of the Trojan and Turkey Point RPV supports led to the preliminary conclusion that within the plants' design lives, small flaws could result in structural failure under certain accident loadings.
However, owing to the number of assumptions needed in 1
2 d
1 performing the analyses, the uncertainty in the conclusion was i
L significant.
In this regard, the fracture analyses essentially g$
were inconclusive.
The conclusion in Ref. 3 that neutron radiation could significantly i
reduce..the fracture resistance of the Trojan RPV supports depended to a large degree on the assumption that the FFIR data were influenced by a fluence-rate effect.
HFIR has a softer flux spectrum (i.e. a much larger ratio of low energy neutrons to fast neutrons) than typical materials testing reactors (MTRd used to obtain radiation damage data. Therefore, another possiv1.iS was that the low energy _
neutrons were active in damaging the steel.
The NRC staff performed an initial evaluation of this possibility based on approximations of i
the HFIR flux spectrum and integration to lower neutron energies than were used in Ref. 3 to calculate the expected damage to the structural supports. These calculations indicated that the soft flux spectrum was a plaud'O ;xplanation for the data obtained at HFIR.
Further work is nemstr; to resolve the discrepancy.
D On January 11, 1989, the Office of Nuclear Reactor Regulation (NRR) issued a request to the Office of Nuclear Regulatory Research (RES),
to perform:
(1) a failure consequence evaluation of RPV support failure; l2) a probabilistic fracture mechanics risk analysis of the i
limiting RPV supports; and (3) structural tests, if necessary, to show the capacity of cracked RPV supports. The Division of Engineering, RES, responded on January 31, 1989 stating that the first of the three items was to begin immediately, the second would begin after
'the steff had made more progress and the thir.d would be deferred pending the results of the first two. The RES staff identified additional work needed to resolve many of the uncertainties in the ORNL analyses.
The results of the investigation reported in Reference 3 and more recent preliminary analyses, including materials and structural evaluations performed by the staff and its contractors, were presented at the joint ACRS Materials and Metallurgy / Structural Engineering Subcommittee Meeting on March 23, 1989 and at the full ACRS Meeting on April 6, 1989. The presentations at the ACRS meetings asserted that further research and analyses are needed to quantitatively evaluate the integrity of the supports but preliminary structural evaluatiori of the Trojan RPV supports, including conservatively high accident loading and significant low temperature irradiation, led to the conclusion that there is no immediate safety concern.
C.
Purpose The purpose of this task action plan (TAP) is to assess the short-term and long-term radiation effects on reactor pressure vessel supports when exposed to low-temperature, low-flux radiation. The strain rate effect on RPV support fracture will also be assessed. The TAP is based on-the current knowledge of the issue, including results of work previously performed and preliminary results from on-going efforts at the time the plan was developed. The plan will be periodically 3
l
e - - -
r reviewed,-and revised if appropriate, as results of various tasks and.
subtasks become available.
-11.
Plan f or Problem Resolution I
A.
General Approach The general approach _for resolution of GSI-15 is described below.
Task I represents the main effort:
collection of information on domestic reactors and the current plant-specific RPV support design margin, development of potential alternative solutions and identifica-tion of the viable _ones,. development of general RPV support review c
criteria, and preparation and issuance of the GSI-15 resolution package.
There are a number of supporting tasks, many of which were initiated prior to the preparation of this TAP.
i ORNL performed an initial survey of the support structures of domestic
-l reactors and identified Trojan as the plant that appears to have the most immediate potential problem.
Further neutron radiation assessment by the staff of the_ Trojan reactor support structure indicates that j
the problem is probably one of long-term aging rather than an immediate safety concern.
However, the analysis should be considered preliminary because of large uncertainties in the original mechanical properties i
of-the A-36 steel from which the structure was fabricated, the unknown effect of flame-cut holes in the structure, the strain rate effect on i
t support f racture, and the actual radiation exposur.e. af. t he structure l
[
and its effect on the material properties.
/
Task 1,.in part, will include a multi-disciplined team review to i
verify that the most vulnerable plant (s) (identified by the initial ORNL survey) has(have) been correctly identified and thct the crucial locations in those RPV support structures have been found.
The review will include examination of neutron shield tank and long column RPV supports in more detail than could be done by ORNL within the scope of their contract.
In evaluating plant RPV support vulner-1 I
abilities, special attention should be paid to a number of factors, such as:
the proximity of these supports relative to the reactor 4
core; unusual support features (e.g., grout holes, flame' cutting, j
etc.); location and value of maximum stress (tension stress condition J
is of particular concern as it is condusive to the propagation of eny flaws); and ef f ect of strain rate (due to accident loadings) on supp;rt fracture.
Current up-to-date plant-specific information on RPV ~
I supports, obtained from licensees (or owners groups) or by responses to a 50.54(f) request (if necessary), will be used for this verifica-
- tion, q
S The TAP is designed to allow simultaneous pursuit of several technical
-paths, any of which could lead to a resolution, it is recognized that there are inefficiencies in this parallel approach, but it does minimize the time needed to reach a conclusion.
The approach was selected to meet the Commission guidelines regarding schedular c
commitments for resolving generic issues.
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g I
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Task 2 is a continuation of the Trojan plant evaluation to reduce the uncertainties ~ in the initial ORNL study.
This effort includes (1) further neutron radiation review, (2) material properties review, (3)-
Trojan RPV support structural analyses, (4) Trojan-specific dosimetry and flux attenuation evaluations and (5) evaluation of radiation embrittlement of the RPV support materials.
Experience gained in i
study of the Trojan plant should result in information that will permit licensees to efficiently perform similar analyses of their 1
plants, if this is needed to implement the resolution of GSI-15.
Task 3 will provide radiation parameters (flux, fluence, spectrum) at
' locations of interest which might be critical from a safety viewpoint
-I as identified in the detailed plant survey (Task 1).
The radiation analyses performed as part of Task 2 should serve as guidance for-l other plants.
Because RPV supports involve many designs and several
)
materials, both the neutron ' parameters and the material's sensitivity i
to radiation must be considere'd..
j The resolution of GSI-15 will take a two-tiered approach:
initial ef forts will aim at a preliminary resolution and a longer-term ef fort, if needed, to reach a final resolution.
The plan is to propose a preliminary resolution within two years; if accepted, of j
course, further work on the issue will be unnecessary, and j
implementation will begin.
If not, another two to three years of
{
effort will be needed to develop a final resolution.
There.are several on going or planned programs which could have significant impact on the resolution of GSI-15.
There are nine such y
activities listed in the section of this TAP entitled "Related Work."
Because they are'under the control of other (than DSIR/RES) NRC l
organizations and subject to changes in allotment of funds, the TAP allows for a preliminary issue resolution even in the event that some of them have not been completed.
It may be necessary to adopt I
conservative values of some uncertain parameters to achieve a viable h
preliminary resolution.
Once a preliminary resolution has been 4
defined, the need and justification for developing a final resolution will be evaluated based on the status and perceived impact of "Related
- Work" items.
The evaluation will take into account such factors as reported progress, anticipated completion dates, funding and the potentiel significance of the revision of the preliminary resolution.
Some of the studies may take a relatively long time to complete; in 4
order to avoid delaying the proposed resolution of GSI-15, the results of -these 1 ng-term studies may be considered to be confirmatory for l
the final resolution of GSI-15.
[
The several tasks which comprise this TAP and related work items under the guidance of other NRC organizations are shown in the chart l
on Fig. I which should be an aid in visualizing the overall plan j
while reading the following sections.
)
1
ii B.
Specific Tasks for Issue Resolution 1.
Task 1 - Develop General RPV Support Review Criteria and Resolution Package This ef f ort is the main task of the TAP which will develop the I
resolution for GSI-15.
Subtask 1.1 Review of Domestic Reactors and Identity RPV Support Problems Estimated Level of Ef fort:
25 staff-months (contractor)
Estimated Completion Date:
Preliminary First Quarter of FY 91 Final >FY 93 l
Contractor:
INEL and r1PD Network (OSIR)
FIN:
L1296, G1169 An initial survey of domestic reactors regarding RPV supports was completed.by ORNL and reported in Ref. 3.
With plant-specific information obtained from Subtask 1.2 (S/T 1.2), all j
the domestic reactor types will be independently reviewed by l
another contractor to verify that the most vulnerable plant (s)'
has(have) been identified.
In addition, the most critical location (s) of the RPV support structures in the most vulnerable 3
plant (s) will be verified and the specific potential problems will be identified.
These reviews will be performed with an.
I integrated approach.
The review team will be multidisciplined.
As a. minimum, the review' team members collectively will have i
backgrounds in reactor. physics / nuclear engineering, material science / engineering, and structural mechanics / stress analysis.
Information obtained from Task 2 and results from Subtask 3.1 l
will be used as a basis for a preliminary conclusion.
Results from item 4 and preliminary results from items 1 and 7 (see section entitled."Related Work")' will be incorporated into Tasks 2 and 3.
If the preliminary results are found to be insufficient to resolve the issue, further evaluation will be performed by l
continuing under.5/T 1.2 and Task 3.
S/T 1.2 will employ results i
from items 1 and 8 ("Related Work"); Task 3 will employ results from items 2, 3, 5, 6 an;I 7.
This subtask will b* coordinated with item 9, "Related Work" (contract for NRR interface with licensees), which will be managed by the NRR staff.
Subtask 1.2 Obtain and Evaluate Current Design Data for RPV Supports and Assess Margin Estimated Level of Ef fort:
2.7 staff-months (contractor)
Estimated Completion Date:
First Quarter of FY 93 Contractor:
INEL (NRR, RES/DSIR)
FIN:
L1296 6
The plant-specific design data that apply to current RPV support structures will be obtained by contact with licensees.
- Also,
,the_ allowance (if any) for irradiation damage incorporated in the original design will be obtained.
This information will be used by S/T 1.1.
This information may also be needed to determine the additional' design margin resulting from the revision of GDC 4 (i.e., eliminating the requirement that the RPV support structure withstand an instantaneous double-ended break of the RCS piping) and whether this additional margin would permit use of a conservative irradiation damege correla-tion.
If a 50.54(f) letter is deemed advisable to. expedite the securing of the information, a draft letter will be prepared and trans-mitted to NRR.
Subtask 1.3 = Develop Potential Alternative Solutions Estimated Level of Ef fort:
10 staff-months (contractor)
Estimated Completion Date:
Preliminary FY 91, Final FY 93 Contractor:
INEL (DSIR)
FIN:
L1296 Develop and evaluate potential alternative solutions. _ Based on the preliminary results of 5/T 1.1 (which will address the Trojan RPV supports) cnd: findings from.the Tasks and related work used in 57T 1.1, determine viable 60ternatives and justify.
the choices on the basis of the technical findings.
If further evaluation is necessary to resolve the issue, S/T 1.3 will continue _and, using the results from S/T.1.1 related to domestic reactors in addition to Trojan, provide and evaluate a more comprehensive set of viable alternatives.
Subtask 1.4 Develop Cost / Benefit Analysis Estimated Level of Effort:
15 staff-months (contractor)
Estimated Completion Date:
Preliminary FY 91, Final FY 193 Contractor:
INEL-(DSIR,DRA)
FIN:
L1296 A Cost / Benefit analysis will be developed under this subtask for use by the staff in preparing a Regulatory Analysis _in accordance with the guidance established by RES for the; resolution of generic issues.
This effort will include a quantitative cost / benefit analysis of the viable alternatives identified in S/T 1.3.
S/T 1.4 will follow the pattern set in S/T 1.3, i.e., preliminary analyses will address the Trojan RPV supports and further work, if necessary, will address a broader basis.
Subtask 1.5 Develop Resolution Package Estimated Level of Ef fort:
7.5 staff-months (DSIR)
Estimated Completion Date:
Preliminary FY 91. Final FY 93 7
1
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Information obtained from S/Ts 1.1 to 1.4 will be employed to formulate the GSI-15 resolution package, designed to represent the NRC staff position on the resolution of this generic safety issue.
The information obtained from these subtasks will include both qualitative and quantitative information.
Preliminary resolution package will be developed using preliminary information from S/Ts 1.1 to 1.4.
If these subtasks must. continue to a broader basis, the development of a resolution package will include the additional findings.
2.
Task 2 - Evaluation of Irradiation on the Trojan Plant RPV Supports Estimated tevel of Ef fort:
15.4 staft-months (contractor)
Estimated Completion Date:
Preliminary-First Quarter FY 91; Final Fourth Quarter FY 91 Contractor:
to be determined, & INEL- (OSIR)
FIN: -L1296 This task involves an assessment of the ef fects of radiation and other factors on the expected behavior of the Trojan Plant RPV supports under accident-level loading.
An initial review of the Trojan neutron radiation analysis reported-in Ref. 3 will be done by DSIR with a follow-on, more detailed neutron irradia-tion review by a yet-to-be-determined contractor.
With the help of the licensee, a review of the Trojan RPV support material properties will be conducted by DSIR/INEL.
Also, the structural analyses by the Trojan AE (Bechtel) and by a consultant to PGE (R. L. Cloud Associates) will be reviewed in advance of the Trojan RPV support analysis (see Item 1, "Related Work," below).
There are other "Related Work" items' which, when completed, may influence the recommendation for GSI-15 resolution at the Trojan i
plant. They are: Items 2 and 3, which will provide a more exact estimate of the radiation exposure which the RPV supports will receive; Item 5, which is planned to obtain post-irradiation mechanical property measurements-of RPV support steels; and items 4'and 6, which should result in measured property changes from radiation exposure in actual plant operation.
Only. Item 4, under which samples from the Shippingport plant neutron shield tank will bc tested, has a schedule compatible with the plans I
for Task 2.
If early results from the other items are available and relevant to the Trojan analysis,-they will be used in the proposed resolution; otherwise, they will be treated as con-tributing to later confirmatory research.
Clearly, accurate determinations of radiation parameters and the structural steel response will enhance tae Trojan RPV support evaluation.
Based on results from any or all of the above, the specific plan for resolution of GSI-15 at Trojan will be developed.
It is expected that the knowledge gained from Trojan plant studies will aid considerably in developing alternative solutions that may be applicable to a number of plants.
8
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5 lC 3.
Task 3 - Irradiation Analyses This effort will provide radiation parameters which will be used 3
in analyses to estimate the long-term changes. in mechanical
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properties of critical RPV support components.
a(
Subtask 3.1 Preliminary Evaluation of low-Flux Embrittlement J-761s ated Level of Effort:
e Estimated Completion Date:
FY'90 Contractor:
FTN:
1his subtask will attempt to resolve the discrepancy between the lif1R,- MTR, and Shippingport reactor damage results.
Initial I
evaluation-of the effects of low-temperature low-flux neutron embrittlementi on the Shippingport reactor shield tank indicated a factor of ten less embrittlement than observed in the HFIR 3
surveillance specimens.
In order to serve as a source of pre-i liminary resolution of the TAP, the reason for the discrepancy between the HFIR and Shippingport results needs to be determined, if possible.
New-information detailing the effects of the thermal neutron efficiency has been suggested as an explanation of the discrepancy between the HFIR and MTR results (ref. 4).
Con-sequently, more *.<ork needs to be done to investigate how the Shippingport results would be modified by this thermai neutron efficiency effect.
Thisl work will be done initially by NRC staff in DSIR/EIB.
It is expected that this work would begin in the first quarter of FY 90 and be completed in the third quarter of FY 90.
If.
additional work is required, then a contractor will be used.
Subtask 3.2 - Specific Radiation Parameters Estimated Level of_ Effort:
12 staff-months (contractor) 1 Estimated Completion Date:
Preliminary FY 91; Final FY 92 Contractor:
To be determined (DSIR) y The great variety of RPV supports in domestic commercial nuclear reactors will necessitate several specific analyses to 1
'].
determine the irradiation parameters of interest at any locations judged to be important to safety because of Task 1 reviews.
The work done as part of the review of the Trojan RPV supports (see Task 2) will be used to reach a preliminary completion of S/Ts 1.1 and 1.3.
Also, it will provide the basis for analysis of other RPV supports.
To the extent that it is relevant and available, the results of programs listed in the following section (Related Work) will be used in these analyses.
Also, the fact that several materials may be involved in the locations cited in Task 1 reviews will require that available post-irradiation test results be analyzed to estimate the mechanical properties ef RPV supports as functions of time.
l 9
C.
Related Work There are several planned or on going technical programs under the direction of other (than DSIR/RES) NRC organizations which are directly related to the resolution of GSI-15.
Some should provide important foundation stones for the final resolution.
The schedvies for each of the programs given below are dependent to various d9grees on availability and allocation of funds in future fiscal years; the TAP allows for r,reliminary issue resolution even if those pregrams beyond the con'.rol of the Task Manager and his management arr not completed on",chedule.
The specific use of information provided by-these prograr,s in the development of a final issue resolution will be determine 1 in about two years (cf. Section ll.A of this TAP),
immediately after a preliminary resolution has been defined.
1.
Consequence Evaluation of Embrittled RPV._ Supports i
Estimated Level of Effort:
24 staff-months (contractor)
Estimated Completion Date:
Preliminary (Trojan) Second Quarter FY 90; Final FY 91 Contractor:
LLNL (DE)
FIN:
B6021 This program will evaluate the reserve load-bearing capacity of the Trojan-RPV supports, working f rom the assumption that one or more of the horizontal support beams is cracked completely and that the SSE and "small break" LOCA occur independently.
The initial phase of the study will consider the consequences of the bounding case of complete failure of all of the Trojan RPV supports.
This work, taken to completion, will address qualitatively the consequences of RPV support failure for support structure designs different from'those at Trojan--shield tanks for example.
The rationale is that while Trojan's design may be limiting from a fracture standpoint, the consequences of support failure at Trojan may not be the limiting case.
The work was initiated in FY 1989 and the " bounding case" analysis of Trojan is expected to be completed by the end of CY 1989.
The more detailed analysis, if warranted, will begin in FY 1990 and is scheduled to be completed in FY 1991.
1 2.
Trojan Cavity Dosimetry Measurement Estimated Level of Effort:
26 staf f-months (contractor)
Estimated Completion Date:
FY 92 Contractor:
National Institute for Standards and Technology (DE)
FIN:
B6224 Using the techniques ' developed under other NRC funded research, this program will seek to determine the actual neutron flux and energy spectrum in the vicinity of the RPV supports in the Trojan plant.
This work will reduce one significant source of uncertainty in the earlier ORNL analyses since the flux and 10
v l:
energy spectrum used in those analyses were based on expert opinion-and inference from results obtained in other plants.
Reducing this source of uncertainty will allow a better assessment of the " critical" crack size for the accident loads
.j considered.
Further, it will help reduce the uncertainty in the probabilistic fracture mechanics analysis to be performed for the Trojan plant.
A meeting was held with the utility
- on April 12, 1989 to determine
.if it is feasible to make these measurements at the Trojan f acility.
The utility appeared to be very favorably disposed to make the measurements and agreed to supply.NRC with design information and power distribution measurements that might be needed to design'a test rig.
It appears possible to place reactor _ flux monitor sets at several locations of the cavity region to obtain data permitting a more' precise characterization of the fluences j
and fluence rates at the'vossel supports.
The test rig could be installed at the next outage in April 1990 which_would allow enough time to design and construct the test rig.
The measure-ments would be completed and results reported in FY 1992.
v 3.
Flux Attenutiation in Trojan Biological Shield Wall
\\
Estimated Level of Effort:
12 staff-months (contractor)
Estimated Completion Date:
FY 92 I
Contractor:
B0415 a
This study will determine the attenuat-lon of fast neutron flux l
.as a function of position along the horizontal support beam in-i the Trojan RPV supports.
The study would use state-of-the-art transport computations, and would consider not only the i
attenuation of the concrete but also transport of neutrons along the support beam.
Adjustment calculations will be made based on the cavity dosimetry measurements in Related Work Item 2.
This work would resolve one uncertainty in the earlier ORNL
-analyses of the Trojan plant, allowing emphasis on the_ contre.1-ling variables and a more accurate assessment of.the " critical" crack size for the accident loads considered.
These results also would reduce the uncertainty in the probabilistic fracture mechanics analysis to be perfnrmd for the Trojan plant.
4.
Testing of Shippingport Neu'ron Shield Tank Estimated Level of Effort:
21 staf f-months (contractor)
Estimated Completion Date:
SY 91 Contractor:
ANL (DE) flN:
A2256 As part of a larger effort, samples from the inner and outer cylinders of the shield tank from the decommissioned
- Portland General Electric.
11
m 4
Shippingport' reactor have been obtained.
These samples'are being used to determine the degree of embrittlement for that shield tank using Charpy specimens, microhardness measurements, and metallographic examination.
Also, an attempt'is being made p
,to experimentally determine the total fluence received by the
-inner cylinder.
These measurements, coupled with the' revised transport calculations performed by Westinghouse, will provide 1
a reasonably clear picture of the neutron flux and energy spectrum for the shield tank over the life of the plant.
This information, coupled with the embrittlement data obtained from the Charpy specimens, will provide another data point for evaluating the effects of low-temperature -low-flux embrittlement.
The work was started in FY 1988 and should be completed by FY 1991.
5.
MTR Irradiation of Structural Steels Estimated Level of Effort:
24 staf f-months (contractor) f Estimated Completion Date:
FY 91 Contractor:
Materials Engineering Associates (DE)
{
FIN:
85848 1
This study will determine the shift in nil-ductility temperature
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after nigh flux _ neutron irradiation, providing a comparison between the HFIR pressure vessel materials and materials commonly-useri in RPV supports.
Irradiation will be performed in a Materials Test Reactor (MTR) that has been used.in earlier NRC Benchmark Experiments to provide comparability with other MTR irradiations of similar' materials, and in particular.with the MTR irradiation of the HFIR material.
It is expected that specimens from several heats of A-36 and A-2128's P 1 will be irradiated at approximate.ly 150*F to a fluence of appiqy mately 1018 n/cm2, E > 1 MeV. -The shift in nil-ductility temperature will be determined from the shif t in the Charpy energy transition at the 15 f t-lb energy level.
The earlier ORNL analysis of the Trojan plant RPs supports assumed that the A-36 material used in those supports would respond to neutron irradiation in the same manner as the A-2128 material used in the HFIR.
Since there are no irradiation damage data on A-36, this study is designed to validate this assumption.
The work to be performed will provide an assessment of how A-36, A-212, and other grades of steels typical of reactor vessel supports respond to low-temperature, high-flux irradiation.
Although this work will help resolve uncertainty in the ORNL analysis of the Trojan RPV supports, it will leave open the question of how these materials will respond to low-flux irradiation.
12
\\'
The results will be used in the probabilistic fracture mechanics analysisL of the Trojan plant (Item 8, below) and will contribute ito the overall understanding of the susceptibility to embrittle-ment of RPV support structures.
6.
Embrittlement Effects in the BR-3 Shield Tank Estimated Level of Effort:
80 staff-months (contractor)
Estimated Completion Date:
Mid FY 93 Contractor:
To be determined (DE)
The Belgians are decommissioning ;he BR-3 reactor and currently
.are making plans for using components taken from the facility to assess plar.t aging.
Specimens taken from the shield tank could be used in.the same way as those taken from the Shippingport shield tank to evaluate low-temperature, low-flux embrittlement.
This suggestion has been made to the-appropriate Belgian authorities and further discussions are-planned.
Since the Belgian plans are not finalized, a firm plan for NRC's participation cannot be developed.
This activity is being pursued actively, and it is hoped that the effort could begin in early FY 1991 and=could be completed by mid-FY 1993.
7.
Low-Temperature Low-Flux Damage Correlation Development Estimated Level of Effort:
36 staff-months (contractor)
Estimated Completion Date:
FY 92 Contractor:
To be determined (DE)
One of the greatest sources of uncertainty in the ORNL analyses of RPV supports is the correlation between neutron flux, fluence',
and shift in nil-ductility temperature. 1The correlation used in the ORNL analyses was based on a significant extrapolation of the results obtained from the HFIR.
The approach taken in developing this correlation may be unduly conservative for.RPV-support structures.
This possibility is supported by the' pre-liminary results from the Shippingport reactor shield tank inves-tigation which indicate much less embrittlement than observed in the HFIR surveillance specimens.
While the preliminary Shippingport results are not conclusive, they do clearly show that low-temperature, low-flux embrittlement is not fully understood.
The results of the HFIR study, the Shippingport study, the BR-3 study, and other DOE and NRC funded work evaluating low-temperature, 3-low-flux embrittlement will be used to develop a mathematical model to describe this embrittlement.
This model would then be used in lieu of the ORNL extrapolation in the probabilistic fracture mechanics analysis of the. Trojan plant as well as other specific plant analyses performed in resolving GSI-15.
13 l
1
I i
y l
L 21t is expected that this work would begin late in FY 1990 and would be completed and reported by the end of FY 1992.
8.
Probabilistic Fracture Mechanics Analysis of the Trojan Support Structures-1 Estimated Level of Effort:
40 staff-months (contractor) l Estimated Completion Date:
FY 93-1 Contractor:
To be determined (DE) i This study will evaluate the probability of failure of the supports at the Trojan plant as a pilot study.
However, the work has been deferred until some of the other hardware-related studits (Items 2 through 7) can be completed to help' reduce some of the uncerta_inty in the results.
Special emphasis will be placed on developing reasonable distributions for initial flaw ize and operating temperatures for the support structures.
The deterministic analysis reported in NUREG/CR-5320 will serve _as j
a reference study for this offort.
However, it is anticipated l
that additional work will be necessary to develop more appropriate fracture mechanics models and to improve the models describug i
loading rate effects on fracture toughness.
I This work currently is scheduled to begin in FY 1990 and to be completed in FY 1993.
The final schedule will depend on the completions of the hardware-related-research tasks.
9.
NRR Interface With Iicensees Estimated Level of Ef fort:
4.0 staf f-months (contractor)
Estimated Completion Date:
Fourth Quarter of FY 90 Contractor:
Pal Associates (NRR)
FIN:
L1191 This contract will provide technical assistance to NRR relative to the NRR interface with licensees regarding GSI-15 activities.
111. Schedules and Priorities Prior to the assignment of GSI-15 to DSIR, several projects had been j
either started or planned because of the perceived importance of the ORNL analysis of the HFIR surveillance capsule examinations.
Although clearly germane to a full understanding of the importance of the'HFIR results to the integrity of RPV supports, t hose projects developed autonomously rather than as parts of an integrated, unified plan.
Therefore, some of the work described in Section II involves schedules which do not fit well with the DSIR Task Action Plan.
To accommodate those irregularities, two steps have been taken.
- First, the overall plan for resolution involves two phases (see Section II-A, above):
a preliminary resolution and, if necessary, a final resolution.
Second, DSIR has categorized the nine activities described in Section Il-C as either very important or less important to the resolution plan l
14 1
c.
1 1
is (obviously,-all are important to some degree or they would not be included in-the TAP).
With these generalities in mind,: schedules and priorities can be discussed.
Estimated completion dates f or'each Task, S/T and related item can be j
found in the project headings in Sections Il-B and 11-C.
' chart-illustrating how the various projects' interrelate is attacheu is Figure 1.
i for purposes of this TAP, a common start date (June 1, 1989) was adopted for all the Tasks conceived as part of this TAP and for those projects.
which were already underway at the time the TAP was drafted.
Because o review of the Trojan RPV supports may lead to a resolution which can be implemented generically, figure 1, shows both the shorter planned program and,the additional effort should it be necessary, inspection of Figure 1-g
- will show that although all the projects discussed in Sections ll-B and Il-C-can be' utilized in developing a broad-based generic resolution, only a limited number are to be used in reaching a preliminary resolution.
Specifically, the preliminary resolution requires the completed ORNL analysis (Ref. 3), the_ portion of item I related to the Trojan plant, the i
results f rom the destructive examination of the Shippingport neutron shield tank (Item 4) and the results from Subtask 3.1, Preliminary Evaluation of Low-Flux Embrittlement.
Results from those projects will feed into Tasks 1
2 or 3 to provide the technical basis for the part of S/T 1.1 which addresses the Trojan RPV supports.
The rest of the plan for a preliminary resolution (the early work under S/Ts 1.3, 1.4 and 1.5) comprise the standard path toward a resolution package.
Should it be found that a solution for the Trojan plant cannot be implemented on-a broad (generic) basis, additional work will be done along the lines of Figure 1.
The determination of the relative importance of the several projects resulted in the following.
Tasks 1, 2 and _3 were judged very important (VI) although it should be obvious that resolution of the issue by imple-menting the Trojan plant recommendation would render those segments of.
Tasks 1, 2 and 3 related to other plants less.important (LI).
- Likewisa,
- those activities directly in support of the-Trojan analysis were judged VI, namely:
the Trojan related segment of item 1, Item 4, and early results from item 7, if relevant.
Because the probability is high.that the additional ef fort (Fig.1) will be necessary, some supporting projects must be rated VI.
Specifically, Items 1 (continued), 2, 3 and 7 (continued) were judged VI; Items 5, 6 and 8 were judged L1, For ease of reference,
~
the_several projects, their schedule dates and rankings were assembled and listed in Table 1.
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94 oesee Box N urn ber fig t Limited logic diagram of the activities important to the resolution
( Ar bitrar y)
^^*
of Generic Safety issue 15.
Title
- TAO E vA T2 Task / Item sed /I NE L SOB
- Wor k Days Cont tetor 30,01-89_O9 30,-O' Finish Date Start Date inaicei.e u u si sta r t j
l en8 0 9 00.is - o/
no a:
T an k,
. Table I, Programs in Support of GSI-15 Start ** Complete Date Designation
- Title (shortened)
Date (prelim./ final)
Ranking ***
$/T 1.1 Review Reactors; Problems 6-1-89 12-90/1-93 VI
-5/T.1.2 Design Data and Margin 6-1-89
-/12-92 VI
$/T-1.3 Alternative Solutions 6-1-89.
1-91/2-93 VI S /T 1. 4 Regulatory Analysis 6-1-89 2-91/4-93 VI S/T 1.5 Resolution Package 6-1-89 4-91/5-93 VI Task 2 Trojan RPV Supports 6-1-89 10-90/9-91 VI S/T 3.1-Prelim. Eval. of 10-1-89
-/4-90 VI Embrittlement-S/T 3.2 Specific Rad. Parameters 6-1-89 11-90/9-92 VI
. Item 1 Consequence Evaluation
' 6-1-89 3-90/9-91 VI Itam 2 Trojan Dosimetry 6-1-89
-/9-92 VI Item 3 Trojan Flux Attenuation 6-1-83
-/30-92 VI Item 4 Shippingport Testing 6-1-81
-/10-90 VI Item 5
- MTR Irradiation TBD 9-90/9-91 LI Item 6 BR-3 Embrittlement 12-1-90
-/3-93 LI Item 7 Damage Correlation 8-1-90 9-91/9-92 VI Item 8 Probabilistic F.M.
3-1-90 9-91/11-92 LI Item 9 NRR Support 6-1-89
-/7-90 VI e We,
,g
- S/T = Subtask; " Items" given in TAP Sect. II-C.
- 'See text (TAP Sect. III)-for explanation of given dates; TBD = to be determined.
VI = very important; LI = less inportant (see TAP Sect. III).
17 3