atw - International Journal for Nuclear Power | 04.2019

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atw Vol. 64 (2019) | Issue 4 ı April

OPERATION AND NEW BUILD 220

(Figure 9). As the allowable crack

length is 4.9 inches and it is greater

than 4 inches. Thus, brittle failure is

not expected to occur.

The evaluation against ductile failure

showed that the allowable circumferential

projection of the crack length

is 16.36 inches (Figure 10). As this

value is greater than 4 inches. It is not

expected ductile failure to occur.

These conditions were also

evaluated with the R6 Failure

Diagram, Figure 14. For this purpose,

the following parameters were

calcu lated:

and

.

The results showed that this

arrangement has structural integrity

and can continue its operation. A

critical condition is expected along

the circumferential projection. There

is a tendency to a fragile fracture. It is

advisable to inspect this crack periodically.

6.3 Unsafe helical crack

A helical crack, which has a length

of 18”, was postulated. Its components

in the axial and circumferential directions

are 7.19 inches and 16.5 inches,

respectively. The reactor operates with

100 % of the output power and the flow

through the core is 107 %. The two

headers of the RRC are in operation

and 100 % of the flow of water has

been passing through the core.

The projection of the crack in the

axial direction is evaluated with Figure

7. The allowable crack length, in

accordance with Fracture Mechanics,

is 11.6 inches. It is bigger than

7.19 inches. So, it is acceptable.

Regarding the limit load collapse

analysis, it was carried out with Figure

8. The allowable crack length is

11.11 inches. As, it is bigger than

7.19 inches. It is accepted. These evaluations

were completed with the Failure

Assessment Diagram, Figure 15.

In a second phase, the projection in

the circumferential direction is evaluated,

considering the principles of

fracture mechanics. In accordance

with Figure 9, the allowable crack

length is 4.9 inches. This should not

be accepted, because the crack projection

(16.5 inches) is bigger than the

allowable crack length.

The same analysis was done with

the Collapse Limit Load analysis. The

allowable circumferential crack is

16.36 inches. However, the crack

projection is 16.5 inches. Under this

condition, it can be accepted. In order

to confirm these results, this situation

was analyzed with the Failure Assessment

Diagram. For this purpose,

the following parameters were

calcu lated:

and

.

These values are located outside of

the safe zone. It is illustrated in Figure

16 and it is confirmed that the structural

integrity of the riser has been

compromised. It can be expected a

failure in which brittle behavior will

be predominant.

7 Conclusions

The helical or diagonal cracks that

may take place on the riser close to the

weld of the riser brace weld. It was

considered that a torsional mode of

vibration around the axial axis of the

riser generated the loading conditions

for the crack propagation. The operational

loads that could take place were

considered in the methodology, which

was applied.

It is considered that the system has

enough structural integrity when the

conditions that avoid ductile and

brittle failures along the circumferential

and axial directions are fulfilled.

Otherwise, the component has to

be repaired. One alternative is to

substitute the damaged part. However,

it should to be cut and a new replacement

component should be

welded. These operations should have

to be done below the water level and

during the outage of the nuclear

power plant. Under these conditions,

it is difficult to get a good quality in

this job. It would be advisable to

install a reinforcement structure, in

such way that a compression load

must be applied to avoid fracture

mode I on the crack. Besides, torsion

and bending have to for limited.

Regarding the inspections, they

have to be done periodically. Crack

propagation has to be monitored and

the structural integrity of the reinforcement

frame has to be evaluated.

Misalignments, deterioration and

corrosion have to be avoided.

Acknowledgements

The authors kindly acknowledge the

grant for the development of the

Project 211704. It was awarded by the

National Council of Science and

Technology (CONACyT).

Statement

The conclusions and opinions stated

in this paper do not represent the

position of the National Commission

on Nuclear Safety and Safeguards,

where the co-author P. Ruiz-López is

working as an employee. Although

special care has been taken to maintain

the accuracy of the information

and results, all the authors do not

assume any responsibility on the

consequences of its use. The use of

particular mentions of countries,

territories, companies, associations,

products or methodologies do not

imply any judgment or promotion by

all the authors.

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October 1990, pp. 1-1, 1-4.

Authors

Pablo Ruiz-López, Ph.D.

Comisión Nacional de Seguridad

Nuclear y Salvaguardias

Head of the Licensing Area

México

Luis Héctor Hernández-Gómez, Ph.D.

Juan Cruz-Castro, M.Sc.

Gilberto Soto-Mendoza, M.Sc.

Juan Alfonso Beltrán-Fernánde, Ph.D.

Guillermo Manuel Urriolagoitia-

Calderón, Ph.D.

S.E.P.I. Zacatenco, I.P.N.

México

Operation and New Build

Failure Analysis of the Jet Pumps Riser in a Boiling Water Reactor-5 ı

Pablo Ruiz-López, Luis Héctor Hernández-Gómez, Juan Cruz-Castro, Gilberto Soto-Mendoza, Juan Alfonso Beltrán-Fernánde and Guillermo Manuel Urriolagoitia-Calderón

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